Skip navigation to main content.
NREL - National Renewable Energy Laboratory
About NRELEnergy AnalysisScience and TechnologyTechnology TransferTechnology DeploymentEnergy Systems Integration

NREL is exploring a unique system-of-systems concept to energy systems integration. This approach considers the relationships among electricity, thermal, and fuel systems and data and information networks to ensure optimal integration and interoperability across the entire energy system spectrum. Learn more about this new approach to energy systems integration, read Energy Systems Integration: A Convergence of Ideas.

Explore the animation below to learn more about energy systems integration.

Energy Systems Integration (ESI) optimizes the design and performance of electrical, thermal, fuel, and data pathways at all scales

If you need further assistance with the animation below, contact the ESI webmaster.

Utility-scale solar power plants produce megawatts of electricity and are connected to transmission lines. Photovoltaic plants (PV), sometimes called central-station PV, use flat module technology to produce electricity. Concentrating solar power technologies project heat or light using mirrors to concentrate the sun's rays on a heat-transfer material.

Large-scale wind farms produce electricity from wind in remote locations. They can consist of several hundred wind turbines and cover hundreds of square miles. The land between the turbines can be used for agriculture or other purposes. Wind farms can also be located offshore.

Geothermal power plants use steam produced from reservoirs of hot water found a few miles or more below the Earth's surface to produce electricity. The steam rotates a turbine that activates a generator, which produces electricity.

Hydropower plants use the gravitational force of falling water to generate electricity. Hydropower is the cheapest way to produce electricity, but there are few places where new dams can be built economically.

In nuclear plants, a reactor splits uranium atoms into smaller elements, which produces heat in the process. The heat is used to superheat water into high-pressure steam that drives a turbine generator.

Fossil-fuel plants burn coal, natural gas, or oil. These plants use the chemical energy in fossil fuels to superheat water into steam, which drives a turbine generator. Coal is the fossil fuel of choice for most electric companies. Natural gas comes in second; petroleum is third.

The electricity transmission system is the electric backbone that moves electricity produced at power plants to transformers, which step up the voltage to reduce energy loss while the electricity travels along the grid, and the distribution system.

Illustration of a region with seven numbered buttons that indicate technologies. The technologies are (1) solar energy, (2) wind energy, (3) geothermal energy, (4) hydroelectric power, (5) nuclear energy, (6) fossil-fuel energy, and (7) electricity transmission. Return to overview layer Solar energy Large-scale wind Geothermal  power plants Hydropower plants Nuclear plants Fossil-fuel plants Electricity transmission system

Large rooftop photovoltaic systems and solar community gardens are medium-scale distributed generation systems that connect to the electricity grid. The size and structure of these shared systems vary depending on the resources and requirements of the area they serve.

Fleets and mass transit, such as busses and light rail systems, typically deploy medium- and heavy-duty alternative fuel and advanced vehicles.

Plug-in hybrid electric vehicles (PHEVs) provide dispersed and mobile energy storage that can be aggregated. Controlled charging and discharging in public parking garages could provide electric power ancillary services. Grid-to-vehicle charging can occur when demand is low, and vehicle-to-grid discharging can serve as a supply source when demand is high or supply is lost.

District heating and cooling systems produce hot water, steam, or chilled water at a central plant and then distribute the energy through underground pipes to buildings connected to the system. The water is returned to the central plant to be reheated, or rechilled, and recirculated.

A combined heat and power system uses a fuel, such as natural gas, to power a prime mover, such as a gas turbine, to which an electric generator is attached. Waste heat from an existing industrial operation can also be recovered and used to generate electricity.

An electricity distribution system delivers power from the transmission system to end-use applications. A step-down transformer first converts the high-voltage electricity from the transmission lines to lower voltages. In the United States, end-user voltages range from 10 kV to 20 kV.

Illustration of a community with six numbered buttons that indicate technologies. The technologies are (1) photovoltaics, (2) fleets and mass transit, (3) plug-in hybrid electric vehicles, (4) district heating and cooling, (5) combined heat and power, and (6) electricity distribution. Electricity distribution system Combined heat and power system District heating and cooling systems Fleets and mass transit Plug-in hybrid electric vehicles Photovoltaic systems Return to overview layer

Photovoltaics convert sunlight into electricity. Rooftop photovoltaic systems connect to the electric power system via an inverter and can be used to charge batteries.

Solar hot water systems use the sun to heat water. Solar hot water systems come in a variety of configurations, depending on design and complexity, but a typical system consists of a solar collector, a fluid system to move the heat from the collector to its point of use, and a hot water tank for storage.

A wind turbine at a home or business can provide electricity when the wind blows. Small-scale wind turbines (100 kW and smaller) typically connect directly to the grid or are used to charge batteries.

Plug-in hybrid electric vehicles (PHEVs) use electricity stored in batteries to power an electric motor and a fuel, such as gasoline or diesel, to power an internal combustion engine or other propulsion source. Using electricity to run the vehicle reduces fuel consumption. PHEVs may also be able to provide electricity to the power grid when demand is high.  

Ground source heat pumps take advantage of the nearly constant temperature of the earth to heat and cool buildings. Geothermal heat pumps use much less energy than conventional heating systems.

Smart appliances can be programmed to run when electricity rates are lowest. When used in mass, they have the potential to increase the efficiency of the electric power system and reduce the cost of electricity—with little effect on the lives of energy users.

Smart meters are advanced utility meters that measure electricity consumption and power quality and communicate the information back to utilities for monitoring and billing purposes.

A battery bank is a small, off-grid power system that can provide temporary power for a home or business when all other systems, such as wind and solar generation, are not available.

An energy management system works with utility smart meters and communicates information to allow homeowners and businesses to manage, control, and reduce their energy costs and carbon footprint.  

Illustration of a house with nine numbered buttons that indicate technologies. The technologies are (1) photovoltaics, (2) solar hot water, (3) wind turbine, (4) plug-in hybrid electric vehicle, (5) ground source heat pump, (6) smart appliances, (7) smart meter, (8) batteries, and (9) energy management system.
Photovoltaics Solar  hot water Wind turbine Plug-in hybrid electric  vehicles Ground source heat pumps Smart appliances Smart meters Battery bank Energy management system Return to overview layer
Illustration of the electricity pathway through the residential and commercial; campuses, cities, and communities; and national and regional scales.

Electricity Pathway: Electricity is an energy carrier that delivers power in the form of electrons from energy sources to points of use. The electric power system delivers electricity primarily from large, central-station power plants via high-voltage transmission and low-voltage distribution systems to customers.

Illustration of the thermal pathway through the residential and commercial; campuses, cities, and communities; and national and regional scales.

Thermal Pathway: Thermal systems carry energy in liquid or gas form for heating and cooling applications. In homes and businesses, water and air are typically used as thermal energy carriers. At larger scales, district plants provide heating and cooling to multiple buildings in urban environments.

Illustration of the fuel pathway through the residential and commercial; campuses, cities, and communities; and national and regional scales.

Fuels Pathway: Gas and liquid fuels are transmitted through pipes from refineries and natural gas production plants to end-use applications such as building heating systems and transportation fuels.

Illustration of the data pathway through the residential and commercial; campuses, cities, and communities; and national and regional scales.

Data Pathway: Information and communication technologies allow a better understanding and control of systems by linking sensor data from multiple locations to control centers.

Illustration of three stacked planes, progressing in size from small (top) to large (bottom).  The top plane represents the residential and commercial scale. The medium plane represents the campuses, cities, and communities scale. The bottom plane represents the national and regional scale.

Residential & Commercial

At the residential and commercial level, an example of energy systems integration is a combined heat and power system that uses fuel, such as natural gas, to produce heat and electricity simultaneously. Integration also occurs at this scale where systems, such as solar hot water and geothermal pumps, are combined to achieve greater, more efficient power solutions for homes, multifamily units, and commercial buildings. Energy systems at this scale are typically low-voltage (less than 1,000 V) and range from kilowatts to megawatts in size.

In most cases, these small-scale systems have a single owner, and they operate under a single set of local rules and regulations. Typically, a small-scale system is located behind a single meter for each type of energy infrastructure (for example, electrical or fuel), but it can communicate demand and generation information to a higher level. A number of technologies can be integrated at a small scale, including transportation applications when used for individual mobility.

Learn what NREL is doing in small-scale residential and commercial integration.

Campuses, Cities, & Communities

Aggregation is needed to optimize energy systems over geographic distributions. Mixed-use and higher-density developments allow the cost-effective integration of systems such as transportation. At the community, city, and campus level, an energy management system may need to incorporate a variety of energy sources and manage loads at an aggregated level. Energy systems at this scale can range from megawatts to multi-megawatts.

At a campus level, there may be a single owner of all the facilities. At the community and city level, there are usually multiple owners, but all are within a specific regulatory area, such as a utility service territory or local jurisdiction. Electrical systems at this level include distribution and subtransmission systems. Transportation at this level starts to include fleets and local public transportation.

Learn what NREL is doing in medium-scale campus, city, and community integration.

National & Regional

At larger regional and national scales, energy systems integration covers geographically dispersed systems such as utility service territories and balancing areas. These systems typically integrate much larger generation technologies, such as large wind farms, concentrating solar power plants, large photovoltaic plants, and pumped hydro systems. The systems operate across multiple regulatory areas and jurisdictions and usually require that a number of regulatory issues be addressed to allow for integration.

Electrical systems on a national and regional scale include transmission systems. Transportation systems include long-haul mobility and freight.

Learn what NREL is doing in large-scale regional and national integration.

Learn more about what NREL is doing in these areas of energy systems integration research and development: