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Stephen Ward Caravan & Boats

the 'LPG' specialist on the Isle of Wight

SOLAR PANELS & Off Grid

With the environment and saving the planet in mind using Solar Panels has never been easier, so here is some advice for touring caravans.


Battery Type


Normal 12v leisure batteries are 85ah. They weigh between 16-18kg, and the bigger 110ah is 21kg. So thinking about off-grid power when you have a touring caravan, the weight is critical not to eat into your MLPT "Maximum Permissible Laden Weight" this is the amount difference between your maximum towing weight and the weight of the overall caravan unladen.

This can be anything between 200kg and 250kg. Considering this weight includes food, clothing, carry on items such as awnings, water contains etc. so adding solar panels will add to that weight.

If you want to keep your leisure battery in good condition ( See my page on batteries) while storing the caravan or inactive for a long time, then a 100watt solar panel is more than adequate.

For the more serious Off-Grid camping, Lithium Batteries are the way to go. These are expensive, but there are many advantages.

Firstly they are much lighter. A 100ah battery is about 12kg, and some of them can be stored on their side depending on the space you have. In this modern world, they are also Bluetooth connectable via an App to your smartphone. This means you get real-time data on the charge condition and voltage of your battery.

Secondly, a lithium battery can be used until it is flat 0% and then charged again multiple times without damaging the battery. There are circuit boards built into the battery to prevent

overcharging and overheating. They need looking after; they don't like the cold as they rely on a chemical reaction, so cold can hinder or stop them from working. So internal storage is essential, i.e. bedlocker. If you are intending to occasionally charge the batteries on mains 230v power as a backup, then you will require a specific charger capable of Lithium. The current chargers installed in caravans are only designed for Gel/AGM/lead Acid battery charging.

At around £600(May 2021) for a battery, they are a serious investment, but one that is worth the convenience, weight and performance you will get.


Solar Panels and Controllers

There are two types of panels:

Polycrystalline and Monocrystalline

The first Polycrystalline is usually cheaper due to the construction of the silicone cells. These panels are good for occasional charging use, i.e. keeping the leisure or starting battery topped up while a vehicle is not in use. They are also good for keeping a battery charged in a garage.

Monocrystalline are designed to give maximum photovoltaic power, the conversion of light into electricity. These panels also give an excellent conversion to low-level light and yield 30% on average more power than the Polycrystalline.

Controllers

There are two types of controllers:

PWM (Plus Width Modulation) and MPPT (Maximum Power Point Tracking).

MPPT controllers are the best. They will convert and operate with your Monocrystalline Solar panel and yield more power in low light conditions and overcast days. A good quality controller is essential not only to give you the correct power voltage but also work flawlessly.

So what do I like to use?

I like the Victron controllers. They are easy to install, wiring is very simple. The smart connected controllers, you can use their App to monitor the system giving you data on voltage, amp generated. They also have tracking through real-time graphs, giving you data throughout the day. Essentially they give you power consumption used against power generated.

I always install a Victron MPPT Control. This is a small instrument that connects to the MPPT controller via a VE Cable you buy separately. This gives you the same data you get on the app, but as we all know, sometimes you don't get a signal on your phone and this will allow access at all times.


Cables

The further the batteries are away from the MPPT controller the bigger the cable is required direct to the batteries. I installed two solar panels on a twin axle caravan. The batteries were in the front nearside bed locker with all the other electrical equipment; however, the panels were on the flat part of the roof over the rear and the controller in the wardrobe, which meant the cable needed to travel the length of the caravan to the front under the floor. I used a 6mm heavy duty twin cable to minimise voltage drop over the 5-meter length. 10amp current over 5-meter drops .3volt, which is 2.4%. If you use a 1.5mm cable, you lose 9.7% or 1.2volt. This may not sound a lot but remember, on cloudy dark days, you want as much energy into those batteries.

So from there, you can power your 12volt system. Either you can feed directly into the leisure system powering the original caravan 12volt electrics keeping the leisure battery charged, or if you are installing some extra batteries, then create a separate fused system with a battery isolation switch. From this system, you can install separate USB points and 12volt cigarette lighter sockets that only draw power from the lithium or separate batteries, leaving the leisure battery as a separate power source.

4mm twin cable will give you a maximum of 25amp draw. Since USB only drawer a maximum of 5v and cigarette sockets 150volt or 10amps is more than adequate.

Here are some 12v power table examples.

The formula for working out the amps is easy.

Wattage divided by 12 volts = Amps.

Laptop 41 watts = 3.2 amps

12v TV 28 watts = 2.3 amps

1 x LED strip light 400mm 15 watts =1.2 amps

Please note a 3-way fridge with gas, electric and 12v of Dometic or Thetford. The 12volt is designed to run off the vehicle engine power only. The average fridge 12v element is 125watt, so it will pull 10-16 amps of power and will flatten a battery very quickly.

There are fridges designed specifically for 12volt only. The small fridges can drawer as little as 1amp. It is advised to use 3-way fridges off-grid using the LPG gas.

My recent off-grid installation comprised of two 340watt Monocrystalline panels, a Victron Smart controller connected to two 100ah Lithium batteries. This system, on a bright sunny day, was producing over 25amps of charge power per hour to those batteries. This would mean you could switch all the interior lights on, the pump, the TV, the USB sockets, and plug in a TV and laptop and still not drawing more than the charge the panels were putting into the battery!


COST

Currently a decent 100watt Moncrystalline panel and controller to charge a battery is between £150 and £250 depending on size. Bigger panels producing more power are 300w or above are about £250 each and a controller about £200.

Fitting and installation costs are per job but on average about £500 with all the extra USB sockets etc.

Any more information or advice please contact me.