Turbine in Series: Pros & Cons

[Pranav Jha]

Why can't we use turbine in series so that the the remaining kinetic energy of water after passing through one turbine can be used to turn another turbine?

 

[Drakkith]

Are you sure that we don't do this?

 

[torquil]

After a turbine has extracted energy from a stream of high energy water, the water flowing out of it at the other end is less energetic (lower pressure).

So it depends on how much pressure is left in the water after flowing through each turbine, the cost of a second turbine, the efficiency of each turbine, and the cost of building more water channels from the reservoir and so on.

 

[russ_watters]

And note, a hydro turbine is generally extracting much more potential energy than kinetic energy. And you can never extract all of the kinetic energy, otherwise your water won't be moving anymore and if it isn't moving, how is it getting through a turbine?

Anyway, the constraints here are rapidly diminishing returns vs rapidly increasing turbine size (and therefore cost). For example, since kinetic energy is a square function of velocity, cutting the velocity in half extracts for you 3/4 of the starting kinetic energy in a water stream. To keep the mass flow rate constant, the output has to have twice the cross sectional area as the input. If you halve the velocity again, you again double the size of your output again but only extract an additional 1/5 (about) of your starting energy. Double the size of the output a third time and you've extracted more than 98% of your available kinetic energy.

 

[pmacias]

There are several pros and cons to using turbines in series. One potential benefit is that it allows for a more efficient use of the kinetic energy of water, as you mentioned. By passing the water through multiple turbines, the remaining energy can continue to be harnessed, resulting in a higher overall energy output.

However, there are also some drawbacks to this approach. First, it can be more complex and expensive to set up a series of turbines compared to just one. This is because each turbine must be designed and installed to work in conjunction with the others, adding to the overall cost and maintenance requirements.

Additionally, using turbines in series can also pose a risk to the environment. As the water passes through each turbine, it can cause changes in the water's flow and speed, potentially disrupting the ecosystem and affecting aquatic life.

Another consideration is that using turbines in series may not always be necessary or practical. In some cases, the initial turbine may be able to harness enough energy from the water without the need for additional turbines. In other cases, the terrain or size of the water source may not allow for multiple turbines to be installed.

In summary, while using turbines in series may have some potential benefits, there are also challenges and limitations that must be carefully considered. Each project should be evaluated on a case-by-case basis to determine the most efficient and sustainable approach for harnessing the energy of water.