6 volt vs 12 volt deep cycle batteries

Tooltime

I have a home that we will be moving in this next month. The house is off grid and there will be a famliy of 4 living there full time. I have to start putting the numbers together as to the power I will be needing. I may start off small and build to a completely renewable energy system. At first I see the generator running a lot. what I have learned so far is:

Batteries should be sized to last 3-4 days

never run them down below 50%

Solar panels need to be 20% larger then your daily use??? (not sure if I got that one right)

today, the question is do I start out with 6 or 12 batteries.

I will be going 24v input into my inverters.

Cariboocoot

Re: 6 volt vs 12 volt deep cycle batteries

Welcome to the forum.

The first thing you really need to do is get some number, as accurate as possible, for your daily usage. This is all-important for sizing the inverter and the battery bank. The PV array will be sized to recharge that battery bank according to the available sunshine at your location.

I advise against the 3-4 days worth of battery, as that usually means you end up with a lot of battery and a lot of PV that isn't used most of the time. Most manage with a battery bank designed for daily 25% Depth Of Discharge, knowing that there's another 25% available if the next day proves to be cloudy. On Day 3 you start the gen.

The choice of 12 or 6 Volt batteries comes from the capacity needed. Have a look at this to get an understanding of the issue: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

In the short version, the single string of higher capacity 6 Volt batteries is preferred over parallel strings of 12 Volt units.

The choice of a 24 Volt system is probably a good one, but don't rule out 48 Volt before you know how much power you'll actually be dealing with.

vtmaps

Re: 6 volt vs 12 volt deep cycle batteries

Welcome to the forum. You know, and Cariboocoot has emphasized, that you MUST know your loads before you can design a system. Its like buying a truck... if you buy a half-ton pickup and discover that you need a one-ton, you've got a problem.

Tooltime wrote: »

I may start off small and build to a completely renewable energy system.

Bad idea. You can't convert a half-ton truck to a one-ton truck, and you can't convert a small renewable energy system to a large one.

Tooltime wrote: »

At first I see the generator running a lot.

It used to be common to start with a generator-battery-inverter system and add on the solar at a later time. That's not such a good idea now because of the federal tax credits on renewable energy systems. Let's suppose that you are going to spend $15,000 on a system. About $2,000 of that will be for the panels, the remainder will be labor, electronics, trenches, conduit, batteries, etc. If you install the panels when you commission the system, the whole system is eligible for a 30% tax credit. If you install the panels later, only the panels are eligible.

--vtMaps