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Calculating your energy needs

The first step in designing a Renewable Energy System is to appreciate that it is easier and more economic to reduce consumption through energy efficient appliances, than it is to generate more power. The government has introduced an energy labelling scheme which labels all appliances with their efficiency rating (A-G), always buy 'A' rated appliances.

A typical preparatory measure then, might be to install energy efficient lighting or exchange electrical heating appliances with alternatives (e.g. gas/wood). Spending pennies here will save pounds later.

Next you need to examine in detail where your power will be going, and attempt to reduce this to an acceptable, but comfortable minimum. In order to assess individual power needs a form, to be filled in, is included in this document.

To complete the “Load Assessment Table” first make a list of electrical appliances that make up the Load (i.e. anything electrical in your house).

For small systems, using more efficient 12 volt DC appliances is generally better than their 240 volt ac counterparts (even though the initial purchase of a 240 volt appliance is usually cheaper). These can be lights, laptops, printers, fridges, travel kettles etc. Also heavy duty 12 volt power tools are readily available. With part or whole DC systems, make a seperate list of DC and AC appliances.

For larger systems (e.g. conventional house), a quality high power inverter transforms the battery power into 'normal' mains 240 volt AC, and feeds into the house cicuits (sockets and lights etc) exactly as normal. This inverter needs to be sized to match your energy needs, though expansion is often possible later on should situations change. For pure 240V AC systems you only need to fill in the AC section of the table.

Next to each appliance write its POWER CONSUMPTION. This may vary widely between similar appliances. This figure is normally found on a data-plate on the back of the appliance. The given figure will be the maximum value, not the average, so it is usually appropriate to reduce this value somewhat. A list showing approximate values for popular appliances can be supplied on request - this can help you fill out the form.

The next column is the HOURS OF USE per day for each appliance. Ideally this should be done for every month of the year as seasonal variations are important, however for simplicity: Mid-summer and mid-winter values will suffice. Please note that refrigerators and freezers are only actually on for about 12 hours a day in the summer and 8 hours in winter.

If the POWER CONSUMPTION and HOURS OF USE column are multiplied together the result is the DAILY CONSUMPTION, expressed in watt-hours. This is the most important column, in that it shows how much ENERGY is being used by each individual appliance, indicating which are the most demanding (and expensive to run) overall.

Click on loadtable to download a word document which you should fill in and email back to us.

Once we receive your form we can start to design (without any cost to you) an appropriate renewable energy system tailored to your individual ENERGY NEEDS.


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