Peter Quilty — 5 May 2016

Why do I need a solar regulator?

Most 12V solar panels on the market have an output voltage of 18-22V, while the charging voltage of a 12V battery ranges from 13-14.4V in different charging stages. We need a regulator to drop down the voltage, detect the battery’s state of charge and apply adequate voltage to the battery in different charging stages.

Why aren’t solar panels designed with an output between 13-14.4V so we can connect the panel directly to the battery?

Firstly, different voltage needs to be applied to a battery in different charging stages and we definitely need a device to regulate the voltage. A solar panel designed for 12V has an output of 18-22V because the voltage output has to be higher than the charging voltage to allow the electricity to flow into the battery. It also needs to accommodate voltage drop in the cable, and that is why it’s considerably higher than 14.4V.

Can I charge 12V batteries from a 24V panel?

Most regulators with PWM technology are designed for both 12V and 24V systems, but the voltage in each system has to be consistent. A 12V panel charges a 12V battery, and a 24V panel charges a 24V battery. But regulators with MPPT technology are able to charge a 12V battery from a 24V panel, although not the other way around.

Can you power an RV entirely by solar power?

It really depends on the build and the use of the RV. In the case of an RV that spends long periods parked up in the bush without the vehicle engine running – and which is fitted with a large range of electrical appliances such as a washing machine, toaster, fridge and air-conditioner – it is very unlikely that a solar system could power everything indefinitely.

But if an RV spends a couple of hours driving, allowing the alternator to charge the battery and it doesn’t have air-conditioning, it’s likely that you will be fine with a 1kW solar system and never need a generator again.

If I can’t power everything by solar, why should I use solar at all?

Solar is clean and quiet and leaves less carbon footprint. With a decent solar system, most campers can get away with not using a generator or just carry it as a backup in case of bad weather. For the others, solar will reduce the run time of a generator significantly.

However, if there are high energy appliances, such as heaters and air-conditioning, running in the caravan all the time, solar may be a waste of money.

How many solar panels are required to produce enough electricity for your RV needs?

Because of the limited roof space, most RVs can only fit up to 1-1.5kW systems. A 1kW system will be enough to run LED lighting, a TV, a 12V fridge up to 30L, and other appliances which only run for short periods of time.

What’s the optimal setup and how is it calculated?

An RV system has to have at least 500W otherwise it won’t be enough to run the fridge. But, ideally, five 200W 12V solar panels, or as many as possible, would be recommended. Considering using smaller panels in tighter areas? I would recommend an MPPT regulator coupled with 24V panels because a 1kW system with a 12V panel would require an 80A regulator but with a 24V panel, 40A will be enough. So if you can get 24V panels for the same price as 12V panels, you will be saving money on the MPPT regulator (you will have to use a 12V panel if a PWM regulator is being used).

A 1kW system would pump out about 50-55A in the best case scenario. The average sunlight in a day ranges from 4-6 hours, depending on the season, so if the panels are fully exposed to the sun all day, you could get 200-300Ah of energy. You need to work out your total energy consumption and design the solar system accordingly.

How important is monitoring solar system performance?

A solar system runs autonomously and is maintenance free. But there are a couple of things to keep an eye on. The first thing would be the battery voltage. Most deep-cycle batteries are not designed for deep discharge. Any deep discharge will shorten the life expectancy of the battery. It’s not recommended to draw energy from the battery when the voltage is lower than 12V. So it is essential to have the battery voltage displayed at all times and turn off your non-essential appliances when the battery drops under 12V. This is something you need to do even if you don’t have a solar system.

How can I find out how my system is performing?

The best thing to do is to get a power meter and measure the accumulated charging amp hours. Alternatively, you can just use a multimeter to measure the amps going into your battery when the panel is fully exposed to the sun.

What is the cost of a full, optimal solar setup?

A good starting point would be a portable 120W panel with MPPT regulator (preferably with digital readout); around $400-$500.

Inverters and battery chargers are not part of the solar system and most campers would already have them working with their existing system. However, as a guide, a 1000W 12V pure sine wave inverter would cost about $500 and a battery charger would be about $300.


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