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To relocate or add extra PV panels..advice required

Solar Photovoltaic (PV)

Last Post by apollogrid 10 months ago

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WesleyP1874

(@wesleyp1874)

Active Member Member

Joined: 1 year ago

Posts: 14

Topic starter 20/03/2025 12:48 pm [#2213]

Hello, if anybody can offer advice please.

Six months ago we had 11x420w panels fitted on a SSW facing roof, with a 3.6Kw Solax Invertor. The supplier quoted an annual estimated generation figure of 3300Kwh on the MCS certificate. However we will be lucky if we get near 20% of this figure! The reason being, they took no account of the shading from a wood opposite in their calculations. I've had the system looked at by a separate local expert, he thinks that when shading is taken into account we will only get about 775kwh per annum out of the system.

The equipment was supplied under an ECO4 Scheme. Fair enough, we haven't paid for it ourselves, but it should still be fit for purpose and capable of generating a good return on the investment. I raised my concerns with them, and have been offered two solutions. One of which is to fit optimizers to the existing panels, but I'm told that only works if shading is partial and moves with the sun, such as that from an individual tree or chimney. The other option proposed is to relocate the panels on the other side of the house, but that is opposite the path of the sun through the day. (Using a website called Suncalc.org to see this)

My idea would be to double up on the panels already installed. I believe Solax invertors can go up to 200% oversizing on panels, especially as the output of the existing panels is so low. I don't want panels removing and leaving holes in the roof! I didnt kno anything about ASHP and PV systems when this work was originally done, but I do now! Any advice greatly appreciated thanks.

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Judith

(@judith)

Prominent Member Member

Joined: 2 years ago

Posts: 510

20/03/2025 3:29 pm

What does your Suncalc website say for June sunshine?
Our neighbours have tall trees but in the 6 months of summer we still get good generation.

This is a day of our generation showing the effects of trees. It’s all the shoulders on what should be a nice smooth curve.

Do you have any photos of the house roof in summer? Is it in sun say 10am to 4pm when the sun is highest?

The optimisers will help if part of the roof is shaded.

Some installers are cowboys I’ve seen panels on north facing roofs with a steep hill on the north too!

If it were me I’d wait a full summer before considering changes, they may not be necessary. Only results will tell.

2kW + Growatt & 4kW +Sunnyboy PV on south-facing roof Solar thermal. 9.5kWh Givenergy battery with AC3. MVHR. Vaillant 7kW ASHP (very pleased with SCOP 4.7) open system operating on WC

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Judith

(@judith)

Prominent Member Member

Joined: 2 years ago

Posts: 510

20/03/2025 5:55 pm

This is a sun curve once it is above the trees, nice and smooth. Do you have any access via an app to anything from your system? @wesleyp1874

2kW + Growatt & 4kW +Sunnyboy PV on south-facing roof Solar thermal. 9.5kWh Givenergy battery with AC3. MVHR. Vaillant 7kW ASHP (very pleased with SCOP 4.7) open system operating on WC

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WesleyP1874

(@wesleyp1874)

Active Member Member

Joined: 1 year ago

Posts: 14

Topic starter 20/03/2025 6:39 pm

Hi I do have yes..just found that facility today! I have a spike in power at about 10.45 every day, which I think might be the sun coming through the gap in trees. Its a spike not a gentle curve

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Judith

(@judith)

Prominent Member Member

Joined: 2 years ago

Posts: 510

20/03/2025 6:55 pm

It looks normal up to 10:30!

2kW + Growatt & 4kW +Sunnyboy PV on south-facing roof Solar thermal. 9.5kWh Givenergy battery with AC3. MVHR. Vaillant 7kW ASHP (very pleased with SCOP 4.7) open system operating on WC

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WesleyP1874

(@wesleyp1874)

Active Member Member

Joined: 1 year ago

Posts: 14

Topic starter 21/03/2025 11:53 am

The same thing seems to happen every day. Builds up and then drops right down. I'll check this weekend but I suspect the sun is out unshaded by the trees opposite for a short time.

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Judith

(@judith)

Prominent Member Member

Joined: 2 years ago

Posts: 510

21/03/2025 3:11 pm

Have a look at your roof and where the sun is falling. It’s not rocket science if the sun is on all of the panels you’ll be generating the most. If it’s on half of the area you’ll get half the power if the panels have been wired in two blocks or less than half if they’ve all been wired together. Thats where optimisers come in, to help get the most from your panels.

2kW + Growatt & 4kW +Sunnyboy PV on south-facing roof Solar thermal. 9.5kWh Givenergy battery with AC3. MVHR. Vaillant 7kW ASHP (very pleased with SCOP 4.7) open system operating on WC

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JohnR

(@johnr)

Estimable Member Member

Joined: 1 year ago

Posts: 106

21/03/2025 9:41 pm

You can't forecast the annual generation by simple extrapolation from the winter six months. I have a winter tree shading problem (some of the trees are 80m away) which means that my October-March generation is little over one quarter of the annual total https://monitoringpublic.solaredge.com/solaredge-web/p/site/public?name=Liden#/dashboard. The shading problem was allowed for in the output forecast and micro-inverters were fitted.

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apollogrid

(@apollogrid)

New Member Member

Joined: 10 months ago

Posts: 1

13/06/2025 4:38 am

The situation you are currently experiencing is representative and reflects many of the problems that can be faced when installing a PV system through the ECO4 government subsidy scheme.

Firstly, the original installer made a clear design error when he gave an estimate of 3,300kWh per annum without taking into account shade from the trees. The actual annual generation is now only about 775kWh, far less than expected, and you have every reason to question it.

It is recommended that you retain all records of correspondence and third party assessment reports and formally complain to the MCS Certification Body or ECO4 Project Management to request a re-examination of the design for reasonable compliance. The advice on optimisers is accurate: optimisers are only effective where there is ‘localised moving shade’ on the panels, and will have very limited effect if your whole row of panels is permanently shaded.

In addition, while moving the panels to the other side of the roof may seem like an option, if the new location is not south-facing or has insufficient sunlight conditions, there may still not be a significant improvement in power generation, and it is recommended that you perform a sunlight simulation analysis using a tool such as PVGIS before making a decision.

In contrast, your proposal to add more panels and over-allocate the Solax inverters is more realistic, as the Solax 3.6kW inverters typically support up to 200% DC input, so in the case of the current panels' very low output, adding additional panels will improve the overall efficiency of the system, while avoiding the need to remove the panels, which would leave holes in the roof.

However, it is still important to check that there is no breach of the ECO4 subsidy and that there is sufficient safe roof space before implementation. The overall advice is to formally feedback on the quality of the installation, assess the light conditions in the new location and prioritise additional panel capacity as a remedial measure, subject to compliance.

This post was modified 10 months ago by Mars

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