One of the toughest things for me to do, was to calculate the power that was needed every day for your Solar Powered System. I’m not sure why this was so hard for me, because once you understand how it works it’s pretty simple.
I find the simplest way to calculate power consumption is by calculating how many WATTS each electrical “whatever” takes. A 60 Watt Light bulb for example needs 60 Watts of Power PER HOUR while turned on. Most appliances don’t give the Wattage required, but do give the 2 components needed to calculate wattage.
Volts X Amps = Watts
Any kind of appliance that you plug into a wall socket in a regular powered home is either 120 volts (Which is the case for me, in Montreal, Quebec, Canada) or 230 Volts. (Europe, far off places I never had a chance to visit) . The amperage it takes will be written on the appliance. My Laptop Power supply says it has an input of 110-240 Volts (and I know HERE it’s 120) and 1.5Amps . 120v X 1.5a = 180 Watts per hour
It’s fun to calculate in Wattage because it’s universal, regardless of the voltage you’re running at. You must do this for every electrical thing you wish to have in your house. Calculate the wattage per hour, and then guess how many hours per day they will be in use.
Now to calculate how many Watts you have available from your battery bank. Lets say you have 4 X 6 volt batteries @ 225 amp. You have 2 ways of configuring the batteries, a 12 volt system @ 450 amps, or a 24 volt system @ 225 amps. Lets say we’re setting it up in 12 volt mode which means we have 450 amps to play with.
12volts X 450amps = 5400 Watts
Ok that SEEMS great, but in order to keep batteries alive for as long as possible, you’re not supposed to use more than HALF of their capacity. (Some people say not to discharge more than 20%!) Although I only recommend Deep Cycle Batteries (which means that they CAN discharge alot and recharge alot) it’s still in the best interest of the batteries not to drain more than %50. All this to say, we have 2700 Watts to play with. If you don’t have any heavy electrical appliances (Fridge, washer, Blow Dryer) 2700 Watts is pretty decent. Lets pretend after doing the math of what we want to power on Solar, that we need 2000 watts a day on average. So far so good, our batteries give us 2700 watts to play with, except after just a little over a day, we’ll have used all the wattage we have !! (without going into the “emergency” battery power that we’re not supposed to touch)
This is where the solar panels (or other power making devices) come in. The Solar panels are going to be our battery chargers. We said we need 2000 Watts per day, so our Solar Array needs to be able to generate atleast 2000 watts every day. Solar Panels are calculated in Watts also. A 100 Watt Solar Panel will generate 100 Watts of power going into your batteries, PER HOUR of peak sunlight. I calculate 4 hours a day of Peak Sunlight on average. (In Montreal, Quebec) To generate 2000 Watts of power every day (which is the minimum we need to generate) we would need 5 100 Watt Solar Panels. (We would therefore be creating 500 Watts per hour of sunlight X 4 hours = 2000 Watts)
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