Feeding an MPPT charger from a hydro turbine - Page 1
Forum section: electronics / general

author: Rx7man
author_rank: Regular Contributor
timestamp: November 27, 2020, 07:24:27 pm
content: I've been looking into building a microhydro project, ~5kw pelton wheel, 1 or 3ph 240VAC generator... I was thinking the best way to simplify controls for it would be to rectify it and feed an MPPT solar charger/inverter to a 48V battery bank, and have the whole house run off the inverter... I can't find the ebay link to the one i was looking at before, but it had up to 500V solar input capability (so sqrt(2)*240V would be well within operating limits)We have pretty steady water flow for generating at least 2kw, the highest demand appliance we have is of course the range/stove/oven and hot water tank, if we have a steady 2kw power input we wouldn't need to have a gigantic battery bank, and we'd never be deep cycling the batteriesHas anyone done anything like this?

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 27, 2020, 11:52:13 pm
content: Take a look at wind MPPT controllers, which are very similar to hydroelectric.

author: Gregg
author_rank: Super Contributor
timestamp: November 28, 2020, 12:00:15 am
content: This guy has some good pointers:https://www.youtube.com/user/MrHydrohead/videosI have a friend that has a smaller Pelton wheel setup that I help him with; it produces 17 amps DC at 27 volts continuously and uses an automotive type alternator modified with a permanent magnet field. There is a set of large flooded lead acid batteries powering a 4500 watt true sine wave inverter that supplies all the power he can use with propane for stove and hot water. The excess power is dumped to resistors that keep the power house from freezing. It does require some maintenance. A big concern with high pressure water turbines is wear on the impeller wheel from any sand or grit in the water; it is well worth the effort of installing a suitable strainer setup from the beginning.

author: richard.cs
author_rank: Super Contributor
timestamp: November 28, 2020, 03:23:15 pm
content: You might find this interesting:https://ludens.cl/paradise/turbine/turbine.htmlIn his case he had a single phase generator of around 6 kW output and no storage. Instead the electronic frequency controller load sheds heating, etc. as larger loads are switched in. Perhaps not an option if you only have 2 kW to play with. What is your expected peak load?You probably don't want MPPT tracking on a turbine, by its very nature it will try to suck as much energy out of the turbine as possible and it if designed for something with an instantaneous response like solar probably get confused by the rotational inertia. I would expect it to repeatedly stall the turbine by sucking all the rotational kinetic energy out. MPPT for a turbine would need a much, much lower control bandwidth, and probably doesn't offer too much benefit. More likely you want to control for the rotational speed / AC frequency that you know corresponds to peak efficiency.Whatever happens, if you have a fixed flow rate you will need to provide a constant-power load, even when any batteries are full. Otherwise the turbine will overspeed.

author: Rx7man
author_rank: Regular Contributor
timestamp: November 29, 2020, 06:46:34 am
content: 2kw should be what we can produce continually, depending on creek flow and irrigation demands, at times we should have plenty to make 5kw, which is probably going to be a little short of peak load.. we don't use a whole lot of power, lets say about 1500W continuous, then some high demand loads like the stove/oven, 3kw hot water tank (with a bit of current sensing from the stove and a solid state relay it would be easy to kick that out while cooking)I'll have to look into those solar charger/inverters a bit more, you'd think you can set some parameters for the MPPT... I'll look into those wind ones as wellWe already have a swiss made pelton wheel on order, I think it's a 20 or 23mm nozzle with pintle to adjust it (peak flow around 100gpm, ~100+PSI dynamic head), it doesn't have the mechanics to control it at this point (I'll work on that when we get it).. we're still hashing out exactly which generator we need/want, there is one available with the turbine, but since it's designed for 220/380V 1/3 phase, which doesn't work well for north america without having transformers, etcthe invertor/batteries are probably going to be the last thing we buy, once we get things up and going we might just have the oven/range on grid power and all the smaller stuff on a direct feed from the turbine

author: Rx7man
author_rank: Regular Contributor
timestamp: November 30, 2020, 09:07:22 am
content: Here's the unit I'm thinking of using.. it can charge from the grid side so I guess I'll just do it that wayhttps://www.ebay.com/itm/164344391499?_trksid=p2334524.m570.l5999&_trkparms=gh1g%3DI164344391499.N36.S2.typeWATCH_ITEM_ENDING_SOON.R6.TR6

author: richard.cs
author_rank: Super Contributor
timestamp: November 30, 2020, 09:54:14 am
content: Well, if you want to go to DC for battery charging or feeding the an inverter designed for solar then three phase is strongly preferred as you can simply rectify it with no/minimal filtering and get good DC.I'm not sure I follow what you are intending with that inverter. Grid tie with a 48V battery pack? With the turbine feeding in at 48V? That is also a European model.As you have a grid connection have you considered simply running the generator in parallel with it? That works with either a synchronous or an induction generator. You would then generate whatever your mechanical input allows and import/export the difference between usage and consumption. No inverter or batteries required which is good from a cost and reliability perspective, just some simple islanding protection. With a little more complexity you could also allow it to run islanded with just a peak load limit of your current generation.

author: Rx7man
author_rank: Regular Contributor
timestamp: November 30, 2020, 04:32:22 pm
content: good catch on the EU model, means it's probably 50hz as well, the 220/240V could be fixed with a center tapped transformer, especially if the 120V loads are light (or balanced) in comparison to the 240V load, right?since there's considerable distance between the turbine and house (250m), I'm probably going to go higher voltage... due to UL requirements (and cost of UL certified stuff), I'm probably not going to backfeed into the gridI wouldn't mind if the charger and inverter were separate units, I just haven't found any in the size I need... I've contemplated using a forklift battery, but they seem to mostly be 36V which makes for harder inverter selectionMaybe this would be the better optionhttps://www.ebay.ca/itm/LV-MK-split-phase-solar-inverter-6000w-48v-120v-230v-160A-mppt-solar-charger/133399295918?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20200520130048%26meid%3Da477ede373924155840a2f4ec7fdac58%26pid%3D100005%26rk%3D6%26rkt%3D12%26mehot%3Dpf%26sd%3D353163077767%26itm%3D133399295918%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv5PairwiseWebWithDarwoV3BBEV2b%26brand%3DMPP+Solar&_trksid=p2047675.c100005.m1851

author: David Hess
author_rank: Super Contributor
timestamp: December 01, 2020, 07:46:04 pm
content: Quote from: richard.cs on November 28, 2020, 03:23:15 pmInput current needs to be limited to avoid overheating the windings. Like any source, generators have an impedance and if matched, maximum output power is provided. However this impedance is much lower than the practical impedance and would destroy the generator if matched. The same applies to RF power amplifiers which are also deliberately not impedance matched on their output for maximum power. Solar cells have a much higher impedance so shorting them results in current limiting instead of destruction.

author: richard.cs
author_rank: Super Contributor
timestamp: December 01, 2020, 11:00:42 pm
content: Quote from: David Hess on December 01, 2020, 07:46:04 pmIsh, unless the generator is very much marginal for the turbine, it's unlikely that it ispossiblefor a working maximum power control scheme to overheat the windings. Current is proportional to torque, so an overcurrent inherently means excess torque is required of the turbine and it will slow down significantly, with stall torque only about twice the torque at the maximum power point (based on some unscientific eyeballing of some Pelton turbine curves). Slowing down means that it looses voltage, so to get high enough current to do damage means the controller is walking far away from the maximum power point. Consider that even if you just shorted the generator output the turbine only has enough torque to produce double current, and whilst the generator would eventually overheat under that condition it would take tens of minutes if not several hours.Yes, of course you need protection for the generator, any MPPT scheme might fail and do something wild, chasing down some local-optimum rabbit hole, or its electronics might simply fail S/C, but the algorithm shouldn't walk there in normal operation because it is far from maximum power. Given the very limited short circuit current and slow overheating a simple thermal circuit breaker is likely all that is required to protect the windings, though actually more thought is probably needed - you don't want to remove all load or itwilloverspeed and be destroyed.*Another way of looking at the impedances is that the generator is a transducer, mapping rpm onto voltage, and torque onto current, in both directions.** Yes, the impedance of the windings is low, but that has to be summed with the transformed mechanical impedance of the driving source. If driven by a low-impedance mechanical source whose speed falls little with increasing load then the electrical output of the generator looks low impedance and its windings could easily be damaged by overcurrent. When driven from a high-impedance source like a Pelton turbine the speed(torque) characteristic is mapped onto a voltage(current) characteristic and the generator electrically looks and really is high impedance. The rotational inertia of the generator, which acts to keep the speed constant over a short timescale appears at the output terminals as a capacitance acting to keep the voltage constant over a short timescale. The generator output,when driven by a Pelton turbineis a moderately high resistance, much higher than the winding resistance, in parallel with a large capacitance that corresponds to the rotational inertia. It's this capacitive output characteristic that I was suggesting may confuse a solar MPPT scheme and cause it to oscillate.If a MPPT scheme is used then it should match the load impedance to the transformed mechanical impedance, not the much-lower winding impedance. I am still unconvinced it offers much benefit however given the maximum power point of the turbine-generator is hugely predictable, occurring essentially at constant speed/voltage and at a torque/current pretty much only dependent on water flow. A 3-phase transformer and rectifier to battery voltage with a dump load to prevent overcharge would probably work well so long as the generator has no voltage regulator (or it is disabled). The turbine then runs with its speed regulated by the battery voltage, and pushes a current set by the water flow into the batteries, with some proportion of that current dumped resistively once the batteries are full.****This needs some careful consideration, An overload protection that open-circuits the winding is definitely bad unless some backup system then kicks in to load up the turbine and prevent overspeed. Given there's no requirement for fast overcurrent protection an optimal scheme might have some slow-acting device that simply shuts off (or deflects) the water flow in the event of sustained overcurrent or high winding temperature. Additionally you need something independent of the inverter and fast-acting that prevents overspeed if the load is lost, most likely involving the relatively quick application of electrical load or even a short-circuit.**This assumes a permanent magnet generator, or a wound field machine with fixed excitation. If the generator includes a voltage regulator then it's still true, but the constant relating the mechanical and electrical properties is dependent on the field current and the voltage control loop will try to take out all the impedance. That then makes the generator look zero impedance until it runs out of control range and is pretty much guaranteed to cause trouble with any MPPT scheme.***Assuming there's no desire/need/ability to store water for later in the year a resistive load dump is a lot simpler than trying to regulate water flow.

author: Rx7man
author_rank: Regular Contributor
timestamp: December 02, 2020, 09:54:48 am
content: Really interesting in depth look at it, thanks!The pelton wheel will have a needle jet so the flow is controlled, it has the jet but at this point the mechanics and electronics of actuating it are to be determined... Depending on the season, I may have other uses for the water (irrgation in particular), so I may also have it on a timer and scheduledEverything is a balance... one fellow (not here) recommended a high voltage DC generator or permanant magnet alternator, but I haven't found anything in the 5kw size, and with about 250 meter electrical cable run, I'm going to want pretty high voltage, DC doesn't lend itself nicely to voltage changes, direct end use, or anything else...We could have gotten a 220/380V generator with the turbine (from Europe, we're in Canada), and I'm sure I could have made something work with enough effort, if I ever have to change something out it just gets too hard to match things up again. I have a little 10kw diesel generator with a Stamford head on it, it can be configured for darned near any voltage from 120v to 480V 3ph delta or wye, I might look for something similar

author: richard.cs
author_rank: Super Contributor
timestamp: December 02, 2020, 10:38:43 am
content: Quote from: Rx7man on December 02, 2020, 09:54:48 amPerhaps something as suggested above then, but with a slower-acting control loop that operates the needle valve based on battery state of charge (assuming you still want to use batteries). Generally I would try to avoid a design where the needle valve is part of a fast-acting control loop that attempts to regulate turbine speed. There be dragons.Quote from: Rx7man on December 02, 2020, 09:54:48 amYes, I think a conventional wound-rotor is better. Most people with large permanent magnet alternators seem to home-build. 3-phase allows easy production of low-ripple DC if you want to battery charge or feed an inverter.Quote from: Rx7man on December 02, 2020, 09:54:48 amThat level of flexibility sounds good. Presumably it's wound rotor with electronic voltage regulation? Ideally you'd pick one with brushed rotor connections and external regulator (in the sense of not being a lump of inaccessible electronics built into the armature) so that you can freely do whatever you want with the rotor field.What I've not seen here is a clear statement of what you want to achieve. You have a grid connection, and are planning on keeping it, so just want to reduce costs? Or net CO2 emissions? Or just have fun designing and building small scale hydro?Given you have a grid connection then it is almost certainly more cost effective to make use of it and avoid batteries unless you want them for other reasons. Energy shovelled into and out of batteries works out very expensive once you account for the cost and lifetime of the batteries. That then suggests a grid tie setup (with or without export as suits your local regulatory environment) so larger loads can seamlessly draw a mix of grid power and locally generation. That leaves you either where you can in using an existing inverter design, or parallel synchronous operation of AC generator and grid.That said, if you definately want batteries, there's plenty of ways to make that work, and there might then be scope to loose the grid connection entirely.

author: Rx7man
author_rank: Regular Contributor
timestamp: December 02, 2020, 06:40:38 pm
content: Since part of the penstock of this system, at least for now is above ground and we can get down to -25C in the winter, we will have to shut down the hydro system for a few months of the year, and that will kinda force our hand into keeping the grid service..We are doing this for a combination of reasons, reduce grid power costs, backup power for a zombie apocalypse, and just as an investment into the propertyThe only thing about doing a 3 phase system is I'd need a transformer to get true 240V rather than the 208V between legs... I'd have to see if my large appliances have an issue with 208V to know if that's really going to be a problem, range, clothes drier, as long as the electronics don't have a hissy fit about it should be ok, just heat a little slowerMy logic behind having a battery system as well is that my peak loads will certainly be greater than my generator power delivery during minimal flow seasons, but I'm not going to need large amounts of power for a long time.. Say my peak load is 6kw (Oven and a few miscellaneous things) and I can only produce 2kw, the oven will only draw that intermittently once it's warmed up, so I can draw the balance from battery bank.. since its only a brief load and they'll get recharged before long and not get deep cycled, this ought to help with battery life, and I also shouldn't need a gigantic battery bank, I can get decommissioned ~200AH 12V AGM batteries at a pretty reasonable price, 4 of them for a 48V system, gives me about 10kwh of capacity (Plenty!).. I could probably get away with an automotive deep cycle battery too, but I've found their quality to be a bit dodgy in comparison to truly commercial options.How closely does turbine speed really have to be regulated? I will have some induction motors (fridges, freezers), what's a reasonable acceptable deviation from 60hz? +/- 5hz? if the generator/turbine have a significant inertia you should be able to stay within that reasonably easily, you would want a dummy load for safety no doubt thoughThe stamford I have is brushless, the only electronics on the rotor is a set of 6 rectifier diodes.. this PDF gives the wiring options my current generator has, though this is a much bigger modelhttps://www.stamford-avk.com/sites/stamfordavk/files/AGN154_D.pdf...I'd definitely run the wire to be able to make use of the 3ph option if I wanted to later

author: richard.cs
author_rank: Super Contributor
timestamp: December 02, 2020, 09:41:21 pm
content: Quote from: Rx7man on December 02, 2020, 06:40:38 pmBeing from the UK I don't have much experience of those temperatures. Would it actually freeze up given the high velocity of water through the penstock? Do you know how far above freezing the liquid water arriving at the property is (I am blindly assuming here that your water source doesn't entirely freeze up)? We could estimate the heat transfer through the penstock walls and compare it with your mass flow X heat capacity to see if it will actually freeze.Quote from: Rx7man on December 02, 2020, 06:40:38 pmTo me wanting to reduce costs suggests avoiding batteries, unless you have unusually expensive grid power or access to unusually cheap batteries if would almost certainly be cheaper top pull the peaks from the grid. But perhaps arrange the system so thatsomethingworks without grid power, just perhaps not your peaks.Quote from: Rx7man on December 02, 2020, 06:40:38 pmThe incompatibility of split phase and 3 phase is the principle disadvantage of the North American system. Still, my understanding is that most 220 V appliances work OK on 208 V.Quote from: Rx7man on December 02, 2020, 06:40:38 pmThe economic argument: I am not sure what's a reasonable price in this context, but let's say for the sake of argument that the 200 Ah 48 V battery was $500. Capacity if you run them empty is 9.6 kWh, but lets say you never discharge below 50% to get a good cycle life out of them, so call it 4.8 kWh. At 50% depth of discharge you might expect to get 1000 cycles out of the batteries, so the total energy throughput is 4800 kWh at a cost of $500, so the electricity from the batteries is costing you just over $0.10 per kWh. If you run that calculation with your actual battery price and compare it to your grid power cost, I would expect it to be cheaper to source the peaks from the grid.That's not to say you shouldn't got for a battery solution for any number of other reasons (energy independence, fun, zombie apocalypse), but I think the cost argument is weak.Quote from: Rx7man on December 02, 2020, 06:40:38 pmFor many types of loads +/- 5Hz is probably OK, but I suspect that a lot of inductive loads may start to enter saturation by 55 Hz. It might be safer to regulate for 65 +/- 5 Hz, higher frequency is generally less damaging though motors will rotate correspondingly faster.Matching generation to load by controlling the water flow is possible, but needs care, not least because you have a lot of inertia in the water column in the penstock. If the electrical load is suddenly removed you cannot shut the needle valve instantaneously or the pressure would spike. This can be handled, but there's a reason fast control is often done by deflecting the jet. Correspondingly, opening the needle valve when load is applied does not result in an instantaneous increase in flow, again because of the inertia of the water column. It might be worth an analysis of what your rotational inertia actually is, and possibly even the addition of a deliberate flywheel if you wanted to go with that approach.Frequency control would be an advantage of direct parallel operation with the grid, the grid essentially will source/sink unlimited energy to keep the generator rotating at 60 Hz. It can be combined with a slower control loop on flow to prevent significant export, or a faster electronic dump to prevent any export. The downside is mainly regulatory, what extra bits of approved hardware you need to prevent accidently islanding.Quote from: Rx7man on December 02, 2020, 06:40:38 pmOne of the types where there's a stationary voltage regulator that puts a controlled field into a small stator, which excites a separate auxiliary winding on the rotor to produce three phase that's then rectified to DC for the main rotor field?This type of thing?https://www.semanticscholar.org/paper/Condition-monitoring-of-brushless-three-phase-with-Sottile-Trutt/edd6a34632844f8f66cb8ba6185d8f18e780a3a8/figure/0That's not too bad, there is an interaction of rotational speed and field that you don't get with a brushed machine but you can still control it to do anything you like by accounting for that. Plus of course you get the reliability of having no brushes.

author: Rx7man
author_rank: Regular Contributor
timestamp: December 02, 2020, 11:30:24 pm
content: when it gets cold here, the water is VERY cold, If we get a snowfall into the creek before it ices up, we have a lot of ice crystals in the water that will ice over any screen,As it stands right now, there's about 400m of 7" aluminum pipe above ground (part of the irrigation system), then there'll be another 300m of buried 4" fiberglass pipe, though it won't be buried very deep (probably 2ft)The biggest problem with freeze-up is that it's a slow process, first the screen ices over, then you get air in the line, things freeze because of reduced flow, and finally there's only a trickle at the end which will mean your turbine freezes up too.. easier to just shut it down before that happens and be safe.I think we could get quite a long life out of a battery set, and even weak batteries can probably do OK since with a 48V system the amperage demand would be far less.. if we need 3kw additional power from the batteries, that's only 65amps, if I only need it for 10 minutes before I can at least put some charge back in, that's about 11 amp hours.. It really depends on which batteries I find and the priceFor the inertia of the water in the pipe, I don't think you'd notice it very much, in the 7" line the water never needs to move quickly (except when the irrigation is running, and that's a constant flow), certainly would be a good idea to have a pressure relief valve there just in case it shuts down really fast... The flywheel idea is good too.. I have a 400 lb flywheel that's designed for 1000 RPM, that would be a whole lot of kinetic energy to absorb transient loadsThe nozzle on this turbine is 22mm, if I'm doing the math right, that's capable of 250GPM @ 150PSI dynamic head = ~15kw in an ideal worldI may need to swap out nozzle for low flow times, perhaps go down to a 14mm nozzle, with far less head loss, I'd be at about 165 PSI and 100gpm max = 7kw idealI have a lathe and milling machine, so I can make custom nozzles no problemI also have a 4" magnetic flow meter much like this onehttps://www.ebay.com/itm/ABB-WaterMaster-DN-100-4-Electromagnetic-Flow-Meter-Remote-Transmitter-FEW3/303604098724?hash=item46b036e6a4:g:Q4kAAOSw56Re8j8Jthat I'll put in the line and with a pressure transducer, I can crunch lots of numbers and figure out efficiencyIf I could get that much power all the time I definitely would be going direct and forgetting about battery systems, but I don't think I have the flow in the creek to support it... going to have a fair bit of transmission line loss, transformer loss at the other end, etcThanks for the insight and questions to ask myself!

author: richard.cs
author_rank: Super Contributor
timestamp: December 03, 2020, 12:27:26 am
content: Did you have a chance to read through Manfred's setup (ludens.cl)? I know it's a very long page but there's good stuff in there and a second page on the electronic load controller. He went with a 3 nozzles the same size and one half the area, and then just runs more or less nozzles depending on the season. It sounds easier than swapping them out. His setup is about 8 kW in the rainy season but he has much worse transmission problems than you - 600m rather than 250m.Actually, your 250m is pretty much on the limit of what you'd want to do at 380 L-L, so if 480 V L-L is a winding option on the generator I'd be inclined to go with that and take it down to something more usable with a transformer at the load end.You seem pretty settled on batteries, that's cool I just wanted to make sure you'd thought about it. I guess that gives you a few possible architectures:Generator 3-phase, transformed down to ~48V and rectified to charge batteries. All loads via the inverter from 48 V* Simple* Need a larger inverter* Inverter can be grid tied or not* Can generate split phase from the inverterGenerator produces AC supply which is used directly, inverter and batteries in parallel to boost supply for large loads* Needs active frequency control (via flow rate, load, or both)* Generator can be split phase if wanted* Not a standard inverter feature?* Not immediately obvious how to incorporate a grid connectionGenerator running in parallel with grid* Frequency management no longer an issue (unless islanded)* Can run islanded with the addition of frequency control* Battery and inverter combination set to prevent export and provide peaks. This is pretty much what a powerwall does so i guess it must be a somewhat standard inverter feature?* Everything just runs off the grid on loss of generator or inverter.There are probably others I've not thought of, but do any of those approaches appeal to you?

author: Rx7man
author_rank: Regular Contributor
timestamp: December 03, 2020, 05:42:04 am
content: I'm definitely going to go with a 480V wound generator, probably 8AWG copper or 6AWG Aluminum... I'll try and source it used, so maybe it'll be bigger if the price is right... the reason I'm going with fiberglass 4" pipe is we found some for $20 for a 30ft length and it's rated for 300PSIOne good reason for a 480V system is 2:1 transformers are relatively easy to find, and you could use an autotransformer too depending on grounding requirements which reduces the cost... I wouldn't be opposed to 600V either if I find the stuff I need but it'll probably be harderI already have a few smaller 480-240V transformers, I think I have a couple 1 to 2 kva ones alreadyEach one of the scenarios you list has SOME desirable feature about it!.. probably a good idea to nail down exactly what I'm going to have for a supply, and at this point I think 480V 1ph is going to be the most readily available for both generators and transformers, probably wouldn't be a dumb idea to run a 3rd conductor if you change your mind later though... After that, start making power, start running stuff and finding out the limits of things and add inverters/batteries, etc as needed.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 03, 2020, 01:17:13 pm
content: What heating fuel do you use if it's not electric? Might be worth considering a CHP setup for the winter.

author: Rx7man
author_rank: Regular Contributor
timestamp: December 04, 2020, 04:41:43 pm
content: we use wood for all our heating.. what's CHP?

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 05, 2020, 04:48:40 am
content: Quote from: Rx7man on December 04, 2020, 04:41:43 pmCombined heat and power, wood is difficult to do CHP with but possible using steam engines or Stirling engines.

author: richard.cs
author_rank: Super Contributor
timestamp: December 05, 2020, 10:09:51 am
content: Quote from: NiHaoMike on December 05, 2020, 04:48:40 amOr gasification but that has it's own exciting problems.

author: Rx7man
author_rank: Regular Contributor
timestamp: December 05, 2020, 11:07:23 pm
content: Ah, OKI visited some people that have a large scale hydro project for multiple families on their farm, 250kw generator, VERY old pelton wheel, 12" penstock and 220 PSI, got a few tips from them... They also make a some remote monitoring systems and other electronics and one of their companies is my ISP (very techy people), They gave me a nice little tour, they have a pick-n-place machine, etc.. I will try to get them to send something in to the EEV blog Mailbag... They monitor voltage, amperage, power factor, etc, both peak and RMS in realtime for each service.. the boards are 12 or 16 channel, he says he'll sell me a couple that have a couple defective IO's so I can play with them for cheap.. that will be fun! They gave me a little inductive current sensor that's pretty accurate, so that'll be fun to play with as well.. They have a good spreadsheet for figuring out hydro power parameters.. Seems like 4kw is no problem at all even with an conservative efficiency of 60%... By the looks of it we'll either run a 4 pole generator at 1800 RPM, direct drive, or a 6 pole at 1200 RPM.. we'll have to have a test run on the pelton wheel and get exact measurements before we make a final decisionI've attached a couple pictures of the pelton wheel