solar panel wiring
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Solar panel wiring, materials?
I want to buy a solar panel to charge deep cycle batteries and charge electronics off the DCB. I don’t know how to wire everything up though or what materials ill need. Inverter? Gauge of the wire? Ampmeter?
You need to have some idea of what power you need or you will most likely be disappointed.
Batteries rated at 100Ah can deliver about 20A for a few hours. This corresponds with 240W ber 12V battery, so you can say after losses, 200W of AC. If you wish to power 200W or less, that is fine. If you want more, you need more batteries. It is best to connect them in series for 48V or something like that. This keeps the current in the more practical 20A range, and the cables are smaller and cheaper.
When it comes to charging the batteries, the larger panels are around 100W panels. These deliver a current of about 5A to charge the battery. This is the peak, when the full sun is at right angles to the panel and high in the sky, so delivering about 1200W/m^2.
Let us say that there are 5 hours a day equivalent full sun. You can look up your region on the internet in most places. That gives 25Ah per day. That is all you can hope for with one x 100W panel per day.
If you have more than 12V in the battery, you will need a panel for each 12V of the battery, so that is 4 panels minimum for a 48V battery.
As there are only 25Ah from a panel per day, and it takes 1.4 times the Ah to recharge the batteries, we can expect to take 6 days to recharge a 100Ah battery that is not being used. This can be improved by having more solar panels. Thus 8 panels would produce 50Ah per day for a 48V system (to charge in 3 days). As you can see you have to work out a usage pattern for your electricity that suits the limits of your panel string.
Other things you need:
The cable size must be big enough to carry the current safely. It will most likely need to be bigger again to minimise the voltage drop. That depends how long the cable is. Generally it should not exceed about 5m, and that probably means the next size up in cable. You can check all this from cable suppliers tables of resistance per meter and current carrying capacity. There are 2 main cable sizes. The cables connecting solar panels together and to the battery. In a series chain this should be 10A cable (for 5A panels) or larger to minimise voltage drop. If there is more than 1 series chain, wire each string separately to the charger where they are commoned together. The cable from the charger to the battery needs to be bigger to suit the added currents of more than one string.
The other cable size is from the battery to the inverter. It should be at least big enough for the maximum current the inverter can draw. This should be 20 or 30 Amp cable considering 100AH batteries. It should be larger so that the voltage drop through both cables is less than 1% overall. Don’t skimp on this. Take the next size up if in doubt. The load side of the inverter is 120/240V AC so leave it to an electrician to make sure it complies with regulations.
Charging control:
A solar charger connects between the panel string and the battery. It needs to suit the maximum current from the panels, as well as the voltage of the battery. If you get an MPPT charge controller that is better. It adjusts the charge current to maximise the power obtained from the panels as conditions change. I think an ammeter for charge current is a good idea. This can be in series with the charger and the battery. A ten amp meter will suit for a single string, ec.
Safety:
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The solar panel side of things doesn’t need a fuse because the panels are inherently current limited to less than the cable can carry, by their nature. Between the charger and the battery should be a fuse, mounted near the battery. It is rated to the cable size, so if you have 20A cable, 20A fuse. The reason for this is that the battery connects to the charger, so if you short something in the charger the battery current is there to make a fuse necessary.
There must be a fuse between the battery and the inverter. There may be some sort of battery fuse in the inverter. This fuse prevents a fire if the inverter should fail. It is rated to the inverter maximum current, or allow a little more for surges. It should not be higher than the cable current rating.
If you connect an ammeter (rated for max inverter current) between the battery and the inverter, it will help you determine what is happening with power consumption. Alternately, have an ammeter in the AC distribution side.
If you have sufficient power (like 1kW or more) you can consider a grid tied system , that uses no batteries. You need to get that done professionally anyway.
The batteries need to be located outside in a well ventilated situation.
Solar panels need to be well ventilated. Allow fre air around the back. The inverter and charger also need good ventilation for cooling, and should not be in the sun ever. Obviously electrical parts are protected from the weather, vermin, ants etc.
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