Microturbine See Also: Combustion Turbine Small combustion turbines (25 to 100 kilo-Watts), mass-produced at a low cost, combine the reliability of commercial aircraft auxiliary Power systems (onboard electric generation - see Generator) with some of the design and manufacturing techniques used in automotive turbochargers. In three to five years, from August, 1996, they could provide reliable, low-maintenance power to meet onsite electric demands in the commercial sector for under $300/kw. Since they lower efficiencies than standard combustion turbines (28 to 32 percent), their application could prove vulnerable to significant Natural Gas price increases. Microturbine Update from the August, 1997 issue of Electric Light & Power Gas-turbine powered generators ranging in size from 25 to 250 kW will provide the electric power industry with a variety of opportunities to meet the challenges of the deregulated and competitive market. These Microturbine generators have a low initial cost and are highly efficient, multi-fueled, reliable and lightweight. Distributed generation will enable Distribution utilities—especially the rural electric industry—to reduce the traditional cost of service by skillfully integrating small gas turbine generators into the distribution system to reduce, avoid or defer traditional generation, bulk transmission and distribution upgrades. In addition, distributed generation will enable utilities to expand their services to include providing baseload power, thermal Energy and or value-added energy services to existing and new customers. History of GT Engines The use of small gas turbine generators is not new. It has more than 25 years of field experience. Allison Engine Co. (a division of Rolls Royce) initially developed small gas turbines in the 1960s for ground transportation. The first major field trial began in 1971 with the installation of Allison GT404 turbine engines in six Greyhound buses. By 1978, the six buses had logged more than a million miles and the turbine engine was viewed by Greyhound management as a technical breakthrough for intercity coach transportation. Other systems were developed for the U.S. Army Patriot Missile System and military installations at Aberdeen, Belvoir, Elgin and White Sands. Some of the benefits of these GT generators include: fuel consumption reduced from 48 gal hr to 16 gal hr compared with previous generators; frequency stability at rated load at 0.1 percent; free shaft starting to minus 50 F without Heaters; multi-fuel capability (natural gas, diesel - see Diesel Engine, Propane, ethanol, alcohol, JP, gasoline); reliability requirements met; and Sound level requirements of less than 90 Decibels. GT generators for distribution systems are being developed by International Power and Light in association with Allison and General Electric Co. (GE). GE will design the controls and inverter and will be responsible for site Engineering, installation and field maintenance. The power plant has a single shaft with the generator, Air compressor and turbine mounted on air bearings which require no lubrication. The power electronics converts the high frequency alternating current to direct current. An inverter converts the dc power into either 480 Volt, 3-phase, 60 Hz Alternating Current (AC) power or 230/400 V, 3-phase, 50 Hz ac power. The 25, 50 and 250 kW plants can be online in a matter of hours. They can be installed almost anywhere—on a pole, platform, in a Substation, roof, vault or pad. Maintenance costs are low at less than $0.005/kWh. Mean time between overhauls exceeds 30,000 hours. The units are virtually vibration free and have a small sound signature. The small size and light weight of the GT generators enables a utility to install the units at almost any location and to implement centralized maintenance procedures. The units needing maintenance or repair can be replaced at the generation site and brought into a central shop. Even the 250 kW unit can be carried in a pickup truck. The estimated installed cost per kW for the 50 kW Microturbine power plant is about $350 and the 250 kW unit is about $225/kW. Operation is simple. The power plants are fully dispatchable (see Dispatching) from a central operating center via any two-way communication link or they can be monitored and controlled locally. Low maintenance and overhaul expenses are less than $0.005 per kWh which includes a major overhaul every 30,000 hours or about every three to four years. The power plants have air bearings so no lubrication is required and they are also air cooled so no liquid cooling system is required. Exhaust heat rates may be used to estimate the capability of the units to provide Water heating, space heating, absorption Refrigeration, absorption space cooling and heat for industrial processes. Firm power case studies show that a 250 kW load can be served by six 50 kW units with a total investment of $105,000 and annual costs of $54,238 at $0.0496/kWh. A 750 kW load can be served with four 250 kW units for an investment of $225,000; an annual cost of $152,091 for $0.0464/kWh. In each case, the annual load factor is 52 percent and installing one generator more than is needed to meet the peak (see Peak Demand) load provides 100 percent contingency. Amortization is over 20 years at 10 percent interest. Maintenance is calculated at $0.005 kWh and with a natural gas fuel cost of $2.65/1000 cubic feet. Firm power at less than 5 cents/kWh is competitive with most power from central station generators delivered over traditional T&D facilities. The cost of power for these cases rises to a little more than $0.09/kWh with diesel fuel at $0.85/gal which is still competitive in many areas. The efficiency of the small gas turbine supplying only firm power is approximately 30 percent. Efficiency can be increased to about 75 percent as a cogeneration project using the exhaust heat for heating water, absorption refrigeration or cooling, space heating and industrial processing. As a cogeneration application, the project can be economically feasible even with more expensive fuels such as diesel. Peak shaving using demand-side management techniques have been used for more than 50 years. However, controlling customers' loads has not been very successful from the standpoint of economics or customer relations. Small gas turbines will enable utilities to shave peaks economically and at the same time provide capacity for emergencies. Shaving peaks will increase overall system efficiency, which will reduce investments in traditional generation, bulk transmission and distribution facilities. Shaving peaks will also enable a utility to serve incremental loads growth in areas where there is a shortage of substation and or distribution feeder capacity. Incorporating Technologies During the past 50 years, three major products were developed which have enabled utilities to increase the efficiency of the distribution system: mobile radios, capacitors and computers. In all three cases, it took the utility industry many years to adopt these products because they were new and in those days, there was no real incentive to increase efficiency. The rural electric utilities were the ones that finally took the lead in applying these technologies. Today, all utilities have many incentives to increase efficiency— including survival. Deregulation has unleashed a multitude of organizations that are poised to skim the cream off the crop of customers and to take over the most lucrative customers and service areas. They include electric and gas utilities, independent power suppliers and energy service companies. The availability of small low-cost, highly efficient gas turbines provides the utility industry with a fourth technology to improve efficiency. Any utility can become an independent power supplier or an energy service company to provide these services: firm power to isolated communities, commercial centers and industries; peak shaving for utility systems to reduce the incremental cost to serve additional loads; peak shaving for large commercial and industrial establishments to reduce demand charges; standby and emergency power; and uninterruptible power supply (UPS).