Off-grid Solar Systems that Work like a Dream: It’s All About Voltage

Do you want a 12 Volt/24 Volt/48 Volt System?
 
I’ve just got power. And it’s sweeeet! What's more, this system functions better than my old system in Turkey, despite being privy to a lot less sunshine. This is because I’ve learned a thing or two about solar power in the meantime. A large tranche of this knowledge comes from my nearest neighbour Brian, who happens to be an engineer, and has one of the most efficient small solar systems I’ve seen. Yeah, I lucked out yet again, I know:)
 
My vecinos have three 250 watt solar panels. Their solar system runs a full-sized fridge freezer, washing machine, toaster, kettle, massive flat screen TV with surround sound, the well pump, lights, blender, hairdryer, vacuum cleaner, and powers another small guest cabin with small water heater… Yup, it’s pretty flipping amazing.

These three panels get a lot done!

​Needless to say, when I came to install my own solar system, I had a long, long chat with Brian first. What’s the secret to such a slick system? It’s a 24-volt set up, not your standard 12 volts.
 
Huh? What does that mean?
 
Now, if you’re an electrician, or some engineer type who knows all this stuff, you can zone out right now. Heck! Why are you even here? This, as with all my posts, is an overview for the majority of us bumbling mortals who can just about wire a plug, but get a bit lost after that.
 
The difference between 12V/24V and 48V Systems
Previously unbeknown to me, there are three types of independent solar power systems: 12V, 24V, and 48V. Most people automatically set up a 12V system because both the batteries and panels are (nearly always) 12V, so it seems like a no-brainer.

My 12V batteries wired in series for a 24V system.

In truth, 12 volts often isn’t the best way to go. It’s not hard to wire a couple of panels or batteries up in series to create a 24V system instead, so don’t let that put you off. (Just get an electrician to do it for you, if you don’t know what wiring in series means).
 
Think of it this way:
A 12V system is like driving an old 2CV. Yes, it will get you from A to B, and if you only need to drive to the supermarket and back, it’s fine. But if you’re hitting the motorway, or planning a Pan-American road trip while towing a caravan, it’s going to get pretty uncomfortable.

The 12-volt system can be a bit of a jolting ride. Photo by Lothar Spurzem (https://commons.wikimedia.org/wiki/User:Spurzem)

​A 24V system is like driving a Honda Civic. For most of us, this is plenty good enough. You can cruise comfortably and economically with your family on the motorway without worrying about a burn-out. You will be a little more prudent with your power usage than you would on-grid, but you should be able to run most appliances well on a 24-volt system.

For most of us, a Honda Civic gets us comfortably where we need to go.

A 48V system is like driving a Range Rover. This is for businesses or loaded individuals who want to splurge on power like it’s going out of fashion (which in a way, it is). I’m not going to waste time outlining 48-volt systems, because if you’ve got enough money for this you’re wealthy enough to pay a consultant:)
 
Here’s a rough outline of what a 12V and 24V system would look like, plus the types of appliances you can run well on each.

​Bear in mind, it’s not just the voltage. You need enough battery power to run your system when the sun’s not shining, and you need enough wattage margin in the inverter, too (see my beginners’ guide to solar power if this doesn’t make sense).
 
NOTE: You can run a fridge or washing machine on 12 volts. It’s totally possible. But take it from me, you’ll soon be ragging your inverter and emptying your batteries. If you have 300 days of sun a year, you may manage. If you don’t, it gets much more annoying, and ultimately expensive, because you will have to replace your batteries, inverter, or both before too long.
 
Advantages of 24V systems:
1. The system is more efficient. You lose less power all around.
2. Reduced fire risk.
3. Better inverter efficiency converting to 240 volts. The inverter doesn’t have to work as hard to keep the AC output constant.
5. Larger usable voltage window for the batteries (in practice this means you have more power to play with).
 
If you are a numbers- and wires-lover just itching to geek out on this stuff, head to these sites to satiate your curiosity:
http://solarhomestead.com/best-battery-bank-voltage/
https://pangeabuilders.com/what-is-the-advantage-of-a-24v-system-over-a-12v-system/
 
My System
At present I’m only using small appliances, so I could feasibly get away with a 12V system, but... here’s the thing: I know I’m going to upgrade in the future, because I want a fridge and possibly a washing machine. So, what I did was buy a 24V inverter, and created a 24-volt system, even though I only have 230 AH of battery power, and two 60-watt solar panels.

My small system with a big inverter, ready for when I add batteries and panels in the future.

​Do I notice a difference with 24V?
Heck yes. A lot.
 
In Turkey I had a 12V system with a good 400 AH of batteries, in a country with 300 days of hardcore sunshine a year. So there was no lack of solar clout. But if we went three days without sun, I was out of power. I also burned my 600-watt inverter out after about three years (which is to do with an inadequate inverter as much as the system voltage).
 
Here in northern Spain we have 300 days of rain a year! I have only two 115 AH batteries. But I’m yet to run out of power. Even on a rainy day I get enough to charge my laptop. I’m observing that the batteries charge faster because there’s less power loss between the panels and the batteries. I notice the batteries lose power more slowly too. So to be honest, I’m a bit sold on 24 volts and would probably prefer a system like this even if I was only running the small stuff.

The rain doesn’t stay mainly on the plain in Spain, it was a total lie. But I’m still in power.

​Many thanks to Brian for explaining this lot to me while simultaneously showing me how to make soda bread (I learned a lot that day). The car analogy is all his, though I admit I swapped the brands, because I like 2CVs better than Minis.
 
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