shading question

[openspaceman]

Since getting my battery and using the Growatt web interface I have noticed a fairly steep rise in power once the sun gets onto my SW facing panels fairly late in the morning, about 10:30 currently. You will see from the attached picture that the last panel still has some shading at this time.

How significantly is this going to affect the other panels' outputs.

[nowty]

Depends on how your inverter deals with shading. Some people think (especially installers as they can sell you a more expensive system) you need a Solar Edge system or use voltage optimisers, but this is not always the case.

Before the system starts up in the morning, the panels will show open voltage circuit to the inverter and that wont matter much whether the panels are shaded or not.

So the inverter has a starting point of the max voltage or another way of looking at it, the total amount of panels you have and therefore roughly know where the voltage range of the max power point should be. The inverter will start by allowing the current to flow and as the current flows the voltage of your panels drop. The max power point tracker (MPPT) of the inverter will attempt to manage the voltage and current from the panels to gain the sweet point of max power. Once found the voltage operating range will be close to this point in most conditions, so the MPPT hangs around that point and makes only small adjustments to stay at the the max power point.

Shading is like a broken down vehicle on a single track road and potentially severely restricts the current flow. But the panels have bypass diodes which allow current to flow around the shading or like a passing point on a single track road for other vehicles to get around.

But the bypass diodes only work if the MPPT drops the voltage sufficiently by allowing a lot more current than it would normally allow. Some inverters, especially older models, are severely affected, losing maybe 90% of the power as the inverter stubbornly refuses to find the new max power point.

Some inverters like my SMA ones have a shade management function where if its selected, it does what's called a Global Peak search from time to time. This is in order to search for a second higher peak in a voltage range where normally it would not expect to find one. On an unshaded string I turn this function off because its unnecessary and lowers the total yield by maybe 1% because it occasionally searches outside the normal MPPT range. But on a shaded string its fantastic as once its found a new higher peak, it then sets this as the new max power point to stay around until the next global search. However the inverter can only drop the voltage down as low as the MPPT will operate so if too many panels are shaded it wont work.

Another way around it is to use voltage optimisers on every panel like a solar edge system. Some can work only fitted to the shaded ones where each optimiser acts as a separate MPPT to the individual panels, therefore actively bypassing them and works with most inverters whether they have the global peak function or not.

Quite often you only experience bad shading in winter time when there is next to nothing being generated anyway so does not do much to reduce the overall annual yield. Also if its a cloudy day shading obviously does not affect the yield either.

[nowty]

openspaceman, I am trying not to be nosy here as there is a reason I am asking.

What is your normal annual kWh yield and roughly where in the country do you live, like county will do or even South coast, etc.

As you have a SW facing 4kW system I can work out what your normal annual yield should be, and if it isn't far off I would not worry about the shading.

Example my main 4kW SSW facing unshaded system on the south coast makes around 4000 kWh a year and if you live in say NE England an unshaded syatem would be 3,500 kWh.

[openspaceman]

Hi Nowty

I am in NW Surrey and average yield has been about 3600kWh year on year.

My nosy comment was more related to FIT as I had a bit of flack from a neighbour about my payments were at the cost of his standing charge, water under the bridge now.

[AE-NMidlands]

Hi Nowty
My nosy comment was more related to FIT as I had a bit of flack from a neighbour about my payments were at the cost of his standing charge, water under the bridge now.

but that is still worth airing. It gives us an insight into the views from outside "our bubble."
https://www.businessjuice.co.uk/energy- ... ity-price/
says

The Feed In Tariff or FiT is another scheme to encourage renewable energy, this one rewarding small scale generators. FiT adds around 1.6% or nearly 0.16p/kWh to our average unit rate.

and I believe that all the historic ones will continue, being uprated at RPI. However I can't spot a date on that, or how it applies now.
It's interesting that both gas and electricity are subject to charges for both Transmission and Distribution costs... The man in the street would see that as being charged twice!
A

[nowty]

Hi Nowty

I am in NW Surrey and average yield has been about 3600kWh year on year.

My nosy comment was more related to FIT as I had a bit of flack from a neighbour about my payments were at the cost of his standing charge, water under the bridge now.

Running through PVGIS (solar calculator) your unshaded annual yield would be about 3,800 kWh.

https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html

So sounds about right then considering all those chimneys, aerials and that higher roof lip very nearby the bottom right edge of your array. If you were under 3000 kWh a year, I'd be more concerned.

As your neighbour has probably more import without solar panels, I'd blame him for pushing up the market prices from too much grid demand.

[openspaceman]

Nowty I made a typo there transposing two digits, over nearly ten years the average is 3060kWh and the alignment is nearer WSW than SW as best I can judge with a compass

[nowty]

Nowty I made a typo there transposing two digits, over nearly ten years the average is 3060kWh and the alignment is nearer WSW than SW as best I can judge with a compass

Still OK as WSW unshaded is 3,400 kWh at your location so your only about 10% down which is what I would expect with the chimneys, etc.

[John_S]

If it is just one corner of the solar array that is getting the shade, it might be worth considering a Tigo Optimiser. You only need Tigos on panels with shading, not on every panel.

There are You tube Videos from M C Electrical, an Australian installer who doe a good job of explaining how they work and the differences between the different types and what works best where etc.