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Glen Powell

• Mar 18, 2012

• #21

Power one would be a good choice as its MPPT starts at 100v however you would be right on the knuckle for maximum input power so could be classed as undersized, A steca 2010+ with slave will give you multiple MPPT and start at 80v which means even on a very shaded roof useful electricity will generated.

As already stated in this post the shaded panels can pull down the rest of the system.

In my opinion if the system is incorrectly designed and the installer has given you a different product then that product should be equivalent or better than the original specification. This should all be at the cost of the installer, if he has made a mistake he can rectify it and sell on the inverter or claim it under his insurance variant on the insurance cover that is.

I do not have PVsol on my home computer so cannot do any simulations to assist you but maybe I could look at this in work should I get 5 minutes unless one of the guys on here have it to hand. What I will say is PVsol does not like the steca as it is a combination inverter system so it will not give you the option to string it correctly on the simulation software.

Some people will say this install is an ideal candidate for micro inverters, please do not go down that route, they sound good in principle but they do need a lot of power from the panel before they start up.

 

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Glen Powell

• Mar 18, 2012

• #22

Which SMA some also have a high start voltage?

 

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Glen Powell

• Mar 18, 2012

• #23

Maybe a samil solar river 3300TL would be better sized its just a shame that the MPP range starts a 200v which is not good for shading issues.

 

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moggy1968

• Mar 18, 2012

• #24

to be honest, if your voltage is dropping to that amount then your output will be so low as to be irrlevant anyway. voltage isn't the main thing affected by shade, current is. picking between, say, 120v and 200v as start up current is pretty meaningless if it is just for reasons of shade or trying to extend the time the array is generating in a day (rather than total voltage limitations due to the number of panels). Most systems will still be generating good voltage right at the end of the day when current is down to 0.1a
voltage is affected more by temperature.

 

Last edited by a moderator: Mar 18, 2012

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Glen Powell

• Mar 18, 2012

• #25

I totally agree but if there is only 3 panels shaded he could put them onto the single string, better with 4 to ensure maximum production from the rest on the other string as both the powerone and steca are capable of unbalanced loads.

 

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moggy1968

• Mar 18, 2012

• #26

hmmn, tricky, might be worth sacrificing one panel onto the smaller string to get the voltage up.

 

OP

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Dave-geo

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• Mar 27, 2012

• #27

Another update!

The system has now been connected temporarily on one string. This brings the string voltage in line with the inverter so the MPPT is now working. The difference in output is incredible at about 45% increase.

Of course the shading now drags down the complete system not just the one string and this is shown well in the following graph from yesterday. It is a huge improvement but the shade is still a considerable problem. If you look at the graph the early morning production is poor when three panels are shaded. When the shading is reduced to just one panel there is a big jump in production followed by a further jump when the system is shade free




I now have to work out what the final solution should be and believe I have three choices.

1. Install PowerOne inverter on two equal strings of seven panels. This would be a simple operation and only involve changing the inverter. The downside is 7 panels would still be dragged down by the shading.

2. Install PowerOne and change the strings so ten panels work on one string and four on another, the four panels are the ones that receive shading from the chimney. This would minimise the shading issue and still give a decent string voltage on the four panels. The PowerOne should be able to deal with the unbalanced strings. The problem with this is the 50° roof pitch as I expect we would require scaffolding to complete this.

3. Change the system over to Solar Edge. Then the shading is only a problem on the individual panels. The downside is the cost of the power boxes and again scaffolding may be required.


Any thoughts on which of the above options would be best and if would be scaffolding be required?


Any comments would be really appreciated.

Note - Image above is correct, thumbnail below is previous Monday and I can not work out how to remove it!

 

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Last edited: Mar 27, 2012

SolarCity

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Arms

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723

• Mar 27, 2012

• #28

Thanks for the post. This is really handy data.

To answer your question, I would personally go for the Solar Edge system. If the cost is an issue then I'd go for the Power One option. I would definitely check out getting 4 panels onto one of the strings and see how it comes out.

 

OP

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Dave-geo

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• Mar 27, 2012

• #29

SolarCity said:

If the cost is an issue then I'd go for the Power One option. I would definitely check out getting 4 panels onto one of the strings and see how it comes out.

Click to expand...

Thanks for your reply.


Regarding cost I am quite happy to pay for the power boxes on a Solar Edge system but believe this should be subsidised by the cheaper inverter that would then be used.


Scaffolding is the real issue regarding cost. If we went for a 10/4 string split then scaffolding may be required and likewise may also be required to fit the powerboxes on a Solar Edge system. Therefore I think the cost should be split between the installer and me but we can’t agree on that at present.


He also hasn’t confirmed if scaffolding would even be required hence my question regarding this.

 

SolarCity

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Arms

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• Mar 27, 2012

• #30

I'd say that a Solar Edge system would be an upgrade and that is reasonable that you should expect to pay the difference.

However, I think that as the inverter was badly installed in the first place I wouldn't expect to pay anything towards scaffold nor replacing of the inverter.

 

J

jupestar

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33

• Mar 27, 2012

• #31

interesting post and it's a tough call with out seeing the job it's hard to know. power one, or solar edge both good options. if you need a scaffold might as well do the solar edge, but without seeing it istough.

i will add this, my dad had one of the first fit eligible installs. and had a steca inverter which lasted less than a year, it completly stopped working. the installer replaced it with a fronius but changed it to single string mppt (despite there being a big chimney right in the middle). i suggested he complain that they changed a dual steca to a single mppt which was not suitable for his install. he did and now has a power one. he's been monitoring it a bit,not crazy, but just keeping an eye, and he swears blind he got best production from his fronius.... and looking as his scribblings, hes actually right. the higher voltage by having all the panels on one string was actually better.... no real point to that story other than you can do all the computer simulations you want in real life it doesn't always work out.

 

Last edited: Mar 27, 2012

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Glen Powell

• Mar 27, 2012

• #32

I would check out the total tech spec of the optimum start up wattage before choosing solar edge, you may not be happy with the results, see if you can get a sale or return deal.

 

LightGEN

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• Mar 31, 2012

• #33

I haven't checked to see if the panels already installed are in their compatibillity list, but how about Enecsys Micro-Inverters? Enecsys had some production issues last year but these seem to have been resolved - we installed a system, based on these, at the beginning of December and we're happy with it so far.
SMA is launching a micro-inverter some time soon.

 

OP

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Dave-geo

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• Apr 1, 2012

• #34

A further update!

Since connected to one string to increase the voltage to suit the MPPT the increase in performance has been tremendous. The voltage is now fine at all times even when shading occurs however we still need to decide on a permanent solution.

I am really surprised at the problem the shading causes. I have placed below a picture of the complete roof and chimney to show our system. It is 14 Bosch 245w panels on a 50° roof facing due South.



With the three panels shaded as shown below the system will only generate 0.35Kwh



As soon as we reach the stage of shading shown below (less than 10 minutes after the previous photo) the generation shoots up to 1.95Kwh. Does that seem correct? I have been able to replicate this on every sunny day so it is not a one off occurrence.



There is a further progressive increase to a peak around solar noon of 2.85Kwh as the shade clears the final panel.

Is it possible to use any computer modelling to see which panels should be put in a separate string? It is ok looking at them now but more difficult for me to predict what will happen at other times of the year.

We are also still looking at SolarEdge as a way to overcome the problem but are concerned at the point Glen made earlier regarding the start-up wattage, I haven’t been able to find much information on this.

Any further help or comments would be really appreciated.

 

LightGEN

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• Apr 1, 2012

• #35

I've now checked and see four, apparently different, Bosch 245W panels listed in the Enecsys compatability list. All are model number c-Si M60 - M245 3BB followed by either 11, 13, 14 or 17 to differentiate the four different models.

 

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Gary K

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DIY

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70

• Apr 1, 2012

• #36

Do Bosch allow clamping on the short side? If not, I suggest you get your installer do do the job correctly so that you do not have warranty issues and whilst he has got the scaffold up( at his cost), you can fit the micro inverters as required.

 

OP

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Dave-geo

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• Apr 4, 2012

• #37

I have checked the specification sheet and as Gary says clamping is not allowed on the short side for these panels. What would be the reason for this and is it really something that should be corrected? To alter this now would be a large job and mean ripping the roof apart again which I am not keen on.

 

SolarCity

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Arms

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• Apr 4, 2012

• #38

The reason is generally that the frame hasn't been designed to take the flex when clamped on the short sides. Some manufacturers have a stronger frame and they have passed their panels to be installed in this way - In reality, I doubt that you would have too much issue. However, I would say that if you left them this way then your warranty is effectively over.

 

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Earthstore

• Apr 4, 2012

• #39

I believe it is called fiscal loadings, ie will the panel break when it is covered with snow, also as pointed out it may well flex with the wind and break anyway.

The shading is not good to be honest, but as the sun gets higher in the sky the effects will be less, of course they will be worse all winter.
I hope this helps.

 

G

Gary K

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DIY

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• Apr 4, 2012

• #40

I'm sure its a daft question but why couldn't you put the 2 panels that are on the right, to the right of the chimney under the solar water panels? The shading would then effect fewer panels as the shade obviously can't be to the left and right of the chimney at the same time.