System Design, Hydro Power

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3toddr asked Mar 21, '24

System Design, Hydro Power

Hello, I am currently looking at installing an off grid Hydro system in the UK, there is good flow all year round producing ~15kw 24/7, or about 91kW if the turbine was sized for peak annual production. however my problem is the flow durations curves indicate a 1 in 5 year chance that there wouldn't be enough flow for about 19 days running, we could always run a generator on an ATS, but ideally we would want to run a more efficient and long term solution. My first idea would be to have the Turbine connected through the AC1 of a quattro and treat it like a generator as the waveform and voltage is of Grid quality, with plenty of mechanical inertia and capacitors for power factor correction. And then as a backup connect the Diesel Generator currently in use on to AC2, with a start stop relay connected, Could anyone point out any major flaws in this plan and hopefully recommend and alternative. The continuous load is approximately 2.7kW with a peak of around 17kW, and I hope to install load shedding relays to ensure the turbine isn't overloaded, perhaps using an inverter charger to assist instead. I would be interested if Victron enables you to set a minimum draw on a generator because the Turbine will trip out when it is only being run at just less than 1kW, and if it doesn't have this feature could it be rigged up to set a dump load to maintain a current draw on the Turbine?

offgrid

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matt1309 commented · Mar 21 at 05:24 PM

Hi @3toddr

I've been thinking about this for awhile.

I was torn between a setup you've described above ie where turbine outputs voltage/frequency for direct usage. ie 240vac single phase 50hz and you manage those conditions as you describe above.

Compared to the route I've seen lots of microhydro systems go.

Where they generally have several smaller penstocks and several smaller micro hyro generators (sized so that they can freespin without risk of damage so you don't need to worry quite as much about quite as robust dump load infrastructure).

These micro hydro generators are generally three phase and are bridge rectified to DC then passed into a MPPT controller which feeds a battery. Which is then inverted to 240vac to use. Rather than outputting the 240vac 50hz like your proposed system.

I'm honestly not sure what the better system is so curious to see what responses you get.

First 1 works without a battery and only needs one penstock pipe/generator.

Second you can use a 3phase generators, and multiple of them. You can probably control output easier without needing to adjust loads to keep frequency/voltage in check. Given you've got lots of smaller pipes rather than one big one you can probably get cheaper more consumer products/electronic valves. However it does rely on a battery and has a few extra conversion steps to get to 240vac.

Very jealous you're able to build the system. If you're anywhere near South Wales I'm happy to lend a hand. Itching to gain experience working on such systems, even if I'm only needed for donkey work!

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3toddr matt1309 commented · Mar 21 at 05:47 PM

The reason for looking at one larger turbine is we currently have a 4 inch ductile iron penstock with a head of about 130 meters, which used to supply an old quarry, and we can take about 80 l/s whilst maintaining a min flow of 11 l/s. We have had a good quote to reline this, there are no current leaks so we could probably get away without lining it. I think the main benefit of going almost AC coupled and just using the inverter to support changeovers and assisting the turbine, is the reduction of loading on the inverter, and the removal of switching in the MPPT, which I am led to believe are commonly the part to have problems. Also with almost all of the loads attached being AC it avoid the conversion losses and we can reduce the size of batteries needed and the complexity of the DC Bus charge controlling etc. I have never really seen anyone except larger municipal Island Grids going for a renewable AC source as the primary mover. My main concern really is frequency control and preventing any over speeding. Sadly we are only in a concept phase at the moment and I am led to believe the environment agency take a while with abstraction permits, and we have to rebuild a damaged weir, but still so far somehow cheaper than a Grid Connection! But once they have consented we would not turn down an extra set of Hands!

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matt1309 3toddr commented · Mar 21 at 09:52 PM

Ahh makes sense. That's a tonne of water.

You could go one Pelton wheel multiple generators but you're right. Woukd grt complicated with gearing etc. Yeh I've heard mppt algorithms can be funny/got to get one that accounts for time delay of turbine changing speed under different loads.

You seen this guys series. Has the similar setup to what you describe. With dynamic dump loads that maintain frequency/rpm/voltage. And if they are maxed out and still more water then he has rpm sensor and frequency sensor that if they fall too far out of their limits it releases electro magnet that puts shield in jet stream to turn off turbine before issues arise. A nice fail safe if dump load/freuqnecy controller fail for any reason

https://youtube.com/@mrhydrohead?si=drEQOf7ZY_LayLeP

@ me on here whenever you need a hand. Happy to have any involvement/help where I can. Especially if you're not too far away

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hjohnson commented · Mar 24 at 12:16 PM

It really depends on the scale of your project. I work with a small scale hydro project that has a nameplate capacity of 275kVA, 2400V 3phase. At larger scales like that, direct generation works. That said, that turbine/generator combination is feeding an entire small community, so we have a pretty significant load shedding system to keep the generator from being overloaded in the winter.

The key thing is maintaining the line frequency and protecting the generator/turbine itself from overspeed (or underspeed). We have an oldschool flyball governor on the system that will keep the turbine spinning at less than about 610rpm or so (12 pole, 3 phase generator, produces a nominal 60Hz). The load shedding system, in turn, acts a bit like a loadbank governor and keeps the line frequency closer to 60Hz by controlling every hot water tank and boiler heating element in town. If the frequency starts getting too high, it can force excess power into the boilers in the large buildings. If the line frequency gets too far out of whack, the protective relays kick in and drop the generator, causing the mechanical governor to do its thing and deflect water, protecting the turbine from overspeed.

The problem with smaller scale direct generation is dealing with load transients. In direct generation you’re literally relying on the rotational momentum of the generating system to carry you through while the governor reacts. If you’re spinning 1000kg of metal, this is practical. If you’re just spinning something small, not so much. Depending on the time of year, our water can get low enough that someone turning on an oven or a clothes dryer causes enough of a frequency drop that the protective relays kick in and kill the power. We’re looking at adding a Eaton microgrid inverter/charger to resolve this.

The problem you’d have with using something like an MPPT is I don’t know how well it would react to a) the non-DC voltage of even rectified 3 phase, and more importantly, if your batteries get full, the input to an MPPT typically goes open circuit, which would unload your generator potentially causing it to overspeed.

If you’re going really small scale, say 20kVA or less, another option would be to treat the generator more like an automotive alternator (even using a large frame alternator) and use something like a Wakespeed WS500 to modulate the excitation current. You’d still need a mechanical governor to protect the turbine/generator, but that would probably be better than trying to go through something that wasn’t designed for it.

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3toddr hjohnson commented · Mar 25 at 02:49 PM

Hello, I’m very interested in the system you operate. Do you have any capacitor banks for very fast frequency response? The turbine I’m planning on installing is a impulse turbine so I am less concerned about damaging the turbine during an overspeed, it’s bearing etc are rated at 12,000 rpm and as we are planning to run 50hz we will probably run it through a 1500rpm generator, and during a surge in demand or drop I’m hoping the flywheel, capacitors and charge controller would assist before the frequency drop triggers the protective relay on the turbine I’m just curious if it possible to run a turbine like a Generator would run on a victron system, as my load acceptance calculation are about the same as the old diesel we currently run off. We would be able to draw to the design flow rate about 11/12 months, so theoretically it should be able to work as a generator input on the charge controller, but I would be very interested to see if adding capacitance or a charger inverter on the larger system would fix some of these issue I am bound also to face.

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