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Solar and storage glossary

The words you meet on datasheets, product pages and quotes when you buy panels, inverters and batteries, explained in plain terms, with what to check before you order. Each term links to related terms and to the matching part of the catalogue.

€

€/kWh (price per kWh of storage)

A battery's price divided by its capacity, to compare batteries of different sizes.

On SolarGear.eu the €/kWh is the battery price divided by the capacity stated by the manufacturer, shown ex. VAT and with your country's VAT. It is a quick comparison, not the whole story: also look at usable capacity, cycle life and, for high-voltage systems, the cost of the control box and the minimum number of modules. It is not the cost per kWh delivered over the battery's life, which also depends on the cycles.

See also Nominal and usable capacity, Control box (PDU, BMU, high-voltage box), Cycle life

In the catalogue: Batteries and storage

€/W and €/Wp

Price per watt, to compare inverters and panels of different sizes.

For inverters, €/W is the price divided by the rated power; for panels, €/Wp is the price divided by the peak power. It makes sizes and brands easy to compare, but check what is included (meter, Wi-Fi dongle, backup box) and, for panels, whether you are buying single modules or a full pallet.

See also Wp and kWp (watt-peak), Pallet

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A

AC coupling and DC coupling

Two ways of connecting a battery to a PV system.

With DC coupling, panels and battery share one hybrid inverter, with fewer conversions and slightly higher efficiency: the usual choice for new systems. With AC coupling the battery has its own inverter, connected on the AC side next to the existing PV inverter: the usual way to add storage to a system that is already running, without touching the PV side.

See also Hybrid inverter, String inverter (grid-tied)

In the catalogue: Hybrid inverters

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B

Backup / EPS

The output that keeps loads running during a power cut.

When the grid fails, a hybrid inverter with EPS (emergency power supply) disconnects from the grid and powers the loads from the battery and panels. Some models back up the whole house, others only a dedicated output for essential loads, sometimes with a separate changeover box. Check the backup power in kW, the switchover time and whether extra components are needed.

See also Hybrid inverter, Off-grid and on-grid

In the catalogue: Hybrid inverters

Battery module

A single battery unit that combines with others to build a larger system.

A module holds the cells, a BMS or slave board and the terminals. Low-voltage modules are usually complete batteries that can also work alone; high-voltage modules are building blocks that only work in a tower with its controller. The manufacturer states the minimum and maximum number of modules for each inverter, and mixing different models or generations is generally not allowed.

See also Tower (stack), Control box (PDU, BMU, high-voltage box), Cluster

In the catalogue: Batteries and storage

Bifacial panel

A panel that also produces energy from light reaching its back.

Bifacial modules have a transparent back, usually glass, and collect light reflected from behind. The gain depends on the surface below and the mounting height: worthwhile on ground mounts and flat roofs with light surfaces, small on a panel mounted close to a pitched roof. The datasheet states the bifaciality factor and the output with a given rear-side gain.

See also Wp and kWp (watt-peak), Isc (short-circuit current)

In the catalogue: Solar panels

BMS (battery management system)

The electronics inside a battery that monitor and protect the cells.

The BMS measures the voltage and temperature of every cell, balances them and stops charging or discharging when a limit is reached. In a solar system it also tells the inverter, moment by moment, how much current the battery can take or deliver. That is why battery and inverter must be officially compatible: without working BMS communication, charging is not properly controlled and the warranty can be at risk.

See also CAN and RS485 communication, Control box (PDU, BMU, high-voltage box), LiFePO4 (lithium iron phosphate)

In the catalogue: Batteries and storage

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C

C-rate

Charge or discharge current expressed relative to capacity.

1C is the current that would fully charge or discharge the battery in one hour; 0.5C takes two hours. For a 100Ah battery, 0.5C means 50A. The C-rate on the datasheet gives the maximum continuous power the battery can supply or absorb: on a small battery a large inverter may be limited by the battery, not by its own rating.

See also Ah (ampere-hour), kWh and kW, Cycle life

In the catalogue: Batteries and storage

CAN and RS485 communication

The data links between battery, inverter and meter.

CAN and RS485 are the most common communication buses between a battery's BMS and the inverter; RS485 is also used for meters and monitoring. A matching plug is not enough: inverter and battery must speak the same protocol, which is why manufacturers publish compatibility lists. Many inverters let you select the battery protocol in the settings.

See also BMS (battery management system), CT clamp and energy meter

In the catalogue: Batteries and storage

Control box (PDU, BMU, high-voltage box)

The controller of a high-voltage battery tower.

In a high-voltage system each tower needs a control box, called PDU, BMU or high-voltage box depending on the brand. It contains the main switch, the protection, the contactors and the master BMS that talks to the inverter. It is often sold separately: when you price a high-voltage battery, add one control box per tower.

See also BMS (battery management system), Tower (stack), Low-voltage (48V) and high-voltage battery

In the catalogue: Batteries and storage

CT clamp and energy meter

The sensor that tells the inverter how much power flows to and from the grid.

A hybrid inverter needs to know the power at the grid connection point to charge the battery from surplus, cover consumption or limit feed-in. It measures it with current transformers (CT clamps) or with an energy meter connected via RS485. Check which meter or CT the inverter supports: often it is in the box, sometimes it is an accessory.

See also Zero export (feed-in limitation), CAN and RS485 communication

In the catalogue: Hybrid inverters

Cycle life

How many full charge and discharge cycles a battery is rated for.

Cycle life is the number of cycles a battery can deliver, at a stated DoD, temperature and C-rate, before its capacity falls to an end-of-life value, usually 70–80% of the original. Warranties are given in years and often also in cycles or total energy delivered (throughput), whichever comes first. A home battery that does roughly one cycle a day uses up to about 365 cycles a year.

See also DoD (depth of discharge), C-rate, LiFePO4 (lithium iron phosphate)

In the catalogue: Batteries and storage

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D

Datasheet

The manufacturer's technical document with the product's ratings.

The datasheet lists voltages, currents, power, efficiency, dimensions, certifications and operating conditions. It is the reference for checking compatibility, battery with inverter and panels with MPPT, and it is what the installer and the grid operator will ask for. Product pages on SolarGear.eu link to the manufacturer's datasheets and manuals where available; if in doubt, the manufacturer's latest version prevails.

See also IP rating, Grid connection rules (grid code)

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G

Grid connection rules (grid code)

The technical rules an inverter must meet to connect to the grid in each country.

Each country has its own connection standard, for example CEI 0-21 in Italy or VDE-AR-N 4105 in Germany for low voltage, many of them based on the European standard EN 50549-1, plus the requirements of the local grid operator. The inverter must be certified for it and set to the right country profile. Before you buy, check that the model is approved for your country; the grid connection procedure is handled by the installer.

See also Single-phase and three-phase, Zero export (feed-in limitation)

In the catalogue: String inverters

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H

Hybrid inverter

One unit that manages panels, battery and grid together.

A hybrid inverter converts solar power, charges and discharges the battery and exchanges energy with the grid, deciding at every moment where the energy goes. Its battery input is either 48V or high voltage, never both, and many models have a backup output. It is the usual choice for a new system with storage, or for a system you plan to add a battery to later.

See also Backup / EPS, Low-voltage (48V) and high-voltage battery, AC coupling and DC coupling

In the catalogue: Hybrid inverters

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I

IP rating

The degree of protection against dust and water.

The first digit refers to solid objects and dust, the second to water. IP65 means dust-tight and protected against water jets: suitable for outdoors, ideally sheltered from rain and direct sun. IP20 or IP21 products are for indoor use only, and for an outdoor installation the operating temperature range matters as much as the IP rating.

See also Datasheet

Isc (short-circuit current)

The highest current a panel can produce.

Isc is the current with the panel's terminals short-circuited, slightly above its operating current (Imp). Large modern panels have high currents, so check that the string's Isc stays within the inverter's maximum short-circuit current per MPPT. Bifacial panels can produce more current than the front-side rating, so leave a margin.

See also Voc and maximum PV input voltage, Bifacial panel, MPPT (maximum power point tracker)

In the catalogue: Solar panels

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K

kWh and kW

kWh is energy (how much); kW is power (how fast).

Battery capacity is given in kWh: 10kWh can supply 1kW for ten hours or 5kW for two hours. Inverter ratings are in kW, the maximum power available at any instant. You need enough kWh to cover your evening and night-time consumption, and enough kW for the appliances that run at the same time.

See also Nominal and usable capacity, C-rate, Wp and kWp (watt-peak)

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L

LiFePO4 (lithium iron phosphate)

The lithium chemistry used in almost all home and commercial storage batteries.

LiFePO4, also written LFP, is a lithium-ion chemistry with an iron phosphate cathode. Compared with the nickel-based chemistries used in many cars, it is more thermally stable, lasts thousands of cycles and contains no cobalt; its lower energy per kilogram hardly matters for a battery that stays on a wall. A cell is nominally 3.2V, so 16 cells in series make the 51.2V battery that the trade calls 48V.

See also BMS (battery management system), Cycle life, Low-voltage (48V) and high-voltage battery

In the catalogue: Batteries and storage

Low-voltage (48V) and high-voltage battery

Two battery families that work with different inverters.

Low-voltage batteries run at about 48–51.2V and grow by adding modules in parallel; they pair with 48V hybrid inverters and inverter/chargers. High-voltage batteries connect modules in series up to a few hundred volts, so currents are lower and efficiency at high power is better; they need an HV hybrid inverter and usually a minimum number of modules. The two are not interchangeable: choose the battery and the inverter together.

See also Parallel and series connection, Tower (stack), Hybrid inverter

In the catalogue: Batteries and storage

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M

MPPT (maximum power point tracker)

The circuit in the inverter that gets the most power out of a string of panels.

Panel output changes with light and temperature, and the MPPT keeps adjusting voltage and current to stay at the point of maximum power. Strings on the same MPPT should have the same orientation and number of panels; with two or more MPPTs an inverter can handle two roof faces. Check the MPPT voltage range and the maximum current per MPPT against your panels.

See also Voc and maximum PV input voltage, Isc (short-circuit current), Parallel and series connection

In the catalogue: Hybrid inverters

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N

N-type and TOPCon cells

The cell technology used in most new high-efficiency panels.

N-type cells use silicon doped differently from the older P-type (PERC) cells, and they lose less output over time and in the heat. TOPCon (tunnel oxide passivated contact) is today's most common N-type design; HJT (heterojunction) is another. For a buyer this means higher efficiency, a better temperature coefficient and usually lower degradation than PERC.

See also Back-contact panel, Bifacial panel

In the catalogue: Solar panels

Nominal and usable capacity

Nominal is the energy the battery stores; usable is what you can actually draw from it.

Nominal capacity is the total energy of the cells (voltage × Ah). Usable capacity is what is left once the BMS and inverter settings keep a reserve at the top and bottom. When you compare batteries, compare usable kWh, and check on the datasheet whether it is stated at 100% or at a lower depth of discharge.

See also DoD (depth of discharge), kWh and kW, €/kWh (price per kWh of storage)

In the catalogue: Batteries and storage

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O

Off-grid and on-grid

A system without a grid connection versus one connected to the grid.

An on-grid (grid-tied) system is connected to the public grid: it uses solar energy first and exchanges the rest with the grid. An off-grid system runs on its own, from panels, battery and often a generator, so battery and inverter must cover every load in every season. Many hybrid inverters can do both, but an off-grid system needs more storage and careful sizing.

See also Backup / EPS, Hybrid inverter, Self-consumption

In the catalogue: Solar kits

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P

Pallet

The full packing unit of panels, shipped by freight carrier.

Panels are shipped stacked on pallets of a few dozen modules, depending on the model; buying a full pallet lowers the price per Wp and the risk in transport. Pallets travel by truck, not by courier: the address must be reachable by a lorry, and if there is no forklift, ask for a tail-lift delivery. Check the packaging before you sign the delivery note.

See also €/W and €/Wp, Wp and kWp (watt-peak)

In the catalogue: Solar panels

Parallel and series connection

Parallel adds capacity at the same voltage; series adds voltage.

In parallel the voltage stays the same (for example 51.2V) while capacity and current add up: this is how 48V systems grow. In series the voltages add up while the Ah stay the same: this is how high-voltage towers and PV strings are built. With panels it works the same way: modules in series form a string, and strings in parallel share an MPPT.

See also Low-voltage (48V) and high-voltage battery, Cluster, MPPT (maximum power point tracker)

In the catalogue: Batteries and storage

Power optimiser

A DC device behind each panel that keeps it at its best operating point.

An optimiser lets each panel work at its own maximum power point, reducing losses from shading or mismatch, while conversion to AC still happens in a central inverter. Some optimisers only work with inverters of the same brand, others with any inverter: check before you buy. Many also offer module-level shutdown to lower the DC voltage on the roof.

See also Microinverter, MPPT (maximum power point tracker)

In the catalogue: Microinverters and optimisers

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R

Rack battery

Modules mounted in a 19-inch cabinet or rack frame.

Rack batteries use the 19-inch format of server cabinets: the modules slide into a metal cabinet, with the controller at the top or bottom. The format is common in commercial and technical rooms because it is compact and easy to service. Check whether the cabinet is included or sold separately, and how many modules it holds.

See also Battery module, Cluster

In the catalogue: Batteries and storage

Reverse charge (intra-EU VAT)

Invoicing without VAT between businesses in different EU countries.

When a business with a valid VAT number buys goods from a supplier in another EU country, the invoice is issued without VAT and the buyer accounts for VAT in its own country. On SolarGear.eu this applies to EU businesses whose VAT number is valid on VIES. Private customers pay VAT: Italian VAT in Italy, the VAT of their own country elsewhere in the EU.

See also VIES

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S

Self-consumption

The share of your solar energy you use on site instead of feeding it into the grid.

Solar energy used in the building replaces electricity you would buy at the full retail price, while energy fed into the grid is usually paid much less, if at all. A battery raises self-consumption by shifting daytime surplus to the evening. Size the system on your consumption profile, not just on the roof area.

See also Zero export (feed-in limitation), Nominal and usable capacity, Off-grid and on-grid

In the catalogue: Solar kits

Single-phase and three-phase

The type of grid connection, which decides which inverter you need.

Most homes have a single-phase supply; larger homes, farms and businesses often have three-phase. A single-phase inverter goes on a single-phase supply, while a three-phase inverter spreads power evenly across the three phases. In many countries the grid rules limit how much a single-phase inverter may feed in, so larger systems often have to be three-phase.

See also Grid connection rules (grid code), Hybrid inverter

In the catalogue: Hybrid inverters

String inverter (grid-tied)

An inverter that turns solar DC into grid AC, without a battery.

A string inverter takes one or more strings of panels and feeds their energy into the building and the grid. It does not manage a battery, so it costs less per kW than a hybrid and is the standard in commercial and industrial systems. To add storage later you can use AC coupling with a separate battery inverter.

See also MPPT (maximum power point tracker), AC coupling and DC coupling, Single-phase and three-phase

In the catalogue: String inverters

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T

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V

VIES

The European Commission's system for checking EU VAT numbers.

VIES (VAT Information Exchange System) confirms whether a VAT number is valid for trade between EU countries. We check your number there before issuing an invoice without VAT. If it is not enabled for intra-EU transactions (in some countries this has to be requested separately), the invoice must include VAT.

See also Reverse charge (intra-EU VAT)

Voc and maximum PV input voltage

A panel's voltage with no load, and the limit the inverter must never exceed.

Voc (open-circuit voltage) rises as temperature falls, so a string's voltage peaks on a cold, sunny morning. Multiply the panel's Voc by the number of panels in series and add the margin for the lowest local temperature: the result must stay below the inverter's maximum DC input voltage. Overvoltage can destroy the inverter and is typically excluded from the warranty.

See also Isc (short-circuit current), MPPT (maximum power point tracker), Parallel and series connection

In the catalogue: Solar panels

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W

Wp and kWp (watt-peak)

A panel's power under standard test conditions.

Wp is the power a panel delivers under standard test conditions (STC: 1000W/m² of irradiance, 25°C cell temperature); real output is usually lower because of heat, angle and dirt. A PV system's size is given in kWp: twenty 500Wp panels make 10kWp. How many kWh per year each kWp produces depends on location, orientation and tilt.

See also kWh and kW, €/W and €/Wp

In the catalogue: Solar panels

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Z

Zero export (feed-in limitation)

A setting that stops or limits power flowing into the grid.

With zero export the inverter reduces its output so that nothing, or only up to a set limit, goes into the grid, based on the meter or CT reading. It is used where the grid operator allows no or limited feed-in, or where feed-in is not paid. With a battery it wastes less, because the surplus is stored instead of being curtailed.

See also CT clamp and energy meter, Grid connection rules (grid code), Self-consumption

In the catalogue: Hybrid inverters

↑ Back to the index

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