Caravaners and motorhome people
tend to be good practical DIY'ers so the job of fitting a solar
panel to the van and running a bit of wiring here and there
will not be to daunting an exercise. But, what does get the
grey matter stirring is the OHMS Law and getting the specification
right. So here is where I will try to lay the method out for
all to see and hopefully with a bit of help from your friends
be able to have a good solar system up and running.
One thing worth saying is that the technology has moved on a
pace with all the protection for your batteries in place and
it is also now very affordable. It is also worth saying that
the best solution for some people is a mixture of sun and wind
power, but for now we are concentrating on the solar solution.
First of all we need to know what the caravan/motorhome energy
needs are when the caravan/motorhome is at a site with no
power plugged in. It is of course perfectly feasable to have
a system to make the site power connection a thing of the
past by adding an inverter
into the system for your 240 volts AC needs.
So here is the working out - we will need to detail the caravan
/ motorhomes equipment and the current ratings, NO don't start
running away just yet, generally this will be detailed on
the product label or in the user guide and will be stated
in Amps, if not then read of the watts and divide by 12 for
a twelve volt system (Watts
÷ 12 volts = Amps).
If the information we need is not on the product label then
give the manufacturer a ring and ask for it, they will be
only to pleased to discuss this with you. So lets start with
an example of the energy needs of a typical caravan / motorhome
(although appliance Current/Amps figures displayed below are
entirely a fictitious example):-
Reminder - Don't forget when
a caravan is connected to the towing vehicle with engine running
the fridge and equipment are powered by the towing vehicle engine/alternator
not the caravan battery(s). Same of course applies to a motorhome
each time you start the engine.
|Wall lights x 4
|Fridge (12 v)
Solar Panel manufacturers are starting to state their solar
panels in 'Watt Hours Per Day' written as Wh/d, you can divide
this figure by the panel nominal voltage of around 16 - 19
volts to get the very approximate Amp figure for the day which
is the most useful. Knowing how many Amp hours (Amph) you
can expect from a solar panel is what we want to know! These
manufacturers figures are normally based upon a mid summers
day as regards the number of sunlight hours the panel received.
Getting all the figures into Amps makes the most sense as
batteries are at the heart of your system and are all rated
and stated in Amp hours, plus, this is the bank where all
your free power is deposited!
The fictitious example
figure of 78 Ah in the table above is a very high figure for
the average caravan / motorhome and it would be best trying
to reduce it if at all possible. Try fitting led lighting
fittings where possible or by limiting the number of hours
appliances are turned on for. This can all help with reducing
the Amp hours and will help with the cost and size of the
solar panel(s) you will need to put back the 78 Ah into the
battery bank each day.
Lets look now at the solar panel size required for the summer
period to put back the 78 Ah into the battery bank, there
are a number of scenarios here to be considered.
First of all let me say
- that I don't like running my batteries anywhere near to
the bottom of their operational range, so this will be reflected
in my working out below, and depending where your caravan
/ motorhome is sited in the UK the amount of sunshine hours
will differ a lot so allowances will have to be made. Remember:
what would be sufficient solar panels in the summer will not
be sufficient in the winter!
Obviously if the engine is started and you are motoring for
a number of hours each day then the batteries will be charged
and may well fully charge your battery bank in that time.
So in this scenario you will be best to fit a smallish solar
panel as a topping up exercise, normally a 30 - 40 watt panel
would be sufficient. Of course the added bonus will be that
during your time away from your caravan/motorhome your batteries
will be kept topped up ready for your next trip.
On the other hand you may be moving off every 2 - 3 days and
need to keep the batteries topped up while you are at a site
without mains power. In this scenario you will have stored
in your fully charged battery bank around 30% of your leisure
battery banks safe usage, lets say for example you have a
battery bank of 200 Amph then you will have 60 Amph of safe
use before the next charge from starting the engine. So if
we divide the 60 Amph over say the three days stoppage reducing
the 78 Ah daily power requirement by 20 Ah then we need to
only replace 58 Amph per day by solar power before the next
charge at say day 4. In this instance a solar panel(s) with
a output of 150 - 175 watts would be necessary.
Usage 78 Amph per day - 20
Amph stored safe energy (60 Amph over three days) = 58 Amph
needed each day from solar panels. On day 4 the battery bank
will need charging as it will be 60 Amph down, so it is time
to move on!
The solar panels could be made up in a combination of different
ways, you could have some flexible panels mounted on the roof
and have a portable panel or two which you could plug in when
your caravan/motorhome is at a site. Remember though at the
end of day 3 your battery bank is approximately 60 Amh down
and is ready for a charge. This is a good option for smaller
caravan/motorhome with little option for mounting permanent
solar panels. It is also worth mentioning here that flexible
panels do not have as good a power output as the rigid panels,
so the portable panels are worth having. You must of course
keep an eye on the battery state at all times. Following this
sort of calculation will look after your batteries.
In this scenario you would be staying for indefinite periods
of time In your caravan/motorhome and need to cover your energy
requirement completely. To get an output of 78 Ah from a solar
panel you would need panels to the value of 250 watts baring
in mind this will be fine for the summer period when the light
is good. For a mid winter period you would need to double
this panel wattage output at least. It could also be worth
considering a wind generator for this time of year.
If panel mounting space is at a premium then you can consider
using wind power as part of the supply. These wind power generators
can be noisy with a little vibration and of course you have
to keep away from the blades when spinning which can be a
Solar panel regulator
- stops the power from
reversing back into the panel overnight and stops overcharging
of the battery bank. This model costs around the £20
Whatever scenario fits your particular situation you will
need to fit a regulator to stop the power from reversing back
into the panel overnight and to stop overcharging the battery
bank when fully charged. These regulators nowadays are very
inexpensive and come either in a very basic model or with
lots of facilities for monitoring the whole battery management
side of things. They can be purchased for as little as £10
and go up to the 70's or more.
Note: Solar power
- Is not an exact science working out solar panel sizes (array)
is very much based firstly on a calculation as in the table
and scenarios above, but there are other factors to consider.
Wiring runs, air temperature, and of course the intensity
of sunlight which none of us can forecast, these all affect
the performance of our solar power system overall. Therefore
solar panel sizes used in our examples above are a guide only.
Generally it is prudent to go a bit bigger on the solar panel
sizes as a good regulator holds back any excess.
Putting an ammeter and voltage meter in the system means you
can keep an eye on the charge and discharge rates and then
make any adjustments to your solar system that are needed.
Perhaps you might need an extra solar panel or an additional/larger
leisure battery. Nothing can beat having the system up and
running to see what you are actually achieving on an average
the live experiment page
Other pages to help you with
the installation are:-
To communicate with us over
technical issues please use the Solar
Chat Forum, also take a look at the Solar
Warming - it's why we are making changes to our way of life!
David Bellamy has a very interesting article on global warming
where he gives another point of view, Read