Total Roof Area and Area Suitable for Solar - Estimated
from a countywide 2006 Solar Radiation model. The model calculates and ranks incoming
solar radiation every 25 square feet in the County, using roof pitch,
orientation, and shading from surrounding structures and trees to provide the
best estimates possible.
Potential System
Size - calculated from the optimal roof area and panel specifications. Our
calculations are based upon the SunPower 225 panel delivering 207 w/m2.
Potential Annual
Output - 1,490 kWh per installed kW. This is calculated by multiplying potential system size by 5.3 hours of generation per
day and a 77% de-rate factor which take into consideration electrical losses and other environmental factors like soiling.
Potential Cost
Savings - Potential Cost Savings are calculated for each utility, based
upon selected rates for each utility.
Potential Annual
Emissions Savings - The carbon dioxide emission reductions for Southern California are 724 lbs of carbon dioxide reduced for every MWh of
solar electricity (CA Climate Action Registry General Reporting Protocol,
Version 3.1, Table C.2 - CO2 Emission Factors by eGRID Subregion).
Figure 1 - Solar Radiation Model
Solar Model
The model was generated from high-resolution imagery and
elevation information acquired in 2006 by the LAR-IAC (Los Angeles Region Imagery
Acquisition Consortium). LAR-IAC included roof-top and ground elevation
every 5 feet, and 4-inch color and infrared photography.
The Solar Radiation Model calculated solar insolation
(amount of sunlight) every 5 feet in the county using the "Area Solar
Radiation" Analysis tool from ESRI (Environmental Systems Research Institute).
Building roofs were modeled by finding all locations where the height was
greater than 8 feet and the NDVI (Normalized
Difference Vegetation Index) had a value that did not represent vegetation
(< 0.1).
The amount of insolation was ranked based upon estimated
payback times, and those areas of the roof that are suitable for solar are used
to calculate other estimates. Payback times are complex to determine, and
depend upon factors such as solar panel models, their angle, system losses, and
financing, to name a few factors.
Your solar installer will be able to give more detailed
estimates based upon your specific situation, but the solar portal provides
generally accurate guidelines of what you can expect.
See the table below.
|
Rank
|
Raw Solar Insolation (kWh/m2/day)
|
System Payback (Years)
|
|
Suitable
|
>
4
|
<
15
|
|
Unsuitable
|
<
4
|
15+
|
For those looking to dive deeper, our assumptions are listed
in the table below:
|
Factor
|
Assumption
|
|
Panel
orientation
|
In-line
with roof
|
|
Panel Efficiency
|
18%
|
|
Conversion Efficiency
|
82%
|
|
Installation cost per watt
|
$10 before rebate
|
|
Energy costs
|
$0. 21 per kWh*
|
|
Rebate
|
50% of installed cost
|
Energy Costs vary between utilities and rate tiers (from
$0.11 to $0.33). We use the values from Glendale Water and Power (below) to estimate system payback times.
|
|
Tiers
|
|
|
1
|
2
|
3
|
4
|
5
|
6
|
|
Edison
|
$0.12
|
$0.15
|
$0.24
|
$0.29
|
$0.34
|
|
|
LA DWP
|
$0.11
|
|
|
|
|
|
|
Pasadena
|
$0.09
|
$0.10
|
$0.11
|
$0.13
|
$0.15
|
$0.17
|
|
Burbank
|
$0.10
|
$0.14
|
$0.16
|
|
|
|
|
Glendale
|
$0.15
|
$0.18
|
$0.21
|
|
|
|