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How to power your RV with one solar panel and go anywhere the sun is shining
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How to power your RV with one solar panel and go anywhere the sun is shining

20 mins 08 Feb 2021
So, you're wondering if it's possible to power your RV equipment with solar energy? It is. Solar panels are modern and reliable, and they will do their job just fine regardless of whether you are on the road or stopped somewhere. However, figuring out how many solar panels is needed for an RV might be confusing. This article should help you with this task.

Solar panels for RV are a viable modern choice

A decision to try solar panels for your recreational vehicle is a big step, but a reasonable one. There are several advantages of solar energy that make the switch from AC-generators to a PV system much more appealing:

  • solar panels make no noise and produce no smell
  • almost no maintenance is required
  • sunlight is free so panels pay for themselves overtime - no need to worry about fuel for them
  • a switch to renewable energy helps in the fight against the global warming
Of course, there are things to keep in mind while going solar. The upfront cost may be considerable and it takes several years for panels to pay for themselves. Obviously, installing solar panels makes you dependent on the sun. Finally, panels on RV are never going to give as much energy as promised — but we'll get back to it later.

Take a test ride to calculate your energy needs

To understand how many panels to install, first you have to calculate your energy needs. There are several ways to do it.

The first one is purely theoretical: you take your appliances one by one, estimate their daily hour usage and do the maths. For example: if your TV uses 90 Watts and you watch it 3 hours a day, then TV needs 270 W per day. The wattage can be found on the appliances. The final sum is the power that you would need from solar panels on a daily basis. However, this method is far from perfect — it's hard to predict how much time a certain device is going to be used on a given day.

Another way to find out how much energy you'll need from the sun is to simply go for a ride. The purpose of this trip is testing your battery, so avoid using AC-generators for charging it along the way. After a day or two, check how much load your battery still has. It can be checked via charge controller if you have one, or with a voltmeter which sometimes comes with an RV battery. For example, a fully charged 12 V battery has a voltage of 12.6 V or a little more, but when it's half discharged, the voltage drops to around 12.1 V.

Example: Let's say you have a fully charged 300 A/h battery, and after two days of driving around you are left with 50% of the initial charge. So, you've spent 150 A/h in 2 days which means the average daily energy consumption is 75 A/h.

If you're using lead-acid deep cycle batteries, there's no way you consume more than that. They are just not meant to be discharged deeper than 50% of their load. This is not very convenient, which probably made lots of RV owners switch to lithium-ion batteries lately. They are more expensive than lead-acid batteries, but better in almost every way.

  • Lithium-ion batteries occupy less space and weigh around 75% less than lead-acid batteries.

  • Their acceptable Depth of Discharge can go up to 90%.

  • Partial state of charge is less of a problem.

  • It takes twice as much time to charge up a lead-acid battery than a lithium-ion battery of the same capacity.
It's important to note that lithium-ion battery capacity is measured either in Amp-hour, like lead-acid batteries, or in Kilowatt-hour. However, it is easy to translate one into the other: just divide kWh capacity of the battery by its voltage.

RV solar panels are going to perform at 60-80% of their rated power

The most popular solar panels for RV usually range from 100 W to 160 W. However, they take up too much space, which is an obvious point of concern. That's why some campers go for more expensive, but high energy dense 300-350 W panels. To save even more space, you can look for a higher efficiency rating: for two solar panels of the same size operating under the same conditions, if one has a 20% efficiency rating and the other – 15%, the first will produce more electricity than the second.

The panels on the roof of your recreational vehicle are never going to perform at their best. When installing solar panels at home, you sometimes can customize their angle and direction. An RV moves around, so the panels on its roof rarely ever get perfect conditions, including an angle at which it is installed. On average, they're going to produce around 60%-80% of their maximum power. Thus, as a rule of thumb, your solar system should generate about 20% more energy than you normally need a day.

A safe estimation for a 100 W panel would be around 6 Amps of current an hour. Let's say, this panel gets 5-8 hours of work time — it should bring around 30-50 A/h into the battery. To cover the daily energy need of 75 A/h you would need two, or better three 100W panels or rather one 300 W panel.
Another way to calculate the amount of power you're going to get from panels over a day is to sum up their rated power output, multiply it by the number of working hours and take around 60-80% of this number.

Example: A 300 W panel gives 1.8 kW over 6 hours in perfect conditions, but in reality you end up with around 1.25 kW. If your daily energy need is 75 A/h or 900 W, assuming that you use a 12 V lithium-ion battery, one 300 W solar panel will again be enough to cover it.

Panels on RV require additional equipment and extra care

In addition to solar panels you are going to need an inverter and a charge controller. The panels produce DC which is not suitable for most appliances, so an inverter is going to turn it into AC. Charge controller prevents the battery from overcharging. You could probably skip the charge controller if 1) the voltages of the panels and the battery are matching; 2) the battery is too big for panels to charge it on their own. However, it's not that big of an investment for the safety of your battery. What's more, an MPPT-controller can maximize the amount of current your battery gets.

Solar panels are fragile, so make sure you've affixed them properly or the next bumpy road can become the last trip for them. Panels on the roof of a recreational vehicle get dirty much quicker than the ones which are a part of home systems. So, clean them occasionally to improve their performance. As for the rest, RV solar panels are very low-maintenance.

To wrap it up, a switch to solar energy is viable not only for homeowners, but for campers as well. Panels are silent, don't need any fuel and pay for themselves overtime. To determine the necessary amount of solar power, first you have to calculate your energy needs. And keep in mind that panels are not going to perform at their full capacity.
Illustrations – Marina Fionova
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