Discrepancies in SAPs

[cj]

Have other people had substantial differences in the SAP calculation between different suppliers?

Quote 1
PV Solar (UK): 22 x 180 Watt = 3,960W x 1100 hours pa, 4,356 KWh/Year 90 degrees, 1% shading,
SAP Calculation = 3,881 KWh
Roof angle 36 deg, orientation 245 deg, Fit 41.3p (Sic) = FIT £1602 p.a. + Export £58 (25% of SAP x 3p) + £349 saving off my electric bill = £2009 saving p.a.   = 14% return, cost £14,500

Quote 2
M&S
18 x 220 Noble panels,3.96 kWp, Estimated output 2,164kWh pa = FIT £894 p.a. + Bill saving £138 pa, + Est Export £32 = £1,032 saving p.a., Cost £14,940
(incl monitoring)

Quote 3
Southern Solar
16 x 245W Sharp, 30 deg South facing, = FiT £1,100, Bill saving £173,  export Payment £40, = £1,313 savings pa  Break even 10 years,  Cost £14,646

Which? example for a 2.2kWp system is £770 FiT, £30 Export, £120 pa bill reduction.

Actual 26/4/11 to 29/6/11 = 924 kwH, (= £400 calculated FiT, £14.32 Export) from Quote 3.


Finally, any suggestions on what percentage of a typical years generation should have occurred in the last 9 weeks? (West Midlands)

[supremetwo]

Why many smaller panels? I got 16x250Wp around £1k less.

Finally, any suggestions on what percentage of a typical years generation should have occurred in the last 9 weeks? (West Midlands)

Try the map at BDPV:- http://www.bdpv.fr/carte_installation_en.php

 

[cj]

The number of panels is what was suggested by the installers. These figures are for the same roof. The quote I accepted had been reduced very slightly when I pointed out Sharp had the new 245W panels, made a very small difference, but they also reduced the additional scaffolding costs  to cover bridging a conservatory on a 9 metre run.  It is not the actual cost I am concerned about, but the difference in similar installed kwp to the estimated payback from 4356 Kwh down to 2,164 Kwh.

The Navitron http://www.navitron.org.uk/page.php?id=140&catId=65 site shows a typical Example site as: 2.1kW South facing = 1824 kWh £789.79, £27.35 Export, £197 Bill reduction.

(My location is South West, with early evening ie 18.30hrs shading.)

[BruceB]

It looks like incompetence I regret.  One of the points of the SAP calc is that is is simple with not many variables so should allow you to compare between suppliers.  And we all have to use it.  It does under-estimate by 10-20% in my opinion in the south of England.  We are allowed to use other estimates in addition (I generally use PVGIS and SMA Sunny Design), but must show SAP 2005.

Inputs are:
kWp of panels
Overshading - none or very little, modest, significant, heavy
Tilt of collector - horiz, 30, 45, 60, vert
Orientation of collector - S, SW, W, NW, N, NE, E, SE

And the answer pops out.
The very best SAP 2005 will give you for 3.96kWp is 3301kWh (south, 30 degrees, no shading)

Regards
Bruce

[JohnS]

You probably have seen the May results here so as to get an idea of what otheres produce

http://www.navitron.org.uk/forum/index.php/topic,14019.30.html

You actual results look fine.  In that 9 week period I produced 563kWh from a 2.1kWp system but I am a little further south so might get more sunshine.

In my first year I got about 1850kWh which was a bit above expectations.  From my understanding the SAP figures are quite conservative.  So about 800-900kWh per kWp per annum sounds right for actual production, a bit more if you are right on the south coast which is more sunny.

Your income figures are all a mismash of units.  The quotes seem to be the old FIT rate of 41.3 and your actual the new of 43.3.  I would say that your first quote was too optimistic and the second too pessimistic.  

[cj]

Yes I was surprised to see Solar PV (UK) used an incorrect rate (41.3p) yet was very optimistic in their payback, hence the figures I posted as they were given.  If only I knew as much 3 months ago that I know now, I would have had more quotes, and on the same basis and queried why they differed so much.

I note http://www.navitron.org.uk/forum/index.php/topic,9750.msg159443.html#msg159443  also though Solar PV was optimistic.

(Sorry I seem to have posted this topic in the wrong thread)

[regen]

Here in West Wales my installer came up with 4400 for a 3.96 kwp ground mounted south facing system with no shading .  SSE queried this saying it was high and said 3200 was nearer the mark.  At the time I told SSE that i expected the answer to be somewhere in the middle- Just passed 3200 today with another 49 days to go!

Regen