Dear Mr. Solar:
We are just getting really interested in living off the grid. Our question is, how do you properly figure out how much energy you need to operate your home appliances? Is there a formula you use? We are a family of four and my wife wants to keep her kitchen electric things and her computer. We would also like to enjoy the stereo and TV. Are we asking too much, or what? We
want to be self-sufficient but don't want to return to the dark ages. Please help if you can.
T.O.A.
Jackson, Tennessee
Hello Thomas:
As an example of how far things have come, when Fran and I began living off the grid, we worked things out by the seat of our pants, having started with only one solar panel and a Sears Roebuck battery. We have gone from that to the life of Riley--and completely off the grid, as our closest neighbor is 8 miles away. We do use a propane stove for cooking, but we have and use all of the other electric kitchen appliances, as you'll see below.
The short answer to your question boils down to money. At this time, the only situation in which solar is economical is in very remote locations, where the utility company may charge upwards of $10 per foot to bring in power. It doesn't take a very sharp pencil to see that this comes to over $50,000 per mile. We live in such a location, and now, with so many people wanting to escape from city life, places like this are becoming increasingly more attractive.
The cost of setting up a photovoltaic system, including batteries, controls, inverter, and solar panels amortized over 10 years, will come to about $0.30 per Kilowatt Hour. So, in terms of dollars, you can have a complete independent solar-powered household system for somewhere between $10,000 and $30,000 depending on exactly what your needs are.
You did not specifically mention solar, however, so I must tell you that a wind or microhydro system generally costs much less, if you have suitable resources at your site. For people connected to the grid, for example, it can be economical to install a wind generator and sell your excess power to your utility company. You must, however, install it in a windy location, and to asses that, we would recommend that you set up a wind meter or totalizer to give you a good idea of what you'll be able to produce prior to making the investment. As for microhydro, it only costs about $0.05 per KwH if you have a source with enough water volume and the proper fall, or head.
Although you have asked a very simple question about using a formula, to explain it completely in this column is difficult. Typically, when you size a renewable energy system, you must plan for the number of electric loads that you require. This should include lights, any electric cooking items such as toaster oven and microwave, the refrigerator, pump, washer, TV and stereo, fans, computer, power tools, and small appliances.
Then you need to check the manufacturer's label on each item to determine the wattage of each appliance. If the nameplate lists only voltage and amperage, it's a simple matter to figure wattage by multiplying the rated volts by the amps. Most people find that it's easiest to make a list of all the appliances and note the wattage figures next to each. So, an incandescent light may use 60, 75, or 100 watts; a TV 150 watts; a vacuum cleaner 600 watts; a washing machine 450 watts; a fan 65 watts; a refrigerator 400 watts; and so forth.
After that, you must take into account how many hours per day each appliance is used. This shouldn't be taken lightly, as it can make a big difference in an annual or even a monthly calculation. Lights, for example, are used for longer periods in the winter than in the summer; and a washer--though it may be rated at 450 watts--may only run for 30 minutes a day. A blender at 350 watts has a lot less impact than a ceiling fan at 100 watts, because the fan may run for 8 or 10 hours a day. A refrigerator may be the trickiest to figure, because it runs in cycles; a 50 percent usage factor is a good conservative number.
To get the total watt-hours used per day, you'd multiply the number of hours the equipment is used times the wattage for each appliance, and total the figures. Then, to take inverter efficiency and losses into account, the total should be increased by about 15 percent--or multiplied by 1.15--to allow for this adjustment factor.
This, of course, is only the consumption side of the equation--how much energy you need to operate your home. To properly build a system, you'll need to size the PV modules, based on the number of hours of daily sunlight you receive at your location, figure your battery storage needs based on the number of days you wish the system to be autonomous (in the event of cloudy weather), and decide whether a backup generator is cost-effective for your situation.
Most people, once they've calculated their power usage and totaled what it will cost to generate that power, reconsider how important many of these appliances really are to the household, and look for ways to invest in energy conservation, such as installing compact fluorescent lighting and switching to more efficient DC appliances where practical.
We teach an accredited college course as well as our own non-accredited course on the Internet, which goes into all of this much more thoroughly. This is a 3-hour course, requiring about 45 hours of study for the student. For more information, go to www.doithomestead/education, and you'll be able to see an outline of both courses.
As for your concerns about lifestyle conveniences, Fran and I certainly do not live in the dark ages. We have and use a full complement of electrical appliances, with power generated 100 percent by solar panels. We now have both AC and DC power in our home; originally we had only DC current, then with the development of reliable inverters added the AC in the late 1980's. We currently have the following DC appliances and equipment:
Two 19 cubic-foot Sunfrost refrigerator-freezer combinations, a pressure pump for household water, all of our lights, our indoor pool pump, and pumps to move heat and hot water around.
We use a Trace SW4024 inverter for most of our AC needs and a small Exeltech inverter for critical loads such as our laser scanner and printer. We have AC power for the following items:
Washing machine, dishwasher, coffeemaker, can opener, bread maker, trash compactor, two computers with their related equipment, and two televisions sets. We also run the pump for our indoor swimming pool filtration system, the woodworking tools in our shop, a hair dryer, electric toothbrush, shaver, massage bed, and electric blanket, and an electric meat grinder as well as other homestead items. Believe me, even though you may live beyond the grid there is no need to suffer.
We have gone from our first single solar panel to currently generating 12,500 watt-hours per day on a clear day. To generate this amount of power we have installed:
- 10 Solarex 120-watt panels for 1,200 rated watts,
- 24 Siemens 53-watt panels for 1,272 rated watts,
- 11 British Petroleum 100-watt panels for 1,100 rated watts,
- and a low-RPM propane generator for backup.
I would like to point out that at times we need this generator for cloudy days. The most we've used it in the past 14 years is 43 hours total, one year because of lack of sun or wind.
Editor's Note: In addition to the Do-It Homestead website, more detailed information on sizing and installing a household PV system can be found in The Solar Electric Independent Home Book [Stock No. 8103], available for $16.95 plus $4 shipping and handling from BackHome Books (see inside front cover for order form).