Solar Panels for Caravanning and Camping to recharge batteries.

Time after time when you go camping or caravanning there is no mains electric hook up to connect to, and you have to use your 12 volt leisure battery for powering your lights and other equipment. Experienced caravanners know it’s very easy to flatten your battery in no time at all and have to be careful what they switch on and for how long al well. Here are a few tips on basic battery care.
 
1. Battery rating in Amp Hours (AH)
A battery rated at 100 Ah should deliver 1200 watt or power (12 volt times 100 Ah) but in doing this you’ll flatten your battery to 100% DOB depth of Discharge.

2. Number of cycles a battery can be charged and discharged.
   Discharging your battery 100% every time will reduce the total number of cycles by half, so its best only to discharge your battery by up to 50% DOB depth of discharge and your battery will last twice as long, so a 100 Ah battery can supply 600 watts of power for best results.

3. Battery Voltages
   13.4 Volts fully Charged
   12.1 Volts 50% Charged
   10.8 Volts fully Discharged
   Voltages taken with a volt meter and battery not under load (supplying power to appliances)

4. Charge Voltages
   14.4 Volts via solar panel regulator/charger.
   13.6 Volts float charge.

5. Example of what can be used from a 12 volt battery rated at 100 Ah
   a. TV total wattage 45 watts for 4 hours 45 Watts times by 4 hours = 180 watts
   b. Lights, 2 lights each 50 watt each 12 volt halogen for 1 hour = 100 watts
   c. Radio 25 watts for 3 hours = 75watts
   Total wattage = 180 + 100 + 75 = 355 watts
   
   If you only want to discharge your battery to only 50% to make your battery live longer you really have 50 Ah or 50 Amps at 12 volt battery.

Using Ohms law, Watts divided by the voltage gives you amps
355 watts / 12 volts = 29.5 Amps, this means you have a battery at 70 % DOB depth of discharge.

You can recharge a battery with a solar panel, but need to use a regulator / charger so the battery will re charge at the correct voltage.
If you don’t use a regulator you will cook the battery with high voltage and permanently damage your battery. Here is a good old saying to remember “batteries don’t die they are murdered”.   
A solar panel will have a voltage from 18 volts to 35 volts or even greater the solar charger regulates the solar panel voltage to the correct charge voltage of 14 .4 volts.

What size solar panel do I require to recharge my battery?

This depends on the following
The battery size in AH
What total power in watts are going to be taken off the battery during the day.
Battery temperature.

Lets say you want to take 30 amps out your battery during the day and you have a 100 Amp 12 volt battery. Now you need to re charge the battery during the day with a solar panel. A 60 watt solar panel has a voltage of 25.3 volts and maximum current of 3.25 amps. If you are reducing the voltage from 25.3 volt to 14.4 volts to charge the battery the current can increase from 3.25 amps to over 5 amps depending on how much sunlight falls onto the solar panel. If you are charging your battery at 5 amps per hour you only need six hours of sunlight to recharge your battery, if you double the size of the solar panel to 120 watts then you only need half the time to re charge the battery.

This is not always the case as the sun is not always shinning and solar panel may be facing the wrong direction so reducing the possible maximum generation possible. The solar panel always wants to be at 90 degrees towards the sun so it generates the maximum out put possible. A solar panel laying flat on a roof of a caravan will generate half the current for the same size solar panel pointing in the correct direction, it’s the same with a solar panel not facing the sun or if there is any shade on the solar panel the output is greatly reduced, that why people fit more solar panels than required to keep their batteries fully charged but its not required if you turn your solar panel towards the sun during the day.

Camping is different all together to caravanning, things have to be smaller, lighter and easy to carry. Going to music festivals is a common thing these days and people need only a light to see at night time and be able to recharge their mobile devices to stay in contact with other people.
I’ve developed a small compact device which uses a 20,30 or 40 watt solar panel with a solar regulator and a small 7 Ah 12 volt battery. The battery will recharge a Iphone 5 at least 5 times without any sunlight. The 20 watt or 30 watt solar panel will recharge the battery while are out enjoying yourself and you can recharge you mobile device on your return.