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Micro Hydro

Micro-hydro systems are typically defined as 300 kW and less. The limit is set to 300 kW because this is about the maximum size for most stand alone hydro systems not connected to the grid, and suitable for "run-of-the-river" installations.

A small micro-hydro generator that receives flowing water under pressure (from an elevated dam or stream), uses the power of the water to turn an impeller, and the impeller's shaft turns the electric generator to make electricity.

To better understand how a micro turbine works, a water pump works in reverse of a hydro generator.  For a pump, electricity is used to turn a motor at high speed (eg. 1720 rpm).  The motor shaft turns an impeller.  The impeller is in an enclosed case flooded with water.  When the impeller turns, it sucks water in from the pump's suction inlet pipe, and forces the water out of the pump at significant pressure and flow through the pump's discharge pipe.  The water pump is the exact reverse of  a micro turbine.

This model of micro-turbine needs at least 6 feet of head (ie. the water supply must be from a source of water that is at least 6 feet in height above the top surface of the water discharging from the turbine.

The turbine produces DC electricity that can be used to charge batteries, or used directly to power some electrical load.  An inverter can be used to change the DC to AC power (standard household current).

On a $/kW-hr, over its expected life, micro-hydro will produce some of the lowest cost power from any available source, typically as low as $0.03 per kW-hr.

Here we see a water source coming from the top of the hill, with a pipeline bringing it down the hill to a turbine at the base of the hill.

As we descend the hill, the pressure inside the pipe increases, 15 psig pressure for every 33 feet we descend down the hill.

Water level can be controlled, and the amount of water flow can be measured by use of a V-notch weir.
The flow rate in a stream can be estimated by sounding the depth of water at various points across the width of the stream.

A float on the surface of the water can be used to estimate the velocity of the water flow in the centre of the stream.

Calculus can be used to obtain the total cubic meters per second of water flow from this simple data collection.


Old mill ponds can be refurbished and retro-fitted with the latest in high efficiency turbines, generating sufficient electricity to power an entire house or farm, with sufficient power to justify commercial export of power to the local electrical grid.

Large siphon turbines use grid power and electric motors to run the turbine as a pump to get water flowing up the high side of a dam, then down the other side by gravity and siphon.

Once the flow is established, the grid power to the electric motor is cut, but the water continues to flow due to the siphon action.  The electric motor on the turbine then becomes a generator, sending power back to the grid.  If the siphon is lost for any reason, the process is repeated, re-establishing power generation.

10 kW siphonic turbine (large blue object in foreground, with dark blue motor/generator and red V-belt cover), 11 siphon intake pipes in mill pond edge can be seen along right edge of photo.
5 kW siphonic turbine installed at old mill pond
Low head turbines of 200, 500, and 1,000 watt turbines that need just 1.5 meter head.

They are ideal for remote locations, and need minimal civil work to install

They can be installed on a side stream, at a dam, or a rapid/falls in a river.

Durable, low-head bronze propeller to produce power on a head of 2 to 10 feet

~90 watts at 2 feet of head with ~450 gpm

 up to 1000 watts at 10 feet of head with 1000 gpm

In-stream, submersible generator.  Also available with prop shroud to protect prop from damage and fouling.

Rated at 96 watts (8 Amps output current for a 12 volt system at 9.2 mph or 8 knots or 4 m/s current; or 4 amps peak at 24 volts DC; or 2 amps peak at 48 volts DC.

Water speed greater than 4 mph (3.75 knots or 1.79 m/s) is highly recommended or power output will not be significant. Power output increases with faster water speed.

Francis-style turbine for heads as low as 3 ft.  while producing 2.2 kW of power.  Life expectancy of 50 years with 7 to 10 years between bearing changes.
Water coming from 60 ft. up the mountain (white pipe) is used to generate up to 5 hp of power for woodworking using a water motor, powered by a modern turbine.
Hydrological resource data can be collected to show the total amount of water flow available at different times during the year.

The red shows the water without the hydroelectric system, the blue is with the hydroelectric system.  All the available water resource is only used for a few months during the summer, at the time of lowest stream flows.  At other times, there is excess water flow.

The above data is summarized into one graph, the FDC (Flow Distribution Curve), showing the water flow rate vs. the % of the year that that flow is exceeded.

An optimum turbine needs to be selected.  Too big, and it can only operate at spring and fall runoff.  Too small, and it misses the large opportunities but stays running year round.

The optimum turbine often is able to operate 80% to 90% of the year.

A typical microhydro site will cost $2,500 to $10,000 per kW capacity to construct.  Refurbishing of prior, abandoned sites can be considerably cheaper.  Typically, sites have a 50 to 100 year life cycle with only minor maintenance required (clean away debris weekly, bearing replacement, etc.).  When operated at 60% capacity, the system will usually pay for itself in 3 to 10 years, and thereafter is pure profit.
The most efficient turbine wheel design depends on the available head, specific speed of the turbine, and the kW produced.

A Pelton wheel turbine is one of the simplest and most efficient designs for high head micro-turbines.  Microturbines may have a wheel diameter of 3", where the largest dams (eg. Niagara Falls, James Bay Hydro, etc.) the turbines can be 30 ft in in diameter or larger.

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Page Last Modified:   04-May-2009 05:45:36 PM -0500