Commercial Energy Glossary: Key Terms Explained for UK Businesses

When we discuss energy solutions with clients, we cover a broad range of technical terms that aren’t always common knowledge. This glossary is designed to demystify the definitions and abbreviations you’ll encounter across the commercial energy sector.

Reflecting our work as a UK commercial renewable energy installer, this glossary spans six areas: general electrical terms, solar PV, battery storage, EV charging, the finance and funding options used to pay for these projects, and the UK energy policy and compliance landscape that shapes them. Definitions are written for the decision-makers we work with most often; Operations Directors, Facilities Managers, CFOs and Sustainability Leads. If you’d like help applying any of these to your site, get in touch.

General Electrical Terms

• AC Power – Alternating current, which periodically reverses direction. The form of power supplied by the grid.
• Amps (A) – The unit of electrical current.
• Breaker – A protective switch that automatically interrupts the flow of electricity when an overload or short circuit is detected.
• Charge Bands – DUoS unit rates are billed across three time-of-day bands — “red”, “amber” and “green”. Costs are highest in the “red” peak periods and lowest in “green” off-peak periods, which is why load shifting can reduce bills.
• Current – The flow of electrical charge in an ordered direction, measured in amps.
• DC Power – Direct current, which flows in one direction only. Solar panels and batteries generate and store DC.
• DNO (Distribution Network Operator) – The companies that own and operate the local cables and substations bringing electricity from the transmission network to your premises (for example, National Grid Electricity Distribution or UK Power Networks). Your DNO must approve grid connections for new solar, storage and EV charging capacity.
• DUoS – Distribution Use of System charges, applied to your bill to recover the cost of distributing electricity across local networks.
• Earth – The common return path for current and a fundamental safety requirement of any compliant installation, as set out in the IET Wiring Regulations (BS 7671).
• Frequency (Hz) – Measured in hertz (1Hz = one cycle per second). The UK grid operates at a nominal 50Hz, which NESO balances in real time.
• G99 / G98 – Engineering Recommendations from the Energy Networks Association governing how generation and storage above (G99) or below (G98) defined thresholds connect to the grid. Most commercial solar and battery projects require DNO sign-off under G99.
• Inverter – Equipment that converts direct current (DC) into alternating current (AC), or vice versa. Central to any solar or battery system, since panels and batteries are DC while the grid and most equipment are AC.
• Joule (J) – The SI unit of energy, equal to the work done when a force of one newton moves an object one metre.
• Junction Box – An enclosure containing a junction for combining and protecting electrical cables.
• Kilowatt (kW) – A unit of electrical power equal to 1,000W. Used to describe the power rating (instantaneous capacity) of solar arrays, inverters, batteries and EV chargers.
• Kilowatt Hour (kWh) – A measure of electrical energy consumption equal to using 1,000W (1kW) for one hour — the unit you’re billed in. One of the most important energy terms to understand in our sector.
• Megawatt / Megawatt Hour (MW / MWh) – One thousand kilowatts (power) or kilowatt hours (energy). Common units for larger commercial and utility-scale generation and storage.
• NESO (National Energy System Operator) – The publicly owned body that balances Great Britain’s electricity system second by second and plans the wider energy network. NESO took over from National Grid ESO on 1 October 2024 under the Energy Act 2023.
• TNUoS – Transmission Network Use of System charges, which recover the cost of operating and maintaining the high-voltage transmission network. Largely levied as a fixed residual charge since the Targeted Charging Review.
• Transformer – Equipment that steps voltage up or down so power can pass between circuits operating at different voltages (learn more about how transformers feature in HV/LV infrastructure).
• Triad – Historically, the three half-hourly periods of highest national electricity demand between November and February, once used to set part of a business’s transmission (TNUoS) charges. Following Ofgem’s Targeted Charging Review, from April 2023 most of this cost moved to a fixed, capacity-band standing charge — so “Triad avoidance” now offers little benefit for most businesses. A small locational element remains.
• Voltage (V) – A measure of electrical potential difference; effectively the “pressure” pushing current through a circuit.
• Watt (W) – A unit of electrical power that quantifies the rate of energy transfer (one joule per second).

Terms Used in the Solar PV Sector

Solar photovoltaics convert sunlight directly into electricity. These terms cover the technology, performance and safe installation of commercial rooftop, ground-mounted and carport systems.

• Access Ladder – A ladder providing safe access, generally to the rooftop of a site where solar is to be installed.
• Array – A connected group of solar panels. Panels wired in series form a “string”; multiple strings make up the array.
• Clamp – The component used to secure panels to the mounting rail.
• Degradation Rate – The gradual annual decline in a panel’s output, typically quoted as a percentage per year and underwritten by a manufacturer’s performance warranty.
• D-marc Edge Protection – A health-and-safety measure that makes a roof working area safe from falls. D-marc edge protection should be used on roofs pitched over 15°, in line with the Work at Height Regulations 2005 (HSE guidance).
• Irradiance – The solar power hitting a surface per unit area (W/m²). Combined with site orientation and tilt, it drives expected yield.
• kWp (Kilowatt Peak) – The maximum output of a solar system under standard test conditions, used to size and compare installations (read our explainer on what kWp means).
• MCS (Microgeneration Certification Scheme) – A recognised quality mark and standards framework for renewable technologies and their installers (MCS).
• Mounting Rail – The rail system to which solar panels are fixed.
• MPPT (Maximum Power Point Tracking) – Inverter electronics that continuously adjust the operating point of an array to extract the most power available in the current conditions.
• O&M (Operation & Maintenance) – Ongoing servicing that keeps a system safe and performing to spec — see our aftercare service.
• Orientation & Tilt – The compass direction (azimuth) a panel faces and the angle from horizontal. In the UK, south-facing arrays at roughly 30–40° typically maximise annual generation, though east–west layouts can better match commercial demand.
• Performance Ratio (PR) – The primary measure of a system’s efficiency, expressing how effectively it converts available sunlight into usable AC electricity after real-world losses.
• Photovoltaic (PV) – The effect by which certain materials generate DC electricity when exposed to light. The “PV” in solar PV.
• Safety Rail – Temporary or permanent edge protection used where a roof pitch exceeds 15° to prevent falls during installation and maintenance.
• SEG (Smart Export Guarantee) – The scheme requiring larger licensed electricity suppliers to pay small-scale generators for surplus electricity exported to the grid.
• Self-Consumption – The share of generated solar energy used on site rather than exported. Higher self-consumption usually delivers the strongest commercial return.
• Solar Panel (Module) – A device using photovoltaic cells to convert sunlight into DC electricity. We install solar panels for businesses as one of our core services.
• Warranty – A manufacturer’s assurance that equipment will perform to a stated standard for a defined period. EvoEnergy solar customers are additionally protected by the Independent Warranty Association (IWA).
• Weather Station – On-site sensors that measure conditions such as irradiance and temperature, used to verify that a PV system is performing as expected.

Terms Used in Battery Storage

Commercial battery energy storage lets a business store electricity, whether self-generated or bought cheaply off-peak and use it when it’s most valuable. These terms cover capacity, performance and safety.

• BESS (Battery Energy Storage System) – The complete system that stores electrical energy for later use, comprising battery modules, an inverter/converter, controls and safety systems.
• BMS (Battery Management System) – Electronics that monitor and protect each cell, managing temperature, voltage, balancing and safety to maximise performance and lifespan.
• C-Rate – The rate of charge or discharge relative to capacity. A 1C rate fully charges or discharges the battery in one hour; 0.5C takes two hours.
• Cycle Life – The number of full charge/discharge cycles a battery can complete before its usable capacity falls to a defined threshold (often 70–80%).
• Depth of Discharge (DoD) – How much of a battery’s capacity has been used in a cycle. Higher usable DoD means more accessible energy from the same nameplate capacity.
• Energy Arbitrage – Profiting from the price difference between cheap off-peak charging and high-value discharge or export.
• IEC 62619 – The international safety standard for industrial and commercial secondary lithium batteries, one benchmark for specifying compliant storage (IEC).
• Islanding / Backup – The ability of a battery system to keep critical loads running during a grid outage by safely disconnecting from the network.
• kVA (Authorised Supply Capacity) – The maximum power your site is contracted to draw from the grid. Storage and demand management can keep a site within its kVA limit and avoid costly upgrades.
• Lithium Iron Phosphate (LFP / LiFePO₄) – A lithium battery chemistry widely used in commercial storage for its strong thermal stability, long cycle life and safety profile.
• Load Shifting – Charging when electricity is cheap (or solar is plentiful) and discharging during expensive periods, reducing reliance on peak-rate grid power.
• Peak Shaving – Discharging stored energy during demand peaks to reduce a site’s maximum import, lowering capacity (kVA) and certain network charges.
• Power Rating (kW) vs Usable Capacity (kWh) – Two distinct figures: power (kW) is how fast a battery can charge or discharge; capacity (kWh) is how much energy it holds. Both matter when matching a battery to a site’s load profile.
• Round-Trip Efficiency – The proportion of energy put into a battery that can later be retrieved, after charge/discharge losses. Commercial lithium systems typically sit around 85–95%.
• State of Charge (SoC) – The current energy level of a battery, expressed as a percentage of its usable capacity.
• State of Health (SoH) – A measure of a battery’s current usable capacity against its original specification, indicating ageing and degradation.

Terms Used in EV Charging

Workplace, fleet and destination EV charging is increasingly part of a commercial energy strategy, often paired with solar and storage. These terms cover hardware, connectors and the smart-charging standards that govern them.

• AC vs DC Charging – AC charging relies on the vehicle’s onboard converter and suits workplace and destination sites; DC (rapid) charging converts power in the unit itself for much faster top-ups.
• Back Office / RFID – The management platform (and access cards or app authentication) used to control access, monitor usage and bill drivers across a charging estate.
• CCS (Combined Charging System) – The prevailing DC rapid-charging connector standard in the UK and Europe, combining Type 2 with two high-power DC pins.
• CHAdeMO – An earlier DC rapid-charging connector standard, now less common on new UK installations than CCS.
• Charge Rate (kW) – How quickly a charger delivers energy. Typical workplace AC units are 7–22kW; rapid DC chargers range from 50kW to ultra-rapid 150kW+.
• Charging Modes (Mode 3 / Mode 4) – Defined in IEC 61851: Mode 3 covers dedicated AC charging with communication and protection; Mode 4 covers DC rapid charging via an off-board converter (IEC).
• Dynamic Load Management (Load Balancing) – Software that distributes available power across multiple chargers in real time, preventing overload and often avoiding an expensive grid connection upgrade.
• EVSE (Electric Vehicle Supply Equipment) – The technical term for an EV charger: the unit, cabling and controls that safely deliver power to a vehicle.
• OCPP (Open Charge Point Protocol) – An open communication standard between chargers and management software, letting operators avoid vendor lock-in and integrate hardware from different manufacturers.
• OZEV (Office for Zero Emission Vehicles) – The government body administering EV grants and schemes, including support for workplace and fleet charging infrastructure (OZEV).
• Rapid / Ultra-Rapid Charging – High-power DC charging (typically 50kW for rapid, 150kW+ for ultra-rapid) suited to fleet depots and high-throughput sites.
• Smart Charging – Charging that responds to price, grid or solar signals. In Great Britain, most private chargepoints must meet the Electric Vehicles (Smart Charge Points) Regulations 2021 (DESNZ guidance).
• Type 2 Connector – The standard AC charging connector across the UK and Europe (IEC 62196), used by most workplace and destination chargers.

Finance & Funding Options (UK)

Few commercial energy projects are paid the same way. The right route depends on whether you want to own the asset, preserve capital, or pay only for the energy produced. These terms cover the main funding models and the UK tax reliefs that improve the business case.

• 50% First-Year Allowance (FYA) – Lets companies deduct 50% of qualifying special-rate expenditure (which includes solar PV and battery storage) in year one, with the balance written down at 6% thereafter. Made permanent in 2023; useful where annual spend exceeds the AIA cap.
• Annual Investment Allowance (AIA) – A 100% first-year deduction on qualifying plant and machinery, up to a permanent limit of £1 million per year. It applies to companies and unincorporated businesses, and usually covers a typical commercial solar or storage install in full.
• Business Rates Exemption – In England, eligible new rooftop solar and qualifying on-site storage are exempt from the business-rates uplift they would otherwise create, currently until 2035 (rules differ across the UK nations, check your local position).
• CAPEX (Capital Expenditure) – Buying the system outright. The business owns the asset, keeps all the generation and savings, and claims the available capital allowances, typically the strongzest long-term return (CAPEX).
• Capital Allowances – The mechanism by which a business deducts the cost of qualifying plant and machinery, including solar, battery storage and EV charging equipment from its taxable profits (gov.uk).
• Full Expensing – A permanent 100% first-year deduction for companies on new main-rate plant and machinery. Note: solar panels are classed as special-rate assets, so they do not qualify for full expensing, a common misconception in solar marketing. Use the AIA or 50% FYA instead. (EV charge-point equipment has its own 100% first-year allowance, currently to 31 March 2027.)
• Green Loan – Lending specifically structured to fund sustainability and renewable-energy investments, often on preferential terms (learn more here green loan).
• Lease to Own – Spreading the cost over an agreed term while retaining ownership of the system at the end of the agreement (learn more here lease to own).
• Operating Lease vs Finance Lease – Under an operating lease the funder retains ownership and the allowances, and you expense the payments; under a finance lease the risks and rewards of ownership effectively sit with your business. The distinction affects both accounting treatment and who claims capital allowances.
• Payback Period – The time taken for energy savings and income to recover the initial investment.
• PPA (Power Purchase Agreement) – A funder installs, owns and maintains the system on your site at no upfront cost, and you buy the electricity it generates, usually at a rate below grid prices. Capital allowances accrue to the asset owner, not the host (PPA).
• ROI / IRR – Return on Investment expresses total gain against cost; the Internal Rate of Return annualises that return for comparison against other capital projects.
• VAT (Commercial) – Commercial solar is standard-rated at 20% VAT (normally recoverable by a VAT-registered business), unlike domestic installs, which are zero-rated until 31 March 2027.
• Writing Down Allowance (WDA) – The ongoing annual deduction for assets not fully relieved in year one. The special-rate pool (e.g. solar) is written down at 6% on a reducing balance; the main-rate pool reduces to 14% from April 2026.

UK Energy Policy & Compliance

Commercial energy decisions sit within a framework of UK targets, reporting duties and support schemes. These terms cover the policies and obligations most relevant to businesses investing in solar, storage and EV charging.

• Capacity Market – A scheme that secures the electricity supply needed at peak times by paying generators, storage and demand-response providers to be available when called upon.
• Clean Power 2030 – The government’s action plan to run Great Britain’s electricity system predominantly on clean, low-carbon power by 2030, accelerating grid, renewables and storage deployment.
• Climate Change Levy (CCL) – An environmental tax on electricity, gas and other fuels supplied to business. Electricity generated and consumed on site from your own renewables is not subject to CCL, adding to the saving from self-consumption.
• Contracts for Difference (CfD) – The government’s principal mechanism for supporting large-scale low-carbon generation, awarded through competitive auctions that guarantee generators a fixed “strike price.”
• EPC (Energy Performance Certificate) – A rating of a building’s energy efficiency. Solar and efficiency measures can improve a commercial EPC and support MEES compliance.
• ESOS (Energy Savings Opportunity Scheme) – A mandatory scheme requiring large UK undertakings to audit their energy use every four years and identify cost-effective savings. The Phase 4 compliance deadline is 5 December 2027.
• MEES (Minimum Energy Efficiency Standards) – Regulations restricting the letting of commercial property below a minimum EPC rating, making on-site efficiency and generation increasingly relevant to asset value.
• Net Zero – The UK’s legally binding target, under the Climate Change Act 2008 (as amended), to reach net zero greenhouse gas emissions by 2050. See our guide to reducing your company carbon footprint.
• REGO (Renewable Energy Guarantees of Origin) – Certificates issued per MWh of renewable electricity, used to evidence the green origin of supply and underpin renewable tariffs.
• Scope 1, 2 & 3 Emissions – The Greenhouse Gas Protocol categories: Scope 1 covers direct emissions you own or control; Scope 2 covers purchased energy; Scope 3 covers indirect emissions across your value chain. On-site solar primarily reduces Scope 2.
• SECR (Streamlined Energy & Carbon Reporting) – A mandatory framework requiring qualifying large UK companies and LLPs to disclose energy use, emissions and efficiency measures in their annual reports.
• SEG (Smart Export Guarantee) – The scheme requiring larger licensed suppliers to pay small-scale generators for electricity exported to the grid.

Commercial energy projects bring together several disciplines at once; solar, battery storage, EV charging and the electrical infrastructure that ties them together, alongside the finance models that fund them and the policy framework that rewards them. Understanding the language is the first step to confident, well-evidenced decisions: knowing the difference between a kW and a kWh changes how you size a system; knowing that solar is a special-rate asset changes how you claim tax relief; and knowing your ESOS or SECR obligations changes when you need to act.