1880s solution - In 1879, only 11 years before my father was born, a direct current electric central station in downtown San Francisco was thought to be the optimal power supply system. It replaced on-site direct current ("DC") generators powering arc lights. It was the first central station power system, beating even Edison’s far better publicized Pearl Street station. Edison’s central station commenced service three years later in 1882 in the Big Apple. His central station also supplied DC but it supplied electric energy for incandescent light bulbs instead of arc lights.
Customers of Edison's central station in New York City at 255-257 Pearl Street could receive DC service for their light bulbs only if they were located within a half mile of the station. The DC technology could transmit electric energy only short distances at the low voltages safe for customers’ use. That is because it was very difficult and expensive to vary the voltage of DC electric power after it left the generator. You could transmit DC Power at a high voltage – using fewer amperes and thinner copper wires – and then step it down to a safe voltage at the customer’s meter with a high voltage DC motor and a low voltage DC generator, but it would be terribly expensive to do so.
Another DC central station was soon operating in London to serve loads within a half mile of No. 57 Holborn Viaduct. Gaslight company exclusive rights to dig in the streets prevented Edison from digging up the streets in London to lay his distribution feeders, but he discovered that the Holborn Viaduct had been equipped with channels and raceways in which the wires could easily be installed, much to the dismay of the gas companies.
Soon thereafter alternating current ("AC") central stations commenced operation in the US since when using alternating current, electric energy could be transmitted at high voltage over thin copper wires and stepped down to low voltage with an inexpensive transformer. Its deliveries were no longer limited to a half mile – electric energy could be transmitted economically for several miles. The higher the voltage, the further it could economically be transmitted. At today’s extra high voltage, energy can be transmitted for hundreds of miles.
I show here how the ability to transmit electric energy economically for many miles, coupled with the development of steam turbine-generators with great scale economies, led to a system of ever larger steam turbine generators fueled with coal or nuclear fuel supplying our base load electric energy requirements. Their sizes reached as high as 600,000 to 1.4 million kilowatts.
Why was this desirable? It was because these giant generating units could generate with far greater fuel efficiency and could be constructed for far lower cost per kilowatt. That was only advantage in generating power in one place and delivering it to another place many miles away to serve a load there. There are many disadvantages.
With distribution lines one could collect load at many points in a load center to be served from a single distribution substation, and with transmission lines from that substation to a generating unit one could collect load at many load centers. These remote loads could be served from that giant generating unit which enjoyed scale economies of fuel efficiency and cost per kilowatt of capacity. These considerations dominated power supply planning for the next one hundred years.
Then over the next twenty years when gas prices were only 40% to 50% higher than the price of coal per million BTUs, the aero-derivative gas combustion turbine and combined cycle system with technology borrowed from the airline industry took the lead in supplying base load energy. These aero-derivatives and combined cycles could generate even more efficiently in somewhat smaller unit sizes, 50,000 kW to 400,000 kW but still very large compared to typical individual loads or even the size of a typical load centers.
Power and Its Problems
The United States, after 120 years, now has the largest power system in the world, with a generating capacity of some 900,000,000 kilowatts with an impact on productivity that makes our standard of living among the best in the world. But it is beset with problems.
It is dependent on natural gas for a large part of its base load energy supply and the current outlook for natural gas is short supply and a price about 3 times as high as coal. That is so high relative to coal that some aero-derivative simple cycle gas combustion turbines are being mothballed and even the combined cycles are no longer competitive with the giant coal fired steam turbines.
The transmission system has not kept up with new generation and load since compulsory wheeling was first perceived as a threat in 1989 and then became a reality in 1992.
Restructuring has caused power flows to take new pathways off the backbone transmission designed in an earlier era when most power flows took place among the major generating plants owned by each utility in its service area and the major load centers of that utility, or over the ehv transmission linking the backbone systems of each member of a power pool.
The result has been cascading outages which black out major cities and large areas over several states. The exposure of the long transmission lines to the weather, can also, based on the experience of recent hurricane Isabel, black out millions of customers for period ranging up to one or two weeks.
Toxic pollution is causing state governments to litigate with the federal government and killing asthmatics and those with emphysema. Greenhouse gases threaten global warming. Transmission lines are snaking through the wilderness and threaten to invade suburbs in good neighborhoods such as in Southwestern Connecticut.
Litigation over NIMBY (not-in-my-back-yard) is becoming ever more prevalent as citizens protest the invasion of their neighborhoods by immense noisy, smoke belching coal fired power plants. Recently widespread blackouts have been caused by cascading generating plant and transmission line outages.
Just coming on the scene is a new form of power generation called the stationary “fuel cell”. It works like a battery except instead of being recharged with electricity, it requires only to be refueled with natural gas or some other fuel, usually a hydrocarbon which contains hydrogen that can be released during reforming. (Automotive mobile fuel cells will likely consume pure hydrogen.)
Instead of burning fuel in a Carnot cycle to generate power, it converts hydrocarbons to electric energy and heat by an electrochemical reaction and as a result has drastically lower emissions of toxic pollution. Because it is more efficient in converting hydrocarbons to electric energy or electric and useful thermal energy, it will significantly reduce emission of greenhouse gases per kilowatt hour of energy generated.
The emergence of this new type of generation may change the optimal system design back to generation designed to supply individual load centers or even individual load sites – perhaps with DC electric energy.
A discussion of the optimal system of generation, and how it has changed over time, together with how it works, will set the stage for discussing what will be the optimal electric power system design for the 21st Century.
Part II Continued Next Week....
blog comments powered by Disqus