# Living Building Energy Calculations

## Energy Calculations

### Solar Panels

Calculations of the site’s total square footage dedicated to solar panels include the roof structures of all buildings and levels.

100 SF of solar panel arrays is approximately 1,000 watts (1kWh per 100 SF). The following equation will be used to calculate the Solar Capacity of all panels on the CPAT site.

[System Watts] x [de-rate factor] x [days] x [SH] x [A corr]/1000 = kWh per year

where

System Watts = your array’s nameplate DC rating @ STC for each module (ex. 5 kW-DC = 5,000W)

De-rate factor = constant that accounts for temperature losses in more realistic environments other than STC (common factor is 0.77, but can be adjusted for specific sites)

SH = Sun Hours, measured in watts per meter squared per hours per day.

A corr= Azimuth correction from due south (1.0 if azimuth is 180 degrees or due south)

Sun Hours average found on solar insolation tables. It is presumed that the panels will be oriented due south, so 1.0 was entered for the azimuth component.

#### Calculations

100 SF = 1 KW;  therefore an estimated photovoltaic array square footage of 10,000SF would be equal to a 100KW size system.

Where:

(100KW)(0.77derating factor)(365 days/year)(4.4sun hours)(1.0az) = 123,662 kWh/year.

Producing enough energy to power 8.833 homes in one year. The average household in America consumes about 14,000 kilowatt-hours (kWh) per year, according to the Department of Energy.

### Digester

500 ft2 digester footprint is designed to handle 2,000 tons of feedstock or manure per year, and will produce 580,000 kilowatt hours of power annually. In addition, the plant’s combined heat-and-power unit will produce up to 2,000 million Btus of heat in a year.

### Wind Turbines

The Darrieus Turbine, vertical axis, medium sized. W find energy production increases exponentially with turbine size and height (in the hundreds of thousands of kWh/year), but 100 ft turbines with 500 m2 swept areas are not ideal for this site.

Swept-Area method

AEO =  (P/A) x (A) x (8,760 h/year) x (efficiency coefficient) x (1 kWh/1000 W)

where

AEO = Annual Energy Output

P/A = Power Density (wind power)

A = Swept Area (Darrieus rotor = 0.65 Diameter*Height)

Wind speeds at 66 ft above the ground are 160-200 W/m2, and swept area for small sized Darrieus Turbine is 4.9 m2 intercept, with a 20% energy coefficient.

AEO = (160-200 W/m2) x (4.9 m2 ) x 0.2 x (1 kW/1000 W)

AEO = 1375-1700 kWh/yr

Take the median of this calculation and multiply by 5 for the number of turbines on the site.

1537.5 kWh/year * 5 = 7689 kWh/year

### Combined Energy Totals

123,662 kWh/year + 580,000 kWh/year + 7,689 kWh/year = 711,351 kWh/year

#### Energy Needs

DOE 2008 data (page 119 of document): average energy cost per square foot is \$2.51

The site has a gross square footage of 60,534.

\$2.51*60,534 = \$151,940/year. Using the national average of \$0.09/kWh, it is estimated that the site will use 1,688,226 kWh/year.