How to Calculate Battery and Solar Panel Size

How to Calculate Battery and Solar Panel Size

There is not very much info on the net showing you how to calculate the size of batteries and sola panels for your caravan. Quirks have gone to a lot of trouble to illustrate actual set ups for the various main uses for solar power - it is turning into a huge industry in Australia and rightly so as it is the way of the future don't you think? The system as provided on most A'vans works very well indeed and we have zero complaints with the exception of batteries wearing out. If you are buying your first A'van we suggest you opt for at least a 50 watt panel if you intend using the 12 volt system for more than running just lights. If you have an A'van without Solar there is a very good chance that it is "solar ready" so we strongly suggest you get your dealer to fit the factory items. Alternatively you can go down the Quirk's track. If we were setting up from scratch we would probably favour the Unisol units as they work better in shade - exactly what happens when you camp in the bush. They seem to be 20% dearer though than the system offered by A'van and they are bigger. Anyway the story below shows you how to estimate power consumption. The only thing they seem to have overlooked is the 10% you lose when anything passes through an inverter. If you haven't got solar and feel it's too dear think about this. If you intend going around Australia for say a year if you stay in parks on non powered sites your accommodation bill will be reduced by on average $2.50 per night. This equates to almost $1000.00 - this will EASILY buy you a 50 watt solar system. You could say you get it for nothing and it's there to use when you get back from your trip and certainly makes your rig more attractive resale wise.

SOLAR BATTERY SELECTION FOR RV's

When designing a system for a motor-home, caravan etc., it is assumed that the auxiliary or house battery will be recharged on a regular basis from the vehicle’s alternator when driving or that there is a generator included for battery charging when the Recreational Vehicle is stationary for any prolonged period of time.

Load Profile :

1 x 12V Fisher & Paykel C170T fridge/freezer
10 hours use of 20 watt lighting per day
2 hours use of 34 cm colour television/video per day
2 hours use of radio per day
Daily load profile is 1kWh/day

Equipment Profile :

1 x Electronic Battery Isolator (to suit maximum alternator charging output of 100 amps)
2 x Solarex SX80U 80 watt solar modules
1 x PL20—20 amps digital voltage regulator
1 x Concorde PVX 12V 253Ah sealed battery or
1 x Federal 9C12 12V 253Ah vented deep cycle battery
Battery fusing, solar fusing

Retail Price : To supply the above equipment :-

$3,035.00—including sealed maintenance-free battery or
$2,860.00—including vented, auxiliary battery

Optional extra’s :

What inverter (to change your DC battery power to 240VAC 50Hz power) will be determined by the wattage of the 240VAC equipment to be used. Some possible choices suitable for use in recreational vehicles are :

Selectronics 12V 350 watt sine wave (mains equivalent) inverter $913.00 (to run small coloured television, video, laptop computer)
Selectronics 12V 1300 watt sine wave inverter $2079.00 (to run microwave, or power tools, plus smaller AC loads)
Latronics 12V1300watt modified square wave inverter $1639.00 (to run power tools, microwave etc.) Or

You may decide an inverter/charger would be more suitable—e.g. if you regularly stop at powered sites or you regularly use a generator, an inverter/charger can provide your AC supply and your DC battery charging from a single piece of equipment :-

Trace DR1512 12V 1500watt modified square wave inverter/charger $2000.90
Trace UX1112ESB 12V 1100watt modified square wave inverter/charger $1647.80

The 12V/24VDC Fisher & Paykel C170T low voltage refrigerator quoted $2050.00

Note : Based on the above equipment profile and assuming 5 hours of full sun charging per day, the solar modules should provide 50 amps of charging to the 12 Volt auxiliary battery. The load profile shown above is ~ 1kWh/day (= 85Amps/12V per day). Using the quoted battery capacity of 12V 253Ah, the power consumption per day is 35 amps MORE THAN the daily solar contribution. The battery capacity will provide the daily shortfall. Therefore, using the figures quoted, the recreational vehicle could remain stationary for 4-5 days without running the vehicle’s engine or a generator to recharge the battery.

The 12 volt Fisher and Paykel fridges mentioned in the story range in price from $1620.00 for the 115 litre model and $2052.00 for the two door C170T - 117 litre + 55 litre freezer. Isn't it wonderful that these people give you prices on the web? Lots more info on Quirks excellent website.