Grid tied micro hydro using Pump As Turbine

[Dassie]

Hello everyone,

We’ve successfully managed to beat load shedding (ie. planned power outages) during the summer months on our farm in South Africa.

Our setup includes:

• 8 Deye hybrid 12 kW 3-phase inverters
• 48 Shoto SDC-10 Box 5 batteries
• 1 x 10 kW and 2 x 20 kW grid-tie inverters feeding into our microgrid.

The Challenge: Winter Is Approaching!

Proposed Solution:

We’re considering using excess irrigation water to drive a Pump As Turbine (PAT). We’ll couple it to a 9.3 kW single-phase generator alternator (currently unused, previously powering the main house via a Lister diesel engine).

Here’s the plan:

1. Rectify the AC power output from the alternator to DC (using 50A full bridge rectifier, appropriate smoothing caps and dump & discharge resistors).
2. Feed this DC power into the MPPT input of a 10 kW or 20 kW grid-tie inverter.
3. Use the generated power to supply our base load during the night (minimum 10 kW), potentially reducing our battery usage and reliance on utility.

We have several unused 3-phase grid-tie inverters (Goodwe, SunnyBoy, AE, MicroCare, Fronius Synmo, Hauwei, etc.). The current pump’s RPM reached a maximum of 3500 during an initial test. With a 70 m head and a 160 mm PVC pipe diameter, water supply isn’t an issue—our dams overflow consistently in winter.

Questions:

• Is a VFD needed before rectification?
• Is a switch mode power supply a better option, to convert AC-DC?
• If possible, is there a more efficient way to do this?

Let me know your thoughts.

 

[Tom.G]

It turns out that there is commercially available equipment to connect 3-phase power from wind turbines to the grid. Just replace your existing generator (motor) with a 3-phase one and buy an off-the-shelf interface.

See https://www.physicsforums.com/posts/6131692 for a successful project.

Cheers,
Tom

 

[Rive]

Some parts of your questions are a bit off in a way that makes me suspect that I missed a point entirely.

Is a VFD needed before rectification?

VFD is a special AC (sometimes: DC) to AC conversion device. It converts 50 or 60Hz to DC, and then DC to adjustable frequency AC. Unless I miss something here it's not needed, it would only cause unnecessary loss.

Is a switch mode power supply a better option, to convert AC-DC?

The first step of an SMPS is an AC to DC conversion, then a DC to DC conversion. It would just introduce further loss, unless I miss the point here too.

If possible, is there a more efficient way to do this?

Be sure that your high current rectifier setup is up to the task (frequency, current).

 

[Dassie]

@Tom.G
Off-the-shelf solutions are a bit pricey in my area, especially considering that we only have about 4 months of sufficient rainfall to keep the turbine running, so ROI would take a while!

@Rive

• I was thinking that a VFD could be used to bump up the frequency of the AC, prior to rectification, to reduce the ripple voltage on the DC side? Just a thought...
• I read a post where someone's inverter was having an issue with dirty DC after rectification, and that he solved the issue by using a SMPS.
• Stay tuned...

So I ran a test today with a smaller 300W single phase AC pelton generator.

Using a 50A 1000V full wave bridge rectifier for AC-DC conversion, I connected two 45uF 440V capacitors in paralell on the DC side, including a light bulb and switch for discharge, then straight to one of the MPPT's of a SunnyBoy Tripower 12kW grid tie inverter.

We opened the valves, and then.... EUREKA!

It worked like a charm, producing way above what we expected it could. The peak power measured was 580W with the voltage staying around 250VDC (see attached image).

The next step is to take our old Lister generator apart and fit the alternator to the old pump, and then, hopefully, produce anything between 8 - 10 kWp.

I will keep you posted on the results!

(Also see attached snippet from SunSynk manual, showing schematics of wind turbine integration. My layout is exactly similiar, except that I left out the smoothing resistor, used smaller caps, and generating single phase instead of 3 phase AC.)