What appliances can I run from my motorhome or caravan solar power system?
In the last few months I have had a number of emails from people wanting to know if they can run this appliance or that appliance in their motorhome or caravan. Unfortunately, as is often the case, the answer is not just a simple “yes” or “no” – but a resounding “it depends”.
You see things have changed a lot in the solar power world in the last few years, the impossible has become possible and the impractical has become affordable. The cost of solar panels has dropped from over $10per watt (where it sat for many years) to a far more reasonable, $1per watt. This change has had a massive impact on the size of solar array that can reasonably be afforded by Joe Average.
Years ago, when asked “how much solar should I put on the roof of my caravan or motorhome”, I would do some careful calculations to work out how much would be needed to cover the average daily requirement. These days, my answer is simply “cover the roof”. At a measly $1/watt, there really is not good reason to scrimp on the panel aspects of the installation. With this change came a corresponding change to the question “what can I expect to be able to run from my solar electrical system”.
I guess to keep the purists off my back I should say first off that of course you can run almost anything from a well-designed and well-built solar electrical system. That said, there are still some practical limitations and some reasonable limits you need to be aware of.
A little theory (easy stuff – I promise)
I find that it often helps people understand a standalone solar electrical system if we use a water analogy…
Think of the batteries as large buckets – these buckets are able to hold a fixed amount of water (electricity). You can’t just keep putting water into a bucket when it is full. Dealing with this is the job of the solar regulator. When the battery (bucket) is full of electricity (water), the regulator (automatic valve) turns off and stops the battery bank from being overcharged.
In our water analogy, the solar panels are like a magic water-maker. These water-makers can make a few litres of water each hour (but of course only when the sun is on them). Add more panels and you will get more electricity each hour they are in the sun.
Appliances, (lights, refrigerators, TV sets etc) are like taps – when you turn them on the water (electricity) flows out of the bucket (battery) and is used up.
Great, now that we have the water analogy working, let’s think about what happens if we take just a little more water out of our buckets each day than the water-makes can replace. Clearly it won’t be long before the buckets are looking a bit empty. Now, unlike buckets, batteries are very expensive AND they hate being empty. An empty battery is a dying battery. The more empty your batteries, the faster they are dying.
It should be quite obvious by now that we MUST have enough solar panels to at least put as much electricity into our batteries as we use each day. This is absolutely critical for a successful solar electric system.
From this (using Sherlock-Holmes-type deduction) we can now answer the question – “What appliances can I run from my motorhome or caravan solar power system”. Answer – “it depends on the size of your roof”.
There are a few other components that need to be discussed…
- The inverter – this needs to be correctly sized to handle the maximum concurrent load. For example if you want to be able to run the toaster (say 700 watts) AND the microwave (say 1500 watts) at the same time, you will need an inverter no smaller than 2200 watts (I’d say 2500 watts minimum to be safe). DO NOT just buy a 5000 watt inverter while telling yourself “bigger is better”. Instead, buy the smallest inverter that will do the job. Larger inverters are less efficient most of the time.
- The solar regulator needs to be sized to handle the maximum current that the solar array can produce.
- The batteries need to be sized to hold enough electricity to carry you over the dark times (night and bad weather). In this case bigger is better – the only downside is that they are really heavy and really expensive.
Ok, so that is all the theory – what about real practical examples? I’m glad you asked … let’s look at our electrical system. Our system has been evolving in the ten years we have been living in our motorhome, we started with just 160 watts of solar. We have added panels and upgraded components every few years to cope with our growing electrical needs. We now have just over 1200 watts of solar on the roof, a 2000 watt inverter charger and a 40amp regulator (not MPPT). This set-up allows us to run almost anything we want in our motorhome.
- One small (65 ltr) 24 volt freezer (normally full of fish if all is going well).
- One large (220 ltr) 24volt fridge-freezer (set to keep beer at the correct temperature).
- A 240v electric rice cooker (used most days – I like rice with my fish).
- A 240v vacuum cleaner (the low voltage ones are useless in comparison).
- A (quite power hungry) 240v television (for about 3 – 4 hrs each night).
- Electric blankets (when it cold at night).
- A small microwave oven.
- A bread maker – used about two or three times each week.
- Two laptop computers (for (an embarrassing) 5 – 6hrs each day).
- A satellite internet system.
- Of course we charge phones, tablets, cameras, electric helicopters (really!), use an extractor fan while cooking, run lights and all the normal stuff.
To be honest, in the winter when sunshine is a bit more difficult to find, we need to be a little more careful and if we have a few days of overcast weather, we have to either run our generator or turn the computers off (noooooooo!), but in general we manage quite well.
So what appliances are NOT practical to run from solar?
- Air conditioning – the average solar/battery system will not (and should not) run an air conditioning system.
- Electric cooking – the exception to this is microwave ovens and microwave convection cookers (when used “within reason”).
- Electric water heating – yes, there are some exceptions involving dumping excess solar etc, but as a general rule water heating should be gas powered.
- Electric room heating. It’s not a good idea to plug in your 2kw electric fan heater. Consider a diesel heater (or just go north) when it gets cold.
Things that are ok, but should be used with caution include:
- Hair driers (when used for a few minutes that’s fine – if you use your long hair for enticing princes up castle walls, it’s probably a good idea to dry it in the sun.)
- Coffee makes, these use quite a lot of power, but generally only for a short time.
- Electric fry pans – this is really cooking with electricity – use with care.
I hope from our example you can see that a properly sized and setup electrical system can allow a caravan or motorhome to be a home-away-from-home and run almost any electrical appliance you could want. So, cover your roof in solar panels, buy the right sized inverter and enjoy travelling Australia (and try to leave some fish for us!).
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