Solar for RV: Picking the right panels and everything that goes along

Just a while ago solar panels weren't a viable option for an RV: they were bulky, fragile and inefficient. As more modern models were introduced to the market, trailer owners started using them more and more. Today solar panels are a great choice for campers for several reasons. Solar panels:

• make you less dependent from RV parks' electricity
  
• produce no smell or sound
  
• last for 20-25+ years
  
• require almost no maintenance
  
• pay for themselves overtime
  
  

The main disadvantage of a solar panel system is the high initial cost of all the equipment and PV modules themselves. However, solar installations pay for themselves rather quickly and start to bring in money in 6-8 years.

However, a solar installation on top of an RV is different from a home solar panel system. The primary issue is space constraints. This makes the choice of panels especially important.

Okay, space is a concern, but how many panels can fit on an RV roof exactly? Let's say, the width of a standard RV is around 6 ft and the length is 20 ft. We end up with around 120 square feet. But there is a TV antenna, AC, forehead area, an outdoor unit... In the end you have about 50-60 square feet for panels, which is enough for about 6 modules. Of course all these numbers vary depending on your particular RV, but it's important to consider them before purchasing panels.

When space is limited, it makes sense to go for the most efficient panels to generate the maximum amount of energy from a square foot. Monocrystalline panels are the best in that regard. Polycrystalline modules are a middle-of-the-road choice: they offer relatively high efficiency, but cost less than monocrystalline panels. Thin film panels, on the contrary, aren't well suited for the job. While being very light, they have the lowest efficiency and the shortest lifespan – 10-15 years.

The most popular panels for RVs are 100W. However, 300-330W panels, which are widely used in home installations, are also great for trailers and it's better to opt for them if you need a powerful array.

Fortunately you don't need a lot of power for all the devices in the RV. To get the exact number of panels, figure out your energy spendings first.

Sit down with a paper and a pen and write down all the electric appliances you have in your RV. Make two tables – for AC and DC devices – and include:

• wattage or amperage indicated on the rating plate labels of those appliances;
  
• the number of hours you use them daily.
  

For AC devices, multiply the power rating by hours. For DC devices, multiply the amperage by hours and by 12 V, a standard for RVs. You'll have a list of daily energy consumption for every device in watt-hours. The sum will be the energy you need to get from solar panels to power everything in your RV.

Let's make an example. Imagine we have a trailer and we want to switch to solar energy. Here are two lists of our devices in RV.

The tables show that we consume approximately 3.5 kWh – this is how much energy we need to generate with solar panels daily to power everything.

Generally, solar panels on RV don't perform at their maximum capacity. Since RV moves around, panels aren't always facing the sun in the best way or at the best angle. What's more, they get dirty faster, and their performance greatly depends on the weather. Therefore, we'll assume that panels operate at 70% of their capacity. To take that into account, let's raise our bar for daily energy needs:

3.5 kWh ÷ 0.7 = 5 kWh

Let's say we are in California, where the yearly average of peak sun hours is 5.6. Thus, the power output of our solar array should be:

5 kWh ÷ 5.6 h = 892 W

We can get this amount of power with nine 100 W panels. Don't forget that space is an issue, so three 300 W panels can be a better choice.

Panels are not the only thing you'll have to find. For an RV solar installation, you'll also need an inverter to convert DC from panels to AC for appliances. Since you’ll probably also want to use your appliances at night, you'll have to purchase a battery and a charge controller as well.

The size of your charge controller should equal the size of your solar installation / voltage of the solar system. In our case, where combined power of panels is 900 W, the size of the controller should be 900 W / 12 V = 75 A or preferably a little above that number.

The size of your inverter also should be comparable to the size of the solar array. Here, a small 1000 W inverter will do just fine.

An RV usually has its own battery, lead-acid or lithium-ion. The capacity of the first type is usually measured in amp-hours, the second one uses kilowatt-hours. Its size depends on energy needs. We estimated ours at 3.5 kWh. If you want to have energy backup in case of emergency, multiply this number by 2 so you can have enough charge for two days without working panels.

Let's say we want to buy a new lithium-ion battery that has enough capacity for two days without additional charging.

3.5 kWh * 2 days = 7 kWh

To figure out the number of amp-hours that you need, divide the energy needed by the battery voltage – usually it's 12 V.

3.5 kWh ÷ 12 V = 291 Ah * 2 days = ~600 Ah battery