Primary and secondary energy: definitions, sources and examples

Primary energy is energy found in nature before any conversion takes place: sunlight, wind, water, crude oil and natural gas. Secondary energy is obtained by converting a primary source: petrol from crude oil, for example, or electricity from sunlight, wind or gas.

The distinction may sound like something from a textbook, but it helps make sense of energy bills, consumption figures and comparisons between technologies. When you charge an electric car, the energy reaching its battery has already been through several stages: it started with a source, was converted, transported and converted again.

This guide explains the definitions, gives examples of primary and secondary energy sources, and explores why electricity is considered secondary energy and what that means for solar PV and EV charging.

What are primary and secondary energy?

There are four definitions to keep in mind. The first two describe where energy comes from; the other two describe the stage at which it is supplied or used.

• Primary energy: energy contained in a natural resource before it is converted into another energy product. Examples include solar radiation, wind, crude oil and natural gas.

• Secondary energy: energy obtained by converting a primary source or another energy product that has already been processed. Examples include petrol, diesel, electricity and industrially produced hydrogen.

• Final energy: energy delivered to the end user. It is the electricity recorded by your meter or the fuel you put in your tank.

• Useful energy: the share of final energy that provides the service you need, such as lighting, heating your home or moving your car.

These are not four stages that every energy supply must pass through. Natural gas delivered to a home is both a primary energy product and final energy. Petrol at a filling station is both secondary and final energy.

Examples of primary and secondary energy sources

Primary energy sources can be renewable or non-renewable. Secondary energy products are obtained by converting primary sources.

Renewable primary sources

• sunlight: solar radiation

• wind

• water: hydropower, tides and waves

• geothermal heat

• biomass: wood, agricultural residues and organic waste

Non-renewable primary sources

• crude oil

• natural gas

• coal

• uranium

Secondary energy products and carriers

• electricity

• petrol, diesel and kerosene produced by refining crude oil

• industrially produced hydrogen

• heat supplied through district heating networks

“Primary” does not mean clean, and “secondary” does not mean polluting. Oil and coal are primary sources but are fossil fuels; electricity is secondary energy but can be generated from sunlight. Environmental impact depends on the source and the processes involved, rather than on the category alone.

Which are not primary energy sources? Electricity, petrol, diesel and industrially produced hydrogen are examples of secondary energy products. A battery is not an energy source either: it stores energy supplied from elsewhere.

Why the sun is behind most energy sources

The sun is the origin of most of the energy sources we use, including some that do not seem solar at first glance.

• Direct use: solar PV and solar thermal systems convert solar radiation into electricity or heat.

• Wind: uneven heating of the atmosphere causes air to move.

• Water: the sun drives evaporation; water then falls at higher elevations and supplies rivers and hydropower reservoirs.

• Biomass: plants store solar energy through photosynthesis.

• Oil, gas and coal: these formed from organisms that lived millions of years ago, storing energy originally captured from the sun over geological timescales.

The main exceptions are geothermal energy, which comes from heat within the Earth; nuclear energy, which comes from atomic nuclei such as those of uranium; and tidal energy, driven mainly by the Moon’s gravitational pull.

The difference between primary and secondary energy: practical examples

The distinction comes down to one question: is the energy available in this form in nature, or has it been produced by converting something else? In the first case it is primary; in the second it is secondary.

Extracting or transporting a resource does not make it secondary. Crude oil pumped from a reservoir remains a primary energy product. It becomes a secondary product when it is converted into something else, such as petrol in a refinery.

From crude oil to a petrol car

Crude oil (primary) → refinery → petrol (secondary) → fuel tank (final energy) → movement (useful energy). During combustion, a substantial share of the energy is released as heat rather than converted into movement.

From natural gas to the home

Extracted gas is primary energy. When supplied to a boiler, it remains a primary fuel delivered as final energy. If it is used in a power station, it is converted into electricity: a secondary energy product.

From sunlight to the socket

Solar radiation is primary energy. PV modules convert it into direct current, and an inverter converts that into alternating current. The electricity can then be used in the home, stored, exported to the grid or used to charge a car.

From wind and water

Wind turns a turbine’s blades, while water flowing from a higher elevation drives a hydropower turbine. In both cases, a generator converts movement into electricity.

Source or carrier? Hydrogen illustrates the distinction. Most hydrogen used today is produced through industrial processes, such as water electrolysis or conversion of natural gas. This makes it a secondary energy carrier, whose environmental impact depends on how it is produced.

Final and useful energy: the complete chain

Final energy is energy delivered to the user; useful energy is the share that provides the required service. The efficiency of the equipment determines the relationship between the two.

Electricity measured at the meter, gas delivered to your home, petrol bought at a filling station and district heating supplied to a building are all final energy. Light from a lamp, heat warming a room and a car’s movement are useful energy.

Here are two examples of the full chain:

• Gas boiler: gas in a reservoir (primary) → processing and distribution → gas at the meter (final) → boiler → heat in the home (useful).

• Electric car charged with solar PV: sunlight → PV modules → inverter → household electrical installation → EV charge point → onboard charger → battery → motor → movement.

A heat pump works differently: it can supply more heat than the electrical energy it consumes because it draws heat from the air, ground or water. Its coefficient of performance, or COP, expresses this ratio; it does not mean the heat pump creates energy.

To compare technologies, you need to consider the whole chain, rather than final energy alone. Two systems can provide the same amount of heat or the same driving distance while using very different amounts of primary energy.

Is electricity primary or secondary energy?

Electricity is secondary energy. The electricity we use is produced by converting primary sources such as sunlight, wind, water, natural gas, coal or uranium.

This is why electricity is described as an energy carrier. It transfers energy from where it is generated to where it is needed, through the grid. It is versatile and can be converted into light, heat or movement, although the efficiency depends on the equipment used.

A kilowatt-hour provides the same amount of electrical energy to a washing machine whether it comes from solar panels or a coal-fired power station. What changes is the primary source, the upstream losses and the emissions associated with generation.

The convention used in energy balances

Official statistics use a particular accounting convention. Under the method used by the International Energy Agency (IEA) and Eurostat, electricity generated from solar PV, wind and hydropower is counted directly as primary energy. For coal, gas and nuclear power, the energy input to the power station is counted instead: the fuel’s energy content or the heat produced by the reactor.

The physics remains the same: solar panels still convert only part of the sunlight they receive. The convention provides a way of accounting for very different sources.

It also makes the conversion losses in thermal power stations visible. According to Eurostat’s Energy in Europe, 2026 edition, end users consumed 66% of the energy available in the European Union in 2024: roughly two-thirds. The remaining 34% mainly comprises losses during electricity generation and distribution, energy used by the energy sector itself, and non-energy uses such as asphalt and bitumen production. It is therefore not all wasted energy.

Does solar PV produce primary or secondary energy?

With solar PV, sunlight is the primary source, while the electricity generated by the panels is secondary energy because it results from conversion. It is counted as primary energy in statistical energy balances under the convention described above.

The route is short. Solar cells convert part of the incoming radiation into direct current; the inverter converts it into alternating current compatible with the household installation and the grid.

The electricity can then be:

• used immediately by household appliances

• stored in a battery

• used to charge an electric car

• exported to the grid

Direct self-consumption is the shortest route: the energy does not need to be exported and electricity imported later. Battery storage shifts energy use over time, from midday to the evening, for example, but adds conversion stages and associated losses.

Not burning fuel during operation does not mean a system has no environmental impact. Manufacturing, transport and the end of life of its components also matter. These are lifecycle considerations, however, rather than part of the distinction between primary and secondary energy.

Energy losses, efficiency and storage

Each conversion involves losses, usually in the form of heat. Energy does not disappear; some of it becomes unavailable for the intended purpose.

Efficiency measures how much of the energy entering a system becomes useful output:

Efficiency (%) = useful energy output / energy input × 100

If a system receives 10 kWh and delivers 9 kWh of useful output, its efficiency is 90%. The remaining kilowatt-hour has been dissipated as heat.

In a chain of devices, efficiencies are multiplied, not added. An inverter operating at 96% efficiency followed by a stage operating at 90% gives an overall efficiency of approximately 86.4%, rather than their average of 93%.

Batteries do not generate energy. They receive it, store it electrochemically and release it, with losses during charging and discharging. Their value lies in making energy available at a different time. This applies to both home batteries and electric vehicle batteries.

When discussing efficiency, it is important to define what is being measured: the PV module, inverter, battery, charge point, car or the entire chain from the original source to movement. Different system boundaries produce different results.

An energy management system (EMS) does not improve the conversion efficiency of individual components. It can, however, decide when they operate: for example, increasing charging power when surplus solar generation is available and reducing it when other household demand rises.

Primary and secondary energy in electric car charging

Charging an electric car brings the whole chain together in one action. Neither the charge point nor the battery generates energy: energy comes from a primary source, is converted into electricity and is transferred to the vehicle.

When electricity comes from the grid, its primary sources depend on the generation mix at that time. The route is:

• Primary source → power generation → transmission and distribution grid → household electrical installation → charge point → onboard charger → battery → motor.

With solar PV, the chain is shorter:

• Sunlight → PV modules → inverter → charge point → onboard charger → battery.

Home battery storage adds another stage, which can be useful when the car is away during daylight hours.

With alternating current (AC), typically used for home charging, the car’s onboard charger converts the electricity into direct current. With direct current (DC) rapid charging, conversion takes place in the charging station, which supplies DC electricity directly to the battery.

A smart home charge point such as Dazebox Home does not change the nature of electricity, but can help you use it more effectively. Depending on the model and installation, it can schedule charging, adjust power to the capacity available in the home and make greater use of solar generation. Dynamic power control requires suitable monitoring and control equipment.

Charging also involves losses, and there is no single percentage that applies to every car. Losses depend on charging power, temperature, battery condition, the onboard charger and systems operating during the session. This is why the energy recorded by the meter does not exactly match the energy stored in the battery.

An EMS can coordinate solar PV, battery storage and EV charging, and provide an overview of energy flows through an app, provided the components are compatible and the installation is configured for these functions. Learn how energy management systems work.

Common misconceptions about primary and secondary energy

• “Primary” does not mean “more important”. It means energy is present in a natural resource before conversion, for example in sunlight, wind or crude oil.

• Primary sources are not all renewable. Oil, natural gas, coal and uranium are primary sources too, but their reserves are finite.

• Secondary energy is not necessarily polluting. Electricity is produced through conversion, but generating it with solar PV has a different environmental impact from generating it by burning coal.

• Using electricity does not mean using energy with no environmental impact. An electric car does not burn fuel while driving, but assessing its emissions also requires considering how its electricity was generated.

• A battery does not produce energy. It stores energy supplied to it and releases it when needed, with losses during charging and discharging.

• Industrially produced hydrogen requires energy. Producing it uses electricity or other energy resources, so its impact depends on the production process.

• Not all the energy you consume delivers the result you want. Gas supplied to a boiler is final energy; heat warming the rooms is useful energy. Some energy is lost during operation.

• Solar panels do not automatically make a home independent of the grid. Panels generate electricity during daylight, while homes also consume energy at night. A battery can store some generation, but complete independence requires a system specifically designed for it.

Frequently asked questions about primary and secondary energy

Is petrol a primary energy source?

No. Petrol is secondary energy: it is produced by refining crude oil, which is the primary source.

Is natural gas a primary energy source?

Yes. Gas extracted from a reservoir is a primary energy product, including after processing and transport. It becomes the input for a secondary product when converted into something else, such as electricity or hydrogen.

Are all primary energy sources renewable?

No. Sunlight, wind, water, geothermal energy and biomass are renewable. Oil, natural gas, coal and uranium are primary sources but are non-renewable.

Is hydrogen an energy source?

Industrially produced hydrogen is a secondary energy carrier. Producing it requires electricity, heat or fuels, and its environmental impact depends on the production method.

Does a battery produce energy?

No. It stores energy received from an external source and releases it when needed, with losses during charging and discharging.

What is the world’s most widely used primary energy source?

Oil. In the IEA’s Global Energy Review 2025, covering 2024, its share of global energy demand fell below 30% for the first time. The subsequent Global Energy Review 2026, covering 2025, reports a further 0.7% increase in oil demand. That figure measures annual growth, rather than oil’s share of the total. The comparison concerns overall energy use, rather than electricity generation alone.

Understanding where your energy comes from

Knowing whether energy is primary or secondary helps distinguish the original resource from the electricity delivered to a socket. Before comparing technologies, consider which form of energy is being measured, at what stage in the chain and for which purpose.

In a home with solar PV and an electric car, the chain is relatively short and easy to identify: generation, optional storage and charging. Using electricity as it is generated avoids additional stages; storage adds flexibility, with some energy losses to account for.