A brief introduction to the concept:

Sizing a system properly is critical to ensure you get the very best value and return on your investment.  Every region has a different energy production expectation and every utility company has a different policy on how they bill you for solar.  This is normally referred to as “NET METERING”.  Some utility companies have very favorable net metering policies, some don’t.  The different variations are limitless and you must check with your utility company to know for sure.  If your utility company does not buy any of your surplus power and you have a choice…then you need to switch utility companies.  For the sake of keeping it simple here are the two most commonly found practices:

  • Your utility company gives you full credit for your solar energy production and does not discount any overproduction. These guys normally allow your kWh credit to roll over from month to month and will settle-up with you at the end of the year.
  • Your utility company discounts or does not give you any credit for surplus solar production. They allow net metering but if you produce more over the course of a billing cycle you only get full credit for what you use.

If your utility company is really sticking it to you and your electricity cost is higher than the national average with peak demand and/or time of use charges, it may warrant looking at a hybrid battery system but that is another subject altogether.

Example #1 is easy, add up the kWh’s you use each year, divide this number by kWh’s every KW of equipment will produce in your area and that will give you the KW system size that you need.  Assuming you get full credit, you can offset your entire bill over the year when you total up all your charges and credits for the year.

(before and after bill)

Example #2 is also relatively simple.  Basically, you want to design your system to not overproduce too much because you won’t get fair credit for your overproduction.  If you do, you are basically throwing that surplus solar energy away.  Or worse, you are giving it to your utility company who in turn is selling to the guy next door for full price.  In this case we would want to build up a system to generate just enough power to offset your lowest bills throughout the month with minimal overproduction.  Whether you are gas and electric, all electric, hot summers will affect how your actual bill from month to month throughout the year will look.  For the sake of simplicity, we will target a 70% annual offset if you think your utility company may not have a full credit net metering policy.

(before and after bill)