PV Solar Shading Question

billythestickboy

Hi,
Hoping someone can help with this question.
We've been looking into PV Solar panels for a while and now just getting round to getting quotes.

We've got a SouthSouthEast facing back roof so thought we'd be a good candidate.

First quote agreed and after a site survey thought we could fit 10 panels on the roof and recommended some SunPower panels to maximise the harvest.

Second quote didn't measure but thought we'd only get 6 panels on the roof. He also thought the trees in our back garden would cause shading issues so didn't think it would be worth our while.

I've been back to the first company who said the trees are far enough away not to cause any shading issues.

The nearest tree is 25m away but they are taller than the house (big Ash trees)

So the question is should I be worried about the shading?

I've got a third quote coming tomorrow, so they might help decide.

thanks
Andy

Cardew

You should be concerned as shading is a very real problem with any solar PV installation.

25 metres, for trees taller than the house, is close IMO; and trees grow!

Martyn1981

Hiya Andy, cheeky answer, but why bother guessing? This is the perfect time of year to check for shading as we are into the bottom 3 months (1.5 either side of winter solstice).

So pop outside when it's sunny, morning to evening and look for shade where the panels will go. This will give you a very good idea. The further from Winter solstice the higher the sun will be, especially with a near south orientation.

If there is shading, this can be addressed with 'clever' systems, but will cost a bit more, and only reduces the negative effects of shading, can't eliminate it.

As to roof size, if you can measure the roof, should be simple (famous last words) to guestimate the number of panels that can be fitted. Measure from inside if necessary.

Mart.

alleco

Hi Andy

Shade is an issue, but not an absolute killer... So, what do I mean by that?

The more light that falls onto solar panels the better. Shade reduces the amount of light so reduces the output. But not only that, shade actually does something funny to the voltages and currents in the electrical circuit running through the panels.

The inverter (changes DC to AC electricity) manages the voltage and currents in the system to get the most power from the panels. The inverter looks for a "maximimum" power point. With shade, some inverters struggle to find the maximum power point. Some inverters can still find it. Those inverters that don't find the maximum power point will control the voltages and currents to give you a much lower output. If you have an inverter that does find the maximum power point then you won't notice much effect, other than loss of shade.

It's easier to explain in graphics, and you may wish to look up SMA Optitrac.

Another way around shade is to control each panel individually.

So, your installers should conduct a shade survey, using sun-path analysis and this will work out the effect of the trees. The key is not the height, or the distance, it's all about angle.

Fruit_and_Nut_Case

billythestickboy wrote: »

...thought we could fit 10 panels on the roof...

...thought we'd only get 6 panels on the roof...

It wasn't obvious to me* when I was planning my system but not all panels are the same dimensions. They are typically (but not always) rated as 250W but the more efficient ones are smaller physically, permitting more to be fitted in a given space.



* but I can be slow on the uptake.

jimjames

These photos show the difference shading can make

http://uk-solarpanels.blogspot.co.uk/2011/11/choosing-best-position-to-install-pv.html

We chose the upper roof for ours as it minimised the shading on the panels. It sounds like your trees are a similar distance to the ones causing shade on our roof

You can also see here how shading affects - this was from an open velux window and caused big drop in output even only covering 2 panels.

http://uk-solarpanels.blogspot.co.uk/2012/07/effect-shade-solar-panels-output.html

billythestickboy

Hi,
Thanks folks, that's really useful info.

Martyn, I've been out checking at various times of the day and it's mostly been clear of shading from what I've seen. Certainly when I went up on the roof at midday with the guy who gave me a quote last week there wasn't any shading then.

Jimjames, I've just read through your entire blog, which has given me lots of insight into what's likely to be generated when and also how optimistic/pessimistic the outputs on the quotes are. (I like my stats so it's really interesting to see how it varies month by month and day by day.) Also, we're in Kent, with a similar roof set up to you, so it all seemed very relevant.

Both companies that have measured have assured me that 10 panels is the number that will fit.

So, I'm pretty much set on a set up using 10 SunPower panels to maximise the harvesting potential. They are more expensive but look like they will generate more and the SunPower warranty seems really good. There's not many companies that are authorised to install the SunPower panels so I've asked a couple of others that install in Kent to see if they can beat the price I've been quoted.

I don't just want to compare on price, so the other 2 big variables seem to be the guarantees that come from the installers (do they cover labour if a panel/the inverter fails under warranty etc...) so I guess I'll be reading through lots of small print for that one. Secondly, what inverter they choose, it seems to be "Samil Solar river" or "SMA Sunnyboy". Can any of you very helpful people direct me to any reviews on those, please?

Thanks for all the help, I feel much more confident going forward on this now!

Andy

Martyn1981

billythestickboy wrote: »

Hi,
Thanks folks, that's really useful info.

Martyn, I've been out checking at various times of the day and it's mostly been clear of shading from what I've seen. Certainly when I went up on the roof at midday with the guy who gave me a quote last week there wasn't any shading then.

Hiya Andy, that sounds promising. But just double check if there is much/any shading when the sun is further to the east and west, when it's also lower. Obviously further from December (nearer to June) there should be less shading with the sun higher and clearer of the trees.

If there is any shading, even if it travels across the roof, the panel(s) affected can cause drag on the rest of the system. This is when you'll need to configure the system appropriately, perhaps multiple strings, micro-inverters, power optimisers etc, or perhaps, just a good quality inverter with good shade management (see next bit*).

billythestickboy wrote: »

Hi,


I don't just want to compare on price, so the other 2 big variables seem to be the guarantees that come from the installers (do they cover labour if a panel/the inverter fails under warranty etc...) so I guess I'll be reading through lots of small print for that one. Secondly, what inverter they choose, it seems to be "Samil Solar river" or "SMA Sunnyboy". Can any of you very helpful people direct me to any reviews on those, please?

Thanks for all the help, I feel much more confident going forward on this now!

Andy

SMA are very well respected, but a little expensive. Samil are much cheaper but also building a strong reputation. Found a few comments regarding/comparing them:

[PV Owner] My Samil is still going like a train, and hasn't missed a beat since installation - they are very configurable using the provided software, and I'd continue to recommend them as a very viable "alternative" to some of the better known names. They're very widely used and respected "down under"

[PV Installer] Remembered the other point with them [Samil's] is that [*]they don't have a full scan function to mitigate shading like the SMA and Aurora versions do, so we don't use them in shaded conditions, in unshaded conditions though they ought to outperform the SMA & Aurora by a percent or 2. Proton magazine gave Samil a very positive review as well.

If you want to do some background reading, check their main sites, but I find this shop useful - not a recommendation - but handy source of comparisons, info, datasheets, prices etc. as you click on makes and models:

http://www.swithenbanks.co.uk/shop.php?c1=Inverters%20and%20Batteries&c2=Grid%20Tie%20Inverters

Mart.

Jule_Alain

I came accross a very interesting website with more info on this product:w
w.archiexpo.com/architecture-design-manufacturer/solar-shading-1297.html

Fruit_and_Nut_Case

Jule_Alain wrote: »

I came accross a very interesting website with more info on this product:XXXXXXXX

I call :spam: on this.

The link is nothing to do with the thread. It is to products designed to provide shading from the sun!

This poster has two posts, both pimping the same web site.

lisyloo

I have solarEdge.
I've been very pleased with my system which has produced up to 25kw (3.9KW system) averaging about 11kw and that's Feb->May.
It's performed above expections.

I don't claim to be an expert but if there's any detail I can provide or questions then let me know.

It was marginal in our case but we felt it reduced the risk for us.
I like the fact that if anything goes wrong with any single panel I'll be able to notice it because they are monitored individually and the web portal/dashboard is good.