If you are thinking about installing a solar electric (PV) or solar hot water (SHW) system in your home, there are a few things you should consider in planning your system. One of the most frequent questions I get is “What size system do I need to offset my electric bill?” While I can give you an estimate of the size of the system, you should be considering what your overall goal is for renewable energy. Do you want to be free of paying the electric company, or do you just want to lower you electric bill? Are you looking for a reliable back-up system to carry you through power outages? Are you looking to save on your fuel bill for heating domestic water? Or do you just want to “do something” about climate change? All of these are reasonable objectives, but what you do to meet these goals will vary from household to household.
Because most people get a monthly electric bill, it is fairly easy to determine what size PV system is needed to offset the costs. A typical household uses around $100 per month of electricity, or around 500 kilowatts (kW). To generate this amount of electricity would require an eight kW system, due to inefficiencies, cloudy days, etc. At a cost of approximately $5 per watt, this system would cost about $40,000. When faced with this number, most people say “Well, maybe I don’t want to make all my own electricity.” When we design a system, we can build in expandability to allow adding more capacity in the future, so that, eventually, people can get to energy independence, but do it in affordable stages.
When asked how much hot water people use, most have no idea. Vendors of solar hot water equipment have developed systems that will meet the needs of a family of four, or six, or more people, usually by upgrading the storage tank size and adding collectors. We ask people if they have unusual hot water needs (e.g., babies in diapers, teenagers, day cares), and size the system accordingly. But looking ahead to potential future uses of the system will allow planning for, and installing, a system that will provide years of free hot water.
So, what are you planning for your house?