Steve Hegedus, Institute of Energy Conversion ELEG620 April 5, 2009 slide#1Grid Connected Residential PV and Two Years Producing Solar Electricity in Delaware(and dispelling some Solar Myths)Steve HegedusInstitute of Energy ConversionUniversity of DelawareSteve Hegedus, Institute of Energy Conversion ELEG620 April 5, 2009 slide#2Outline1. Major markets and grid connected applications of PV2. Available sunlight - concept of average daily sun-hours3. Effect of array orientation - tilt, south-facing, shading4. Effect of temperature5. Shading - series connected PV cells 6. Inverter - critical component7. My system• System sizing and output prediction, comparison to load• Wiring, layout, installation • Cost8. Other PV grid connection issues and recent developmentsSteve Hegedus, Institute of Energy Conversion ELEG620 April 5, 2009 slide#3Trends in PV Markets: 1990-20061001011021031041990 1992 1994 1996 1998 2000 2002 2004 2006total world PVgrid connected resid+commcommunicationsrural off-grid central >0.5 MWMWP capacity installed each year• Grid connected PV driving market growth• Centralized (util) PVNegligible until recent, Rapid growth in EU of projects >10 MWSteve Hegedus, Institute of Energy Conversion ELEG620 April 5, 2009 slide#41.8 kW Solar Array in Newark, DESteve Hegedus, Institute of Energy Conversion ELEG620 April 5, 2009 slide#5Grid connected design issues Net metering is enabling policy ¾ Utility buys back energy at selling price (reversible meter)¾ Grid is your back-up and your “battery”¾ Full credit for excess daily production, nothing wasted Either maximum PV you can afford or maximum fit on roof Partial or total offset house/business load Aesthetics of increasing marketing value (color, form factor, stand-off) Few systems w/battery to store excess, backup select loads¾ Improve reliability, security, grid to charge/equalize battery¾ Increase cost, complexity, less efficientSteve Hegedus, Institute of Energy Conversion ELEG620 April 5, 2009 slide#6Some terminology: Power vs Energy Power: output of module or array in Watts (W) or kilowatts (kW) or megawatts (MW) under Standard Test Conditions ¾ STC= “1 sun” or 1000 W/m2 of AM1.5 sunlight, module at 25°C, ¾ A 200 W module produces 200W only under specific conditions¾ Power is instantaneous output from the PV  Energy output of module or array in kW-hrs is what you want¾ Energy is power integrated over time ¾ Energy is what you pay for on the electric bill (13.5 cents/kW-hr)¾ Energy is output over period of varying sunlight, angle, temperature Goal is to calculate daily/monthly/annual energy from module knowing PV power@ STC and location and tiltSteve Hegedus, Institute of Energy Conversion ELEG620 April 5, 2009 slide#7You want ENERGY (kW-hrs) produced but PV modules are rated in peak POWER (kWatt) at standard test condition “1 sun”??To calculate daily PV energy (kW-hrs) produced, mult size of array in kW by # hours of equivalent full sun for your orientation times 0.8 for losses → ac kW-hrs!6 am 12 pm 6 pmSolar array output (kW)•Blue curve is hourly PV power output•Area under blue curve is daily kW-hrs•Same area as red square•Width of red square is equiv hours offull sunlight (PV prod max output)• Height of red square is output under 1 sun• Widely available parameter for varioustilts, tracking options on monthly basis3-6 hrs1 sunSteve Hegedus, Institute of Energy Conversion ELEG620 April 5, 2009 slide#8Solar Hours: notable concept worth repeatingThe number of solar hours is equivalent to the number of hours of full STC sunlight at 1000 Watt/m2So it is equivalent to number of kilowatt-hours/m2Allows simple and direct conversion between STC power (# kilowatts) of PV and energy produced (# kilowatt-hrs of energy)Account for all system losses with single derating factor (same as Performance Ratio)Steve Hegedus, Institute of Energy Conversion ELEG620 April 5, 2009 slide#9Example: simple but accurate calculation Assume a 1.8 kW rated PV system (9 - 200 Watt @ STC modules) installed in Delaware at 45° tilt Annual daily average hours of peak sun for DE = 4.6 hours Assume no shadowing, oriented due south Assume 80% derating factor for many small system losses¾ 6% for inverter efficiency, 7% for temperature, 2% resistance¾ See PV Watts for complete list and range of losses  So, 1.8 kW x 4.6 hrs/day x 0.8 x 365 days = 2400 kW-hrs/year Comparison: my system produced 2350 kW-hrs (2007),2244 kW-hrs (2008) Actually have 3% shading, so 2400 x 0.97= 2330 kW-hrs/year Installer (Solar Pathfinder chart) predicted 2282 kW-hrs/yearSteve Hegedus, Institute of Energy Conversion ELEG620 April 5, 2009 slide#10Solar only works where its sunny and hot, right?Wilmington has72% as much annualsunlight as PhoenixSunlight is relatively evenly dispersed over large fraction of USSolar cells work better in summer?1501601701801902002102207580859095100105110-20 0 20 40 60 80 100 12040 60 80 100 120 140 160PV module rated at 200 Watt standard test condition (77 F)Module Power (Watts)Percentage full output (%)outdoor air temperature (F)module temperature (F)Output decreases about 0.3% for each degree F (-0.5%/C)Module temperature 40-50 deg F higher than air temperatureWait, it gets even better-Wilmington DE vs Phoenix AZ Compared to 25°C STC rating, actual temperature costs:¾ Module in Wilmington loses about 7% ¾ Module in Phoenix loses about 13% Wilmington has only 72% as much sunlight as Phoenix So PV module in Wilmington can generate 78% as muchenergy as in Phoenix!  Modules in Wilmington and Minneapolis MN have same annual output (+3% difference in sun hours, -3% due to T)Steve Hegedus, Institute of Energy Conversion ELEG620 April 5, 2009 slide#13But what about the pitch and orientation of my roof? Do PV modules work if they aren’t facing exactly towards the sun?Steve Hegedus, Institute of Energy Conversion ELEG620 April 5, 2009 slide#14Solar radiation on a tilted surfaceSteve Hegedus, Institute of Energy Conversion ELEG620 April 5, 2009 slide#15Does my roof have the right slope for solar?Conclusion: Tilt is almost irrelevant (for annual output)!!123456JanFebMarAprMayJunJulAugSepOctNovDecmonthly available