Final Report

Solar Panel Cleaning

System

Design Project II: Exercise 3

Arthur Mallet Dias

Harry Garstka

Loic Gueganton

Richard Stone

Harri Worman

UNIVERSITY OF BRISTOL

ENGINEERING DESIGN

27 March 2015

Solar Panel Cleaning System


MEng Engineering Design Year 2

27 March 2015

Arthur Mallet Dias, Harry Garstka,

Loic Gueganton, Richard Stone, Harri Worman

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Table of Contents

Executive Summary ......................................................................................................................................... 4

Nomenclature Used Throughout Report .......................................................................................................... 4

1. Introduction and Design Specification .................................................................................................... 5

Introduction .................................................................................................................................... 5

Brief ............................................................................................................................................... 5

Stakeholder Needs .......................................................................................................................... 5

Research ......................................................................................................................................... 6

1.4.1 Selected Base Module ................................................................................................................ 6

1.4.2 Consumable Use in Current Solutions ....................................................................................... 6

Design Specification ...................................................................................................................... 7

2. Design Alternatives and Proposed Solution............................................................................................ 8

Idea Generation Process ................................................................................................................. 8

Results from Idea Generation ......................................................................................................... 8

Down Selection Process ................................................................................................................. 8

Proposed Solution ........................................................................................................................ 10

2.4.1 Modifications Made to Initial Design and Resultant Advantages Offered .............................. 10

2.4.2 Potential Problems Arising Due to Modifications ................................................................... 10

3. Design Definition of Proposed Solution ............................................................................................... 11

Final Design ................................................................................................................................. 11

Presentation of Final Design Including Operation Procedure ...................................................... 12

Orthographic Projection Showing Key Dimensions .................................................................... 13

General Assembly Drawing with Parts List ................................................................................. 14

4. Proving Calculations and Technical Feasibility .................................................................................... 15

Structural Analysis ....................................................................................................................... 15

4.1.1 Material Selection .................................................................................................................... 15

4.1.2 Stiffness Calculation ................................................................................................................ 15

Gearbox Calculation..................................................................................................................... 17

4.2.1 Force and Torque Required to Move Up Panel ...................................................................... 17




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4.2.2 Gearbox Ratio Required .......................................................................................................... 18

Energy Analysis of Device Operation .......................................................................................... 18

Battery Power Usage .................................................................................................................... 19

Manufacturing Considerations ..................................................................................................... 19

Actuation and Control Systems Used ........................................................................................... 20

5. Cost Analysis ........................................................................................................................................ 21

Comparison to Other Methods ..................................................................................................... 21

Device Manufacture Cost ............................................................................................................. 21

Machining Costs .......................................................................................................................... 22

Running Costs .............................................................................................................................. 22

Payback Period ............................................................................................................................. 22

6. Evaluation ............................................................................................................................................. 23

Evaluation against Specification .................................................................................................. 23

Commercial Feasibility ................................................................................................................ 24

Improvements and Uncertainties .................................................................................................. 24

Overview and Conclusion ............................................................................................................ 25

Bibliography .................................................................................................................................................. 26

Appendix A – Gallery of 15 Rejected Ideas ................................................................................................ 27




Appendix B – Idea Down Selection ............................................................................................................. 31

Appendix C – Spreadsheet Used In Energy Analysis ................................................................................. 32

Appendix D – Components Used For Prototype ........................................................................................ 33

Appendix E – Software Code ....................................................................................................................... 34

Appendix F – Cost Analysis Sources and Assumptions ............................................................................. 37

Appendix G – Evaluation Diagrams ............................................................................................................ 40




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EXECUTIVE SUMMARY

The following report outlines the process and result of designing a cleaning robot for use in the solar industry,

to autonomously clean solar panels. It contains an exploration into the design process used, a definition of the

final design solution, the functionality and operation of the device justified with relevant calculations, and a

business case for its commercial viability in the market.

The report begins with an explanation of the steps taken to reach the design solution, including the scope of

research conducted, and a detailed design specification which was referred back to throughout the report.

Convergent and divergent idea techniques were used to generate a range of ideas and filter them down to

reach to the final design; an adjustable rail-mounted cleaning robot to fit any panel size or configuration.

The final solution was then defined through the use of detailed technical drawings and CAD renderings with

operation descriptions. No water was used in the operation of the device. The device was composed mostly

of aluminium, styrene, and HDPE, using omnidirectional wheels and an Arduino chip to move around and

clean the panel, being guided by the rails.

After the device had been defined, a full energy was performed, and it was found that the 12V battery would

need to be swapped out and recharged every 380 panels on average. Cost calculations followed, and the cost

per panel was determined to be 3.81p, with an expected price of 20p, assuring commercial viability.

Our final design solution was then rigorously checked against the design specification outlined earlier in the

report. A self-critical evaluation was then performed, identifying weaker areas of the design, for example the

inability to efficiently clean bird excrement from the panel. From this evaluation, aspects of the device to

improve were outlined for future development.

NOMENCLATURE USED THROUGHOUT REPORT

The terms ‘solution’ and ‘device’ are used interchangeably throughout this report.

Cell

A solar ‘cell’ is a photoelectric cell which converts light energy directly into electricity.

These are the smallest unit capable of performing this function, making them the building

blocks of all photovoltaic devices.

Panel

The term ‘panel’ is used interchangeably with the term ‘module’, both throughout this

report and in industry. These are comprised of an assembly of multiple solar cells, all in an

integrated group and oriented in one plane. A typical panel size is 1×1.6 m, which is made

up of 60 cells.

Table

A ‘table’ is a collection of modules, again all orientated in one plane, which are all mounted

on a supporting structure. A table is comprised of many modules extending in the

horizontal direction, and one or two modules extending in the vertical direction.

Portrait

orientation

Since modules are almost always rectangular in shape, they will have one long side and one

short side. When the long side is facing vertical and the short side horizontal, this is

considered to be a ‘portrait orientation’ of the module.

Landscape

orientation

Likewise, when the short side of the module is facing vertical and the long side horizontal,

this is considered to be a ‘landscape orientation’.




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1. INTRODUCTION AND DESIGN SPECIFICATION

Introduction

In today's climate of a mounting desire for energy production and increasing environmental concerns,

renewable sources such as solar energy are encountering widespread use. Solar energy systems work by

harnessing light energy transmitted from the sun’s radiation, and converting this into electricity through the

use of photovoltaic (PV) panels.

There is a major issue associated with PV panels, however, concerning the accumulation of dust and

contamination on their surfaces; which, over time, can lead to a significant reduction in their energy

generation capability, in addition to causing potentially irreversible damage to the panel. This report will

outline the design and build process of a device to autonomously clean the surfaces of solar panels, in order

to combat this problem.

Brief

It is assumed that the proposed solution is required to support a business case for developing a solar panel

cleaning product, which could be sold to companies specializing in solar farm installation and maintenance.

Therefore, maximising the internal rate of return over the lifecycle of the solution is the core design driver

for this project. In turn, this can be achieved by optimising the device to incur the lowest possible financial

cost during its operation.

Many factors have a significant influence on financial operating costs. For

example, minimising consumable use and the need for skilled labour will

reduce the expenses incurred by the device. Likewise, autonomous operation

of the device is essential as it also links back to reducing labour costs. A

graphical depiction of how two factors influence the final design are

illustrated in Figure 1.

It is also beneficial for the design to be adaptable, as this will mean it could be used by different operators for

a larger number of panel types, ultimately supporting the business case further. This will be pursued as a

secondary design driver throughout the development of the solution.

Stakeholder Needs

The question and answer session gave the opportunity for initial engagement with the client. Following this,

a 20,000 module, 5MWp site was chosen as a typical case for which the proposed system would be required

to clean. A rough estimate of the price to clean a panel for this type of site using current cleaning methods

was given to be around 25 pence. Time taken is not a priority.

Sources of water and mains electricity are not always available at solar farms, imposing two limitations on

the design. Firstly, it means the device must be battery powered. Factors such as the repeated cyclic

conversion of kinetic energy to irrecoverable gravitational potential energy (GPE) as the system traverses

Low cost

Operational simplicity

Autonomous operation

Figure 1: A hierarchy showing how

many design factors ultimately link

back to minimising financial cost.




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vertically across the panels must therefore be considered, as this decreases the efficiency of the power output.

Similarly, water consumption must be minimised due to logistic constraints, and this will be explored in

greater depth in Section 1.4.2 next.

Research

Research was conducted into a range of areas in order to understand the design requirements, which are

pivotal in designing the most suitable cleaning system for the brief given. From this, a detailed design

specification (given in Section 1.5) was produced, which captured all findings.

1.4.1 Selected Base Module

Research was conducted on a range of popular manufacturers to determine the extent to which their panels

were used in the UK, the amount of data available on them, and their similarity to the standard panel

dimensions of 1×1.6 m. The Suntech STP2XX range [1] was agreed upon as the basis for the design, being

in widespread use throughout the UK [2] and with a large amount of datasheets available online.

1.4.2 Consumable Use in Current Solutions

Over the lifetime of the cleaning system, initial setup costs will become negligible, and instead the operating

costs will be dominated by consumable expenses. Therefore, it was necessary to investigate the financial

impact of these consumables on the cleaning operation, the findings of which are presented in Table 1. The

normalised cost of labour evidently imposes the most substantial contribution to overall financial costs.

1 Where normalised costs are per module, this is for a typical 20,000 module site as described in the Q&A. 2 Using the example given with the 5MWp Toyota installation from the Q&A session. 3 This is the mean value of two separate quotes given for different delivery locations; one was for a delivery

to a site near the water depot, and the other for a delivery approximately 80 miles away. 4 This setup involves a Hyundai HY1000Si-LPG 1 kW petrol generator connected to a rectifier, which is used

to provide DC power to charge the battery after it has been depleted.

Table 1: Costing of common consumables used during solar panel cleaning operations.

Consumable Expenditure Per Normalised cost Per1

Labour

£ 8.00 Person/Hour £ 0.331 1×1.6 m module

Assumptions: Only unskilled labour is required so wages can be relatively

cheap at £8/hour; 18,000 modules takes two weeks to clean with 10 workers2;

Workers clean for 7 hours per day for 5 days per week.

2,000 L water bowser

delivery to site

£ 391.153 Delivery £ 0.059 1×1.6 m module

Assumptions: 300 mL used per module; Quote from water-direct.co.uk [3].

DC power used to

recharge battery4

(up to) 2.7

litres of petrol 9 hours use £ 0.360 kWh

Assumptions: A 1 kW inverter generator is used [4]; Generator is operating at

maximum efficiency; Petrol price is a standard UK rate of £1.20/litre.




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Design Specification

Table 2: Requirements Specification Key: D/W = Demand/Wish; Wt. = Weighting; H/M/L = High/Medium/Low; Mod. = Modified

# D/W Wt. Requirement Source Acceptance Criteria / Method of Testing Mod.

Performance

1 D

Must be able to clean the entire

surface area of a 1640×992 mm

Suntech ‘STP265S-20/Wem’

module

Research

A visual check of the panel surface will be performed

and all dust and bird excrement must be removed after

the cleaning process

18/2/15

2 D Must be able to clean one whole

solar panel table autonomously Brief

The final design must clean a table of 10 by 2 panels

unassisted

3 D Must not damage solar panels

during cleaning Q&A

After cleaning, there will be no visible defects on the

panels, and their peak power output must not deteriorate

4 W H Desirable be able to clean panels

without a water supply Research

Functionality will be tested without water to check there

is no deterioration in cleaning quality 22/2/15

5 W M

Should be able to clean more than

one type of panel from a given

manufacturer

Brief The design will successfully clean two separate models

(Suntech 250w and 265w)

6 W L

Desirable to be able to clean

panels from more than one

manufacturer

Brief Both 265w polycrystalline variants of panels from

Suntech and Q Cells will be cleaned successfully

7 D Must be able to traverse gaps

between tables autonomously Brief

The device will traverse gaps between tables without

any manual intervention from any workers 13/2/15

8 D

Must be able to remain in

continuous use for an acceptable

period of time before failure

Brief At least 3000 tables must be cleaned by a single device

before breakdown 09/2/15

Physical Characteristics

9 D

Must only require one worker to

operate and handle, whilst

remaining safe and comfortable

for them

Research

No individual part of final design will weigh more than

15 kg, and will be labelled as appropriate depending on

the shape, to conform to LOLER legislation [5]

14/2/14

10 Must not require anyone working

at height to be attached to panel Research

Workers will be able to be fully attach the device to the

panel whilst remaining standing on the ground

11 D Must be easy to transport between

the depot and solar farm site Q&A

The device, together with all associated parts, must fit

inside a container from a standard box truck, with

dimensions 6096×2400×2375 mm [6]

14/2/15

12

Must be able to withstand

vibrations encountered during

worst case transport conditions

Q&A

Device must show no deterioration in operation after

test stated in MIL-STD-810G Section 2.1.2: Vibrations

Encouraged During Transportation (Mission/field

transportation) [7].

Economics

13 D Must maximise internal rate of

return to support business case Brief

Price charged per panel must be less than 25 pence to be

beat current competitors

14 D Must have a long product life Brief Product lifetime must exceed 10 years

Environmental

15 D

Must be able to operate as normal

within a standard range of

temperatures in the UK

IEC

SPECS

Between the temperatures of 5°C and 40°C, the device

should show no reduction in performance or failure

16 D Must not release any chemicals

onto the ground during operation Q&A

The only acceptable by-product of the design, if any,

can be water

Legislation

17 D Must not be excessively loud for

any workers operating [8]

Maximum noise level must not exceed 85 dB in

accordance with the Control of Noise at Work

Regulations 2005




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2. DESIGN ALTERNATIVES AND PROPOSED SOLUTION

Idea Generation Process

The necessary functions required from the device were split device into three categories: method of cleaning,

method of movement across panels, and method of traversing gaps between tables. A morphological chart

(shown below in Table 3) was derived to encompass all of these, after which brainstorming was employed to

generate a range of ideas, with each following a different permutation of the functions. By the end of this

process, 15 unique design ideas had been created, ranging from simple concepts like a rail mounted scrubber

to less conventional methods such as utilizing recyclable polystyrene film to cover the panels entirely. See

Appendix A for a full list of the 15 ideas generated.

Table 3: The morphological chart used, with paths taken to achieve the two final designs highlighted in red and blue.

Cleaning

method Air/water jet Mop Scrubbing

Rollers /

Rotational Vacuum Wiping

Movement

across panel Wheels Suckers Rails

Caterpillar

tracks Detachable

pulleys

Hovering /

flying

Traversing

tables

Three bar

mechanism Make a

bridge

Spring

system Attachment

rails Flying Big wheels

Results from Idea Generation

After sketching the ideas out, it became apparent that there was universal difficulty in traversing the

gaps between tables autonomously, due to the large distances involved. Although feasible solutions

were produced, none were economically viable, and as a result this requirement was removed.

As all the ideas were viable with or without water, it was decided to omit the use of water in all designs

to save on consumable costs, to ensure specification Requirement ⑬ was met.

The removal of water from the solutions created a new problem of how to remove stubborn dirt or bird

excrement from the panels. After a brief brainstorm, the use of a sensor to identify and forward the

location of dirt/excrement to a manual cleaner was considered.

In addition, due to lacking the water to wash away frost from the panels, operating in near-zero

temperatures would no longer be possible with this no-water approach.

Since labour is the largest consumable cost (see 1.1.3), requiring only one worker to use the device was

set as an additional requirement. Taking into account the existing requirement to have the operator

move the device manually between tables, this meant that the device had to be portable by one person,

and must therefore have a minimal weight.

Down Selection Process

After these decisions had been made, all of the 15 ideas underwent down selection. The down selection

techniques used (and in brackets, the number of ideas they each eliminated) were: checking against the




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specification (3); technical feasibility calculations (3); and a weighted ranking table (7). These are all

individually explored in more detail below.

1) Firstly, all 15 designs were checked against the specification, ruling out any ideas which did not meet

the requirements. This stage eliminated three of the less conventional ideas, with recyclable covers for

the panels and two preventative methods being removed from the fifteen.

2) Basic technical calculations were then carried out to remove any unfeasible ideas. Three more ideas

were eliminated, including the helicopter, which required a power output of 7kW just to remain in

hover; see Appendix B for the full calculation.

3) Finally, a series of pairwise comparisons were performed on all of the main design drivers, in order to

evaluate their relative importance. These were all then employed as weighted evaluation criteria to rank

the remaining nine ideas. A sample of this ranking being applied to three ideas is shown in Table 4.

The top two highest ranked ideas from this table became the final design ideas which were taken forward into

the final development stage. These two ideas are shown in Figure 2 and Figure 3 below.

Table 4: A sample of the weighted ranking table, applied to three design ideas (out of nine in total). Idea 4 was

one of the two final ideas chosen to proceed to the development stage, due to its high weighted score.

Evaluation criteria Wt.* Idea 4 Idea 8 Idea 13

Score/5 Wt. Score Score/5 Wt. Score Score/5 Wt. Score

No. of workers required 3 5 15 4 12 4 12

Skilled labour required 3 5 15 2 6 4 12

Degree of autonomy 3 5 15 3 9 5 15

Ease of use/set-up 3 3 9 3 9 3 9

Power/water consumption 2 4 8 3 6 3 6

Simplicity of design 2 4 8 4 8 4 8

Quality of cleaning 2 2 4 2 4 2 4

Overall adaptability 1 4 4 3 3 2 2

Robustness of design 1 3 3 3 3 2 2

* Wt. = Weighting / Weighted Total: 81 Total: 60 Total: 70

Figure 2: The first final design idea. A rotating scrubber would be

moved around the panel using a system of two detachable pulleys.

Figure 3: The second final design idea. A rail mounted wiper

spanning the vertical distance of the table would move

horizontally across the panels.




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Proposed Solution

The wiper design was ultimately favoured over the pulley system, primarily due to its greater autonomous

capability. Whereas the pulley system could only operate on limited widths of a table at a time before it would

have to be manually reattached to the next adjacent section, the wiper could run continuously across long

spans of a table. However, several refinements still had to be made to resolve remaining issues before a

satisfactory final design was reached, and these are detailed below.

2.4.1 Modifications Made to Initial Design and Resultant Advantages Offered

Vertical motion across the panels was incorporated to resolve potential cleaning

difficulties arising from solely horizontal motion. A uniform downwards pressure must

be exerted by the wiper across the whole vertical height of the panels in order to clean

them effectively, but this would be difficult to achieve due to the panels’ inclination.

Wheels were incorporated to provide this vertical motion, however they still need to

cope with the horizontal motion required across panels, and so omnidirectional wheels

similar to those shown in Figure 4 were chosen to be the most suitable for this purpose.

The device would be guided by a second pair of parallel vertical rails, preventing the

motion of the wheels from deviating from a straight vertical line. These rails would

feature quick-release clips on one end to assist their attachment to the top of the panel,

to ensure they could be handled safely by a single worker, in accordance with

Requirement ⑩.

A feature from one rejected idea, an extendable coil acting as a loaded spring which

allowed the rail span to be varied (Figure 5), was modified into a telescopic approach.

A wheel assembly similar to that found in modern roller coasters was also incorporated

into the final design, to secure the rails against the panel edge.

The fixed wiper was replaced with a detachable rotating brush to help increase cleaning

effectiveness further. The detachability element also allows for brushes of varying

widths to be installed on the device (namely 1 m or 1.6 m to accommodate for both

portrait and landscape panel orientations), which conforms to Requirements ⑤ and ⑥

concerning adaptability.

2.4.2 Potential Problems Arising Due to Modifications

There are geometric issues associated with the pair of vertical rails remaining parallel to each other. The

design must ensure this condition is met, otherwise kinematic constraints will be introduced which will

prevent the device from moving up the rails. Lateral bracing between the rails could fix this issue.

The issue of repeated cyclic conversion of kinetic energy to irrecoverable GPE arises due to the vertical

motion across the panels. This introduces inefficiencies into the device which would increase power

consumption, therefore extra care needs to be taken to ensure that the battery life of the device remains

high enough to be in use for a substantial time before it needs recharging.

Figure 4: A typical

omnidirectional

wheel [13].

Figure 5: An initial

approach to varying

the rail dimensions.

Figure 6: The proposed

wheel assembly.




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3. DESIGN DEFINITION OF PROPOSED SOLUTION

Final Design

Four ultrasonic

sensors to detect

perimeter of

table, allowing

for autonomous

movement of

device.

Housing for cable between main

device and stepper motors in rails.

Retractable reel ensures there is

never any slack obstructing device.

Supplies power from main device

to steppers (in yellow).

Telescopic rails to provide

adaptability for different

table configurations.

Rail struts provide

lateral bracing and

rigidity to eliminate

kinematic constraints.

Hinges and quick

release clips allow

rails to be detached

from main device.

Detachable brush allows

for brushes of different

widths to be installed to fit

panel orientation.

Easy access to inside of

the device allows for

battery replacement

during operation. Handles

on the main housing for

easy pick up.

Interlocking gears to

drive brush. Gear train

for wheels and brushes

are different so they

can rotate at a different

RPM.

Stepper motors placed in

each end of the rail, used

to move a predetermined

distance horizontally

Omnidirectional wheels

allowing movement in

two directions without

compromising surface

cleaning




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Presentation of Final Design Including Operation Procedure

1•Module on the ground with support rails.

2

•One operator picks up the device and place it on the bottom right of a table.

3

•Rails are hooked on to the top of the panel removing the need to work at height.

4

•Rails are attached to the module with quick release clips.

5

•Rails are hooked on to the bottom of the panel and length adjusted if needed.

6

•Operator presses start on the top of the device.

7

•Device moves up the panel and cleans. Detection of excriment is recorded.

8

•Ultrasonic sensor is activated. The device stops moving.

9

•The stepper motors are activated and the device moves right one panel width.

10

•The device then moves down the panel. Process is repeated.

11

•Repeated until the ultrasonic sensor detects the edge on the panel.

12

•The device moes to the bottom of the panel ready to be removed.

1 2

3 4

5

7 8

9

10

11 12

6




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Orthographic Projection Showing Key Dimensions

Solar Panel Cleaning Device




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General Assembly Drawing with Parts List

Solar Panel Cleaning Device




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4. PROVING CALCULATIONS AND TECHNICAL FEASIBILITY

Structural Analysis

Structural analysis was focused on the critical components of the design such as the rails. Further development

would include analysis and material selection for the reaming components. However, in order to prove the

technical feasibility of the design, this approach was deemed sufficient

4.1.1 Material Selection

The weight of the rails had to be minimised in order to remain safe for one worker to handle them, in

accordance with Requirement ⑧. However, they also had to be as stiff as possible to ensure no kinematic

constraints were introduced into the device. Therefore, the rails were modelled as light, stiff ties for purposes

of material selection. From this, the relevant Ashby material index [9] could be derived, which was:

𝑀 =

𝐸

𝜌

Eq. (1)

This index was used to display all materials with a high stiffness to weight ratio, and therefore determine

which general class of materials would be suitable for use in the rails. Aluminium was chosen due to satisfying

this ratio, in addition to being relatively inexpensive and readily available from most stockists.

A specific grade of aluminium was then chosen, which matched closest to the required material properties.

Since the rails would be circular hollow sections, the aluminium used had to be formable so that it could be

extruded into the necessary shape; it also had to be weldable so that wheel assembly housing could be joined

to either end of the rails. Finally, it had to offer a high corrosion resistance, as the rails would be exposed to

the outside environment. Neither machinability nor strength were sought after characteristics. Using these

criteria, and the aluminium database provided on www.aluminium.matter.org.uk [10], Aluminium 1200 was

selected to be the most suitable grade to use for the rails.

4.1.2 Stiffness Calculation

The rails spanning the vertical distance across panels would experience some deflection under their own self

weight. This must be minimised to ensure no kinematic constraints are introduced to the device as it moves

across them.

Objective: Calculate the worst case deflection/span ratio for the

pair of vertical rails.

Free body diagram of model used, showing all forces:

The UDL resulting from the self-weight of the beam is shown in

Figure 7 to the right.

Assumptions:

The beam is modelled as being flat for simplicity, instead of being inclined at 32° to the horizontal as it

would be in practice.

The beam is fixed at both ends, due to the welds joining the rails to the wheel assemblies.

Figure 7: A free body diagram of the model used.




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The self-weight of the beam can be modelled as a uniformly distributed load.

The worst case deflection occurs when the 1×1.6 m panels are in the portrait orientation, and there are

two panels per table in the vertical direction (i.e. the span of each rail is 3.2 m).

Data used:

Density of aluminium is 2700 kg/m3

Young’s modulus of aluminium is 70 GPa

Circular hollow section used for rails has an inner and outer diameter of 28 mm and 30 mm respectively

Formulae used:

𝜔 = 𝜌𝑔𝐴 = 𝜌𝑔

𝜋(𝑑𝑜𝑢𝑡𝑒𝑟2 − 𝑑𝑖𝑛𝑛𝑒𝑟

2)

4

Eq. (2)

Where: ω = UDL (N/m); ρ = density of aluminium (kg/m3); 𝑔 = acceleration due to gravity (m/s2); A =

area of each rail section (m2); 𝑑𝑖𝑛𝑛𝑒𝑟 = inner diameter of each rail (m); 𝑑𝑜𝑢𝑡𝑒𝑟 = outer diameter of each rail

(m).

𝐼 =

𝜋 (𝑑𝑜𝑢𝑡𝑒𝑟4 − 𝑑𝑖𝑛𝑛𝑒𝑟

4)

64

Eq. (3)

Where: I = second moment of area of each rail section (m4); 𝑑𝑖𝑛𝑛𝑒𝑟 = inner diameter of each rail (m); 𝑑𝑜𝑢𝑡𝑒𝑟

= outer diameter of each rail (m).

𝛿𝑚𝑎𝑥 =

𝜔𝑙3

384𝐸𝐼

Eq. (4)

Where: 𝛿𝑚𝑎𝑥 = maximum deflection at mid-point of beam (m); ω = UDL (N/m); l = span of beam (m); E

= Young’s modulus of aluminium (N/m2); I = second moment of area of each rail section (m4).

Calculations and result:

𝜔 = 2700 × 9.81 ×

𝜋(0.032 − 0.0282)

4= 2.41 𝑁/𝑚

Eq. (5)

𝐼 =

𝜋 (0.034 − 0.0284)

64= 9.59 × 10−9 𝑚4

Eq. (6)

𝛿𝑚𝑎𝑥 =

2.41 × 3.23

384 × 70 × 109 × 9.59 × 10−9= 3.06 × 10−4 𝑚 = 0.3 𝑚𝑚

Eq. (7)

𝐷𝑒𝑓𝑙𝑒𝑐𝑡𝑖𝑜𝑛/𝑆𝑝𝑎𝑛 𝑟𝑎𝑡𝑖𝑜 =

3.06 × 10−4

3.2≈ 1: 10,000

Eq. (8)

Conclusion:

Considering this is a conservative estimate due to assuming the rails lie flat, in addition to taking into account

the worst case deflection possible, this is an extremely small deflection/span ratio which will not introduce

any kinematic constraints into the device.




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Gearbox Calculation

All energy analysis for the proposed solution was performed using a spreadsheet, due to the ease of

automatically calculating a range of values; please refer to Appendix C to see this in its entirety. Numerous

motors were trialled for use in the device by inputting their operating torque, RPM and power rating into the

spreadsheet, and analysing the resultant breakdown of energy expenditure produced. This process allowed a

single, optimised motor to be chosen for the device based on its energy characteristics, which ended up being

an 80 W, 12 V DC motor from RS Components [11] (RS Stock Number: 321-3192).

4.2.1 Force and Torque Required to Move Up Panel

Objective: Calculate the minimum force and torque required for

the device to be able to move vertically up the panel.

Free body diagram of model used, showing all forces:

All forces and the torque acting on a single wheel of the device

are shown in Figure 8 to the right.

Assumptions:

The coefficient of friction between the glass panel surface and rubber device tyres is 0.6.

The device moves up the panels at a low velocity, i.e. the situation can be treated as a static case.

Equivalent inertial force (during initial acceleration) and aerodynamic drag are both negligible.

Rolling resistances on the device tyres are negligible, since they are not pneumatic.

Data used:

Coefficient of friction between panel surface and device tyres is 0.6

Mass of device, excluding rails, is estimated to be 10 kg

Typical inclination angle of panels, given in the Q&A session as 32°

Diameter of device tyres is 100 mm (therefore radius is 0.05 m)

Formulae used:

𝐹 = 𝑚𝑔(sin 𝜃 + 𝜇 cos 𝜃) Eq. (9)

Where: F = required force (N); m = mass of device excluding rails (kg); g = acceleration due to gravity

(m/s2); μ = coefficient of friction; θ = inclination angle of panel (°).

𝜏𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑 = 𝐹𝑟 Eq. (10)

Where: 𝜏𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑 = required torque (Nm); r = wheel radius (m).

Calculations and result:

𝐹 = 10 × 9.81 (sin 32 + 0.6 cos 32) = 102 𝑁 Eq. (11)

𝜏𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑 = 102 × 0.05 = 5.1 𝑁𝑚 Eq. (12)

Figure 8: A free body diagram of the model used.




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Conclusion:

This result alone infers no design implications. It must be followed through with a gearbox calculation in

order to produce a meaningful outcome.

4.2.2 Gearbox Ratio Required

Objective: Calculate a suitable gear ratio which provides enough torque for the device to be able to move

vertically up the panel, whilst maintaining a suitable speed.

Data used:

A torque of 5.1 N is required to move vertically up the panel, as given in Eq. (12)

A desired vertical speed going up the panels of 0.25 m/s is chosen (discussed in Section 4.3)

The DC motor chosen has an output RPM of 8311, and a maximum output torque of 0.092 Nm

Formulae used:

𝐺𝑅 = (

2𝜋

60 𝑅𝑃𝑀𝑚𝑜𝑡𝑜𝑟)

𝑟𝑤ℎ𝑒𝑒𝑙

𝑣

Eq. (13)

Where: = gear ratio required; 𝑣 = desired velocity (m/s).

𝜏𝑎𝑡𝑡𝑎𝑖𝑛𝑒𝑑 = 𝐺𝑅 𝜏𝑚𝑜𝑡𝑜𝑟 Eq. (14)

Where: 𝜏𝑎𝑡𝑡𝑎𝑖𝑛𝑒𝑑 = torque attained with gearbox (Nm); 𝜏𝑚𝑜𝑡𝑜𝑟 = output torque of motor (Nm).

Calculation and result:

𝐺𝑅 =

2𝜋

60× 8311 ×

0.05

0.25= 174

Eq. (15)

Using a combination of two 30/10 and two 50/10 spur gears, a gear ratio of 225 can be achieved:

𝐺𝑅𝑎𝑡𝑡𝑎𝑖𝑛𝑎𝑏𝑙𝑒 = 3 × 3 × 5 × 5 = 225 Eq. (16)

𝜏𝑎𝑡𝑡𝑎𝑖𝑛𝑒𝑑 = 225 × 0.092 = 20.7 𝑁𝑚 Eq. (17)

𝜏𝑟𝑒𝑠𝑒𝑟𝑣𝑒 𝑓𝑎𝑐𝑡𝑜𝑟 =

20.7

5.1= 4.06 𝜏𝑎𝑡𝑡𝑎𝑖𝑛𝑒𝑑 ≫ 𝜏𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑

Eq. (18)

Conclusion:

The reserve factor associated with this torque produced is 4, which is well within an acceptable limit; the

device should never be expected to fail in moving vertically up the panels.

Energy Analysis of Device Operation

When deciding the vertical and horizontal speed for the device to move along the panel, two factors had to

be considered; power consumption, and labour costs. Since labour costs are considerably higher than power

costs (refer to Section 1.4.2), a relatively fast speed of 0.25 m/s for both vertical and horizontal motion was

chosen. Although a slower device would have been more energy efficient, the lower operating cost resulting

from the increased speed supported the business case design driver of Requirement ⑬.




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With the device travelling vertically up and down the tables, GPE losses can be calculated. Two portrait

panels per table in the vertical direction were assumed in this calculation, as this maximum height difference

created the worst case scenario for energy losses. Using the spreadsheet, and 0.25m/s device speed, the mean

energy per panel was calculated to be 445J, with 9% of all energy being expended as irrecoverable GPE.

This inefficiency was accepted as a satisfactory value, since it was likely that the vertical motion would

improve cleaning quality. Additionally, this loss did not make up a significant proportion of the total energy

output; a much greater proportion of energy went into rotating the roller brushes, with an estimated power

consumption of approximately 40W during cleaning. This is required to overcome large friction losses during

rotation, due to the small downwards pressure exerted by the brushes on the panel.

Battery Power Usage

A 12V, 7000mAh, rechargeable NiMH D battery pack from RS

Components [12] (RS Stock Number: 777-0387) was selected to power the

12V, 80W DC motor due to its high capacity. With a current rating of 11A,

the average current supplied to the motor was assumed to be approximately

7A, although in practice this could vary and would need to be measured

empirically for a more precise value. At these estimated levels of current

drawn from the battery pack, it could be expected to deliver enough current

to clean approximately 380 panels before becoming fully depleted.

Despite its high capacity, the battery has a very low duration. There are two feasible solutions to overcome

this problem: connecting more than one battery in series, and charging batteries on site. Taking a portable

1kW petrol generator to the site, and connecting it to a rectifier, would be necessary if recharging was

implemented. In order for this to work, an additional battery pack and a small amount of petrol would need

to be brought with each device. The cost of this additional battery would be outweighed by saved labour costs

by negating the need to wait for charging times. Additionally, the device has been designed for the battery to

be easily removable and replaceable, so this would not present an issue to the workers efficiency wise.

Manufacturing Considerations

It was decided standard parts would be used where possible in order to keep costs low. Details of the

manufacturing processes required to make the few bespoke parts can be seen in greater detail in Sections 5.2

and 5.3. The final design exhibited a high degree of modularity; for example, the brush length and rails could

both be varied depending on the two possible panel orientations.

Issues arising due to the kinematic constraints of the device might hinder its technical feasibility. There are

two major kinematic constraints associated with this design, listed below:

i. Rails and their guiding holes

Because the device guiding holes which slide along the rails are set at a fix distance apart, the distance

separating the rails needs to be constant along its entirety. The prototype included an additional plate at

the top and bottom of the rails (see Appendix G) which fixed the distance between the rails. This, in

Figure 9: The battery used for




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conjunction with the rungs along the rails, acted as lateral bracing and increased the rails’ stiffness,

resulting in a rigid design and ensuring the concept is technically feasible.

ii. When the wheels are traversing from one module to the next

There may be issues with the rail wheels making a true connection with the second table. During

prototype testing this became an apparent issue. The groove of the wheel running along the side of the

device may not fit straight into the slot of the second table if not perfectly inline.

Actuation and Control Systems Used

Figure 10 illustrates the control system

implemented in the device. The

prototype manufactured proves the

system is feasible, including the feature

of detecting bird excrement via infrared

reflective sensor. The location could

then be recorded by calculating the

distance travelled from the device

starting point. This information could be

passed on to the operator via SMS

message. However, this last step was not

implemented in the prototype and would

need further development before

implementation. Figure 10 also includes

‘clicker switches’ which would be

placed in each rail. These would be

activated by pressure as an alternative to

the ultrasonic sensors if they were to fail.

Figure 11 illustrates the circuit diagram

for the device, as it would be connected

in the design. No problems were

encountered during the use of Arduino

for the prototype project development,

and as a result the use of Arduino has

been included in the final design.

However, it may be more feasible to

replace the Arduino chip with a bespoke

Integrated Circuit for use in the final

design, as these are better suited to being

mass produced.

Figure 10: The control system used by the device

Figure 11: Circuit diagram for device with Arduino




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5. COST ANALYSIS

For sources, detailed notes, and a full list of the assumptions used for all the tables below, see Appendix F.

Comparison to Other Methods

To show that the device will be competitive against other solutions currently on the market, the ranking table

above was created, considering three aspects of importance to customers. The average weighted rank

considers the ranking in cost to be twice as important as the other factors. The device is shown to be much

cheaper and easier to set up relative to other solutions.

Device Manufacture Cost

Shown above is the full parts list as per Section 3.3, with all associated costings calculated, giving a total cost

of £2,271 for each device. The parts have been split into two sections, those that can be sourced directly to

an external supplier (see Appendix F), and those that will need to be manufactured according to the following

Section 6.3. Higher quality parts have been sourced where possible, and the expense of £1,110 on machining

the parts should ensure that Requirement ⑭ is met.

Table 5: A table comparing a range of the most popular cleaning methods. See Appendix F

Table 6: The full costing for the manufacture of our device. See 6.3 for a breakdown of machining




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Machining Costs

Running Costs

When on site, the device will spend 34% of its time being manually moved between tables, assuming a table

of 20 panels and a moving time of 100 seconds. As a result, one employee can be expected to manage the

operation of three devices at a time. With the assumption of a half hour travel time to and from the site each

day, a 35 hour working week, and 14.4 seconds spent cleaning each panel, the cost per panel is only 3.81p.

This creates a profit of 16.19p per panel, confirming that the price of 20p is viable as per Requirement ⑬.

Payback Period

Using the assumptions listed above, a total of 1500 panels can be cleaned by each device per day in use, for

4500 total. With the manufacturing cost for each device known, a payback period can be calculated; for the

full table see Appendix F. The profit over time has been marked in green below. With the start-up cost being

three devices (£6812), only 9.5 days are required, assuming non-stop cleaning for six hours per day. To mirror

the situation of solar panel cleaning companies, an additional graph, for their theoretical existing product with

a cost only 5p greater, has been added, with no start-up cost assumed. Even with the cost to implement the

design, it has resulted in more profit than its previous method in only 31 days.

Table 7: A brief guide to the machining and costs required for each part. See Appendix F for a more detailed breakdown.

Table 8: A breakdown of the running costs to run our device on a daily basis.

Figure 12: A graph showing expected payback periods and marginal profits, with three devices in operation.

Overtakes after 31

days

Payback period of 9.5 days

-10000

-5000

0

5000

10000

15000

20000

25000

30000

0 10 20 30 40 50

Pro

fit

(£)

Days in Use

New Design Compared With Existing Costlier Method

Example

System With

Cost

8.8p/Module

Our Device

With Cost

3.8p/Module




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6. EVALUATION

Evaluation against Specification

Table 9 evaluates the final design against the product specification. This process highlighted areas of

uncertainty which would need further development if the concept was taken further.

Table 9: Meeting The Specification Key: ‘R’ = Requirement number from Specification; Y/N/P/U = Yes/No/Partially/Unknown

R Met? Discussion

1 P Having no access to the 265w Suntech panel was a hindrance. However, the prototype is capable of cleaning all areas of

the demonstration panel. As the device doesn't use water bird excrement and tough dirt might still be an issue.

2 Y The device can move autonomously around demonstration panel will ease. Therefore it can be assumed that it will meet

this specification point.

3 P

Like with Requirement 1, this cannot be fully tested without the 265w Suntech panel. However upon inspection of the

demonstration white board after device operation, no visible flaws could be seen. Additionally, the loads exerted by the

device are below the maximum allowed on the panel as declared in [1].

4 Y

The device cleans without water. It is able to clean all dust off the panel, however it is unable to clean some bird

excrement. It will be described in 7.4 as an improvement that will be added to the device in order to counter this. For

now, a reflectance sensor is being used to identify where the excrement is and tags it on a counter.

5 Y

The two driving factors for the design were cost and modularity. By having extendable rails the two identified lengths

can be catered for and cleaned. By having replaceable wheels, like different heads for a screwdriver the necessary wheel

design can be selected for the appropriate support structure. This wish was fulfilled.

6 Y As previously mentioned, the ability to extend the rails and swap the rail wheels means the device is capable of cleaning

between panels with vertical length 2.6m - 3.2m (all commercial panels). This wish was fulfilled.

7 N This specification point was ruled out early in the design process as mentioned in 3.2. Instead the device is manually

moved from one table to the next.

8 U Unable to test this as the prototype is not a fair reflection of the final design in terms of build quality.

9 Y

Both the mass and moment of inertia of the device have been set to an acceptable level with regards to LOLER

legislation [5]. Heavy components are all at the centre of the device, whilst the rails are kept lightweight. The only

components which increase the overall inertia significantly are the steppers used to drive the rail.

10 Y Specification point fulfilled.

11 Y Dimensions can be seen from the working drawings that this module fits into the selected van.

12 U This cannot be checked currently as we have not made the final device. However the prototype has been designed to be

as rigid and structurally sound as possible. If needed a transportation box could be manufactured to be placed in the van.

13 Y As shown in Section 6.4 and 6.5

14 U

Currently we do not have the final design so cannot test this. Provided the system is taken care of when moving it from

transport vehicle to cleaning the device should not fail. The most likely part to fail is the rails do to bending. However

added struts increase rigidity. Replacement of brushes would extend device lifetime.

15 P

Due to the electronics being able to operate within these temperatures, the most likely issue to do with temperature

would be kinematic constraints. The rise in temperature could make the rails expand meaning that the “guide holes” on

the device would need to be able to cater for this. Another kinematic constraint issue could be the gears inside the




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R Met? Discussion

gearbox expanding causing gear locking. Material selection would need to be further investigated here for a further

iteration.

16 Y No fluids are supplied to the device. This desire was fulfilled.

17 Y

The use of relatively low power motors (due to low mass of the device) means that noise levels during operation will be

below 85dB. The generator used to recharge the battery may need to be looked at further for this may produce

substantial noise.

Commercial Feasibility

As has been discussed in Section 6, with the price per panel set at 20p and the cost at only 3.81p, the profit is

16.19p per panel. Not only has this satisfied Requirement ⑬, but it has achieved profit at a significant margin,

while remaining cheaper than the other cleaning solutions on the market. Although the manufacturing cost of

£2,271 for each of the three suggested devices could be seen as unappealing to more frugal investors, the fact

that only 42,000 panels (see Appendix F) must be cleaned to repay this £6,812 investment can make this a

viable venture for more local businesses. Thinking critically about the assumptions for these calculations, the

significant buffer given by the 16.19p profit per panel means that even if the internal costs for a company are

wildly different to the predictions, the solution can be remain confident of being economically viable.

Improvements and Uncertainties

From the conclusions drawn in table 9 and information gathered during the prototype build, areas of

uncertainty and improvement were highlighted. Table 10 elaborates on the further development needed.

Table 10: Issues and uncertainties with suggested improvements. Key: I/U = Issue/Uncertainty no.; Apx = Appendix

I/U Issue or Uncertainty Development Needed Diagram

1

Effective cleaning of bird

excrement

Development of a modular/add on water system which deploys water when

excrement is detected would solve the issue. n/a

2 Ultrasonic sensors failing. Integration of emergency trigger switches in the end of the rails to stop

device if sensors fail. Prototype code has proved it is feasible. n/a

3 Kinematic constraints of the rail. Inclusion of rungs between the rails help. However, the prototype proved that

one solid piece (rather than two) at the end of the rail improves stability. Apx G: 1

4 Low battery capacity

Operator could bring spare battery packs and a portable ~1kW petrol

generator to site connected to a rectifier, so that a full battery is always

available at any one time

n/a

5

Small strip of panel surface is not

cleaned due to gaps in the brush.

De-align the front and back brackets which mount the brush bearings to the

device, ensuring front and back brush do not miss the same 'strip' of panel. n/a

6 Cantilever solar panel frames. Development of the wheel assembly on rail would solve this issue. Apx G: 2

7

Gaps in tables might stop the

device from moving.

Larger wheels running along the panels might be able to move across smaller

gaps. Designs for such components would need to be developed. n/a

8

Current telescopic arm design

might not be technically feasible.

Prototype building highlighted an alternative method. Rail endings should

move freely along rail with fasteners to hold the ends in the correct position. Apx G: 1

9

Technical feasibility of the cable

housing hasn’t been demonstrated.

Build a prototype demonstrating the cable reel can hold the cable under

tension at all time, ensuring it retracts when needed. n/a




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Overview and Conclusion

The two driving objectives for the design were modularity (Requirement ⑤ and ⑥), and reducing cost. As

a result the design is able to be used for a comparatively low cost compared to market contenders. The

elimination of water and the low mass of the device reduce consumable costs at the expense, respectively, of

not cleaning bird excrement and not being able to house a larger battery. This had to be done to compromise

for low cost in line with specification point ⑬. For sites with a lot of bird activity, it is likely that the use of

the device will be sub-optimal unless the addition of a water compartment is included as mentioned in Section

7.4.

Despite these flaws, the information stated in the report suggests that the design altogether remains

commercially and technically feasible. Table 9 illustrates that the device has met most of the design

requirements, and the objective evaluation listed here reflects its potential success in industry. In Table 10,

the areas in greatest need of improvement are highlighted, making development on the design a simple and

viable path to explore for the future.




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BIBLIOGRAPHY

[1] Suntech Power, “Multicrystalline products,” 21 April 2014. [Online]. Available:

http://shangde.fanyacdn.com/imglibs/files/stp265_wem(mc4_265_260_255).pdf. [Accessed 29

January 2015].

[2] EvoEnergy, “Case studies,” 16 July 2012. [Online]. Available:

http://www.evoenergy.co.uk/business/case-studies/. [Accessed 29 January 2015].

[3] Water Direct, “Water Supplies,” 23 October 2012. [Online]. Available: http://www.water-direct.co.uk/.

[Accessed 05 February 2015].

[4] Hyundai Power Equipment, “Hyundai HY1000Si-LPG Dual Fuel 1kW Inverter Generator,” 04

September 2012. [Online]. Available: http://hyundaipowerequipment.co.uk/hyundai-hy1000si-lpg-

dual-fuel-1kw-inverter-generator/. [Accessed 05 February 2015].

[5] GOV.UK: Health and Safety Executive, “Lifting equipment at work,” 12 March 2013. [Online].

Available: http://www.hse.gov.uk/pubns/indg290.pdf. [Accessed 03 March 2015].

[6] MV Commercial Ltd., “Box Vehicles,” 19 December 2010. [Online]. Available:

http://www.mvcommercial.com/box-vehicles.html. [Accessed 04 February 2015].

[7] “MIL-STD-810: Environmental Engineering Considerations and Laboratory Tests,” United States

Military Standard, 2008.

[8] GOV.UK: Health and Safety Executive, “Noise Regulations,” 20 November 2012. [Online]. Available:

http://www.hse.gov.uk/noise/regulations.htm. [Accessed 07 February 2015].

[9] M. Ashby, in Materials Selection in Mechanical Design, Butterworth-Heinemann, 1992, p. 109.

[10] aluSELECT, “Wrought Alloy Applications,” 01 October 2002. [Online]. Available:

http://aluminium.matter.org.uk/aluselect/01_applications.asp. [Accessed 18 March 2015].

[11] RS Components, “DC Motor, 80.16 W, 12 V dc, 6.35mm Shaft Diameter, 8311 rpm,” 6 October 2014.

[Online]. Available: http://uk.rs-online.com/web/p/dc-motors/3213192/. [Accessed 15 March 2015].

[12] RS Components, “NiMH D HT × 10 7000mAh 12V Pack,” 06 October 2014. [Online]. Available:

http://uk.rs-online.com/web/p/d-rechargeable-battery-packs/7770387/. [Accessed 15 March 2015].

[13] Omni-directional wheel image, [Online]. Available: http://www.robotshop.com/en/100mm-

omnidirectional-wheel-brass-bearing-rollers.html. [Accessed 23 March 2015].




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APPENDIX A – GALLERY OF 15 REJECTED IDEAS




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APPENDIX B – IDEA DOWN SELECTION

Sample calculation for Helicopter Idea 12: Actuator Disk Theory

Objective: Calculate the minimum power output for the helicopter to remain hovering above the panels.

Assumptions:

Thrust loading and velocity are uniform across the rotor disk

Viscous effects such as drag are ignored

Air is incompressible

Data used:

Helicopter mass, including mass of motor and water supply tank, is estimated to be 40 kg

Length of each rotor blade is estimated to be 0.4 m

Density of air at sea level is 1.225 kg/m3

Formula used:

𝑃 = √𝑇3

2𝜌𝐴

Eq. (19)

Where P = power output required for hover (W), T = thrust from rotor blades (equal to the total weight of the

helicopter) (N), ρ = density of air at sea level (kg/m3), A = disk area swept out by rotor blades (m2).

Calculation and result:

𝑃 = √(40 × 9.81)3

2 × 1.225 × 𝜋 × 0.42 = 7004 𝑊

Eq. (20)

A list of all design ideas eliminated as part of the down selection process. Idea 4 was the final one chosen.

Idea # Main Reason for Rejection

1 Repeated vibrations induced may cause damage or fatigue to the panels

2 Design is too complex; likely to have many problematic maintenance issues and/or high possibility

of breaking down

3 Actuation systems required would be too complex to incorporate into design; not very feasible

5 Tracks prevent full cleaning coverage of panel

6 Issues due to manoeuvrability due to large turning circle which would be required

7 Operating cost of running pump and filter system continuously would be too high

8 Too much power would be required to lift hovercraft off surface of panel

9 Orientation of panel may present issues; requires lots of pre-installation

10 Would not be autonomous as continuous human interaction would be required

11 Wasteful in long term as polystyrene would degrade so consumable expenses will be high

12 Too much power would be required to provide necessary lift (see below)

13 Three-stage telescopic handle would be very difficult to manufacture

14 Design offers no advantages over current methods of cleaning

15 Would be difficult to clean whole area of panel thoroughly; not very feasible as a large torque

would be required to swing mechanism




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Conclusion:

Clearly, a required power of 7 kW is unfeasible when compared to other cleaning methods, which only require

power on the order of a few watts to operate effectively. This would incur massive running costs due to the

large amounts of consumables required, rendering this idea not viable for a business case.

APPENDIX C – SPREADSHEET USED IN ENERGY ANALYSIS




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APPENDIX D – COMPONENTS USED FOR PROTOTYPE

0.00 10.00 20.00 30.00 40.00 50.00

Ultrasonic Sensor

Normal Motor

Stepper Motor

Micro Switches

Omnidirectional Wheels

Rail's bar 3m Axles

Gears

Belt

Belt Pulleys

Bearings 20mm (Brushes)

Bearings 10mm (Axles)

PVC Pipe for Brushes

Components Used For Prototype Costing

Quantity

Price/Unit (£)

Total Price (£)




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APPENDIX E – SOFTWARE CODE




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APPENDIX F – COST ANALYSIS SOURCES AND ASSUMPTIONS

To obtain the price per panel for these cleaning methods, we posed as a representative of the 30,000 module

Hullavington solar farm in the UK (postcode SN14 6ED), and requested quotes from a range of companies

for each other the methods. This is summarised in the table below.

For the time taken per module and relative difficulty to set up, information was gathered from the online

discussions with the company representatives above. In addition, an employee of the solar farm industry who

installs panels on a daily basis, Steven Smith, was contacted for his verdict and opinion on the times we had

generated from the email discussions. These were then adjusted to give the values in the table above.




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In the table above, the sources for the individual cost and retailer have been numbered above, and correspond

to the sources in the table below. The mass column above was calculated from CAD files for those parts that

would be machined, or the masses provided by the suppliers for those parts that were bought directly. For

several items, no mass was provided online, and so where a star (*) is marked next to the mass, this value has

been estimated based on similar products. The material cost above is not a generic price found online, but is

the validated cost as sourced from the suppliers in the table below. The machining costs shall be discussed in

a subsequent table.




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For the machining costs in the report (Table 7), the work required from the external machinist was considered

to be either skilled or unskilled. Skilled work was charged at £40 per hour, and unskilled at £20. the own

estimates and assumptions from the familiarity with the part designs was used to give a time required to

complete the part.

For Table 8, looking at the running costs, no new sources were added but a number of assumptions and

references were used. An assumption of £20 per hour was made for the labour, and a cost of petrol of £25 for

an hour of driving. As the work is unskilled, both of these terms are obviously overestimated, and this was

done to ensure we weren’t basing the commercial viability off assumptions that any possibility of being

flawed. The electricity cost was referencing Section 1.4.2 where it had previously been determined. The

device was assumed to be in use for six hours per day, with an hour travelling time, and with a speed per

panel of 14.4 seconds while in use. The size of the farm was irrelevant to the calculations here as the device

was already assumed to be in constant use.

For the payback period graph Figure 12, no additional sources were used here either, but the assumptions

were identical to Table 8 (see paragraph above). Cleaning 1500 panels per day (per six hours, being at 14.4

seconds per panel), the revenue was calculated by multiplying this number of panels by 20p. The cost was

simply this number of panels multiplied by 3.81p. The profit was then simply the difference between the two,

as expected. The start-up cost of £6,812 was then subtracted from this profit to give the profit over time. For

the example device used by solar cleaning companies already, the same process was used, as the device was

cleaning at the same speed, but the cost was 8.81p per panel, with no start-up cost. As a result, profit increases

slower, but starts at £0 as opposed to -£6,812, eventually being surpassed by the design at 31 days.




27 March 2015



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APPENDIX G – EVALUATION DIAGRAMS

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Final Report

Documents

Transcript of Final Report