Say you want to buy a solar plant.
The cost of the install + Interest will equal some amount of money to be paid out per month. I'll call this Outgoing$Monthly.
Power generated per month will be sold on the market for some amount of money. I'll call this Incoming$Monthly.
Set Incoming$Monthly = Outgoing$Monthly.
This would be the point at which your investment broke even on a monthly basis (not including maintenance cost at the moment, this is just to include interest expense into the equation). It's not going to be quite right, because of seasonal variation, as mentioned below, but I'm not looking for anything exact, just a rough way to start gauging cost / benefits.
The end result will be a relationship between the Installation Cost per Watt, Interest Rate, and Required Sales Price of Energy produced in order to break even.
I'll skip to the chase, for those that don't want to read through the whole thing.
Cost/kWp ($/Wp) = Rate ($/kWh) * C2/C1
Note that the assumed interest rate for purposes of this post has been set and absorbed by C1, and the Insolation Ratio has been absorbed into C2.. Other assumptions and logic are pointed out below.
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