Over the past 10 years, solar panel technology has become more affordable to consumers. As a result, many people have found the idea of adding panels of their own to their RVs appealing. It has allowed them to travel farther “off the grid” and stay out longer drydocking.
If you are considering making the leap to solar panel technology there are some things you need to know before you start. Most people first ask, how much solar power do I need for my RV? The answer is as unique as fingerprints.
Power and Panels
Determining how many solar panels you need for your RV depends on your daily electrical usage. One key factor you need to understand is that your solar panels do not run anything in your RV. What they actually do is recharge your house batteries.
When you ask, “How much solar power do I need for my RV,” what you really need to ask is, “how many solar panels do I need to keep my batteries from running dry?”
Amps, Volts, and Watts
Before we go any further, you first have to understand what each electrical measurement means and what it does for your electrical system.
Volts: Volts measure how strong the electrical current runs through the wires from one point to the other. An example of volts would be pushing your child’s car toy on a flat surface. If it is a longer track, once you release the toy, you will see it slow down the further it goes. Same thing with electricity. With your solar panels, if they have a weak voltage, then your batteries will take longer to charge than if they had a strong voltage.
Watts: Watts measure the rate in which power is being used. To understand this, think of your freshwater tank. For most drivable RVs, there is at least one kitchen sink and one bathroom sink. Other water lines would include the toilet, the shower, and the outside shower. In this scenario if you were actively using all of your water lines, there are 5 “watts” of water being used.
Amperage (Amp): Amps measure the amount of electrical current. An average car battery has 48 amps at full charge. This means that if you use 2 amps a day, then you have 24 hours of power before you need a recharge.
Amp-Hours (aH): Simply put, aH is how much power you are using. Your coffee maker could use 1 aH. Your TV, 4-6 aH. This measurement, for our purposes is how much power is used or stored in your batteries.
Finding Your Amp-Hour per Day Figure
To figure all of this out, you don’t need to be a math genius or engineer. Before installation, you need to first determine what your house batteries can do. In your control panels, you should have a battery voltage display that shows you where your power level is at.
To save yourself from having to change out your batteries, do not let your battery power go below 50%. This will lengthen their lifespan and keep their power capacity from diminishing too much. For perspective, as long as your volt meter is at 12.0 or better, you are okay.
The first thing you need to do is pack up and go dry dock camping. Give yourself three to four days out there. Once parked, make sure your batteries are fully charged. At sundown, turn off your generator, solar panels and any other source of power that would charge your batteries. What you are trying to do is determine how long you can go just on house battery power.
After 24 hour period, check your voltage meter and record the difference. Once you have gotten close to that 50% mark, that is when you want to turn on your generator. At that point you can determine how many amp-hours per day you are using.
For example, imagine you have two house batteries that have a rated for 100 amp-hours each. That is 200 aH. A fully charged battery will have about 12.6 volts. Once you turn all of your power sources off, the test begins.
After the first day, you read your voltage meter and it says you now have 12.3 volts. Now you have about 70% of what you first started with. On the second day, you now read 12.0 volts which is down to 40%. This is when you want to turn your generator back on, to recharge your batteries. Now we know that you are using 60% of power in two days.
Using our example, 200 aH multiplied by 60% is 120 aH. We then divide that between 2 days of use, and you have found that you are using 30 amp-hours each day.
Matching Your Panels to Your Amp-Hours
Now that you know your amp-hours per day, you now need to determine how many panels you are going to need. The general rule of thumb with 100 watt solar panels is that they can produce about 30 aH per day. For our example, two panels would work perfectly.
There are a number of variables you have to take into account before you order your panels and equipment. There are many things that can decrease the efficiency of your panels.
– Dust in the air
– Dirt on your panels
– The weather (cloud cover, rain, etc)
– Indirect sunlight due to shade
– Panels not being directly pointed at the sun
– Temperature (the hotter the panel is, the less efficient it is)
In order to achieve peak efficiency, your RV would have to be in lab-like conditions which are almost impossible to reproduce out in the world. To refer back to our example, having a smaller third panel may be right for you to give you some additional charging support.
What you do not want to do is overcharge your batteries. What we mean is that it will not do your batteries any good to have four full panels. Your batteries can only charge at 12 volts. A charge larger than that is just wasting energy potential.
Equipment Needed for Solar Power
To install your panels correctly and have them do what they are supposed to do, you will need additional devices to make it work.
Batteries: You want your house batteries to be deep cycle batteries (Group 25, 27, etc). They can be lead-acid or lithium-ion.
Power Inverter: This device converts your battery power to your household AC power. Your RV may already have one of these for your house batteries. You may have to upgrade it to handle larger power outputs if you increase your battery bank.
Battery Monitoring System: Some older RVs have a light up bar that goes from green to red. One that gives you actual numbers can give you more accurate readings.
Solar Charge Controller: This device manages the charge going into your batteries from the panels themselves. There usually is a diode on the panels that prevent the electricity from reversing direction. If this diode is not properly in place, you could destroy your solar panels.
Other Ways to Charge Your Batteries
The ideal situation for your solar panels are to be stationary for a long period of time in direct sunlight. Your RV may have other sources of power already equipped.
Installed Generator: Most motorhomes have a built-in generator that can charge your batteries while you are using your electronic devices. The more devices that are using the generator, the less is going toward your batteries
Alternator: Newer motorhomes have a second alternator installed for the purpose of charging your house batteries. Older RVs may only have one, but the alternator charges both the engine and house battery banks.
Shore Power: When you are plugged into a campground or your home’s grid, like your generator, it is charging your batteries while running your electrical devices.
Is Solar Power Worth Having
While solar panels are becoming more affordable, you can still expect to pay out in the early four-figures to get everything set up. If your RV has house batteries, part of the system is already set up. Also, newer coaches now have solar panel plugs where you can plug in portable panels that sit on tripods.
If your RV isn’t prewired, installation can still be done yourself. Do your research before you get started. You are dealing with electricity and you are going to be drilling into your RV’s shell.
The good thing about solar power is that there isn’t much maintenance required. The panels are built to take road conditions and there are not any moving parts that wear down. Your biggest concern would be making sure your system is wired correctly to prevent burn outs.
Once set up, the advantages can be worth it. Your neighbors will appreciate you not having to turn on your generator. Also, your dry dock experience can go as long as your water tanks hold out. With your panels recharging your batteries everyday, electricity is no longer a concern. For campgrounds that have different levels of campsites, from just a place to set up to a full hook up situation, you can save money by parking on the less expensive raw site.