You may have seen them resting on roofs at a campground, offered as an option at a dealership or even propped up in a sunny parking lot with wires running back to an RV. Solar panels are now ubiquitous among RV enthusiasts, providing observers of the off-grid lifestyle with an extra boost of power while forgoing toxic emissions and unsustainable fuel sources.
In decades past, solar power was thought of as an incredible but idealistic solution to our planet’s climate woes: a wonderful concept but simply too expensive and underpowered to meet the average household’s energy needs. Hefty and cumbersome, they were considered impractical even for many stationary installations, let alone for use on a moving vehicle. But times have changed, and thanks to the invention of lighter materials and highly efficient energy conversion technologies, it’s never been a better time to power your RV with the sun.
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Lower costs and higher efficiency aren’t the only factors that play into the rise of solar power – in recent years, we’ve experienced a massive shift in public consciousness and concern for the planet’s future. As we’ve become increasingly aware of environmental issues such as fossil fuel usage and pollution, the popularity of solar power and other alternative energy sources has skyrocketed.
Solar power allows us to reduce our environmental impact while still maintaining all the comforts of modern life, so what’s stopping everyone from ditching their generators and harnessing the sun? Well, despite their wide availability and recent optimizations, solar power systems can still be a bit intimidating to those without an electrical background. Many people, upon seeing the calculations and wiring that are required for installation, feel daunted and decide against using solar panels for their RVs.
If you’re hesitant to explore RV solar power because of the math, science, and engineering involved, put your fears to rest: it’s not as complicated as it may seem! Read on to learn more about how solar power systems work, how to calculate your personal energy requirements and how to optimize your RV for solar. You’ll be soaking up the sun in no time!
Sun 101: The Basics of Solar Power
Before we can address the issue of RV solar power, we first need to understand the different components of a solar power system and the energy they produce. Let’s take a look beneath the surface of a solar panel and take an electric journey through the wires and waves.
#1 – Solar Panels
Many people think that a solar panel itself is all there is to a solar power system, but it’s simply the most visible of the components. A solar panel is an assembly of solar cells, usually made of silicon and protected by glass, that charges your batteries by use of a phenomenon known as the photovoltaic effect.
The photovoltaic effect occurs on a subatomic level. When light hits certain materials, such as silicon, it induces movement in the materials’ electrons. The newly-energized particles generate an electrical current as they flow through the solar panel’s circuitry and into the rest of the system.
Stronger light generates more electrical activity, so solar panels work best when they receive direct sunlight for long periods of time. Some solar panels have motorized mounts that can tilt the panels to follow the sun as the day progresses. Others are thin and flexible, allowing them to keep a low profile on curved roofs and absorb the sun from many angles.
A solar panel’s power output is usually given in watts (W). The higher the wattage, the more power the panel can provide. However, the stated wattage represents the maximum power the panel can generate; the actual output will vary depending on factors like temperature, light intensity, cloud cover, equipment quality, age, and cleanness.
#2 – Batteries
Solar panels don’t directly power your electrical devices. Rather, the electricity they generate is stored in your RV’s batteries. From there, power is drawn as needed to operate electrical devices.
The majority of RV batteries are 12 volt (V) lead-acid batteries. Scientifically speaking, voltage is the measure of electrical potential between the positive and negative terminals. Practically speaking, voltage can be used to monitor the charge status and overall health of the battery.
A battery’s voltage rating is just an average – the actual voltage at any given time will vary depending on the battery’s current state. For example, when fully charged, a 12V battery’s voltage could go up to 12.9V, and it could drop down to 11.4V when fully discharged. While it’s receiving a charge from the solar panels, its voltage could measure as high as 14V!
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#3 – Charge Controllers
Most solar panels for RVs are rated at 12V, so it’s reasonable to assume that they’ll put out 12V of power. But the panel’s voltage rating, like a battery’s, is just an average, and in practice, the voltage can be a lot higher – up to 20V when the panel is in very bright sunlight. If your 12V RV battery received a 20V power surge from your solar panel, it could be damaged and even start a fire – not good!
Thankfully, most RV solar power systems include a charge controller to prevent situations like this. After the electricity leaves the solar panel it passes through the charge controller, which monitors and regulates the flow to keep everything running optimally. By limiting the power the battery receives at any given time, the charge controller ensures the safety and longevity of your solar power system.
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Adding Up the Amperage: How to Calculate Your RV’s Power Consumption
To find out how much solar power you’ll need for your RV, you’ll need to add up the power consumption of all your devices and appliances. You can then compare this number to your battery capacity to determine how long your batteries can power your RV, and from there you can calculate how much solar power you’ll need to generate per day to maintain your energy requirements.
#1 – Power Conversions
When calculating your power usage and the capabilities of your solar power system, you’ll come across three units of measurement: volts, amps, and watts. Volts measure electrical potential, amps measure current and watts measure power. The three are interrelated; if you know two, you can find the third by plugging the values into the equation Watts = Volts * Amps.
Your battery’s capacity is measured in amp-hours (Ah), typically between 70 and 90Ah per battery. Amp-hours are calculated by multiplying amps and hours. A battery with 80Ah of charge could provide 80A for one hour, 1A for 80 hours or 5A for 16 hours – any combination so long as the product of the two values equals 80.
This makes it easy to figure out how long your battery could run your RV’s DC equipment, since DC power consumption is often measured in amps. Take a look at your built-in lighting, water pump or exhaust fans and you’ll see an input rating given in amps. A 2A fan run for one hour will deplete your battery 2Ah; run it for two hours and it’ll use up 4Ah.
But what about AC equipment? Many of the more powerful devices that you plug into your RV’s wall outlets, such as microwaves and hair dryers, run only on 120V AC power and state their power consumption in watts, not amps. To find out how long your battery can run these devices, you’ll need to use the equation from before: Watts = Volts * Amps.
Let’s use an example of a 1000W microwave designed to run at 120V. We can rearrange the equation to calculate for amps: Amps = Watts / Volts. 1000 divided by 120 is 8.33, so the microwave’s amp rating is 8.33A.
#2 – Accounting for Losses
Built-in DC equipment runs directly off the battery, but anything you plug into the wall outlets receives AC power through your RV’s inverter. Even devices like phone chargers that state input requirements in amps still rely on AC power because they’re plugged into your wall outlets; the DC conversion occurs in the device itself.
The inverter draws 12V DC power from the batteries, converts it to 120V AC and passes it along to the outlets. During this conversion, some power is lost; the exact amount depends on the efficiency of the inverter but is generally around 10-15%. For this reason, you’ll need to add around 15% to your power consumption calculations to account for the conversion loss.
So our aforementioned 8.33A microwave will actually draw around 9.5A from the battery due to the inverter. A 1A phone charger will draw closer to 1.2A. You don’t need to perform this calculation for each and every device; just add up all your amps and then add 15%.
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#3 – Tallying the Total
Now that you know how to convert the various units of electricity, you can calculate approximately how many amp-hours you drain from your batteries each day. Just take each AC device’s amp rating and multiply it by the number of hours you use it per day.
If your TV uses 0.5A and you use it for three hours a day, the TV’s total amp-hour draw is 1.5Ah. Your 8.33A microwave used for 10 minutes (or 1/6th of an hour) a day draws 1.38Ah while your 2A computer charger used for five hours draws 10Ah. Add up all of your equipment’s amp-hour totals, add 15% to the new total to account for conversion loss and you’ll get your total AC amp-hour draw.
Next, calculate how many amp-hours your built-in DC equipment draws each day. Five 1A lights run for six hours a day will draw 30Ah; your 2A exhaust fan run for three hours a day will draw 6Ah. When you’re done, add everything up but don’t include the extra 15%; because these devices run directly from the battery, they circumvent the inverter and thus its associated power loss.
Finally, add your AC and DC amp-hour totals and you’ll get the total amount of power consumption per day. Very conservative electricity usage could result in a total as low as 15Ah per day, meaning that one 90Ah battery could power your RV for six days. On the other hand, a large RV with many lights, screens and appliances running all day could easily surpass 150Ah a day – you’d need multiple batteries just to make it through a 24 hour period!
#4 – Battery Matters
As you can see, your battery capacity must be adequate to supply your power requirements – if it’s not, no quantity of solar panels will suffice to power your RV! And it’s not enough to simply have enough capacity to meet your daily usage needs. Lead-acid RV batteries can be damaged if they fall below 50% capacity; even if they’re not physically damaged, letting them discharge past 50% repeatedly will significantly shorten their lifespan.
You’ll want a total battery capacity of at least twice your daily amp-hour usage, but ideally more. Should you get caught in a rainstorm or otherwise not receive enough sunlight one day, you’ll be powerless unless you’ve got extra batteries all charged up and ready to power your RV. To be on the safe side, aim for four times your daily amp-hour usage in battery capacity.
Judging the Panel: How Many Solar Panels Do You Need for Your RV?
The final step in calculating our solar power requirements is picking the panels themselves. Here’s where things get a little tricky, because a solar panel’s power output is heavily dependent on external factors.
#1 – Panel Perfection?
A 100W solar panel only puts out 100W when conditions are absolutely perfect: it’s receiving direct noon sun on the entire panel, the glass is clean, the air is clear, the temperature inside the solar cell is around 77 degrees Fahrenheit and the panel is free from any damage or deterioration. In this scenario, the panel will generate its full stated power of 100W.
But in the real world, things rarely work out so perfectly. Maybe you’re up north in autumn and the daylight is dwindling; what little there is gets obscured by clouds for half the day. Or you’re exploring the southwest and while the sun’s strong, temperatures are high and dust seems to permanently coat the solar panels.
So your 100W solar panel won’t actually put out 100W, at least not for extended periods of time. Because the actual output is so dependent on the environment, it’s impossible to give a universal figure.
However, there’s an easy way to estimate how much solar power you’ll need to run your RV. Remember the amp-hours per day that you calculated? Get that figure ready – you’ll need it for these next steps.
#2 – The Final Countdown
Since solar panels are rated in watts, we can make our calculations easier from this point by converting our amp-hours to watt-hours (Wh). Just multiply your daily amp-hours by the battery’s voltage to get the watt-hours. Suppose you use 80Ah a day and your battery is 12V – 80 times 12 is 960, so you use 960Wh a day.
As a rule of thumb, a 100W solar panel produces around 360Wh of power a day. This figure will be lower in the winter and the north, and higher in the summer and the south, but you can use 360Wh as an average for your estimates.
You can use this rule of thumb to find out your required solar panel wattage: divide your daily power consumption in watt-hours by 360, then multiply the result by 100. If you use 960Wh a day, you’ll need around 260W of solar panels. For ease of purchasing, you may need to round up your result to a more common number, such as a multiple of 50 or 100 watts.
If you have a large RV with plenty of roof space, you can install multiple solar panels to meet your power requirements without issue. Smaller RVs present more of a challenge; you’ll need to use fewer solar panels with higher efficiency. You may want to invest in a tilting panel mount so your panels can move with the sun throughout the day, maximizing the rays they catch and thus the power they generate.
Living Solar-Fully: Optimizing Your RV for Solar Power
Solar power may not produce as much energy as other sources like generators or grid power, but you can make the most of it by cutting back on your energy usage. No, this doesn’t mean you have to give up your TV or live by candlelight! There are many easy ways to reduce your energy consumption without sacrificing your comfort or enjoyment of your RV.
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#1 – A Bright Idea
If you use compact fluorescent (CFL) light bulbs in your RV, consider switching them to LED bulbs – you could cut your lighting power usage in half! A 12W CFL running on your 12V battery uses 1A, but a 6W LED uses just 0.5A. It doesn’t seem like much at first, but switching all your lights to LEDs can really add up when you consider how many lights you have and how long you run them for each day.
#2 – Screen Time
Looking for an excuse to get a new TV? Well, here’s a good one: modern LED TVs use a third or less of the power of CRT TVs. A 24” CRT TV uses around 120W, or 1A, while a 24” LED TV uses just 40W, or 0.3A – that’s a big difference in battery drain when you’re binge-watching for hours!
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#3 – Alternative Appliances
Kitchen appliances are some of the most power-hungry devices out there. Blenders, microwaves, coffee machines and electric kettles are notorious battery drainers. Thankfully, there are plenty of ways to keep your RV kitchen running while still saving energy!
Many microwaves, especially older and larger units, use huge amounts of power: up to 1,500W in some cases. Consider replacing your microwave with a newer, smaller one. Recent models are engineered with efficiency in mind, so it’s easy to find one that uses less than 1,000W.
Coffee machines, though convenient, are just as consumptive as microwaves if not more so! Topping out at 1,500W, your coffee maker could be putting a surprising amount of stress on your power supply. Many RVers swear by percolators, French presses and other non-electric coffee brewing methods – it’s not quite as quick as pushing a button, but it only takes a little extra effort to save a lot of power.
Product data was last updated on 2019-07-15 at 13:56.