The effects of shading on solar PV

Martyn1981

zeupater wrote: »

.... or that for your location, mornings are generally cloudier than afternoons !

That's why I suggested comparing to PVGIS as I thought (hoped) that the climate model would take this into account. For Devizes (just a random pin) E v's W is very similar.

Clearly, this isn't foolproof, but comparing relative performance against targets may show up any shading anomalies. However, you probably also need to check the euro-efficiency ratings of the inverters too. The difference between my best and worst is about 5%.

Mart.

theboylard

That's a nice article, explains things quite well although there is a little confusion over hard/soft light/shade, but I'll forgive them that for the insight given!

Interesting comment about certain panels:
"The only company that does not add silver to their cells to my knowledge is Sunpower, as their solar cells are made with a different process to allow more light to be collected. The tradeoff is more harvesting capability per module in exchange for letting even tiny amounts of shade completely devastate production."

So their opinion is to not use Sunpower if you know you have shade issues, or are considering some kind of optimisation (SolarEdge stylee or micro-inverters)?

Intersting too how having 2 or more strings introduces a possible issue (volatge mismatch) - this may explain why SolarEdge suggest single strings?

Although they finish the piece being quite dismissive of optimisation, some of the comments in the article clearly indicate they aren't from round these parts (Northern California), which might explain why they wouldn't install on a roof that suffers shading!

Still, a good read and may lead to a better understanding for some of the explanations given by installers.

pinnks

Mart,


Devizes is not that far away from me, so my morning and afternoon data is probably not dissimilar.
My inverters are bot SMA 1600TL and 4000TL, which, from memory, have similar efficiency. (just checked - the 1600 is 95%; the 400 is 96.4%)


So, we know thru shading has a significant impact from the photos are associated generation numbers but I think I have lost the plot in terms of how to get a handle on the probable impact.

Martyn1981

pinnks wrote: »

Mart,


Devizes is not that far away from me, so my morning and afternoon data is probably not dissimilar.
My inverters are bot SMA 1600TL and 4000TL, which, from memory, have similar efficiency. (just checked - the 1600 is 95%; the 400 is 96.4%)


So, we know thru shading has a significant impact from the photos are associated generation numbers but I think I have lost the plot in terms of how to get a handle on the probable impact.

Apologies, but I did have a good chuckle at the lost plot part.

So, if we keep making general assumptions, assume weather is balanced (over a year) in your location (quite a big assumption), then the 5.5% difference drops to 4% when including the inverter efficiencies.

TBH, think I've lost the plot too now, but if the assumptions are fair at this stage (even if wrong!) then 4% is simply to close to call, and even if it's right, then probably not worth bothering with?

Just thought of another issue, and this one will give you a headache, but where are you getting the split generation figures from? Do you have 2 TGM's, or are you reading off the inverters?

Meters are pretty accurate, but still have a tolerance of about 1%. Inverters can be out by more, my SB2500 is 1% lower than the ESE TGM, my SB1200 is about 2.5% less than the ESE TGM (extrapolated from a 2 week delay in switching the smallest system on), and my SE2200 is about 1% more than the WNW TGM.

So there's another potential reason for 1 or 2% of difference. :doh:

Mart.

KevinG

Waywardmike wrote: »

There is a lamp post outside my neighbours house that in dec-feb casts a shadow across the bottom corner of the panels in the afternoon, and the impact is huge, sadly there's nothing I can do about it

Exactly the same here, except it's a telegraph pole. Luckily it only affects the winter months but it's the main reason I get less than I should in winter.

pinnks

Reading all of my posts I am more concerned with the "auto correct" on my typing - or my typing skills on the tablet, or both - lol.

Coming back to topic, I am taking the generation from the inverters but also have two generation meters - two completely separate systems - and my inverters are also less accurate than the meters but by about the same amount on a time basis, so I guess we can finally disregard one potential variable.

Leaving aside the maths and percentages and the variables, the fact remains that over a 2 to 3 hour period each day my panels range from fully in sun, to one with shade, then two etc from then chimney shadow and the from the main roof ridge. But even when the sun is coming from partially behind that roof 3 panels remain un-shadowed.

Clearly the impact of that will range from virtually zero on cloudy days to something akin to the guessed impact in the linked PDF. The maths could suggest something up to perhaps 100kWh per year, or £16 FiT plus self consumption making that up to say £25 (cooking etc at that time of day); or perhaps up to 4 times that as noted in the PDF.

The lower guesstimate suggests, "nice academic exercise but POs would never repay the retrofit cost" while the upper could suggest a payback period of 10 years if the retrofit costs £1k - which realistically should lead one perhaps to the same conclusion.

Only a DIY retrofit would change that I think but I think one would need to do a fair bit of research on the DC side of the equation before embarking on that, not to mention investing in a scaffold tower (always fancied one of them - lol).


So the answer seems to be, nice idea but go spend the money on a holiday or put it towards some batteries or whatever...

organum

Very useful thread thank you all.

My understanding after reading all this is that power optimisers are the preferred option ignoring cost.

I was surprised about the documented effect small amounts of shade has on output and this mirrors my new installation, an E/W 8+8 panel installation, where odd branches from a tree on the W side cause large drops in output which sometimes recover.

Is it correct that PO is the preferred option ignoring cost?

Thanks.

zeupater

organum wrote: »

Very useful thread thank you all.

My understanding after reading all this is that power optimisers are the preferred option ignoring cost.

I was surprised about the documented effect small amounts of shade has on output and this mirrors my new installation, an E/W 8+8 panel installation, where odd branches from a tree on the W side cause large drops in output which sometimes recover.

Is it correct that PO is the preferred option ignoring cost?

Thanks.

Hi

No, not really .... If you have shading issues ... or ... need to have panels at loads of different angles/orientations ... or ... have a mix of different makes/capacities ... or ... have a poorly matched set of panels then micro-inverters or optimisers might just prove to make a difference ....

.... the downside - you have more connectors and some electronic equipment up on the roof where it rains, blows, gets foggy and is comparatively inaccessible if something fails - and talking about failing, there's more bits of kit to fail. Forget anything you hear about being "half as likely to fail" as a standard inverter, with 16x more items to fail, then the likelihood would logically be 8x higher ....

If you have no specific NEED for micro-inverters or optimisers then it's best to stick with a standard inverter in a readily accessible place ..

HTH
Z

Martyn1981

organum wrote: »

My understanding after reading all this is that power optimisers are the preferred option ignoring cost.

The problem is, you can't really ignore the cost. I'm slowly buying in to all the additional SolarEdge claims for maximising panel performance (as described by Zeup). But .... will all those extras add up to 6%? That's quite important since the SE kit will probably add £300 to a £5,000 install. Even if SE adds 6% to generation, you've only broken even.

For single storey installs, garage, bungalow etc, I suppose you could risk having more kit that might fail. But personally, with a SE system that does everything (and more) that I hoped it would, if you don't have shading, I'm not convinced it's worth the risk.

Hopefully I'll be proved wrong, and my PO's will last 25yrs or more, but for an unshaded break-even gamble, why bother?

Mart.

Martyn1981

I should add, in case it's not already clear, I'm pro SolarEdge in the right circumstances. Also these are high efficiency systems, with very good warranties.

The company seems well respected, and was recently floated on the Nasdaq stock exchange. It looks to have a bright and sunny future (sorry ) since it caters to the 'good roof but has issues' market, which is presumably much larger than the 'good roof, no issues' market.

It also means that for a given roof space and panel system, a bit more clean energy can be generated, a good thing, but there is a cost involved.

Mart.