Residential and small commercial wind generators require battery backup for periods when the wind doesn't blow. They usually generate low DC voltages suitable for battery charging and the size of the battery bank depends on the size of the load that should be supplied and on the length of time the load is expected to operate on battery power. This is the stored power. The configuration of the battery bank and how the batteries are wired together depends on the output voltage of the wind generator and the amount of power to be stored.

- Skill level:
- Easy

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## Instructions

- 1
Look up the rated voltage of the wind generator from the generator nameplate. The voltage controller connected between the generator and the batteries will keep the voltage near this level. The lowest battery voltage commonly in use is 6V DC, so the generator voltage is likely a multiple of this. Smaller wind generators rated less than 1,000 watts will run at 12V DC or 24V DC, while larger ones rated several thousand watts will run at 48V DC.

- 2
Calculate the kWh per day (24 hours) for each load that will be supplied from the wind turbine or battery bank and add them. A load of 1,000 watts might only run for half an hour per day for a total of 0.5 kWh. A load of 10 watts might run continuously for a total of 0.24 kWh. An average battery such as that from a golf cart or a marine battery will hold about 1 kWh. In the worst case without any wind, the loads will run only off the batteries, so the number of batteries needed is about the total number of kWh times the number of days the batteries are to supply the load. For example, total power of 12 kWh per day for two days will require 24 batteries.

Note that only a fraction of the rated power of the wind generator will be available for the load because the rated power is given for a fixed, relatively high wind speed. Depending on the average wind speed, available power will be considerably less. A 1,000-watt wind generator may effectively supply only 500 watts on the average over a longer period of time and generate about 12 kWh per day. When it does generate 1,000 watts during a windy period, excess power will go to charge the battery bank.

- 3
Calculate how many batteries wired in series and in parallel are needed. To match the voltage of the wind generator, the batteries must be connected in series until their voltages add up to the desired amount. For a 24V DC generator and 6V DC batteries, four batteries must be wired in series. For batteries wired in series, the plus terminal of each battery is connected to the minus terminal of the next battery. For four batteries of 6V DC in series, the voltage between the first terminal of the first battery and the second terminal of the last battery will then be 24V DC.

Take the total number of batteries from Step 2 and divide by the number of batteries required for the generator voltage. This gives the number of batteries that must be wired in parallel. If a total of 24 batteries is required, dividing by the four batteries needed to get 24 V DC gives six batteries to be wired in parallel. Batteries wired in parallel have all their plus terminals connected and all their minus terminals connected.

- 4
Wire up the batteries in the calculated series/parallel configuration. The easiest way to do this is to line up the series-connected batteries lengthwise and place the rest of the batteries in a grid beside them. Wire up the series, lengthwise rows by connecting the plus terminal of the battery at the top left of the grid to the minus terminal of the next battery in the row and so on. Repeat for the second row and other rows. Then, connect together all the minus terminals of the first batteries of the rows and wire together the plus terminals of the last battery of the rows. Now the batteries in the rows are all connected in series and the rows are connected in parallel.

For the example with 24 batteries, there would be six rows of four batteries each. The four batteries of each row would be connected in series and the six rows would be connected in parallel.

Connect the voltage controller and the load to the top right corner of the grid and to the bottom left corner. Connecting across the corners in this way equalises the battery loads by compensating for the lengths of the connecting wiring.