You’ll recall in my previous solar article, I left off wondering what to do when the power grid is “down.” Utilities require PV systems to automatically shut down when its utility connection “goes down.” That is required by code to prevent exporting PV voltage back on the wires and electrocuting some unsuspecting lineman working to fix it. The sun is still shining, so what to do?
Batteries are the answer! You’ll need them to maintain power in your home or business when the grid is down. A huge surge in interest is creating a backlog of demand by buyers wanting batteries to better control the available energy for their homes and businesses. Used in conjunction with a well-designed solar PV system you have a solution that can keep you going indefinitely. No more running for gas for your generator. No concern about food spoiling in your refrigerator or freezer. No worry about internet access. No worry about charging your cell phone.
Batteries are still expensive, so getting size right is important. To do that, review your lifestyle and your power consumption habits by reading your monthly electric utility bills for the last 12 months. Open a spreadsheet and record the kWh usage for each month in one column and the daily kWh average in the next column and the dollar amount of the bill in the third. Get the total kWh purchased for the year, your averaged daily use and your annual spend. You’ll see a seasonal pattern with usage increasing as you get into spring and summer, peaking in late summer/fall, then falling off into winter.
Air conditioning is our primary driver of that seasonal increase. Got a pool? It’s a close second with its pumps and heater as an additional load. Do you still have incandescent lights? Switch to LEDs. Have large south-facing windows? Tint them. Have single pane windows? Get thermopanes. Changes like these helps cut down your electric usage and spend. Fortunately, it also the cost of your PV system because it reduces the needed size to carry the household loads. Why spend an extra $10 or $20,000 to buy a bigger PV system just to support inefficiencies?
An important exercise in the design of your system is to designate your “critical loads.” These are the parts of your house you want to keep powered up while you’re on just batteries when the grid is down. To maximize the useful capacity of your batteries you need to know this and limit your use to them. Usually you’ll include your refrigerator and freezer, lights and outlets in the kitchen, lights and outlets in the in the master bedrooms, the garage door opener. Instead of the relying on your main whole house air conditioning system for the whole house, add and power a mini split AC or window AC for the master bedroom. At least you’ll have a cool refuge until the grid is back on line.
Batteries have a very bright and hypercritical future in this new solar age. We’ll explore that future in my next article.