Optimisers or micro inverter?

[The Solar King]

It is the lack of independent empirical data that makes realistic appraisal difficult for both customer and installer.

I understand the National Solar Centre are doing some side by side testing, but I have no knowledge if string vs micro vs optimiser is one of them. Producing identical shade environments for each array could also be tricky.

It is likely that this is very much horses for courses. It is difficult as an installer to wholeheartedly recommend something you can't be sure provides the incremental benefits claimed by the manufacturer. The claims for Enphase and Solar Edge are very seductive. On a 4kW system the incremental cost of Enphase is double that of Solar Edge.

The one small Enphase installation we undertook, (6 x 265w panels) where there were multiple shading objects, has outstripped the performance prediction. (sorry, it is not on line as customer has got rid of internet!!!).

Running Solar Edge through PVSol shows a good gain in an East West installation over a dual MPPT string inverter. I haven't had time to do the same with Enphase. I would conclude that in some circumstances, their use is of benefit, but not in all.

 

[mbuckhurst]

I've got a system of 14 panels, each with their own Enecsys micro-inverter, I've just found out the hidden costs of on panel set-ups. These are configured as 1 set of 5, 2 sets of 4 and 1 on it's own, basically a string inverter in this setup simply wouldn't work. So far to date the system has outstripped all generation predictions significantly and on the whole I'm very pleased with the output, especially considering the number of shading issues the panel has to deal with.

One of my panels started producing considerably less than the other nearby panels, so I contact my installer, this is around 22 months after the system was installed. First reaction is send out an electrician (callout £60) to determine the panel isn't the problem, then contact Enecsys, it appears to be a software fault, this may or may not be fixed over the air, if not, then a replacement will be sent, and another callout fee for the electrician, so roughly £120 or around 15% of the annual income from the panels.

Fortunately for me the faulty unit is on a single story flat roof with plenty of space, so no need for scaffolding, otherwise we're looking at an additional £100-200 for that.

The cost of this shows that if it happens you can extend the payback period considerably, and if it happened towards the end of the life of the system it might be better to ignore the failure and reduce the output of the system, rather than pay for the replacement.

I suppose the flip side is that you can ignore the problem on a single panel if more cost effective to do so, not an option if you have a string inverter. I just hope this is a single one of failure and I can look forward to no more for the majority of the system life.

mike

 

[SolarCity]

Didn't the installer offer a warranty on their work?

"I suppose the flip side is that you can ignore the problem on a single panel if more cost effective to do so, not an option if you have a string inverter."

Maybe, but panel failure is incredibly unlikely. If ever you're going to have a problem on your roof, it will be from a micro-inverter/optimiser. Not a problem as long as the installer/manufacturer is prepared to support them.

 

[mbuckhurst]

Didn't the installer offer a warranty on their work?

"I suppose the flip side is that you can ignore the problem on a single panel if more cost effective to do so, not an option if you have a string inverter."

Maybe, but panel failure is incredibly unlikely. If ever you're going to have a problem on your roof, it will be from a micro-inverter/optimiser. Not a problem as long as the installer/manufacturer is prepared to support them.

It is warrantied, against poor workmanship, which I guess if there's a software fault on an Enecsys inverter it would be difficult to claim it was the installer's fault - I'm not happy about this reaction but can't really see how I can do anything else (the call out was for a 5 minute visit, so hardly justifying the £60 fee). I'm going to try and get something from Enecsys, but am not holding my breath.

What I meant on the single panel failure, if I had an inverter fail on the higher roof mounted panels, thus knocking out a single panel, it would cost in the region of £200 in today's money to install the inverter replacement before the cost of the inverter was considered, so you're probably looking at a cost of at least £300 to replace, if you're in the last year or two of the FITS scheme, it's doubtful whether it would be worth spending the money.

mike

 

[Worcester]

if you're in the last year or two of the FITS scheme, it's doubtful whether it would be worth spending the money.

Yes it will be - how much do you think 'leccy is going to cost in 18-23 years time

 

[Gavin A]

Yes it will be - how much do you think 'leccy is going to cost in 18-23 years time

won't it be too cheap to meter after the gas fracking revolution?

[/George Osbourne mode]

 

[mbuckhurst]

Yes it will be - how much do you think 'leccy is going to cost in 18-23 years time

That's a very interesting question, so I did some maths, from a government source (probably about as reliable as a Bernie Ecclestone testimony), it seems the annual average price rise between 2004 and 2011, works out at 15% per year, this means my faulty panel would generate around £400 of electricity for it's final year if this trend was constant and continued for the next 23 years.

I estimate the current cost of repairing a single inverter, on my more inaccessible parts of the roof at around £300 today, so factor in a small inflationary rise over the period would mean that it would actually be worthwhile getting it repaired so long as I could expect 16-18 months of further generation from the panel at whatever time, even if FITS was no longer paid, just so long as I use or get paid for 100% of the electricity

This of course doesn't take into account FITS, but at a guess this would significantly shorten the period required to generate pay back for the repair.

So there you have it, you're correct it probably would be worthwhile repairing no matter what time it happened.

mike

 

[The Solar King]

Here is an option suggested to me recently by someone who should know:

Use micro inverters for those panels affected by shade and a string inverter for those not. Interesting idea in the right circumstances.

 

[SolarPro]

Enphase outperforms Solareddge according to the ONLY independent test results available from PV evolution labs at :- dated Sept 2013 so very current.
http://www.metgen.co.uk/assets/download/index/assets/122/

There are three U tube videos available here about why Enphase is better
Enphase Inverters | Solar PV & Renewable Energy Trade Supplier | Metgen, UK

It is interesting to read that you found a review in which Enphase outperforms SolarEdge. I found two recent reviews that show the opposite.
One is by the US NREL-institute, also from 2013.
SOLAREDGE POWER OPTIMIZED INVERTER SYSTEM OUTPERFORMS STRING AND MICRO INVERTERS IN NREL-DESIGNED INDEPENDENT TESTING | AltEnergyMag Press Release

The other one is by the German Photon test-laboratory also from 2013. I haven't got this link available at the moment, but I will look it up.

This is important to me since both products (Enphase and SolarEdge) are hot in the market.
Especially because the warranty on the central inverter of SolarEdge can be extended to 25 years and then the their offer is considerably cheaper than Enphase.

SolarPro
Netherlands