SOLAR PV TECHNOLOGY. Eric Buchanan Renewable Energy Scientist West Central Research and Outreach Center Wcroc.cfans.umn.edu

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1 SOLAR PV TECHNOLOGY Eric Buchanan Renewable Energy Scientist West Central Research and Outreach Center Wcroc.cfans.umn.edu

2 Solar Energy Technology Two ways to harness energy from the sun: Convert sunlight into electricity Photoelectric materials convert sunlight into DC electricity the PV effect Convert sunlight into heat Thermal collectors can heat a fluid or air to provide heat to a building or water system Can also provide cooling via a sorption chiller

3 Solar Energy History Solar Electric 1839 Bequerel discovers PV effect 1954 Bell Labs develops first module 1960 s Used by NASA Too expensive for anything else 1970 s Gains ground after energy crisis Today Used everywhere Boom and bust cycle more dependant on incentive policies

Sunlight to Electricity The PV effect When photons add enough energy to electrons, they cross the band gap and become available for conduction Layers of

4 Sunlight to Electricity The PV effect When photons add enough energy to electrons, they cross the band gap and become available for conduction Layers of specially treated semiconductors create an electric field that pushes the available electrons to the surface The band gap determines what kind of light will work

Sunlight to Electricity Photoelectric materials Mono-crystalline silicon (15% to 20% eff.) o More difficult to make and higher cost o Better longevity?? Polycrystalline silicon (12% to 16% eff.

5 Sunlight to Electricity Photoelectric materials Mono-crystalline silicon (15% to 20% eff.) o More difficult to make and higher cost o Better longevity?? Polycrystalline silicon (12% to 16% eff.) o Most common simpler to make Thin film uses less material Amorphous silicon (a-si) (6% to 8% eff.) Cadmium Telluride (CdTe) (10% to 12% eff.) Copper Indium Gallium Diselenide (CIGs) (10-13% eff.) Multi-junction (up to 40%) o Expensive, primarily space applications

6 Sunlight to Electricity

7 Sunlight to Electricity The power produced by a solar cell is equal to the voltage times the current: P=V*I B C D A E MPP = Maximum Power Point, MPPT = Maximum Power Point Tracking o The operating point is determined by the load resistance o Charge controllers and inverters with MPPT adjust the load resistance to keep the panels at the MPP

8 Sunlight to Electricity Cell output changes with conditions Increasing maximum power point Standard Test Conditions (STC): 1000 W/m 2 25 deg C AM 1.5 solar spectrum Cell output changes when cells are combined Parallel Series

9 Sunlight to Electricity Cells are combined to make a module and modules are combined to make an array They can be connected to produce any voltage and current combination Series Typical cell values: V ~ 0.5 volts P ~ 2 watts Parallel

10 Sunlight to Electricity PV Panels (modules) Mounting angle equal to site s latitude, facing south

11 Sunlight to Electricity PV Panels ($ $4/Watt) Most panels have a year warranty 80% of rated performance after 20 or 25 years 0.5% degradation per year (NREL study) o 78% of rated performance after 50 years Panels that track the sun have higher outputs Single axis tracking increases output by 28% Dual axis tracking increases output by 36% o PVWatts model predicts solar panel performance (NREL)

12 Sunlight to Electricity There are 2 ways to install a solar PV system Grid tied Excess electricity is sold to a utility company (net metering) Grid Tied System Stand alone Uses batteries to store electricity for dark times

13 Sunlight to Electricity Grid tied system considerations The electrical grid provides storage Net metering (<40 kw) Inverter is more expensive ($0.70/W) Converts DC into AC must match grid sinewave Shut-off for power outages Typically 96% efficient with a 10 year life Micro inverters work on each module o Eliminate high DC voltages, solve shade and mismatch issues o AC modules combine inverter & panel as one unit

Sunlight to Electricity Stand alone system considerations Batteries are expensive ($1-3/W) Deep cycle lead acid Have a 5 to 10 year life Batteries are about 80% efficient Must be

14 Sunlight to Electricity Stand alone system considerations Batteries are expensive ($1-3/W) Deep cycle lead acid Have a 5 to 10 year life Batteries are about 80% efficient Must be properly stored A charge controller is needed o Prevents over and under charging o Maximum power point tracking A back-up generator may be needed Simpler inverter costs less ($0.50/W)

15 The Solar Industry Solar PV US grid tied PV installations rose 102% in 2010, 40% in 2011 US installations doubled in 2011 (2GW) 74% of cell production is from China & Taiwan Sources:

16 The Solar Industry Solar PV DOE s Sunshot Initiative aims to get installed PV costs to $1/Watt by 2020 (6 cents/kwh) Current prices* Module: $1.32/Watt Inverter: $0.52/Watt System: $2.91/Watt *NOT installed, Jun

17 Data & Modeling National Renewable Energy Labs (NREL) has developed a free PV modeling tool Simply enter your zip code & system details Uses historical insolation & weather data Outputs monthly energy production (kwh) and savings based on local utility rates

18 US Fish & Wildlife 21.6 kw system Solon 225 Watt panels (96) 4 separate arrays Sunny Boy 5000 inverter by SMA America Inc.

19 US Fish & Wildlife Annual Totals (kwh) Actual = 30,900 PV Watts = 25,741 Model is 20% low

20 UMM PV System Two 1.5 kw pole mounted systems One fixed One with 2 axis tracking Enphase microinverters Web based monitoring

UMM PV System Comparison (kwh) Oct Nov Actual 356 259

21 UMM PV System Comparison (kwh) Oct Nov Actual PVWatts % Diff. -12% -14% Annual Ave: Tracking is 36%

22 Van Gooch Home 7.74 kw system Kyocera 215 Watt panels 36 panels pole mounted 7kW grid tie inverter Seasonally tilted (manually) 30 deg in summer 60 deg in winter

23 Van Gooch Home PVWatts Comparison Annual Totals (kwh) Actual = 10,861 PVWatts = 9,631 Model is 11% low

24 THANK YOU Eric Buchanan Renewable Energy Scientist West Central Research and Outreach Center Wcroc.cfans.umn.edu

William Haman, P.E. IAMU Energy 2013 Conference, Ankeny, IA October 1, 2013

Iowa s Solar Energy Potential, The Basics William Haman, P.E. IAMU Energy 2013 Conference, Ankeny, IA October 1, 2013 Who is the Iowa Energy Center? A Little History Created by the 1990 Iowa Energy Efficiency