Stephen Ward
Caravan & Boats

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 between 85 Ah and 110 Ah. They weigh between 16-18 kg, and the bigger 110 Ah is 21kg.

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 So, when you think 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 difference between your maximum towing weight and the caravan's unladen weight.

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This can be anything between 200kg and 250kg. Considering this weight includes food, clothing, carry-on items such as gas, awnings, water & waste containers, etc., adding solar panels will increase that weight.

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If you want to keep your leisure battery in good condition (See my page on batteries) while storing the caravan or leaving it inactive for a long time, then a 120-watt solar panel is more than adequate.

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For more serious Off-Grid camping, Lithium Batteries are the way to go. They are now slightly more expensive than a Gel or AGM Battery, but they are coming down in price and offer many advantages.

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

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Secondly, a lithium battery can be used until it is flat (0%) and then charged multiple times without damaging the battery. There are circuit boards built into the battery to prevent overcharging and overheating, and some come with their own battery management systems that can be connected to multiple batteries.

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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., a bedlocker or a locker insulated against the cold. The new lithium batteries are much better at handling cold and can operate at minus-degree temperatures; some even have integrated heaters.

 

You can purchase a heated lithium battery that can be stored in a normal outer locker. Most caravan and motorhome leisure chargers can charge lithium batteries, but you can also purchase dedicated lithium battery chargers with a built-in battery management system.

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At around £185(Aug 2026) for a 100ah battery, they are an alternative, Curently Renogy do a 100ah heated version for around £249, so that can go in a normal outside locker and a 300ah battery for £570 that is just slightly bigger than a 100ah battery in size, expensive but one that is worth the convenience, weight and performance you will get.

 

Remember, the bigger the battery, the bigger the charger you will need to handle the amp-hours and larger solar panels. 

 

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 silicon cells. These panels are good for occasional charging, i.e., keeping the leisure or starting battery topped up when a vehicle is not in use. They are also good for keeping a battery charged in a garage.

Monocrystalline cells are designed to give maximum photovoltaic power, the conversion of light into electricity. These panels also deliver excellent conversion at low-level light and, on average, yield 30% 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, yielding more power in low-light conditions and on overcast days. A good quality controller is essential not only for delivering the correct power voltage but also for operating flawlessly.

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So what do I like to use?

I like the Victron controllers. They are easy to install, and wiring is very simple. With smart connected controllers, you can use their App to monitor the system and view voltage and amperage data. They also provide real-time tracking via graphs, giving you data throughout the day. Essentially, they show you power consumption relative to power generated.

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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.

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Complete battery management systems incorporate an Inverter/Charger, Smart Solar MPPT Controller, and a GX device to integrate with the batteries, such as the Victron EasySolar.​​

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Cables

The further the batteries are from the MPPT controller, the larger the cable required to connect directly 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 was in the wardrobe, which meant the cable needed to run 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.

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

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

Here are some 12v power table examples.

The formula for calculating 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

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Please note a 3-way fridge with gas, electric, and 12V from Dometic or Thetford. The 12-volt is designed to run on the vehicle's engine power only. The average 12v fridge element is 125 watts, so it will draw 10-16 amps and flatten a battery very quickly.

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There are fridges designed specifically for 12volt only. The small fridges can draw as little as 1amp. It is advisable to use 3-way fridges off-grid with LPG.

My recent off-grid installation comprised two 340-watt monocrystalline panels and a Victron Smart controller connected to two 100 Ah lithium batteries.

 

 

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This system, on a bright, sunny day, was producing over 25 amps of charging power per hour to those batteries. This would mean you could switch on all the interior lights, the pump, the TV, and the USB sockets, plug in a TV and a laptop, and still not draw more than the panels put into the battery!

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COST

Currently, you can purchase a simple solar panel kit with a 120-watt panel and controller that will keep an idle battery topped up (i.e., in storage) for around £100. 185-watt installation kit with a Victron Smart Controller for about £395; however, they do have offers.

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OFF GRID

With technology moving rapidly each year, new kits are being brought to market. Getting the right off-grid equipment will give you more freedom when using it. However, inverting 12-volt battery power to run mains 230v equipment has its drawbacks and limitations.  

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Here is a quick calculation and formula for battery power and inverters. Usable power for lithium batteries is about 85%-90% of capacity. Usable power of normal lead-acid batteries is 50%.

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If you use a 12V 100Ah lithium battery (90% usable capacity = 1080 Wh), a 90% efficient inverter, and run a 100-watt appliance: 

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• 100Ah x 12 volt x  0.90 \text{ (usable power) \ = 972 Wh or usable power.

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• 972 Wh ÷ 100W ≈ 9.7 hours of runtime.

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If that same battery were a lead-acid type limited to 50% depth of discharge, your runtime would drop to roughly 5 hours. 

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A 32-inch 12-volt TV uses 21 watts per hour, 

1.75 Amps per hour.

Water Pump: 36 watts per hour, 3.0 amps per hour.

LED lights can be 20 watts in total, 1.6 amps per hour. These don't sound like a lot, but remember, the battery is going to be without any charge at night, so summer, 8 pm and 5 pm, approximately 9 hours. In winter, between 3.30 pm and 10 am, so approximately 16 hours and everything in between. I know you're not using your pump every hour, nor the TV, but careful power consumption calculations will save you from being frustrated by power loss and battery failure in the end.

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So my advice. Use as much direct 12-volt power as you can; limit your inverter power; get the best kits you can afford. Use gas for heating, hot water, and your fridge's power.

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Full off-grid kits, including batteries, inverters, chargers, cabling and battery management equipment range from around £2500 to over £6000.

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My labour charges for Fitting and installation are per job, but on average, about £200 for fitting a single panel with simple connections, to over £1500 for fitting a panel with all the extra USB sockets, etc., and inverter connections.

For any more information or advice, please contact me.