One of the many reasons there are so many sheddies across Britain and the world is the innate desire to get away from it all. This burning desire for freedom and leisure can complicate things a bit when you don’t have access to electricity. Some might like it that way, nothing but the sun and a fresh beer, but some might also want some a few home comforts. In the spirit of doing it yourself, installing an off-grid solar electricity supply could be a nice addition to your pride and joy.
If you’ve never thought about putting a few panels on the roof of your shed, or been unsure about how to do it, here’s the lowdown. There are four basic components: the panels, the batteries, a charge controller to charge the batteries, and an inverter to switch the batteries’ energy to AC for your appliances. For the typical hands-on sheddie, a system like this shouldn’t be a problem. Let me explain how it works.
Panels come in a range of sizes, from 80 watts to 250 watts, meaning on a bright summer’s (or winter’s) day, they will put that amount out, every hour. Even without direct sunlight, panels can still work; just don’t put them behind a tree! Plonk it on a south-facing roof and on a good summer’s day a single 250W panel can put out close to 1000W. But what about the size? Well, even the smallest shed (except perhaps the tardis ones!), has two square meters of roof-space – enough for a 250W panel.
Then comes the charge controller. This device will take the electricity from your panels and put it into your battery bank. It maximises the output of your panels, and charges your batteries the way they like to be charged. It’s a pretty straightforward component that is worth having; just make sure it’s an MPPT (maximum power point tracker) so that you get the most out of your system. Other than that, it does exactly what it says on the tin.
Next is the most important component, the batteries. A mesmerising device (for some), a battery will quietly do the work that some underground peat bogs have been doing for millions of years, store your energy. They can come in all shapes and sizes, so getting it right is key to making sure your lights don’t go out before you’re ready to call it a night. A battery will have a voltage (V) and an amp-hour (Ah) capacity.
The whole system will want to run on the same voltage, so if it’s a 24V system, you’ll want two 12V batteries, or four 6V batteries wired together. Next, you look at the amp-hour capacity and multiply this by the voltage, to get the full capacity of your battery bank. Depending on the way you wire the batteries, either the voltage or amp-hour capacity will increase. So, if we use four 6V, 100Ah batteries, wired in series, then 24V x 100Ah = 2400W battery bank. The thing about batteries is that they don’t like you discharging them more than 50%; but they reward you by lasting longer. This gives you 1200 watts of power.
To get an idea, if you’re using 5 fancy (also rather cheap) surface mount LED lights for the evening, then you’ll use: 5 lights x 5 watts each x 6 hours = 150 watts. A laptop uses around 40W an hour, and an amplifier will use slightly less. If you’re putting it in your shed, I’d suggest going for a maintenance-free gel or absorbed glass mat (AGM) lead-acid battery.
Finally, to wrap it all up, there’s the inverter. A battery provides electricity in direct current (DC), and your typical household appliances are designed to run in alternating current (AC). This is where the inverter steps in. Two things to look out for here: the voltage of the inverter (make sure it matches the battery bank), and the output.
The output will come in two figures, continuous and surge. Continuous output is the maximum amount of power the inverter likes to put out over an hour. You should consider all the appliances you’ll have running normally, simply add up their wattage. Surge output is a brief spike in output to accommodate high loads, such as toasters, or kettles. Typically British (google the ‘TV Pickup’ phenomenon), kettles have a surprisingly high draw (2000W) so make sure you bear this in mind.
As well as these four components, there are a few additional things, such as the wiring and breakers to consider. Some final pointers:
What voltage do I want to run the system on? The higher the voltage, the more efficient the system, as less electricity is lost as heat. Your options are 12, 24 and 48V. Higher voltage also means more batteries so there is a compromise to be made. I’d advise 24V.
How do I know how much power I need? Your appliances have a power rating on them; this figure is the amount of electricity it uses over an hour. Add these up, easy!
What about winter? As much as you may want to use a system like this during winter, the great weather bestowed upon us during this gloomy period is not enough to recharge your battery bank if you have designed it for use in the summer. It is better to leave it during this period and allow the solar panels to keep the batteries fully charged.
Is it safe? This is up to you. Electricity can be dangerous. Make sure you do some research, speak to a professional installer, include the right circuit breakers, and be sure to put the system in a safe place away from children.
Batteries! You should know a bit more about them before purchasing. Most importantly, they don’t like to be left in a partially discharged state for a long time. Make sure they recharge to 100% as soon as possible.