A simple solar electric power system.
A friend of mine asked me to explain how solar electricity works to his son, so I put together this very simple solar power system. It cost about $110 all up to set up. The panel was about $55, the regulator was $25 and the battery $26.
The system consists of one 20 watt solar panel, an 8 amp hour battery, a solar regulator and a dual cigarette lighter plug.
This is it in a bit more detail. For simplicity, I glued the power regulator to the battery.
This regulator was a cheapie I brought on eBay. The two leads from the solar panel plug in on the right, with a separate contact for the positive wire and negative wire. The middle two leads connect to the batter and the ones on the left to the load.
The solar power comes in at anything from 0 volts to about 22 volts in full sunlight. The regulator feeds power from the solar panel into the battery at a regulated voltage. This regulator will let a maximum of 13.8 volts into the 12 volt battery. That's fine, the battery will happily handle 13.8 volts. The regulator also controls power out of the battery. When the battery reaches 11.8 volts, it will cut off the current to the output of the system. In this case, the system provides power to a basic dual outlet cigarette lighter.
There is no reason why a small car or van power system can not be as simple as this. A system like this though won't power much. It might power a laptop for a couple of hours at the most. It would run some LED lights fine all night, or a small radio.
Regulator.
The regulator here is a little one rated 20 amps but it is a real cheapie, with no fuse protector so it is not something I would use on a full scale power system. While it may seem like a good idea to buy a cheap power regulator, it will severally limit your system if you plan to expand in the future. You will want one with built in fuse protection. Expect to pay about $100-$125 for a good one. The regulator I use is a 25 watt one that is on the left, above the red switch in the photo below.
Ideally you would want a larger solar panel capable of producing more than 20 watts. Something above 50 watts would be nice. On my main system I have 272 watts of solar panels, but my system is designed to power a 12 volt fridge and a few appliances. Generally the more solar panels you can afford the better. But even a small system with 60 watts of solar panels can produce useful power that will run a TV set for a while.
Battery.
You would also want a larger capacity battery. A 85-100 amp hour battery will power a small TV for a few hours or a laptop for a few hours and some lights and a radio as well. You also have to match your battery capacity to your solar panel. If you have a large capacity battery, but a small solar panel your panel will not be able to charge up your battery fast enough, leaving you with a battery that will go flat too often and die sooner. As a very rough guide, and I am really simplifying a whole pile of mathematics here, the minimum amount of watts of solar panels you will need to charge a battery is roughly equivalent to the number of amp hours of battery capacity. So, if you have an 85 amp hour battery, you should be aiming at having a minimum of 85 watts of solar panels.
Yes, I know I said I've simplified it a lot. There are many factors that will affect this. For example, if you use less than 85 amp hours of power a day, the excess power generated by your solar panels will ensure your battery remains charged. If you are in a place with longer sunlight hours you may need less powerful solar panels. If you live closer to the equator you will need less solar power because your panels will be facing the sun more if you mount them flat on top of a vehicle. Also, on winter days you may need more solar power because days are shorter.
But generally at a rough guide, if you have the same number of watts of solar panels or more than the number of amp hours of your battery, you generally should not flatten your battery. If you do find you are flattening your battery you will probably need more solar capacity, or will need to use less power. Or it could be as simple as not using thick enough wire on your system.
Wiring.
Thin wiring is the bane of a solar power system. Little basic speaker wire will not do the job. Take a look under the hood of your car. See the main lead that comes off of your battery? You're going to want to use wire about half as thick as that. At a minimum you will need 6mm cross section wire. That is typically about as thick as a drinking straw, if not a little thicker. But the thicker the better up to a point. Pretty much when you start to get wire as thick as jumper leads you would not want to go bigger. Naturally thicker cable costs more. The wiring I am using in this demo solar power setup is about the minimum I would use, and only for short runs.
So, in a nutshell that's a basic solar power system.
