Solar Power Design

When you’re installing your own solar power system, you’re going to need to know something about solar power design. That means you need to understand how much electricity you have to generate to power the load in question. This will give you an initial idea of the cost and viability of what you’re trying to do.

Lets say for instance you were out in a rural shack in Arizona in Summer and wanted to power a 1000 W air conditioner to keep cool. When dealing with solar power design, you always want to go with the ‘worst case scenario'. So let’s imagine that we need our air conditioner on 24 hours a day.

How much energy do we need per 24 hours then? It’s reasonably easy to calculate. 1000W x 24 hours = 24kWh. Let’s give ourselves some leeway and put in an extra ~25% to account for losses of power in the cables and general inefficiency considerations. This brings us to 30kWh.

>>Click here for a great solar power design guide<<

Next we need to figure out how much sun we’re going to get. This is known as insolation. In the Arizona region we get an average insolation of 7 kWh/m2/day in Summer (You can find details of these calculations on the web).

Now for our solar power design, we need to calculate how big a solar panel array we’re going to need to generate the necessary power. We need 30 kWh/day and a 1m² solar panel might give us about 100 W peak power. In that case we would need 30 m² of solar panels. However, Arizona only gets the equivalent of about 7 hours of peak power per day, so we need to multiply by just over 4 to be guaranteed our required 30 kWh per day, meaning 120 m². Quite a lot indeed, but this is a rather extreme case of needing a large amount of consistent power all day and night.

We need to store the vast majority of this energy for use in the hours of darkness. For this we need to know what sort of battery set up we need. We don’t want our batteries to go into deep discharge as you’ll know if you’ve ever left your car lights on for a long time; the battery is never the same afterwards. So we want to be reasonably kind to our batter array and only discharge it by say ¼ if possible. This consequently means that the battery should be able to hold 4 times what our heater will be drawing.

We showed earlier that we’ll be drawing perhaps 24 kWh/day after losses. We need this to be only ¼ of our battery’s capacity so let’s say we need a battery capable of delivering 100 kWh/day for our particular solar power design.

Now we need to convert from energy language to battery language. Batteries are normally rated in amp-hours so to convert back to Amps from Watts we need to know the voltage of our system. Let’s say we’re using a 24 V system. Our load is 100,000 Watt hours, so we divide by the voltage to get about 4200 Amp hours. Consider that an average car battery is about 50 Amp hours and you’ll see how big a battery you need to be ensured of being nice and cool in your cabin!

In this article we just wanted to show you the basic considerations and a back of the envelope calculation for a solar power design. There are much more detailed instructions on how to plan for your needs in the solar guide in the link below. Have a look at our page on solar savings to find out how much you can expect to save

>>Click here for a great solar power design guide<<

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