Solar panels for motorhomes
Being autonomous is the dream of motorhome users. We consume about 30 Ah in summer and 60 Ah in winter. Every day (if there is a television), driving for 1 hour recharges the service battery between 6 Ah and 10 Ah depending on the installed alternator; so, if we drive little or not at all, we must find one of the ways to recharge the battery is the photovoltaic solar panel.
Electricity production from solar panels
The efficiency of photovoltaic solar panels is defined as the share of solar radiation transformed into electricity. It varies from 6 to 8% for amorphous silicon panels, to 46% for the currently most efficient technology.
The efficiency of a photovoltaic installation is estimated at between 15 and 17% (in 2007 in Europe). Currently, solar panels have an efficiency of 15%; in the laboratory, we already obtain 25%; experts believe that we will obtain 50% efficiency in 2050. So solar panels have a future, but what about today?
A 100 W solar panel (latest generation) produces in our latitudes with a sunny sky:
- 23 A/h per day in sunny summer
- 50% of this value in spring and autumn
- 25% of this value in winter
These values are true at the latitude of France, but the closer we get to the equator the more electricity we produce; it also follows that if we take these values taken in Morocco in winter, we will produce as much electricity as if we were in autumn in France.
These values are calibrated for an outside temperature of 25°C; the efficiency decreases by 4% for each increase of 10°C, so at 45°C a solar panel produces half as much.
Example :
So if we install 300 W of flat panels on our roof, we will recharge the service battery (in our latitudes) with a sunny sky:
- 69 Ah per day in summer (Ah = ampere hour)
- 35 Ah per day in spring and fall
- 17 Ah per day in winter
But these values must be divided by 2 on overcast days!
If we have a 150 A/h service battery (of which we must not consume more than 75Ah otherwise it will be killed), we can hold without driving:
- in summer, we cover our needs in all weather conditions (consumption base 30 Ah/day)
- in spring and autumn, we last 5 days (if bad weather) to unlimited (if sunny) (base 40 Ah/day)
- in winter, we last 2 days
Advantages of a solar panel
Benefits :
- it produces energy at good cost
- it is insensitive to vibrations
- It has a long lifespan: its lifespan is at least 20 years
- it does not consume energy
- it requires no maintenance, apart from periodic cleaning
- it makes no noise when operating
- it is frostbitten
- A solar panel only produces electricity if the roof is exposed to light, so there is no question of placing it under trees; in this case, you no longer produce electricity!
- Power production decreases in cloudy weather
- Electricity production decreases very sharply in winter in our latitudes
- Electricity production decreases in very hot climates
- They must be cleaned regularly otherwise they produce less.
The importance of the regulator
There are 2 technologies: PMW and MPPT
PMW regulator is cheaper and less efficient, but it is used for 1 panel only
The MPPT regulator is smarter, so it gives more current from 2 solar panels; it is also more expensive.
Also, if you have a gel battery, only an MPPT regulator can charge it properly, because it is much smarter than a PMW regulator.
The power of the regulator depends on the power of the installed solar panels. To simplify, you divide the number of watts of your solar park by 10 and you get the amperage required for your regulator; so for 300 W of 12V solar panel, you need a 30A regulator.
