The problem with solar power or any renewable energy source is the storage of the electricity. You see, the sun shines all day but you normally use electricity at night, for lights,TV or anything else when it is dark outside.So where to put the electricity when it is not produced? Unfortunately all the human race in its ingenuity could come up with are batteries. A technology that did not change too much in the last 50 years. There are other means, mainly hydrogen, but they are not feasible for the private individual yet. Same for fuel-cells or other technologies.

So we are stuck with batteries. The easiest way is to use 12V batteries, they are the easiest to find and to manage. Also there are rather inexpensive converters available that will transform the 12V battery power into 220V alternative household current.

solar batterie

Solar Batteries are a good but unfortunately expensive choice

Since I live in Europe, where we have a standard voltage of 220V alternative current, it is rather easy to calculate how much anything will use in terms of power if you convert the 12V batteries into 220 alternative current. The workload the electricity has to perform is measured in amperes or A. That is the number written on your batteries for example 55A on a small car battery.

Lets say we have a small TV set and it says on it 40 watts. The formula would be W(atts) : V(olts) = A(mpere) per hour. So in our case 40 : 12 = 3.3 meaning that our TV will eat 3.3A off our battery per hour or 3.3A/h. The problem with this is, that you always have losses, cable and heat and others so for ease of use a better way to calculate is to divide by 10. This way you have kind of a "reserve". In the case of the TV we see that we should calculate with 4A/h to be on the safe side. Everything you put on at the same time you can simply add up. So 5 lights a 20W, a TV with 40W, and lets say a satellite receiver with 30W are together 170W and will drain our battery with 17A/h.

So far so good, our 55A car battery will last with all our light on and with the TV blazing a bit over 3 hours, right? After all, 17A times 3 hours would be 51A, right? Wrong.


car batterie

Car Batteries are cheap but not necessarily cheerful for a solar installation

The problem with car batteries is, that they are not build to be completely discharged. They are the easiest and cheapest batteries to get, but unfortunately also the least durable ones. You should never discharge them more then 30%, in our case we got about 1h energy before we start damaging the battery. So, when getting the battery bank, look at the ampere rating and just use a third of it in your planning. Thankfully one can put the batteries together, so out of 4 80A Batteries you can easy make 1 320A battery by simply wiring them together. You connect the + pole to the next + pole and all the - poles to the other - poles. With this you double or triple the Amperes and with that the available power reserve.

Better, but more expensive, are specially made solar batteries. These can be discharged up to 80% and because of that take up a lot less space then car or truck batteries. They will also last much longer. A car battery can be recharged about 300 times, solar batteries 500 and some times up to 800 times. You will need quite a lot of batteries and you should not save by buying them. They are the most important part of the entire installation.