Designing a DIY Solar power kit
Storing solar energy and batteries
Now you know how much energy you're going to need each day you can start thinking about storing enough of it. Thankfully we've batteries to do this job but choosing the right one is very important. Not too big so you can charge it up easily and not too small so you don't empty it completely and run out of power.
Completely emptying a battery is a very bad thing to do to it. Solar power system batteries last longer if you only drain them about 50%, but If you completely drain one you run the risk of trashing it in one fatal foul swoop!
Batteries are rated in Amp hours or Ah. They are available in a huge variety of shapes and sizes and range from just a few Amp hours to two or three thousand. Solar system batteries are not the same as car batteries and are usually called deep cycle batteries even though you really shouldn't deep cycle them very often!
On the last page we touched on why we use Watts to measure power requirements for our solar system, and here is why. Because batteries are rated in Amp hours and are normally 12Volt we need to be able to calculate how much power in Watts that equates to. Watts are equal to volts multiplied by Amps (remember the VA on the last page) so a 80 Amp hour 12 Volt battery has 80Amps multiplied by 12Volts = 960 Watt hours of power stored in it.
This high quality Mastervolt battery has a capacity of 160Ah. It's a 12V battery so it can deliver or store 12 * 160 = 1920 Watt hours of power
Our daily energy requirements are 540 Watt hours so if we only drain this Mastervolt battery by 50% we will still have plenty of spare capacity:-
- Mastervolt battery capacity is 1920 Watt hours
- Discharged by 50% leaves 960Ah (1920 divided by 2)
- Our power requirements are 540Watt hours
- Capacity less requirements: 960Wh - 540Wh = 420Wh. Which is more than enough spare capacity
Choosing a battery for a solar kit