The history of power conversion can be traced back some 4000-years ago with small-site installations involving water wheels doing some form of mechanical work. Crude forms of windmills appeared during a later period. While the combustion of biomass to raise steam first appeared in ancient Egypt, the first practical uses of steam power began during the early 19th century. The development of electrical generation and transmission technology during the late 19th century resulted in the development of large-scale power generation installations. Economy of scale involving higher efficiency and less manpower per megawatt of output gave the mega-power installations the competitive edge over most small-scale power generation installation.
Except that small-scale power generation never quite disappeared. Ongoing research and development by hobbyists, enthusiasts and companies that directed marketing efforts at the small-scale power market continued throughout the 20th century. By the late 20th century these efforts resulted in the appearance of more efficient small-site technologies such as low-power water turbines of under 1-megawatt output that can operate at over 80%-efficiency. Several new small-scale thermal power technologies have appeared that show future promise. A partial list of technologies includes small-scale nuclear power generation.
Toshiba of Japan recently unveiled a micro-reactor fuelled by an isotope of lithium-6 that could generate 200-Kw output for up to 40-years and with a byproduct that would be free from radiation. The Toshiba technology could operate as a co-generative technology that can provide heat for a building during winter, or use the exhaust heat to energize an absorption refrigeration air conditioner system during summer. An American research group claims to have developed a method of directly generating electric power for a period of up to 28-years from radioactive isotopes and without using a reactor. The Strontium 90 byproduct is expected to be free from radiation.
Research is underway in other radiation-free nuclear technologies that involve the fusion of boron to isotopes of carbon or to protons. One byproduct would be the metal element beryllium that can be chemically bonded to any of oxygen, nitrogen or aluminum oxide to form a metallic compound with high specific heat. A future generation of thermal storage compounds and mixtures may involve oxides, nitrides, and aluminates of beryllium.
The Hyperion Energy Group has developed a prototype small-scale reactor and power system of 25-Mw of output. The compact system can be transported in a highway semi-trailer of railway car. A single installation can be housed underground on the premises of a single large industrial property or single large industry that has large demand for electric power. It can provide heat or the combination of heat and power. There would be enough heat from the latter concept to energize a water-based steam-vacuum refrigeration system that could cool water to 5-deg C (41-deg F) and provide cooling for a campus of buildings during summer. The cost of leasing and operating such a unit is expected to be cost-competitive with grid commercial power rates. The manufacturer plans to exchange the unit every 5 to 8-years when they plan to recharge exhausted units at their factory.
Cost competitive small-site power generation involves a range of technologies that includes fossil fuels and renewable energy. A new range of micro turbine engines of up to 250-Kw and even up to 500-Kw of output is presently being tested. These units can operate on a wide range of liquid and gaseous fuels. Many buildings in large cities in the NE USA already have micro turbine engines of up to 100-Kw of output installed in their basements and capable of providing back-up power during severe weather and when grid power is unavailable.
Several externally heated engines of under 100-Kw of output are being researched while others are under development and being tested. Companies such as Enginion and Amovis in Germany and Cyclone Engines in the USA have undertaken pioneering work in developing a new generation of small-scale reciprocating engines that operate on supercritical steam of some 4000-psia and 1200-deg F. The thermal efficiency of these engines is on par with that of a modern commercial diesel engine or thermal power station. The exhaust heat can either provide heating for a building or it can drive absorption refrigeration cooling technology.
These new generation steam engines compete directly with an evolving new generation of Stirling-cycle engines, thermo-acoustic engines and evolving solid-state thermoelectric power conversion. The two latter engine concepts involve using fewer moving or sliding mechanical components than the former. Thermo-acoustic engines involve converting heat to low-frequency standing sound waves in a pressure chamber. One solid-state variant can convert sound waves to some 2-Kw of electric power at over 30% efficiency. A larger variant can produce some 50-Kw at over 40% thermal efficiency where the standing sound waves energize a linear alternator.
The thermal conversion efficiency of traditional solid-state thermoelectric technology has for several years rarely exceeded 6%. However, new research being undertaken by groups such as Johnson Electromechanical in Texas promises to raise that level of efficiency to over 30%. The promise of cost-competitive, efficient, solid-state thermoelectric power conversion operating on concentrated solar thermal energy or biomass combustion would have widespread application in many countries.
Several companies and groups have made grade strides in reducing cost and raising efficiency is solar and wind technologies. The cost of solar photovoltaic technologies has been dropping per kilowatt of output for several years and the trend may be expected to continue into the long-term future. New generation concentrated solar PV power competes directly with new developments in concentrated solar thermal power generation and that trend may be expected to continue into the foreseeable future. Photovoltaic windows will likely appear in office towers and high-rise apartment buildings within the next decade.
Numerous advances are underway in coastal and offshore oceanic power involving wave conversion technology and kinetic turbine technologies that convert power from ocean currents and tidal currents. Suitable waves occur off the American east and west coasts. While some offshore ocean wave installations may be extensive, there are locations where shore-based installations may serve the electrical power needs of small neighborhoods or small groups of buildings. Kinetic turbines may be placed at the mouths of numerous small ocean inlets or in fast rivers and streams of suitable depth to generate local power for small communities.
There has been ongoing research and development in high-altitude wind power conversion. Skypower, Makani Wind Power and Magenn Power are all testing and evaluating airborne technologies that carry electrical generation equipment aloft. The Makani group proposes to install wind turbines on to kites. Research from Delft University in the Netherlands involves a concept known as a ladder-mill that involves the movement of a series of kites to draw energy from winds at over 1000-ft elevation. The ladder-mill uses ground-based electrical generation equipment.
Kite enthusiasts who build super kites that involve multiple control lines and stacks of super-kites have begun to apply their expertise to high-altitude wind power conversion using ground based electrical equipment. Adjusting the kite control lines changes the kites' angle of aerodynamic attack and also changes the tensile force on the control lines. The control lines of multiple groups of kites are linked to winches and one-way clutches that drive a drive shaft and electrical generation equipment. Some groups of kites pull outward while other groups of kites retract in an ongoing repeating cycle. Kite wind power is projected to become a cost competitive technology.
Economic regulation of affordable, cost-competitive small-site decentralized power generation would be quite unnecessary. The demand for electric power is expected to greatly increase in many nations one the current economic depression is resolved. The post-depression period would likely be a period of economic growth where more generation capacity will have to be brought on line. Small-site decentralized generation could grow rapidly during an absence of economic regulation and can co-exist with mega-power installations in an expanding electric power market. The very nature of small-site decentralized generation technology encourages the kind of market competition that would keep power prices competitive.