As many of you know, I have a number of vehicles in my possession, but it does come with a few drawbacks - the most annoying one being flat batteries.

I simply do not have the time to drive all my cars enough to keep the Batteries fully charged, and some of them sit in the garage on a trickle charger to keep the voltages topped up so that they can be driven whenever I fancy. Earlier in the year, I bought a GMC truck for camping, and with the winter weather now on its way this will now be parked up for a while and the battery will undoubtedly go flat.

And this got me thinking about Solar Power and what would actually be involved in keeping a battery alive.

Like many of you, I have also tried those little panels sold in the car accessories shops that plug into the cigarette lighter socket with absolutely no success whatsoever. They suffer from a few issues, one of which is that unless your lighter socket is powered all of the time, then they will not offer any charge unless you ignition is switched on, and that just isn`t practical. Another problem is that they often sit on the dashboard behind the windscreen - you know that big bit of glass that has various layers in its construction to prevent the amount and type of UV light passing through, and as a result can reduce the charging capacity of your little panel by as much as 80%. But the biggest issue with those little panels is their size - they are just not big enough to make any difference. Small Motorcycle Battery maybe . . . . A Car Battery? Not a hope.

So, I have just undertaken a crash course in Solar Panels, and thought I would share this with you.

There are lots of spammy leaflets doing the letterbox rounds about Solar Energy and how it can save you money on your electricity, but I stopped taking any notice of those when they said that it would take around 18~20 years to get your money back from your investment - but the Manufacturers claimed the Solar Panels only had a lifespan of around 15 years - maths just doesn`t add up. Not interested in powering the house, I just want a panel to charge my car(s) and a quick search on the Interweb brings up a whole host of panels of various shapes and sizes.

Most of the panels operate at the same voltage from bugger all at night to 20 Volts or so in strong sunlight - the differences in physical sizes relate to the amount of current that they can produce, but basically range from 5 Watts to 100 Watts. There are a few calculators on the net to ensure you get the right wattage for your own needs, and most websites will then confuse you with talk about bilge pumps on boats or fridges in motorhomes, and making sure you have enough power to keep these running and how to connect multiple panels together. It was a minefield to follow, the calculations were impossible, and I figured I that it would be far easier to approach it from a completely different perspective instead. Whats the biggest one I can physically fit on my roof? - as better to have too much power than not enough. (POWEERRRRR . . . . Too Much Clarkson methinks) The most common and largest single panel I could find was a 100 Watt one, but even these can vary dramatically in price (£70~£300), so have a good shop around. The panel I was looking at came in a big metal frame and while it may have been great on the garage roof it was just far too big and too ugly to fit on the roof of the van.

After some more searching, I came across some semi flexible panels, and an 80 Watt one was about the right physical size for my van roof. Again, there are various quality and price differences here, but I opted for a slightly more expensive £160 Marine version as used on the decks of boats. The reason for going for this one is that it had a plasticized gel surface that if cut or damaged, sticks itself back together again, and was tough enough to be walked on. (To me, that means possibly Seagull proof) Being semi flexible, I could also then just bond it to my curved roof with some Sikaflex sealant.





There were a few other things I liked about this panel, and they were nothing to do with the performance, it was more about the aesthetics. This panel not only had the electrical connector on the same side as the solar cells, making it suitable for bonding to a flat surface, but also only had one two core cable coming out, unlike most of the cheapie ones that had 2 separate cable for positive and negative. That can make a big difference when drilling a hole in your roof, as you only need one cable, and for anyone brave enough to do this, I can strongly recommend using a cable gland from the Marine Industry. They are very expensive at £18 a pop, but they are waterproof to the point of being submersible.





So you now have 2 wires inside, but its not as simple as connecting them to a battery just yet. Before that is done, you need to have an understanding of what you are actually trying to do. In basic terms, to charge a 12V car battery, we need to have an available voltage that is higher than this. So if your Solar panel is kicking out, say 15V on a sunny day, it will charge your battery, but if it is cloudy and you only have 10V, then it will drain your battery. That's an important concept to get your head around, because if the sun is shining, then you can expect your battery to get charged, but at night, when there is no sun, your battery will now be "powering" the Solar Panel and blowing it to pieces.

Thankfully, you do not have to worry about switching it on and off yourself, as what you need is a little device called a "Charge Controller". Again, these can vary in price from between £10 to £100 and from fully programmable ones to fully automated ones with built in USB sockets for charging your phone. Whichever one you choose, its important to make sure that it can carry the current from your Solar panel. In my case, my 80W panel can run at near 7 Amps, so I would need a controller of at least 10 Amps capability (always bigger). Because this was going in my van, I also decided to go for a Dual 20 Amp Charger, so that the Solar Panel would not only charge my main battery, but would also charge a secondary leisure battery in the back. This controller cost me £25 and had the added advantage of being able to prioritize which battery got charged through its programming and button pressing, which is no more difficult to do that setting the time on your watch.





As you can see, the wiring is about as basic as you can get. Two wires in the middle from the Solar Panel, and I have put these via a switch so that I can kill the system dead if I want to work on the vehicle with everything dead, and two wires out to each battery via a fuse. There is an option for adding an external thermometer, but I couldn`t see the point, especially as there was an internal one built in. Other than that, there is a simple LED number display with a button for programming, and 2 lights to tell you which battery is being charged.

I do like bells and whistles though, so because this unit was to be mounted in the depths of the roof panels, I decided to add the optional remote meter that was available for this model (£35). This then gives a live update of the state of charge in each battery, and shows what the panel is doing at any given time.





And thats about it. What initially seemed very complicated is very simple indeed, not only that, but its kept the battery in the van in full charge for many weeks now. The power of the panel I have, even in poor sunlight, is more than enough to fully recharge a dead battery inside a week, and plenty enough for me to run a TV and some lights in the back when I am camping without jeopardizing the power from the Leisure battery either.

I`m going to stick another one of these on my garage roof in time with a couple of "Fly leads" so that I can quickly connect up to whichever car is in there at the time, as well as keeping my bike charged too.

If you shop about, you can pick up a 40 Watt panel and a 10A controller for under fifty quid, and that may be a great thing to stick on your garage roof (and your Christmas list) so that your Buggy remains ready for use at any time, even though it probably won`t come out to play until the weather gets better.

Dave, I have solar panels on the roof, 250w each and 25 year guarantee. They do degrade with time so the guarantee is for minimum 80% output after 25 years. Have had them nearly 4 years and they will be paid for within 7 by the payment I get and payment guaranteed for 25 years
Payment rate has reduced now so payback time will be different but panels should be cheaper as well

If you put one on your garage roof then why not fit an inline plug and a socket in each vehicle for ease of use

Quote from: Doon L001 on October 14, 2016, 07:12:41 AM
If you put one on your garage roof then why not fit an inline plug and a socket in each vehicle for ease of use

Thats exactly what I plan to do.

I have just been looking at solar panels to power a pump in my garden pond, that I am hoping to build over the winter. They are cheap now and it saves plugging more into the mains with the ever rising electric prices

These new cars are a pain with there constant power drain for immobilisers and alarms even a month in the summer and you can be struggling to start them! I can leave my tractors most of the winter and they will still start without a boost!

Rob

i've had a look at this in the past and it seems a good way to go, one thing has me wondering thou.
a solar panel gets hot under full sun and degrades due to thermal cycle and decay. that why most house installations use free standing panels and some harvest the heat as well as the electric energy.
assuming the roof is well insulated, how will it shed its heat on a 30 degree c day? as it cant dump it in the surface.
have you noticed an elevated temperature in your installation, and doo they come in green?

With a little panel like that you probably wouldn't see much heat causing an issue with the panel.

As for big solar panels for houses (250w beasts making several kW's of power when linked together) They are mounted on racks that allow for a gap between the roof and the panel. That allows for good cooling from wind and also some meaty structure supports to stop them flying away in the wind. Between 5 to 15cm is normal, depends on the roof and panel type to be honest.

For charging batteries to keep a few cars topped that are sitting in a garage a single large domestic rooftop panel on the garage would be more than enough. Just like the setup you have now, but a 200w or 250w panel.

From then on, you would be better getting an MCS cert'd company in to cover every inch of roof space possible. You still get OK rates for solar installs which are guaranteed for 20 years, and their are still good deals from the Government to help pay for them.

Look into the Tesla power wall