The problem with using these units is they are designed for solar-electric arrays that put out a defined high-voltage limit that isn’t too much higher than the system’s running voltage. However, in a DC hydro turbine, the open-circuit voltage is twice the running voltage. So using an MPPT controller directly with a hydro turbine is limited to low-voltage systems.
One “bleeding edge” method is to connect the hydro in parallel with a solar-electric array at about the desired voltage, and the array will “clip” the peak voltage at about 10% above its rated open-circuit voltage. The modules act like giant zener diodes protecting the MPPT controller in high-voltage conditions. Many small hydro systems are on seasonal creeks that dry up in the summer, so a PV array is already a part of the off-grid hybrid system. The MPPT controller gets the maximum output from both components of the renewable energy system.
I would love to see some real numbers comparing the efficiency between the different manufacturers’ turbines. If independent testing showed their efficiency under specific conditions, it would aid in deciding which turbine to install. There are newer products available, but I hesitate to invest in lower-cost turbines if the savings is negated by lower output.
All I have is my own tests of Harris units that back up the claims of up to 70% efficiency. I always use these turbines except for low-head sites where the Turgo wheel on the ESD turbines can handle higher flow and faster rpm. With their simpler, nonadjustable magnets, the APM turbines might be a lower-cost alternative if the efficiency is still high. PowerSpout turbines have some interesting features, including a built-in voltage clamp that works with MPPT without other electronic tricks, or with higher voltage grid-tied systems.
Educate yourself as much as possible before getting expert help. The more you know, the better questions you can ask. Read older articles in Home Power and online. I find the best level of expertise is on the fieldlines.com forum. I try to answer questions about hydro posted on that site.
There are a limited number of people with experience with multiple hydro systems, so you will have to choose someone who can see all the possibilities of your site and create a system that does what you need. Any RE dealer can provide the batteries and inverters, but you may have to search harder for someone local to design and install the hydro system.
My personal off-grid system includes two Harris hydro turbines. One is producing about 200 W at 24 VDC from 35 feet of head. The other is currently putting out about 1,000 W at 70 VDC from 110 feet of head into an OutBack Power Systems FLEXmax 80 MPPT charge controller.
During times of higher flows, the larger magnets in the second Harris turbine boost the energy output. The old configuration topped out at 920 W, and it’s now more than 1,000 W. I haven’t completed testing this arrangement to find its maximum output.