Converting AC to DC for a micro-hydro turbine

You will find that most micro-hydro turbine systems are rectified to DC and then inverted to AC for this very reason.

Have a look at some of the Renewable Energy sites and you will find "Off the Shelf" solutions for this step as well.

This primarily to ensure Syncronisation with the Mains power and ensure you power quality matches the requirements of the equipment attached.

These units will also Isolate the Output from the renewables in the case of a mains failure in the case of a Grid-Tied system to protect those working down stream from your site.

Please check local legislation and check that your Grid-Tied system is compliant before connecting.

Regards,
Sapper

downstream, ho ho.

I know its all a bit 'old hat' but perhaps the best solution is mechanical with a motor- alternator. You would rectify the turbine outputs to DC then drive a DC motor which drives a flywheel and AC alternator. the unit should be governed to produce a set frequency. The flywheel will provide smoothing.

Hello gusmenocal

Up until a few years ago, it was more efficient to use a DC Generator on the Turbine, rather than an AC Alternator.

The Kaplan Turbine Runner is quite efficient in low-head situations, but is rather complex, requiring the adjustable pitch blades to be operated by the central rod which is controlled by a servomechanical/electronic system.

The Kaplan Runner was an efficient development of the vertical Francis runner, which is far simpler in operation.

As you are intending to have 34 of these units, each delivering between 1kW and 2kW, if Kaplan Runners are used, the costs of maintenance are going to be quite large, in proportion to the total power output obtained.

Check out using the vertical Francis Turbine Runner, before you commit to purchasing the units.

Remember the larger each individual unit is, the more efficient the Turbine +Generator/Alternator combination is.

Is your "wastewater" Sewerage?

You refer to "Wastewater" and I presume you mean sewerage, if so, you could use bacterial digesters, in enclosed large concrete tanks, and use the biogas from the digesters to run a high-speed turbine, and perhaps generate a few thousands of kW, dependent on waste-stream input.

The effluent can then be dried/sterilised via the surplus heat (the exhaust from the biogas burning in that high-speed turbine), bagged and on-sold as high-grade sterilised fertiliser.

There are efficient operations of this nature, in various locations around the World.

Appreciate further advice re the proposed installation.

Kind Regards....

Thank you for your reply. The water in question is the final effluent which has already been cleaned and sanitized with chlorine. The weirs that I mentioned are dumping the water into the final outfall conduit which empties into the local waterway.

The Kaplan turbines that I have in mind (see attached photo) have fixed blades. I'm trying to keep the design as simple as possible in order to maximize the cost of installation to power production ratio. The units come standard with AC alternators only. The manufacturer will not provide DC generators, so I need to smartly and inexpensively convert the AC output to DC and then invert it back to AC with a grid-tie inverter. The spec's for the units are as per my previous post.

You mentioned that if using a Kaplan turbine "the costs of maintenance are going to be quite large, in proportion to the total power output obtained". Other than cleaning and greasing the bearings at regular intervals, what other maintenance would be a large expense?

Regarding your comment regarding using and vertical Francis turbine, do you have a recommended manufacturer that you could refer me to?

Hello again gusmenocal

Kaplan Turbine Runner with fixed blades is less efficient, but because there is no complex servo-mechanism along with the central shaft and associated adjustable pitch blades, it should be more efficient than a vertical Francis Turbine, for the same water head.

As you intend using the Kaplan Turbine Runner with fixed blades, it is as you say, very minimum maintenance.

I would thus be using the same units you propose purchasing.

Kind Regards....

Sir:

The manufacturer that I am intending to use has larger turbines than the one I previously mentioned, that can handle larger flows. However, according to the spec's for these turbines, a larger head is needed to produce maximum rated power. For example, one turbine is rated as follows:

6 m head, .151 m3/s flow, 5000 W, 220 VAC, 1500 RPM, permanent magnet generator.

Since I intend to rectify AC to DC and then invert DC back to AC, could I use this turbine with the 2.5 to 5 meters head range and 05 to .14 m3/s flow range? If so, how can I determine what the wattage output would be through the variable head and flow ranges? I feel that this would be very similar to the way a wind turbine works with varying wind speeds.

Many of "answers" suggest different turbine types.

Lets here look at an electrical diagram of alternator i.e. generator with AC output. This kind of machine (example: an alternator in any car) must have an exciting winding as a synchro machine which will need a DC voltage to create electromagnetic field inside the machine. So ? Car alternator (usually three-phase) has three diodes to convert AC to DC. First (power) rectifier has high current diodes and second (for exciting DC current) has three smaller diodes and voltage regulator.

This type of generator gives you DC regulated output. In the car thick wires connect it to its batteries and loads. It is another solution that works from a shaft running someway from 100 rpm (idle speed) to thousands rpm These ready - from shelf, would be 12 and 24V rated units with required power (up to 1000 W and more).

The Connection to the AC grid is your converter DC/AC

Have you concidered using a pelton wheel??

http://en.wikipedia.org/wiki/Pelton_wheel

or a geared water wheel to generate the power??

There are more efficient micro-hydro generators around, specifically designed for applications similar to yours.

There are too many to list here.

I would suggest you have a look at and compare some of the alternate options while you are still at the design stage.

Regards,

Sapper.

Hello Sapper

The Pelton Wheel Turbine is not efficient at the low head as in this situation, as it needs at least 10 metres head to obtain reasonable efficiency.

The higher the head of water, the more efficient the Pelton Wheel Turbine becomes, being used at installations with over 350 metres head, for many years.

Kind Regards....

What you say about the Pelton wheel entirely correct for large systems, Micro-Hydro systems are still effective in the range we are discussing.

What I was getting at however, is that there are more options worth considering before he builds anything.

Regards,
Sapper

Thank you for joining the discussion. Do you have any data to support that a pelton wheel type turbine would be a more efficient option than a kaplan for the site parameters stated in my initial post?

Here's one I grabbed off one of the Australian RE sites.

Turgo 1900W Stream Engine (Regulator Excl.) [HYD-060] $3900.00

Click to enlarge Click to enlarge The Stream Engine employs a brushless, permanent magnet alternator which is adjustable, enabling the user to match turbine performance with available water supply or turbine output to daily electrical load demand. The Stream Engine is capable of continuous outputs of over 1 kW (more than 24 kWh/day - depending on loads, timing of usage and available battery storage), while requiring virtually no maintenance. The Stream Engine micro hydro systems employs high efficiency, precision-cast parts, and non-corrosive alloys for long life and durability. The Stream Engine is designed for use in battery-based power systems, with electricity generated at a steady rate, and stored in batteries for use at higher rates than is generated. During times of low demand, power is stored. An inverter is used when residential AC power is desired. Water from a stream is channelled into a pipeline to gain enough head (the vertical distance the water falls) to power the system. The Stream engine operates at heads of about 2m and upward. The water passes through a narrow nozzle causing it to accelerate before striking the bronze turgo wheel. The turgo wheel then turns the generator shaft. Up to 4 universal nozzles can be installed on one Machine. Nozzles are adaptable in sizing from 3mm to 25mm. Stream Engine is available for 12, 24, or 48 volts. "Balance of System" & Other Components Rainbow Power Company offers system design services. Also available are "balance of system" components including batteries, inverters, and charge controllers. Batteries are an integral part of the self-sufficient energy system. Lead-acid, deep-cycle batteries are usually used in conjunction with solar, small wind, micro hydro and hybrid (incorporating multiple energy sources) systems. Deep-cycle batteries are designed to withstand repeated charge and discharge cycles typical in renewable energy systems. Inverters Batteries can supply only DC (direct current) whilst most appliances use high voltage AC (alternating current). In certain cases where DC lights and appliances are available they may be preferable to their 240V AC equivalents. Refrigeration is one example. Inverters are used to convert DC into AC so that stored battery power may be used, as needed, by appliances and other loads. Contact Rainbow Power Company for our wide selection of inverters and batteries www.rpc.com.au Only needs 2m or 6' of fall and basically a pelton sideways. I can direct you to more options once I get home as I am doing this from my work machine. The advantage to thes is you can use several nossles to take full advantage of the water that is flowing...This particular unit is nearly 2kW. Hope this helps, Sapper.

you just remended me of an old textbook which compared a number of different hydraulic power sources. Surprisingly the most efficient was the overshot waterwheel, with efficiencies around 98%.

That is what I originally thought of..Unfortunately, it does not fit with this application due to head height restrictions.

Sapper...

back in 1993 I read of an application using an off-the-shelf impeller pump matched to a three phase motor, the motor was driven by the grid at below its synchronous speed (obviously) a head of water was then used to drive the impeller (the flow in the opposite to normal direction - making it a turbine) which took the motor into its generating quadrant. I thought the application was a wonderful use of standard components and because of the three phase coupling the generated electricity was automatically synchronized. I think that this application lacks volume or head but thought I would throw it in as I have not heard of this use before or since. BTW the efficiency of the impeller was surprisingly high (high 90's) I recall.

We would all be curious to see how this turns out but I like the air pump idea so much I voted for it. Appropriate technology with not too many conversion losses.

to Hux

Do you think that a 3 phase motor being driven by a turbine or any other mean has ever produced electricity on a scale that can be practically used?

Yes Hux,

This technology was also used in windmill power generation.

But it's not widely used any more, due to the irregularity of the neccessary windspeeds to constantly be above the "syncspeed".

It cost too much (in power) to start up a inductive syncronous motor/altenator.

and then when it's up and producing (KWs) then the wind dies.

An inductive syncronous motor will become an altenator and supply energy to the grid (if you have an excess) when it's driven appx. 5 to 10 % above the sync. rpm.

Depending on its design characteristics the amount of "overdrive" will vary, but generally 5-10 % is in the correct ballpark.

I'd shure like to know where you found such an off the shelf impeller.

if you remember; please let me know.

best regards

Jens

the electronics man

You wrote:-

But it's not widely used any more, due to the irregularity of the neccessary windspeeds to constantly be above the "syncspeed".

Maybe I misunderstood what you meant but the way its done is to control the speed of the alternator by the use of variable pitch props, to a speed slightly above the local frequency (50 or 60 Hz), then connect.

Once they are connected, speed is effectively controlled by the grid, increasing blade angle to increase speed ONLY results in an increased load generation, the windmill does not have the necessary power to affect the frequency of the grid directly.....

Yes Andy,

You understood me correctly, you just explain it a different way.

The result is the same.

But my explanation is easier for someone NOT in the industry to understand I feel. I did not find your explanation at all helpful, sorry!!!

You right, but.. as usually it is BUT.

"Explain the problem and its solution as simple as possible BUT not too simple"

I was instructing - teaching - lecturing - training - conducting tests and experiments and found that the most effective are DIAGTRAMS and other Drawings as well as graphs of functions and results of measurements.

See? In the knowledge transfer transmitter and receiver MUST have the same level of "understanding". Better is if the transmitter has all the levels the receiver has + some extras.

Returning to the original question/problem: It seems the author of the question has some level of certainty how to use free water power, he also knows the best his facility and its needs. For me it seems he needs more strict designing variants of electrical system including generator - to - grid connection, and here I see more than one solution. Using just a text exchange communication this topic cannot be satisfactory solved. I suggest: First contact via voice than design several diagrams, fill blanks in the Data Input form and create initial technical documentation = design project. It is rational way in the engineering world!

Not the way you have put it!!

Herr Germany,

I see from all of your previous posts on this thread that you are very good at criticizing the ideas and proposals of others, yet I have yet to see any idea that you have suggested or that you support. However, I was surprised to find that you did not criticize my alternative idea for pumped water storage/regeneration!

Are you saying that Gus should not attempt this energy salvage project because he is doomed to failure due to high equipment cost and low return on investment?

I just want to be sure what is your position, since you did not seem to take one on anything, except to criticize or reject all the ideas of others (except me!).

Andy,

Look at the explanation 123southern gives, he explains it yet another way.

It seems to me he is an instructor in this field.

Maybe a bit easier for you to understand him.

I'm a retired college teacher, but NOT in this field.

(electronics and programming though)

Hi

I would like to contact you, maybe voice via Skype? Or maybe we can try A Conference with Andy too?

Electronics is controlling The World!

I read about this in a book, (I can't find references to it anywhere), describing the project, it was micro hydro possibly in Canada, the guy who carried out the project had assistance from a university and the surprise for them was how efficient an impeller pump was when used as a turbine. They were expecting inefficiency and prepared offset that against convenience, but the measured values were remarkably high. The generated output was around 10kW. It was consistent as there was a reliable head, the component cost was low; a standard induction motor and centrifugal impeller, there were safety features, a no-volt release for the situation described by johnbob, and to answer yvcassagnol this is one application where it worked, there are others.

To Hux

THANK YOU!

I like the air pump idea as well, but if that is not feasible, for whatever reason, you are back to square one with your original question.

However, it sounds somewhat inefficient, particularly the use of the inverter to turn rectified DC current back into AC. Especially, considering that you mention variability in head drop, and assuming that makes a difference in your production capacity, since you have no provision to store energy, other than the grid-tie in. Presumably, you are, or will be, selling power to the utility (at wholesale rates no doubt) then buying it back from them (at much higher commercial retail rates) when your peak usage does not coincide with your peak production capacity. While this in itself is not an energy efficiency issue, it certainly is a fiscal efficiency issue!

If it is possible to connect the fluid output of the weirs to a central holding tank or reservoir, you should be able to store the energy as potential energy and only use it as needed, by using one central generator (or several synchronized ones) to create the power on demand, shutting off the reservoir discharge (and therefore conserving energy) when not needed. This would also help you shift your commercial energy consumption to lower cost off-peak periods, and utilize your home-grown energy during the times when the utility charges the highest rates. I am assuming that your energy usage is fairly constant, but even if not, this still puts you in control of your energy usage. It might even prevent the need to ever sell your valuable energy at wholesale rates.

A long time ago, when micro-generation was new, people got away with feeding energy back through their meters, essentially selling power to the utilities at retail rates, and buying it back as needed. When the bean counters at the utilities got wind of that they quickly got the engineers to devise means whereby they would only credit their customers at wholesale rates for any power fed back into the grid, yet still charge the full retail rate for any power supplied from the grid.

Even if it is not possible to collect the weir outflow in one reservoir, perhaps you might still see some savings as mentioned above by using the AC output of the micro-turbines to power many small pump/generators in a closed fluid storage system that includes both an upper and a lower reservoir. Many power companies do this to augment and control their generation capacity at hydro plants, and, until 2005, the Ameren UE company of Missouri even had a stored energy plant (Taum Sauk) that was completely and exclusively used for the purpose. They even had plans to build another similar plant nearby. What ended the project, or put it on hold anyway, after many years of success, was a failure of the earthen reservoir and subsequent flooding of the surrounding area. Despite financial losses from the subsequent lawsuits (due to private property damage and the destruction of a State Park), the company announced plans to reopen the plant after repairs were made. Got to keep those bean counters happy, you know! Besides, insurance is apparently footing most of the bills!

Two points I would note; every time you convert from ac to dc [or v/v] it is not 100% efficient, probably 85 -95% efficient; so you are wasting power and investment if a stage can be avoided.

The other point that must be costed is you have to obtain permission to export to the grid and in doing so reach certain standards of power supply & protection. Notably G59, which as a previous member noted is to protect the REC from working on a line they have made dead only to find you are generating at the other end! This is done by auto disconnection of your generator from the grid if it goes dead, by fault or planned outage. G59 does this by either monitoring RoCoF [Rate of Change of Frequency] or Vector Shift. This protection panel could cost £1,000 and has to be done by an approved electrician.

<Is this scenario feasible for this application? Is there some other option which would be more appropriate?>

scenario feasible? YES

some other option? Again YES--like variable power-rate onto a bus with excitation Control by intelligent dedicated human/robotic operator. This will minimize the inevitable Triple dissipation losses of the rectifier/battery/inverter.Of course you have to work out the bottom line question.

Our discussion just deviated from its original question.

But..

I had a hydro-generating small facility in 80-ies. The turbine was an old fashion vertical unit and as a generator was used regular 100 kW SCIM. Water flow was pretty stable so electrical energy had a nice kWh/month. Problems happened when grid went to zero voltage even for v. short time (less than a second). It happened frequently in a lightning season. So system had electromechanical control and proper electrical protection on the grid/generator side.

This info is to give you a proof of the possible usage of a three-phase non- synchronous motor in its generator mode.

To accommodate the varying flows and heads I am considering rectifying the AC output from the alternator to DC rectifier and then inverting back to AC through a grid-tie inverter for connection to the facility's electrical supply. Is this scenario feasible for this application? Is there some other option which would be more appro.

Its a gross waste of energy due to the losses involved at each conversion.

For example 1000 watts AC converted to DC will probably give at best 800 watts DC. Converted to AC again you probably only have about 640 watts left!! or 64 % of your original energy!!!

The figure could be even worse and you could lose easily 50% of the original value!

Charging normal Lead Acid batteries is not much better as the are only around 80% efficient, due to losses in the charging cycle......but if you have a reasonable surplus of cheap electrical energy, it is often acceptable....

I think that you need to think this through much better. Also, returning energy to the grid, is not well paid and the equipment is expensive too, that may not be worthwhile at all!!!

If the output AC voltage from your generator is the same as a voltage from the grid (called service in the USA), e.g. 220 or 240 Vac, you do NOT need introduce two additional stages i.e. Generator AC to DC and inverter DC/AC to connect to grid. The synchronous generator must have a voltage regulator, asynchronous AC machine will be generator if its speed will be a little above its synchronous value. Read other answers on this forum. First-max power available fron the turbine must be measured, then the calculation and machine selection must be done, then the test performed to avoid overdriving and overcurrent conditions which anyway shall be protected by electromechanical systems.

But, if you will have DC storage batteries connected to DC generator_out/inverter_in you will have another option: keep electric power supply to your loads (inside your facility) in the time of the grid blackout (outage). Here I should draw a diagram so electricians could get the difference!

Off the Shelf/Kaplan-- is it the best choice?

Or may be Bulb type?

2 or 1 unit?

Suggest you look and think with this link:

http://energy.sourceguides.com/businesses/byP/hydro/microhydroturbine/byB/byB.shtml

"Explain the problem and its solution as simple as possible BUT not too simple"

I was instructing - teaching - lecturing - training - conducting tests and experiments and found that the most effective are DIAGTRAMS and other Drawings as well as graphs of functions and results om measurements. How I mentioned before I ran also the hydro-power plant and cooperate in constructing very simple power station on the creek.

See? In the knowledge transfer transmitter and receiver MUST have the same level of "understanding". Better is if the transmitter has all the levels the receiver has + some extras.

Returning to the original question/problem: It seems the author of the question has some level of certainty how to use free water power, he also knows the best his facility and its needs. For me it seems he needs more strict designing variants of electrical system including generator - to - grid connection, and here I see more than one solution. Using just a text exchange communication this topic cannot be satisfactory solved. I suggest: First contact via voice than design several diagrams, fill blanks in the Data Input form and create initial technical documentation = design project. It is rational way in the engineering world!

I offer my Skype (free of charge conferencing via voice in English or ??) for "start over the solution process"

Finally - let me warn you with doing too simple connection to the grid. It could create terrible damage if not done professionally!

Thank you for your input. I do indeed have a level of certainty on how to utilize the untapped water resource at this facility. It is challenging due to the varying head drop and water flows. In my mind the variable power at this site is similar to what one would encounter in trying to install an array of wind turbines.

The logistics of this site are conducive to feeding power back into the facility due to the close proximity of a large electrical panel to the water outlets. The deal that will be struck with the facility is that they will pay me the retail cost of kWh's produced.

I realize that rectifying and inverting the output from the turbine alternators is somewhat inefficient, however the cost of the turbines I have in mind is attractive. I don't see any other option due to the variables. Do you have any other suggestions?

Gus,

I did not realize that you are an outside contractor offering to install and operate the waste energy system. I assumed from your post that you were either an employee of the facility or some hired consultant looking for the best way the facility could salvage the waste energy from the weir streams.

Still, my proposal for pumped water storage/regeneration could have some merit. Does the facility guarantee they will purchase ALL of your power at the retail rate, regardless of their requirements? What kind of deal can you make with the utility (wholesale price?) if the facility does not take all the power? Do you have any energy storage plan in mind?

Perhaps you should at least look at the alternative of a pumped water storage/regeneration system versus rectification/inversion (AC-DC-AC conversion). At the least it will show the facility that you have "done your homework" and looked seriously at alternatives before choosing the most effective one. Obviously, the facility management wants you to succeed, because such a partnership would be beneficial to both of you, so they would want to be sure you are making the best proposal before they approve and enter into a contract with you.

Good luck to you in your endeavor. Always nice to see a technical entrepreneur at work!

Sir:

This facillity will use all of the energy created by the micro hydro system. The amount of power that this site uses is huge. So, the 35 - 40 kW average that this system will generate will all be consumed locally. The deal which will be struck with the facility is that they will pay me the same price per kWh that they are paying the utility. This will pay down the install cost. Once the system is paid for, the power purchase agreement will convert to a perpetual revenue sharing agreement (75%-25% in my favor). This is a relatively small project, but I am using it as a spring board to get other larger and more lucrative sites from the same facility manager.

Storage of the water is not an option. We must just capture the flow as best as possible without disturbing the current outfall scheme.

You misunderstand me. I did not mean to capture the outflow of the weirs. The pumped water storage/regeneration system would be a closed system, with no fluid input/output, except possibly a small amount of makeup water if there are any losses. Unlike the air pump (trompe) proposed solution, this would still use your system of microturbines to produce AC.

This would be an alternative to the AC-DC rectification and DC-AC power inversion process you are investigating. It would solve the same problem, plus allow for large energy storage with the expense of storage batteries which have limited life and must be replaced periodically.

Many electric generation facilities have such systems as an economical way to shift energy production from off-peak generation to peak demand periods.

In my experience, most managers who review proposals like to see proof that alternatives have been considered before the proposed solution was selected.

Just a thought.

That is very true, if you want to store energy cheaply & efficiently pumping water up to a height and storing it there, releasing the potential energy to drive a turbine when power is needed; it's environmental as well (no pun intended!). No battery banks with acid giving off hydrogen & lead pollution further down the line.

Water towers have been used for many years where water is pumped in times of excess power an retrieved when needed. Also it sounds fitting for a water plant, they will be dealing with familiar technology, nice suggestion.

Oops! Let me correct myself. My original suggestion did including collect the weir outflow to a central reservoir. However, if this is not possible or practical, then the power from the mini turbines could be wired to mini-pumps in a closed system which recirculates water from a separate reservoir to a storage tank and back again through a single turbine generators on an as-needed, or peak-period, basis.

At this facility during times of high flow is when the facility is using the most power. So to store energy at this time would be counter-productive. The power generated by the micro hydro system should be fed back into the plant at such times.

If I were to utilize induction motors on the turbines, how could I make them work with the varying heads and water flows? If this is somehow feasible, it would remove the AC-DC, DC-AC conversions.

This is it!

If demand for electricity has the SAME trend and fluctuation in time as power from the WATER (means kinda of power synchro in restoration) installing asychro S C I Motor to return presently wasted energy is the best solution, also less expensive and maintenance free. In voltage outages SCIM as a generator CANNOT deliver power because it has no source of excitation to keep output voltage when the external source (grid via service) goes down.

Anyway -WARNING!- you have to do tests your new system for transients. If time delay between moment of shutting down of the voltage from service and end of voltage from asynchro machine is less than a second you are in safe zone in dynamic action of your "system". From your description, I cannot see necessity of electromechanical shutting down control system on the mechanical side of the system - too small machines installed, seems to be less than 20 kW in total.

Be sure to have proper electric protection means according to Electrical Code.

About your last your question - any system having SCIM as a generating (returning energy to the electric system running loads-+other motors) must have only connection to the grid for synchronization (60 or 50 Hz). SCIM will naturally run RPM at a little over its synchro speed, e.g. 1870 rpm for 4-pole machine with USA standard 60Hz suppliers. Full power (according to you as a salvage)) from the water minus losses will be returned to the facility. And of course you may select any easy and cheapest mover to utilize the water flow. For insurance purposes do series of tests from minimum to maximum flow rate and of course at the transient times. For Do note how works energy (kWh) meter. It will be your best "inspector". You will avoid any responsibility for the damage/sabotage done while you are not present around your system. The written contract with disclaimers is necessary. Facility manager may expect approval from Electric Company owner of the connection to the service.

I would asked facility manager to give me one of maybe existing in their storage room motors, rated for the same voltage as ones already installed. Or ordered anothers from their nameplates. At least for test when I could get confirmation of my theoretical calculation of the available power from water flow (Max flow Q and head H). I could give you tips what set of meters & data acquisition (for recording results of the tests) you need

I owned small hydropower facility for years with a few more protections and had no problems. Even in the lightning season. But I started with designing project and series of tests.

Good luck and go far!

I believe I see better your project:

From your generating units/station power will be send to the facility electric panel. You will sell energy to the facility. So you do need kWh meter of course. In the case of suggested by another engineer storage tank + a pump - kWh-meter should be bidirectional type. In the case you need an energy storage up to now you have to consider at least two versions: AC/DC converter +electric battery bank + DC/AC converter or Pump/turbine (bidirectional) + alternator (machine to work as generator as well as motor). I believe you can do calculate ROI

I do not know what is a design of the panel: single or three phase?

Does it have undervoltage or similar protection to disconnect it from main feeder or service so voltage down from the service will be immediately disconnect in the black outs? Here is hidden a devil in details.

And a few more details that must be put in the designing diagrams.

I believe, anyway you will be better in the situation without AC/DC +DC/AC converters.

Fell free to contact me via CR4

Many good ideas have been presented here but you should consider the objective. Your customer wants to reduce the overall energy consumption. Your best chance of success it to have the simplest system possible. Anything complex will fail and won't be repaired because it will cost more than you save. You have to look deeper...

I like gaiatechnician's suggestion of directly compressing air to inject in the process up stream. They need that anyway and could turn off the main blower. The exact airflow is not very critical. You can add more than needed without consequence which solves your varying head problem.

If you want to stay with your micro-turbine, can you run a small agitator for each turbine. This way you don't need to parallel them. Agitation in used water plant is needed but the amount is not critical either. I am sure that they have a large agitator that could be replaced or supplemented by many smaller ones. They could even get a better efficiency because of the better pond coverage obtained.

Rectifying the single phase AC will give you pulsating power and harmonics in the generator which will reduce it efficiency. Parallelling many units will require load sharing controls. You are in for a big head hake..

No that is a really good idea.

You can get a few chances to regulate and correct the flow rates charging and supply with the different systems.

With the current technology that is what I would do.

Dear Mr.gusmenocal,

The scenario explained by you is TECHNICALLY FEASIBLE.

DHAYANANDHAN.S