The Great 'Get Paid To Generate Energy' Hunt

zeupater

jackieblack wrote: »

The response I've had from the installers.....

Does this mean
a) reduced output to grid, resulting in reduced FIT payment? In short no. According the system we use (PV Sol a design tool for PV systems) Both inverters will give you pretty much the same yields. The Diehl is actually 0.1% better. Diehl are a huge company and their inverters extremely reliable. We have to use approved products and follow working regulations as we are MCS accredited.
b) that the Diehl will be operating at higher capacity/ under more 'strain' - By having a smaller inverter the overall efficiency of the system will increase, because of the climate we live in the inverter will never have the maximum input going through it and therefore will not be under strain.
(for lack of a more technical expression) - something I have been told will shorten the lifespan of an inverter?

Also, the Diehl appears to be (based on a random sample of websites) a cheaper inverter (£200-£300 cheaper on average) than the Fronius that I have been quoted for. - The Diehl is cheaper because it is a smaller inverter, as mentioned above we have to pick the equipment we use carefully to be able to operate under MCS.

Overall the either the IG30 or the 2100s could have been specified in the design as they will are nearly identical in productivity.

Is this correct?

Hi

I really do love it when this kind of thing happens ...... I'd be tempted to go back to the installer and ask for a comparison of manufacturers efficiency at 85% of installed array capacity .... The problem with comparing specs & efficiencies comes down to quoted figures being based on 'nominal' output ... If all things were equal the limiting effect of the smaller inverter would be about 25kWh/year.

I expect that there was a clause in the quotation which allows the installer to fit a suitably equivalent alternative .... personally I wouldn't consider the substitution of a 1750W(nom)/1900W(max) for a 2500W(nom)/2650W(max) as being a direct equivalent, it may well be a more suitably sized inverter, but that's not the reason or basis for the change. As you are expecting what has been quoted you should consider demanding an equivalent spec inverter or, as Jon has mentioned, a suitable price reduction for the downsizing & rebranding (emphasis on the downsizing) .... chances are that if you do this an IG30 will magically appear ...... looks like a typical margin increase exercise to me ...

HTH

Cardew

If a lower rated inverter was better suited to the system, why specify the larger one in the first place?

jackieblack

Cardew wrote: »

I suspect also where you live in UK is a factor to be considered.

You are a lot less likely to exceed the max rated output for any length of time living in Northern Scotland than if you lived in Southern England.

I live in north-east Essex ( although I usually tell people I live on the Suffolk border - I can see it from my house! )
I've always understood this is one of the driest & sunniest places in the country (lots of people around here have palm trees growing in their gardens!) my roof is almost perfectly south facing and several people have told me that it would not be surprising if my system produced more electricity than the expected/estimated figures quoted to me.

jackieblack

zeupater wrote: »

Hi

I expect that there was a clause in the quotation which allows the installer to fit a suitably equivalent alternative .... personally I wouldn't consider the substitution of a 1750W(nom)/1900W(max) for a 2500W(nom)/2650W(max) as being a direct equivalent, it may well be a more suitably sized inverter, but that's not the reason or basis for the change. As you are expecting what has been quoted you should consider demanding an equivalent spec inverter or, as Jon has mentioned, a suitable price reduction for the downsizing & rebranding (emphasis on the downsizing) .... chances are that if you do this an IG30 will magically appear ...... looks like a typical margin increase exercise to me ...

HTH

Quote does say 'IG30 or similar'

One of the reasons I went with this quote was because I needed the installation done between specific dates and was promised this would be done.
Now they're saying there is no stock of IG30s and they don't know when they'll be able to get one. They would be sourcing this Diehl inverter specially to enable installation within my dates.

Cardew

jackieblack wrote: »

I live in north-east Essex ( although I usually tell people I live on the Suffolk border - I can see it from my house! )
I've always understood this is one of the driest & sunniest places in the country (lots of people around here have palm trees growing in their gardens!) my roof is almost perfectly south facing and several people have told me that it would not be surprising if my system produced more electricity than the expected/estimated figures quoted to me.

The quote you should have been given will take into account your area for the predicted annual output in kWh i.e. electricity units you will generate. e.g. 2,000kWh pa.

The factor being considered here is the peak output in kW at any given time. e.g a max of, say 2.3kW.

There is no question that in mid-summer around noon on a cloudless day your output will exceed the ability of the Diehl to handle that power. However most of the year the Diehl will cope.

The question is will the supposed greater efficiency of the Diehl for the majority of the year outweigh the 'lost' output in summer.

jackieblack

Cardew wrote: »

The quote you should have been given will take into account your area for the predicted annual output in kWh i.e. electricity units you will generate. e.g. 2,000kWh pa.

The factor being considered here is the peak output in kW at any given time. e.g a max of, say 2.3kW.

There is no question that in mid-summer around noon on a cloudless day your output will exceed the ability of the Diehl to handle that power. However most of the year the Diehl will cope.

The question is will the supposed greater efficiency of the Diehl for the majority of the year outweigh the 'lost' output in summer.

So is there any way I can find the answer to that, please?

zeupater

jackieblack wrote: »

So is there any way I can find the answer to that, please?

Hi

The 25kWh loss I mentioned in the earlier post is around the loss which you would expect if all efficiencies were equal between the two inverters based on the array size you mentioned and using 'real world' historical performance data from an existing array as a basis. Remember, 25kWh is worth around £300 over the lifetime of the system (if the inverter lasts that long !)

What you will be told by installers about undersized systems being more efficient etc is really to be questioned. Manufacturers are really good at quoting efficiency data on their literature, but if you look at the efficiency curves for inverters you'll find that they are usually most efficient (DC(IN)/AC(OUT)x100) in the lower regions of their operating band with most reaching maximum efficiency at around a third of maximum load before tailing off by a percent or two .... SMA show example efficiency curves on their literature ( http://download.sma.de/smaprosa/dateien/5682/SB1200_3000-DEN102310.pdf ), Fronius & Diehl don't. What does become clear when comparing different inverters is that there is no direct relationship between the inverter capacity and the point at which they cut in, for example (http://www.diehlako.de/fileadmin/diehl-ako/downloads_photovoltaik/Prospekte/Brochure_WR_S-EN1007_731534_AF.pdf) shows a difference of only 4W between a 1.8kW(max) and a 4.2kW(max) system in the same range, so effectively no difference in the origin of the efficiency curve.

A study conducted in Belgium ( http://www.esat.kuleuven.be/electa/publications/fulltexts/pub_1057.pdf ), so not that far from Essex (sorry, Suffolk county line ), seems to conclude that the reasoning for undersizing inverters is purely an investment/cost choice (either to the installer or customer) and that on larger systems (2kW +) it is recommended to keep the rated inverter capacity close to the array capacity (kWp).

It all comes down to cost .... either to what the customer is willing/able to pay or margin to the installer, in your case I suggest it's the latter ..... so push for a 'more equivalent' inverter, one which will fully match, or surpass, the performance of the IG30 on which you signed contracts.

HTH

zeupater

jackieblack wrote: »

Quote does say 'IG30 or similar'

One of the reasons I went with this quote was because I needed the installation done between specific dates and was promised this would be done.
Now they're saying there is no stock of IG30s and they don't know when they'll be able to get one. They would be sourcing this Diehl inverter specially to enable installation within my dates.

Hi

Following on from the post above, I've just been reading the specs on the Diehl inverters ...... looks like the Diehl 2800S (2400W(nom)/2600W(max)) is close to being the Fronius IG30's (2500W(nom)/2650W(max)) twin brother ..... might be an idea to ask for performance comparison on the 2800S through the installers configurator software if they're in free supply .....

HTH

jackieblack

Cardew wrote: »

If a lower rated inverter was better suited to the system, why specify the larger one in the first place?

I asked them
If the two inverters are nearly identical in productivity, but the Diehl is cheaper, why do you not use this one 'as standard'?

and got this reply:

It really depends on the system we are designing, say a 13 panel system for example we definitely use the IG30 and not the 2100's. So in this case it just so happens that there was two inverters that we could use, it would also depend on what modules we were using, shading, geographical position within the UK, orientation and slope of the roof.

I understand your need to make sure you are getting what you paid for and honestly the Diehl 2100s is a good inverter for your system.

I'm not convinced.....

zeupater

jackieblack wrote: »

I asked them
If the two inverters are nearly identical in productivity, but the Diehl is cheaper, why do you not use this one 'as standard'?

and got this reply:

It really depends on the system we are designing, say a 13 panel system for example we definitely use the IG30 and not the 2100's. So in this case it just so happens that there was two inverters that we could use, it would also depend on what modules we were using, shading, geographical position within the UK, orientation and slope of the roof.

I understand your need to make sure you are getting what you paid for and honestly the Diehl 2100s is a good inverter for your system.

I'm not convinced.....

Hi

Is your 2.2kWp system a 13 x170W panel installation ? ..... if so I'd question why they would have originally planned to 'definately not' use the Diehl 2100S on your 13 panel install ..........