Correct Inverter Choice?

[babba]

Meanwhile, I'd like to say some about the 'shade' and the 'dual mppt' issue.
As some of the panels are in shade sometimes, a dual-mppt is needed. I agree with MEP ELEC LTD, who said----

"I think a dual MPPT would be better as when the three panels are shaded then all 14 are working to the three shaded panels !!!if a dual MPPT was there the 7 on the unshaed string would work to full."

The voltage of the shaded panels will drop. If the two strings are not equal in voltage, the higher will charge the lower_this will reduce the lifetime of the panels!!!

Got a question on the back of this Quote

..what about the bypass diodes...?????

 

[Dave-geo]

Hi dave, I think there is severe problem with the system.I have check the pramater of the inverter as well as the panel.
Inverter, MPPt 230~500v, input power 4600w, output power 4400w.
Panel, 245w, open voltage37.7V, operating voltage 30.1V.

Are you sure there are in two separate strings? If so, the system's open voltage is 264V, operating voltage is 211V(which is out of the inverter's MPPt voltage range), which is too low for the inverter. It means the inverter can't working properly...

Meanwhile, I'd like to say some about the 'shade' and the 'dual mppt' issue.
As some of the panels are in shade sometimes, a dual-mppt is needed. I agree with MEP ELEC LTD, who said----

"I think a dual MPPT would be better as when the three panels are shaded then all 14 are working to the three shaded panels !!!if a dual MPPT was there the 7 on the unshaed string would work to full."

The voltage of the shaded panels will drop. If the two strings are not equal in voltage, the higher will charge the lower_this will reduce the lifetime of the panels!!!

Thanks Kyle this is really useful information.

The system is two strings, typical DC voltage is 220-228 so as you say the MPPT cannot work. I hadn’t spotted that before.

I have just spoken with the installer and his first thought was to put it onto one string to increase the voltage. I mentioned that the shaded panels could then have an adverse effect on all the panels and he agreed. He then volunteered to change the inverter to a twin MPPT model which I guess is the best outcome given this situation.


I have asked if he could supply an inverter which gives me some decent output of stats/information as the HE-t is very good for this. He has agreed. Any suggestions for the most appropriate inverter for this system that will give me lots of information as well?


Regarding the life of the panels mentioned in a previous post what is the best way to maximise that? Do the bypass diodes help or do they only help output when in a shaded system and is this a potential warranty problem if things do go wrong in the future?


Thanks to everyone who has posted on this thread it has really helped me.

 

[babba]

I vote for a power one 3.0 outd

 

[kyle simpson]

My friend explained to me that the shaded panels are not to be re-charged and its life-time shall not be affacted by the bypass diode, sorry, I made a mistake...

Anyway, the power points of the two strings are not the same when there is a shade, so the inverter will not find the Max. power point of the PV array, it's sure that there is a little bit waste of power in this panels. Do you agree with it?

And the most important problem in this system is that the array voltage is not in the inverter's MPPT voltage range...

 

[Dave-geo]

An update on my situation.

I have spoken with the installer and he has agreed to change the inverter to an SMA with twin trackers. This would be free of charge to me and although he made a mistake in fitting the original inverter I believe this is a responsible approach by him.

The second option would be to change to a Solar Edge system. He would change the inverter free of charge and fit the power boxes free of charge. I would have to buy the power boxes and pay for the scaffold.

I believe given the harsh shading to three of the fourteen panels that the Solar Edge system would be a significant improvement. I need to budget about £650.00 for the power boxes and maybe £400.00 for the scaffold so it is not a cheap option having already paid for the system. Do you think it is worth the extra at this stage? It appears that the installer might actually be making some money if we go this way due to the reduced cost of the inverter and limited work required to fit the power boxes.

If we went with Solar Edge would we be better using just one string instead of the current two? The DC run is about 24M.

I have to supply the power boxes. Any suggestions of a supplier who would deal direct with a consumer at a sensible cost? As you can see I have budgeted £400.00 for the scaffold, is that about right for a width of 7M and height to gutter of about 5.5.M?

Thanks for all your help it is really appreciated.

 

[Glen Powell]

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.

 

[Glen Powell]

Which SMA some also have a high start voltage?

 

[Glen Powell]

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.

 

[moggy1968]

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.

 

[Glen Powell]

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.

 

[moggy1968]

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

 

[Dave-geo]

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!

 

[SolarCity]

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.

 

[Dave-geo]

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.

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]

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.