question

Kris Harbour Natural Building avatar image

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 - Solar Charge ControllerHydro and Wind Power
2 |3000 characters needed characters left characters exceeded

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

2 Answers
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


1 comment Share
2 |3000 characters needed characters left characters exceeded

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

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.

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

14 comments Share
2 |3000 characters needed characters left characters exceeded

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

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

markus avatar image markus ♦♦ Kris Harbour Natural Building ·

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

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

markus avatar image markus ♦♦ Kris Harbour Natural Building ·

: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


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...


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(

or 6.) gain more fall height as you need less water then.

or 7.) to have an MPPT setting in future firmwares, to limit the MPPT Voltage window

" What are your head, flow and efficiency calculations?"

Hm, I used the anti scientific approach, when building my system. Build it as good as possible and see what it gets ;o) The system is limited by nature anyway, not by calculations ;o)

So I have 2 turbines, 1 produces continuous power of 600W, and the second one produces a continuous power of 1200W. The first one has one nozzle, the second one has 2.

Hi Thanks for taking the time to write all of that. The new turbine i have built can be seen on my youtube channel here, you will also see my old turbine that i have been useing for a year a nd a half now. https://www.youtube.com/channel/UC5rT7F0PGNuD54rJ9kzgWzw?view_as=subscriber

everything you wrote does make sense and was great info. it seems from what you have said that using mppt charging for your system works because you have fixed flows and therefore you dont have an variation in optimal rpm and instead of needing to fix the voltage you can fix the max charging current and i can see how that would work and it sounds like a nice simple solution for your setup. The problem is my system is very variable. my stream can go from a trickle to a torrent and then back to a trickle again in 24 hours and that is common for where i live in wales. Having a high level of control is really important in most cases due to the fast changing of flows. The only thing that makes my system viable is that i can change the flows as the water leval changes. the new turbine has 4 nozzles and this will all be controlled by a micro controler that i can open and close nozzles from my computer.


The best way i have found to get the correct voltage is to use a controler that i can fix the voltage to 50v. this means at low flow im a little bit off and at max flow im a little bit off optimal rpm but in the middle of the flow range 50v is the optimal rpm. this has worked really well and i think it would work better for your system to as it would have the same effect as your current limiting but instead limit the rpm. The problem is there is only really two controlers that have that function. one is the tristar and the other is the outback. both controlers are very expensive and the tristar has some design problems in my opinion. The victron controler seems a nice product but is really missing this function that would make it quite useable for hydro. If it had the ablity to fix the voltgae or set a % of open circuit voltage this controler would work well for hydro.



I could indded change my system voltage it 48v and get closer to the correct voltage and i think that would fix it. The thing is i am trying to make a versatile product and find a controler that will work in other situations to and if the victron controler had that function to fix the voltage it would be useable for a massive range of battery voltages and head and flows. I have emailed them and asked if they would want to work with me to maybe add the feature, i am waiting for a replay from them. if not i will try a outback controler as that has the function to fix a voltage or fix % of open circuit making it more suited to hydro. The way you have your system nice but it really only works if you have fixed flows and thats not what im trying to do as it isnt possible in my location. As for making a list of max amp settings, that would work but i am reluctant to have to change those every time i change somthing as i can open and close valves 5 times a day and i think it would be silly to do that when i can just get a different controler that will fix the voltage where it should be anyway. I just hope victron will work with me to add the feature as i think it would be a very useful thing for us hydro enthusiasts

kris harbour

Oh and to address the option of making the PMA match battery voltage. that is not an option either due to the losses involved in line loss if i was install a turbine on a 12v system. at 50v losses are quite low without having huge cables.

markus avatar image markus ♦♦ Kris Harbour Natural Building ·

!