Efficiency of Lights and Appliances

Everyone that lives with a solar electric system cares more about the efficiency of their lights and appliances than people who live with utility supplied electricity. This is because solar electric systems have a high initial cost. A good example can be demonstrated in lighting. If you use 4 100 watt lamps, 5 hours a night in a PV powered home in the southwest US you will about 4 times as many panels and batteries to do the same job as 4 25 watt florescent lamps. You will save over $2000 in the system cost - just by changing the type of bulb you use. Try it in the Virtual Solar Engineer.

Televisions, radios, VCRs, computers and other solid state electronics are no problem for solar electricity. The key word is solid state. If you have an old TV that uses vacuum tubes, forget it. It will cost you much more in PV panels and batteries to power the old TV than to pay for new TV and the panels and batteries. You'll have a new TV and it will cost you less!

Water heaters, ovens and space heaters that are powered by electricity are called electrical resistance heat. Just like an all electric home, trying to power these with solar electricity will cost you big bucks! Think about solar water, space heater or solar cooker to do part or all of this work and use propane or wood to do the part that the sun doesn't take care of.

Microwaves, toasters and hair dryers are another matter as they are typically used for only very short periods each day. They will increase your usage, but they are used in many solar powered homes every day. Just be conservative.

Refrigerators that are sold in department stores are generally not efficient enough to be powered by solar electricity. Improvements have been made in the last few years but they still use a lot of power. A refrigerator usually runs about half to three quarters of the time depending on the temperature of the room that it's in. 16 hours a day is a good guess. Super efficient refrigerators run much less due to higher insulation, more efficient motors and greater care in manufacturing. They will almost always pay for themselves in PV powered homes even though they cost $1600 to $3000. Propane refrigerators are also an option, and in fact may be a good choice if you have other appliances running on propane. At a dollar a gallon for propane it takes about ten years for a super efficient refrigerator and the panels and batteries to run it to equal the cost of a propane refrigerator and the propane to run it. This time of payback, of course, goes down as propane goes up. Try the cost of a system to run a regular AC refrigerator in the Virtual Solar Engineer and you will find that if you use 350 watts 16 hours a day in a good location with 5 days of storage the cost of the PV system will be over $10,000. Now try it with an efficient DC refrigerator using 65 watts of power for the same amount of time and same location and days of storage - you will find that it only costs about $2400 to run this refrigerator.

An efficient refrigerator pays for itself immediately when you consider the cost of the PV system that powers it. Always plan on buying an efficient refrigerator for use with PV systems or plan on using propane models.

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