The Many Questions and Challenges with DIY Hydroelectric Generators
The concept of building your own hydroelectric generator seems simple at face value: use gravity to impart as much force as possible onto a turbine, which spins a generator, thus generating electricity. If you’re like the bloke over at [FarmCraft101] trying to DIY this with your farm pond and a lot of PVC pipes, you may have some significantly more in-depth questions, especially pertaining to what kind of generator to use. This and other questions, some of which were raised after the previous video in which the first prototype generator was assembled, are answered in this follow-up video.
When you DIY such a hydroelectric system, you have a number of options when it comes to just the turbine design alone, with the Kaplan-style turbine being one of the most straightforward ones – especially if you use a fixed pitch instead of adjustable – but you can go pretty far in the weeds with alternatives. As for the sharp drop-off after the turbine in the used design, the technical term is a draft tube, which is actually more efficient in this kind of low head, high flow hydroelectric dam situation.
After getting his money back for the unusable ‘3 kW’ generator, there were three options left: try an EBay special, get a purpose-built one from a US company, or rewind an alternator stator for higher voltage output than the standard 12/24V. Ultimately option four was chosen, as in ‘all of the above’, so that comparison is coming up in a future video.
There were also questions from viewers about why he opted to rectify the AC power from the generator and use DC transmission to the nearest farm building. The main reason is efficiency, as DC transmission lines lack the skin effect losses. The other is that the grid-tie inverter that he plans to use needs DC input anyway. Not having to deal with AC transmission issues like losses and reactive power shenanigans is a major plus here.
Once the three new generator versions are being tested it will be interesting to see how they perform. One thing with the Kaplan-style turbine is that too fast RPM induces cavitation, which will erode the propeller pretty quickly. Generally car alternators require a pretty fast RPM, so that may not work out too well. There is also the question of the DC voltage generated, as for DC transmission you want to have as high a voltage as possible to reduce the current.
The purpose-built generator he purchased tops out at 48V, which is quite low. The goal is to have at least 230 VAC before rectification, so a step-up transformer may be needed. Unfortunately three-phase transformers are pretty pricy again, making the rewound alternator seem less crazy. The wild card here is perhaps whether the EBay-purchased generator is a diamond in the rough and works out of the box as hoped.
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