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An EPRI White Paper

DC Power Production, Delivery and Utilization

A PV-DC case study, distribution warehouse, Rochester, NewYork, continued

Figure 18 shows power from the DC solar system, along with the net utility power consumed by the lighting.Around noon, all of the power for the lighting is supplied by the solar array. An important element here is that the efficiency of solar to lighting is nearly 100%. Only minimal wiring losses are encountered when no grid power is used.

Value

The PV-DC application has been a successful effort for this distribu- tion center, which is dedicated to bringing more “green” and sustain- able business practices into its facility operations. The payback on their investment at the Rochester location, after rebates and acceler- ated depreciation, is approximately 12.6 years, as shown in Table 3.

Table 3. Payback on investment from DC-powered

lighting system

System cost after rebate

$72,000

Approximate power savings per year @ $0.10 per kWh

$4,000

Value of system accelerated depreciation, per year, for 5 years, at 30% effective CTR

$4,320

Simple payback

12.6 years

If in an area where avoided peak cost is $0.20 per kWh, then simple payback would be 5.84 years

Designers estimate that the system will produce energy for an ad- ditional 7.5 years, generating power valued at $60,000 at 2006 elec- tricity rates in Rochester. Note that in areas where the avoided cost of peak power is higher than $0.20 per kWh, the payback on investment can drop to under 6 years, meaning that, the facility would enjoy free peak power from the solar PV array for at least 14 years after the investment is returned.That equates to an $112,000 benefit at today’s rates. Either return-scenario grows in value as electricity prices rise.

Data and photographs for this case study courtesy of Nextek Power Systems.

Figure 18. Power consumption by DC lighting system

Frito-Lay Rochester Green DC lighting load shedding with daylighting & occupancy control

kWatts 35

Irradiance ( /m^2) or temperature °F 1,000

30

25

20

15

10

5

-

Net load shown to utility

900 800 700 600 500 400 300 200 100 -

Actual DC lighting load with load shedding Net utility required after load-shedding AND solar Daylight levels DC solar Lighting load without load shedding

0:00

6:00

12:00

18:00

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June 2006

Page 22

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