Glossary: what the words on a solar listing mean

Plain-language definitions for the terms that turn up in product names on this index, what they change in practice, and which ones are marketing. Where a term maps to a metric on our pages ($/W, W/m², $/W/m²) we say so. Nothing here is a recommendation for a brand.

The three numbers on our panel pages

$/W (price per watt): the listed price divided by the rated watts. The purest cost measure of a panel. Everything else being equal, buy watts, not panels.
W/m² (watts per square metre): rated watts divided by the panel's face area. This is module efficiency × 1,000 by definition (a 22.8% module makes 228 W/m² at standard test conditions). It matters when roof space, not budget, is the limit: a 240 W/m² panel gets you the same array in about 15% less roof than a 205 W/m² panel.
$/W/m²: the $/W figure divided by the panel area. Low means cheap per watt and compact. Use it when both roof and money are tight; use $/W alone when roof is not the constraint.
Rated watts (Wp) are measured at STC (1,000 W/m² of sun, 25 °C cell temperature). Real panels on a real NZ roof run hotter and see less light, so a 440 W panel typically produces 300 to 380 W at midday in summer. Every panel is derated the same way, so the numbers still compare fairly.

Cell types: what "N-type", "P-type", "PERC", "TOPCon", "HJT" and "back-contact" mean

The silicon wafer in a solar cell is doped to make it either P-type (boron) or N-type (phosphorus). That one choice drives most of the technology names below.

Term	What it is	What it changes for you	Status in NZ listings (2026)
Mono / monocrystalline	Cells cut from a single silicon crystal (black, uniform).	Higher efficiency than poly. Essentially every new panel is mono.	Universal. "Mono" on a listing is not a differentiator any more.
Poly / polycrystalline	Cast silicon, many crystals (blue, speckled).	15 to 18% efficiency, cheaper per panel, more roof per watt.	Old stock only. If it is cheap per watt and you have roof to spare, it still works.
PERC (Passivated Emitter and Rear Cell)	The refinement that made P-type mono the standard from about 2018 to 2023. Extra rear passivation layer bounces light back into the cell.	20 to 22% modules. Slightly higher first-year degradation (LID/LeTID) than N-type.	Now the budget tier. Perfectly good panels, priced accordingly.
N-type	Wafer doped with phosphorus instead of boron. The base for TOPCon, HJT and most back-contact cells.	No boron-oxygen light-induced degradation, better temperature coefficient (loses less output when hot), better low-light performance, longer warranties (30-year output warranties are common).	The current mainstream. "N-type" alone tells you the wafer, not the cell architecture.
TOPCon (Tunnel Oxide Passivated Contact)	N-type cell with a thin oxide plus polysilicon layer on the rear.	22 to 23.5% modules. Same production lines as PERC with extra steps, so pricing sits close to PERC. Higher bifaciality (about 80%).	The bulk of new grid-tie stock in NZ. Most "N-type bifacial dual-glass" listings are TOPCon.
HJT / heterojunction	N-type wafer sandwiched between thin amorphous-silicon layers.	22 to 24% modules, the best temperature coefficient of the mainstream types (about -0.24%/°C vs -0.30 for TOPCon and -0.35 for PERC), very high bifaciality (90%+). More silver in manufacture, so usually a small premium.	Available from a handful of brands; a minority of listings.
Back-contact / BC / IBC / HPBC / ABC / TBC	All the metal contacts are moved to the rear, so nothing shades the front. IBC is the generic name; HPBC (LONGi), ABC (Aiko) and TBC (TOPCon back-contact) are makers' variants.	The highest module efficiencies on sale (23 to 24.5%, so 230 to 245 W/m²), a clean all-black look, and good shading tolerance in the newer designs. Usually the highest $/W of the mainstream types, and lower bifaciality than TOPCon/HJT.	Growing fast; several NZ listings carry HPBC 2.0. Sort the panels page by W/m² and BC panels sit at the top.

Rule of thumb: cell type sets W/m² and how the panel behaves when hot and shaded. If your roof is big, sort by $/W and any of PERC/TOPCon/HJT is fine. If your roof is small or shaded, pay attention to W/m² and shading tolerance, and BC or HJT earn their premium.

Panel construction terms

Bifacial: the rear of the cell is also active, and the panel has a transparent back (glass or clear backsheet). Extra yield comes from light reflected off the surface below the panel. Realistic gains: 5 to 15% on an open ground mount over light gravel or concrete, close to zero when flush-mounted on a dark roof with no gap. The rated watts on the listing are front-side only unless it says otherwise, so bifacial does not change $/W; treat the rear gain as a bonus, not a spec. Bifaciality (rear output ÷ front output) is roughly 70% PERC, 80% TOPCon, 90% HJT, 60 to 70% BC.
Dual-glass / glass-glass: glass on both faces instead of glass front and polymer backsheet. Heavier (about 25 to 33 kg for a 60-cell-class panel versus 20 to 24 kg), but far less moisture ingress, and it is why 30-year output warranties have become normal. Most bifacial panels are dual-glass by necessity.
Half-cut / half-cell: each cell sliced in two, doubling the cell count and halving the current per string. Less resistive loss and better partial-shade behaviour (the panel is effectively two panels wired in parallel). Standard on almost everything now.
Shingled: narrow cell strips overlapped like roof tiles and glued rather than soldered. No visible busbars, high packing density, and every strip is in parallel within a group, so shading tolerance is good. Common on higher-end 100 to 400 W portable and RV panels as well as some rooftop modules.
Busbars / MBB / 0BB (zero busbar): the ribbons collecting current from a cell. Multi-busbar (9 to 16 thin wires) cut shading and resistance; zero-busbar designs use fine wires embedded in the encapsulant. Manufacturing detail; not worth choosing on.
Full black / all-black: black frame and black backsheet or glass. Looks better, runs a couple of degrees hotter, costs a few watts. Cosmetic.
Rigid / fixed: framed glass panels for roofs and racks. Flexible / semi-flexible: no glass, thin polymer laminate, bends to a curve; lighter, glue-down, but shorter life and lower efficiency; for boats, campers, roofs that cannot take frames. Folding / blanket / portable: fabric-mounted or hinged panels for camping. These sit on our "Portable and flexible panels" page.
Cell count and size (54, 60, 66, 72, 78 cells; M10 182 mm and G12 210 mm wafers): bigger wafers and more cells simply mean a bigger, higher-watt panel. Residential roofs mostly use 54 to 66-cell (400 to 500 W, about 1.7 to 2.1 m²); 72 to 78-cell (550 to 720 W, 2.6 to 3.1 m²) are commercial and ground-mount sizes that need two people to lift.

Warranty and durability terms

Product warranty covers defects (12 to 25 years). Performance/output warranty promises the panel still makes X% of its rating after Y years (typical: 84 to 89% at 25 or 30 years for N-type). Both only matter if the seller and the maker are still around in NZ; check the NZ office or distributor.
Degradation: first-year loss (1 to 2% PERC, under 1% N-type) then about 0.4% a year (0.25 to 0.4% for N-type).
Temperature coefficient (%/°C of Pmax): how much output drops per degree above 25 °C. Cells run 20 to 30 °C above ambient, so a panel at -0.30%/°C is losing about 8% on a warm day. Lower magnitude is better; HJT is best, then BC and TOPCon, then PERC.
LID / LeTID: light- and light-plus-heat-induced degradation, a P-type PERC problem, largely absent on N-type.
PID (potential-induced degradation): losses from high system voltage and humidity; look for "PID resistant" on any panel going into a coastal NZ site.
IEC 61215 / 61730: the base safety and durability tests. IEC 61701 salt mist and IEC 62716 ammonia are the ones that matter for coastal and farm sites.
CEC / Clean Energy Council listing: an Australian approved-modules list that NZ lines companies and installers commonly ask for. Not a quality ranking, but a panel not on it can complicate an NZ grid connection.

Batteries

LFP / LiFePO4 (lithium iron phosphate): the chemistry in almost every home and off-grid battery sold in NZ now. Safe, 3,000 to 6,000+ cycles, tolerant of partial charge, no cobalt. NMC (nickel manganese cobalt): higher energy density, used in EVs and older Powerwalls; rarer in new home storage. AGM / gel / flooded lead-acid: cheap per Ah, half the usable depth of discharge, a fifth of the cycle life; still sold for boats and budget off-grid.
kWh vs Ah: home batteries are quoted in kWh; 12/24/48 V batteries in Ah. Ah × V ÷ 1,000 = kWh. Our "12/24/48V batteries" page converts to $/kWh for you.
BMS (battery management system): the electronics that stop cells being overcharged, over-discharged or too cold. Every lithium battery has one; the question is whether it talks to your inverter (CAN/RS485 comms) so charging is coordinated. "Comms-capable" or "closed-loop" batteries pair with a listed inverter; dumb batteries need voltage-based charging.
Low-voltage (48 V) vs high-voltage (200 to 500 V) home batteries: LV batteries pair with most hybrid inverters and can be paralleled; HV batteries need an HV-capable inverter, run higher efficiency and are usually one brand end to end. Not interchangeable.
Cycle life and depth of discharge (DoD): a 10 kWh battery at 90% DoD gives 9 kWh a day; at 6,000 cycles that is about 16 years of daily use.

Inverters and system words

String / grid-tie inverter: converts panel DC to 230 V AC, no battery port. Hybrid inverter: grid-tie plus a battery port and usually a backup output. Microinverter: a small inverter under each panel (or pair); per-panel monitoring and shading tolerance, AC on the roof, more units to fail. Off-grid inverter/charger: 12/24/48 V DC to 230 V AC with a mains charger built in; not grid-export devices.
MPPT (maximum power point tracker): the circuit that keeps the array at its best voltage. Inverters have one to four; "2 MPPT" means two independent roof faces can each be optimised. In off-grid gear, "MPPT" is the solar charge controller type; PWM is the cheaper, less efficient alternative.
Optimiser: a per-panel DC-DC box (Tigo, SolarEdge) that mitigates shading and gives panel-level data with a string inverter.
AS/NZS 4777.2 / 5033: the inverter grid-connection standard and the PV array installation standard NZ electricians must work to. Export limit: the kW your lines company lets you push to the grid; typically 5 kW single-phase, moving to 10 kW on many networks in 2026.
DC isolator: the switch that disconnects the array; since AS/NZS 5033:2021 a rooftop isolator is no longer required, one at the inverter is.

Close to market: what is coming, honestly

As of 2026, these are real but not (or barely) on NZ shelves. Nothing here should stop you buying now; a panel bought today at a good $/W is not obsoleted by a lab record.

Perovskite-silicon tandem panels: a perovskite layer on top of a silicon cell, capturing more of the spectrum. Certified cell efficiencies passed 34%; the first commercial modules (around 24 to 27%) shipped in small volumes from 2024/25 to selected markets. The open question is outdoor durability over 25 years, which is why the big makers are still in pilot lines. Expect mainstream volume from about 2027 onward, at a premium first. Not in NZ listings yet.
Back-contact goes mainstream: HPBC 2.0, ABC and TBC lines are ramping and prices are converging on TOPCon. Expect BC panels to move from "premium all-black" to the default in the 24%+ segment over 2026 to 2027. Already visible in this index.
TOPCon refinements (TOPCon 2.0, edge passivation, 0BB) push mainstream modules toward 23.5 to 24% without a price step. This is where most of the "N-type" stock will keep improving quietly.
Larger, higher-watt formats (600 to 750 W) are already here for commercial and ground mount; not a residential trend because of weight and roof fit.
Sodium-ion batteries: cheaper raw materials, good cold performance, safe, but lower energy density (bulkier per kWh) than LFP. Cell makers announced mass production for 2025/26 and the first 12 V drop-in and small stationary packs are appearing (one sodium 12 V battery is in this index). Home-storage sodium packs at LFP prices are a 2027-plus story.
LFP keeps getting cheaper: cell prices fell steeply through 2024/25; the practical effect in NZ is more kWh per dollar and 5 to 10 kWh home batteries becoming an ordinary line item.
Balcony / plug-in solar and battery kits (large in Germany, appearing in Australia): in NZ these still need to meet AS/NZS 4777 and lines-company rules like any other grid-connected inverter, so "plug and play" claims do not remove the electrician.
Solid-state batteries: EV-focused and years from home storage; ignore for now.
Thin-film (CdTe, CIGS): real at utility scale overseas, effectively absent from NZ retail. Flexible CIGS is the one you may see, for boats and vans.

Reading a listing critically

The watts in the title are STC watts; W/m² tells you if the panel is current-generation (over 215 W/m²) or older stock (under 200).
"Grade A", "tier 1", "premium" in a title are not specifications. Tier 1 is a bankability list of manufacturers, not a quality grade of the panel.
"Bifacial" does not raise the rated watts. "Up to 25% efficiency" on a marketing line usually refers to the cell, not the module; use the number on the datasheet.
A price without a datasheet (no model number, no dimensions, no Voc/Isc) is a listing you cannot design around. Our size column shows a dash for those.