How Quickly Are Solar Panels Improving? The Efficiency Trajectory

Solar panels have improved dramatically over the past fifteen years — in both efficiency and cost. But the pace of improvement is often misunderstood. Panels are not doubling in efficiency every few years. They're improving steadily, in incremental steps, generation by generation.

Understanding this trajectory helps answer the question that almost every prospective buyer asks: should I wait for better technology?

The efficiency timeline

Efficiency in solar panels is the percentage of sunlight hitting the cell that is converted into electricity. A panel rated at 22% converts 22% of the light energy landing on it into electrical power.

Here is how mass-production residential panel efficiency has evolved:

These are mass-production figures — what you can actually buy for a residential installation. Laboratory record cells now exceed 26%, but those results don't translate directly into what ships on a pallet to your installer.

The three technologies on the market today

PERC — the outgoing mainstream

Passivated Emitter and Rear Cell (PERC) technology uses p-type silicon with a passivation layer on the rear surface to reduce electron recombination. It dominated the residential market from roughly 2018 to 2023, and many PERC panels are still being installed today.

At 21–22% efficiency, PERC panels remain perfectly good performers. Their limitation is a slightly higher annual degradation rate (~0.50% per year) and a tendency toward light-induced degradation (LID) in the first year of operation.

TOPCon — today's mainstream

Tunnel Oxide Passivated Contact (TOPCon) panels use n-type silicon, which avoids the boron-oxygen recombination issue that causes LID in PERC. They degrade more slowly (~0.40% per year), perform better in warm conditions, and have pushed mass-production efficiency to 22.5–24%.

TOPCon now accounts for an estimated 75% of Chinese manufacturing output as of 2026, and is the default technology in most new UK residential installations. Prices have converged with PERC, making PERC increasingly hard to justify.

HJT — the premium option

Heterojunction Technology (HJT) sandwiches n-type crystalline silicon between layers of amorphous silicon. The result is the best temperature performance of any mass-market cell (-0.24 to -0.26%/°C) and the lowest degradation rate (~0.30% per year).

HJT panels reach 23–25% efficiency in mass production. The catch is cost — manufacturing HJT cells requires more complex deposition processes, keeping prices above TOPCon. In UK conditions, where cell temperatures rarely exceed 35°C, much of HJT's temperature coefficient advantage is less relevant than in hotter climates. The low degradation rate remains valuable over a 25-year system life.

What's coming next: perovskite tandems

The technology generating the most excitement in solar research is perovskite tandem cells — a structure that stacks a perovskite cell layer on top of a conventional silicon cell, capturing different parts of the solar spectrum in each layer.

Lab perovskite tandem cells have demonstrated efficiencies exceeding 30%. The challenge is durability: perovskite materials degrade faster than silicon under real-world conditions, and scaling production without losing the efficiency gains has proven difficult.

Commercial perovskite tandem panels are expected to begin reaching the market between 2027 and 2030. Several manufacturers are working toward commercial products. When they arrive, they could shift mass-production efficiency beyond 26–28%.

Bifacial panels — which capture light on both front and rear surfaces — are also becoming more common. For UK domestic rooftop installations they offer little benefit (the rear face is against the roof), but for ground-mount commercial arrays with a light-coloured or reflective surface beneath, rear-face yield gains of 5–30% are achievable.

Should you wait for better technology?

This is the question the efficiency trajectory always raises. The answer is consistently no, and the maths explains why.

Each generation of panels improves efficiency by roughly 1–2% per year across mass production. In practice, that means the panels available in twelve months will be incrementally better — but not transformatively so.

Meanwhile, every year you delay means a year of paying full grid electricity prices for every kWh you use. At current rates, a typical household with solar saves roughly £400–£700 per year on electricity bills. A one-year delay costs you at least one year of those savings.

The efficiency gain you'd get by waiting: perhaps 1% more output from a system of the same physical size. On a 6 kWp system that generates around 5,400 kWh per year, 1% is 54 kWh — worth roughly £13 at current unit rates.

You'd wait twelve months and sacrifice £400–£700 in savings to gain £13 in annual generation improvement. The maths does not favour waiting.

Cost: the real story

Panel efficiency often gets all the attention, but cost reduction is where solar's transformation has been most dramatic.

The cost per watt of solar panels has fallen by approximately:

• 99% since 1976 (from ~$76/W to under $0.20/W at wholesale)
• ~90% since 2010 in the UK

What you pay today for a fully installed solar system would have bought only the panels fifteen years ago — and those panels were half as efficient.

The best time to install solar was ten years ago. The second best time is today — and today's panels are substantially better than those installed a decade back, at a fraction of the cost.

For a comparison of the specific panel models available in the UK right now and how TOPCon and HJT options stack up, the panel technology comparison guide covers the current market in detail.

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