This glossary explains twenty key solar energy terms in plain language, including MCS certification, Smart Export Guarantee, distribution network operator, kilowatt peak, and other terms you will see in solar panel quotes and installation documents.
Reference
Solar Energy Glossary
Plain-English definitions of 20 terms you will see in solar quotes, installer reports, and energy advice across Scotland.
- MCS (Microgeneration Certification Scheme)
- The UK's quality assurance scheme for small-scale renewable energy installations. Only MCS-certified installers can register your system for Smart Export Guarantee payments and most grant or loan schemes. It covers both the installer company and the products they fit.
- SEG (Smart Export Guarantee)
- A government-backed scheme requiring large energy suppliers to pay you for surplus electricity you export to the grid. Rates vary from 3p to 15p per kWh depending on supplier and tariff. Replaced the Feed-in Tariff in 2020.
- DNO (Distribution Network Operator)
- The company that owns and operates the local electricity distribution network. In Scotland this is either SPEN (south) or SSEN (north). Your installer must notify or apply to the DNO before connecting a solar system to the grid.
- kWp (kilowatt peak)
- The maximum power output of a solar panel or system under standard test conditions (25°C, 1000 W/m² irradiance). A typical Scottish home installs a 4–5kWp system. Used to compare panels and size systems.
- kWh (kilowatt hour)
- A unit of energy equal to using 1,000 watts for one hour. Your electricity bill is measured in kWh. A 4kWp system in Scotland generates roughly 3,400–3,800 kWh per year.
- EPC (Energy Performance Certificate)
- A rating from A (most efficient) to G (least efficient) that shows a property's energy efficiency. Required when selling or renting. Installing solar panels typically improves your EPC by 1–2 bands.
- G98
- The connection standard for small-scale generators up to 3.68kW per phase (16A). Requires notification to the DNO only — no formal application or approval wait. Most single-phase domestic solar systems under 3.68kW connect under G98.
- G99
- The connection standard for generators between 3.68kW and 11.04kW per phase. Requires a formal application to the DNO and written approval before connection, which can take 6–10 weeks. Applies to larger domestic systems and most commercial installations.
- HES (Home Energy Scotland)
- A Scottish Government-funded advice service offering free, impartial energy-saving guidance and interest-free loans for renewables. HES loans cover up to £7,500 for solar PV and £6,000 for battery storage.
- ECO4 (Energy Company Obligation 4)
- A UK Government scheme obliging large energy suppliers to fund energy efficiency improvements for low-income and vulnerable households. Can cover solar PV, insulation, and heating upgrades at no cost to eligible homeowners. Runs until March 2026.
- Gas Safe Register
- The official registration body for gas engineers in the United Kingdom. It is a legal requirement for anyone working on gas appliances to be on the Gas Safe Register. Relevant where hybrid heating systems combine solar with gas boilers.
- TrustMark
- A UK Government-endorsed quality mark for tradespeople and firms. TrustMark-registered installers have been vetted for technical competence, trading practices, and customer service. Required for certain grant-funded work.
- RTE (Round-Trip Efficiency)
- The percentage of energy put into a battery that you get back out. A battery with 90% RTE returns 9kWh for every 10kWh stored. Higher RTE means less energy lost as heat. LiFePO4 batteries typically achieve 92–98% RTE.
- Self-Consumption
- The proportion of solar electricity you use directly in your home rather than exporting to the grid. Without a battery, self-consumption is typically 40–55%. Adding a battery can push it to 75–85%, maximising savings.
- Feed-In
- The flow of electricity from your solar panels into the grid. Also refers to the now-closed Feed-in Tariff (FIT) scheme which paid homeowners a fixed rate per kWh generated. New installations use the Smart Export Guarantee instead.
- Inverter
- A device that converts the DC (direct current) electricity produced by solar panels into AC (alternating current) used by household appliances and the grid. String inverters serve the whole array; microinverters sit behind each panel for independent optimisation.
- Hybrid Inverter
- An inverter that manages both solar panels and a battery in one unit. It directs surplus solar power to the battery before exporting to the grid, and draws from the battery before importing. Simplifies installation and reduces cost compared to separate inverters.
- Microgeneration
- Small-scale electricity or heat generation, typically under 50kW for electrical and 300kW for thermal. Most domestic solar PV systems (3–6kWp) fall within the microgeneration definition. MCS certification specifically covers microgeneration technologies.
- LiFePO4 (Lithium Iron Phosphate)
- A lithium battery chemistry prized for safety, longevity, and thermal stability. LiFePO4 cells last 6,000+ charge cycles (15–20 years of daily cycling), do not contain cobalt, and have very low fire risk compared to other lithium chemistries. Used in most modern home storage batteries.