Probably every mobile home sold in Spain carries at least one solar panel, but the reality is that the vast majority of users do not know how many solar panels are necessary for their way of traveling or even if it is not even necessary.

We will start with types of plates. There are different types of solar panels, but the most widespread in the motorhome world are monocrystalline or polycrystalline 12V. The difference between one plate and another is the glass, one of them is uniform and another is made up of a heterogeneous mixture of crystals, although at first glance it is not appreciable, and we see a crystal.

In polycrystalline solar panels the performance is worse because the light does not pass through a homogeneous crystal. Does this mean that a 150W polycrystalline solar panel is worse than a monocrystalline solar panel? Absolutely not, a 150W solar panel is a 150W solar panel, either monocrystalline or polycrystalline. The difference will probably lie in their size, monocrystalline solar panels will probably achieve the same power as a polycrystalline one but on a smaller surface.

There are more expensive and cheaper solar panels, in addition to their materials being better and more durable, the difference usually lies in the ability to give more power per unit area.

So, do I need the highest performance solar panel? This will depend on the power we want to install, if we want to have 150W in our motorhome, it will generally not matter, since there will be no problem in being able to place this plate on the roof, if instead we want to have 750W, we probably cannot install 5 normal plates 150W and we will have to resort to smaller plates that give the same performance to be able to place them all on the ceiling.

Once legacy here, how much power do we need? Before continuing I would like to define some terms. 3 amps at 230V is not the same as 3 amps at 12V. In general, we talk about currents in motorhomes, since batteries measure their capacity in amperes. A 100A AGM battery has approximately a real 70A, but these are at 12V, if instead we used an inverter to convert it to 230V and we want to power a coffee maker, we no longer have 70A, if not 3.65A. This is because the only thing that is constant in terms of electricity when we change voltages is energy, and this is neither the Volts nor the Amps, but rather the watts. To calculate the watts the formula is very simple:

Therefore, in the example that we have put, a battery has 70A, and the battery is 12V, so it has an available stored energy of approximately 840W. If we are at 230V and we have 3.65A and we multiply we obtain the same 840W, this is why, in order not to be wrong, we must always speak in watts.

Well then, how much power do I need?

Let's do an example calculation. Seeing the consumptions that appear in the devices we want to use. It is important to indicate that the watts that appear in these devices are those that they consume throughout an hour.

• Microwave: Actual consumption about 1500W / h if we use it 10 minutes 2 times a day we use it 10 minutes, therefore 20 minutes is 1/3 of an hour. So 1500/3 = 500W.
• Nesspresso: Actual consumption about 1250W / h. We use it 10 minutes 1 time a day which is the same 1/6 of an hour. So 1250/6 = 210W.
• 12V TV: Real consumption about 20W / h. 3h a day. 20 * 3 = 60W
• Led lights: We calculate about 4 simultaneous led bulbs, for about 5 hours with a consumption per led bulb of approximately 5W we have a total consumption of 5 * 4 * 5 = 100W
• Charge 4 mobiles. Approximately the battery of a mobile phone has about 10W pulling at the top, so another 40W.

The sum of all these consumptions is:

500W + 210W + 60W + 100W + 40W = 910W

To this we can add a security 10% to assume the consumption of the electronics of the refrigerator, the heating, etc. Thus:

910W * 1.1 = 1000W

We already know how much we consume day by day, but how much power does a solar panel give us a day? Approximately and according to the advice of the manufacturers we can make the calculation based on the following assumption. A solar panel, in summer, has approximately a 65% of performance over the nominal power, and approximately we can take advantage of 5 hours a day, so a 150W plate will give us approximately:

150W * 0.65 * 5 = 487W

So with approximately 2 solar panels of 150W it would be enough, but what about winter? In winter we have less sun, so we tend to calculate it, for safety more or less in half and each plate would give us about 250W, so you would need 4 plates of 150W.

So do I have to install 4 boards? Not necessarily, with these 4 plates I know that for these consumptions I am practically autonomous, but what if I only put 2 plates? If we place two plates in summer we have practically autonomy but not in winter.

If we know that we consume 1000W a day and that in winter the 2 plates provide us with about 500W, it means that we lose 500W daily.

If we start with two fully charged 100A batteries because we have made a long trip, and we want to be unemployed for a few days to go sightseeing, when will the batteries run out?

100A AGM batteries have approximately 70th reais, if we carry 2 batteries we will have about 140A. As the battery works at 12V, our available power is:

140A * 12V = 1680W

If daily we lose 500W

1680W / 500W = 3 days of autonomy.

Remember that it is not convenient to take the battery to very low levels, so this third last day I would try not to use the microwave, in this way I give it some margin. Also keep in mind that to recharge 2 batteries that are very low you will have to circulate, a lot, at least 6 or 8 hours.

A couple of things before we finish. It is important to bear in mind that even if you do not consume anything, it is good to always put a solar panel, AGM batteries when they have a discharge that does not charge in about 2 weeks or a month is sulphated, and this part is not recovered, a solar panel it will not help the batteries last longer. (We can talk about a change from having to change in 1 or 2 years to changing it between 3 and 5 years, this is more than double).

On the other hand, these calculations are for normal regulators, there are some high performance MPPT regulators that can obtain up to 20% of power, so with these a single plate in summer would give us about 600W instead of 500W, and in winter about 300W instead of 250W. Therefore, if we are in critical powers, because the consumptions are high, it is a great help. If instead our consumptions are small, and the solar panel is more than enough, it does not make sense to spend more on this type of regulator.

We hope that with this little article it will be clear how much each user needs to install power in solar panels, or failing that, how much autonomy they have approximately with the installed power.