What is the best way to overcome the problem of shade from a chimney?

[FB.]

Actually, I think you'd be surprised. Which is why PV Sol is such an excellent piece of software.

You can try different string set ups and it will recommend a best option. No guess work. I've been trying to post a video to show you what I mean.

My concern - and reason for suggesting a left/right split - is there are two different causes of shading, and the shading is at different times of day.
The left-most panels are affected by the chimney in the afternoons and evenings at any time of year.
The lower row of panels are affected by the neighbour's roof around mid-day in winter.

I worry that mixing left and right might end up with a complex mix of shading almost all day. But by splitting off the right-most eight panels they benefit from no shade at any time of day during spring, summer and autumn (when about 90% of annual generation occurs).

But as already said by others: two strings and getting the inverter to scan the voltage should keep losses to manageable levels. However you configure it I would expect it to meet the SAP-2009 estimate for a 3.7-4kWp array that isn't shaded.

 

[SolarCity]

This video shows the shade cast on the roof over a year. It's a long watch but an interesting one.

[video=youtube;49dUf4sYIus]http://www.youtube.com/watch?v=49dUf4sYIus[/video]

It's worth nothing how the shade cast by the chimney affects the array at different times of the year. Shade cast in the winter if far less of a worry than shade cast in summer and you'll notice that the chimney tends to affect the lower row of panels only in the summer months.

 

[telectrix]

What is the best way to overcome the problem of shade from a chimney?


Knock it down???

come on geordie. knock it down is a plumber's solution. as electricians we would carefully demolish it brick by brick, stacking said bricks neatly in the garden for the client to make a water feature from it, being careful not to shade his PV array.

 

[compmad1]

Any chance of some pictures? (maybe screenshot captures from google maps)

The shading might not be as bad as you fear and there are lots of clever tricks which could be used to get the best from the panels even if they suffer hard shadow at certain times of day.

Thanks. I did upload a picture from Google Earth, but being new to the forum, I don't think I am allowed to at the moment. Solar City have put up some good pictures with the PV Sol Expert software. Thanks for all the advice you are giving.

 

[FB.]

Ah, it faces SSE which makes the neighbour's roof shadow on the lower panels worse than expected.

I still wonder if landscape layout (two rows of five or six in landscape close to the apex) - or at least exploring its possibilities with the software - would help the upper row's bypass diodes gradually adjust the panel output so that maybe even without voltage scanning the loss of just one-third of a panel could be sufficiently close to the optimum voltage that the inverter would find it or not be far from it even if tracking a false peak.
The chimney knocking out one-third of a panel in a string of eight is only going to change the voltage going through that string by 10V (out of 240V) which won't be far from the optimum of the curve.

 

[SolarCity]

No, it faces just 10 degrees off south towards west.

 

[FB.]

No, it faces just 10 degrees off south towards west.

Ah, you set the view from the West, rather than the convention for maps which is South!

Looking at the video I wonder whether the changing shade conditions (and the angle from which the shade comes) are sufficiently gradual that a single string of fifteen panels might work surprisingly well because the panels will be affected one-by-one and by only 2% as each bypass section drops out (giving time for the MPPT to adjust).

In summary: I think the shading looks worse than it actually will be in the real world. It will be a nuisance but probably not enough to affect the array's ability to reach its SAP target except in really cloudy summers when we all will struggle! I think sensible design and a quality inverter would deal with most of the problems. I wouldn't be over-keen on micro-inverters because of the hassle if they go wrong (especially if the company behind the warranty is no longer trading at some point in the future).

 

[SolarCity]

Yes, I suppose that is the beauty of the software. No guesswork - just accurate models.

 

[SPARTYKUS]

Not a solar chap but really enjoyed this thread, faskin ating.

 

[Worcester]

@SolarCity, just watched the video..
I would normally have chosen a string inverter (Power One or SMA both with their shading options switched on) configured with the heaviest shaded panels in a single string, configured similar to how FB suggested.
However this summer we did some playing around with string inverters and Solar edge and noticed that at certain times of day the string inverters where up to 30% down on power compared to the SE when we had shading similar to that from the neighbour's roof, i.e only covered a part of the bottom of the panel. - We were actually staggered at the result and so double checked it.

SE is a far better solution than micro-inverters in most cases - See my comments in a previous string about start up voltages on micro-inverters. However you still have to weigh up the extra cost of the Solar Edge over the potentially improved output..

 

[SolarCity]

The extra yield predicted isn't that great. I can imagine at certain times the increase may be 30% for a short amount of time but the modelling doesn't suggest that this would make much difference over the year.

 

[Worcester]

The 30% wasn't across the whole day. It happened to be during the peak sunny periods in the summer (remember that ) when we did the experiments, and we were only measuring instantaneous power, not total energy for the day..

 

[Dave-geo]

I had a very similar problem to this when my system was installed and received a lot of help from this forum the thread is here http://www.electriciansforums.co.uk...ergy-forum/53090-correct-inverter-choice.html

Here is a picture of my shading.



In addition to the chimney I have shading of the bottom panels during winter from nearby trees.

You would have to read the thread to get all the details but the system performed very badly and we changed to SolarEdge.

I have been very pleased with the SolarEdge system. For me it seems to have been a very good solution. The extra cost was not that significant (this was installed when a 4Kw system cost 10-12K) You can also factor in the monitoring which is something you might might have to pay for with other systems.

What the monitoring does prove is how much is lost per panel due to shade, see image below which shows total output per panel since installation.



This shows that there is not much loss due to the shade with SE installed, before the loss was huge albeit on a poorly installed system.

The only downside for me has been trying to deal with SE as a consumer. They really don't want to deal with consumers and for this reason getting the monitoring setup was a nightmare. I still don't have full access so I am unable to update the tariff changes when they happen which is really disappointing. If you do go down the SE route make sure your installer is willing to register your system and update tariffs in the future because you cannot do this easily yourself.

Hope the above is useful.

 

[Geordie Spark]

come on geordie. knock it down is a plumber's solution. as electricians we would carefully demolish it brick by brick, stacking said bricks neatly in the garden for the client to make a water feature from it, being careful not to shade his PV array.

Sorry Tel ... I wasn't thinking - must have been a "Senior Moment".

 

[wersolaruk]

I would strongly recommend people research manufacturers financial situation a certain microinverter company aren't posting great profits compared to solar edge who seem to have it cracked. Enphase and solar edge are made in the same factory in china so quality is there on both products, as for bypass diodes conducting on micros it has a great effect and can totally knock out the inverter making it useless in shading conditions, but as for solar edge it works on a fixed string voltage and is not reliant on min voltages coming for panels the optimiser and inverter work together to adjust the voltage on the panel to optimal output, Dc to dc optimisation is the way for my company and it does not cost 1k extra to install either around 600

 

[whinmoor]

Good thread. Very educational and great contributions from many sources. A couple of thoughts:

1) Have you considered reducing to 14 panels and increasing wattage on each? You could get rid of that 6.7% stinker. Maybe go for Yingli 275s x 14 = 3.85kWp. Combined with the Power One 3.6, this might work ok. Or even BenQ 325s x 12 = 3.90kWp and kick out 3 weak performers.

2) Have you considered going over 4kWp and installing on the opposite roof surface? You could cover both sides and go for G59 or maybe just a few on the other side and stick with G83. Yes, it would increase the overall cost, but it might reduce the pence per watt/peak figure. It could be a real goer with an Immersun-type device. The FiT level isn’t that much lower for the 4kWp-10kWp band these days (13.50p v 14.90p).

 

[Gavin A]

it does not cost 1k extra to install either around 600

fair enough, I'd not checked the pricing recently, seems to work out about that for microinverters

 

[compmad1]

I had a very similar problem to this when my system was installed and received a lot of help from this forum the thread is here http://www.electriciansforums.co.uk...ergy-forum/53090-correct-inverter-choice.html

Here is a picture of my shading.

View attachment 20971

In addition to the chimney I have shading of the bottom panels during winter from nearby trees.

You would have to read the thread to get all the details but the system performed very badly and we changed to SolarEdge.

I have been very pleased with the SolarEdge system. For me it seems to have been a very good solution. The extra cost was not that significant (this was installed when a 4Kw system cost 10-12K) You can also factor in the monitoring which is something you might might have to pay for with other systems.

What the monitoring does prove is how much is lost per panel due to shade, see image below which shows total output per panel since installation.

View attachment 20972

This shows that there is not much loss due to the shade with SE installed, before the loss was huge albeit on a poorly installed system.

The only downside for me has been trying to deal with SE as a consumer. They really don't want to deal with consumers and for this reason getting the monitoring setup was a nightmare. I still don't have full access so I am unable to update the tariff changes when they happen which is really disappointing. If you do go down the SE route make sure your installer is willing to register your system and update tariffs in the future because you cannot do this easily yourself.

Hope the above is useful.

Thanks for the info. In what way was yours a poorly installed system?

 

[Dave-geo]

Thanks for the info. In what way was yours a poorly installed system?

It was a rush job to beat the FIT tariff drop deadline in December 2011.

Fitted on two strings the voltage was not high enough for the inverter. The inverter was not a good choice where you have shade, there are much better choices such as SMA and Power One.

The standard of roof work and internal cabling was poor although this was partially rectified when the installers revisited to install the SolarEdge.

My best advice would be take your time, do your research and preferably use a contributor from this forum for the install. It looks like you are doing all three so will probably get it right.

Hope that helps.