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Author Topic: PV efficiency  (Read 257 times)
Jr. Member
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Posts: 64

« on: April 01, 2019, 12:48:31 PM »

I hope this isn't too stupid a question but would be great to know if it is.
After 2 years I have finally got the Enphase monitoring gizmo for my 4 kwh system.
If I have full sun and clean panels should I be expecting to see a full 4kw? It is a nice day right now, not a cloud in the sky and the panels are all lit up but I see a maximum of 3.1kw. Looking back at the data over the last few weeks the most it has done is 3.6kw.
Maybe it is the heat of the sun as well? Would love an explanation if anyone knows.
Hero Member
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Posts: 968

« Reply #1 on: April 01, 2019, 01:49:18 PM »

One factor affecting the output of an array is the physical position of the panels. To achieve the maximum output, the panels need to be in the optimal position. Ie east to west orientation and angle towards the sky.  All PV panels info label or spec sheet should give some guidance as to performance degrading due to temperature constraints.

A bright cold sunny winters day (with snow on the ground) will sometimes beat a hazy, hot sunny day for peak output, although  the summer day has of course more hours of irradiation so total daily output may be better.


8 KVA Lister TS2 Startamatic Genny
24 Volt 1000amp battery bank
Outback VFX3024
4.6 Kw PV array permanently ground mounted
Outback Flexmax 80
2 X Flexmax 30 PV CC
2.5 Kw wind turbine H Piggot design 4.5 Mtr Dia
12 Mtr free standing Tower.
u/floor heating from oil boiler cross linked to 12 Kw
Sr. Member
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« Reply #2 on: April 01, 2019, 01:56:44 PM »

Maybe it is the heat of the sun as well? Would love an explanation if anyone knows.

That'll be part of it.  I think the quoted panel output figure is for 25'C panel temperature.
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« Reply #3 on: April 01, 2019, 02:05:30 PM »

Sunís rays should be normal to the panel when a maximum conversion is required.  

Panel rating is under standard conditions.  

Sunís rays will be attenuated by the distance travelled through the atmosphere and by any particles suspended in same.   Output needs other factors to be taken into account such as changes due to panel temperature.

There is no reason why more than the rated panel output cannot be achieved under certain conditions.
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« Reply #4 on: April 01, 2019, 02:07:53 PM »

So many hidden variables - the pitch angle of your install (shallow or steep), how close to south it is for the mid-day peak, how clean they are, ambient temperature, how hazy or not the sky is, is there a breeze, potential shading etc etc etc.

For what it's worth my system is nominally 3.06kWp and it's never gone above 2.8kWp.  Sometimes individual panels (I'm on SolarEdge) do go beyond their rated capacity for short periods of time - I have 218W rated panels and for a few minutes on the sunniest and breeziest late mornings in April a couple of panels will get up to 230W, but they soon come back down again.

The main thing is are you getting a good consistent and useable output over the course of the days, weeks and months rather than what the max rated peak is - would you be able to consume 4kWp vs 3.1kWp in any case or would it be exported?

3.06kWp SolarEdge system with a split array:
2.18kWp 10x South facing, plus 4x West facing 880W

Mk1 ImmerSUN DHW diverter
4kW PowerVault Battery
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