Update on Distributed GenerationLynn Coles
R. W. Beck Co.
My definition of "Distributed Generation" (DG) is a generation source 1 KW to 5 MW in size which is located near to the load, or at least at weak points in the power distribution system. It is often is used to gain a benefit from both heat and power. Among the technologies currently included in DG are reciprocating engines, turbines, fuel cells, solar technologies, wind power, and inertial storage.
Reciprocating technologies include diesel and natural gas fired engines coupled with generators. This technology is fully mature, offers the lowest initial cost per KW, and is excellent for backup or peaking applications. Disadvantages include high maintenance, moderately high fuel costs, and high emmissions. A newer branch is Stirling engines, which have yet to gain popularity.
Among the Turbines used for DG are small combustion turbines (1000 KW to 10000 KW) and also Micro Turbines (only marketed by Capstone at 30 KW). The larger types are a fully mature technology, run on natural gas or liquid fuels, are excellent for peaking applications, and are very good for CHP (combined heat and power) utilization. They are competitive in cost and have better emissions than the reciprocating DG units. The micro turbines also run on natural gas or liquid fuels, but represent an emerging technology. Emissions are moderate, and efficiency is somewhat superior to other turbines due to the use of air bearings (reducing maintenance) and electronic rephasing of the power to 50 or 60 cycle from a very high frequency to DC initial conversion. Initial Cost per KW is higher than reciprocation, but lower than other currently competing technologies (about $800 / KW).
Fuel Cells are an emerging technology with lots of promise, but currently very high initial cost. 0NSI makes about the only commercially available units, but the cost exceeds $3000 per KW. Best points for this technology are the promise of very high efficiency (better than 50% as opposed to less than 35% for most competing technologies), and very "clean" operation (no bad emissions). A bank in Omaha uses a fuel cell system as failsafe support to its credit card operations and has had zero outages. Assuming they become popular and in "mass production" is is felt that PEM fuel cells may become comeptitive in initial cost with reciprocating engines in the future (< $500 / KW). If this happens, the efficiency and pollution advantages would make this the source of most promise and best overall economics.
Other technologies include Photovoltaic, Solar-Thermal engines and Wind Turbines. Generally these cannot be sited just "anywhere", so really don't fit my restictive definition of "DG". A couple that are truly independent of locationa are Hybrid (Fuel Cell with MicroTurbine), and Flywheel Storage. The latter is an excellent low cost solution to short term outage, while an engine generator is started. It shows lots of promise for hospitals and other places where brief outage is unacceptable.
In the short term there is very limited market for DG. Traditional power is generally too cheap for DG systems to compete. Exceptions are non-attainment areas, and other areas where power costs are high. The large market could develop if the "fuel cell" technology can deliver as promised giving great improvements in efficiency, emission and competitive initial costs. Today is is possible to obtain DOE money for demonstration sites. Federal plans for Demand Side Management will play a major role in the economics and development of the industry.
Current barriers to DG development include: Interconnection standards, Air emissions issues, High utility backup rates, utility contracting provisions, stranded costs issues for existing utilities, and a large "hassel factor".