It would ultimately be less expensive to do a combined cycle facility to produce 1000 Megawatts. You would be cutting the number of gas-turbines by more than 1/3 to generate say 600MW+/- and making up the difference with the waste heat boiler(s) / steam turbine(s) capacity for the other 400MW+/-.
If you want to talk about 'expensive', a stand-alone, self-contained gas-turbine generator MobilePac would certainly qualify. mobilepacusa.com Your're going to need 40 of them (..at 25MW each..) to produce 1000MW. Each of the P&W mobile units totally duplicates all the complexity of the one sitting next to it, so you get no economy-of-scale as you would by combining overall control, group ducting, group cooling, mounting foundations, etc.
For a stationary 1000MW 'gas-turbine only' power facility there would be terrible duplication of costs. You need to realize that the intake air for the gas-turbines has to be refrigerated down to 50 degrees F. or less. The jet engine in each MobilePac unit is the roughly same power plant hanging under the wing of a Boeing 777 that is designed to fly at 35000 feet. It's rather chilly outside at 30,000 feet, you may recall. When you are talking about 40 25MW units, you are going to want to have a central chilling plant to provide the intake air cooling. At least 2/3's of the chillers (..most likely ammonia compressors..) in a Chilling Plant could be driven by steam turbine motors powered from the Combined Cycle boiler.
If a 40 25MW gas-turbine generator plant was the way to go for stationary power plants, TVA, ConEd, PacGas&Elec, Duke Energy, and others would already be doing it that way. That's not to say it can't be done and still be profitable in the end, it would just be silly not to take advantage of the economies involved in putting the turbine-generator sets into common buildings and group-feeding / group-extracting the chilling and waste heat recovery that would be involved.
Rule of thumb for stand-alone piston generators up to the 5MW range is $1000/Kilowatt. Hence, the USSE plant is going to cost somewhere around $1B any way you look at it. The heat-rate of spark-ignited, turbocharged, piston generators is much higher than that for gas-turbines (..and you can use the jacket water from the engines to preheat boiler feed water..). That dictates doing some form of waste heat recovery for gas-turbines in a group setting to achieve an equivalent heat-rate. Huge coal-fired and gas-fired powerhouses are only 32% efficient at fuel-to-electric energy conversion, so USSE evenetually has to compete with cheap clean coal as a fuel source. When you are talking 250MW up to 1000 MW that's quite a challenge even with the Carbon and Green Energy Credits to sell on the CBOT.
USSE still has the right idea, it just need to be refined by some engineering resources like Fluor-Daniel, Bechtel, Stone & Webster, Sergeant & Lundy, Duke Power, etc., that do REALLY BIG PROJECTS and who aren't coincidentally trying to sell packaged, mobile, 25 MW gas-turbine generator sets to make their CEO happy. There is some practicality to have the plant build up in 50-100 MW modules, and being able to "..Peak.." on demand, rather than run 1000 MW falt out 24/7/365; all that needs to be analyzed and designed into a comprehensive and ultimately effective and profitable generating station.
John :-)
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