Knowledge Bank

Synopses & Jargon Buster

For each technology that we offer, we have collated a wealth of supporting information.

We aim to cover everything from how the technology works to the savings and income streams that the technology offers. We have also provided guidance on how to choose the right product for your situation, with access to datasheets that we feel are likely to be of interest.

You can also download information packs and brochures. Simply fill in the form and we will email whatever downloads you require to your email address.

Solar PV

Solar panel technology has come a long way since Spirit started in 2010. Key milestones including, photovoltaic panel types becoming ubiquitous, all-black panels, size and mounting standardisation, enormous efficiency increases, and payback periods and IRR’s becoming remarkably more attractive.

To boil it down, solar panels turn solar energy from the sun, into electrical energy, which can then used in your home, or exported to the grid for tax-free income.

Solar PV Terminology

AC-coupled – A term to describe the configuration of a solar PV and battery system where both energy sources are connected separately to the AC supply of the building via independent inverters, in contrast to DC-coupled systems (see definition below).

Clipping – A situation where the solar inverter is unable to convert all the potential electricity generation of a solar array into usable electricity due to reaching its maximum output rating (in kW). Under these conditions, the inverter operates at a suboptimal power point (see MPPT definition) to restrict the amount of power coming from the panels, with the extra potential energy generation being effectively lost.

DC-coupled – A term to describe the configuration of a solar PV and battery system where both energy sources are connected on the DC-side of the same inverter(s). In this configuration, DC electricity produced by the solar panels can be directly charged to the battery (once converted to the correct voltage) without any intermediary conversion to AC and then back to DC as per AC-coupled systems. DC-coupling is therefore a more efficient way of charging a battery with PV generation.

Export limitation – Refers to a restriction placed on the amount of electricity that can be exported back to the grid from a renewable energy system, such as solar PV and battery storage. This limitation can be imposed by the DNO in response to an application to connect a certain amount of generation capacity. It is possible to generate more electricity on site than the export limit as the electricity generated by on-site generation is first consumed by the site loads, before any excess is exported to the grid.

Export meter – An electricity meter used to measure the amount of electricity that is exported from a building back into the grid.

Feed-in Tariff (FIT) – The UK government subsidy scheme (introduced in 2010 and closed in 2019) which guaranteed payments for the electricity generated by renewable energy systems, as well as the electricity exported to the grid. Owners of FIT systems have to submit a generation meter reading to an energy supplier (the ‘FIT Licensee’) every quarter, and then receive a payment at a set unit rate (p/kWh) for both generation and export (deemed to be 50% of generation for systems under 30 kW). FIT contracts are either 20- or 25-year duration for solar PV, and these systems cannot be upgraded during the contract term, so any additional PV and/or battery storage systems need to be kept separate.

G100 – The standard governing the operation of export limitation schemes. Only systems that are G100 compliant can be used for export limitation.

G99 – The standard governing the connection and operation of grid-connected generating systems greater than 16 A (3.68 kW) per phase. Systems of this size need permission from the DNO prior to connection. This permission is gained through making a ‘G99 application’.

G98 – The standard governing the connection and operation of grid-connected generating systems less than 16 A (3.68 kW) per phase. Systems of this size do not require permission from the DNO.

Generation limit – The maximum total installed capacity (in kW) of generating units (e.g. solar PV and battery storage) permitted by the DNO for a given electricity supply.

Generation meter – An approved meter used to measure and record the total amount of electricity generated by a renewable energy system, such as solar PV.

HH metering – Short for Half-Hourly metering, is an electricity metering type common for large commercial buildings whereby electricity usage is recorded and logged at half-hour intervals. The HH usage data can then be downloaded for analysis, which is very useful when modelling forecasted solar PV self-consumption.

Hybrid inverter – A term used to refer to an inverter that can have both solar PV and battery storage connected to it. A hybrid inverter is an example of a DC-coupled PV and battery system, and is also technically an inverter/charger (see below).

Inverter – A power electronics device that converts DC electricity (from solar PV or battery storage) into AC electricity which can power home appliances and be exported to the grid.

kWp – Kilowatt peak, a unit representing the maximum output power of a solar photovoltaic (PV) system under optimal conditions.

Microinverter – A power electronics device used to convert the direct current (DC) electricity generated by individual solar panels into alternating current (AC) electricity. Typically, one microinverter is used per solar panel and installed below the panel up on the roof, as opposed to a standard ‘string inverter’ which has multiple solar panels connected to it in series-connected ‘strings’ and is typically installed in the loft or other suitable internal space.

MCS – Microgeneration Certification Scheme, is the standards organisation for small-scale renewable energy systems, such as solar PV and battery storage. MCS certifies products for use in renewable technology systems, and accredited installers can certify their installations, which is typically a requirement for SEG eligibility.

MPPT – Maximum Power Point Tracking (MPPT) is a feature of solar inverters (and DC charge controllers) that optimises the power output from the solar panels by adjusting the voltage and current of operation to find the point of maximum power generation. Typically, single-phase solar inverters have either one or two MPPTs, and one or two strings of solar panels can be connected to an MPPT.

PV – Photovoltaics, refers to the technology that converts sunlight directly into electricity using semiconductor materials, typically silicon-based solar cells.

PV optimiser – A power electronics device that optimises the DC power output of individual solar panels within a string. Typically, one optimiser is used per solar panel and installed below the panel up on the roof. PV systems with optimisers still require an inverter to convert the DC power from the panels into AC power to feed into the building supply.

Shading – The effect of objects blocking the sunlight from directly hitting the solar panels. Typical objects that cause shading of solar arrays are chimneys, taller neighboring buildings, and trees. Shading has a considerable impact on the potential generation of solar panels and therefore needs to be assessed during the design stage.

String inverter – A power electronics device used to convert the direct current (DC) electricity generated by series-connected ‘strings’ of solar panels into alternating current (AC) electricity. It is typical for between 3 and 12 solar panels to be connected in series to a single-phase string inverter, and up to 20 panels for larger commercial 3-phase inverters. String inverters are the standard inverter type used in solar PV systems as they are more cost-effective than microinverters and easier to inspect and replace as they are installed in accessible locations either within the building or outside.

Battery Storage

Battery storage has become a staple of the solar energy market in the last 5 – 10 years. There’s a number of reasons for this, but they ultimately boil down to them becoming more reliable, larger, and cheaper, making them a cost-effective addition to almost any residential solar system.

Solar battery storage works by storing excess solar generation from your roof, so you can use it later, such as when the sun goes down, or when your usage exceeds your current solar generation. Additionally, you can take advantage of the mantra ‘Buy Cheap, Use Peak’, where you sign up for a variable rate tariff with an energy provider, then the battery charges up at an off-peak rate, so you can use that power when the rate goes up to it’s peak, saving ]yet more money.

Some modern batteries, such as the Tesla Powerwall 3, and GivEnergy All in One support ‘battery back up’, so that if you have a power outage, the battery will rapidly kick in and power your home almost seamlessly.

Battery Storage Terminology

DC – Direct current (DC) is an electric current that flows in one direction only. The voltage of DC electricity is also of fixed polarity, i.e., it does not vary between positive and negative like AC voltage. DC electricity is the form of electricity that solar panels and batteries produce directly, which necessitates the use of an inverter (see separate definition) to convert these sources of electricity into AC power which can then be used within buildings or exported to the grid.

Depth of Discharge (DoD) – The percentage of a battery’s total storage capacity that is used relative to 100% being fully charged. For example, if a battery with a total capacity of 10 kWh discharges 5 kWh (from fully charged), its DoD would be 50%. DoD is sometimes restricted by manufacturers to prolong battery life and can be a condition of the battery warranty. For example, if the same 10 kWh was restricted to 90% DoD, then the maximum permitted discharge from the battery would be 9 kWh, leaving 1 kWh remaining.

Battery cycles – One battery cycle is a full charge and discharge of a battery. For example, if a battery has a total storage capacity of 10 kWh, a full cycle is when the battery has been charged with 10 kWh of electricity and then discharged 10 kWh of electricity.

Export limitation – Refers to a restriction placed on the amount of electricity that can be exported back to the grid from a renewable energy system, such as solar PV and battery storage. This limitation can be imposed by the DNO in response to an application to connect a certain amount of generation capacity. It is possible to generate more electricity on-site than the export limit as the electricity generated by on-site generation is first consumed by the site loads, before any excess is exported to the grid.

Gateway (Tesla) – The energy management and monitoring device installed alongside Powerwall 2 or 3 in a complete Tesla Powerwall system. The current model (“Backup Gateway 2”), introduced in 2019, contains the relay that disconnects the grid supply to enable off-grid operation.

Generation limit – The maximum total installed capacity (in kW) of generating units (e.g., solar PV and battery storage) permitted by the DNO for a given electricity supply.

Inverter/Charger – A power electronics device that can convert DC electricity (from solar PV or battery storage) into AC electricity, as well as convert AC electricity into DC electricity to charge a battery.

MCS – Microgeneration Certification Scheme is the standards organisation for small-scale renewable energy systems, such as solar PV and battery storage. MCS certifies products for use in renewable technology systems, and accredited installers can certify their installations, which is typically a requirement for SEG eligibility.

SoC (State of Charge) – The amount of battery capacity available relative to the total capacity of the battery, typically as a percentage figure. For example, if a battery has a total storage capacity of 10 kWh, a SoC of 70% means that there is 7 kWh of available energy stored within the battery.

Workmanship warranty – A guarantee provided by an installer that they will cover the cost of rectifying any defects that arise from the installation of the equipment supplied. Spirit provides a 5-year workmanship warranty for domestic solar PV systems and a 2-year workmanship warranty for commercial solar PV systems.

EV Charging

Electric vehicle (EV) charging has quickly become a central part of the transition to cleaner transportation. Over the past decade, improvements in charging technology, availability of public charging stations, and home charging solutions have made EVs more convenient and accessible than ever.

EV charging works by connecting your electric vehicle to a power source, either at home or a public charging station. Home chargers typically use slower AC power, perfect for overnight charging, while public chargers, and some home chargers , particularly on a 3-phase supply, can offer rapid DC charging, providing a quick top-up for longer journeys. Advances in smart charging technology also allow you to take advantage of off-peak electricity rates, saving you money by charging your vehicle when energy prices are lowest.

EV Charging Terminology

EV – Electric vehicle

AC Charging – Charging an electric vehicle using alternating current (AC). Most home and public chargers use AC, which requires the car's onboard charger to convert AC to DC for battery storage. AC charging is typically slower than DC fast charging.

DC Fast Charging – Direct current (DC) charging allows for faster charging rates since it bypasses the vehicle’s onboard charger and directly supplies DC power to the battery. These chargers are commonly found at public charging stations, or sometimes on 3-phase residential properties.

Type 1 Connector – A single-phase connector mostly used in North American and some Asian EV models. It allows for AC charging at lower power levels.

Type 2 Connector – A European standard connector for AC charging, capable of both single-phase and three-phase charging. Most public chargers in Europe use this connector.

CCS (Combined Charging System) – A fast-charging standard that combines a Type 2 AC connector with additional pins for high-power DC fast charging. Widely used in Europe and North America.

CHAdeMO – A DC fast charging standard commonly used by some Japanese EV manufacturers. It allows for bi-directional charging, enabling Vehicle-to-Grid (V2G) applications.

Vehicle-to-Grid (V2G) – A system where EVs can return electricity back to the grid when needed. This is possible through bi-directional charging technology, which allows energy stored in EV batteries to be fed back into the power grid.

Vehicle-to-Home (V2H) – Similar to V2G, this technology allows an EV to supply electricity to a home, providing backup power or balancing energy consumption.

kW (Kilowatt) – A unit of power that measures the rate of energy transfer. In EV charging, it indicates the speed at which a charger can supply electricity to an EV.

kWh (Kilowatt-hour) – A unit of energy that measures the total amount of power transferred over time. It indicates the energy capacity of an EV's battery.

Charge Point Operator (CPO) – A company or organization that owns and operates EV charging stations. They are responsible for the maintenance and operation of the infrastructure.

RFID (Radio Frequency Identification) – A technology used to access EV charging points. Many public chargers require an RFID card or tag for authentication before starting a charging session.

Smart Charging – An intelligent charging system that optimizes charging times and rates based on various factors, such as electricity tariffs, grid demand, and renewable energy availability.

Home Charger – A dedicated charging unit installed at a residence, allowing convenient overnight charging of an EV. Typically, home chargers use AC power.

Public Charger – An EV charging station available in public places such as parking lots, shopping centers, and highways, providing varying power levels, from slow to fast charging.

Charging Rate – The speed at which an EV is charged, usually measured in kW. Higher charging rates result in shorter charging times.

Charging Cable – The cable used to connect an EV to a charging station. Some stations have tethered cables (built-in), while others require users to bring their own.

State of Charge (SoC) – A percentage measure of the current charge level of an EV's battery relative to its total capacity.

Industry & Spirit Terminology

AC - Alternating current (AC) is an electric current that periodically reverses direction and changes its magnitude continuously with time, in contrast to direct current (DC) which only flows in one direction (see definition below for further details). AC is the form in which electricity is delivered to buildings and used by most appliances. The voltage of AC electricity also alternates between positive and negative. In the UK, the direction of current and voltage in our electricity supply changes 100 times per second, as the two values oscillate at a frequency of 50 Hz.

Consumer Unit (CU) - One of the names used to describe an electrical enclosure that distributes electricity from the mains supply to individual circuits around a building. It contains the circuit protection (in the form of MCBs, RCBOs, and RCDs – see individual definitions) for all connected circuits and acts as a central hub for the electricity supply. Other common terms that are used interchangeably include distribution board (DB) and fuse board/box. It is typical for a house to have only one or two CUs.

Customer Number – The unique reference number generated for each of our customers and included within most documentation we provide (5-digit unless you were a very early customer of ours!). This is incredibly helpful to have to hand when calling us for support!

DC - Direct current (DC) is an electric current that flows in one direction only. The voltage of DC electricity is also of fixed polarity, i.e., it does not vary between positive and negative like AC voltage. DC electricity is the form of electricity that solar panels and batteries produce directly, which necessitates the use of an inverter (see separate definition) to convert these sources of electricity into AC power which can then be used within buildings or exported to the grid.

Distribution Board (DB) - A generic term for an electrical enclosure that distributes electricity from a main supply to individual circuits via circuit protection (such as MCBs, RCBOs, and RCDs). In residential properties, distribution boards supplying standard household circuits are typically referred to as consumer units, as well as the outdated terms fuse board and fuse box.

Difference between DNO and Energy supplier - A Distribution Network Operator (DNO) is the company responsible for operating and maintaining the electricity distribution network in the UK. The distribution network comprises all of the electricity infrastructure (cables, substations, transformers, etc) between the National Grid transmission network and the buildings that consume electricity (both commercial and residential). There are only 9 main DNOs in the UK covering 10 large regions, and you can’t choose your DNO! By contrast, an energy supplier is a company that purchases electricity from generators and sells it to consumers, and consumers are free to choose their electricity supplier.

DNO - Distribution Network Operators are responsible for operating and maintaining the electricity distribution network in the UK. The distribution network comprises all of the electricity infrastructure (cables, substations, transformers, etc) between the National Grid transmission network and a building's electricity supply. Their role includes ensuring reliable electricity supply, managing connections, and maintaining infrastructure within specific geographic regions. It is the DNO that assesses how much solar and battery capacity can be installed at a given premises.

Export meter - An electricity meter used to measure the amount of electricity that is exported from a building back into the grid.

Feed-in Tariff (FIT) - The UK government subsidy scheme (introduced in 2010 and closed in 2019) which guaranteed payments for the electricity generated by renewable energy systems, as well as the electricity exported to the grid. Owners of FIT systems have to submit a generation meter reading to an energy supplier (the ‘FIT Licensee’) every quarter, and then receive a payment at a set unit rate (p/kWh) for both generation and export (deemed to be 50% of generation for systems under 30 kW). FIT contracts are either 20- or 25-year duration for solar PV, and these systems cannot be upgraded during the contract term, so any additional PV and/or battery storage systems need to be kept separate. When the FIT closed in March 2019, a replacement export-only payment scheme was introduced, called Smart Export Guarantee (SEG).

G100 - The standard governing the operation of export limitation schemes. Only systems that are G100 compliant can be used for export limitation.

G99 - The standard governing the connection and operation of grid-connected generating systems greater than 16 A (3.68 kW) per phase. Systems of this size need permission from the DNO prior to connection. This permission is gained through making a ‘G99 application’.

G98 - The standard governing the connection and operation of grid-connected generating systems less than 16 A (3.68 kW) per phase. Systems of this size do not require permission from the DNO.

H&S - Rules implemented in our company to ensure the safety and well-being of all employees and anyone else involved. I think this was another joke lol.

HH metering - Short for Half-Hourly metering, is an electricity metering type common for large commercial buildings whereby electricity usage is recorded and logged at half-hour intervals. The HH usage data can then be downloaded for analysis, which is very useful when modelling forecasted solar PV self-consumption.

kW - Kilowatt is a unit of power equivalent to 1000 watts, used to quantify the rate at which energy is produced, consumed, or transferred.

kWh - Kilowatt-hour, a unit of energy representing the amount of energy consumed or produced by a device or system operating at a power of one kilowatt continuously for one hour.

MCB - A Miniature Circuit Breaker (MCB) is a circuit protective device which disconnects the circuit if its current rating is exceeded. The purpose of an MCB is to protect a circuit against potential damage (heat) due to overload or short circuit. MCBs are installed within distribution boards.

Microinverter - A power electronics device used to convert the direct current (DC) electricity generated by individual solar panels into alternating current (AC) electricity. Typically, one microinverter is used per solar panel and installed below the panel up on the roof, as opposed to a standard ‘string inverter’ which has multiple solar panels connected to it in series-connected ‘strings’ and is typically installed in the loft or other suitable internal space.

PPA - A contract between an electricity generator, such as the owner of a solar PV system, and an electricity buyer, typically a business that occupies the site where the electricity generation is produced, whereby the buyer pays the generator a fixed rate for the electricity they consume from the generating system. This fixed rate is typically below the grid electricity rate, and therefore the buyer saves money on their electricity bill without any upfront cost for the installation of the generating system, and no ongoing maintenance costs for the system either.

RCD protection - A Residual Current Device (RCD) is a circuit protective device which disconnects the circuit(s) if there is an imbalance between the outgoing line and return neutral currents. The purpose of an RCD is to minimise the risk of electric shocks and fires caused by earth leakage current. RCDs are installed within distribution boards and typically monitor more than one circuit.

RCBO - A Residual Current Breaker with Over-Current (RCBO) combines the functionalities of a Residual Current Device (RCD) and a Miniature Circuit Breaker (MCB) into a single unit. It is designed to provide both protection against electric shocks and protection against overcurrents (such as short circuits and overloads).

SEG - The Smart Export Guarantee (SEG) is a government scheme that requires larger electricity suppliers to offer a payment to small-scale, low-carbon generators for surplus electricity they export to the grid. It replaced the Feed-in Tariff (FIT) scheme which closed in March 2019.

Sub main - A circuit originating from the main distribution board (or consumer unit) of a site and supplying a secondary distribution board (or consumer unit). For example, the cable between the main consumer unit in the house and a consumer unit in a garage or outbuilding.

Workmanship warranty - A guarantee provided by an installer that they will cover the cost of rectifying any defects that arise from the installation of the equipment supplied. Spirit provides a 5-year workmanship warranty for domestic solar PV systems and a 2-year workmanship warranty for commercial solar PV systems.

Financial Terminology

Payback Period – The time it takes for the savings generated by a solar and/or battery system to cover the initial investment cost. For example, if a system costs £5,000 and saves you £500 annually, the payback period would be 10 years.

Internal Rate of Return (IRR) – A percentage that represents the profitability of a solar and battery system over its lifetime. A higher IRR indicates a more attractive investment, showing how effectively the system generates returns compared to its cost.

Net Present Value (NPV) – The difference between the total savings generated by the solar and/or battery system over its lifetime and the initial cost, adjusted for inflation. A positive NPV means the investment is expected to be profitable in today’s terms.

Value Created – The total financial benefit produced by the solar and/or battery system over its lifespan, including savings on energy bills and potential earnings from exporting excess electricity back to the grid.

Yearly Returns – The annual financial gain from the solar and/or battery system, typically measured as a percentage of the initial investment. This includes energy savings and potential export payments.

First-Year Savings – The total amount saved on electricity bills in the first year of using the solar and/or battery system. This includes the reduction in purchased electricity due to self-consumption of solar energy.

Unit Cost With a Solar and/or Battery System – The cost per unit (kWh) of electricity. With a solar and/or battery system, the unit cost can decrease significantly since you are generating your own power.

Unit Cost Without a Solar System - Without a solar and/or battery system, the unit cost is based solely on the price set by the energy provider.

25-Year Savings – The total amount of money saved over 25 years by using a solar and/or battery system. This long-term perspective helps illustrate the financial benefits of the system over its expected operational lifespan.

Electricity Price – The cost per unit (kWh) of electricity from the grid, which is an important factor in calculating savings from solar energy. Rising electricity prices increase the savings potential of solar and battery systems.

Warranty – A guarantee provided by the manufacturer that covers defects and performance of the solar panels or battery system for a specified period, typically 10-25 years for solar panels and 5-10 years for batteries.

Workmanship Warranty – A guarantee provided by the installer that covers any defects in the installation process of the solar and/or battery system.

VAT Rate Exemption – Solar and/or battery systems for residential properties in the UK are eligible for a VAT rate exemption (currently 0%), reducing the overall cost of installation and making these systems more affordable.

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