We did some simple arithmetic, made some broad generalizations about usage, and applied some basic rules of thumb.
Here are the assumptions we made:
We assumed that you will use every single item that you selected from our list for a certain amount of time, every single day.
Of course, we don’t really expect that you will use every single appliance every single day, but assuming so sets up a “worst case scenario” so that your system is more likely to cover all of your energy needs. Our times estimates are based on our own personal usage, since we figured that we’re somewhat normal people.
Click here to see how many hours of usage we allotted per item
We assumed that you would be comfortable using up to 50% of your battery capacity on a “worst case scenario” day.
To get the longest life out of your batteries, it’s best to shallow cycle them (use only about 20-25% of their capacity before charging them again). Most battery manufacturers say that it’s okay to discharge your batteries by 50%, and beyond that you’d be shortening the lifespan of your batteries.
We assumed a ratio of 1 watt of solar to 1 amp hour of battery (for a 12 volt system).
Our general rule of thumb is:
- For 12 volt systems: 1-1.5 watts of solar to 1 amp hour of battery capacity
- For 24 volt systems: 2-3 watts of solar to 1 amp hour of battery capacity
- For 48 volt systems: 4-6 watts of solar to 1 amp hour of battery capacity
We assumed that you might want to add one more solar panel.
If our charge controller recommendation seems a bit oversized, that’s because we wanted to give you some wiggle room in case you decide to expand your system at a later date. Many of our friends started with small solar systems (less than 300 watts) and expanded later. Keeping this in mind, all of our solar panel recommendations allow for the addition of one more solar panel (of the same wattage and voltage as the original recommended panel).
We assumed that you’re as in love with 12 volt systems as we are.
12 volt appliances (refrigerators, fans, etc.) are easier to find than 24 volt or 48 volt appliances. In addition, 12 volt systems are inherently safer than 24 or 48 volt systems. So we stuck with 12 volt system recommendations if possible, and switched over to recommending 48 volt systems for the larger 250 watt solar panels. The downside to a 12 volt system is that the cable sizes have to be thicker, which makes them more expensive.
One Last Thing …
Unless you already keep track of your energy consumption (with the exact same appliances that you will be running off your solar power system), you won’t really know what your actual usage is going to be until you install and use your system. Factors like temperature and amount of daily sunlight will also have an effect on your system, so don’t be surprised if your system ends up being undersized or oversized. You may have to add either solar panels or batteries to fine-tune your system.
The numbers that we recommend for your system should be taken as a starting point only. You should do your own calculations, take into account your own personal usage, location (sunny vs. cloudy), hours of direct sunlight, and check the energy consumption of the actual appliances that you plan to power with your solar power system. SolarLoco makes no claims or guarantees as to the completeness or accuracy of the information presented herein.