How Much Solar Do I Need for My RV?

Posted June 18, 2020

So you're considering switching to an RV solar panel and wondering where to start? Look no further because today’s post will cover what you need to know to correctly calculate your solar array and battery bank needs. We’ll do this in three steps that include sizing your battery bank, calculating your power needs, and determining your solar requirements.

Sizing Your Battery Bank

To estimate your total energy requirements for an RV solar panel, sum the daily usage of all the appliances in your RV like our example below. You can find common watt ratings with a quick Google search or by looking at the labels on your appliances. In the extended example below, a total of 139 amp hours are needed daily.

Amp Hour Calculation: Watt Hours ÷ Volts = Amp Hours

As mentioned above, batteries are rated in watt hours or amp hours. For this example, you would need a battery or bank of batteries with a capacity that adds up to more than 139 amp hours or a means to recharge at a rate that is equal to or faster than the rate you’re consuming. Remember, these calculations are on a daily use basis.

Calculating Power Needs

The second step is to determine your maximum power requirement for your RV solar panel. From our example above, we calculated 139 total amp hours are necessary daily, however, it is important to also consider the continuous and peak discharge current your battery is capable of handling. Summing the total watts and dividing by the voltage of your battery will return current in amps if all appliances were in use at the same time: (2,356 watts ÷ 12.8 volts = 184.1 amps).

Current Calculation: Watts ÷ Volts = Current

If your current in amps exceeds the continuous rating of your battery, you should limit the number of appliances used at one time or increase the number of batteries you have connected in parallel. If you exceed the peak current rating for longer than recommended, the battery’s monitoring system (BMS) will shut the battery down. Keep in mind, some appliances require extra power to start, which would also increase your current requirement for a short time. If you do not have enough current available to cover starting the device will not work. To have a consistent supply of day-to-day power you’ll need a reliable method of replenishing what you use, which brings us to sizing your RV solar panels.

Determining Solar Requirements

Solar is commonly available in 100-300 watt panels. Panel watt ratings are based on maximum efficiency. The temperature, weather, and time of day all affect how much power solar panels can generate. You will generate about 30 amps of power for every 100 watts of solar panels you have. You can use this as a general guideline while panel shopping. Check for yourself as you review panels by finding the output power or optimum current rating, most will be in the 5.3-5.7 amp range. Presuming you have six usable hours of sunlight in one day each 100 watt 5.5 amp panel will generate 33 amp hours daily (5.5 amps x 6 hours = 33 amp hours).

To replenish the energy used in the extended example above (139.1 amp hours) you would need an array of panels totaling 500 watts. We arrive at this calculation from the guideline that each panel will produce about 30 amp hours per day in ideal conditions. If using five 100 watt panels that works out to 5 panels x 30 amp hours daily = 150 total amp hours, thus covering the 139 amp hours in the estimate. Although 150 amp hours would cover the minimum daily necessary, it’s a good idea to oversize your array to build a cushion. Depending on how reliant you are on solar power as your only source, it’s a good idea to build in 20-25 percent capacity above your requirements to be sure you’re not left short on a cloudy day or if you use more than expected.

These basic calculations provide the essential information necessary to size your RV solar array. Please contact us if you have any questions or would like assistance selecting the best RELiON batteries for your RV needs. A useful related topic we cover in our Tech Tuesday series is Solar Charge Controllers Explained, which can be found here.

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