low output until all panels in sun

[davey_b]

I have an electricity monitor on our 4kw pv system so I can see what the output is and I noticed today that about noon when all but the last 2 panels were in full sun it was outputting 0.3kw. As the sun moved and that last 2 panels came into full sun it went up to full output of over 3kw in about 10 minutes.

We have a solarmax 4200s inverter but I forget what the panels are. My question is if most of the panels were in full sun why wasn't the output high? Why would the 2 end panels need to get sun for it to give a decent output?

Any thoughts much appreciated.

Dave

 

[FB.]

My question is if most of the panels were in full sun why wasn't the output high?

Because a solar array is only as good as the weakest link.

Why would the 2 end panels need to get sun for it to give a decent output?

The shaded cells are not producing as much electricity, so they work at a slower rate than the cells in sun, creating a bottleneck which forces all the other panels to work at a lower rate. Usually bypass diodes in each panel would help to allow power to shunt itself around the bottleneck to some extent.
There may also be problems with the inverter tracking an incorrect optimum voltage, since this optimum will keep changing as panels come into and out of the sun.

 

[FB.]

There may also be problems with the inverter tracking an incorrect optimum voltage, since this optimum will keep changing as panels come into and out of the sun.

To clarify:

When daybreak arrives, no panels have sun but they have enough daylight to generate an output to wake the inverter. 16 panels running at their optimum 30V each for a total of 480V.

Then the sun comes up and twelve of the panels are in full sun while the other four activate bypass diodes because the shaded four are creating a bottleneck. Twelve panels running at optimum 30V each means the array would be best at 360V, but the inverter only scans a small voltage difference either side of what was the optimum at startup, so it doesn't see the new (and very different) optimum voltage so continues to run the array at 480V and therefore way off the optimum voltage for maximum power. As panels come on-stream or off-stream during the day, the optimum voltage will be jumping about all over the place and power production will be well below expectations.

Some inverters will periodically check a wide voltage range for a change in the maximum power voltage. This feature was introduced about a year ago when the tracking of sub-optimal voltage peaks was found to be a problem.

The bottom line is that solar arrays were never intended to be installed where shading occurs. Certain inverter and panel configurations can get mostly around the problem.

 

[SolarCity]

Do you have a picture of the array that you can show us?

It sounds like you're suffering from heavy shading which could seriously affect your potential yield.

What inverter do you have and how long have you had the system installed?

 

[Earthstore]

In my opinion your inverter is a little too large, and your system has not been designed with the shading problem that you have, there are ways to negate the effects of shading but sadly some companies that were installing PV did not have a clue.

From the information that you have given so far, you could have increased your total
generation by having a slightly smaller system and not mounting panels in the shaded area, which would have cost a little less to install but your peak output would be slightly lower.

From what you say, maybe I would have installed a 3.5KWP system and maybe a 3-3.5KW inverter.

As said before some pics would be helpful, panels shaded and unshaded, and maybe inverter too.

I hope this makes sense to you

 

[davey_b]

We had the system installed last September. There was issues with low output and they came back in April and looked at it and output was better. Then I noticed that when it was at peak power it would suddenly drop to 0 and then climb back to nearly 4kw. It was saying "Vac 10 min too high" and "Frequency too high" (see video of this error here: Solarmax error log - YouTube and status log: Solarmax status log - YouTube)

The inverter was replaced but now this inverter is saying "Failure fan2" so I'm going to contact solarmax about this tomorrow.

It's a Solormax 4200s inverter and we have 16 Canadian Solar CS6P panels.

Here is a picture of our array.

As you can see we're getting full sun, it's pretty much straight on the panels and there is a wee bit of shading on the end panels and we're only getting 0.37kw!

 

[The Solar King]

What is the orientation of your house, i.e. is it south facing or near to it?

How many panels could be moves to the left of the solar thermal array?

 

[davey_b]

House is south facing, slightly south west.

Could probably move 2 panels but seems crazy that it can't be set up to cope in this situation and generate a decent amount when it has a bit of shading.

 

[jason121]

Do you have a log burner ?:gettree:

 

[jerriais]

I'd definitely go for Tigo optimisers in this sort of shading case

Products | Tigo Energy

They'll make sure each panel is always producing at it's maximum and you can also monitor the whole system online without changing your inverter.

Ask you local installer if they can do it, or if you're in SE England we'll be happy to quote. I'd imagine it wouldn't take long to recoup the cost considering how much power you're losing now through the shading and poor string design.

Matt T
SunSmart Energy Ltd

 

[davey_b]

Right so am I correct in saying that with this inverter and panels there is no way to get this working properly without either replacing it or retro fitting an optimiser? If that's the case I'm minded to tell the installer to remove it as it's not fit for purpose.

 

[whinmoor]

You've had the system for nearly a year now. Did your quotation say how much output to expect per year? Presumably you're not on target to hit the prediction? If you're miles off, it might be worth having the installer around for a "chat" about why it's under-performing (assuming they are still trading).

Would it be possible to relocate some of the panels to the left or under or above the thermal? Even then, optimisers would probably be a good idea with all those trees.

 

[davey_b]

Right, thinking of going back to installer and suggesting they either install optimisers on each panel or remove the system. Will optimisers like these http://www.buypvdirect.co.uk/Solar_Edge_Power_Box resolve this problem?

On a separate issue solarmax say I need a 2nd replacement inverter as the fan has failed in this one!

 

[davey_b]

Just thinking, if they're having to replace the inverter anyway would it be as easy to install an inverter that has this technology built in? If so what products do that?

 

[The Solar King]

This is one of those where hindsight is a wonderful thing. Was the Solar Thermal installed first? Ideally I would have swapped the position of the two as the ST is less affected by shading than PV and it is easy to compensate by increasing the size of panel used. As it is you appear to have 6SqM of ST which is pretty hefty unless you are using a large amount of hot water.

The PV should have been modelled in something like PVSol to assess the effects of shading and optimise panel placement.

Before going any further, get the issues of the inverter sorted, to ensure this is not the root cause of the problem. If it is shutting down when hot due to lack of fan cooling, the system is hardly going to perform as intended. Where is the inverter located? A roasting hot attic won't help.

With regard to optimisers, they will make some difference, but they are unlikely to come for free. The enhancement in performance needs to be assessed against the incremental cost. Some optimisers require a matching inverter. Solar Edge are about top launch a inverter independent unit, and as yet I have not seen any pricing.

As already suggested, check what performance prediction you were given when you agreed the purchase. Do talk to your installer. It is in everyone's interest to resolve this positively and amicably.