Solar panel, inverter and battery efficiency - Updated September 2023
Solar panel efficiency
A more efficient panel converts more of the sun's irradiation into electricty than a less efficient one. Correct?
A popular JinKo 440W panel is 22.02% efficient.
Whereas their 475W model is 22.01% efficient.
So clearly simply producing more power, 475W over 440W, is not what makes a panel more efficient at converting the suns rays to electricity.
Solar panel efficiency is based on power output relative to physical size.
In the example above, the JinKo 475W panel is a slightly larger panel than the 440W model.
What we should really call this metric is 'Roof space efficiency', not simply 'efficiency'.
For example...
The dimensions of the JinKo Neo N 440W (0.44kW) panel are 1.762m x 1.134m so 1.998108 sqm.
(0.44kW / 1.998108)x 100 = 22.02% efficiency
Therefore if someone were able to produce a 600W panel that was the same size as the 440W...
(0.6 / 1.998108)x 100 = 30% efficient.
The boffins say that 30% efficiency is the likely upper limit for affordable silicon-celled solar panels.
We'll have to wait and see about that.
When we started our solar installation business in 2011 panels were 190W (0.19kW) and smaller...1.27664sqm.
So they had an efficiency of (0.19 / 1.27664)x 100 = 14.88%
So in 12 years, panels have gone from 15% to 22% efficient.
26 x 190W panels would take up 33.193 sqm of roof space for 4.94kW max. output.
Now we can get 7.31kW of output from that same 33.193sqm.
So a 7% efficiency gain has delivered a 48% increase in output per sqm of roof.
The most efficient panels.
Almost every panel on the market today (Sept 2023) is between 19 and 23% roof space efficient.
I've seen datasheets for panels with slightly over 23% efficiency but for now, that's all they are....datasheets.
The panels themselves aren't here in Australia yet. Sometimes they never get here.
If they are too expensive they won't sell, so no-one bothers to import them.
Of the panels that are available here and now in Perth, Western Australia the four most efficient are:-
Risen 440W and Longi HiMo6 440W both at 22.5%, Sunpower Maxeon 3 420W at 22.2%, JinKo Neo N 440W at 22.02%
One of the least efficient is the REC Alpha Pure R 410W at 21.2%. It's a premium priced panel.
However when REC bring in the 430W version of this panel soon the efficiency jumps to 22.3%
More power output from the same sized panel means greater efficiency.
Ironic that the Risen panel, one of the cheapest we can buy, is equally the most efficient, but there you have it...
Panel dimensions are 1.722 x 1.134 so (0.44kW / 1.952748sqm) x 100 = 22.5%
Does efficiency matter?
When we are talking about one panel being 22.5% efficient and another 22.02% efficient, that equates to 0.68sqm of roof space for a 6.6kW system.
(15 Risen 440W x 1.952748sqm) = 29.29sqm total or (15 JinKO 440W x 1.998108sqm) = 29.97sqm.
0.68sqm less roof space for 6.6kW of Risen 440W.
No big deal for most homes.
Solar inverter efficiency
Solar panels make DC power.
The inverter converters this DC power into AC power to be used in your house.
The inverter's efficiency is how much of the DC power is lost in the conversion process.
Heat will also play a role in this efficiency.
The hotter the inverter's internal temperature, the less efficient it becomes.
Whilst there's a bit of truth in the theory that active cooling an inverter with a fan improves efficiency, it's not the whole truth.
The components and design of the inverter and the quality and effectiveness of its heat sink are far more important than any fan.
The most efficient inverter I've measured on the hottest of Perth Summer days doesn't have a fan, but the worst by far also doesn't have a fan.
Solar battery efficiency
A 'DC coupled' battery, where the battery is plugged directly into a hybrid solar inverter is more efficient than an 'AC Coupled' battery.
With DC coupled the DC panel power goes into the battery unconverted. It stays DC.
Then when the house needs some power from the battery the inverter converters it to AC.
One conversion only, minimal losses, especially with higher voltage batteries that operate at similar voltages to the string of panels.
'AC Coupled' batteries, like Tesla Powerwall 2 and many others work very differently.
First the existing solar inverter converts DC panel power to AC for house loads and export back to the grid.
The meter of the 'AC Coupled' battery detects any surplus solar power flowing out to the grid and draws from the grid an exactly equal amount.
That's how the battery is charged. Always from grid power, but the cost is cancelled out by the house electricity meter than nets the ins and outs.
The AC Coupled battery has it's own inverter/charger that charges the battery with the AC grid power.
The battery itself can only output DC power, so when the house needs power from the battery, there's another DC to AC conversion needed.
Each conversion results in some power losses, so AC Coupling a battery is less efficient than the simple one conversion of a DC Coupled battery.
What about all-black panels?
All-black panels typically have a black backsheet instead of the usual white one.
This stops little strips of white being seen in the gaps between solar cells. More aesthetically pleasing.
The theory is that a black backsheet makes a panel less efficient.
Black absorbs more heat than white, a hotter solar panel makes less power than a cooler one.
All of the above is true, but I have to say, I monitor thousands of solar installations and I can't see any difference.
Black backsheet panel sites perform equally well, at least here in Perth, as white backsheet panels sites.
The only difference is usually cost.
An all-black 440W JinKO Neo N Satin costs $15 a panel more than a white backsheeted Neo N 440W
Not surprisingly the more expensive panels are almost universally all-black.
You buy top of the line, well they've got to look good don't they?
REC panels, Sunpower Maxeon, higher prices, but all-black.
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This review was written by Andrew MacKeith, Solar4Ever service manager since 2011.
Most recent update April 2021
