Panel efficiency is one of the most quoted figures in a solar quote. It is also one of the least understood. A salesperson mentions that a panel is 22% efficient. The number sounds either impressive or oddly low. The conversation moves on without anyone explaining what it describes. No one discusses whether it should change the decision.
This guide sets out what efficiency actually measures. It covers when it genuinely matters for a Perth home. It also covers when it matters far less than people assume. We look at other specifications on a datasheet that often have a bigger effect on system energy output.
What Efficiency Actually Measures
Solar panel efficiency is the share of the sunlight landing on a panel that is converted into usable electricity. A panel described as 22% efficient converts 22% of the solar energy hitting its surface into power. The rest is reflected or lost as heat.
That figure might sound modest. It is worth putting in context. Efficiency has climbed steadily. Panels that were around 15 to 18% efficient a decade ago have been replaced by mainstream panels in the 20 to 22% range. Premium products push higher again. That progress is precisely why a modern panel of the same physical size produces far more power than its predecessor.
Why Efficiency Really Means Power Per Square Metre
Here is the practical translation. Efficiency describes how much power a panel makes from a given area. A more efficient panel produces more watts per square metre than a less efficient one of the same size.
That reframes the question entirely. Efficiency matters most when roof space is limited. Every square metre has to work harder. On a large, simple, unshaded roof there is often room to reach the desired system size with either panel. Efficiency becomes far less important than durability, warranty and long-term output.
When Efficiency Matters, and When It Does Not
- It matters when the roof is tight. A small, complex or heavily obstructed roof will fit more capacity with higher-efficiency panels. This can be the difference between a system that covers household usage and one that falls short.
- It matters for high-consumption homes. A household with a pool, ducted air conditioning and an electric vehicle needs a large system. Efficiency helps fit that capacity onto the available roof.
- It matters less on a big, simple roof. If there is ample north-facing space, the target system size can usually be reached comfortably either way.
- It is a separate question from quality. A high efficiency figure says nothing about how well a panel will hold up over twenty-five years in Perth conditions.
The Specifications That Matter Just as Much
Efficiency is one line on a datasheet. Several others have at least as much influence on how much energy a system actually delivers over its life. This is especially true in a hot climate.
| Specification | What it means | Why it matters in Perth |
|---|---|---|
| Efficiency (%) | Share of sunlight converted to electricity | Decides how much capacity fits on the roof |
| Temperature coefficient | Output lost per degree above 25°C | Very important; panels run hot through summer |
| Degradation rate (% per year) | How quickly output fades with age | Decides total energy across 25 to 30 years |
| Power rating (W) | Output under standard test conditions | A lab figure, not a guarantee of real output |
| Construction and certification | Glass-glass, salt-mist rating and similar | Determines survival in coastal, hot conditions |
The temperature coefficient deserves particular attention in Perth. Panels are rated at 25 degrees. A roof in February sits far above that. A panel that loses less output per degree of heat will out-produce a nominally more efficient panel. That other panel fades badly when hot. Similarly, a low degradation rate compounds over decades. A small annual difference becomes a large gap in total energy by year twenty-five.
Efficiency and the Long Game
The most useful way to think about a panel is not the headline percentage on day one. Think instead about how much energy it delivers across its whole life. That depends on how much it converts. It depends on how well it holds up in heat. It depends on how slowly it degrades. It depends on whether it is still performing in year twenty-five with a warranty that means something.
This is the thinking behind the panels Positive Energy Solutions specifies. The SunPower P-Series combines strong output per square metre with a maximum degradation rate of 0.40% per year. It has glass-glass construction and IEC 61701 maximum-severity salt-mist certification for coastal Perth homes. It is backed by a 30-year warranty covering product, performance and labour. There is no grey area. Efficiency helps a system fit the roof. The rest of the datasheet decides what it is still producing decades later.
Frequently Asked Questions
What is a good solar panel efficiency?
Mainstream residential panels today generally sit in the 20 to 22% range. Premium products go higher again. Anything in that band is capable. The more useful comparison is between panels of similar efficiency. Look at their degradation rate, temperature behaviour and warranty.
Do more efficient panels produce more electricity?
They produce more electricity from the same area. This matters when roof space is limited. On a roof with plenty of room, a similar system size can usually be reached with either panel. You use slightly more of them.
Does efficiency drop as panels get older?
Yes, gradually. Every panel degrades over time. The annual degradation rate on the datasheet tells you how quickly. A lower rate means more output remaining in later years. That is where a large share of a system’s lifetime value sits.
Does Perth heat affect panel efficiency?
It does. Panels are rated at 25 degrees and produce less as they get hotter. This is why the temperature coefficient is such an important specification for Western Australian roofs.
Look Past the Percentage
Efficiency is a useful number, particularly for a constrained roof. It is one figure among several. The panels that deliver the most over twenty-five years are the ones that combine sensible efficiency with strong heat performance. They also have low degradation and a warranty that will actually be honoured.
Talk to the local team about the right panel for your roof and your usage: positiveenergy.com.au/contact/
About the Author
Jason Wiktorowicz
Sales Manager, Positive Energy Solutions | Perth, WA
Jason has been at the centre of Western Australia’s energy transition for over a decade. He was Orchestration Lead on Project Symphony. That is Western Australia’s largest virtual power plant pilot. He was Stream Lead on Project Encore. He worked directly with AEMO, Western Power and Energy Policy WA. He worked on how distributed energy resources connect and operate on the SWIS. That work included developing and rolling out CSIP-AUS. It is now mandatory for all new Western Australian grid connections. He also led Emergency Solar Management. It was the first program of its kind in Western Australia. He led VPP for Schools, which provided direct market benefits through Supplementary Reserve Capacity. He led REBAR, the Western Australian Residential Battery Rebate scheme.
His earlier career spanned Synergy, Infinite Energy and Curtin University’s Sustainability Policy Institute. He co-authored peer-reviewed research on net-zero urban precincts, solar integration and peer-to-peer energy trading. It was published in the journal Urban Planning in 2018.
At Positive Energy Solutions, Jason leads sales with a focus on system design accuracy and long-term performance. Positive Energy Solutions installs solar and battery systems, EV chargers and heat pumps. We hold partner accreditations with Fronius, SigEnergy, iStore and SunPower.
10-year installation workmanship warranty. Positive Energy Protection, powered by Omnidian, performance monitoring included on all systems.
