Dan Martin
September 25, 2022

How Many Solar Panels Do I Need to Run My Bus Conversion?

Installing Solar Panels on Your Bus Conversion: 

The Basics

One of the most common projects for DIY solar enthusiasts is to install solar power on your bus. Solar power can give you the freedom to park away from ground power or to drive almost anywhere in the world without the fear of your fridge running out of power.

While the question of “How Many Solar Panels do I need to power my bus?” may seem simple, the answer depends on what you plan to power inside your bus. Powering a single outlet for charging your phone will require far less energy than a space heater!

There are several kinds of bus setups. Most have separate electrical systems for automotive functions (like turning your engine over), and for coach functions (like vent fans or your water pump). You can typically only use coach functions if you already have a battery installed in your bus. We can use this as a base for our solar installation.

To know how many solar panels you need, we first need to get a good guess of how much energy your appliances will drain. We can think about this energy that powers your appliances using watts and watt/hours.

Calculating Your Energy Needs: 

Watts and Watt/Hours

You’ve probably heard the term Watts before. Watts are used to describe the rate that a given appliance uses power. Watt/hours is a description of the amount of energy that’s being used per hour. We can think about the energy in batteries in terms of a given number of watt/hours.


We turn on a 100-watt refrigerator. In one hour, our 100-watt refrigerator will have drained 100-watt/hours from our battery. (1-hour X 100-Watt drain = 100 Watt/Hours.) If we run this refrigerator all day and night, it will drain 2400 watt/hours per day, keeping in mind that a refrigerator generally does not run constantly

Our first step in calculating the amount of energy that we’ll need is to look up the watts of our appliances and then multiply them by how long we expect them to run. You can find the watts drained by most common appliances through Google. Alternatively, you can use SanTan Solar’s Solar Energy Calculator to calculate the watt drainage from multiple appliances at the same time.

Once we know our wattage drain each day, we need to buy enough solar panels to cover both our projected use plus projected cloudy days and inefficiencies in our setups. Solar panels come rated with a wattage rating. A 300-watt solar panel, for example, will provide around 300-watt/hours of energy for each hour it receives sunlight.

There are other important factors to keep in mind before buying your solar panels. If you plan on setting your solar panels up in a set-it-and-forget-it style by installing them on your roof, you must first think about how many solar panels realistically fit.

How many panels can we put up there?

Area of Your Bus

Most 35’ buses have around 280 square feet of area on their roof. This is the entire area of the roof, not taking into account any vents or other blockages.

If you’ve ever seen the roof of a bus, you know that the vents and windows make this unrealistic. If we optimistically plan to cover half of our roof with solar panels, we’d end up with about 140 square feet.

Solar panels can produce around 15 watts per square foot, so that means we’d generate around 2100 watts per hour of sunlight if we cover all available space. If we gather sunlight for five hours per day, we’d generate just over 10,000 watt/hours per day. This is more than enough to power most applications but still limits what we can do inside our RV.

Battery Bank

When you’re setting up your solar panels, it’s a bad idea to run them directly into your appliances for a variety of reasons. Solar power installations always include battery banks so that you can continue to use power even when the sun is down.

You can read other articles on our site to learn more about other batteries and their pros and cons, so we’ll just be doing a quick overview in this section.

There are two main types of batteries, lead-acid deep-cycle batteries, and lithium batteries. Lead-acid deep-cycle batteries are cheap but can be damaged easily if you’re unfamiliar with their limitations. For example, letting them get below half charge will cause permanent damage to lead deep-cycle battery.

Lithium-ion batteries are superior in almost every way and have the price point to prove it. Tesla uses Lithium batteries in their solar wall installations, for example. These batteries can be up to ten times as expensive as lead deep-cycle batteries, however.

We want to make sure our battery bank has enough energy storage for our drain, which we can again calculate using SanTan Solar’s Calculator.

A bus roof, fully outfitted with solar panels.

Click here to read our other article explaining setting up your solar panels in parallel vs in series.

Solar Charge Controller

Solar charge controllers are an integral part of your solar setup. They perform several important jobs.

They limit the amount of voltage coming from the panels into your battery bank. Too high of a voltage can damage your batteries. They also disconnect the current when your solar panels are out of sunlight to reduce draining batteries.

There are two main types of solar charge controllers, PWM and MPPT (Maximum Power Point Tracking). PWM (Pulse Width Modulator) performs all the functions that are described above, but are “dumb.” They simply cap the voltage coming into your battery so as to not damage them.

MPPT (Maximum Power Point Tracking) solar charge controllers are similar in the above-listed functions, but they are “smart,” in that they convert excess voltage into current which results in a faster charge time. This allows you to wire your solar panels in an easy high-voltage formation without wasting energy.

MPPT controllers are more expensive than PWM controllers, but many people find them worth the extra investment.


Most appliances use electricity in the form of AC also known as alternating current. Solar panels and batteries both provide energy in the form of DC or direct current. In order to power most appliances inside your bus (like a refrigerator, TV, or toaster) you’ll need to use a device to convert the DC energy coming from your panels and battery into the useable AC form. A device that performs this conversion is called an inverter.

Not all inverters are created equal! Some can provide a huge flow of power all at once and some are cheaper and smaller. Be sure to check the rating for whichever inverter you buy and compare it to your projected load.

Some users attach their inverters directly to their Solar Charge Controllers. Running your inverter directly to your battery bank runs the risk of over-discharging your batteries. Lead deep cycle batteries will be damaged if they ever run below 50% charge. However, this does typically limit the amount of current you’ll be able to draw from your batteries.

A few tilting panels on a bus conversion.

IMPORTANT NOTE: Many appliances have a larger “startup” wattage. A refrigerator, for example, will draw a few hundred watts while running but can draw more than a thousand watts when it’s first activated. Be sure your inverter is designed to handle your appliance’s larger startup load!

Weatherproofing and Safety

When working with electricity, use common sense safety precautions. Be sure to check your cables periodically for corrosion, and waterproof any holes you drill while installing your wiring in the roof of your bus. Electrical shorts (the visible arc of electricity) can reach temperatures of 35,000 degrees Fahrenheit and ionize the air.

Always include disconnects like circuit breakers or fuses between the different parts of your system to avoid melting wires or damage to different components.


Installing solar energy into your bus is a complicated yet rewarding project. You’ll gain the freedom to camp almost anywhere without paying for electrical ground hookups or worrying about using all your gas to power a generator.

Article written by Dan Martin

Dan Martin is a digital marketer helping solar companies grow and scale. Dan helps write and manage the marketing efforts at SanTan Solar, helping solar become more affordable for everyone.

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