Oftentimes the term RV is associated with a motorhome. In truth, recreational vehicles or RVs come in many shapes and sizes. Some are motorized while some are not.

Examples of non-motorized RVs are caravans, travel trailers, camper trailers, pop-up campers and fifth wheel trailers. Motorized RVs include motorhomes, campervans, truck campers and other mobile homes made from old buses, cargo trucks, bread trucks and so on.

Initially only used for recreation, as the name suggests, RVs are now also used as permanent mobile homes or for off-grid living. Whatever the purpose, RVs usually need some form of air conditioning, be it to cool or to heat the air within.

Air conditioners are one of the biggest power guzzlers among all the electrical devices in an RV. That has caused the belief that solar air conditioners for RVs are not possible. However, this is not really true. It is possible to run air conditioning off solar power in RVs if certain conditions are met.

Photo by Togo RV on Unsplash

Problems with solar air conditioners

To understand how solar air conditioning can work for RVs, it is necessary to first know the issues involved.

1. The cost of the unit and solar system

Because an air conditioner (A/C) uses a lot of electricity, a large battery bank and a high output solar or photovoltaic system are required to keep it running for hours. As you may already know, high capacity solar batteries are very costly. A good A/C unit doesn’t come cheap either.

However, if you are going to stay off grid for long periods in a warm place, having a solar-powered air conditioner can be a life-saver. The price tag for this comfort is not just worth it; it will be necessary.

2. Poor insulation of commercial RVs

Some commercial RVs are not too well insulated because they don’t have thick walls. Because the walls aren’t thick, heat from the sun and solar panels are transferred into the vehicle, especially if there is no airflow between the solar panels and the roof.

Consequently, the RV gets very hot when parked under the sun in warmer climates. In return, more power is needed by the A/C to cool the interior.

Air cooled by the A/C can also seep through cracks in the body of the RV. Large expansive windows may offer picturesque views but the sunlight streaming in heats up the interior.

Having fewer and smaller windows, as well as boosting wall and roof insulation will go a long way in reducing the power usage of air conditioners.

2. Start-up power surge of solar air conditioners

When air conditioners are just switched on, they pull a massive chunk of power known as starting watts then taper off to smaller wattage consumption when the cooling mechanism has stabilised. Here are some common wattage ratings for different units: 

  • 7,000 BTU A/C = 1,700 starting watts; 600 running watts
  • 10,000 BTU A/C = 2,000 starting watts; 700 running watts
  • 13,500 BTU A/C = 2,750 starting watts; 1,250 running watts
  • 15,000 BTU A/C = 3,500 starting watts; 1,500 running watts

The surge during startup can drain out a solar battery if the solar power system is small or not able to cater to this sudden jump. To address this issue, you can install a component called an A/C soft start system which can drastically reduce starting watts.

It can be cheaper than scaling up or investing in an RV’s existing solar power system. The soft starter allows you to have a smaller inverter to supply power to the air conditioner. It smoothens out the startup power demand of the A/C compressor by almost 70%. Another solution to this issue is to install a mini-split instead of a rooftop unit.

How to power an RV air conditioner with solar

Photo by Togo RV on Unsplash

It is feasible to power even the largest air conditioning unit with solar energy but the solar installation must be designed to cater to its needs. In order to do that, you should answer the following questions which are arranged in the most logical sequence possible. From there, you can get a better estimate of how big your solar system should be.

1. What is the size of your RV?

For a small RV, one A/C unit will suffice. A 20-footer will probably need two units to cool both the sleeping and living quarters properly.

2. How many solar air conditioners do you need for your RV?

The amount of units you need also depends on your personal requirements. Some people are happy with an A/C near the sleeping quarters while some want to cool the entire interior.

3. What type of RV air conditioner do you want?

There are 3 types: mobile vertical ones, window installations and roof-mounted A/Cs. Each type has its pros and cons, and different power consumption. Since cool air is heavy, it makes more sense to install the roof-mounted type.

Of these, there are models which run on either AC or DC. Those that use DC power can be powered directly by solar panels or the battery bank without the need for a solar inverter.

The most recent type of solar air conditioner even has an integrated window. It is ideal for those who want a skylight as well as an air conditioner.

The built-in air conditioning units in RVs have 2 kinds of systems: evaporation system and compressor system. The former has lower power consumption but increases the humidity. The latter can dehumidify room air and integrate heating.

4. What is the starting and running wattage required by the solar air conditioner?

In order to provide enough power for an RV air conditioner, you’ll need to understand how much electricity the unit on your specific RV requires. Many motorhome roof A/C units require somewhere between 1,700 and 3,500 starting watts and running watts of 600 to 1,500. 

The lower the BTU, the lower the starting watts and running watts; and vice versa. BTU stands for ‘British Thermal Units’. It is a unit used to represent the amount of energy needed to raise one pound of water by one degree (Fahrenheit) at sea level. The bigger the BTU, the more air it can move and the more powerful the cooling effect.  

5. How much solar power do you need for other appliances in the RV?

For fulltime off grid living, your solar panels and solar batteries will provide power directly to all of your electronics in the RV. The solar system generates DC power. In order for an AC electrical appliance to use this power, it has to be converted from DC to AC by the solar inverter.

If you have mostly 12-volt DC electronics, you will consume less power compared with AC electronics. That is because some power is lost during the conversion of AC to DC and vice versa. Similarly, some energy will be lost during conversion from solar panel to the battery to an electrical appliance.

You’ll need to calculate the total power needs of your RV for 24 to 48 hours, including that of the A/C unit.

Calculating solar power needs

Let’s say you settled on one 13,500 BTU air conditioning unit for your motorhome. This unit will have 2,750 starting watts and 1,250 running watts. Running this A/C unit for 4 hours a day will draw:

  • First hour: 2,750 + 1,250 watts = 4,000 watts
  • Second to fourth hour: 1,250 watts x 3 hours = 3,750
  • Total watts for 4 hours: 7,750 watts

You also need to take into account the power needs of other electrical appliances on a daily basis. 

Let’s take a ballpark figure of another 3,600 watts for running everything electrical in the RV in a day. But of course, not all appliances are going to be used 24 hours a day. Realistically, you might be using only half of that on a daily average. 

Total daily power need = 7,750 + 1,800 watts = 9,550 watts 

If you are using a Renogy 800-watt solar panel (the highest range in the market for RVs), this is how many panels you would need to run all the electrical items:

9,550 watts ÷ 800 watts = 12 solar panels 

Don’t forget the solar panels can’t generate electricity at night, so for the other half of the day, you will rely on your battery bank capacity. There are other ways to shave down dependence on solar panels. 

The last essential piece of your solar installation is the solar inverter. Its size should address the startup surge of the solar air conditioner. The safest way is to choose an inverter that is rated 700 to 1200 watts higher than the starting wattage of your RV air conditioning unit.

Other off-grid solutions for RV air conditioning

  1. Generator for A/C first start

Motorhomes come with a generator. You can use this to fuel the power surge during the A/C startup.  

  1. Hybrid inverter and small generator

The hybrid inverter has a Load Support feature which can be used together with a small generator to power the A/C unit. 

  1. Volta Power Systems

It is a complete power system that is smaller, lightweight and more powerful than current motorhome power systems. The charging power comes from a high performance alternator, the power is stored in a giant lithium-ion battery bank and the power is converted/inverted through a massive system. 

 Conclusion

For those with a small RV with limited roof space, it may not make much sense to invest in solar power because you won’t have enough space on your roof for the number of panels that you’ll need. The same can be said for those who only use the RV for short vacations and don’t live in it. 

If you’re using the RV to live off-grid, a solar system can help you save quite a bit of money on gallons of fuel running a generator at night. Solar power can be used to provide a supplementary energy source, if not to fuel 100% of the RV. 

With careful calculation and the right solar equipment, it is possible to have a solar-powered air conditioner in your RV. You just need to install a big enough system to enjoy air conditioning while boondocking.

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