Wednesday, October 08, 2008

Cost of Electricity - Batt and Gen

There is simply no way to discuss energy, whether alternative sources of energy or ways to conserve it, without an understanding of what energy costs. The cost varies dramatically, depending on what kind of energy, where it is coming from, and what it is being used for. This is why I advocate for LED's for flashlights, but not for my living room light.

There is also no way for an individual to predict the exact costs of their energy use, but reasonable calculations can be made. Here I will make some reasonable calculations for different kinds of electric power sources that might be available during power outages, camping, working outdoors, or other times when the commercial power is not easily available. (As we shall see, commercial electricity is one of the most cost effective sources of energy available to the individual.)

To make this survey more readable, I will make calculations for all costs in US$ per Kilo Watt Hour (KWH), just to limit the use of very small numbers. (So I will say commercial power is $.15 per KWH, rather than $.00015 per watt hour)

One of the most expensive sources of electricity is the common, throw away battery. Using a reasonable cost per battery of $.35 for AA and $.80 for D cells, and a reasonable power yield of 2 watt hours for AA alkaline Batteries and 15 watt hours for D-Cell alkaline Batteries will automagically provide:
$175 per KWH for AA cells
$53.33 per KWH for D cells

(You don't even want to think of the cost for the coin shaped cells used in watches and hearing aids, which I have also seen in headlamps that fit on the bill of a cap)

The most common small rechargeable batteries today are NiMH based. AA sized batteries of this type can reasonably put out 1.5 watt hours for each of over 667 recharge and discharge cycles. It typically takes 50% more electricity to charge them than you get back each time, so these numbers add up to 1 KWH for ($.23 in electricity and the $2.27 cost of the battery) $2.50. This of course ignores the cost of the battery charger, but that might not be too much of a factor if you are using several batteries. This is not really the ideal for this kind of battery, so really judicious use of rechargeable batteries, or use of larger ones could make the cost much less. It does require a commitment, however, to use the batteries throughout their (typically two year) life span.

A 3kw Honda generator set, providing 2KW continuous, uses about one gallon of gasoline every 3 hours, and requires 1/2 maintenance ($15, including oil and spark plug) every 50 hours. After 900 hours this would be $135 for maint and $1200 for gas (at $4/gal) = $1335.
Generator cost about $2000, and after 900 hours could be worth $1000
1800KWH for $2335 = $1.3 per KWH

This is an almost ideal usage pattern for a generator set, and normal use would be intermittent and variable loads. True cost per KWH for a small gasoline powered generator would likely be two or more times as much.

Typical throw away flashlight batteries . . . $50 to $175 per KWH
Typical gasoline generator electric power. . . $1.30 or more per KWH
Typical rechargeable batteries . . . . . . . . . . . . $2 to $3 per KWH (or less)
Typical household electric power . . . . . . . . $0.15 per KWH

Now, knowing somewhat, the cost of energy, it is possible to begin discussing ways to reduce energy costs and return on investment for various energy saving or energy producing products.

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