Environmental Engineering Reference
In-Depth Information
electricity. The following is a list of assumptions made for the purpose of
levelized cost estimation:
System rated power = 50 kW
System rated energy = 300 kWh per cycle
Number of cycles per day = 1
Number of days operating per year = 150
Operating lifetime of system = 35 years
System lifetime capital and operating cost = $300,000
System round-trip efficiency = 50%
Photovoltaic solar system levelized cost = $0.03 per kWh
The levelized cost of the stand-alone system is found by summing the total
energy (stored) over the lifetime of the system and then dividing the total
costs by this energy result:
(300 kWh) ∙ (150 days) = 45,000 kWh per year
(45000 kWh/year) ∙ (35 years) = 1,575,000 lifetime kWh
($300,000)/(1,575,000 kWh) = $0.19 per kWh stored
This result, a levelized cost of 19¢ per kWh, is higher than the cost of energy
from most generating sources. However, this cost cannot be directly com-
pared to generating costs because this system does not generate. The value
of the storage system lies in the ability to capture variable or low cost energy
and deploy it as needed.
FutureProspects
Underground pumped hydroelectric energy storage is a feasible means of
storing energy that has not been comprehensively analyzed. Further, no
UPHES system has ever been built. Research and analysis are desperately
needed to examine possible UPHES installations, both large and small.
Over the past three decades, enabling technologies needed for UPHES
have grown, matured, and become more efficient. These include excavation
techniques, high-head hydro machinery, and geologic analysis techniques.
Technologies developed to extract oil and coal deep below the surface
provide starting points for building UPHES systems. The current growth
of variable renewable energy that could greatly benefit from economical
