Solar energy is a free renewable energy source and can be used to generate power whilst you are on your travels.
By using solar panels the sun’s energy can be converted into electrical power and used to trickle charge your battery or directly power your appliance.
Maximum power output when in direct sunshine, however the solar panels still produce power in overcast or on rainy days
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These equations are key to working out what panels you need
Power in Watts(W) = current in Amps (A) x Voltage in Volts (V)
Energy in Watt hours (Wh) = power in Watts (W) x time in hours(h)
Battery capacity in Amp hours (Ah) = energy in Watt hours / Voltage in Volts (V)
How to work out how much solar power you need
Choosing the right panel for you can be a challenge – too small, not enough power or too big and not all the power you generate is used.
A simple method to find out the right solar panel for you, is to go on holiday with a fully charged battery and don’t connect it to an electric hook-up or recharge it and see how long it lasts before the battery is flat.
On the battery there will be the rating of your battery marked in Ah, normally caravan batteries come with either a 85Ah or 110Ah battery, but check to make sure that the battery capacity is.
So if your battery lasted for 3 days and it was a 85Ah battery then you used 28Ah per day (85/3 = 28). This is not an exact science, but gives an indication to what you power consumption is.
You therefore need a solar panel to trickle charge you battery by 28Ah per day during sunlight hours.
To calculate the size of panel you will require then battery capacity x voltage = Energy
28Ah x 12V = 336Watts, assuming there are 8 sunlight hours in a Summer’s day 336/8 = 42Watts per hour are required, so a 60Watt panel would suffice.
Work out your power consumption from the appliances
Okay so perhaps you don’t want to flatten your battery, so how can you work out the power consumption in your caravan?
These examples may assist you:-
Your main light in the caravan is a fluorescent strip type with 2x8W tubes, therefore 16W in total. The voltage in the caravan is 12V, so to work out the ampage is Wattage / Voltage = 12W/12V = 1.3A. If the light is on for 5 hours per day then that is 1.3A x 5hours = 6Ah (Amp Hours) required per day. If you have a fully charged 110Ah battery, then just using this light for 5 hours per day the battery will last for 110/6 = 18 days.
Another example, you have a 700W microwave, therefore the Ampage is 700/12 = 58A. However it is only used for 10 minutes so 58 x (10minutes/60minutes) = 10Ah. Your microwave will probably be plugged into an power inverter so there will be inefficiency, however these figures are only an approximate guide.
Add these together and you need and you need 10Ah+6Ah = 16Ah. Convert into wattage 16Ah x 12V = 194W.
Assume 8 hours of sunshine per day in Summer then 194W / 8hours = 24W per hour is required from your solar panel. So a 30-45W panel will do