How come? Conventional electricity plants also convert heat to electricity. That doesn't sound fundamentally different from your business.
Was your input temperature too low? That would explain it. At low temperature differential, you have lower efficiency and need much bigger machinery for the same output.
That said, fusion has a chance to be competitive, because the temperature will be higher. (Obviously, the thermodynamic limit is in the billions of Kelvin, but a practical power conversion system will operate in the range of 500-1000 Celsius.) But for the foreseeable future, it won't be competitive.
Our heat sources were typically in the 500-600C range, with plant exhaust flows containing about 80-150MW of energy. Current tech can convert that with about 20% efficiency.
Not at all like conventional electricity plants, the heat is already being created in industrial processes and is a waste product.
We're familiar with delta-T and thermodynamics. Current off the shelf technology can easily hit half of the Carnot limit at most delta-Ts. That's not the point, the point is the "fuel" was free, and the price was "close" to existing sources as these things go (about 2x the price of natural gas) and even with a carbon market and climate mandates, it's impossible to get investment.
If you go to an existing power market, there is generally already enough supply for the existing demand. And all of that supply is a sunk cost. The plants are already built. They're not going to get shut down unless the price falls below solely the operating cost.
Building more capacity can cause the price to decline. In some cases by quite a lot. So nobody is going to want to finance it unless they see that either demand is about to increase or supply is about to decrease.
Which is potentially true in the future. Electric cars will need more generation capacity. A carbon tax that causes existing fossil plants to shut would reduce existing supply.
But it's also potentially not true. Maybe the demand for electric cars will be satisfied by an increase in rooftop solar and not an increase in utility-scale generation plants. We don't know when, or if, a carbon tax will happen in a given market.
You guys also had a specific problem. If you're getting waste heat from natural gas plants, and then carbon prices increase to the point that people stop burning natural gas and switch to alternatives, you're not the ones absorbing that demand, you're the ones getting shut down.
So you're in a different market position than would be the case for fusion after the introduction of a carbon tax.
Wait, what? Coal plants operate with an upper temperature of under 600C, and they approach 40% efficiency. Why do you say it's only 20%?
Either way, it sounds as if a coal plant without the furnace wouldn't be able to compete with "conventional electricity". What is "conventional electricity" then? Open cycle gas turbines? Are they that much cheaper, even including fuel cost?
Those temperatures will also be at higher pressures, while the waste heat I mentioned is at atmospheric pressures. 500-600C is the "crossover zone" where ORC versus steam cycle really depends on the details.
The plants we were looking at were either open cycle turbines (which means turbines in mechanical duty such as compressor stations, since all new turbine power plants are combined cycle) or other industrial processes such as cement production and steel manufacture.
Was your input temperature too low? That would explain it. At low temperature differential, you have lower efficiency and need much bigger machinery for the same output.
That said, fusion has a chance to be competitive, because the temperature will be higher. (Obviously, the thermodynamic limit is in the billions of Kelvin, but a practical power conversion system will operate in the range of 500-1000 Celsius.) But for the foreseeable future, it won't be competitive.