Introduction

If you have flowing water on your property and have an interest or curiosity in renewable energy, hydropower could be right for your business. While most hydropower created in the U.S. comes from large-scale projects, small-scale hydropower can be a great solution for small and medium businesses. Small hydropower systems offer emissions-free power options. This Fact File will help you determine whether a small hydropower system is a good fit for you and how to plan out the system potential itself.

Background

Hydropower systems use energy in flowing water to make electricity. There are several ways to harness the moving water. Run-of-the-river systems are often used for microhydro and sometimes small-scale hydro projects. In run-of-the-river hydro projects, part of a river’s water is diverted to a channel, pipeline, or pressurized pipeline that sends it to a waterwheel or turbine. The moving water rotates the wheel or turbine. This spins a shaft. The shaft motion can be used for mechanical processes, like pumping water. Also, it can be used to power an alternator or generator to create electricity. A large-scale hydropower project generates over 30 megawatts (MW) of electricity. Small-scale hydropower systems generate between .01 to 30 MW of electricity. And microhydro systems are even smaller and generate only up to 100 kilowatts (kW) of electricity.

Determing hydropower head

You must have access to flowing water to build a small hydropower system. Next, you will want to determine the amount of power you can obtain from the flowing water on your property. The power available at any moment is the product of flow volume and head.

Head is the vertical distance that water falls. It’s typically measured in feet, meters, or units of pressure. Most small hydropower sites are considered low or high head. The higher the head the better because you will need less water to create a certain amount of power. You can use smaller and less expensive equipment. Low head is a change in elevation of under 10 feet (3 meters). A vertical drop of less than 2 feet (0.6 meters) will most likely not work for a small-scale hydroelectric system. When determining head, you need to consider gross head and net head. Gross head is the vertical distance between the top of the pressurized pipeline that conveys the water under pressure and the point where the water releases from the turbine. Net head equals gross head minus losses due to friction and turbulence in the piping.

The most precise way to determine gross head is to have a professional survey the site. For a rough estimate, you can use U.S. Geological Survey maps of your area or the hose-tube method.

The hose-tube method for determining head includes taking stream-depth measurements across the width of the stream you will use for your system. This is done from the point at which you want to place the pressurized pipeline to the point at which you want to place the turbine. You will need the following:

• An assistant,
• A 20–30 foot (6–9 meters) length of small-diameter garden hose or other flexible tubing,
• A funnel, and
• A yardstick or measuring tape.

Stretch the hose or tubing down the stream channel from the point that is the most practical elevation for the pipeline intake. Have your assistant hold the upstream end of the hose, with the funnel in it, underwater as close to the surface as possible. In the meantime, lift the downstream end until water stops flowing from it. Measure the vertical distance between your end of the tube and the water’s surface. This is the gross head for that section of stream. Have your assistant go to where you are and put the funnel at the same point where you took your measurement. After that, walk downstream and repeat the procedure. Continue taking measurements until you reach the point where you plan to site the turbine.

The sum of these measurements will give a rough estimate of the gross head for your site. If your initial estimates look promising, you will want to get more precise measurements with a professional survey.

Determing hydropower flow

The amount of water falling from a possible micro-hydropower site is called flow. It’s measured in gallons per minute, cubic feet per second, or liters per second.

You can simply determine your stream’s flow by obtaining data from these local offices:

• The U.S. Geological Survey
• The U.S. Army Corps of Engineers
• The U.S. Department of Agriculture
• Your county’s engineer
• Local water supply of flood control authorities.

Small system economics

An easy equation can help you estimate the power output for a system with 53 percent efficiency. This efficiency amount is representative of most small hydropower systems. Simply multiply net head (the vertical distance available after subtracting losses from pipe friction) by flow (use U.S. gallons per minute) divided by 10. That will give you the system’s output in watts (W). The equation looks this: net head [(feet) x flow (gpm)]/10 = W.

After doing the measurements and equation, if you identify that your site is a good fit for a small hydropower system, the next step is to determine whether it makes sense economically to build the system. Add up all the estimated costs of developing and maintaining the site over the expected life of your equipment. Divide the amount by the system’s capacity in watts. This will tell you how much the system will cost in dollars per watt. After this, you can compare that to the cost of utility-provided power or other alternative power sources. Regardless of the upfront costs, a hydroelectric system will usually last a long time (up to 25 years) and maintenance is not often expensive.

Applicable laws & regulations

N/A

Related definitions

“Turbine” means a rotary engine stimulated by the reaction or impulse of a current of fluid (like water, steam, or air) subject to pressure and generally made with a series of curved vanes on a central rotating spindle.

“Friction” means the resistance to relative motion between two surfaces that are in contact.

Key to remember

If you have concern over the environmental impacts of hydropower projects, know that small, run-of-the-river projects are free from many of the environmental problems large-scale projects have, because they use the natural flow of the river. Due to this, they cause relatively little change in the stream channel and flow. Many small-scale projects do not require a dam at all. Thus, effects like oxygen depletion, increased temperature, decreased flow, and rejection of upstream migration aids like fish ladders are not difficulties for many run-of-the-river projects. Large-scale dam hydropower projects can have all these issues, however.

Real world example

In 2012, a rancher in Colorado wanted to reduce energy costs by retrofitting an existing center pivot with a new small hydropower turbine. A site evaluation identified a head of 126 feet and a flow of 560 gallons per minute (gpm). These site conditions provide enough pressure to not only pressurize the sprinklers but also produce 5.2 kW of power. Using gravity to feed the sprinklers and make energy eliminated the need for pumps and drive systems. This helped lower the rancher’s operating and maintenance costs.

Due to site incentives, the only out-of-pocket cost to the farmer was the purchase of the turbine. The total project cost for the irrigator was $13,000 and a grant took care of $6,000. The expense to the irrigator was $7,000 with an annual energy savings of about $2,100. This ends up in a payback period of about 3.3 years. With a roughly 20-year life expectancy of a turbine, this put the total annual cost of the hydropower project at $350.00/year over 20 years.

An irrigator can expect to get over 20 years of use from a single turbine if turbines are properly maintained. In this case, installing a small hydropower system and getting rid of the electricity consumption of a center pivot, the total savings over a 20-year period will be about $35,000 for this rancher.