I get a lot of questions from people starting out with solar power on how to get the Amp Hour rating for the solar batteries they will be using. Here is a step by step on that…

• Determine which appliance or electric device will you power with your solar batteries via your solar power system and get their corresponding wattage input. For example:

light bulb (20watts).

• Calculate how many hours in a day will you run the above. For example:

light bulb (5hrs/day)

• Get the watt-hrs/day of each. For example:

light bulb (20watts x 5hrs/day = 100watt-hrs/day)

• Get the amp-hours per day by dividing the watt-hrs/day value by the voltage of the battery you will use, say 6V or 12V. For example:

100 watt-hrs/day divided by 12V = 8.33 amp-hrs/day

• Take into consideration the discharge level, usually 50%. For example:

8.33 amp-hrs/day divided by 50% = 16.66 amp-hrs/day or Ah

In conclusion, you will need at the least a 16.66 Ah rating battery to run a 20watt light bulb for 5 hours each day.

Here are some basic tips on how to extend the life of your batteries.

• Install batteries in sets. Do not replace one or two batteries only. The best practice is to install them all at the same time and replace them all at the same time too.
• Keep batteries in the correct temperatures as specified by the manufacturer.
• Avoid moving the batteries once installed.
• Make sure the battery connections are properly connected and there is not post corrosion.
• Do a regular yearly check up on your batteries. Test the electrolyte the voltage and charge of all batteries to see how good it is holding up and if they need to be replaced.

Deep cycle batteries are the exact opposite of your car batteries. While a car battery is designed to expend a high voltage for a short amount of time via the start engine phase, a deep cycle battery is designed to give out a constant voltage throughout a long time. Golf carts and boats both use deep cycle batteries.

Solar batteries that go on deep cycle batteries should never be allowed to discharge below 50%. Anything below 70% and your batteries will permanently lose capacity as sulphation starts to set in.

Here are some things to consider when it comes to solar batteries…

Temperature

One of the biggest factors affecting any kind of battery is temperature. There are batteries designed specifically for the area you want to install your solar power system. A cold climate would need a different designed battery from one that is made for hot and humid environments. Check your solar battery manual on the best way to keep them.

Mixing and matching

While it’s common to use different batteries in your remote control or any other electronic device, it isn’t recommended for your residential solar power system. It is important to purchase and install the same type of batteries all at once. Mixing different types, sizes, age of batteries is a definite no-no as the whole battery bank will take the state of the weakest battery.

Amp-hours

All batteries come with an Ah or Amp-Hr rating. A battery that has a 200 Ah (20hr reference) rating would give out 10amps for 20hrs before being discharged. The higher the Ah rating, the more expensive, heavier and longer will the battery hold a charge.

Battery Voltage

Most batteries come in 6V or 12V. To get higher voltage you simply wire these batteries in series and to get higher amp output, you wire them in parallel.

Another common question I often get when it comes to solar electricity and residential solar power is whether you really need a battery bank and a charge controller. Isn’t connecting the inverter or any appliance directly on to the solar panel simpler?

The answer is yes, of course you could. But all you would be doing is risk breaking your inverter or appliance. With solar panels, the voltage it produces varies widely. On extremely sunny days it could produce a lot of voltage while on cloudy days it could produce very little.

This inconsistency is one of the major disadvantages of using solar power and why it isn’t anywhere near close to replacing traditional forms of energy yet.

Going back, with a battery bank, the load smooths out the voltage and basically insulates the inverter from any damage. Another benefit of a battery bank is that during cloudy or rainy days, when there isn’t enough sunshine to make significant power, the battery bank serves as a back up source of power.