Page 387 - Sustainable On-Site CHP Systems Design, Construction, and Operations

360 Ca s e S t u d y 4

Electricity consumption $0.10 per kWh
Natural gas $0.35 per m 3
Steam $14.33 per klb
Chilled water $9.18 per MMBtu or $0.11/ton-h

TABLE 22-4 Baseline Utility Rates

Utility Rates Used for Analysis
The rates in Table 22-4 are used in the analysis to determine the break-even point
between the proposed scenarios. The electricity and natural gas rates shown are for
utilities imported by the campus, and the steam and chilled water rates shown are for
utilities distributed by the CUP to the campus facilities.

Equipment Modules for Economic Analysis
In order to compare the economics of different equipment combinations, the cost and
revenue are determined for each equipment type. These values correspond to a period
of 1 hour, assuming constant campus loads.
As shown in Table 22-5, when the duct burner is not fired, at the baseline gas price
3
of $0.35/m , one cogeneration unit will consume 1710 m of gas worth $598.50 in 1 hour.
3
The cogeneration output for 1 hour will be 4700 kW of electricity plus 25,000 lb of steam.
The delivered electricity rate is $0.10/kWh, and the steam output is valued at $14.33/
klb. In the break-even analysis to follow, the gas cost appears as an expense, and the
electricity and steam values both appear as revenues.
Using the electricity and gas utility rates noted in this case study, the cost of generat-
ing steam by one cogeneration unit can be calculated as follows:
(1710 m × $0.35/m − 4700 kWh × $0.10/kWh)/25 klb = $5.14/klb of steam
3
3
Note, this is the utility cost only, without the fixed costs or other operation and mainte-
nance cost.
Should there be no concurrent demand for the steam generated from cogeneration
waste heat, the steam is assigned a value of zero, and the cogeneration plant would run
as a simple combustion turbine generator. The cost of generating electricity this way,
without fixed costs or other operation and maintenance costs, would be $0.127/kWh
($598.50/4700 kWh). This cost is considerably higher than the locally available electric-
ity market price, and they underline the need for a beneficial use for the steam from
cogeneration in order to achieve a CHP plant competitive advantage.

Cogeneration Unit, without Duct Burners
Gas input 1,710 m 3
Electrical output 4,700 kW
Steam output 25,000 lb

TABLE 22-5 Cogeneration Unit Parameters