How Much Solar Does Your RV Need?

Many modern RVs now feature roof-mounted solar panels and the accompanying electrical systems to store and convert solar energy for use with interior lights and appliances. But how much solar power does your RV need? And will your solar system provide enough?

The answer is a bit complex and, as you’d imagine, requires some math. In this guide, we’ll break down exactly how to calculate your RV’s power needs, choose the right solar components, and figure out how many watts of panels it actually takes to keep your battery bank charged.

RV Solar Calculator

So, how much solar do you really need for your RV? It’s time to crunch some numbers. Get out a pen, paper, and a calculator.

Record Wattage for Electronic Appliances and Devices

Your first step is to list all the devices and appliances that consume energy and record their running wattages. Your list should include appliances installed in your RV and devices you commonly plug into power outlets, such as hair dryers, toaster ovens, and phone/laptop chargers.

The wattage for your RV appliances is typically found in your owner’s manual, online, or on an identification sticker somewhere on the appliance.

If the wattage isn’t listed, you can solve for wattage using this equation:

Wattage = Amps x Volts

If your air conditioner draws roughly 15 amps at 120-volt AC, its running wattage is roughly 1,800 watts. It pulls more surge wattage when starting up, however.

Surge wattage accounts for the additional wattage required to start the electric motor or fan in appliances and generators.

Here’s an example of RV appliances and their respective wattages (yours will vary):

Estimate Daily Usage Hours

Once you’ve listed your appliances and their wattage requirements, revisit each device and estimate how many hours you’ll use it daily. You may run your air conditioner for 8-12 hours a day in the summer, but you’ll probably only run your microwave for a total of 5-10 minutes.

Go back through your list and add a column for usage hours next to each appliance.

Let’s add to our table above:

Select AC versus DC Power

Run back through your list and mark which appliances run on DC and which require AC. AC appliances require an inverter, as we mentioned above, and it’s important to factor in an average 10% efficiency loss.

That means a 1,000-watt air conditioner will actually require roughly 1,100 watts when running on AC inverter power. This comes into play later when calculating daily watt-hours.

We’ll amend our table to indicate whether the appliances are AC or DC. Notice how the wattage changes slightly for AC appliances:

Calculate Daily Watt-Hours of Energy Use

It’s time to calculate the total watt-hours of daily energy consumption you estimate for your off-grid adventures. This gives you the maximum amount of power you expect to use each day. For RVers who travel seasonally, certain climates may require additional appliances such as space heaters or dehumidifiers.

Calculate your energy usage for all seasons to have the most accurate idea of how much solar you really need for your RV. Utilize the highest estimate when designing the ideal solar setup for year-round RV travel.

Let’s add watt-hours for each appliance, as well as a total calculation:

Convert to Amp Hours

With your estimated watt-hours known, you can calculate the amp-hour energy storage capacity your battery bank must provide. To calculate watt hours, you’ll divide watt hours by voltage.

Here are the results of our calculation:

How Should You Use Solar Energy in an RV?

Most RVers use solar panels to trickle-charge their battery bank, not to provide power for an extended boondocking stay. Solar panels can also help you avoid over-discharging your batteries when you aren’t connected to a power hookup.

The power from solar energy is DC, which must then be inverted to AC to power AC appliances.

But realistically, solar energy should be used to supplement your RV’s energy needs, as you would with a portable power station, an onboard generator, or a portable generator. Yes, solar can be used to power an entire RV for a few days. But the limited roof space on most RVs makes installing the requisite number of panels for extended solar viability nearly impossible.

Generally, maximizing your RV’s solar potential is about using available roof space. If you want as much solar collection ability as possible, cover as much of your roof with solar panels as is safe and realistic. You must retain space to access a fully walkable roof for repairs and your annual RV roof inspection. Your panels shouldn’t crowd existing roof accessories, such as your air conditioner and roof vents.

If you’re a full-time RVer who seeks long-term stays, you’ll have more freedom to employ portable solar panels or temporarily mount extra panels on the roof or the ground around your RV. Still, the efficiency of most solar panels makes installing enough of them, with the proper components, cost-prohibitive as a standalone power source for your RV.

Learn more about conserving and creating power when boondocking.

RV Solar Components

Here are the main components installed in RVs with solar capability – also known as solar prep. These components are necessary regardless of the size of your solar energy system.

Solar Panels

Solar panels gather energy from the sun and send it through electrical wiring to your system’s charge controller. Adding solar panels allows you to generate more energy, but you may also need to upgrade other components to safely transfer and store it.

There are two types of solar panels: monocrystalline and polycrystalline. Monocrystalline solar panels are more common for RVs because they provide more efficiency for the limited roof space you’ll have on most units.

Solar Charge Controller

A charge controller takes the energy your solar panels harness and regulates it down to a useful voltage. The energy coming from your panels varies in voltage. A charge controller is essential for converting that voltage to the 12-15-volt range to properly charge your battery bank.

The two main types of solar charge controllers are maximum power point tracking (MPPT) and pulse width modulation (PWM). PWM controllers use older technology and are less efficient, but are more affordable. MPPT controllers cost more, but they’re much more advanced and will deliver greater long-term value for your investment.

Batteries

Your battery bank stores the energy your solar panels generate. They store energy until you switch on an RV appliance and demand energy from your batteries.

There are three main types of RV batteries: lead acid, absorbent glass mat (AGM), and lithium. Lead-acid batteries were the traditional standard, but AGM and lithium batteries are more commonly used in RVs with solar setups today.  

Learn more about the different types of RV batteries.

Inverter

An inverter takes the 12-volt energy stored in your batteries and converts it to 120-volt energy to serve outlets and appliances that require that voltage for safe operation. There are several different types of inverters, but RVs with solar should boast a pure sine wave inverter.

Pure sine wave inverters do the best job mimicking the power you’ll get with a household 120-volt plug. They provide the cleanest energy to reduce the risk of damaging sensitive electronics inside your RV.

Additionally, RVs prepped for solar are equipped with the proper electrical systems to help use the energy that your solar panels harness. These components include but aren’t limited to a battery monitor, battery isolator, bus bar, wires, fuses, breakers, switches, and outlets.

Contact our performance and improvement department if your RV is not prepped for solar and you want to explore your options for adding solar.

How To Choose RV Solar Components

Now it’s time to use our calculations to select properly rated components for our RV’s solar system.

Choose Your Battery Type

Our total amp-hours help us choose the right battery. Our choice will differ based on the type of battery we want.

For lithium batteries, it’s advised to avoid exceeding a depth of discharge of 80%.

That means we must add 20% to our total amp-hours (775 × 1.2 = 930 amp-hours). This converts to a lithium battery bank with a minimum of 11,160 watt-hours of power (930 x 12 = 11,160).

If we choose a 100-amp-hour lithium battery, we’ll need 9.3 batteries to store all the energy consumed daily. You can see how that could be prohibitive, both in terms of storage space and cargo weight.

For AGM and lead-acid batteries, we don’t want to exceed a depth of discharge of 50%, meaning we need to double our minimum amp-hour threshold (775 x 2 = 1,550 amp-hours). This converts to an AGM or lead-acid battery with a minimum of 18,600 watt-hours of power (1,550 x 12 = 18,600). If we choose a 100-amp-hour AGM battery, we’d need 15.5 batteries to store the energy we consume daily. As your depth of discharge increases, you’ll require a larger battery bank (i.e., more energy storage capacity) to compensate.

Choose Your Inverter Size

Your optimal inverter size is based on the combined wattage of the appliances you plan to power. The combined wattages of our five AC appliances above total 5,730 watts. However, it’s safe to multiply by 1.5 to allow for startup wattage requirements (i.e., surge wattage).

So, in this use case, we’d recommend an inverter capable of handling at least 8,595 watts.

Estimate Hours of Sun Exposure to Get Solar Panel Wattage

Most solar experts recommend using four hours of sun exposure as a conservative estimate. Your actual number of sun hours depends on your location and exposure to direct sunlight — you can check your specific area using NREL’s PVWatts calculator, which estimates peak sun hours based on decades of solar irradiance data.

In more southern locations like Arizona, you may receive about 5-8 hours of direct sunlight. You’ll also increase your sun hours if your solar panels can tilt for an optimal angle as the sun moves across the sky.

To stick with a conservative estimate, let’s say you receive four hours of direct sunlight daily. To calculate how many watts of solar panels you’ll need, divide energy consumption (watt-hours) by hours of sun exposure.

9,300 watt hours / 4 hours = 2,325 watts

Considering the fact that most portable and roof-mounted RV solar panels capture between 80 and 440 watts, we’d need anywhere from six to 29 panels. It’s rare that RV roofs have enough space for this many panels, which is why we might also consider a portable generator or power station to supplement and recharge our RV’s battery bank.

Even if we reduced our energy demand to 3,500 watt-hours and were camping somewhere with 8 hours of daily sun exposure, we’d still require 440 watts of solar panels. That would require installing this complete solar kit from Nature Power in the roof space.

Choose Your Charge Controller

Your charge controller must be rated to handle the wattage of your solar panels. A charge controller’s minimum amperage can be calculated by dividing your solar panel’s wattage by your battery bank’s voltage.

Continuing with our energy-intensive RV owner’s example above, we’d divide our required 2,325 watts by 12 volts to calculate an ideal charge controller amperage of 193.75 amps. This means we’d need a minimum 190-amp charge controller to handle this kind of demand.

Our more energy-efficient example would still require a minimum 35-amp charge controller (440/12).

How Much Solar Do You Really Need for Your RV?

If your RV is prepped for solar, but you don’t have any panels yet, consult your manufacturer for their recommendation. The components used in your solar prep will tell you how many watts of solar panels you can reasonably add.

In general, it’s recommended to have about 300 watts of solar panels per 100 amp-hours of battery bank capacity. That equates to a minimum of 600 watts for RVs with a 200-amp-hour battery capacity and 1,200 watts for larger motorhomes and fifth wheels with a 400-amp-hour battery capacity.

Whether your RV is prepped for solar or you’re looking for a complete solar installation, our certified performance and improvement technicians are at your service.

Schedule an appointment today.

What questions do you have about adding solar panels to your RV? Let us know in the comments below.