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It's been 1 year since I installed Solar Panels  (July 7th, 2017), the numbers are in:

My 15 panel 4.2 kW Solar Array has saved me $ 1,435 this 1st Year.

This is 400 sqft (20' X 20') of roof with a Google Sunroof rating of 1,450 Sun Hours/Year. 

You can check your roof's available solar energy at https://www.google.com/get/sunroof

KEY FACTS

With any size solar panel installation the current Payback Period is 4 to 5 years.
Currently available Incentives mean you only have to pay 36% of the total cost.
You have a 1 to 2 year window to install panels at this 64% discount so start getting yourself up to speed. 
TIMING THE SREC CREDITS IS THE KEY.
The value of the electricity your panels will produce is easy to calculate.
 
And the 30% Federal Tax Credit is available through 2019.
The only challenge is working with your installer to lock in a good price for your Solar Renewable Energy Credits (SRECs).
To do this you need to have everything else in place. Use this site to educate yourself on how solar works, get at least three solar panel quotes from different local installers, then select an installer and be prepared to move forward.
 
SRECs are the most complicated part of panel financing but well worth it since they cover about 40% of your installation cost. 
 
Having the solar panel installer setup your SREC contract greatly simplifies the effort.
 

Naperville, Illinois

Every square meter receives 1,500 kWh of solar energy per year.

MATERIAL SELECTION

With this roof being visible from the street, all black panels/frames, racking and flashing were selected. All black panels are 20% less efficient than regular panels but it was decided the added curb appeal made this trade-off worthwhile.
                BILL OF MATERIALS
15 Solar Panels ( 280Watt - All Black )
 - Canadian Solar (Model: CS6K-280M)
 
15 Power Optimizers (Frame Mounted)
 - SolarEdge (Power Optimizer)
Inverter (Converts DC to AC)
 - SolarEdge (Model: SE3800A-US)
Roof Connection (Black Flashing/Post)
 - IronRidge (Model: FM-FF2-001-B)
Racking (Black Rails and Skirt)
 - IronRidge (Model: XR Rail)

Knoch Knolls Nature Center, Naperville, Illinois

72 Panels @ 260W/Panel = 18.7kW System)

Supplies 13% of the power needed for the building

RETURN ON INVESTMENT (ROI)

 
$ 13,000 = The total initial cost before incentives. 
  $  9,100 = Cost after this years 30% Federal Solar Tax Credit ( Saves me $3,900).
  $  4,700 = Cost after my 1st 5 year SREC contact that pays me $220/quarter. ( Saves me    $4,400). 
  $          0 = Cost after 7 years and a few months I will have generated $4,700 worth of electricity.
  $ 600->900 = Then every year the panels will continue to generate at least $600 worth of electricity.
Graph showing Solar Panel Payback Period.
PAYBACK PERIOD

Here is a graphic representation of cash flow from installation through the 25 year life expectancy of the panels.
You'll notice that in addition to generating your own electricity there are two critical sources of income. 
Federal Tax Credit 
You will deduct 30% of the Solar System cost from your federal taxes. (2017/2018)
Solar Renewable Energy Credits (SREC).
Ensure your solar installer sets up your initial SREC contract as part of your installation contract.
Learn more about SRECs here.
The combination of Federal Tax Credit and SRECs gets your payback period between 4 to 5 years. If these two credits were not available it would take around 22 years of generating your own electricity to pay off your panels.

KEY CONCEPT YOU SHOULD UNDERSTAND

You will frequently hear references to the SIZE of a solar array. Usually somewhere between 4 to 10 KiloWatts for residential installations. This is NOT the amount of electricity the array will produce in a year. This number IS the amount of electricity the array will produce in just 1 hour of full sun. To determine the arrays yearly output you need to multiply this array SIZE by the number of hours of full sun available in your location in a year. For my roof this is around 1464 kWh/Year.
So my 4.2 kW Solar Array X 1,464 kWh/year = 6,149 kWh/Year of Electricity.
How do you know how much money you'll save?
Collecting Solar Energy is just like collecting Rainwater. 
Collecting Rainwater
If you multiply the size of the bucket by how frequently it rains you can determine how many gallons you can expect to capture a year.
Bucket Size (5 Gallon) X Annual Rainfall (25 Gallons) = 125 Gallons
 
Then multiply this by the amount you pay for a gallon of water to determine your savings.
125 Gallons X Cost of a Gallon ($ 1.50) = You Saved $ 187.50
Collecting Solar Energy
If you multiply the size of the Array by how frequently the sun shines you can determine how much energy you can expect to capture a year.
Array Size (4.2 kW) X Annual Solar (1,464 kWh = 6,149 kWh
Then multiply this by the amount you pay for a kWh of electricity to determine your savings.
6,149 kWh X Cost you pay per kWh ($ .1135) = You Saved $ 698
Link to find your: Annual Solar Energy
NOTE: 
For accurate collecting capacity calculations, always reduce the Nameplate Array Size (In this example 4.2kW) by 22%. Panels on a roof get hot and so are less efficient (-9%), converting Direct Current to Alternating Current and a few other factors (-13%) are what accounts for this 22% reduction.  

Nike Sports Complex, Naperville, Illinois

45 Panels @ 270W/Panel = 12kW System)

Supplies 30% of the power for Nike Sports Complex

 

KNOWLEDGE IS POWER

I've organized everything I've learned about Solar Energy in these first four sections.
It's best to read them in order starting with "Roof Assessment" then "Energy Production", "Utility Interaction" to "Payback Period".    

North Central College, Naperville  Illinois
Residence Hall/Recreation Center (Res/Rec)
1,632 Panels @ 330W/Panel = 538kW System
Supplies 22% of the power for the building.