Make A Solar Generator

Making your own solar charger isn’t as difficult as many people think and with a small initial investment and using what you already have you can make your own solar charger much more cheaply than those commercially available items and customise them to your specific requirements.

To begin you need to decide what you want in terms of power and what you can afford as the perceived wisdom of idiots is that you need an 100 amp hour battery for a 1500 watt inverter and this is simply plain stupid as you can calculate your battery sizes once you know your inverter capacity and work from there, know your power requirement before specifying your inverter.
Calculating your battery requirement follows a simple formula of what size inverter you need and how long you want that power for which you divide by the battery input voltage and you have your battery size or capacity, and if you use lead acid batteries you never run them below 50% charge or you damage them.

The formula is inverter capacity multiplied by the number of yours you want it to run for and assuming it is a 1000 watt invertor and you want it to run for three hours it becomes:

1000 X 3 = 3000 watts and we divide this wattage by 12 volts so now our equation is 3000 divided by 12 = 250 and the 250 is the battery amps you require and for lithium batteries this is the amperage but as you don’t want to run lead acid cells below 50% capacity the 250 amps is doubled so 500 amps; it really is that simple.

He had already piggy backed his consumer unit and fitted it with a plug which couldn’t be plugged in until the consumer unit was switched off to stop it back feeding the grid and his lighting circuit and some sockets were powered and his piggy back had a 32 amp commando plug fitted to connect to his solar generator and he worked out a 1000W or 1Kw was sufficient and he acquired two pure sine wave inverters of 1000 watts. He required this power for 3 hours as their longest power cut was 2 hours and this gave him some margin and his calculation became:

1000 watts for 3 hours, so 1000 X 3 = 3000 which is divided by the battery voltage which was 12 volts, so now it became 3000 ÷ 12 = 250 so he needed battery capacity of 250 amps and as these were lead acid batteries he didn’t want them dropping below 50% charge he doubled the capacity from 250 amps to 500 amps of battery capacity. Fortune came his way with a cherry picker at work which was being scrapped and it had a brand new set of spare batteries rated as 12 volts and 130 amps, their new cherry pickers had even larger and heavier 180 amp batteries and they were not interchangeable so he got a set of 10 for nothing. 4 X 130 amps = 520 amps and this exceeded his 500 amp requirement and work began by finding a tool box large enough to hold four batteries and his inverter and he got two from a tool retailer selling the stacking plastic toolboxes where the upper boxes were damaged and of no use so he mounted the batteries in the box and made red cables to connect all the + terminals together and black cable for the – terminals and he made an aluminium frame to fit under the box which was drilled and the frame attached with rivets and wheels put in the rear of the frame and a telescopic handle on the front so he could wheel it instead of trying to carry it.

With a metal base the battery clamp was made to clamp the batteries down and with a battery clamp at each end gave fixing points, one of the middle batteries used their claps to attach the MC4 connecter for charging and one end was to be for powering the inverter while the other end was for the 12 volt outlets. He had a 12 volt kettle and needed a cigarette lighter and two USB ports for charging phones and on the 240 volt end he needed to change the inverter outlet from domestic plugs to a blue commando fitting and he decided on a panel mount socket and a double ended plug cable to connect the inverter to his consumer unit.

He found the USB connecters in a local supermarket in 2 and 5 amp ratings and these plugged into a car cigarette lighter so he prised the front off and the circuit was attached to it and the + was connected to the cigarette lighter housing pin with a spring and the – was a spring clip on the side, these were removed and wires soldered on to them. He made a mould and put the circuit section into the mould and poured liquid resin in and this encased it and left just the wires hanging and with all four done he cut holes in the 12 volt and bonded then into the holes and fitted a cigarette lighter which was a 1.4 twist lock and they were fed from the battery through a standard car 15 amp fuse.

On the mains end of the inverter was a single plug and once unscrewed it exposed the wiring and he made a plastic blanking plate and fitted a cable gland to it and attached a commando socket and fitted it to the plate and he made a short double ended cable with plugs as either end and he replicated this with his second box and had two spare batteries.

Two solar panels of around 240 watts were wired in parallel and fitted to his shed roof in their optimum position and ran the wiring into a changeover switch which had two sockets fitted and you had to change over before you could unplug it so at least one generator was charging while the other was in use and this meant you had to plug in the discharged unit before you could disconnect the charged unit. You could have both battery banks charging or swap to either one and this meant always one battery bank was connected to it so it didn’t damage the solar panels. He stuck with the basic PWM charge controller as all it did was charge his battery banks and maintain them and if they were both low he could connect his battery charger to one once power was reinstated and quickly recharge it while solar charged his other.

What did he have connected? He had some of his lighting permanently connected so in the event of a power outage he would have lights; his gas boiler had a dedicated circuit so this always had power to the control circuits and pump, so heat, and he had a choice of other things. He could have the TV on or he could run the fridge/freezer and he adopted the hourly freezer run where he set it to the coldest setting and let it run and after about 4 minutes of running it was at its coldest and would remain frozen all night if it wasn’t opened.

Can you make your own solar generator, actually yes, as long as you can work your battery requirements out and get an inverter which suits your basic requirements and no more, you can keep your battery sizes down as well as the costs. Many people over specify their power requirements and as long as you have light and heat you and your food will survive if you have enough additional power to run your freezer.

A note on batteries:

Car batteries can be used but while they can be much cheaper, are they the better option? Where someone is working to a tight budget then yes would be the correct answer, if there are no or less limited financial restrictions then no would be the right answer, so what are the differences? In simple terms a car battery is designed to provide a huge amount of power for a very short period of time and this would be for starting the car and as anyone knows you do not crank a car for long before it starts, for a diesel engine this may be to draw around 40-100 amps to power the glow plugs for an initial period of seconds before the current draw drops and the starter is cranked.
Car batteries consist of a series of plates which produce the electricity and these are small and fairly light as they discharge a lot of current quickly and the smaller plates can also be recharged quickly, hence why they are made in this way.

Leisure batteries are made differently and instead of flowing a huge amount of current very quickly they are designed to be discharged much more slowly and for a very long time and consequently they do not need to recharged quickly and they have much larger and heavier plates to allow lower discharges for a much longer period of time.

Deep cycle or traction batteries fall somewhere in between for usage as they are designed for larger current discharges and for a longer period of time which is why they are used as traction batteries for commercial batteries such as milk floats as they can have much longer recharge periods of hours.

If funds permit I would go for the leisure battery as a minimum and if your pockets are deeper then go for the deep cycle of traction battery and remember if you want or need several or multiple batteries it can get expensive.

Why not lithium? Because lithium have an inherent problem and that is called “thermal runaway” where an individual cell overheats and can ignite, this in turn causes the surrounding cells to overheat and potentially ignite as well and the resulting fire simply burns as it is a chemical fire which self generates its own fuel and oxygen and fire brigades cannot extinguish them as they simply do not carry the correct fire extinguishing agent which is also extremely expensive. Silly question, where do you intend putting your batteries? If this is anywhere inside your property such as the attached garage and you get such a fire then it is more than likely your home will suffer too and in many cases home insurers are refusing to cover this cost as they are now excluding lithium batteries inside your home or in any structures attached to your home. Look at Luton airport and one lithium battery with thermal runaway causes all of that and despite their continued denials footage has appeared online of the fire starting and this was a lithium battery fire, do you want to run this risk in your home? And do you have children and are you prepared to expose them to this risk.