The force and consistency of flowing water is unmatched by many energy sources. As history shows, one of the most proven and reliable sources of mechanized power is hydro power. Unlike solar and wind, hydro-power works day and night with changes in output typically happening gradually. During the Industrial Revolution the use of hydro-power transitioned from powering grain mills to powering electrical generators. The majority of early electric power plants were water-driven. Since then, our energy demand has increased significantly and hydroelectric power now supplies around 18% of the world power demand (and that number does not include micro-hydro setups). In 2007, according to electrical power generation statistics, hydroelectric provided 36% of the electricity in the renewable sector, coming second to biomass (EIA 2007).
It is important to note that micro-hydro power plants can, in most cases, be easily implemented by the property owners themselves. But what is the limit for micro-hydro power production? Here the legalities get a bit fuzzy, as the ratings vary from state to state, and of course from country to country.Usually micro-hydro is classified as producing about/around 5 kilowatts or fewer, but check with your local hydro expert for more area-specific ratings.
When it comes to hydroelectric, having a preexisting dam is always a plus since these can be grandfathered into your hydroelectric plans, whereas usually you are prohibited from disrupting the water flow of most streams or rivers. You can even use the water flow from a mountain spring if the flow is great enough. Once you have determined if you can do it, you need to determine how you are going to capture and use the power from your water. Water-powered turbines have two main classifications: impulse and reaction. Some examples of impulse turbines are the Pelton, crossflow, and Turgo. A few common reaction turbines are the Francis and the Kaplan/propeller.
High head: High head is typically anything above 100 meters or 328 feet, but this height can be lower for micro-scale systems. With high head you are relying on high pressure to drive your turbine. The turbines best suited for this task are know as impulse turbines, the most popular being the Pelton wheel pictured above. The Pelton is a vertical turbine which uses one or more nozzles, and its best efficiency is met when the wheel speed is half the water speed. For lower head and higher flow, a Turgo turbine usually works well. Turgo turbines are horizontal and can also use one or more nozzles.
Medium Head: Medium head is basically anything between high and low head; that is, more than 10 meters and less than 100 meters. A Francis turbine is commonly used for medium heads. This turbine has fixed blades and also has guide vanes which are typically adjustable. Adjustable guide vanes helps maintain speed with varying water flow or power loads, thus increasing overall efficiency.
Low head: Low head is typically less than 10 meters or 32.8 feet. The Kaplan or propeller turbine is commonly used, and this style turbine looks similar to the style turbine you might find on a boat propeller. It is intended for low head sources with high flow, and is usually custom designed for the site.
After the spring thaw in 2009, Sara and I built and installed a Pelton turbine to utilize the energy of the Townsend Farm's mountain spring. Click to check out the videos from that project, which explain choosing a generator and building a micro-hydroelectric station. At the farm, we used the electricity from the turbine to power the lights in the horse barn.