Size Matters: Building a Budget Solar Power System

There is a lot of good information available on how to size solar power systems but very little of it applies directly to folks who are “going 12 volt”, looking for emergency home power, or “homesteading your home”. One of the stumbling blocks in building a inexpensive photovoltaic power system for your home is figuring out how much power you really need. People often get stuck right there and never get started.

When you do your homework and start to find out just how much energy you are really using and just how big a solar power system you would need, the numbers quickly become overwhelming. Electrical power from the grid is very cheap and most of us use far, far more of it than we ever imagined.

But the task of sizing become much easier if you:

• Focus on your existing critical power needs
• Gradually reduce your power needs by shifting to lower wattage equipment

Critical Power Needs

Your short-term critical power needs are often much less than you think. For someone already working toward local self-reliance, a power blackout lasting several hours to several days might mean keeping some minimal equipment operating.

(Note: 1 watt-hour is 1 watt being drawn over a period of 1 hour.)

Appliance	Power demand	Comments
Refrigerator/freezer	959 watt-hours/day	Energy-efficient model; possibly much less
Computer, laptop	200 watt-hours/day	50 watts, usage at 4 hours per day
Electric blanket	400 watt-hours/day	50 watts, usage at 8 hours per day. (But only during winter when your refrigerator would be drawing less!)
Small battery charger	48 watt-hours/day	6 watts, usage at 8 hrs per day
Highly efficient LED or compact florescent lights	360 watt-hours/day	3 lights with an average of 15 watts each running for 8 hours
Total	1,967 watt-hours/day

Another article (Building Your Own Solar Panels versus Buying Them) discussed a low-cost 520 watt solar power system. If it were running at only 75% efficiency (due to clouds, shadows, etc.), it would very likely be capable of providing you with the power budget above.

(520 watts x 5 hours/day x 76% = 1,976 watt-hrs)

Of course “your mileage may vary” but this gives you some idea about how to size a simple system; one that you could quite easily build yourself.

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