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Solar Power – What Can You Run?

solar powerThere is a limit to what you can run using solar power, based on the size of a small system.

For example things which are not practical to operate on solar power would include anything with a large heating element in it, or a larger motor.

An electric stove or oven, an electric water heater, electric baseboard heating – these are examples of electric heating which consume a lot of energy, and to attempt this with a small solar system would be impractical. Similarly, items such as a large table saw used for long periods of time, or a heavy duty planer, again used for long periods of time would not be practical.

However, having stated that, I do have a large complement of tools and use them on a daily basis with no detrimental effect on my battery system, providing the sun shines.

My solar system consists basically of roughly 500 watts of panels, which feed electricity at 24 volts DC nominal to a battery bank. The power is extracted from there and is inverted to 120 volts AC for domestic consumption.

On a typical summer day, the energy input to the battery bank will be 100 amp hours (AH) and the voltage will normally be in the range of 28 to 30. This yields nearly 3 kwh of power going in.

In theory, you could extract that much electricity in any way you choose. However, it is good to know that if you extract the power slowly, e.g. using a few lights or other low draw, that you will get more than if you extract it quickly, e.g. running a large tablesaw for several hours.

What can you operate successfully on a small solar power system?

Here is a list of household items which we use on a regular basis:

Lights, fridge, freezer, blender, coffee grinder, water pumps, TV, satellite receiver, DVD player, stereo, CD player, ceiling fan (60″), microwave oven, hair dryer, mixer, computer, printer and so on.

In the tool department, I should note that I do a lot of woodworking, there is a tablesaw, planer, routers, power planes, drill press, bandsaw, several drills, bench grinders, mini grinders, tile wet saw, miter saws, electric chisel, electric impact gun, compressors, biscuit joiner and the list goes on.

Used in moderation – which is the key word when one is dealing with solar power – there is very little that you can not use. It is well to note that items with a large power draw should only be used for short periods of time. If you continually give the batteries a break after a heavy draw, they will level themselves out and provide you with better long term results.

One of the more important components of your solar system is the battery bank. The larger bank you have, the less effect any specific draw will have on your system. For instance, if you have a battery bank of 200 AH @ 24 volts, compared to 800 AH @ 24 volts, obviously, the larger bank will hold more energy. The difference would be a factor of 4 in favor of the 800 AH bank. An interesting aside here is that you can actually draw more than 4 times the power using the larger battery bank.

There is something called the Peukert exponent. This is a relatively little known formula which will demonstrate that as you draw energy from your battery bank at a higher rate relative to the size of the bank, the actual amount of power you can use decreases at an exponential rate.

As an example, let us use the case of a 5 amp draw for 4 hours. That would be 20 AH. Or a 20 AH draw for one hour. In theory, both are identical. But because the 20 AH draw is coming out 4 times faster, it will effectively draw the batteries down a greater amount than the 5 amps for 4 hours. In a case such as this, you can see that the larger battery bank will be at an advantage, as the percentage of power that is drawn down is considerably less than with the smaller bank.

Source by Keith Elliott