It's not always 10 years to pay off a solar power installation.
Here is a
solar payoff calculator: http://www.solar-estimate.org/oemestimator?oemid=791 which I got from this website
http://www.altestore.com/howto/Tools-Calculators-Reference/Solar-Payback-Incentive-Calculator/a65/Use the calculator above to find the ROI, return on investment, of your solar panels. Use different numbers to get a better feel for how long it would take to pay off your solar panels. It can even change its calculations if you have to take out a loan for all or part of the solar costs.
Think of three scenarios
1. Completely replacing all your electricity needs with solar panels
2. Just using solar to keep your peak usage low (so you stay in the cheapest rate category)
3. Replace your current vehicle with an electric vehicle and use solar panels to provide enough energy for your vehicle
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1. Completely replace all your electricity needs with solar panels
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Take the number of kilowatt hours (kWh) you use from the month with your highest electric bill, divide that by 150 and that is the size of solar system you will need (in kW, kilowatts). Note: 5 hours of peak sunlight per day, 30 days per month, which gives you the 150 figure.
For example, you used 1500 kWh during the month when you had your highest electric bill so take 1500 and divide by 150. That equals 10, which means you would need 10 kW of solar panels to make all the power you use. Go to the calculator link at the top of this post to figure your payoff. Your numbers will be different so do the calculation based on your situation.
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2. Stay in the cheapest rate category
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Very similar to #1 with the exception that once you find your highest use figure (1500 in the example above) you then contact your electric utility to find out what their tier system is. Most utilities charge you a smaller rate per kWh if you use less power. Find out the maximum number of kWh you can use and still be in the lowest cost tier for your electricity and subtract that from 1500, use that figure and divide by 150 to find out the size of solar you need (in kW).
For example, say your utility charges its lowest rate for usage from 0-400 kWh per month. Subtracting 400 from 1500 yields 1100, divide that by 150 and you find that you will need to purchase 7.3 kW in solar panels. Do the math using numbers from your own situation to get the actual size of your solar panels needed.
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3. Drive an electric vehicle using clean, green solar power
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This one's a little bit more complex only because you have to calculate and compare two different things, the monthly cost of gasoline for your current vehicle and how much solar you would need to fuel your new electric vehicle that replaces it.
Gasoline expenses can be calculated a number of ways. The easiest is just adding up all the receipts from your gasoline purchases per month, some people use a gas card so you get the statement at the end of the month but however you do it you need to figure out how much money you pay for gasoline.
For the purposes of this example I'll start with the number of miles a hypothetical person drives per day, multiply that by 22 (the number of days you drive per month) to get number of miles driven per month. Divide that by the average gas mileage of your vehicle, multiply that by the price of fuel in your area and you get a rough idea of the cost of fuel per month. Phew! So assuming 40 miles per day we get 880 miles per month. His hypothetical car gets 26 miles per gallon and pays $2.80 per gallon for gas so 880/26 and multiplied by 2.80 equals $94.76 but let's just round up to $95. That is this made-up guy's gasoline expenses per month.
Here comes the hard part, figuring out how many kilowatt hours you need per month to drive an electric vehicle. Which electric vehicle will you use? A Chevy Volt or Nissan Leaf uses 200 watt-hours to drive one mile, which equals 5 miles per kilowatt hour(kWh). The original Toyota Rav4-EV uses 300 to 350 watt-hours per mile, 3.33 to 2.86 kWh per mile. A Tesla roadster uses... awww who am I kidding. If you've got to calculate how much solar panels would cost then you don't own a Tesla. Let's take the Nissan Leaf in our example, 5 miles per kWh.
880 miles divided by 5 gives us 176 kilowatt hours used per month for driving our hypothetical EV. Divide that by 30 days in a month (the sun shines even on days you don't drive) and you'll need 5.87 kWh per day. Given 5 hours of peak solar per day we find that we need only a 1.2 kW solar system to drive on sunlight.
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Here is an interesting site that calculates your dollar savings if you drive a Volt, Leaf or Tesla Roadster.
http://www.dteenergy.com/residentialCustomers/productsPrograms/electricVehicles/eVCalculator.html