What size solar panel for RV battery

What Size Solar Panel For RV Battery?

The size of solar panel you will need for your RV battery will depend on battery capacity, panel efficiency and your energy use per day. At a minimum, you are likely to need at least two panels of 100 watts each. For more energy-intensive use (for example, boondocking or camping off-grid for long periods), you could need 1800 watts of solar panels or more.

There are several factors to keep in mind when thinking of using solar power for charging instead of a generator. First, without panels of a suitable capacity, you may not be able to recharge your battery and power your RV.

There is a physical limit to what size of the panel can be installed on the roof of your RV, but ground panels or portable kits are also available.

Are you wondering how much power you need per day, what kind of system is best, or how many panels to buy? Our simple guide to RV solar could help determine the best options for you.

If volts, amps and watts are new or forgotten words, skip to the bottom first for a quick explanation of key terms.

Let’s get started…

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Why use solar power to charge RV batteries?

Solar energy is easy to maintain, affordable and clean source of electricity – ideal for the road! In addition, installing solar panels promotes freedom, independence and sustainable living when travelling in your RV.

Using sunlight to power your RV opens the doors to a wider field of travel opportunities by reducing your reliance on the grid. You will not need to park in locations with a gas-powered generator etc.. and can truly get away from civilization.

When camping off-grid, there may not be any other local means to charge the battery in your RV. However, installing solar panels or carrying a portable charging kit will keep you powered up deep in the countryside and off the beaten track.

The sun is a renewable energy source that can make your power consumption more environmentally friendly and sustainable, wherever you are.

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Why do RVs need batteries?

When an RV’s engine runs, it provides electricity to power everything inside, from lights to devices, by burning gas (petroleum). However, keeping the engine running 24 hours per day to generate electricity would be costly, wasteful and unsustainable in most situations.

A battery is an energy store that enables RV owners to enjoy their vehicles fully when not on the road. When camping, batteries can provide lights, heating in cold weather, air conditioning in hot weather, power TVs, kitchen appliances, etc.

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How can I charge RV batteries?

With the right connector, you can charge RV batteries in several ways. Depending on location and equipment, you may be able to connect to the grid, a gas-powered generator, or renewable sources such as solar power.

The most obvious disadvantage of a solar-based system is that you cannot charge your battery during the night. This is because a solar cell can only operate at a high capacity for perhaps 6 hours per day while the sun is strongest.

Some solar panels will have an even lower efficiency than this. If no light is present, you will not be able to generate electricity at all.

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How does a solar panel work?

A solar panel converts light into electricity. The power, or wattage, of a panel, depends on its physical dimensions, with voltage a key characteristic for battery charging.

Solar panels do not generally connect directly to RV batteries. Instead, they are part of a wider system to power your vehicle.

Before reaching the battery, solar energy will pass into a regulator or solar charge controller (SCC). In many solar panels, the open-circuit voltage is about 22 volts, and the regulator is there to prevent overcharging and battery damage.

Voltage does not vary with light intensity as it currently does. Therefore, a solar panel connected to a 12v battery in full sunlight could potentially continue charging the battery at levels well above 12v.

To prevent damage from too much solar energy input, the solar charge controller detects the existing battery voltage and adjusts panel output down when approaching 14.1 volts. At the same time, it maximizes the current that the panel delivers so that the charging time is as short as it can be.

Solar charge controllers don’t have an inbuilt power supply, and the system relies on battery voltage to operate. So it would help if you connected the chargers to the battery before being connected to the panel itself.

Once connected, the charger will display battery voltage, indicating the state of charge. At this point, you can connect the panel itself to the charger input terminals.

Overcharging can be avoided by using solar charge controllers or switching to a lithium battery system.

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What is an inverter?

An inverter is a device that converts the 12v DC (direct current) power in a battery to 120 volt AC (alternating current) electricity. You can power DC devices directly from the 12v battery, but AC devices need a DC inverter to convert the DC electricity into AC power.

RV appliances, including microwaves, TVs and fans, will use AC, and an inverter is, therefore, an essential component if you wish to use them. When purchasing an inverter, ensure that its output capacity is capable of operating the necessary electrical loads.

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RV battery charging and panel installation considerations

Solar panels can be used for charging all the regular types of RV batteries – lead-acid (wet cell, AGM, gel cell) and lithium – see descriptions below. Calculate your energy needs and check the power of individual panels to buy the right size and number.

RV power systems must maintain a steady battery bank sufficient for all onboard devices. In addition, there are size limitations with an RV compared to a house or apartment, restricting the number of panels or batteries installed.

A solar panel system may be installed on your RV’s roof or placed on the ground around it to capture light. Ground panels can be adjusted to face the sun as they move across the sky and potentially function more hours per day.

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How much power does my RV need?

Before determining which solar panel system will meet your RV’s power needs, you must determine how much energy you use per day. You can find this figure by calculating the total used by all systems and devices in your RV.

You will need to find a panel with at least the same power as your total RV use. As a rough guide, a 100-watt solar panel can produce around 6 amps per hour of peak sun or 30 amp-hours of power per day.

NB In cloudy weather, early morning or evening, you will be able to produce fewer amps per hour and not as many amps overall, so be careful to factor this into estimates.

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What size solar panel do I need to charge a 12-volt battery?

When we talk about the ‘size’ of these panels, we could be referring to physical dimensions or power output in watts. However, it would help to consider both alongside battery capacity in amp-hours when considering installation in an RV as total power and total space are equally important.

Any panel can charge a 12-volt battery with a voltage above 13.6 volts. The open-circuit voltage of an average ’12v’ panel is 21 volts. Always use chargers with a solar charge controller to prevent overcharging and battery damage.

A small 5-watt solar panel is enough to maintain optimum levels of charge in a 12-volt battery. Larger panels should not be used without solar charge controllers.

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How many solar panels does it take to charge a 100 amp hour battery?

If we assume we are charging a battery at 12v and 20 amps, you would need a minimum of 240 watts of solar panels to charge this battery since Power = Voltage  X Current.

To be safe, you might want to purchase a 300w panel or three 100w panels.

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Can a 100-watt solar panel power an RV?

A 100-watt panel is conveniently sized, increasingly standardized and relatively easy to transport in the solar power market. This has made them a popular choice for portable power kits, especially for camping, RVs, and general outdoor and/or off-grid activities.

But remember that a single 100w panel can produce only around 30 amp hours of power per day. You may need 80 amp hours if boondocking or camping, making one 100w panel insufficient to power all RV systems in average weather conditions.

You would likely need two 100 watt panels or more to recharge your battery and power your RV systems on a normal day. However, for intensive use (e.g. running an air conditioner, boondocking or camping off-grid for extended periods), you could need 1800w of panels or more.

The portability of 100w panels makes them an excellent choice for powering a few small appliances in an RV or while camping. As such, they are an ideal introduction to RV solar power.

A single 100w panel could power one of the devices listed for between a few hours (laptop) and a full day (Wi-Fi router):

–     Laptops – 60-watt hours

 

–     Ceiling fan – 35-watt hours

 

–     Certain lamps and lights – 14-watt hours

 

–     LEDs – 10-watt hours

 

–     Wi-Fi Router – 6-watt hours

 

–     Smartphone charging – 5-watt hours

Panels can be networked together to increase total output. For example, if you connect two (in series or parallel), you could get a maximum of 200w.

How big are 100 watt solar panels?

100w panels can vary in size depending on design and efficiency. However, on average, they will measure approximately 47 x 21.3 x 1.4 inches.

How much do 100-watt panels cost?

When buying a 100-watt panel, you can buy the panel alone or purchase a full kit with the panel, solar charge controller, cables, and brackets. For portable solar power kits, a standalone 100-watt panel can be purchased for $100 or less, with a complete 100-watt starter kit costing +$300.

How long will a 100-watt panel take to charge a 12v battery?

The answer to this question will vary depending on sun, panel and charger efficiency, type of battery, temperature, starting charge level etc… For example, with a solar panel of 100 watts, a 12v battery could take anywhere from 5 to 17 hours to recharge fully.

Charging will be quicker if you have several RV panels, an efficient solar charge converter, and a lithium battery. However, with a single RV solar panel, a less efficient converter and a wet cell battery that has been significantly discharged, charging will be slower.

On average, the efficiency of any RV solar panel varies according to factors including quality, manufacturer and materials.

How do you install an RV solar power system?

Many panels are mounted in metal frames designed to be connected to the roof of your RV. Others are intended to be placed on the ground nearby.

If you don’t want to install permanent panel/s in your RV, you can connect a portable solar system or battery pack. These kits typically generate 50w or 200w of power and shouldn’t require special expertise to set up.

What kind of batteries do RVs have?

RVs use “deep-cycle batteries which are designed for regular discharging and recharging providing power over long periods. In comparison, regular car batteries deliver only a short, sharp burst of starting energy.

In general, older types of deep cycle batteries should not be discharged below 50% – 80% according to battery type. For example, we should not use more than 80 amp-hours from a 100 amp hour wet cell battery before recharging. Discharging below 80% depth of charge could damage the battery and reduce its overall lifespan.

There are four categories of modern deep cycle battery types which you can install in your RV.

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Lithium-Ion

Lithium batteries are the newest RV battery technology with significant advantages over older lead-acid batteries. The most significant benefit is the longer-lasting power, with lithium batteries lasting 5 to 10 times longer than a wet cell, gel cell or AGM batteries.

At the same time, lithium batteries can store 4 times as much energy as lead-acid batteries and have a longer life overall. In addition, unlike lead-acid batteries, they can be used whenever needed, run down to zero power without damaging the battery, and do not require constant charging.

Wet cell / flooded battery

This battery type is among the most common. Wet cell batteries require maintenance to keep them working properly and must be regularly topped up with water. They hold charge well when stationary but can be vulnerable to damage from shaking and knocking. Rougher journeys or accidents could cause them to lose charge.

Gel Cell Battery

Gel cells are an example of sealed lead-acid batteries, using sulfuric acid and fumed silica to create a gel-like substance that does not move around. Unlike wet cell batteries, gel cells can be placed in different positions and undergo rough and bumpy travel without losing charge.

Absorbent Glass Matt (AGM)

AGM batteries are another example of sealed lead-acid batteries invented in the 1970s. They contain electrolytes with a mix of sulfuric acid and fibreglass.

These batteries are spill-proof and can be moved around without damage or impairing function. Containing no water, AGM batteries are significantly less heavy than wet cell batteries and hold a charge longer and powering devices more quickly.

Can I install more battery power in my RV?

If your battery doesn’t last long enough to meet your power needs, you can add more batteries to your RV. However, check your vehicle’s size and weight capacity first.

Volts, Amps, Watts – help!

Forgotten all your high school physics and can’t tell your amps from your elbows, never mind how many amps of current are needed? This short reference will make it easier to figure out what size panel you require for your RV…

–      Volts (v): the measure of electrical current flowing to or from a device or power store.

–      Amps (A): the measure of the flow of electrical current.

–      Amp Hours (Ah): the measure of available power stored in a battery.

–      Watts (w): the measure of energy used.

Solar panel and electrical device power are measured in watts, while battery capacity is measured in amp-hours. To make calculations, you can use the two equations below:

–      Watts = Amps X Voltage

–      Amp-hours = Amps X Hours

Calculation working:

A 15w lamp runs at 12v; its current is 15 / 12 or 1.25 amps. So if we use it for 4 hours, we need to use 5Ah (4 X 1.25) of battery capacity.

If you have a wet cell battery with a capacity of 100 amp hours, using your lamp for four hours, therefore, uses 10% of your battery. However, if you had a larger battery of 200 amp-hours capacity, using your lamp for this time would have used only 5% of your battery.

With 200w of solar panel charging at 12v, you could recharge a battery at a rate of 16.67 amps per hour in perfect weather. With 5 hours of strong daylight, you may recharge 83.33 amp-hours per day.

A final word…

We hope we’ve helped you figure out how much power you need and how you can get away from the gas generator. Now it’s time to get outside and make the most of the open road with RV solar!

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