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One of the things you might want to do before installing your home solar power system is to analyse your existing power usage and see what savings you mgiht make.
Bruce, who lives in California, wrote to me pointing out how simple an exercise this can be.
Using one of the cheap tools that are readily available these days (see below for some options), you can measure the number of kilowatt hours (kWh) used by any appliance in your home.
Once you have the kWh measurement, you can use the following simple formula to calculate the cost to run your appliance. In this example, we are looking at the monthly cost.
First, calculate the monthly usage
(wattage / 1000) x hours-per-day x 365 /12
Second, calculate the cost
monthly-usage x your-cost-per-kWh
As an example, let's compare lghtbulbs; a 65 watt light bulb uses 65 watts of electricity when switched on, the equivalent energy saving light bulb (sometimes known as CFL - compact flourescent lamp) uses 18 watts.
If used for 5 hours each day, they will generate a monthly usage as follows:
(65 / 1000) x 5 x 365 / 12 = 9.9 kWh per month
(18 / 1000) x 5 x 365 / 12 = 2.7 kWh per month
Your electricity supplier will probably have a different tarrif to the one we are going to use. Suppliers will have different tarrifs and often have different tiers as well. In Bruce's case, his supplier has a tiered system where the cost per kWh varies with uisage. For the purposes of this example, he has given the top tier rate of 35 cents per kWh. (You should be able to find your tarrif rates on your bill.)
Using the fomula to calculate the monthly cost of these different lght bulbs, we get:
9.9 x 35 cents = $3.465 per month for the incandescent light bulb
2.7 x 35 cents = $0.945 per month for the energy saving light bulb
Those of you who have bought energy saving light bulbs will know they are more expensive than the traditional incandescent variety. Bruce now knows that the cost of a CFL light bulb, $3.00, can be recouped in just over a month. (On his supplier's lowest tarrif of 8 cents per kWh, it would take 11 months to recoup the cost.)
While the point of this item is to demonstrate how to calculate your pwer usage, it is worth mentioning in passing that a number of jurisdictions (the European Union countries and Australia for example) will be phasing out incandescent bulbs in the next few years and only CFL bulbs will be available for purchase.
And what tools can you use for measuring your power usage:
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North Americans | UK & Ireland |
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26 November 2007
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