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# I want to buy a 40W solarpanel how can I calculate how "heavy " the controller and the inverter should be?

The man in the shop told me it would be wise to buy these things too. If I want to use it continiously he advised a battery. How heavy should this be and how can I calculate it for a panel of 80 Watt Thanks in advance

## Discussions

9 years ago

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9 years ago

*all numbers assume 100% efficiency, this is not the case - expect some losses*

Assuming you get 10 hours of 40 watts every day, thats 400 watt-hours per day. (multiply them). Thats 400 watts, for 1 hour, or 1 watt for 400 hours, however you wish to use it. using a 1000 watt panel for 10 hours would be 10,000 watt-hours, or 10kWh (you're used to seeing that unit on your electric bill)

400 watt hours in a 12volt battery is (watts are volts*amps) 400w/12v = 33.3 Amp Hours @ 12V. Batteries come rated in amp-hours. You need as many batteries as it takes to reasonably hold as much charge as you'd reasonably store up in a day or two. Adding more storage is okay if you don't use the power often.

400 watt-hours is a high-end computer running for about 2 hours.

Eg2, 80 watts * 10 hours = 800 Wh

at 12v = 66.6amp hours per day (again, see it as 66 amps, 12volts for 1 hour, or 1 amp, 12 volts for 66 hours)

Inverters are rated in Watts - The inverter can be sized to whatever load you'll put on the system. To charge phones and a laptop, you'd use ~100 watts, and could use the system for 800/100 = 8 hours per day.

To use a 1500 watt space heater, you'd get 800Wh/1500 = 0.53 hour=32 minutes, per day.

Hope this helps!

9 years ago

Do you know what voltage the panels output?

The battery will give you a constant steady supply, with the solar-panel keeping it charged.

You need an inverter

ifyou want to run mains AC devices.Not sure what you mean by a controller though?

L