Methodology

How a score is built

Each product is scored against a published rubric of weighted pillars. Each pillar contains criteria. Each criterion maps a measured specification to a band (0–100 pts). Pillar scores are weighted averages of their criteria. The overall score is a weighted average of pillar scores. The same arithmetic runs on every product. No editorial adjustments.

What happens when a spec is missing

Every criterion declares a missing mode. Floor (40 pts): the manufacturer did not disclose this figure. Non-disclosure is penalised. Neutral (50 pts): this axis is not universally published in this product class. Absence is not penalised but nothing is assumed. Exclude: the criterion is dropped and the remaining pillar weights renormalised. Used for data not yet collected, or for axes that genuinely do not apply to a product.

Classes, not one leaderboard

Products are sorted into market classes (e.g., Premium European, Performance & Value) and judged within those classes. A boutique premium product should not be ranked against a volume residential product on scale, and vice versa. The class system prevents misleading cross-segment comparisons while still publishing all scores.

International publication

review.solar is an international publication. The root international safety standards (IEC 62109 for inverters; IEC 62619 for batteries; IEC 61215/61730 for panels) are the primary certification reference. National grid-connection overlays (AU AS/NZS 4777.2 + CEC; US UL 1741; EU VDE) are market-specific layers applied by regional distributors at installation. A product certified to the international base standard is not penalised for the absence of a regional national listing.

Cell balancing: active vs passive

Passive balancing dissipates excess charge as heat through resistors. Cells stay balanced but energy is wasted and thermal stress is generated at cell level. Active balancing recirculates charge between cells with no heat dissipation. Cells stay tighter across thousands of cycles, producing better long-run capacity retention. Active balancing is confirmed for Sonnen, Tesla Powerwall 3, and Enphase IQ Battery; it is estimated as passive for most other products where BMS architecture is not disclosed.

Warranty degradation guarantee: the clause most consumers never read

An end-point-only warranty (e.g., "≥70% capacity at year 10") permits a battery to lose 25% of its capacity in year two and then stabilise. The manufacturer satisfies the warranty but the customer suffers large early losses during the years of heaviest use. A stepped guarantee adds a midterm checkpoint. A linear annual-cap guarantee limits degradation per year and prevents front-loaded decline. Only Sonnen currently offers a linear degradation guarantee in this product set. Tesla offers stepped midterm + end-of-term. All others are end-point only.

Grid-forming vs grid-following

A grid-following battery needs an external AC voltage and frequency reference to operate. It cannot function without the grid or a running generator to synchronise to. A grid-forming battery creates that reference itself: it can black-start a home from a complete outage, run indefinitely from solar, and synchronise a generator or additional solar to its own microgrid. Sonnen, Tesla Powerwall 3, and Enphase IQ Battery (with IQ System Controller) are grid-forming in this product set. Most modular batteries (BYD, LG, Sungrow SBH, Huawei Luna, LG RESU) are grid-following. Their backup capability depends entirely on the paired hybrid inverter.

Gateway disclosure: not a penalty

Some batteries require a separate gateway or hub for full smart functionality (VPP dispatch, load management, blackout protection). Where this applies, the scorecard shows an amber gateway note. Gateway dependency is not penalised in the score. A gateway mounted at the switchboard can be the correct topology when the battery is installed in a garage, shed, or any location remote from the main electrical panel. The gateway note is a disclosure so the consumer knows a separate box exists and understands its role.

Semiconductor technology: why it matters

Silicon carbide (SiC) and gallium nitride (GaN) switching devices achieve lower conduction and switching losses than standard silicon IGBT, the same transition that transformed EV drivetrains. SiC excels at high-voltage C&I applications (the Fronius Argeno 125 is the first confirmed SiC residential/C&I inverter in this product set, enabling its 99.1% peak efficiency). GaN excels at the low-voltage, high-frequency switching of microinverters (Enphase IQ8). Standard silicon IGBT is mature, field-proven, and cost-effective. The 55-pt band reflects that it is the established technology, not a failing one. Products using SiC or GaN earn a technology premium that reflects genuine long-run efficiency advantages, particularly at partial load, which is where solar inverters spend most of their operating life.

Night standby consumption: the silent lifetime cost

An inverter drawing 10W during 11 non-generating hours per night consumes approximately 400 kWh over a 10-year warranty term. That is energy the household pays for but never benefits from. Fanless residential inverters typically draw 1–3W; smart-fan products 3–6W; C&I products more, though at larger system scales the percentage impact is negligible. This criterion is scored as neutral missing mode. Many manufacturers do not publish standby wattage, and absence of data is not penalised. Products that publish this figure and achieve low standby earn a legitimate competitive advantage.

Reactive power range: voltage management on the real grid

Voltage rise at the end of distribution feeders is the primary physical constraint on solar penetration in most Australian networks. Reactive power injection (Q(U) volt-VAR response) is the tool networks use to manage it. The range of that response (±0.8 pf vs ±0.9 pf, and whether the inverter also supports Q(P) active-power-dependent response) determines how much the inverter can contribute to network stability. All AU CEC-approved inverters support Q(U) response to AS/NZS 4777.2 as a minimum; the differentiation is in whether Q(P) four-quadrant response is also implemented. Huawei SUN2000 is the only confirmed four-quadrant product in this set.

Price

Price changes daily and varies by installer, region, and procurement volume. A score that bakes in price would be stale within weeks. Price context is provided separately where relevant but never affects a rubric score.

Bankability tier (BNEF) and module reliability rankings (PV ModuleTech)

BloombergNEF Tier 1 is a project finance construct. It reflects whether lenders will write debt against a product, not whether it outperforms in the field. PV ModuleTech publishes granular A+ to F manufacturer reliability rankings based on manufacturing quality audits and field data. Both are respected industry signals. Neither affects a score. BNEF's methodology is not publicly disclosed; incorporating an opaque external ranking into a deterministic scoring engine would undermine the transparency we require of every criterion. PV ModuleTech's rankings are proprietary, update quarterly, and would introduce a dependency on data we cannot republish. A score that changes for reasons a reader cannot independently verify is not a transparent score. Both are shown as informational context where available.

Regional availability and certification

Whether a product is available in a specific market, or carries a specific national certification (AU CEC, US UL listing), is shown in notes where known. It is not a rubric criterion. A globally certified product is not penalised on an international publication for the absence of a single national overlay.