The first step in assessing renewable energy options is to conduct a preliminary screening to decide which technologies are worth investigating and which can be eliminated immediately. Preliminary screening involves using resource maps and other basic tools to choose technologies to pursue further. This should occur in the planning phase and can be completed at the agency level with some simple training. There should be no need to hire an outside consultant at this stage.
When narrowing technology options during this phase of assessment, a range of factors are considered, such as:
Available Renewable Resources
Renewable energy resources refer to the amount of energy that can be captured for a particular technology, such as how solar energy hits a particular area or how much energy is available in the wind in a specific location. Renewable energy experts have been gathering and refining this data for decades.
At this stage of assessment, renewable energy resource maps are an easy way to find out what resources are available in your project location. For the preliminary screening, the maps will provide guidance on what technologies should be carried through the next level of assessment.
For more detailed information on any of these or other technologies, see the renewable energy technology resource pages for appropriate technology information.
The solar photovoltaic (PV) map shows national solar PV resource potential and is useful for most solar technologies, including PV, solar hot water, solar ventilation preheat, passive solar heating, and daylighting. The redder/warmer the color, the better the solar resource. This resource counts both the direct solar radiation that reaches the earth, as well as the reflective solar energy that bounces off the ground or other surfaces.
Although some areas, such as the desert southwest, will produce more energy from solar technologies than other areas, this level of screening cannot rule out solar systems anywhere in the country. Local energy costs, incentives, and utility policies affect the economics of these as much as resource. In general, agencies should consider these technologies, at least through the screening phase, for all new construction projects. Although daylighting and passive solar heating may be more difficult to integrate into a renovation project, these technologies should still be considered.
Concentrating Solar Power
The concentrating solar power (CSP) map shows the very targeted solar resource potential used in CSP technologies, such as concentrating photovoltaics, concentrating solar power, or concentrating solar thermal. The map shows only the direct radiation from the sun, as concentrating systems cannot make use of any reflective solar energy.
CSP requires at least 6.0 kWh per square meter per day of direct normal solar radiation, which is indicated by the orange color in the resource maps. In general, if the site is in the desert southwest, CSP technologies are feasible. CSP technologies should not be considered if the site is not in the desert southwestern (or in an international location with a resource of this level).
Ground heat pumps can be implemented anywhere in the U.S. and should be considered for any new construction project. Geothermal direct heat technologies require a geothermal resource above 120°F (50°C) located near the site and should be considered if the appropriate resource is available. A geothermal resource above 300°F (150°C) near the site could feasibly be used for geothermal electricity production. However, the scale and cost of such systems means that this should only be considered if the project warrants a utility-scale power project. Most geothermal resources are located in the western U.S.
The geothermal resource map shows the geothermal resources available in the U.S. Temperature varies by depth, and this map analyzes geothermal resources at depths from three-to-10 kilometers (two-to-six miles). The red and orange colors indicate the most favorable locations for geothermal systems, but the map does not rule out potential locations elsewhere.
The second map shows regions of known or potential geothermal resources for the West. It also indicates known hot springs and wells, which indicate that geothermally-heated water is present. The nearby presence of hot springs is an encouraging sign for geothermal potential, but the hot springs could be caused by a geothermal resource that is not hot enough for economic energy use in a facility. The presence of many hot springs that are characterized as "hot" (greater than 50°C or 122°F) would be a strong indicator of an area that warrants further investigation for direct heat applications.
The wind resource map shows national wind resource potential at a tower height of 50 meters above the ground. The higher above the ground, the better the wind resource. Eighty-meter maps are also available. Orange indicates a class 3 wind resource and pink indicates a class 4 wind resource. The darker the color, the better the wind resource.
If the site has a class 3 wind resource, consider small wind turbine (100 kW or less) or large, low-wind speed turbine opportunities. If the site has a class 4 or greater wind resource, wind may be a good option and even larger, utility-scale turbines may provide economic options.
Lower wind resources are less likely to be economically feasible, but should be reviewed if the site is in a class 2 area and there are nearby pockets of class 3 resources.
Biomass resources are among the hardest to quantify as they can include a range of biomass options, including leftover material from agricultural crops, wood from thinning forests, and even wood waste or municipal solid waste from urban areas. The biomass resource map illustrates the biomass resources available in the U.S. by county. It includes most feedstock categories, but is not all-inclusive for every state, especially Hawaii. Colorado, for example, shows limited resources, but the National Renewable Energy Laboratory (NREL) heats its Research Support Facility partially using a biomass boiler.
If there is a permanent, steady stream of biomass resource within a 50-mile radius of the site, biomass opportunities should be considered further. If the map reveals limited or no biomass resources for the site, do not rule out the technology and consult a local expert for more information.
Remove ocean power technologies from consideration if the site is not adjacent to the ocean. Ocean thermal energy conversion is a potential energy technology in Hawaii and other tropical island communities. If the site is located on the Pacific Northwest or the Atlantic Northeast, tidal energy is a potential technology and could be considered further for coastal properties.
The Federal Energy Regulatory Commission (FERC) regulates U.S. hydropower resources and provides a simplified process for small and low-impact hydropower projects under 5 MW. The Bureau of Reclamation produced a hydropower resource assessment in March 2011, which determined 70 sites with hydropower potential at existing facilities. If the site is close to one of these facilities, hydropower could be a viable technology.
Ability to Connect to Grid
For electricity-generating technologies, such as wind or PV, the renewable energy system typically needs to be connected to the electric utility distribution network or grid to enable the system to integrate safely integrate with the utility grid. The exception to this is a remote facility that gets electricity from on-site sources only and is not served by an electric utility.
The traditional electric utility system and rules were designed for large centralized power plants and not for small on-site power generation by utility customers. As renewable energy and other distributed power technologies have become more cost-effective, many states have developed rules to enable utility customers to interconnect their renewable electricity to the utility grid. These rules often limit the size of the system to be interconnected, and sometimes they do not apply to certain utilities in the state, such as municipal-owned utilities or rural electric cooperatives. Detailed information about these issues is available in the key policies for renewable electricity use section.
The legal ability to connect a renewable energy system to the utility grid is very important to the successful use of renewable electricity technologies. The Database of State Incentives for Renewable Energy (DSIRE) provides a map of interconnection policies by state. The specifications for a successful project are as follows:
- Project is located in a state that has adopted interconnection policies and projects will likely fall within the size limits of the policy.
- Project does not produce electric power.
- Project is not grid connected.
If the project does not fall within successful specifications, the project may still be able to move forward but will require cooperation with utility and/or state authorities to determine the scope of the potential project and any limitations affecting customer-sited generation.