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Kris Harbour Natural Building avatar image
Kris Harbour Natural Building asked

MPPT Charging for Hydro. Victron 150v Blue solar not finding correct Maximum power point

Hi all. i have been running my off grid cabin on hydro for over a year now. i have been useing a tristar mppt controller and fixing the correct voltage in order to load the turbine correctly. this voltage is around 50v under load. That is the ideal speed to load the turbine to in order to catch the most energy from the water. that 50v equates to the turbine moving at half the speed of the water leaving the nozzle, this is the optimum relationship between nozzle volicity and rpm.


Now i have had lots of problems with morningstar and decided to try a victron blue solar controler. I planned on useing the mppt controler to find the best voltage instead of me needing to fix the voltage to 50v. I have plugged it in and at first i found that is would be all over the place and not find a voltage and stick to it. It would sometimes get close to the right voltage but then do another sweep and loose it again. I put this down to the fact that it is acting differently from solar and could do with some large capacitors to smooth it out. I have done this now and tested it and it isnt all over the place anymore but it thinks the maximum power point is at 30v and it simply isnt. The maths says it is at 50v. i have been using it for a year at 50v and that has giving me the most power. (I have done endless testing) But for some reason the blue solar controler seems to think the maximum power point is at 30v My question is why? and has anyone got an ideas? It will sometimes do a sweep and the voltage goes up and as it does the wattage produced goes up to. but then it just goes back to the 30v again. at 30v i am loosing alot of my efficiency because that relationship between nozzle velocity and rpm is off.


Thanks for any help.


kris

MPPT ControllersHydro and Wind Power
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lief ryan avatar image lief ryan commented ·

hi kris, old thread i know but i just wanted to say hello, just out of interest, does your turbine run at around 50v without a load? i have a hydro turbine that i made from a washing machine (i'm in tipi valley near Llandeilo, not far from you) but it runs at anywhere between 100 and 600v depending load, the way i get round that is by using a grid tie inverter that has a very high input voltage range.

all the best

Lief.

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markus avatar image
markus answered ·

Hi.

try to limit the MPPT charging current, to not overload and stall the turbine under the 50V Vmpp.

Best Regards,

Markus

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Kris Harbour Natural Building avatar image Kris Harbour Natural Building commented ·

But then i would be limiting the charging current. the whole reason for this post is because my system runs at over 70% efficiency so i cant just limit the charging current. because then i might as well just accept the large loss from the mppt not finding the right maximum power point

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markus avatar image markus ♦♦ Kris Harbour Natural Building commented ·

You said that you found out, that your turbine has a 50V Vmpp.

How many watts does your turbine produce when running on 50V?

What is the maximum charging current of your MPPT charger?

If your MPPT can do more watts than your turbine at 50V then it is possible for the charger to overload the turbine and brake it even under its Vmpp. Then the power is less at the 30Vmpp found, but the MPPT charger gives not enough time for the wheel to spin up to 50Vmpp again.

To avoid that situation, find out what the continuous power is, that your turbine produces at 50V.

Divide Absorption Voltage through max turbine watts and you get the Amp limit you should set in your MPPT chargers settings as max charging current.

When you have done that, the MPPT will not do a sweep at max power and therefore not brake the turbine down below 50V anymore.

Regards,

Markus

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markus avatar image markus ♦♦ markus ♦♦ commented ·

If you are interested in: This blog article describes my hydro installation:

https://www.victronenergy.com/blog/2019/01/03/diy-ingenuity-hydro-power-mkii-part-i/

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markus avatar image markus ♦♦ markus ♦♦ commented ·

https://www.victronenergy.com/blog/2019/01/23/diy-ingenuity-hydro-power-mkii-part-ii/

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Kris Harbour Natural Building avatar image Kris Harbour Natural Building markus ♦♦ commented ·

Hi, thanks for the reply, I actually decided to try a blue solar because of your blog post. nice to meet you.

The output of the turbine has nothing to do with the 50v. i can open more nozzles and go from 50w up to 500w all at 50v and not exceeding the amp rating of the controler. The 50v is required to make the rpm correct so that the energy in the water is collected. if i limit the charging current i dont achieve anything but loose power. Does that make sense?


On your system are you sure running MPPT is working efficiently for you? my testing is showing that is isnt finding the maximum power point, not for long anyway and then it looses it again. Looking at the video of your turbine in your blog post i can see that your turbine it not at its most efficant rpm as you can see energy being wasted as the water is blasted to the bottom of the housing. that water should have very litter energy left after hitting the turbine. What are your head, flow and efficiency calculations?


The solution you have offered i beleve would only work for a fixed system at fixed flows. my system is very variable depending on flows seasonally. And what nozzles i have open

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markus avatar image markus ♦♦ Kris Harbour Natural Building commented ·

:o)

"I actually decided to try a blue solar because of your blog post. nice to meet you."

I am sure we will get your problem sorted out! Nice to meet you too. Maybe it would help to help you, if you would provide more details of your installation. (MPPT charger used, turbine and generator data, fall height etc.)

"The output of the turbine has nothing to do with the 50v."

Dependent on your setup and setting, (nozzle setting, water flow, pressure, type of generator) the turbine has a Maximum Power Point. This means there is a Voltage, where the turbine generates most watts. The problem begins, when the MPPT charger has more power demand as your turbine can deliver. If you exceed max power, the turbine begins to stall and the RPM go well below under the turbines max power point. We are using solar chargers here, developed to be used with solar panels. Solar panels work different than turbines. Especially when unloaded, a panel will gain Voltage immediately. A turbine needs to spin up again, this takes time. The solar MPPT does not wait long enough for the turbine to raise RPM and therefore it is not possible for the MPPT to find a proper power point in overload condition.

So it is mandatory to limit the MPPTs power, to make it impossible for the MPPT to brake the turbine below its MPP.

Given that (as you wrote) your turbine generates 500W at full power on 50V. This is the maximum you can get out of your turbine regardless what charge controller you would use. (physic limit of your turbine).

As I wrote first, we need to avoid that the MPPT can take more than 500W, for the system to not get inefficient. That would be the case (given you charge a 12V system) to limit the MPPT to 34 amps. 500W/14.7=34

So if the water flow is not constant (not optimal) and your MPP is not either. So the MPP is not at 500W all the time. There are 2 things you could do:

1.) create a list with different amp limit settings, regarding to available water (or open nozzles).

2.) change your battery system Voltage to 48V so your MPPT can not pull down the Voltage below your battery Voltage anymore. This is because the MPPT can only step down, not step up.

"On your system are you sure running MPPT is working efficiently for you?"

Yes ;o) As long as I do not take more power from the turbine as it can deliver...

"Looking at the video of your turbine in your blog post i can see that your turbine it not at its most efficant rpm"

Yes, as long as I do not take all the available power from the turbine, the RPM is above Vmpp.

Regarding to the tests I did with my turbine, the Vmpp of my system is 60V.

My turbine at 60V

My turbine at 55V

I hope what I wrote, makes sense to you, I will be happy to help you further, if you have more questions...

Markus


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markus avatar image markus ♦♦ markus ♦♦ commented ·

There are even more options for you ;o)

3.) use a generator with a Vmpp matching your battery voltage

This depends on the coil windings inside your generator...

4.) as your turbine most probably produce AC, you could think of transforming Vmpp down to your actual batt Voltage...


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markus avatar image markus ♦♦ markus ♦♦ commented ·

or 5.) provide constant water flow to your system (if somehow possible) as it makes everything much more complicated when you have variable water input. :o(

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tilo avatar image
tilo answered ·

Hello,

The fact that you said you had recently also trouble with the Morningstar controller could indicate maybe another problem. Just to discard this possible reason - now in summer there might not be enough water. This can be difficult to detect without a pressure gauge (manometer). I have seen a hydro installation where the owner and his operator were not aware that they did not have enough water, even though they did have a pressure gauge, but did not pay attention to it and/or did not know how to interprete the pressure.

Do you have a pressure gauge installed? How much is the pressure during operation, and how much when you close the tube (and have full static pressure)?

If there is not enough water, your feed stock tube will not be filled completely with water, then you have less pressure, and less water speed at the nozzle, that means lower optimum rpm of the pelton wheel, thus (correct) lower MPPT voltage.

When the MPPT sweeps quickly through the voltage range, it might just temporarily have more power because of the mass inertia of the wheel when it was running at higher speed and then reduces speed.

In case you don´t have enough water, you need to reduce the nozzle diameter.

Regards

Tilo


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Kris Harbour Natural Building avatar image Kris Harbour Natural Building commented ·

Hi Thanks for the reply, yes i have a preausre gauge and very aware of presure drop. i designed the system myself doing all the measurements its a 25.4psi system and i know when the pipe is draining by the presure gage and the output dropping. I can also see it at the intake by seeing if a have excess water. I can also see it by monitoring the free spin voltage. I have monitored it and used it to power my house for a year and a half so im very much in tune with it and i can tell whats going on with it by looking at those things depending on where i am at the time. I also know exactly what flow rate the nozzles do and what it is set at so i can tell by looking at the stream if there is enough water there.


The problem with the tristar controler is that they are not robust and tend to blow mosfets just when you do things like change settings. its a common fault with them and morningstar dont seem to want to change anything so im trying to trile another controler.

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