Onshore vs Offshore Wind Energy: How Location Changes Turbine Design, Costs, Output, and Environmental Impact

Overview

Wind turbines operate according to the same fundamental principle whether they stand on agricultural land, mountain ridges, coastal plains, or kilometres out at sea. Moving air passes across aerodynamic blades, creating lift that turns a rotor. The mechanical rotation is then converted into electrical energy by a generator.

Yet describing onshore and offshore wind as essentially the same technology in different locations overlooks some of the most important differences in modern renewable electricity generation.

Where a turbine is installed affects almost every aspect of a wind project, including the strength and consistency of the wind resource, turbine dimensions, foundations, electricity output, construction methods, transmission infrastructure, maintenance requirements, environmental impacts, financing, planning constraints, and ultimately the cost of the electricity produced.

Onshore wind is currently one of the lowest-cost forms of new electricity generation worldwide. Offshore wind is considerably more expensive to build, but it can exploit stronger and more consistent winds while accommodating turbines that are substantially larger than those normally transported and installed on land.

IRENA estimates that new utility-scale onshore wind projects commissioned in 2024 had a global weighted-average levelised cost of electricity of approximately USD 0.034 per kWh, while average installed costs were around USD 1,041 per kW for onshore wind and USD 2,852 per kW for offshore wind.

The result is not a simple competition in which one technology is universally superior. Onshore and offshore wind solve different energy-system problems.

Understanding those differences is increasingly important as electricity systems attempt to integrate larger volumes of renewable generation while simultaneously expanding grids, electrifying transport and heating, and reducing dependence on fossil fuels.

What Is Wind Energy?

Wind energy ultimately originates from solar radiation.

The Sun heats the Earth's surface unevenly. Differences between land and water, latitude, terrain, and atmospheric conditions create variations in temperature and air pressure. Air moves between areas of different pressure, producing wind.

A wind turbine extracts part of the kinetic energy contained in this moving air.

Most utility-scale wind turbines use a horizontal-axis configuration with three blades. Air moving across the blades generates aerodynamic lift, causing the rotor to rotate. The rotor then transfers mechanical energy to a generator, either through a gearbox or through a direct-drive system, producing electricity.

The amount of power available in the wind increases very rapidly with wind speed. In simplified terms, wind power depends on:

• Air density.

• The area swept by the turbine blades.

• Wind speed.

Wind speed is especially important because the available power increases approximately with the cube of wind speed.

This means that a relatively modest increase in wind speed can produce a much larger increase in the theoretical energy available to a turbine.

Increasing rotor diameter is also important because longer blades sweep a larger area of air.

These physical principles help explain why developers look for locations with strong, persistent wind resources and why offshore environments can be attractive despite their higher construction costs.

What Is Onshore Wind?

Onshore wind refers to wind turbines installed on land.

Projects range from individual turbines supplying local facilities to large utility-scale wind farms containing dozens or even hundreds of turbines connected to national electricity networks.

Common locations include:

• Agricultural areas.

• Open plains.

• Hills and ridgelines.

• Sparsely populated rural areas.

• Industrial sites.

• Coastal areas with favourable wind conditions.

Utility-scale land-based turbines generally have capacities ranging from several megawatts upward, although smaller turbines are also used for distributed electricity generation.

Onshore wind is now a technologically mature form of renewable generation with established manufacturing, installation, and maintenance industries across many markets.

Its principal advantage is relatively straightforward: it is usually cheaper and simpler to build a wind turbine on accessible land than in the ocean.

What Is Offshore Wind?

Offshore wind refers to wind farms installed in seas, oceans, or other large bodies of water.

The turbines operate according to the same aerodynamic principles as land-based turbines, but their supporting structures and electrical infrastructure must operate in a marine environment.

There are two main forms of offshore wind technology.

Fixed-Bottom Offshore Wind

Fixed-bottom turbines are installed on foundations that are attached directly to the seabed.

Common foundation systems include:

• Monopiles.

• Jacket foundations.

• Gravity-based foundations.

Fixed-bottom technology is generally used in relatively shallow waters.

As water depth increases, the engineering requirements and cost of attaching very large structures directly to the seabed also increase.

Floating Offshore Wind

Floating offshore wind is designed for deeper waters where conventional fixed-bottom foundations may become impractical or uneconomic.

The turbine is installed on a floating platform that is secured to the seabed using mooring lines and anchors.

Floating technology could significantly expand the geographical area available for offshore wind because many coastlines with strong wind resources are surrounded by relatively deep water.

However, floating offshore wind remains less commercially mature than conventional fixed-bottom technology and introduces additional challenges involving platform design, dynamic cables, mooring systems, ports, installation, and financing.

The Fundamental Difference: The Wind Resource

One of the most important differences between onshore and offshore wind is the quality of the wind resource.

Over land, wind interacts with buildings, vegetation, forests, hills, and other surface features. These obstacles create friction and atmospheric turbulence.

The sea surface is generally smoother.

As a result, offshore winds can often be stronger, more persistent, and less turbulent than winds over land.

This does not mean every offshore location is automatically better than every onshore site. Wind conditions vary significantly according to geography, weather patterns, distance from shore, water temperature, and local atmospheric conditions.

However, strong offshore wind resources are one of the main reasons developers are willing to accept the much greater construction and infrastructure costs associated with marine projects.

Research comparing closely located offshore and onshore sites in the United States has found substantially greater wind-energy density at offshore locations in some regions.

This demonstrates a central principle of offshore wind economics: developers are generally paying more for infrastructure in order to access a potentially more productive wind resource.

Capacity Factor and Electricity Generation

Installed capacity is not the same as actual electricity generation.

A turbine's rated capacity represents the maximum output it can produce under suitable operating conditions.

A 10 MW wind turbine could theoretically produce 87,600 MWh of electricity over one year if it operated continuously at full output.

In reality, it will not.

Electricity generation varies because of:

• Changing wind speeds.

• Planned maintenance.

• Equipment downtime.

• Grid constraints.

• Curtailment.

• Extreme weather conditions.

This is why the capacity factor is commonly used to compare renewable electricity technologies.

Capacity factor measures the amount of electricity actually generated relative to the amount that would have been produced if the asset had operated continuously at maximum output.

IRENA's 2024 global data indicate an average capacity factor of approximately 34% for onshore wind and around 42% for offshore wind.

These are global averages rather than universal values. Individual projects can perform considerably better or worse depending on their location and design.

Nevertheless, the figures illustrate one of offshore wind's principal advantages: better wind conditions can allow offshore projects to generate more electricity for each megawatt of installed capacity.

Why Offshore Wind Turbines Are Often Larger

One of offshore wind's most important engineering advantages is the reduced importance of conventional road transportation constraints.

Installing an onshore wind turbine requires enormous components to travel from manufacturing plants or ports to the project site.

Transporting large blades, nacelles, and tower sections can require:

• Special road vehicles.

• Temporary road modifications.

• Traffic management.

• Bridge assessments.

• Removal of roadside obstacles.

• Purpose-built access routes.

Very long blades can be particularly difficult to transport around narrow roads, urban areas, bridges, and tight bends.

Offshore components can instead be moved from manufacturing facilities or ports using specialised ships.

This makes it possible to install significantly larger turbines at sea.

Larger turbines can provide several advantages:

• Greater rotor swept area.

• Higher maximum electricity output.

• More energy captured from a given area.

• Fewer turbines required for a given wind farm capacity.

• Fewer foundations per unit of installed capacity.

• Potential reductions in some balance-of-plant costs.

However, increasing turbine size also creates new challenges.

Larger turbines require:

• Stronger foundations.

• Larger cranes.

• Bigger installation vessels.

• More capable ports.

• Greater storage areas.

• Stronger quays.

• More complex engineering.

Offshore turbine growth is therefore closely connected to the development of the wider marine supply chain.

Foundation Design

The foundation is one of the clearest engineering differences between onshore and offshore wind.

Onshore Foundations

An onshore turbine normally sits on a reinforced concrete foundation constructed below the tower.

The foundation transfers the loads created by the turbine and wind into the surrounding ground.

Geotechnical conditions remain important, but construction can generally be carried out using conventional civil-engineering equipment.

Offshore Foundations

Offshore foundations must operate in much more demanding conditions.

They may need to withstand:

• Wind forces.

• Waves.

• Ocean currents.

• Tides.

• Seabed movement.

• Corrosion.

• Marine growth.

• Extreme storms.

For fixed-bottom wind farms, very large steel foundations may be driven or installed into the seabed.

Floating systems introduce an additional layer of complexity.

The turbine is installed on a buoyant platform that can move in response to waves and wind while mooring systems maintain its approximate position.

Engineers must therefore analyse the interaction between the turbine, platform, waves, cables, and mooring system as a single dynamic structure.

These additional requirements are one reason offshore wind costs considerably more to develop than onshore wind.

Electricity Transmission

Generating electricity is only part of the challenge.

The electricity must also reach homes, businesses, and industrial consumers.

Onshore and offshore wind require very different transmission arrangements.

Onshore Grid Connection

Electricity produced by individual turbines is normally collected through a wind farm electrical network.

The power is then transferred to a substation before being connected to the wider electricity transmission or distribution network.

Infrastructure may include:

• Underground cables.

• Overhead transmission lines.

• Transformers.

• Substations.

• Grid connection equipment.

Although grid connection can still represent a major cost and planning challenge, most infrastructure can be constructed and accessed from land.

Offshore Grid Connection

Offshore projects require significant electrical infrastructure at sea.

Typical components include:

• Inter-array subsea cables connecting individual turbines.

• Offshore substations.

• Export cables.

• Cable landfall infrastructure.

• Onshore substations.

• Connections to national transmission networks.

Long-distance offshore transmission can become increasingly complex as projects move farther from shore.

Large projects may use high-voltage direct current systems where this provides advantages in transmitting large volumes of electricity over long distances.

The offshore transmission network can therefore represent a substantial part of the overall cost of a wind project.

Why Offshore Construction Is More Complex

Onshore wind farms already require substantial civil engineering.

Developers may need to construct:

• Access roads.

• Turbine foundations.

• Crane pads.

• Substations.

• Underground electrical networks.

• Grid connections.

The major difference is accessibility.

Workers, cranes, vehicles, and replacement components can normally reach an onshore wind farm directly from land.

Offshore construction requires an entirely different logistics system.

Projects may depend on:

• Specialist installation vessels.

• Heavy-lift cranes.

• Cable-laying vessels.

• Seabed surveys.

• Offshore substations.

• Specialized construction ports.

• Marine coordination.

• Weather forecasting.

• Subsea engineering.

Marine weather conditions can also determine when work is physically possible.

High winds and large waves may prevent lifting operations, turbine installation, cable work, or maintenance.

This dependence on weather windows can lead to delays even when personnel, equipment, and components are otherwise ready.

Maintenance and Reliability

Wind turbines require inspections and maintenance throughout their operating lives.

For onshore turbines, maintenance crews can normally reach the site using road vehicles.

For offshore turbines, access can be considerably more difficult.

Maintenance may require:

• Crew-transfer vessels.

• Service operation vessels.

• Helicopters.

• Specialist technicians.

• Offshore accommodation.

• Heavy-lift vessels for major repairs.

Weather can also make turbines inaccessible for extended periods.

As a result, offshore wind places particularly strong emphasis on reliability and remote condition monitoring.

Modern turbines can use sensors to monitor:

• Vibration.

• Temperature.

• Gearbox condition.

• Generator performance.

• Blade loads.

• Electrical equipment.

• Structural movement.

• Lubrication systems.

Predictive maintenance can be especially valuable offshore because detecting deterioration before a major failure can reduce expensive emergency interventions at sea.

How Do Onshore and Offshore Wind Costs Compare?

Cost is one of the strongest distinctions between the two technologies.

IRENA estimated that wind farms commissioned globally in 2024 had average installed costs of approximately USD 1,041 per kW for onshore wind and USD 2,852 per kW for offshore wind.

Offshore wind therefore required more than twice the average investment per unit of installed capacity.

The difference reflects the additional infrastructure required for offshore development, including:

• Marine foundations.

• Specialized vessels.

• Offshore substations.

• Subsea cables.

• Export cables.

• Port infrastructure.

• More complex installation.

• Higher maintenance costs.

Installed cost, however, is not the only relevant metric.

The levelised cost of electricity, or LCOE, estimates the average cost of producing electricity across the lifetime of a project.

IRENA reported a global weighted-average LCOE of approximately USD 0.034 per kWh for new onshore wind projects commissioned in 2024.

Onshore wind was therefore among the least-cost sources of new utility-scale electricity generation globally.

Offshore wind remained more expensive, with regional average LCOEs in 2024 of approximately USD 0.078 per kWh in Asia and USD 0.080 per kWh in Europe.

These figures should not be interpreted as fixed prices.

Wind project economics can change significantly according to:

• Interest rates.

• Cost of capital.

• Turbine prices.

• Commodity prices.

• Labour costs.

• Grid connection requirements.

• Seabed conditions.

• Supply-chain availability.

• Government support.

• Contract structures.

Financing is particularly important for offshore wind because very large amounts of capital must be invested before electricity generation begins.

Advantages of Onshore Wind

Onshore wind has several characteristics that make it attractive for electricity-system expansion.

Lower Capital Costs

Projects avoid expensive offshore foundations, subsea cables, and specialized marine vessels.

Mature Technology

Onshore wind has been deployed commercially for decades, creating mature turbine manufacturing, construction, financing, and maintenance industries.

Easier Maintenance

Technicians can generally access turbines by road.

Simpler Construction

Construction remains complex but is generally less technically demanding than building turbines in the ocean.

Competitive Electricity Costs

Onshore wind has become one of the world's lowest-cost sources of new renewable electricity.

Challenges of Onshore Wind

Lower cost does not mean that onshore wind is easy to deploy everywhere.

Planning and Public Acceptance

Large turbines can have a substantial visual presence within landscapes.

Common planning concerns include:

• Visual impact.

• Noise.

• Landscape character.

• Proximity to settlements.

• Tourism.

• Property concerns.

• Local opposition.

Obtaining planning approval can therefore become one of the most important constraints on onshore wind development.

Land Availability

Wind farms require significant geographic areas because turbines must be separated to reduce wake interference.

Much of the land between turbines can continue to be used for agriculture or grazing.

However, project developers must still account for:

• Residential areas.

• Protected habitats.

• Aviation restrictions.

• Radar systems.

• Roads.

• Grid connections.

• Environmental regulations.

Wildlife

Wind turbines can affect birds and bats through collision, displacement, and habitat changes.

The scale of these impacts depends strongly on:

• Species.

• Location.

• Migration routes.

• Turbine layout.

• Habitat conditions.

• Seasonal patterns.

Careful siting and environmental monitoring are therefore important components of wind farm development.

Advantages of Offshore Wind

Offshore wind has a different set of strategic advantages.

Strong Wind Resources

Many offshore locations experience strong and relatively consistent winds.

Higher Capacity Factors

Better wind conditions can allow offshore turbines to operate closer to their maximum capacity for a larger proportion of the year.

Larger Turbines

Marine transport makes it possible to deploy turbines that would be extremely difficult to move through conventional road networks.

Very Large Projects

Offshore wind farms can be developed at extremely large scales, with project capacities reaching hundreds or thousands of megawatts.

Access to Coastal Electricity Demand

Many of the world's largest cities and industrial centres are located near coastlines.

Offshore wind can therefore place large amounts of renewable generation relatively close to major electricity demand centres.

Challenges of Offshore Wind

Offshore wind also faces significant barriers.

Higher Costs

Marine construction, subsea infrastructure, and specialised logistics significantly increase project expenditure.

Financing

Projects frequently require several billion dollars of investment before becoming operational.

Supply Chains

Large-scale development depends on access to:

• Ports.

• Installation vessels.

• Turbine manufacturing.

• Foundation manufacturing.

• Subsea cable production.

• Specialist engineering.

• Offshore maintenance capability.

Weather

Construction and maintenance can be delayed by marine weather conditions.

Grid Infrastructure

Large offshore wind farms may require major transmission upgrades to deliver their electricity to consumers.

Environmental Impacts

Potential environmental considerations include:

• Underwater construction noise.

• Seabed disturbance.

• Marine habitats.

• Seabirds.

• Fisheries.

• Vessel traffic.

• Electromagnetic fields around subsea cables.

• Cumulative impacts from multiple offshore developments.

These impacts vary substantially according to project location, technology, species, and construction method.

The Main Differences Between Onshore and Offshore Wind

The most important differences can be summarised as follows:

• Onshore wind turbines are installed on land, while offshore turbines are installed in marine environments.

• Offshore locations often provide stronger and more consistent wind resources.

• Offshore turbines can generally be built larger because marine transport avoids many road transport restrictions.

• Onshore foundations are comparatively straightforward, while offshore foundations must withstand waves, currents, corrosion, and seabed conditions.

• Offshore projects require subsea cables, marine substations, and specialized vessels.

• Onshore turbines are normally easier and cheaper to maintain.

• Offshore wind generally has a higher capacity factor.

• Onshore wind generally has a lower capital cost and lower levelised cost of electricity.

• Onshore projects can face stronger local planning and landscape constraints.

• Offshore projects must address marine ecosystems, fisheries, seabed impacts, and navigation.

• Fixed-bottom offshore wind is commercially mature, while floating offshore wind remains at an earlier stage of large-scale deployment.

Why Turbine Spacing Matters

Wind turbines cannot be installed immediately beside one another without affecting performance.

When wind passes through a turbine, some of its energy is extracted.

The air behind the turbine becomes slower and more turbulent, creating what is known as a wake.

A turbine operating inside another turbine's wake may:

• Generate less electricity.

• Experience greater turbulence.

• Experience different structural loads.

• Suffer increased mechanical fatigue.

Wind farm developers therefore use complex aerodynamic and meteorological modelling to determine turbine positions.

Wake effects apply to both onshore and offshore projects.

They can become particularly important in very large offshore wind regions where multiple wind farms are located relatively close to one another.

As offshore wind development expands, developers and regulators increasingly need to consider whether one project can affect the wind resource available to another.

Wind Energy Is Variable, but It Can Be Forecast

Wind turbines do not generate electricity continuously.

Output changes with weather conditions.

Wind energy is therefore described as a variable renewable energy source.

However, variable does not mean completely unpredictable.

Modern weather forecasting allows grid operators and energy companies to estimate wind output hours or days in advance with increasing accuracy.

Electricity systems can integrate large amounts of wind generation through combinations of:

• Geographically dispersed wind farms.

• Stronger transmission networks.

• Interconnection between countries or regions.

• Battery storage.

• Pumped hydropower.

• Flexible electricity demand.

• Dispatchable generation.

• Improved forecasting.

Geographical diversification can be especially valuable because wind conditions are not identical across an entire country or continent.

Poor wind conditions in one region may coincide with strong winds elsewhere.

Onshore and Offshore Wind Do Not Operate in Isolation

Modern electricity systems rely on combinations of different technologies rather than a single generation source.

Wind can operate alongside:

• Solar photovoltaic power.

• Hydropower.

• Battery storage.

• Pumped-storage hydropower.

• Nuclear power.

• Flexible demand.

• Electricity interconnectors.

• Other low-carbon generation.

Solar and wind can sometimes complement one another because their generation patterns differ according to season, weather, and time of day.

Energy storage can shift electricity from periods of high renewable generation toward periods of lower output.

Transmission systems can move electricity between regions.

Electricity demand itself can also become increasingly flexible.

Potential sources of flexible demand include:

• Electric vehicle charging.

• Industrial processes.

• Heat pumps.

• Commercial buildings.

• Data centres.

• Hydrogen electrolysers.

The challenge is therefore not simply to maximise wind generation.

The objective is to integrate wind into an electricity system capable of balancing generation and demand at all times.

The Emerging Role of Floating Offshore Wind

Floating wind could significantly expand the geographical potential of offshore wind energy.

Traditional offshore turbines are generally installed using foundations attached directly to the seabed.

As water depth increases, this becomes more technically difficult and expensive.

Floating wind avoids this limitation by placing the turbine on a buoyant platform secured to the seabed using mooring systems.

This could allow wind farms to be developed in deeper waters where fixed-bottom construction would not be practical.

Floating wind may be particularly relevant to countries with:

• Deep coastal waters.

• Narrow continental shelves.

• Strong offshore wind resources.

• Limited shallow-water development areas.

However, significant technical and economic challenges remain.

These include:

• Floating platform costs.

• Dynamic electrical cables.

• Mooring systems.

• Port requirements.

• Installation logistics.

• Maintenance strategies.

• Financing.

• Commercial-scale manufacturing.

Floating wind should therefore be viewed as an important extension of offshore wind rather than a replacement for fixed-bottom projects.

Environmental Impact Is About Trade-Offs

Wind turbines generate electricity without burning fossil fuels during normal operation.

This gives wind energy a major greenhouse-gas advantage compared with coal and gas generation.

However, wind energy is not environmentally impact-free.

Wind turbines require significant quantities of materials, including:

• Steel.

• Concrete.

• Copper.

• Aluminium.

• Composite materials.

These materials must be extracted, processed, manufactured, transported, and eventually managed at the end of a turbine's operating life.

Onshore projects can affect:

• Landscapes.

• Birds.

• Bats.

• Terrestrial habitats.

• Soil.

• Local communities.

Offshore projects can affect:

• Marine habitats.

• Seabed conditions.

• Marine mammals.

• Fish.

• Seabirds.

• Fisheries.

• Shipping routes.

The relevant question for climate and energy policy is therefore not whether wind energy has environmental impacts.

It does.

The more useful questions are:

• How significant are those impacts?

• Can they be reduced through better siting and engineering?

• Can they be mitigated during construction and operation?

• How do they compare with the environmental impacts of alternative electricity technologies?

Lifecycle assessment is therefore essential when comparing wind with other sources of electricity.

Which Is Better: Onshore or Offshore Wind?

There is no universal answer.

Onshore wind is generally preferable where suitable land, strong wind resources, planning approval, and grid connections are available.

Its lower capital cost and simpler maintenance make it highly competitive.

Offshore wind becomes especially attractive where there is:

• A strong marine wind resource.

• Limited suitable land.

• High coastal electricity demand.

• Access to ports and offshore supply chains.

• Adequate grid infrastructure.

• Supportive regulation.

• Long-term investment certainty.

Higher offshore capacity factors and very large project sizes can justify the additional cost in suitable markets.

The comparison should therefore be treated as a question of energy-system optimisation rather than technological superiority.

Onshore wind provides lower-cost generation where suitable land exists.

Offshore wind expands renewable electricity potential where geography, population density, or energy demand makes large-scale land development more difficult.

Floating wind could expand this opportunity further.

What This Means for the Energy Transition

The difference between onshore and offshore wind illustrates an important principle in modern energy policy.

Electricity technologies cannot be assessed only according to turbine size or installed capacity.

A complete comparison must consider:

• Capital cost.

• Financing.

• Electricity production.

• Capacity factor.

• Generation profile.

• Grid connection.

• Transmission requirements.

• Maintenance.

• Environmental effects.

• Land or sea use.

• Public acceptance.

• Supply-chain capacity.

• Project lifetime.

• Energy-system flexibility.

Onshore wind performs particularly strongly in terms of cost, technological maturity, and accessibility.

Offshore wind performs particularly strongly in terms of turbine scale, wind resource quality, capacity factor, and the ability to develop very large renewable electricity projects.

The two technologies are therefore more complementary than competitive.

The International Energy Agency expects substantial deployment of both technologies through the remainder of the decade, although onshore wind is expected to continue representing the larger share of global wind capacity additions.

As renewable energy becomes a larger part of electricity supply, the challenge is changing.

The central question is no longer simply whether wind turbines can produce low-carbon electricity at commercial scale.

They can.

The more difficult challenge is determining how to locate, finance, connect, operate, and integrate increasingly large quantities of wind generation into reliable electricity systems.

Onshore and offshore wind use the same basic source of energy, but their economics, infrastructure requirements, engineering constraints, and environmental impacts differ substantially.

Neither represents a complete energy solution on its own.

Together with solar power, electricity storage, stronger grids, flexible demand, and other low-carbon technologies, both forms of wind energy are likely to remain important parts of the transition toward lower-emission electricity systems.

Key Takeaways

• Onshore wind is generally cheaper to build and maintain than offshore wind.

• Offshore wind can access stronger and more consistent wind resources.

• Offshore turbines are generally larger because components can be transported by sea rather than through road networks.

• Offshore wind typically achieves higher capacity factors than onshore wind.

• Onshore wind remains one of the lowest-cost forms of new utility-scale renewable electricity.

• Offshore projects require specialised foundations, subsea cables, vessels, ports, and electrical infrastructure.

• Onshore wind can face planning, landscape, and local acceptance constraints.

• Offshore wind introduces additional environmental considerations involving marine habitats, seabed disturbance, fisheries, and underwater noise.

• Floating offshore wind could allow projects to expand into deeper waters.

• Onshore and offshore wind should be viewed as complementary technologies serving different geographic and energy-system needs.