12V, 24V, 36V or 48V?

Choosing the right voltage for your energy storage is important so here is what we have learned, what we use and why.

So you want to buy some batteries and setup a battery storage system to provide power for various electrical items you have. Before you commit its important to understand at what voltage you are going to create your system as. To get things out of the way early we use only 12V at Mannerfarm so if you want to stop reading now before falling asleep you can. If you want to know why you might choose a different voltage for your battery system keep reading.

There are essentially three very common low voltage systems you will see being 12V, 24V and 48V. You can of course go 36V but this seems to be less common. So why would you look at anything but 12V or why would you not look at going for a higher voltage? It all comes down to application of your system and how much power you need to draw at any point in time. Going back to high school physics:

Power (Watts) = Voltage x Amps

Watts is kind of a good universal metric to work in when working out what you need. Before buying your batteries you need a good understanding about what it is you want to supply load to. Things like lights, refrigeration, TV, Computers are all pretty commonplace items. You need to work out this power budget:

All Lights Combined 150 Watts
Refrigerator  150 Watts
Entertainment System 100 watts
Computers and Electronic Devices 100 Watts
Fans/Air Circulation/Extraction 50 Watts
Diesel Heater 40 Watts
Water Pump 100 Watts
Parasitic Loads 50 Watts
Total Load 740 watts

You will notice this does not include anything with a heating element like oven or hot water system as well as high energy items like microwaves and coffee machines. If you must have items like these then you to evaluate what's really important because they will add an exponential energy requirement to your system. Typically though you can go without a microwave if you have to and use gas for hot water, there are lots of other options.

Anyway now we have a rough total load of 740 Watts its important to then convert this to amperage draw which is Watts divide by Voltage. Because voltages vary lets just stick to whole numbers and round down for simplicity.

12V = 60 Amp

24 = 30 Amp

48 = 15 Amp

Ok, so now you know your potential maximum amperage draw what does this mean in terms of voltage selection when designing your system. There are two factors to consider.

1. The higher your amperage draw the thicker wires you need.

2. The lower your voltage the more voltage sag you get over distance.

In all cases to calculate your wiring requirements there are excellent DC wiring calculators on the internet. when budgeting for a battery system wire is a real cost that a lot of people underestimate and you cannot get this bit wrong. At best you get poor system performance, at worst it will catch fire.  If you use incorrect wire size for your system and you draw high amperage loads that wire will get hot. It can get so hot it will catch fire and that's bad.

You can safely design any system to handle big amperage loads no matter the voltage. It just requires more thought and careful design if using 12V to supply big loads in excess of say 150Amps. So what are the Mannerfarm reasons for using 12V only:

1. Our loads in all our systems are moderate and would rarely exceed 100 Amps (production from solar and wind) and certainly no more than 50 amps (draw).

2. 12V is the most popular low voltage so parts to build systems are incredibly plentiful and cheap to buy. For higher voltages like 24V and 48V components are harder to get and generally more expensive.

3. All of our wire runs are short and so sizing the wiring for our system did not add a lot to the build cost.

4. 12V is a safe voltage to work with. If you go 48V then you are into biting back territory and you must be very careful.

We would only consider a higher voltage system for anything over 150 Amps load or supply. It doesn't mean you can't its just a balancing act between safety and practicality.