Solar Investment Calculator
Plan the Switch

Disclaimers, Notes and Assumptions:

1. This calculator has been verified based on real experience during first year of operations with 1.2kW solar array that produces 1459 kWh/year near Orangeville Ontario, facing due south, panels at 35 degree from horizontal, Sharp 120 (ND123U1 module) watt panels. Daily output determined by using the following multiplier 1459 (actual kWh/year) divided by 1200 (rated kWh) creating a multiplier of 1216/year. In order to calculate daily output the formula Systems size x 1216 (multiplier) / 365 (days in a year) is used as an estimate. A default multiplier if 1150 is used as a more conservative estimate as provided by my solar system provider. All other calculations are based on this estimate. Actual output year to year on this system will vary. Each systems output will vary depending upon the efficiency of the panels, the orientation variation and many other factors. This calculator should only be used to provide rough conservative estimates. The multiplier includes the typical maximum 80% loss in output within the first 20 years.
2. Module efficiency defaults to 14.13% which is the value for the Sharp panels used as a benchmark. This calculator allows you to put in your own values for Module efficiency and Multiplier. The calculator does not change the multiplier input if you increase the efficiency value input. Increasing, for example, the module efficiency value adds that percentage the output equations. So if by default the multiplier is set to 1150 while the module efficiency is increased to 17% from the default 14%, then the daily output is increased by 3%. This suggests you should only change the Output multiplier or the Module efficiency in order to estimate the difference in comparison to the model Sharp panels used for the default values. Leave the Module efficiency at 14.13 if you are changing the Output multiplier.
3. Square footage is based on the Sharp 120 watt solar panel (26.1" x 59") as used in the project that provides the basis for these calculations. Since panels are mounted at a 35 degree angle the square footage is partially vertical and so exaggerates the total square footage required to mount the panels.
4. Borrowing costs and monthly bottom line are based on nominal annual rate input. Borrowing costs are a mortgage rate calculation with principle based on percentage of overall cost input, interest rate of the mortgage as input and amortization period as input. The idea would be to get a Home Equity Line of Credit based on a long term amortization and flexible repayment options and a good interest rate. Calculations based on information from - http://www.yorku.ca/amarshal/mortgage.htm. CONFIRM YOUR BORROWING COSTS WITH YOUR OWN CALCULATOR.
5. Break even does not take into account the cost of borrowing money.
6. Inflation is not taken into account.
7. NPV is net present value - for calculation details see Net Present Value calculation on Wikipedia. I've done the cash flows for 40 years. If NPV is negative it suggests this may not be a good financial investement.
8. The discount rate (the rate of return that could be earned on an investment in the financial markets with similar risk.)
9. Larger solar array sizes will likely have lower overall production levels that this calculator shows by default since there are more areas within a large array for efficiency losses. See the Exhibition Place Horse Palace 100 kW array example for good detailed analysis. Reducing the efficiency parameter in our calculator may be a way of anticipating these losses. According to this example an annual output of a 45 kW Sharp solar array would be 45,000 annually. You may need to reduce the efficiency number in the calculator to match this number more closely for a conservative estimate (keep in mind though that there were some other problems at the Horse Palace and the panels were at 20 degrees angle, rather than the more optimal 32 degrees for Toronto and off azimuth to direct south as well).
10. Another reference example was provided in an article in the Toronto Star. "What does this mean for homeowners looking to take advantage of the new pricing? The Ministry of Energy estimates that a homeowner who wants to install, for example, three kilowatts of solar PV can expect to pay around $30,000 for the panels, equipment and installation."This would provide enough electricity to meet one third of their consumption and would generate about $7 per day," according to a ministry backgrounder. "This payment would result in approximately $2,500 in revenue per year for the homeowner, resulting in about a 12-year payback."To be clear, the solar electricity a residential system generates isn't consumed by the home. All of the power is fed into the electricity distribution system outside your home. Homeowners, in essence, become power generators. Every single kilowatt-hour that's produced generates 80.2 cents worth of revenue for the homeowner.Let's fact check the government's numbers. According to a 2006 federal study, the average one-kilowatt rooftop PV system in Toronto would generate 1,161 kilowatt-hours per year. At 80.2 cents per kilowatt-hour, that works out to $931 annually. A three-kilowatt system would therefore earn $2,793 a year.At $30,000 for such a system, divided by $2,793, it works out to a payback of just under 11 years (excluding interest you may have to pay on the initial capital cost). It means that the remaining nine years in the 20-year contract with the power authority would pay out an additional $25,000 for the homeowner." - Tyler Hamilton, Toronto Star, March 23, 2009, Solar-power feed tariffs windfall for homeowners
11. If you are planning to invest in solar PV in Ontario, read the Community Action Manual put out by Ontario Sustainable Energy Association (OSEA).
12. Future electricity rate. After 20 years it is assumed that the panels will continue to produce at 50% of rated output used for first 20 years and that the future electricity rate (default value) will be 12 cents/kW (approximately double current rates in Ontario). It can be expected that the solar panels will continue to produce electricity for 40 to 60 years.
13. Ontario Feed-in Tariff (FIT) contracts are currently for 20 years at a fixed rate of 80.2 cents/kW for solar PV under 10kW (as of Nov 15, 2009, see the OPA web site for update information on contract terms, rules and current rates).
14. Two types of meter cofiguration are possible with a small MicroFIT configuration. Series meter connections have the generation meter behind the consumption meter and before your electricial panel. In this configuration the OEB has ruled that the LDC must use a "gross load billing" calculation that accounts for the fact that you use the generated electricity before it goes onto the grid and so the amount you use must be added to your consumption amount (this, in effect, reduces your FIT rate by the current price of consumption electricity for the proportion that you consume, while the portion generated in excess of that consumed would be at the full FIT rate, thus making it a good idea to partially reduce the FIT rate in series connection scenarios). Parallel meter connections would not have the gross load billing applied.
15. Delivered electricity rate refers to the combination of electricity (commodity), plus delivery and taxes, you pay to actually consume electricity via the grid. The other version of this to look at would be what will the rate be in 10 years?