Solar
Electric Design Guide
Solar Electric systems are actually quite simple. A Photovoltaic or "PV" Module is used to charge batteries ( much like your car alternator charges the battery in your car ). A charge control, similar to a car voltage regulator keeps the battery(s) from overcharging. The stored electricity can be used when it is needed for lights, TV, radio, appliances, pumping and more, but the devices must be 6, 12 or 24 Volts DC. |
| Key will design your Solar system at no cost to you or obligation
to purchase. Call me, Brent Hazelwood, (270) 683-9871. If you prefer to
can roll your own, the following steps will assist you in calculating the solar panels and batteries required to meet your requirements. |
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| Step #1 - Determine the total load current and
operating time in Ampere-Hours: First determine the load currents the devices that make-up the load. Example: A 12 Volt Domino 620 Remote Terminal (0.09 Amps) with a DatraxRF One Watt Radio Modem. (1.0 Amp). Calculate Ampere-Hours/Day
Domino = 0.09 Amps
times 24 Hours = 2.16 Amp-Hours/Day |
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| Step #2 - Factor in System Losses: For
solar electric systems a factor of 20 % should be added to the loading for approximating system losses and to include a reasonable safety factor. Therefore the Amp-Hour loading should now be multiplied by 2.66 time 1.2 = 3.2 Amp-Hrs. |
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| Step #3 - Worst case (Wintertime) Equivalent Sun Hours (ESH): Location determines the ESH and this is shown on the map below. | ||
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| Step #4 - Determine Total Solar Current Requirements: The total solar current is determined by dividing the total loading plus losses and safety factor by the ESH. Example ESH = 2.2: The solar panels must produce Amp-Hours divided by ESH = 1.45 Amps. A 20 Watt panel will be required (1.6 Amps times 12 Volts) | ||
| Step #5 - Battery Size:
The majority
of solar electric systems include storage batteries to provide operation at night or in combination with the solar modules during periods of limited sunlight. The recommended reserve time capacities vary with the Latitude of the installation site and are as follows: 0- 30 Degrees (North or South) 5 to 6 Days Recommended. 30-50 Degrees (N or S) 10 to 12 Days (US) 50-60 Degrees (N or S) 15 Days The Amp-Hour capacity of the battery bank is calculated by multiplying the total load, plus safety factor (3.2 Amp/Day), by the days of recommended reserve time. If located at 40 Degrees North (New York) (10 Days recommended) , Battery capacity = 3.2 Amp-Hours x 10 Days = 32 Amp-Hours. The smallest marine battery, usually rated at 80 Amp-Hours, would be a good choice. |
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The above capacity is based on the battery required to
deliver power over the
reserve period of 10 Days. Most batteries rate their Amp-Hours over
8 to 10 Hours
(Depth of Discharge = 80%). In this case the battery bank will
be discharged at a
much slower rate. The deeper the discharge the shorter the life of
the battery will be. In the example above the life of the battery
should be very good. |
