Here is a little solar panel installation howto based on our experiences fitting one to the van.
For a simple solar setup you'll need:
- a solar panel
- a solar charge controller
- inline fuse holder
- grommets, bits of wire, terminals and heat shrink tubing
You should also have a soldering iron handy and know how to use it. It's by far the most reliable way to make connections and that's especially important in a rattly, vibrating van!
But before going any further it's a good idea to get acquainted with Ohms law. For those who wander - it's got nothing to do with mediation... It a relationship between voltage, current and resistance.
Without getting into too much detail the main thing you need to know is that dividing Watts by the voltage will give you the current (in Amperes). Most 12 volt appliances as well as solar panels and controllers will be rated in Amps, but some in watts so it's crucial to know how to make this conversion both ways.
So, if your fridge draws 70W at 12V then: 70W / 12V = 5.8A
There are a few types of PV panels available on the market. The two most popular are monocrystaline and polycrystaline. There are many comparisons elsewhere on the net so keeping the long story short, go for monocrystaline. It’s more efficient than poly in most circumstances and not much more expensive.
In an ideal world you should know how much power you consume before deciding on the size of the panel you need. In reality you will probably be limited by your roof space.
In reality you will not get the maximum output from a panel throughout the day (due to movement of the sun) so around 200W will be needed to make that fridge self sufficient.
Note that you can connect multiple solar panels in parallel to combine the power they'll produce. Connecting in series will combine the voltage which is something you probably don't want in this case so don't do it!
We only had enough roof space for a single 100W panel. It’s peak output is rated at 5.6 amps. It won't be enough for complete self sufficiency but it will extend the battery life and keep it topped up when not in use.
UPDATE: To work around the lack of roof space we now also have the capability to connect free standing panels. Most of the time we don't need it but it's handy when free camping for extended periods of time.
A rule of thumb when choosing a charge controller is to get one that can handle slightly more current than the theoretical maximum of your set up. Using Ohms law we know that the theoretical maximum for a 100W panel is 8A (100W / 12A) so a 10A controller will be sufficient.
There are two main technology choices here, either PWM or MPPT. For a small installation PWM is most cost effective. For larger MPPT will probably be more efficient, but also a lot more expensive initially.
We picked up a 10A EP Solar ViewStar PWN controller on Amazon for £45. You can go cheaper than that but it's got a few nice features that are worth the extra:
- different charging modes depending on battery type (flooded, sealed or gel)
- 6 charging stages (all configurable if you’re so inclined)
- temperature compensation
- the digital display shows how much power the panel is producing and how much power is being consumed via the 'load' connection (more on that later on)
- battery over-discharge protection
UPDATE: Since then we upgraded to a 30A controller (also a ViewStar). Mainly so we can connect all appliances to the 'Load' output on the controller which allows for total power usage monitoring. Another reason is the ability to connect additional, free-standing solar panels when needed.
The semi-flexible panels are the easiest to mount. You can simply glue them to the root with tiger seal. Drill a hole for a grommet to run the wires through and Bob's your uncle. The semi-flexible panels are lighter and more aerodynamic than the traditional rigid panels so that's what we'd recommend.
Alternatively here's how I made brackets and mounted a rigid panel before we went the semi-flex route. I used a couple of aluminum L shaped brackets from a DIY store. The idea was to slide the panel from the side into the roof brackets and fasten with some tamper proof bolts. This worked pretty well and was quite sturdy, but it did stick out a bit:
Test the output with a multi-meter before running the cable and connecting to the charge controller:
And hook up the the charge controller:
On the controller, from the left we have:
- Wires from the solar panel
- Wires to the leisure battery. IMPORTANT: make sure to fit a fuse on the positive wire between the battery and the controller! Should be rated at the same value as the change controller (e.g. 10A)
- Load connection to the aux fuse box (optional). From the fuse box power is distributed to all appliances via individual fuses. The load connection is optional and you don't have to connect it to anything. Your appliances can remain connected to be battery as they were before (hopefully via some fuses!). However, using the load connection means we can see monitor power usage and benefit from the controller's battery over-discharge protection.
So far on a sunny day we had this setup generating 4-5A. Even on a cloudy day it does over 1A, which is enough to trickle charge the battery and keep it in good condition.