Case study #1: Part A-Energy Output of a 10 kW Grid-tied Photovoltaic System

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Case Study #1, Part A: Energy Output of a 10 kW Grid-tied Photovoltaic System A company has offered to install a 10 kW photovoltaic system on the roof of your building. The modules would face due south and be tilted at 25 degrees from the horizontal. The company proposes using 200 W “monocrystalline” silicon modules from Sanyo (model HIP 200 BA3). These solar panels produce DC electricity, which will be converted to AC and fed onto the grid using an electronic device called an “inverter”. A 10 kW inverter operating at 93% efficiency will be used. The company tells you that the electricity “exported” to the grid will be purchased by the utility at a net metering rate (i.e., the same rate that you pay for electricity).


1)      How much electricity would this system export to the grid in an average year?

2)      How much would the utility pay for this exported electricity?

3)      Save your analysis to a .RET file!

Additional questions if you finish early:

4)      The sloped area of your roof is around 800 ft2. Is there enough space for all these solar modules? Would there be space for cheaper, 13% efficient modules?

5)      What is the capacity factor for this system? What does “capacity factor” mean? If we had a good estimate of the capacity factor in advance, could we have saved time by selecting “Method 1” for the analysis type on the energy model page?

6)      The DOE indicates that in Virginia, electricity from PV projects displaces the output from power plants having emissions of 0.9 metric tons of CO2 equivalent per MWh. If transmission and distribution (T&D) losses between these plants and loads average 10%, and this PV system is located near loads such that its T&D losses are only 3%, what would be the annual reduction in GHG emissions? Is this a lot? Can you use RETScreen to infer what type of generation (gas, nuclear, coal, oil, hydro, etc.) the DOE assumes PV generation will displace?

Getting stuck? Try this:

  • Start by configuring the “Start Page” for this project. Remember that this is a power project that feeds onto the central grid.  We aren’t doing a financial analysis, in-depth cost analysis, or detailed GHG calculation, so for “analysis type”, “Method 1” will be sufficient. You will probably want to click on “Show Settings” and select “Imperial Units”.
  • Next, select your climate data location.
  • On the energy model page (not the Start page) you will need to select “Method 2” for the “Analysis Type” in order to use the climate data in a calculation of the system output.
  • Not sure what to enter for the azimuth? Click on RETScreen help!
  • Want to see the array size in ft2, not m2? Check “Show alternative units” at the top right of the page.
  • Not sure how to estimate “Miscellaneous losses”? Click on RETScreen Help! There is different help for the two different Miscellaneous losses cells.
  • Note that to convert cents/kWh to $/MWh multiply by 1000 kWh/MWh and then multiply by $1/100 cents.