By Jack Fernard | Oct 9, 2015
“So how does it work?”
It’s amazing how many times my wife and I have heard that question. “A lot like a normal home,” I’ll tell them. “Except I’m plugged into the batteries that are sitting in my garage instead of a power plant miles down the road.”
And that is the gist of it, in a super simplified sort of way. But like a lot of things, there’s a little more to it.
In an off-grid home, your house is essentially running on batteries. Charging of the batteries can be handled in a variety of different ways, but in my case, I’m using photovoltaic panels.
The general rule of thumb to remember is, the more batteries you have, the longer your house can run between charging. And the bigger your solar array, the faster you can recharge your batteries. Easy enough?
There is one more key element that needs to be understood and that is the inverter. The inverter is what converts the DC energy stored in the batteries to AC for your house to use. It is crucial that the inverter be sized to your needs.
For example, let’s say you come home and feel like a hot shower. If you have an electric hot water heater, the element in it will most likely pull around 4000 watts. After the shower, you feel like some food so you go over to your electric range and start cooking. Before you know it, there is a casserole in the oven — probably pulling another 4000 watts — a pot on the large burner and something on the small burner which, combined, are pulling another 3700 watts. So between the shower and dinner, you are pulling 11,700 watts (these are generic numbers; individual numbers will vary). Now keep in mind, this number does not reflect the electricity being pulled by the TV, the fridge, any lighting, a washing machine/dryer, a well pump if you don’t have city water, or air-conditioning.
The inverter that I have is rated at 8000 watts continuous. So about the time I started dinner, the house would be going dark. Obviously, that would be less than ideal.
This is why doing your homework is so crucial when moving to an off-grid system. It is absolutely critical that you know how much electricity each item in your house is using so that you can plan ahead. For example, I switched from electric to a gas range. This allows me to cook as much as I want for as long as I want, without worry. My hot water comes from a heat-pump water heater that pulls 550 watts instead of the typical 4000 watts. Now, shower and a dinner only burns 550 watts, leaving plenty of room for the rest of the house.
So why not switch to a gas hot water heater and use even less electricity? One of the motivations for me going solar was to not use fossil fuels. The electric range had the capacity to overload my inverter all by itself. My gas costs for cooking should be around $15 a month. For my situation, I felt that this was a good trade off. Gas costs for hot water, however, would have been significantly higher. With a heat-pump water heater, I’m still using photovoltaics.
From personal usage patterns to demands dictated by location, each home is different. Knowing how many kilowatts you use in a month is one thing. Knowing how many watts you’ll use at a given moment is something entirely different. Research for your particular situation and know them both!
Whether your motivation for going off-grid is political, environmental, or just a desire to be self-reliant, understanding what your needs are — month by month and moment by moment — will bring you a long way toward a successful home experience.
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