Planning and Execution of Ground Mount Solar Projects ... · 01 basics of ground mount solar...

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prepared forgeneral audience

Planning and Execution of Ground Mount Solar Projects(“Solar 101”)

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intropurpose

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This presentation provides an overview of key concepts related to the planning, design and construction of ground mount solar projects intended for a non-technical audience.

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introoverview

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01 basics of a ground mount solar project 02 project planning

01 basics of groundmount solar projects

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basicsunits of electricity

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• Voltage, V (measured in Volts, V)• potential difference between two

points

• Current, I (measured in Amps, A)• rate of flow of electrons

• Resistance, R (measured in Ohms, Ω)• resistance to electron flow of a

material

V = I x R

Image Source: https://learn.sparkfun.com/tutorials/voltage-current-resistance-and-ohms-law

Water analogy:

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• Voltage is either AC (Alternating Current) or DC (Direct Current).

• In a solar project, the inverters convert from the DC output of the solar panels to AC for use by the grid.

• AC can be single phase or 3 phase.

Image Source: https://learn.sparkfun.com/tutorials/alternating-current-ac-vs-direct-current-dc

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• Power, P (measured in Watts, W)• rate of transfer of electrical energy

• Power losses depend on the current and resistance of a circuit.

For DC systems:

P = I x V Ploss = I2 x R

• Losses can be decreased by using bigger cables (lower resistance) or higher voltage (lower current).

• Transformers change AC voltage for transmission of power over long distances.

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• In AC systems, power can be • Apparent Power, S (measured in Volt-

Amperes, VA)• Real Power, P (measured in Watts, W)• Reactive Power, Q (measured in

reactive Volt-Amperes, VAR)

• Power (P) is what generates kWh ($$$).• But electrical equipment (inverters,

transformers) is rated for the Apparent Power (S), which determines current.

For 3-Phase AC Systems:

S = √3 I x V, Ploss = 3 I2 x R

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• Power Factor, pf, is the ratio of Real Power to Apparent Power.

• Power Factor can be positive (“lagging”) or negative (“leading”) depending on the relationship between the current and voltage.

• Utilities typically specify the power factor for a solar generator while requiring capability to change power factor within a specified range, for example, from -0.95 to +0.95.

• Power factor control is done by the inverters or by power factor correction equipment installed at the substation.

Image By Wikieditor4321 - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=45518724

pf = P / Spf = cos (θ)

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basicssimple schematic

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RecombinerBox

CombinerBoxes

Intermediate Transformer

InverterStrings of Solar Panels

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DC Collector

AC Collector

MMain Step-Up Transformer

Protections, Controls, and Communications

Connection to Grid

Inverter Stations

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RecombinerBox

CombinerBoxes



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DC Collector

AC Collector



Connection to Grid

Inverter Stations

Each panel generates ~40V, 8.5A. They are connected in series to form “strings”

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RecombinerBox

CombinerBoxes



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DC Collector

AC Collector



Connection to Grid

Inverter Station

Output of strings is combined in parallel at combiner boxes and recombiner boxes.

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RecombinerBox

CombinerBoxes



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DC Collector

AC Collector



Connection to Grid

Inverter Station

Maximum Power Point Inverters have two functions

• Convert the dc power into ac.• Control the dc voltage from

the solar array to track the “maximum power point” or curtail the power.

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RecombinerBox

CombinerBoxes



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DC Collector

AC Collector



Connection to Grid

Inverter Stations

Larger projects have multiple subarrays each connected to its own inverter station. Multiple inverter stations are connected to form a “collector system”.

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RecombinerBox

CombinerBoxes



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DC Collector

AC Collector



Connection to Grid

Inverter Stations

One or more transformers step up the voltage to grid level.

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RecombinerBox

CombinerBoxes



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DC Collector

AC Collector



Connection to Grid

Inverter Station

A substation contains the main transformer together with protections and controls equipment required to connect the project safely to the grid.

A substation without a transformer is called a “switching station”.

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basicspiles

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• Different types• Driven piles• Helical piles (1 or more helixes)• Ground screws• Caisson piles• Rock anchors• Or none at all (ballasted system)

• Selection depends on• Frost depth• Presence of boulders• Type of soil / presence of bedrock

• Subsurface risk can impact project cost and schedule.

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basicsgrid interconnection

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• Point of Common Coupling (PCC) is where the ownership changes from customer to utility. • Point of Interconnection (POI) is where the project connects to the existing grid.• PCC and POI can be in different locations if a new utility-owned line is required to connect the project.

Image Source: Hydro One, Form B, Connection Impact Study Application

02 project planning

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planning key principles

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• The best practice for engineering of large capital projects involves a phased approach that begins with Front End Engineering Design or FEED, also called Front End Loading.

• The work completed in each phase is just enough to allow decisions to be made and the project advanced.

FEL1Conceptual

Gate Review

FEL2Pre-

FeasibilityGate

ReviewFEL3

FeasibilityGate

ReviewFEL4

ExecutionStart Up and Operations

Value Identification Value Realization

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planningkey principles

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• In each phase, uncertainty decreases and so does project risk.

• As uncertainty decreases, precision of estimates improves (project yield, CAPEX, OPEX)

Image source: http://wiki.iploca.com/display/rtswiki/2.2+Key+points+to+address+during+FEL

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planningkey principles

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• A gate review is completed after each phase to determine whether to move forward to the next phase.

• The gate review is linked to a spending decision.

Image source: http://www.chem.info/article/2013/12/right-tools-job-front-end-loading

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planningFEL 1 - concept

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Typical tasks:

• Land constraints → Environmental constraints → Available Area→ Estimate DC capacity

• Off-taker constraints• Interconnection availability→ Estimate maximum AC capacity

→ Ballpark energy production→ Ballpark CAPEX, OPEX estimates

→ Preliminary financial analysis

Go / No Go Decision

CAPEX~ $/W

Capacity ~MW/ha

Yield ~kWh/kW

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planningFEL 2 – pre-feasibility

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Typical tasks:

• Environmental site investigation(s)• Desktop geotechnical• Develop layout• Develop single line diagram• Choice and budgetary quotations for

major equipment• PV Modules• Racking• Inverters

→ More precise energy yield and cost estimates

→ More precise financial analysis

Go / No Go Decision

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planningFEL 3 - feasibility

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Typical tasks:

• Off-take agreements awarded / final.• Interconnection studies.→ Interconnection agreement• Site work, studies and consultations.→ Environmental & regulatory permits.• Geotechnical investigation.

• Prepare EPC contract designs and specifications.

→ Request for proposals.→ Bid analysis and selection.

→ More precise energy yield and cost estimates

→ More precise financial analysis

Go / No Go Decision

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planningFEL 4 - execution

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Typical tasks:

• Project finance review and credit agreement execution.

• Kick-off with EPC Contractor.• Construction planning (safety, quality,

staffing).• Detailed design & engineering (50%,

90%, Issued for Construction).→ Building permits.

• Procurement.• Construction.• Testing & commissioning.• Project start-up.

Operations.

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planninga brief word on energy storage…

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• An energy storage system has both a Power rating (Watts) and Energy rating (Watt-hours or Wh)

• Multiples types of energy storage might be appropriate for the same application.

• To select and optimize the energy storage device, first you need to develop specifications.

Image source: http://www.sandia.gov/ess/publications/SAND2013-5131.pdf

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• Consider:• Stakeholder objectives• System requirements• Load/generation profile• Costs (capital + operational)

vs benefits• Operational requirements• Replacement frequency• Technology risk• Environmental risk• And more

planninga brief word on energy storage…

page028Image source: http://www.sandia.gov/ess/publications/SAND2013-5131.pdf

thank you.

Planning and Execution of Ground Mount Solar Projects ... · 01 basics of ground mount solar...

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