The back - pressure system has the following disadvantages:
ß The steam turbine is larger for the same power output, because it operates under a lower
enthalpy difference of steam.
ß The steam mass flow rate through the turbine depends on the thermal load.
Consequently, the electricity generated by the steam is controlled by the thermal load,
which results in little or no flexibility in directly matching electrical output to electrical
load. Therefore, there is a need for a two-way connection to the grid for purchasing
supplemental electricity or selling excess electricity generated. Increased electricity
production is possible by venting steam directly to the atmosphere, but this is very
inefficient. It results in a waste of treated boiler water and, most likely, in poor
economical as well as energetic performances.