Calculator | Solar

Trickle Chargers generally keep batteries maintained when not in use for prolonged periods of time. For a full sized automotive battery, I would recommend at least a 15 watt panel. Battery MINDer makes the SCC015, a very nice unit that also de-sulfates and restores batteries.

50% discharge has to do with capacity. Well, it actually has to do when chemistry. As the battery discharges, the amount of available electrolyte becomes less and less as it becomes diluted with water, a by-product of the chemical reaction that creates electricity. The internal plates also become covered with lead sulfate, which also hinder further chemical reaction.

You cannot accurately measure available AH unless you run a load and determine runtime under that load. But you can measure volts. a 50% discharged 12 volt battery will not read 6 volts. 12.2 volts is closer to 50% discharged. Anything less is severe and will rapidly accelerate sulfation and decrease battery life.

Line 29 is the RAW of solar panels that will (total Watts) be enough for your system based on your calculations. This number may have decimals. Line 30 indicates the voltage system. 1 is for 12 volts. 2 is for 24 volts, etc. If your batteries are in parallel, so too must the panels be in parallel. Only one string of panels is needed. Nothing should be wired in a series with another set. The last line rounds up the number in line 29. If your RAW number was ~7.38, it‘s going to round up to 8. You can‘t have a partial panel. Line 31 is the true number of panels needed, in accordance to the Watt rating recommended.

If your batteries are connected in series for more than 12 volts, then there is was an error in your numbers. The system voltage you enter (line 12) will determine the number in line 30.

Please read through the Walkthrough, which explains how to use the solar calculator. To answer your question, you would need to know the amount of draw on the battery, and how many hours of sunlight you feel comfortable relying on.

As long as both the batteries and the panels are wired similarly (in seres or parallel) it won‘t make a difference in terms of time to charge. You‘re looking at the same amount of power in the end.

The solar calculator was correct. We do recommend three 115 AH batteries and three 60 Watt Panels (in parallel, not series). It‘s actually less than three of each recommended, but the calculator always rounds up to the nearest whole unit. No partial batteries or panels.

Based on what you currently have: To keep a safe discharge level of 50%, we recommend you use a single 115 AH battery under a 2 amp load for no more than 31 hours and 57 minutes. Having 3 batteries will ensure at least 3 days of backup power should the sun forbid to shine. A single 60 watt panel will deliver about 4.5 amps per hour (a total of 31.5 amps in seven hours). This would still not cover the 48 amps draw taken in a single day, hence the need for more than one panel. Our calculator is very conservative. It‘s better to size a little larger to make up for unexpected weather or extra need for longer duration of power.