Intro to PhotovoltaicsTechnological Design

What is Power?Rate at which energy is delivered

Power = Energy Time

• Measured in Watts (W), kilowatts (kW), or horsepower (HP)• Power is an instantaneous quantity• Power does not accumulate• Think gallons per minute

What is Energy?• Ability to do work• Often measured in kilowatt Hours (kWh)

• Since Power = Energy/Time, • Then Power Time = Energy

• Energy does accumulates over time• Think gallons• Gallons = (gallons/min) minutes

Power • Power is the rate at which energy is being delivered or consumed

Power = (Current)(Voltage)P = IV

• Units: Watt (W)

• So if 2 A of current is flowing through a load at 120 V, the Power used by the load is

P = IV = (2A)(120V) = 240 W

How much electricity do you use per month?

• The average household uses 1,200 kWh per month (NREL.gov)

• WWHS main building uses 17,500 kWh per month ~ $3500 power bill

• What is the daily usage?• 583.33 kWh per day ~ $117.00 per day

•Enormous nuclear reactor. Source of energy is “hydrogen burning”

•Approx 1 / 2,000,000,000 of Sun’s emitted energy reaches Earth

•Power that reaches Earth is approx. 15,000 times our total consumption

•Energy delivered in the form of electromagnetic radiation

•Electromagnetic radiation: Oscillating electric and magnetic fields: WAVES

The Sun

Solar Radiation is:49% infrared (animals and NVG’s see this)46% visible (what you see)5% ultraviolet (sun burns)

http://imagers.gsfc.nasa.gov/ems/waves3.html

Radiation Types

• Direct-beam Radiation: Radiation that has NOT been scattered. Is traveling directly from Sun.

• Diffuse Radiation: Radiation that has been scattered, and isn’t traveling directly from Sun.

• Why important?

• Flat-Plate collectors harvest only direct-beam, not diffuse radiation!

• Concentrating collectors – ones that use focusing mirrors – only harvest direct-beam radiation

Solar Constant (S): Amount of solar energy that reaches the upper atmosphere of the Earth per area per time

S = 1,370 W/m2

Solar Constant is independent of Earth’s tilt, cloud cover, etc…

Solar Irradiance: How much solar energy reaches the Earth’s surface

Varies with season, time, cloud cover, …

Irradiance at which PV panels are rated is 1,000 W/m2, called “1 sun”

Definitions

Quantify

We’re usually interested in how much ENERGY reaches (and is collected by) our module each day!

Energy = Power Time

Unit: kWhr/m2/day

This quantity is called solar insolation

Sizing?

• Series and parallel are the same as batteries• For off-grid systems, you must calculate total energy

used during highest month in order to size appropriately• For grid-tied system, you must use tie to the grid and

trade energy when needed.• How much energy from a PV panel do we need for the

daily average energy usage? (Use the numbers we used previously for daily average and average solar insulation in Wilkes county)

How about solar-powered vehicles?• Limited by space• Limits available power• Result?

How about solar charged EV?• Average vehicle is only used for 30 miles a day.• Why not charge while parked in the sun?

Experimentation Procedure• Working in teams of two, use a multimeter to measure the

voltage and amperage of two solar panels individually, in series, and in parallel.

• Part One: Measure and write down the voltage and amperage of each solar panel by themselves in your EDJ

• Part Two: Wire the solar panels in series and write down the voltage and amperage in your EDJ

• Part Three: Wire the solar panels in parallel and write down the voltage and amperage in your EDJ

Questions for your Journal• Write out these questions in your journal:• Current (Amperage): Compare the current in Parts 2 and 3

with the current measured in Part 1.• How much did the current change in each case? (Compare all

thee parts)• How do you connect cells to obtain a higher current output?

• Voltage (Volts): Compare the voltage from Parts 2 and 3 with the voltage measured in part 1.• How much did the voltage change in each case?• How do you connect cells to obtain a higher voltage output?

• Extra* - Take your solar panel outside and keep it hooked to the multimeter, place your finger over one corner of the solar panel.• What happened to the voltage?• Why?