Solar Energy Terminology – IT’S SOLARPEDIA!

Unravelling the Mysteries of Solar Energy:
A Comprehensive Guide to Solar Energy Terminology.

In this journey through solar technology, we delve into the terminology that defines this dynamic field, shedding light on everything from solar panels to grid connections. Learn your solar energy terminology here.


The SolarPV modules are the panels mounted on the roof that capture the energy from the sun/daylight and convert it into DC energy. Modules are typically grouped and connected in series to create a ‘STRING’ using special connectors, MC4s.


STRING INVERTERS are the simplest of SolarPV inverters and have existed since SolarPV became popular. The string inverter takes all the energy from the strings and converts the DC energy into AC energy. This energy is then typically fed into the customer’s electrical system ‘BEHIND THE METER’ for use at that moment. Any power not used by the customer is then exported back to the grid.

MICRO INVERTERS are lower-powered inverters that typically take power from individual modules instead of strings and convert the DC power to AC power on the roof, usually on a one-for-one basis. This energy is then fed into the customer’s electrical system ‘behind’ the meter” for use at that moment. Any power not used by the customer is then exported back to the grid.

HYBRID INVERTERS are smart inverters that look at 4 areas to decide what to do with the energy from the strings:

I. Convert the DC energy to AC for use by the customer on the premises. 

II. Converts some of the DC energy to AC for use on the premises and/or to export to the grid and stores the remaining DC energy in the battery.

III. Stores all the DC energy in the batteries.

IV. Discharges the DC energy from the batteries, converts it to AC and uses it either on the premises, exports it to the grid or both.

AC COUPLED INVERTERS take AC energy from either the output of a SolarPV system or the grid and store it in battery cells until it is required in the premises or for export to the grid.


BATTERY STORAGE SYSTEMS comprise of 2 parts: the battery and the battery management system. For most systems, the batteries are supplied as part of a hybrid or AC-coupled inverter system. Batteries use lithium-ion phosphate chemistry, which is similar to the battery power tools we use at home. Lithium-ion is a tried and tested technology.

Batteries are sized in kilowatt hours (kWh).

  • a 5.2kWh battery will discharge 5.2kW for 1 hour
  • a 2.6kWh for 2 hours
  • a 10.4kWh for ½ an hour, subject to the output of the connected inverter.

The MOUNTING SYSTEM is the means by which the modules (PV panels) are secured to the roof structure, ground, or even floating on a lake. The mounting system ensures the panels are held securely even during heavy wind and maintains the roof’s waterproof integrity. All Chiltern Solar roof mounting systems comply with MCS 012, meaning the mounting system has been tested and certified. We always install the system according to the manufacturer’s instructions, ensuring the mounting of your solar modules is secure and the integrity of your roof is maintained.

In terms of roof systems, there are three types of mounting systems:

IN ROOF: In recent years, In Roof mounting systems have become more popular. In Roof systems involve the removal of the existing roof covering (slate, plain, or pan tile) and purpose-made plastic trays fixed to the roof trusses and the models fixed to the trays.

Whilst this system is more expensive to install, some consider the system to be more aesthetically pleasing.

ON ROOF: This is by far the most common system for SolarPV in the UK. Slates or tiles are removed to allow the fitting of special brackets known as roof hooks to be mounted to the roof trusses; the original slates or tiles are modified and refitted to reform the roof’s weatherproof covering. Aluminium rails are then fitted to the roof hooks, and the modules are fixed to the rails to form a secure array.

 This is not a common system but can be helpful to on roofs that are losing their weather integrity. As the name implies, the solar array is fitted independently of the existing roof system to provide a second weatherproof layer to the building.


OPTIMISERS are devices that maximise the output of strings and mitigate the effect of shading on individual or group modules on the string. They are located behind the PV module and connected to individual modules. They are usually only fitted to modules predicted to suffer from shading.

Bird prevention mesh

BIRDBLOCKERS are typically installed on roof systems that create a space under the modules where pigeons and other small animals try to build a nest in the dryer/warmer environment. A birdblocker is reinforced mesh that is fixed to the outside edges of the module, forming a barrier for the pigeons.

Birdblockers have become more prevalent in recent years. As a standard, Chiltern Solar will normally include Birdblockers as part of the installation package in our proposals for on-roof and over-roof systems. Due to the scaffolding requirements for safety after the installation event, it is significantly cheaper to install a Birdblocker during the original installation than to retrofit it.


All SolarPV and Battery systems must be approved by your Distribution Network Operator (DNO). Depending on the size of the system, this is either completed post-installation in the case of systems with inverter output less than 3.68kW (G98) or pre-installation on systems with an aggregated inverter(s) output greater than 3.68kW (G99). Chiltern Solar will complete all the necessary pre- and post-construction on your behalf to ensure your system is fully compliant.

Distribution Network Operators (DNO) are organisations responsible for maintaining the local grid below 132kV and for voltage levels and frequency to the premises. The DNO has a statutory obligation to maintain your electrical supply supplied at 230v +10% -6% and 50Hz +/-1%. Adding a generation plant to the grid can impact the DNO’s ability to fulfil its statutory obligation, hence the need to agree on any connections over 3.68kW for a single phase and 11.04kW for three phases.

G98 (previously known as G83) is any system capable of generating less than 3.68kW on a single-phase connection, or 11.04kW AC on a three-phase connection must comply with G98. This route is the simplest and provided the inverters are type-tested and approved for G98, all that is needed is for the installing contractor to notify the DNO of the completion/commissioning of the installation. Copies of these notifications will form part of the Handover Pack to the customer.

Please note that if there is any existing generation plant on the electrical connection and the cumulative output of the existing (including standby generators) and additional installation is greater than 3.68kW/11.04kW, then the installation must obtain consent from the DNO prior to construction. This consent must be referred to G99 and approved by the DNO prior to construction.

Chiltern Solar will complete this process on behalf of the customer as part of our pledge for hassle-free installation.

G99 (previously known as G59) is all systems over 3.68kW 1Ph or 11.04kW 3Ph must be approved by the DNO prior to construction via the G99 route.

This process involves formally submitting all relevant design documentation, system schematics, site plans, and notification of which inverter(s) are proposed. This process normally takes up to 45 working days from submission. Following a technical review by the DNO of the local grid conditions, the DNO will make an ‘Offer’ for connection. This ‘Offer’ may be conditional in that it may restrict the size of the overall system, limit export back to the grid, witness testing of the commissioned system by the DNO and/or require a grid upgrade. Once the offer has been made, Chiltern Solar will liaise with the customer and agree on the best way forward.

Most systems below 6kW are normally accepted without conditions by the DNO. However, should the local grid conditions mean the DNO has to reject the application, Chiltern Solar will work with the DNO to gain the maximum connection by reducing the array size and/or acceptance by reducing the export to the grid.

On larger systems, the DNO may demand the fitting of an independent G99 relay that shuts all generating plants on the scheme; this may also involve a “witness test” during which the DNO’s representative will witness the G99 relay shut down generation if the scheme goes outside specific parameters.

Whilst the G99 looks complicated, Chiltern Solar is well versed in the process and will carry out the above for our customers if they wish. All we need is a signed ‘Letter of Authority’, allowing Chiltern Solar to act as your ‘Agent’ in the process.

On completion of the installation, Chiltern Solar will complete all the necessary certifications for the DNO, copies of which will form part of the ‘Handover Pack’ that Chiltern Solar will give to the customer.

G100, the DNO will occasionally allow a larger system if the energy generated is consumed on-site and the amount exported to the grid is limited. This process is known as  G100 and can be particularly useful on larger systems where the client is looking at displacing as much electrical energy from the grid year round. This certification would be discussed at the time of submission.

Please note that G99 and G100 applications can take 45 working days for the DNO to accept, make a connection offer or reject. Chiltern Solar will provide all necessary documents to support your application for connection.


For most domestic and commercial SolarPV systems, planning permission is not normally required as the system is roof-mounted and built under ‘Permitted Development’ rights; the exceptions are in ground mounts, listed buildings and ANOB.

DOMESTIC ROOFS solar panels must be no higher than 200mm on a sloping roof and 600mm on a flat roof.       

COMMERCIAL ROOFS are no longer limited to 1MWp.

Ground mounted solar array
Chiltern Solar | Commercial Roof

GROUND-MOUNT SYSTEMS up to 9m2 surface, no higher than 4m in height and located no closer than 2m from the building’s curb. In reality, this only equates to a 4-panel installation. Only the first array is allowed under Permitted Development, thereafter full planning permission would have to be applied for. 

If the proposed solar system requires planning permission, Chiltern Solar will assist you in submitting all necessary documents to your local authority.

Please note that planning applications can take at least 8 weeks.

Ground mounted solar array

An ISLAND SITE/SYSTEM is a system that is configured to operate without connecting to the grid or, if connected to the grid, automatically disconnects all connections to the grid for safety reasons while leaving the system in operation in the event of a grid failure.

A SolarPV system must shut down in the event of a grid failure unless it can isolate itself from the grid.


BEHIND THE METER is the most common form of connection for most SolarPV systems. The term refers to the point at which the energy from the SolarPV system is injected into the user’s electrical infrastructure. By connecting behind the meter, the system will only import electrical energy from the grid to make up the difference between generated energy and property load.



IN FRONT OF THE METER format is generally only used on solar farms where large-scale generation is sold to the grid or where a large energy user has their own solar farm/generation plant, but it is a significant distance from the point of use, and they use a sleeve agreement to get the generated energy to the point of use.


Displacement of the energy a user would have had to buy from the grid had they not had a generating plant such as a SolarPV system.


This is the excess energy the SolarPV system uses over and above the on-site consumption.


The feed-in tariff was a UK subsidy for eligible systems registered between April 2010 and April 2019. The scheme is now closed for new systems but will continue to operate for up to 25 years for early adopters.

Can I increase my FiT registered solar array?

In general, yes, but you will only receive FiT payments proportional to the original array size; you cannot increase your FiT income. A notification has to be made to OFGEM/FiT Provider to advise in the adjustment.

Can I add batteries to my FiT-registered solar system?

Yes, but again, you have to notify OFGEM/FiT Provider. In addition, the original generation meter has to be changed to a bi-directional meter, and details must be submitted to the OFGEM/FiT provider.


SEG was launched on 1 January 2020 and is a government-backed initiative. It replaces the previous government back scheme referred to as Feed in Tariff (FiT). Systems already registered for Feed in Tariff are not eligible for Smart Export.

The SEG requires some electricity suppliers, known as SEG Licensees, to pay small-scale generators, known as SEG Generators, for low-carbon electricity, which they export back to the National Grid, providing specific criteria are met. 

MPAN (Meter Point Administration Number) is a unique 13-digit reference that identifies each electricity supply point. Your MPAN can be found on your electric invoice.


Chiltern Solar operates an open policy regarding Grid Consent and/or Planning Permission fees. The administration fees incurred by Chiltern Solar in drafting and representing the owner are fixed and openly shown in our proposals. This means that should the scheme not proceed due to adverse planning or grid consent conditions, your deposit, less the admission fees, will be repaid immediately.


Wp/kWp is the unit measurement of a solar module, solar string or solar array. The “p” refers to the term peak.

kW is the electrical measure of power at any moment in time.

kWh is the electrical measure of energy stored or consumed over a period of an hour.

Total Installed Capacity (TIC) – is the summation of all modules connected to inverter(s).

Declared Net Capacity (DNC) – is the total capacity of inverters to the grid.

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