Page 100 - Piston Engine-Based Power Plants

The Economics of Piston Engine Power Plants 91

Table 9.1 Cost and Efficiency Figures for a Series of Reciprocating Engine Systems
Capacity (kW) Total Installed Cost ($/kW) Engine Speed (rpm) Efficiency (HHV, %)
System 1 100 2210 1800 28.4
System 2 300 1940 1800 34.6
System 3 800 1640 1800 35.0
System 4 3000 1130 900 36.0
System 5 5000 1130 720 39.0
Source: US Environmental Protection Agency.

the megawatt and multi-megawatt range. All these larger engines are
built to be able to operate for long periods between maintenance. They
are generally more efficient than the smaller engines too, so their oper-
ating costs are lower.

Table 9.1 shows figures for a range of generic power generation sys-
tems based on reciprocating engines which illustrate these trends. The
costs in this table are in 2010 dollars. (Figures from the US Energy
Information Administration suggest that costs for engine-based distrib-
uted generation systems rose by around 8% between 2010 and 2016.)
The smallest system in the table, with generating capacity of 100 kW,
is based on a high-speed engine operating at 1800 rpm. Efficiency is
28.4% and the cost is $2210/kW. At the other end of the scale a 5 MW
system is based on a medium-speed engine running at 720 rpm. This
has an efficiency of 39.0% and an installed cost of $1130/kW.

The cost-effectiveness of most systems such as those in the
table above will depend on whether they can be used to supply heat as
well as electrical power. All the above systems were assessed for their
cogeneration efficiency when providing hot water. The most efficient
were systems 2 and 3 with overall efficiencies of 78% and 79%, respec-
tively. The least efficient was system 4 at 73%.

The cost of Stirling engines is much higher than for most internal
combustion engines because they are not produced in large enough
quantities to bring about the economy of volume production.
Estimates vary widely, from as low as $2000/kW to as high as $50,000/
kW. The cost of a domestic Stirling engine CHP system with a generat-
ing capacity of 1 kW appears to be around d2000, although accurate
figures are scarce.