School PV not producing expected reduction in bills

darrens1973 · Oct 8, 2015

Hi all, I have been asked by my sons primary school if I can help them ascertain why their electricity bill has not shown much of a reduction since they had a 'free' 30Kwp system fitted nearly 4 years ago.

The generation meter shows 108,000 kwh has been produced, this tallies with the total generation figures on each of the 3 x inverters added together.

They have a generation meter between the PV DB and the existing school DB, whats confusing me is that there is another meter alongside the generation meter with no labeling on it, this meter reads 84000 kwh. Both meters are A1140 Smart meters

The school have to give both meter reads to their 'free' PV Installer - ie the local council.

The arrangement at the mains incomer is a set of tails from the supply meter into a set of tail blocks, this then splits into two to feed the school DB and a separately sub metered DB which feeds the Childrens centre next door, which is nothing to do with the school.

I guess really, the school need to have a meter fitted for the childrens centre so that the PV benefit only affects the schools electricity meter.

I have a schematic sketch but cannot see how to post attachments on here !

Any help would be appreciated.

snowhead · Oct 8, 2015

Where does the PV DB connect in?

And are they looking at Electricity costs or total KWH used?

darrens1973 · Oct 8, 2015

Hi the PV DB is connected to a 63a TP MCB in the School DB
Knowing schools as I do probably only talking £££££
I need to spend some time analyzing their history when I have a spare hour or two.

darrens1973 · Oct 8, 2015

TedM · Oct 8, 2015

30 kWp x 4 years x 900 = 108,000 kWh which is a bit on the low side for somewhere like Plymouth, but not by very much, maybe a slight shading issue.

Sounds like the second meter is an export meter and an export of 84000 kWh is pretty high and would explain why their import bill has not reduced by much - the balance being just 24000 kWh over 4 years. Do you know how many kWh the school import is, from their bills?

The schematic would be worthwhile just in the unlikely event that the PV has been wired up-stream of the import meter - click on the little Insert Image icon and select 'From Computer' and then 'Browse' to attach an image. It is also possible that the import meter is incorrectly configured for on-site generation and has added the export to the import bill.

darrens1973 · Oct 8, 2015

Annoyingly I only get a copy from URL option for a picture and not from computer !!!
What I do not understand is the 2 x meters are literally 500mm apart and both between the PV DB and the School DB, how would this know if its importing or exporting ?
30kwp of PV with a meter between the PV and the school DB will nearly always be exporting !
There are a few large trees that do shade the panels, I have no paperwork to show string layouts - yesterday one inverter was generating 7.9 kw and the other 2 were down to 3 kw each so shading is an issue.

I am trying to get the log on details for their energy portal so I can study their history. My suspicion is the childrens centre is getting free electric to the detriment of the school, I also noticed that half of the school has its own incomer which is not even connected to the PV, also as I explained to them, their energy use in the 4 or 5 good PV months is probably minimal compared to the 7 bad months, especially as they have 7 weeks holiday between the end of May and the beginning of September.
Lighting is their biggest current draw, I walked the site the other day and they have about 30kw of lighting that is on most of the time, half of this is not even on the PV system so has no saving - my next step is to try to beg from our suppliers approx £6k of LED panels and tubes to replact the old T8 flourescents they have, this will save around 20kw an hour, just shows that rather than spending £40k on PV the council would have been better off spending £10k on LED lighting !

Marvo · Oct 8, 2015

darrens1973 said:
Annoyingly I only get a copy from URL option for a picture and not from computer !!!

Try using the 'go advanced' option below the reply box then 'manage attachments' and add your image from there.

Gavin A · Oct 8, 2015

the export meter will be done with CT clamps on the tails from the distro board.

sounds like the school has issues with a lot of their daytime load being on the other supply.