• {{currentSearchSuggestions.title}}
  • {{currentSearchSuggestions.title}}

Energy glossary


Do you know what a wind turbine nacelle is? What do we mean by fuel switching and what does the acronym CSV mean? We’ll guide you through the new world of energy using terminology that’s easy for everyone to understand. Here’s a glossary with all the words you need to know, including the technical ones.


Additional Capacity

Capacity relating to new plants, both consolidated or managed, or the increases in the capacity of existing plants via technological development work. Additional capacity is declared when the first circuit of a plant is connected to the grid and begins producing energy and all the components of the plant are electromechanically complete.

Appears in


A device that converts the mechanical energy created by the rotating element of a turbine into electric power

Appears in

Arch dam

A convex-shaped dam, generally built to dam narrow valleys or gorges that have rocky sides or other stable natural walls.

Appears in

Asset development

Amount of resources that a company invests for the construction of new plants, for increasing installed capacity or improving the efficiency of existing plants.


BESS-Battery Energy Storage Systems

A group of devices, equipment, management and control logic capable of storing electric power so that it can later be fed into the grid. It allows solar and wind power plants to overcome their intrinsic limitations in terms of flexibility and dispatching.

Appears in


Collective term for organic matter that can be used to generate electricity, transformed into fuel or used directly to produce heat. It comes primarily from industrial and urban waste, from energy crops, and from biological products, waste and residues generated by farming, forestry or related industries. It's generally considered a renewable energy source since, unlike fossil fuels, the sources from which it is obtained are produced continuously.

Appears in


Capacity Auction or Capacity Market

A new market created to guarantee long-term price signals and sufficient reliable capacity consistent with decarbonization goals. The mechanism introduces supplementary payment for suppliers of capacity who commit to maintaining and to making their capacity available to the electricity system, if required.

Appears in

CaPex Coverage Ratio

Ratio in percentage between the discounted positive margin generated by the investment in a regulated or risk-free system and the total investment made; it provides a measure of the investment’s exposure to risk on returns relating to fluctuations in market prices.

Carbon policy

A group of policies designed to support the changes the energy sector must make to achieve carbon dioxide emission reduction targets, while simultaneously guaranteeing affordable, reliable energy to consumers. The most commonly adopted market mechanisms are Emissions Trading Schemes (ETS) and carbon taxes.

Carbon tax

Tax levied on fossil fuels on the basis of their carbon dioxide emissions into the atmosphere, the aim of which is to contribute to reducing such emissions.

Coal phase-out

The phase-out of a coal-powered station is always gradual. It is measured with an indicator that represents the evolution of the installed capacity of the plant and provides evidence of its progressive phase-out. When the station ceases to operate, the corresponding capacity is subtracted from the balance sheet.

Appears in

COD (Commercial Operating Date)

During the process of building a power station, this is the date in which the latter starts being paid for the electricity it produces.

Appears in

Commercial & Industrial (C&I) Customers

Commercial and industrial companies of medium or large size. "Industrial" refers to any enterprise that deals with the production of goods, while "commercial" refers to any enterprise that purchases goods or services from another entity for commercial purposes.

Appears in


The process at the end of the construction of a power station which includes activities necessary to guaranteeing that all the station’s components, machinery and systems are working correctly and are capable of doing so safely and efficiently under normal operating conditions.

Appears in

Consolidated Installed Capacity

The maximum power deliverable by generation plants, controlled by an energy company (de jure or de facto) and which it thus consolidates from an economic and financial perspective.

Consolidated net production

The electricity generated by the plants net of grid losses and consumption relative to auxiliary services within the perimeter of companies whole or partially consolidated by an energy company.

Consolidated Renewable Capacity/Total Capacity

The ratio of the Installed Capacity of Power Plants that produce energy from renewables (hydroelectric, wind, solar and geothermal) to the total Installed Capacity of renewable, thermoelectric and nuclear power stations. The trend provides evidence of a gradual shift in the asset portfolio towards a predominance of renewable sources.

Corrective maintenance

A type of maintenance based on repairing faults when they occur. It cannot be planned but depends on when the fault that needs to be repaired occurs. Depending on the component involved, it may be necessary to shut down the plant, thereby causing production losses.

CO2 footprint

The average amount of CO2 that power stations emit into the atmosphere to produce one unit of energy (1 kWh).

Appears in

CSV (Creating Shared Value)

A business model through which it is possible to create economic value for both the business and its stakeholders by producing a benefit for society and the environment.

Appears in


Data-Driven Asset

Indicates the percentage of power plants (in terms of total installed capacity) that are equipped with sensors and software that enable the use of information for digitalized, remote or automated plant management.


A group of operations that remediate, dismantle and remove the structures and components of a power station at the end of its working life.

Appears in


A device installed on the blades of wind turbines to reduce the noise they produce: the name describes its shape, which recalls the serration of a dinosaur tail.

Appears in

Dispatchable or Plannable Generation

Sources of electricity that can be used on demand and dispatched at the request of grid operators to meet market needs. Plannable generators can be turned on or off or can adjust their power output according to an order.

Appears in


The final phase of the process of delivering electricity to the end user after generation and transmission.

Appears in

Dry steam geothermal plant

A system that is more complex and powerful than a flash steam geothermal plant (see definition), using high-temperature, high-pressure steam to produce energy: in this case the steam is sent directly to the turbine.



Ratio of average EBITDA (Earnings Before Interest, Taxes, Depreciation and Amortization) generated by an investment project in the first five years after final delivery, and the relevant investment involved. It provides evidence of profitability of the investment in short/medium term.


EBITDA relating to generation plants that went into operation as part of the plan.

Electricity system

All the components deployed to produce, transmit, distribute and sell electricity. This includes power generation and storage facilities, transmission and distribution grids and all the related infrastructure.

Appears in


A chemical process that uses electricity to break down a substance into its constituent elements. Electrolysis can be used to produce green hydrogen by coupling an electrolyser with a renewable energy plant.

Appears in

Energy balance

The balance between the inward and outward energy flows of a facility or geographical area; it can include the production, import, export, purchase, sale, transportation, transformation and consumption of energy.

Appears in

Energy carrier

Substance or phenomenon (energy system) that contains energy produced from primary sources that can subsequently be converted to other forms, even at a later time or in another location. An example is hydrogen which, unlike raw materials such as fossil fuels, isn't naturally available: it needs to be produced using industrial processes and then stored and transported via pipelines or in tanks before it can be used for various purposes.

Appears in

Energy grid

The infrastructure used to transport energy from where it is produced to the final consumers. In the case of electricity, the classic structure includes two grids: the first is the transmission grid, which transports high-voltage electricity from the generation facilities to the primary substations; from here the second, or distribution, grid transports the medium-voltage electricity to the secondary substations and then, at a low voltage, to the final customer.

Energy intensity

Parameter which measures the energy efficiency of the economy of a country or geographical area: it is the ratio between the gross energy consumption and the gross domestic product (GDP). In other words, it indicates the quantity of energy consumed for each unit of GDP generated.

Appears in

Energy transition

An energy paradigm revolution. In the case of the current energy transition, this means the transition from non-renewable energy sources to renewable sources, and it is part of the wider transition to sustainable economies through the use of renewables, and the adoption of energy-saving and sustainable development techniques.

Appears in

Energy KPIs

Key Performance Indicators (KPIs) relating to a company operating in the energy sector: for example, electricity production, carbon dioxide emissions, the percentage of electricity generated from renewable sources, and the internal consumption of energy and water.

Appears in

Engineering Procurement & Construction (EPC) contract

A contract regulating the relationship with a single supplier that provides the engineering, procurement of materials and construction services, required to build a power station.

Extraction well

A well, sunk into the ground in order to extract steam for the production of geothermal energy.

Appears in


Feed-In Premium (FIP)

A price-based incentive mechanism for renewable energies, thanks to which the producer is awarded a pre-established premium on the market price of energy. The payment of this premium is guaranteed for a period of time and is linked to the economic life of the relevant renewable project.

Feed-In Tariff (FIT)

A price-based incentive mechanism for renewable energies, which grants the producer an "all-inclusive tariff." The payment of this tariff is guaranteed for a period of time linked to the economic life of the relevant renewable project.

Flash steam geothermal plant

A power plant, usually of small dimensions, that extracts fluid composed of water and steam from an extraction well: the steam is separated from the water in a specific device, and channeled to a turbine to produce energy.

Flowing water hydroelectric plant

A plant that converts the potential and kinetic energy of water into electric power using a hydraulic turbine. Its power depends on the so-called drop or height difference between two levels in a water course. It uses the natural power of a water course and thus its electric power production cannot be planned.

Appears in

Free Cash Flow to Equity/Equity

The ratio between the cash flow generated by the investment project available to shareholders (on average for the first 5 years) and the capital contributed by shareholders to the project. It highlights the profitability of the investment in the short/medium term.

Fuel switching

The replacement of coal-fired capacity with other less polluting and more sustainable energy sources, such as gas.

Full Production

This is declared once a plant has been built and is connected to the grid and is able to produce electricity. This is after the completion of reliability tests and the meeting any contractual obligations or grid requirements.



One of the main traditional processes capable of producing hydrogen by transforming a solid or liquid fuel into gas. This is done at high temperatures (of over 1000 °C) and results in the creation of a fuel gas mixture known as SynGas or Synthesis Gas, consisting primarily of carbon monoxide and hydrogen.


A device that converts various forms of energy – mechanical, chemical, light or thermal – into electricity. Generators include dynamos, for the production of direct current (DC), and alternators, capable of generating alternating current (AC).

Appears in

Geothermal fluid

The mix of gas and steam extracted from wells for the production of geothermal energy.

Appears in

Geothermal plant

A plant that conveys the water vapor from the subsoil to special turbines that converting the thermal energy produced by the Earth's heat into electrical energy.

Appears in

Geothermal pool

A natural reservoir resulting from the outflow of hot water from below ground; a geothermal pool is normally not large and is characterized by high concentrations of mineral salts.

Appears in

Gravity dam

A type of dam that generally has a triangular or trapezoid-shaped vertical cross section and a straight, or sometimes curved, horizontal cross section. The stability and resistance of the dam to the pressure of the water solely relies on the weight of the construction.

Appears in

Greenhouse gases

Gases which cause a greenhouse effect within the earth's atmosphere and are therefore responsible for global warming and climate change. The most damaging are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), sulfur hexafluoride (SF6), hydrofluorocarbons (HFCs) and fluorocarbons (PFCs).

Appears in

Green hydrogen

Hydrogen produced via the electrolysis of water in which the electricity used in the process is derived from renewable sources.

Appears in


Unit of measurement for power, equivalent to 1,000 MW, i.e. a billion watts.

Appears in


Heterojunction Technology (HJT)

Solar panel production technique that's considered to be one of the most efficient, both in terms of the energy required for their production and in terms of their energy performance. It involves producing panels consisting of overlapping layers of materials with different characteristics (for example, one layer of crystalline silicon and one of amorphous silicon). The heterojunction is the interface between one layer and another.

Appears in

High-enthalpy (or traditional) geothermal

The production of energy from the Earth’s heat in volcanic or tectonic zones, where temperatures are in excess of 150 °C.

Appears in

Hybrid power plants

Power plants which produce electricity from two or more different sources, which can be either renewable or non-renewable.

Appears in

Hydraulic turbine

Mechanical device that converts the kinetic and potential energy of a liquid into mechanical power.

Appears in


Intergovernmental Panel on Climate Change (IPCC)

International body established in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) to assess the current scientific knowledge on climate change and its potential impacts.

Compare in


A device that converts continuous current (CC) to alternating current (AC). For instance, it is used to convert continuous current from photovoltaic panels to alternating current to be fed into the grid.

Appears in

IRR (Internal Rate of Return)

A discount rate that makes the net present value (NPV) of an investment equal to zero. It provides a measure of the profitability of an investment compared to the internal cost of capital.



Unit of measurement for energy defined as the work done to produce one watt of power for one second.

Just Transition

Energy transition towards a system based on renewable sources done in a way that's fair to everyone, therefore taking into consideration jobs, the security of energy supplies and a fair distribution of the costs associated with the transition.

Appears in


Kaplan turbine

One of the main water turbine models. Developed in 1913 by the Austrian engineer and inventor Viktor Kaplan, it is particularly useful when the water flows down modest gradients and is also suitable for very high water flow rates.

Appears in


LCA (Life-Changing Accident)

An accident with permanent consequences that interfere with the day-to-day life of the victim or reduce their life expectancy.

LCOE (Levelized Cost of Energy)

Cost of producing 1 MWh of electricity, a competitiveness index for generation plants.

Appears in

Low-enthalpy geothermal

The production of energy for heating and cooling purposes using the Earth’s natural heat, via probes sunk into the ground and connected to a heat pump.

Appears in


Managed installed capacity

The maximum authorized power from both consolidated and unconsolidated generation plants, which are managed/operated by an energy company through partnership agreements or asset management contracts.

Monoaxial trackers

Support structures on which the solar panels are placed: they move in order to follow sun exposure every day, on a horizontal rotation axis.

Appears in


Unit of measurement for power, equivalent to a million watts.

Appears in


Non-dispatchable or Non-Plannable Generation

Electricity sources that cannot be turned on or off to meet fluctuating energy requirements. This type of generation is often highly intermittent, which means that it is not continuously available because of non-controllable factors (e.g. weather).

Appears in


Offshore (plant)

Power plant located offshore and mounted on purpose-built structures which are either floating or fixed to the seabed.

Appears in

Onshore/offshore wind power

A plant that turns the kinetic energy of the wind into electricity. The term onshore refers to wind farms on land while offshore means wind farms built on open water, generally at sea or on the ocean.

Appears in


Operating expenditure or costs involved in running the business.

Appears in


Payback period

The number of years it will take for positive flows from an investment to compensate for outgoings sustained. It indicates the riskiness of a project solely in terms of time.

Photovoltaic panel

A device consisting of photovoltaic modules, which in turn are made of photovoltaic cells. The cells convert solar radiation into electric power using the photoelectric effect and are the basic components of a photovoltaic power plant. The most common type of cell is made from crystalline material with a layer of semiconductor material, most often silicon. There are also amorphous silicon cells.

Appears in

Photovoltaic (PV) plant

A plant consisting of a series of modules that convert the sun's radiation into electrical energy through the photovoltaic effect. There are two main types of photovoltaic plant: stand-alone, which isn’t connected to a grid and uses the energy produced on site, and "grid-connected".

Appears in


A group of projects that have been authorized by the Screening Committee and satisfy the project’s set of maturity criteria which are defined according to technology and country.

Appears in

Power Purchase Agreement (PPA)

A contract between an electricity user or corporate client and an electricity producer for the sale of electricity at a pre-established price and for a pre-established period of time. The contract lays out the commercial conditions for the sale of electricity: duration of the contract, delivery point, date/time of delivery, volume, price and energy source.

Appears in

Predictive maintenance

The group of operations that can predict when a particular machine or piece of equipment is developing a defect before it results in a fault. It requires detailed knowledge of the machinery, techniques and instruments used for this task. It enables the early prediction of faults thereby reducing related production losses and avoiding unnecessary corrective and/or preventative operations.

Appears in

Preventative/planned maintenance

Planned maintenance work to review, replace or repair machinery or equipment at the plants before faults develop. The schedule is designed to minimize production losses arising from any halts in generation.

Appears in

Pumped storage hydroelectric plant

(see Storage hydroelectric plant)

Appears in

Pumped storage plant

A type of hydroelectric power station with a lower as well as an upper storage pool or reservoir: the water that generated electricity during the day is stored in the lower storage pool or reservoir and can then be pumped back up to the upper storage pool at a time of day when energy demand is lower (for instance, at night). This means the water that is pumped back up using power can be reused to generate energy at peak demand times. This enables users to take advantage of price differences and provide services grid stabilization services.

Appears in



Renovation, restructuring and efficiency activities for a power plant in order to optimize production.

Appears in

Regulated energy auctions

Auctions for the sale and purchase of long-term electric power, typically developed by distribution companies who purchase electricity on behalf of regulated users. In some cases, they can also extend to consumers or free customers.

Reinjection well

A well that returns the water discharged from a geothermal plant to its original geothermal reservoir.

Renewable energy sources

Energy sources which are continuously replenished. They include the sun, the wind, water and geothermal resources, biomass and the sea.

Appears in


Process which involves carrying out activities to prolong the useful life of a power plant and improve its efficiency, particularly through the introduction of new technologies.

Appears in

Reservoir fill time

At a hydroelectric plant, this term refers to the length of time required for a reservoir to collect a volume of water sufficient to reach useful capacity, i.e. the volume of water needed for the plant to operate normally.

Appears in


Solar collector

A technical term that refers, in solar thermodynamic power plants, to the solar panels that convert solar energy into thermal energy.

Solar updraft tower

A structure that produces electric energy from the natural upward movement of hot air: it is composed of a collector at the base that collects hot air, a tower from which the air emerges, and turbines situated between the tower and the collector.

Start of Construction (SoC)

In the process of building a plant, this is the date on which the building site formally opens for construction work.

Station availability

The percentage of time during which a power station is capable of generating electricity in the reference period analysed.

Appears in

Steam pipe

At geothermal plants, the various pipes that transport steam generated from the Earth to the turbine.

Appears in


Electricity storage system which makes it possible to store electricity until it is required; it's a particularly important technology for intermittent energy sources such as the sun and the wind. The most utilized storage systems are pumped-storage hydroelectricity facilities, but the battery market is growing rapidly.

Appears in

Storage hydroelectric plant

Energy is generated by a plant which has an upper storage reservoir. The flow of water and the electrical power produced by it can both be regulated.

Appears in

Sustainable Development Goals (SDGs)

The 17 Sustainable Development Goals established in 2015 by the United Nations to guarantee future peace and prosperity for humanity. They cover a range of different areas, such as ending hunger around the world, gender equality, climate protection and clean energy for everyone.

Appears in



This term, which has become part of the language, refers to a type of technology used in the production of photovoltaic panels that pairs two different simple photovoltaic cells capable of turning solar radiation of different wave lengths into electricity: e.g. HJT and thin-film perovskite.

Appears in

Thin Film

In photovoltaic panel production, thin film modules are made by depositing a thin layer of semiconductor material on a glass or plastic substrate.

Appears in


An automatic mechanical device that reduces the angle of incidence between a photovoltaic panel and the oncoming sunlight, thereby increasing the power of the solar radiation picked up by the panel and thus the amount of energy produced by it.

Appears in


An electric device used to transfer electric power at different voltage levels.

Appears in


The act of transporting electric power on a high and very high voltage interconnected transmission network with the aim of delivering it to end users in high voltage form and to distributors.

Appears in


Unitary Energy Gross Margin

The ratio of Gross Margin (proceeds from energy production and other proceeds from non-core activities net of variable costs) and consolidated net production.


Watt (W)

International System unit of measure of power. Multiples of Watts are: kW (103W), MW (106W), GW (109W) and TW (1012W).

Appears in

Watt-Hour (Wh)

A unit of measure commonly used to measure electricity and defined as the total power supplied when one Watt of power is maintained for an hour. Multiples of Watt-Hours are: kWh (103Wh), MWh (106Wh), GWh (109Wh) and TWh (1012Wh).

Appears in

Wind turbine

Electromechanical device capable of converting the kinetic energy of the wind (wind power) into electricity.

Appears in

Wind turbine nacelle

Part of a wind turbine located at the top of the tower: it's secured to the rotor. It contains the mechanisms for transforming wind energy into electricity. There are also control systems mounted on top to monitor the generator's operating parameters.

Appears in

Wind turbine rotor

The heart of the wind turbine, composed of a hub to which the rotor blades are attached.

Appears in