Microhydro Equipment & System Design: Page 3 of 3

Intermediate

Inside this Article

A hydro-electric system uses the flow of water down a slope to create electrical energy.
1. Intake; 2. Screen
3. Vent Pipe
4. Penstock
5. Manifold
6. Pressure Gauge
7. Turbine
8. Alternator
8. Alternator
9 Transmission & Power Electronics

9 Transmission & Power Electronics

The farther the turbine is from where the electricity is used, the more expensive it may be to run wire. As with the penstock, you must weigh cost versus the energy loss. Wire used at common battery voltage is heavy and expensive—not because it is DC, but because low voltage has greater wire loss. For example, you’ll need 16 times more copper in a cable for a 12-volt microhydro turbine than you would for a 48-volt turbine of the same power. It is common to use even higher DC voltages—like 200 VDC—feeding a maximum power point tracking (MPPT) charge controller or a grid-tied inverter. (High voltages can be lethal. Stop the turbine and isolate the wiring before working on connections.) The only advantage of AC for power transmission is that you can use transformers to easily step the voltage up at the turbine and back down at balance-of-system electronics. MPPT devices (controllers and inverters) now make this unnecessary.

Most small off-grid hydro systems are battery-based, so the accumulated energy can be stored and used when needed. The battery will not cycle as much of the energy as it would in a PV system, but it still needs to be suitably chosen to maximize its service life. You will need to program the charge controller with the correct voltage settings for your chosen battery type. Larger hydro systems may be able to be used off-grid without batteries, but there will need to be a lot of surplus water power available.

Power electronics—charge controllers and inverters—for microhydro systems have evolved rapidly in recent years, becoming more sophisticated and useful, and less expensive. They can:

  • Convert power. A high DC voltage in the transmission wire is stepped down to battery voltage or converted to grid AC.
  • Maximize power output with MPPT by adjusting operating voltage. Solar controllers and grid-tied inverters can often work as well for microhydro turbines as they do for PV modules. MPPT software finds the best operating speed for the flow conditions. Make sure the equipment is compatible with your turbine and warranted for microhydro use.
  • Charge controllers limit the charging current during most of the battery’s recharging cycle, based on voltage settings for your battery type.
  • Energy diversion serves two functions. First, it protects against turbine overspeed, which can produce noise, wear, and possible damage. Turbines become unloaded when charge controllers limit the flow of energy from the turbine to the battery. Similarly, grid-tied inverters delay connecting the turbine during startup, resulting in overspeed. Diversion of energy to a heating load avoids these issues by keeping the turbine under load.
    The second reason for diversion is to maximize your turbine’s value by using all of the available energy. A well-designed battery system has regular energy surpluses. Rather than using a “dump load,” it’s better to take the opportunity to heat water or even your home.

Go Ahead & Do It!

The five case studies are just some examples of successful microhydro systems. There are hundreds more possible features and permutations, including automatic flow control, AC coupling, crossflow turbines, and reservoir intakes.

Because every site is different, some problem solving is inherent in designing a custom system. But with a good basic design and responsive technical support, the system can be easily tuned. If you have a suitable site, a microhydro system is very worthwhile, providing consistent clean energy.

Web Extras

“Methods: Hydro Measurements” by Ian Woofenden in HP170  • homepower.com/170.14

“Microhydro Turbine Buyer’s Guide” by Hugh Piggott & Ian Woofenden in HP174 homepower.com/174.28

“Harvesting Surplus Energy, Off-Grid” by Hugh Piggott in HP179 homepower.com/179.46

“Microhydro Intake Design” by Jerry Ostermeier in  HP124 homepower.com/124.68

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