Site Assessment

When evaluating a potential site for hydropower development a preliminary site assessment should be completed to determine if further investigation is warranted. The most important consideration is the head and flow conditions. Still, the assessment is broader than the mere existence of a resource; it should include site location, ownership, access, preliminary estimate of head and flow, location of utility connection, water rights, and political or environmental concerns.

Site Location, Ownership, and Access

Ownership and control of the small hydropower development site, and surrounding areas potentially affected through development, is a vital component of site assessment. A developer must have legal access to either a private or public hydropower resource to even proceed with a full assessment. Consideration should be made to ownership and property rights of the intake, pipeline, and outlet as well since these components could be on separate properties. If some components to the facility are existing, such as a dam or pipeline, previous ownership (if applicable) could be helpful to determine what rehabilitation or alterations have been made and may be able to provide as-built drawings of the facility.

Site access, for both construction and maintenance, must be secured. The use of existing roads, especially private and service roads, needs to be confirmed for all components of the system, including intake, penstock, and powerhouse. The access may also need to accommodate the passage of heavy construction equipment. If there is no suitable access, estimating road construction and maintenance costs will need to be part of the assessment.

Estimated Head and Flow

Head and flow are the two most important factors in a site assessment. A preliminary estimate of head and flow provides an estimate of the power generation capacity at the site. Head and flow also determines engineering parameters, including pipeline size, turbine type and size, rotational speed, generator size and output, and even rough cost estimates. Accuracy of head and flow measurements are critical to determining final feasibility; however, at an early stage of development head and flow can be estimated. Determining head at a site requires the measurement of the elevation difference between the intake and water turbine. For a basic, early assessment, this can be measured with a hand-held Global Position Satellite (GPS) unit, approximated from U.S. Geologic Survey (USGS) topographic maps, or even a mapping service such as Google Earth. Flow can be estimated from historic measurements or stream gauges. Measuring head and flow is discussed in more detail in later sections of this guide. Once the head and flow are estimated, the capacity of a hydropower plant can be estimated by the power formula :

Where P = generator power production in kW
η = overall plant efficiency
γ = specific weight of water, 62.4 lb/ft3
Q = turbine discharge in ft3/sec
H = net head in feet

The overall plant efficiency varies between turbine type and system designs; a site-specific turbine performance curve should be used when determining the efficiency under different loads. More accurate efficiency assessments are possible after the plant configuration is finalized and turbine selected; however, for a preliminary estimate, the efficiency can be assumed to be 80 percent. The power formula is then reduced to:

Power (kW) = Head (feet) x Flow (cfs) x 0.068

Location of Suitable Utility Connection

The distance to and types of utility connections is also a vital piece of the site assessment. Electricity generated by the project needs to be delivered to an electric load, either on-site, such as a house or irrigation motor, or through the local grid using electrical switchgear and step-up transformers. The distance to the nearest utility distribution or transmission line, and what type of line it is (e.g., single phase or three phase), must also be determined. If the hydropower site is remote, installing new distribution lines can add significant costs to the project. It may also be cost prohibitive if existing nearby distribution lines need to be upgraded to handle the additional capacity.

In rare applications, hydropower facilities can operate without connecting to the grid and only serve an adjacent on-site electric load. This method is often referred to as a stand-alone, or island, system. Hydropower turbines have difficulty reacting quickly to a sudden change in electric demand without the use of expensive electrical storage equipment (called balance-of-system) and is the reason island generation facilities are uncommon. Balance-of-system equipment is used to condition the electricity, safely transmit the electricity to the load that will use it, and/or store the electricity for future use. This equipment usually includes batteries, charge controller, power conditioning equipment, safety equipment and meters and instrumentation, and depending on the needs of the system, can account for half of the total system costs.

Water Rights

Wyoming water law is based on the “doctrine of prior appropriation.” The first person to put the water to beneficial use has the first right, and is often referred to as “first in time, first in right.” All water in Wyoming is property of the state and the right to use the water is regulated by priority. A permit is required to use water. Water rights are obtained by applying to the Wyoming State Engineer’s Office and obtaining a permit for a specified amount, location, and use. Any water right must be for a beneficial use, which is the overt act of diverting water from a water source and applying it to a specified purpose. Common beneficial uses include irrigation, domestic, municipal, industrial, and power generation. The most senior water right holders (those obtained at the earliest date) are entitled to water prior to junior water right holders, independent of their location along the river. For example, if a junior water right holder is upstream of a senior water right holder, the water must pass the point of diversion of the junior water right to satisfy the senior right if there is not sufficient water to satisfy both needs. Although water rights can be much more complicated than this basic scenario, generally, the more senior a water right, the more certainty there will be water available for use in years of low water supply.

Power generation is generally considered a non-consumptive use, since the same quantity of water diverted is returned to the river. There may be an exemption if a reservoir is constructed to store water or a new canal is constructed to convey water to the hydropower plant, as evaporation may consume a portion of the water. However, since this guide is geared toward low-impact hydropower facilities installing the hydropower plant at existing facilities is assumed.

The Wyoming Water Development Commission also holds in-stream flow water rights in some rivers to maintain a minimum flow to protect aquatic species. These in-stream flow rights may be junior to a senior water right holder, but new hydropower junior rights need to consider their impact even if the water right is non-consumptive. There may be a portion of the river between the intake of the hydropower plant and the discharge where in-stream flows cannot be reduced.

A water right must include power generation or hydropower as a beneficial use before the right can be used in a small hydropower installation. Hydropower can be added as a beneficial use to existing rights by filing for an enlargement of the right that includes hydropower as a beneficial use. If a hydropower facility is added to an existing irrigation system and a new point of diversion is added, or more diversions will be made throughout the year to supply the facility, a new water right application or an enlargement application needs to be filed. This additional application allows the diversion of water outside of the irrigation season.

An individual who owns an adjudicated water right and wishes to change the current use or change the place of use must file a petition with the Wyoming State Engineer’s Office Board of Control requesting permission. A petition for change of use should only occur when changing the beneficial use. When requesting a change in place of use, all pertinent information about existing use and proposed place of use should be specified in the petition. If a change in place of use or change in use is granted, the quantity of water transferred cannot exceed the amount of water historically diverted under the existing use. Furthermore, the amount consumed cannot exceed that under existing use. Finally, such a petition, if granted, cannot decrease the historic amount of return flow or in any manner injure other existing lawful appropriators.

The Wyoming State Engineer’s Office is a useful primary resource for information and assistance on filing new water right applications and petitions, but a professional well versed in Wyoming water law is recommended when applying for a new right or filing any type of petition.

Political or Environmental Concerns

In addition to the technical characteristics of a site, other environmental, cultural, and political factors can influence feasibility. Identifying potentially contentious issues early is important before significant resources are spent studying the feasibility of the project. Potential political or cultural concerns may include nearby historic sites or commercial/recreational activities, such as boating, occurring in the impacted area. In addition, some hydropower turbines can be fairly noisy, so identifying any nearby neighbors that may be impacted is vital. Local zoning laws may also impact where hydropower development may occur.

Although small hydropower is considered a clean, low-impact energy source, potential environmental impacts exist. Specifically, diminished water flows in a waterway could impact aquatic and riparian zone species. Although less likely on existing water projects, evaluating the likelihood of environmental impacts early in the process is critical.