Page 200 - Solar Power in Building Design The Engineer's Complete Design Resource

170 ENERGY CONSERVATION

daylight sensors and occupancy sensors located throughout the area. The goal of the
control architecture is to maintain a lighting nominal level with the use of maximum
daylight whenever available
The strategy of the lighting control system is to provide optimum energy efficiency.
This is achieved by a prioritizing scheme to make use of maximum daylight from the
skylights, harvest the maximum power from the solar panels, and finally provide a
fallback to grid power whenever daylight harvesting and solar power is not sufficient
to maintain the lighting energy requirement.
A number of factors that contribute to the value of this system include the following:

■ Using the electricity generated by the solar panels to power the lighting eliminates
significant inverter losses and improves efficiency by as much as 20 percent.
■ The low voltage control capability of the dc ballasts enables the innovative control
system to be installed easily, without additional ac wiring.
■ Roof-integrated solar panels reduce installation costs and allow the cost of the roof
to be recovered using a 5-year accelerated depreciation formula.

Performance—Occupancy and

Daylight Sensors

Most of the lighting comes on at 3 a.m. All lights are turned on from 6 a.m. to 6 p.m.
The blue line shows the lighting load with the occupancy and daylight sensors con-
trolling the lighting. Between March and mid-June 2005 about 20 to 30 percent sav-
ings have been achieved due to the controls.
An example of energy savings is shown in the following table:

Saved with controls % kWh Saved kWh saved $
$497.02 March—05 4970
31%
$345.80 April—05 3458
22%
$342.85 May—05 3429
22%
$324.75 June—05 3248
30%
$1,510.43 Total 15,104