Step 2 - Add a Battery Charge Controller and Batteries
From SolarPneumaticHybrid
The charger
When you sign up for your free or rented system try and get them to give you an inverter with a built in battery charger. Chances are, they will say no. When that happens, you will have an inverter, but now to add batteries so that your system will work if the power goes out at night, you will have to buy a charger. It helps to know what brand inverter you have because then you can often buy a charger designed specifically to work with that inverter. Also, once you pick a charger, that locks in (I think) the type of batteries you can use. I assume that if I go with Power-Save they will have step by step instructions that even a novice can follow, and then maybe the company that makes their inverters will have a charger made to integrate specifically with that inverter (I hope). I don't have one yet so I'm not the person to give out advice, but so far, from what I've read, I'd look at these two companies: Xantrex and Outback. If you know a better choice for a battery charger, please let me know. If you register with this website you can make you suggestions by clicking on the discussion tab above, or you can edit this article directly.
The batteries
So, until I finish my research, I don't know how to pick batteries nor how many I would need. AGM batteries sound good though. A stack of eight 6V 1600 Amp Hour AGM batteries, from the research I've done so far, sounds like the way to go. So (correct me if I'm wrong) if you pick your batteries first, that will determine which chargers you can use, if you pick your charger first, that will determine which batteries you can use. Now my original plan was that when I got to batteries, I'd just add one battery per month until I had the storage capacity I needed, or until I couldn't charge them all the way each month. But that may be a really bad idea since a block of several batteries wired in series can work for a decade or more, but if you create the same block over months or years, using what you have the whole time as you grow the block. It does not, as a whole last as long, and may wear out years earlier. This is because when you have a series of batteries, if one of the set wears out faster or sooner than the rest, it makes the rest of the batteries work harder than they would have otherwise and thus they all wear out faster. The question is that if over 8 months you add one battery per month and then stop expanding after eight months, will there be a measurable reduction in life of the whole unit or will the whole unit fail 8 months earlier than it would have otherwise? If I built it over 8 months resulting in the 8 failing at the end of the normal life of the first battery put into service, than I would go ahead and build it gradually because then I might find that in practice I only need 6 and therefore save tons of money. If on the other hand by putting the first battery in service 8 months before the last battery and different times for all of the other batteries I take 2 or more years off the life of the whole, than maybe I would not be willing to build it gradually. I hope someone can give me some concrete data and case studies on adding batteries to a stack over time vs building each stack at one time.
