Small solar system project concern

Re: Small solar system project concern

It is important to know whether the 20W draw is continuous, and if not, what is the pattern.

Also, solar/battery system's voltage changes. Say, on 24V system it may change between 22 and 32V, or at least between 24 and 29V. Will your load tolerate such fluctuations?

Re: Small solar system project concern

fadapow wrote: »

... the load will tolerate fluctuations but nothing above +-2V.

This complicates things. The battery voltage fluctuates more than this. If your loads cannot tolerate this, you will need some sort of device to regulate the voltage. The choice of this device will dictate the choice of the system voltage. System voltage will affect battery and panel configuration.

There are DC-to-DC converters that produce regulated voltage. Most commonly, they convert down, so you may use 48-to-24V converter or 36-to-24V converter. I'm not aware of any 24-to-24V, but other people may suggest something.

Re: Small solar system project concern

fadapow wrote: »

Ok thanks for the advice, so say i have the regulated 24V to the device, how can i determine the watt hour requirements of the system? Do i say, since the the system requires 20W, then it will consume 480Wh per day, therefore i would need a panel that can supply 480Wh per day? And if so how do i determine the battery rating, if the system will not receive sunlight for 3 days?

The load you have will depend on the losses in converting device. Assume for now 10% loss, which gives you 530Wh per day.

You start from the battery. For three days, you need 530x3 = 1590Wh. Most batteries cannot be discharged more than 50%, so you need 1590x2 = 3180Wh of battery. This is 265AH @ 12V, 133AH @ 24V, or 66AH @ 48V. Two 6V Golf Cart batteries rated 220AH should be Ok if you go with 12V system voltage. You can use smaller AGM batteries if you need to go with higher voltage.

On the panel side, it all depends on where you are. Assuming 4 hours of sun per day, you want to produce 530Wh in 4 hours, which gives you 133W panel. Because of various losses, you probably need to double that. So one 250W panel would be Ok. It would provide 18A of charging current for the batteries. It is a little bit on the low side and it might be bad for batteries, but two of the 185W panels that you plan to use would be more than enough.