Solar Power for Caravans and Motorhomes
The non technical viewpoint ...
How Many Solar Panels do I Need?
The simple answer here is probably; "as many as you can fit"! The first problem with a caravan/motorhome setup is that you are going to stick to panels on the roof, flat mounted and you could conceivable park anywhere in the world. Touring the outback or desert will result in higher solar gain than say touring in a damp and overcast environment. Back in "Basic Electrical Information" we discussed a thing called a "sun hour". This is a solar term that should give you an average daily output from your solar array based on the total light that falls on your panels. Because we are not getting technical here, let's look at fitting a single 120 watt panel to the roof of your bus. In an ideal world based on 4 sun hours this panel would give you about 480 watts to play with. The roof of your bus is not however an "ideal world" and here flat and with a sheen of road dust on it, let's be a bit more conservative and say 2 sun hours per day max. So your investment in a single 120 watt solar panel will give you about 240 watts to play with. Enough for a few lights perhaps, but way shy of even the most efficient fridge or a few hours of television. Microwave? Forget it!
Some Basic Rules
- The roof holding your solar panels will need to be in the sun
- Partial shade will dramatically reduce panel output even if you have been sold "Shade Tolerant Panels". (In reality there is no such thing)
- A thin film of road dust will reduce the panel output considerably
- A thick film of road dust will will reduce the panel output to almost nothing
- Parking in the shade will reduce the panel output to almost nothing
What Can I Run From Solar?
- Lights - Easy
- Refrigerator - Yes but bet warned, there is a lot more to refrigerator use than meets the eye
- Television - Yes
- Microwave - Yes
- Air conditioner* -No
- Heater - No
* It is interesting just how many people want to run an air conditioner inside their caravan on solar power. This is in fact possible (so is a heater) but the logistics of it are huge. The average small caravan sized air conditioner will use around 1500 watts. To run this unit for just one hour would require an solar array of around 750 watts (say 7 x 120 watt modules). Having an air conditioner on for just one hour per day is very little better than having no air conditioner at all! If you really want an air conditioner then the logical solution is to either use powered camping sites or pack a generator.
Where do I Store the Solar Power?
In a battery bank of course! In order to store this power in a battery bank efficiently you will also need a solar regulator.
The single most important thing to know about a solar system is that everything should be matched to a certain degree.
- The solar array is sized according to the electrical load.
- The solar regulator is sized according to the solar array.
- The battery bank is sized according to the solar array and the electrical load.
- An inverter is sized according to the largest appliance, the maximum number of appliances and the battery bank size.
Where to Next?
A solar power system on a caravan is not much different than a solar system on a house. These information pages should help you understand everything about designing a solar system for both a house and a caravan. The only real difference is that with a caravan installation, the flat mounted panels and the mobility can change the average solar power output dramatically. The other variable is the vehicle itself, the length of stay in one location and the need for backup power.
Specific Caravan and Motorhome Power Considerations
The biggest difference between a mobile solar installation and a stationary (like a house) installation is that the mobile house has a readily available source of power, that being the vehicle alternator. If your planned caravan use is single night stop then drive all day then single night stop, a solar array may not be required. Simply put, you charge your caravan battery bank while you drive, then use it when you are stationary then repeat.