pv logged production analysis ?

[zeus]

Hi All

I've trawled around for some information on this for a while without success, so I guess that either I've been unlucky ... or the information doesn't exist, so ..........

Has anyone with a 'fully matched' array/inverter setup (one where the inverter capacity matches the kWp of the pv array) ever analysed their total production into bands based on a percentage of total production

ie, something like  ....

Location (England (South/Midlands/North) - Wales - Scotland - (South/North) ...... etc
pv Nominal (kWp)
Inverter Max (kW)
Total Production Hours (h)
Total Production (kWh)

10% (of kWp) Band - (h), (kWh)
20% - (h), (kWh)
30% ...... etc
------
Total (h) (kWh)

I think that it would be an interesting exercise in order to understand what conditions are actually producing the bulk of the array output, as well as being invaluable in understanding the affect of limiting the system with an inverter with a lower capacity than the installed pv  ....

Ideas / Comments ...

Regards
 

[nickhlx]

I think I covered this point in my questions to the guy quoting me for my system -

We are looking at around a 2.6 kWp system and the inverters above and below are 2.0/2.5 and 3.0/3.5 kW - however, the difference in cost was about £200, so it would probably be better to go for the larger 3 kW unit, to give some flexibility in being able to add more panels, or not have a unit working at the limit all the time, which can't be good for longevity.

Nick

[wookey]

zeus - I don;t see why it matter whether the inverter is 'matched' or not? The analysis is worth doing in all cases. You just need some way of logging the output to a file then its a bit of perl, or spreadsheet or database foo. I'm not logging mine yet (other than manually via the meter), so no, no data here.

[StBarnabas]

Could do this easily for the StB array if there is any interest.

[KLD]

Zeus,
In OpenOffice the magic function is frequency. Is the attached plot anywhere near of what you had thought of? (It's for a solar thermal system, though  )

Klaus

[zeus]

Hi All

Thanks for replies ....

nickhlx ..... that's the idea behind the thread, to get a feeling for what proportion of the time the arrays are producing at various performance levels, two reasons .... is it cost effective to move to a higher power inverter in a FiT environment & if not what proportion of the time the inverter would be working in the band between nominal and max and what potential production would likely be lost.  

wookey .... the idea of analysis of a system where the inverter rating was equal to/greater than the array is to remove the effect of the inverter truncating the output in high DC conditions.

StBarnabus ..... It would be useful to understand real world daily production profiles, what do you think ..... ?

klaus .... thanks, looking at your analysis, it seems to give the total daily (banded) production against number of days which that output was achieved. This  is quite close to what I was thinking of, but effectively changing the axis to somethng like ..  [%kWp v %hours] .. open to discussion .....


Regards
Z
  

[StBarnabas]

Zeus is this what you were thinking of?

[zeus]

Zeus is this what you were thinking of?

Hi

Thanks, looks interesting, but seems to be a pv version of KLD's data .... it is useful to see the production distribution and I'll see what I can glean from it.

Some background to why I'm looking ....... I've had a number of pv quotations and there is a large difference in the sizing of the inverter when compared with the panel kWp, the worst case being a SB 3300 with a 4.2kWp array, however, the annual kWh in almost every case works out at the same (around 800kWh/kWp per year). There must be a reduction in the annual output (kWh) caused by the limitation of the system by the inverter and this must be directly related to the amount of time where the panels are outperforming the inverter, thats why I'm specifically looking for banded kW production data. As a secondary issue, I'd like to find the same data by month for the winter quarters as I'm interested to see what proportion of the generating time is spent within the %age bands in order to understand what is possible to automatically control on a priority switching basis (probable netbook control)  as power is available.  I've looked for banded insolation data but have drawn a blank, hence the question here.

Regards
Z      

[billi]

 

why should i under size the inverter ?  and not get the matching size ?

Especially if the SB 3300 is considered ,that is less efficient than other bigger Models (some  good makes are even cheaper)

So you loose even more.....

but you can study here and compare  http://www.solar-yield.eu/plant/search

(do not get lost in this Universe  Zeus    )



Billi

[StBarnabas]

Zeus
this is probably more like what you are after.

[zeus]

why should i under size the inverter ?  and not get the matching size ?

Especially if the SB 3300 is considered ,that is less efficient than other bigger Models (some  good makes are even cheaper)

So you loose even more.....
but you can study here and compare  http://www.solar-yield.eu/plant/search

(do not get lost in this Universe  Zeus    )

Billi

Hi Billi

Thanks for link, again the data is consolidated into too large a 'time bucket', I'm looking for what proportion of the available time the system is performing at what level, ideally having this data available by month .... I've looked at climatology/insolation resources without success.

Okay, I understand 16A/phase etc, and the current inverter logistics problems, and that larger capacity inverters from the same manufacturer will increase the overall price and maybe make the quotation uncompetitive, and we're not in too sunny a country ..... but ..... ?

Over the period of FiT payments each 1% of production loss on a 4.2kWp system probably costs something like £500 if the generated income is reinvested  (no I don't want to get involved in a debate on the payback calculation  ) and that's what I want to understand ... what proportion of the overall generation capacity is lost by undersizing by different degrees, so undersizing by 15% results in what loss of generation capacity .... !% ?, 5% ? .... if 1% then it's probably not worth even thinking about, but higher ?? .... then again, there's the other way of looking at it, what's the possible detrimental effect of running the inverter wihin the band between nominal and max capacity for longer periods on the expected life of the inverter, therefore what proportion of the time will the inverter be operating in this band ??, or are the design tolerences on the inverters so great that it doesn't really matter ? .... if that's the case, why is there a difference between nominal and max capacity in the techspecs ? .... it all boils down to a load of obvious & related questions ......

For background, I built my first solar powered radio from a kit in the mid 70's (still got it somewhere  ) and I've had a small off grid setup powering a couple devices for about 4-5 years now, so I'm not a complete novice,  I'm just attempting to make sense of what I've got in front of me and what I'm being told as it looks like there's a lot of conflicting information being trawled out within this sector at the moment (I'll probably ask about inverter siting at some stage as I can't get a straight answer on this either).

Regards
Z

[zeus]

Zeus
this is probably more like what you are after.

Hi

Excellent, spot on, you're a star  ...... i can certainly work with that  .

Zeus

[zeus]

Hi All

Initial quick look at the data looks like about 19% of production is above the 85% threshold, therefore an inverter sized to limit the system to 85% max (not nominal) output on say a nominal 3.96kWp array would result in an overall loss of around £9000 (including compounded reinvestment) over 25 years of the pv FiT scheme ......

Simple logic I know (and certainly open to criticism), but as a rule of thumb and opener for discussion ........  

Z
(Thanks again StBarnabas)

[billt]

Using Navitrons estimate of 750kWhr per kWp per year gives a total output of 78Mwhr over 25 years for a 4kWp array. That's worth about £32,000 uncompounded with 41p FIT, so a loss of £9,000 looks way too much.

Annually it might produce 3,000 kWhr, 19% of that is 570kWhr and you will lose less than 15% of that if your inverter is undersized, or 85kWhr. That's about £880 uncompounded or £1300 at 3% over 25 years. In fact it would be significantly less than that, as the lost power would generally be less than 15%. I also think that 19% of production above the 85% threshold is being unduly optimistic.

[zeus]

Using Navitrons estimate of 750kWhr per kWp per year gives a total output of 78Mwhr over 25 years for a 4kWp array. That's worth about £32,000 uncompounded with 41p FIT, so a loss of £9,000 looks way too much.

Annually it might produce 3,000 kWhr, 19% of that is 570kWhr and you will lose less than 15% of that if your inverter is undersized, or 85kWhr. That's about £880 uncompounded or £1300 at 3% over 25 years. In fact it would be significantly less than that, as the lost power would generally be less than 15%. I also think that 19% of production above the 85% threshold is being unduly optimistic.

Hi billt

I'm simply crunching the figures as below .....

Long term interest rate for investment of 4.2% with tax at 20%, calculated 798kWh/kWp per annum on my roof azimuth & incline, Initial FiT 41.3p & 3p assumed export on 50% generation both invested, an assumed energy inflation of a constant  5% per annum, and an annual inflation rate of 3%, imported energy at 8.9p/kWh, a current  annual consumption of 2900kWh/year and an assumption that this could be realistically halved.

..... and in excess of £9k difference falls out as being the value lost with an 85%kWp cap !!!

StBarnabas's actual production data, my logic, my assumptions. Considering that the data & logic are probably correct, that just leaves the assumptions, but I've tried to be conservative on the assumed figures. Simple spreadsheet exercise & much depends on the reinvestment aspect, and of course, the dataset used may not be typical, but it is currently all I have to go on.

Regards
Z

### Edit .... Just noticed, in your post you have taken 15% of 19% as the lost capacity .... the data shows 19% of generation being achieved above the 85% threshold, so surely that's the loss, 570kWh, not 85kWh.

Z