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System Sizing by Actual Use
There are many ways to calculate what size system will meet your needs. Some are quite involved mathematically, some utilize an accumulating amp-hour meter, and some are basically "rules of thumb". The method that has proven to work the best for us is based on actual use by you the customer.
Our recommendation is for you to go out and "boondock" in your RV (without running your generator or plugging into shore power) for as long as it takes to run your batteries down. Use electricity like you want to and don't change your habits while you're doing it. This will indicate how much power you consume on the average day.
Let's say you were able to "boondock" for two days before you noticed your batteries getting weak.
- First we have to determine what your batteries storage capacity is. Let's say you have two (2) relatively new Group 27 deep cycle batteries that are rated at 100 amp-hours of storage each. This means you theoretically have 200 amp-hours of energy to draw on (2 x 100 = 200). However, only about 80% of that is usable so you really only have 160 amp-hours of energy to draw on (0.8 x 200 = 160).
- Once we have established what your batteries storage capacity is we divide it by the number of days you "boondocked" (in this example it was 2 days). So, 160 amp-hours of storage divided by 2 days = 80 amp-hours of energy consumed on the average day.
- Now we need to determine how many solar panels you will need to replace that 80 amp-hours of energy you consume per day. We will assume that you use you RV during the sunnier half of the year and/or you follow the sun south during the darker half of the year. This will give you an average of five (5) "peak sun hours" per day.
- A 100 watt panel produces an average of about 6 amps per peak sun hour, or about 30 amp-hours per day.
- Given the above example, you would need three 100 watt solar panels to fully recharge on the average day.
It is our experience that most RVers consume between 75 and 150 amp-hours of energy per day depending on their lifestyles and degree of frugality. Which means that some people will only get about one day of boondocking out of the batteries used in the above example. These folks would need three to five 100 watt panels in order to break even on a daily basis. (We have some customers that require more than six 100 watt panels to meet their needs!)
A further, highly recommended approach would be to purchase and install a Battery Monitor
before you go boodocking. These devices record your consumption and give you a reading that tells you how many amp-hours were removed from your batteries. This means there will be no guess work or mental math going on. You will know what you used and can then make an informed decision on what size system you will need to meet your lifestyle.