Solar panel Watts to Amps?

How to calculate the number of solar panels will work on a 40-Amp MPPT controller...

Hey Mike,

I have a 40-Amp rated solar controller. How do I figure how many Watts of solar it can handle? It is supposed to handle 400-Watts of solar panel. Will it handle 600-Watts of solar panels? What’s (Watts) the math formula? -Eric

Hey Eric,

This is pretty easy to figure out with solar panels wired in parallel. You just have to calculate how many Watts are equal to 40 Amps of current at 13 Volts. Note that we don’t use 12 Volts for this calculation since most of the time RV batteries will be around 13 Volts or so while charging. I’ve confirmed this calculation with my engineering friends at Renogy, so I’m reasonably confident that it should work with most brands of MPPT charge controllers.

Let’s Multiply

40 Amps x 13 Volts = 520 Watts

This suggests that a 40 Amp MPPT charge controller can handle 520 Watts of solar panels.

Let’s Divide

500 Watts / 100 Watts per panel = 5 (100-Watt) panels

Now all we have to do is calculate how many solar panels we can use with this charge controller. To reach its 500 Watts of capacity you could use five 100-Watt solar panels, or two 200-Watt panels plus one 100-Watt panel, or any other combination that adds up to 500 Watts.

Can you use 600-Watt of solar panels on a 40-Amp Controller?

While you could connect 600-Watts of solar panels to a 40-Amp MPPT Charge Controller, it will max out at 500 Watts charging during peak solar times. But it shouldn’t hurt anything.

Hope this helps…

Let’s play safe out there… Mike