Before you begin your project, you’ll want to make sure that you can produce enough energy to make your project pay for itself, sooner rather than later. How much solar energy watt power do you need to cover around half of your power bill for example?
This is how you calculate it…
Step One – Find Our Home Much Power You Use
In order to calculate this, you need to get your annual power bill and divide by 12 months in order to get your monthly average kilowatt hour (kWh) use. Remember that in winter you are going to use more than in summer for some areas and so your usage is going to fluctuate. If you only have a monthly bill, then you can use that and round it up if you think that you are going to use more later in the year.
Now you will want to divide your monthly usage by 30 for an average daily power usage amount. If your monthly usage is 840kWh, then your daily will be 28kWh per day.
If you want to produce enough energy to cut your power bill in half, then divide this amount by 2 and that is what you will want your panels to produce every day ie 14kWh per day.
Step Two – Calculate How Many Panels and What Watts You’ll Need
You will need to find out how many hours of direct sunlight you get in order to calculate this amount. You can find this out by checking out the solar insolation map. Once you know how many hours you will receive, you will then devide the number of daily kWh you need by this number.
Lets say for example that you live in California and have 5-6 hours of direct sunlight a day. Taking an average of 5.5, you now divide your 14kWh by 5.5 and you get 2.54
In order to compensate for any loss of energy through wiring, batteries and your inverter, multiply the amount you have by between 1.15 and 1.25
2.54 x 1.25 = 3.18kWh or 3180Watts per day
This means we need solar panels with the capacity to produce at least 3180 Watts of power.
Step Three – Calculate the Costs of Your Solar Panels to Produce This Energy
Let’s take a look at how much it would cost to buy these panels and then how much it will cost to build these panels. To buy panels in the US, the cost is around $4.90 per Watt.
If you need to produce 3180 watts at $4.90 = $15,582
If you are going to build your own your costs per Watt are around $1.66 which means that your cost for generating 3180 watts of energy is $5,278.80.
This still sounds like an awful lot of money, until you take into consideration all the tax brakes you’re going to get.
Step Four – Offsetting Your Tax and Getting Incentives.
Renewable energy tax incentives went into effect on 1st January, 2009. This means that in California, you would receive a tax rebate of around 20% as well as a federal tax rebate of 40% of the rest of the costs.
In our example that means that if you build your own panels, you would be receiving tax credits and rebates in the amount of
$5,278.80 -20% = $1,056.76
$4,222.04 -40% = $1,688.82
Leaving a cost of $2,533.22
This is of course a very rough example of how to calculate your solar panel costs, and should only be used as a rough estimate, but it is possible to see how the savings mount up and when taking into consideration other factors such as offers given by individual power companies as well as sourcing cheaper components, you can easily cut your costs even further.