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The Light is Green



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$ / kW·Hr

How much Energy do we need?

Putting numbers on real world questions.

This is even harder than the Power question... Just kidding.

That's because your energy usage varies with the weather, with the seasons, and how much is actually being done.  Fortunately the energy you need will always correspond exactly to the energy you ask for.  Let me clarify.  Your electric bill is a measure of the energy you demanded form the power company. They didn't care if you used 1600 Watts continuously for the entire 720 hours of the month or 4800 Watts for just 10 days.  They look at the product of power and time hence the kilowatt-Hour (kWhr) units of energy.

It's mostly the same for commercial users, except they use more, and they get bigger quantity discounts for the bigger purchases.  Sometimes big consumers will have to pay a time of day premium, making their day-time electricity more expensive than their night-time electricity.

Here's an interesting fact most folks don't realize.  There is a finite amount of energy you can get from the power company in any given time.  It's a lot, but it's still limited.  It's the rating of your main breaker box times the 720 hours in a month.  For a house that could be 10x more than your regular electric bill.  So, if your bill is ever bigger than that, call the power company... someone probably made an error.

What is the Length of an Average day?

We base our average estimates on an 8-hour day of sunshine.  We alter out panel spacing, increasing out footprint for a constant aperture to extend the time we capture full power.  It's a trade-off that we can adjust if your needs warrant.

What are Aperture and Footprint?

The "aperture" of the panels is the measure of the area that captures sunshine.  The "footprint" is the measure of the roof area that includes the aperture plus the spaces between the rows and columns of actual panels.

We compute a number of design criteria on the potential sunshine available on an hourly, daily, monthly and annual basis, which we determine from the product of the Aperture and the Average day, and we compute the total energy the system will produce over its lifetime using Days per Year and the number of years we expect the system to be in operation (of course we expect it'll last longer).

What are Days per Year in this context?

"Too much sunshine makes a desert." -- Arab proverb 

There are relatively few places on Earth that see 365 days of sunshine per year, otherwise we wouldn't be here...  We take a more conservative estimate.  We base our Energy Cost numbers on 240 days of sunshine per year, or cloudy for 1 out of 3 days.  Of course there are places that get less, but there are also places that get more.  It's just an estimate based on averages.





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Updated: 09/11/10 19:32