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Small Hydropower Basics

Small scale hydropower generation, also referred to as micro-hydro, is a way of harnessing the energy of flowing water and putting that energy to mechanical or electrical use. Typical small-hydro systems are designed to generate 2 megawatts (MW) of energy or less. Harnessing the energy of water as it flows downhill has long been used to power industrial and agricultural operations. Flour mills, for example, used the water of a flowing stream to turn a waterwheel and mechanically drive the flour grinders. Today there are new technologies that allow energy to be captured from moving water and used to mechanically turn a center pivot, or even create electricity. The main benefit of small hydropower generation is the ability to use a device, called a turbine, to extract energy from moving water and convert that energy to power or electricity.

Water at a higher elevation, say on a hillside, has potential energy due to its elevation above the point of use. Site characteristics including the available water and the elevation drop (also called head) determine the water’s potential energy. Potential energy shows up as increased pressure within a pipe full of water – the bottom of the pipe is at higher pressure than the top. Pressure, however, is not enough to spin a turbine. The pressurized water in the pipe must move through a turbine, which converts potential energy to kinetic energy. The amount of moving water, the elevation drop, and friction inside the pipe determine the kinetic energy available for power generation.

The Water Resource

Perhaps most importantly for power generation and irrigation is the ability to control the amount of water and rate at which it flows, both key factors in energy production. The conveyance of the water to the point of power generation can affect how much kinetic energy can be captured. For example, a large diameter PVC pipe has low friction loss because the inner walls of the PVC pipe are smooth, reducing friction between the water and pipe walls, and the large pipe diameter moves more water with less wall contact. Conversely, water in smaller pipe or a rougher pipe will have more friction loss. These three factors – flow, head and conveyance method – are critical in determining how much energy a small hydropower system can generate.

Hydromechanical Systems

Mechanical hydropower systems utilize the pressure of an irrigation system to spin the turbines and drive a hydraulic pump that is responsible for advancing the center pivot around the field. In this instance, no electricity is generated, or needed, to move the center pivot. Mechanical hydropower systems are the most common in Colorado because of their relatively low cost, independence from the larger power grid, and lower maintenance costs. A mechanical small hydropower system (in agriculture) may be right for you if:

  • You use or are considering switching to sprinkler irrigation
  • You believe you have sufficient head/flow to spin a turbine
  • You have legal water rights
  • Your water source is reliable during the irrigation season
  • You have an existing diversion for your water source

Hydroelectric Systems

The other type of hydropower system, hydroelectric, harnesses the energy of the water to spin a turbine and create electricity. Hydroelectric systems can be more costly but may offer an irrigator a way of producing electricity that reduces utility bills. Most commonly, the electricity generated from a hydropower system is transferred to the larger electrical grid and gets used by someone else off-farm. Each kilowatt-hour of electricity generated by a small hydropower system and transferred to this larger grid is credited against the monthly electricity use of a farm. This is achieved through a net metering agreement. A small hydroelectric system (in agriculture) may be right for you if:

  • You use or are considering switching to electric pumps/motors for irrigation
  • You believe you have sufficient head/flow to spin a turbine
  • You have legal water rights
  • Your water source is reliable
  • You have an existing diversion for your water source
  • You are interested in offsetting your grid-supplied electricity with your own power
  • You have the desire and capacity to apply for financial assistance
Last updated: October 18, 2017 at 11:43 am