Solar PV and Battery Glossary for UK Homes and Businesses
If you’re thinking about getting solar panels for your house or looking into commercial solar panels for a business, there’s a good chance you’ve come across a lot of unfamiliar terms. This quick glossary explains the key concepts in plain English, so you can feel more confident when entering conversations with solar panel installers and comparing quotes..
Understanding Power vs Energy (kW vs kWh)
Power (kW)
Power in kilowatts shows how quickly electricity is being used or generated at a specific moment. It is similar to speed. For example, a 2 kilowatt kettle uses electricity at that rate while it is switched on.
Energy (kWh)
Energy in kilowatt hours measures how much electricity is used over time. It is like distance travelled. If a 2 kilowatt heater runs for an hour, it uses kilowatt hours. Your electricity bill and solar export payments are based on kilowatt hours and are often referred to as “units”.
Kilowatt peak (kWp)
Kilowatt peak is the maximum amount of power a solar panel system can produce under ideal test conditions. It is how system sizes are usually described. For example, a fairly typical residential installation might have a 4 kilowatt peak system.
Core Solar Terms
PV or photovoltaic
Photovoltaic refers to the technology inside solar panels that turns sunlight into electricity using semiconductor cells. This creates direct current, or DC power.
Inverter
An inverter converts the DC electricity from your solar panels into usable alternating current, or AC power. This is the type of electricity your home or building runs on. Without an inverter, your solar system cannot power anything as DC electricity is not compatible with any home appliance.
Hybrid inverter
A hybrid inverter does what a regular inverter does but also manages a battery. It can charge the battery from your solar panels when there is excess solar energy or from the grid if you have cheap overnight tariffs, and discharge it when needed to power your property.
AC coupled and DC coupled batteries
An AC coupled battery has its own inverter and connects on the alternating current side of your system. This makes it easier to add to an existing setup, such as one with a Feed-in Tariff.
A DC coupled battery connects directly to the solar side of the system, usually through a hybrid inverter. It is often slightly more efficient when charging from solar panels.
Import and export electricity
Import means buying electricity from the grid.
Export means sending excess solar electricity back to the grid.
Self consumption
Self consumption is the percentage of electricity generated from a solar system that you use in your own building rather than exporting it. Higher self consumption means better savings. So if a system generates 4000kWh and 3000kWh is used in the property with the remaining 1000kWh being exported, this would have a self consumption of 75%.
Time of use tariff
This is an electricity pricing plan where the rate changes depending on the time of day. It is useful for people with batteries who can charge during cheaper hours overnight and then use this energy during the daytime (in addition to energy generated by the PV system) to offset energy that would otherwise be imported from the grid when prices are higher.
Smart meter or SMETS2
A smart meter automatically sends your electricity readings to your energy supplier. The SMETS2 version can record import and export data every 30 minutes. This is often required for getting paid under solar export schemes. Find out more about meter requirements for solar panels here.
Panels and System Hardware: What Each Part Does
Module or panel
Both terms refer to a single solar panel unit. It is a framed rectangle made up of many photovoltaic cells. Most people simply call it a panel.
Array
An array is a group of panels connected together to form a single solar system. Some roofs may have just one array, others may have more depending on the design.
String
A string is a row of panels wired together. Each string connects to an inverter, which helps manage performance and convert the electricity.
Maximum Power Point Tracking or MPPT
MPPT is a feature inside inverters that constantly adjusts the voltage and current to keep each string operating at its best as sunlight changes throughout the day.
String inverter
This is a central inverter that manages one or more strings of panels. It is efficient and simple. If one panel is shaded though, it can affect the whole string’s performance. This type of inverter isn’t able to connect to battery storage systems without a separate battery or hybrid inverter.
Microinverters
These small inverters are installed on the back of each panel. They are useful for complex or shaded roofs since each panel works independently.
cPower optimisers
Power optimisers are installed on each panel and work with a central inverter. They reduce the impact of shading and allow you to track how each panel is performing.
Generation meter
This device measures how much solar electricity your system is generating. Some inverters have it built in, while others need a separate meter.
Export meter
An export meter measures how much electricity your system is sending back to the grid. Most modern smart meters already include this feature, and so separate export metering is not necessary.
DC isolator and AC isolator
These are safety switches. The DC isolator disconnects the solar panel side of the system. The AC isolator disconnects the grid or building side. They are mainly used during maintenance or in emergencies.
Surge protection device or SPD
This device protects your solar system from sudden voltage spikes, such as those caused by lightning or power surges. In many systems, surge protection is required by regulation and depending how/where it is installed, it will also offer protection to your home too.
Bird proofing
Bird proofing is the use of a plastic wire or mesh arrangement to form a barrier around the edge of your solar panel array. It helps stop birds from nesting underneath, which can prevent damage and keep your system running smoothly. Read more about bird guards for solar panels here.
CT Sensor (Current Transformer)
A CT sensor is a small clamp device fitted around the main supply cable to measure the direction and flow of electricity in and out of a property. In battery storage systems, the CT tells the inverter whether the house is importing from the grid or exporting surplus solar. The inverter then uses this signal to decide when to charge or discharge the battery - e.g. charge from excess solar instead of the grid, or discharge to cover household demand. Correct placement of the CT is crucial: if its installed in the wrong location or the wrong way round, the system will not perform as expected.
Energy Monitoring Meter
An energy monitoring meter is a device installed alongside a battery storage system that collects data from CT sensors (current transformers) and communicates this information back to the inverter. It continuously monitors how much power the home is importing from or exporting to the grid, as well as household consumption. The inverter then uses this live data to decide when to charge or discharge the battery.
Earth Rod
An earth rod is a conductive metal rod (usually copper or copper-coated steel) driven into the ground to provide a reliable earth connection. In normal grid-connected solar PV systems, the house already shares the grid’s earthing arrangement, so a separate earth rod isn’t always needed. However, when a home backup system is installed (where the inverter can power the house during a power cut), regulations usually require a dedicated earth rod. This ensures the backup supply has a proper reference to earth so that safety devices (RCDs, MCBs) still trip correctly if a fault occurs.
Batteries and Storage
Battery capacity (kWh)
Battery capacity refers to the total amount of energy a solar battery can store, measured in kilowatt hours. It shows how much electricity the battery can hold when fully charged.
Usable capacity
Usable battery capacity is the amount of energy you can actually draw from the battery. It’s often slightly lower than the total or nominal capacity, due to built-in safety margins that protect the battery from overcharging or deep discharging. Always compare usable capacity when choosing a system.
Depth of Discharge (DoD)
Depth of Discharge is how much energy has been used from the battery, shown as a percentage of its total capacity. Often, inverters will display this on a screen, or the battery will give a rough indication, but usually, you will need to access this via an app. Some battery types can handle deep discharges regularly, but others may degrade faster if emptied too often, a DoD of between 80-100% is typically for most modern, lithium-based solar batteries.
State of Charge (SoC)
State of Charge is the percentage that shows how full the battery is at any given time. For example, a battery at 80 percent SoC still has plenty of stored energy available.
Round-trip efficiency
Round-trip efficiency measures how much energy you get out compared to what you put in. For example, a 90 percent round-trip efficiency means the battery discharges 9 kWh to your home for every 10 kWh that it is charged with either from the grid or the PV panels.
Cycle and cycle life
A battery cycle is one full charge and discharge. Cycle life is the number of these cycles a battery is expected to complete before its capacity noticeably drops. Most battery warranties are based on a certain number of complete cycles.
C-rate
C-rate describes how quickly a battery can charge or discharge relative to its storge capacity. A 1C rate means a battery can go from empty to full (or vice versa) in one hour. Most batteries have a C-rate of 0.5 - so a 5kWh battery can only sustain a max discharge rate of 2.5kW, and oit would do this for two hours.
Backup or EPS (Emergency Power Supply)
Backup power or EPS allows certain circuits in your building to keep running during a power cut. Most standard solar battery systems shut down during outages unless designed specifically with backup hardware and wiring. Depending on the current earth arrangement in your home, EPS systems must usually be installed with an Earth Rod.
Bird-proofing
Bird-proofing is the use of clips, mesh or guards around the edge of your solar panel array to stop birds from nesting underneath. It helps protect wiring and keep your system running efficiently.
Performance and Design Terms for Solar Panels
Orientation
Orientation is the direction your panels face. In the UK, a south-facing system usually gives the best results, but east and west setups also work well depending on usage patterns.
Tilt or Inclination
Tilt is the angle between your panels and a flat, horizontal surface. IN the UK, a moderate tilt of around 30-35 degrees is generally regarded as optimal, balancing energy production throughout the year and helping panels stay clean when it rains.
Irradiance
Irradiance is the amount of solar energy hitting your panels, measured in watts per square metre (W/m²). The more irradiance, the more electricity your panels can produce. In the height of summer, irradiate can be as high as 1,000W/m², in winter this can be as low as 3-5W/m² during dull, cloudy days.
Shading or overshading
Shading from chimneys, trees or nearby buildings can reduce your system’s output. Shading analysis helps you design the best layout and decide whether to use optimisers or microinverters. Modern panels are very effective at mitigating against the effects of shading - it may be better to design the requirement for these out of the system to improve long-term reliability and maintenance costs.
Temperature coefficient
The temperature coefficient shows how panel performance changes as temperatures rise. A lower temperature coefficient means the panels lose less efficiency in hot weather - don’t forget, panel output is correlated with the amount of light available, not heat.
Degradation rate
The degradation rate is the rate at which solar panels lose output over time. Most panels degrade by less than one percent per year, with performance guarantees lasting 20 to 25 years.
Clipping
Clipping happens when the DC power from your panels exceeds what the inverter can handle. The inverter limits output to stay within its limits. A small amount of clipping is normal and often a cost-effective part of system design - clipping may only reduce overall output from your system by 1-2% over a year.
Specific yield (kWh/kWp)
Specific yield is the total energy produced in a year divided by the system size. It’s a handy way to compare performance between different systems or sites, regardless of size. This varies site-to-site based on location, panel orientation and inclination.
Roofs, Mounting and Buildings: How Panels Are Fitted
On-roof mounting
On roof mounting is the most common method in the UK. Rails and brackets are fixed through the roof covering directly to the rafters, and slates or tiles are refitted and weather-proofed around these hooks. Rails fix to the hooks, and the panels fix to the rails sitting slightly raised above your above the roof.
In-roof or roof integrated systems
Roof integrated panels sit flush with the roof surface using special trays or frames. This creates a neater look and can be a good option for new builds or re-roofing projects. However, these systems may run warmer, which can reduce efficiency slightly and they’re generally more expensive to fit.
Flat roof mounting
Flat roof systems use angled frames to tilt the panels. These can be ballasted with weight, such as concrete blocks, or fixed directly into the roof structure with mechanical anchors or fixing points bonded to the roof. Ballasted systems avoid penetrating the roof but need enough space and structural support.
Wind uplift and weather protection
Solar mounting systems must be strong enough to handle wind loads and keep the roof watertight. It is important to use certified mounting kits and follow guidance based on your building’s structure and location.
UK Grid Connection and Compliance for Solar and Batteries
DNO or Distribution Network Operator
The DNO is the company that owns and manages the electricity network in your local area - they’re not your utility company or energy provider. Your installer must notify or apply to the DNO when connecting solar panels or batteries to the grid.
G98 connection
G98 covers smaller systems that generate up to 16 amps per phase on a residential 240V supply, this equates to 3.68kW per phase. For most domestic solar panel systems and small batteries, the process is install first then notify the DNO within 28 days of commissioning.
G99 connection
G99 applies to systems that generate more than 16 amps or 3.68kW per phase. It requires submitting an application and getting approval from the DNO before installation. This process is common for commercial systems and larger homes with high energy demand. It is not a difficult process at all - and shouldn’t be seen as a barrier to installing larger systems.
G100 export limitation
G100 is a method used to limit how much electricity a site can export to the grid. This is helpful when the local network cannot handle full export. It is set up using approved control equipment and must meet technical standards. The limit that your system may need to be set to would be determined by the DNO after doing a G99 application.
Agreed export capacity
This is the maximum amount of electricity your system is allowed to export to the grid, as confirmed by the DNO. It can be unrestricted, limited, or zero, depending on the local network conditions.
Anti islanding protection
Anti-islanding is a built-in safety feature that automatically turns off your inverter during a grid outage. This prevents your system from sending electricity into power lines while engineers are working on them - it’s a legal requirement, and inverters that are fitted must be certified and capable of this safety feature.
UK Solar Schemes, Rules and Documents
MCS or Microgeneration Certification Scheme
MCS certifies both renewable energy products such as panels and mounting systems, and also the companies that install them. Many buyers, lenders and energy suppliers prefer systems with MCS certification as it gives reassurance on quality and compliance.
MCS certificate and handover pack
After your system is commissioned, your installer should provide a handover pack. This includes key system details, estimated performance, warranty documents and user guidance. It is your official proof of MCS installation and should also contain your MCS certificate.
SEG or Smart Export Guarantee
The Smart Export Guarantee lets you earn money for the electricity you export back to the grid. Each energy supplier sets its own rate, so it pays to shop around. To qualify, you usually need a smart meter that records export in half-hour intervals.
Feed in Tariff or FIT
The Feed in Tariff was a government-backed payment scheme that closed to new applicants in 2019. Some older systems still receive FIT payments based on how much they generate and export. If you buy a house and the FiT is paying for energy the system generates, lucky you!
Planning permission for solar panels
Most solar panel installations on buildings fall under permitted development rights in the UK, meaning no formal planning permission is needed.
For homes, there are limits on how far panels can stick out and rules for listed buildings or properties in conservation areas.
For commercial buildings, rooftop systems are often allowed under similar rules but still need to meet specific conditions. Always check what applies to your site and confirm the structural load is suitable.
If a ground mount system proposed is above 9m2 (4-5 panels), then planning permission will be required.
VAT relief on energy saving materials
In Great Britain, solar PV systems and stand alone battery storage systems for homes qualify for zero percent VAT until 31 March 2027. This applies to the full installation, not just the equipment. Energy diverters and EV charge points are also rated at 0%, provided these are installed with the PV system. This 0% rate also applies to replacement inverters and components on legacy systems.
Money and Metering
Unit rate
The unit rate is the cost you pay per kilowatt hour for electricity taken from the grid. This is a key figure on your energy bill.
Standing charge
The standing charge is a daily fee for being connected to the electricity network, applied whether or not you use electricity.
Export tariff
The export tariff is the rate you are paid for each kilowatt hour of electricity your solar system sends back to the grid under the Smart Export Guarantee.
Half hourly data
Half hourly data refers to readings recorded every 30 minutes by a smart meter. Energy suppliers use this to calculate accurate billing and export payments.
Payback or ROI
Payback or return on investment is the estimated time it takes for your solar system to cover its cost through energy savings and export earnings.
Specs and Warranties
Panel efficiency
Panel efficiency shows how much sunlight a solar panel can convert into electricity. Higher efficiency means more power from less roof space.
Temperature coefficient
The temperature coefficient measures how much a panel's performance drops for every degree above 25°C. A lower value means better performance in heat.
STC and NOCT
STC stands for Standard Test Conditions, used to rate a solar panel’s maximum output in a lab. These conditions rare 1,000W/m², at 25°C. NOCT stands for Nominal Operating Cell Temperature and reflects more typical outdoor performance levels.
Product warranty and performance warranty
The product warranty covers faults in the panel itself, usually for 10 to 25 years. The performance warranty guarantees a minimum output level after a set number of years, which often works out at 84 to 92 percent after 25 years depending on cell type.
Inverter warranty
The inverter warranty covers the component that converts solar energy into usable power. Most inverters are covered for 5 to 12 years (with options to extend that often cost as much as a new inverter).
Common Add-ons
PV diverter or immersion controller
A PV diverter sends unused solar energy to your hot water tank, heating water rather than exporting electricity to the grid. With generous export tariffs, fitting these is becoming less common these days.
EV charger integration
EV charger integration allows solar energy or off-peak electricity to charge your electric vehicle through a smart charging system. A smart system will avoid discharging your battery to charge an EV, leaving energy in the battery for your home.
Monitoring portal or app
The monitoring portal or app shows real-time data on your system's performance, including generation, usage, battery levels and grid exports.
Want help choosing the right setup?
If you would like a straight answer on system size, battery capacity and likely savings for your home or site, get in touch. We can run a quick design and give you practical next steps.