Connecticut PV Incentive: What’s PTC and how does that affect My Rebate?

The Connecticut Clean Energy Fund (CCEF), has a state rebate program that is based on the design efficiency of your system.  Typically an installer will calculate how much electricity your PV system will produce and compare it with a similar system under ideal conditions.  Then they apply a design factor to calculate the dollars per watt price.  A more efficient system will help maximize your rebate. 

Ideal conditions to maximize your rebate:

ü      Include having an inverter that is 94% efficient or better.

ü      There can’t be any shading on the site

ü      Panels must face solar south (plus or minus 20 degrees), and they also have to be tilted at a 35º angle. 

The maximum rebate for residents in Connecticut is $15,000, with a maximum system size of 10 Watts.  A maximum rebate will provide residents with $1.75/watt (PTC rating) for the first 5 kW and $1.25/watt (PTC rating) for the next 5 kW.  Rebates are paid based on PTC values.

STC Vs PTC

ü      STC or “Factory Standard Test Conditions,” uses 1,000 watts per square meter solar irradiance, 1.5 Air Mass and 25 ºC cell temperature. 

ü      PTC or “Photovoltaic USA Test Conditions,” deals with more of a real life condition.  PTC rates output using a condition of 1,000 watts per square meter solar irradiance, 1.5 Air mass, and a 20ºC ambient temperature at 10 meters above ground level and a wind speed of 1 meter per second. 

PTC = Real Life Conditions

As you can see the PTC rates output more effectively than STC.  The ambient temperature is a better standard than the factory conditions because silicon solar cells average almost 20ºC above ambient temperature in the real world and an increase in temperature causes cell voltage to decrease. 

PTC Accounts for Temperature

Also cell voltage drops .08 volts/ºC in places that exceeds 25ºC, which shows that the STC rating is not as efficient as the PTC.  Unlike STC, PTC takes account for the fact that the sun is only close to perpendicular for a limited time at high noon.  PTC also recognizes that at other times of the day the sun hits the panels at different angles.  While taking all of these factors into consideration, PTC averages the solar panels yearly output.  The PTC rating tends to be lower than the STC rating since it takes more factors into account, which gives future consumers a better indication of how the solar panels will hold up.  So when buying a solar panels the higher the PTC rating the better.