Solar PV, Cutting through the smoke and mirrors.

patmanrob

Hello.
I am currently looking into Solar PV and am trying to cut my way through the smoke and mirrors that seem to surround them. I want to share what I think I have worked out and ask for clarifiaction if I'm wrong and for the bits I just don't know.

Firstly, The salesmen seem to go on about the efficiency and A - AAA ratings and material of solar panels. Is any of this relevant?
Surely the panels are bench tested for MCS certification on (Possibly literally) a level paying field, so they can be compared. So a 250W panel does exactly the same as any other 250W panel.
If it's monocrystal, polycrystal, unobtanium, Kryptonite or fairy-dust; if it collects 250W the same as any other, what's the difference?

Secondly, is it just me that thinks the tarrif system is un-neccesarily complicated?

I've worked out the formula for FIT and export Tarrif and once you transpose and simplify (Come on, this is 2nd form stuff) there seems to be 2 simple tarrifs, not one really complicated one.
i.e.

If you have a generation meter AND an export meter:
14.9p per Kwh that goes through your Gemeration Meter plus
4.64p per Kwh that goes through your export meter.


If you only have a generation meter:
17.22p per Kwh that goes through your generation meter. Where it goes after that is irellevant.

This means that the KWhs that leave your property are lost to you. , in other words, use 'em or lose 'em.

Or am I wrong about that?

If I am right, it would seem there's no incentive to let the Kwhs go into the grid, So boiling the kids paddling pool on a sunny day is fine!?

Anyway, enough of me yakin' What do you think?

patmanrob.

rustyg

Most people don't actually have an export meter. Only generation is measured.

They assume ("deem" is the technical word) that you use 50% of what you generate and export 50%. So, you receive 4.64p for half of the total on your generation meter.

Or, as you say, you could also consider it as 17.22p on the whole lot. But, that's going to reduce slightly at the end of March.

I hope that makes sense.

WestonDave

As above most people don't have an export meter so the easiest shortcut to thinking about your FIT rate is the generation rate plus half the export rate which in your case comes to 17.22p.

You are right in that a 250W panel is a 250W panel, however, its not quite as simple as that. Some panels will produce slightly more or slightly less for any given level of sunlight, angle of sun etc etc.

Photon labs supposedly park a load of panels in a field under identical conditions and measure the relevant output of them. - if you are really bored here are the 2012 results (can't find the 2013 ones yet!) - http://www.solar360.com.au/files/YINGLI%20YGE%20Photon%20Module%20Yield%20Test%202012.pdf - not every model from every supplier is there but you get the idea! What it does show is that leaving apart the really old panels (pre 2010) there is about 10% variance between the best and the worst. You'd expect older panels to be slightly less effective because they do deteriorate with time.

In terms of boiling your kids in summer - you are right there is little incentive to export as you get paid for it anyway. There are various methods of maximising your use using things like an Immersun which diverts surplus solar power to heat your hot water tank etc.

patmanrob

Thanks, I thought so re FIT tarrif.

Now, all other things being equal, How do I decide between panels? There must be something I'm missing to put in my formula to work out how much "Bang" I can get for a "Buck".

At the moment I have had Two quotes for systems and, trying to simplify the choices, I have two variables I think I should consider.

(I have lots of other numbers given me but they all seem to be guesswork, so I don't think I should pay them much heed, as they can't predict energy prices, FITs and how sunny it will actually be, any more than I can).

As I don't have an export meter, the only thing that would appear to be important to me is how many Kwh the generation meter clocks up, and how cheaply I can get them.

So, the only thing I have to work with are.

1. The bottom line price
2. The Kwh/year (calculated, I presumed, under testbench conditions and therefore comaparable).

Dividing one into t'other I get either

How much each Kwh/year will cost or
How many Kwh/year I get for each pound spent.

One is £1.67 for each Kwh/year, the other is £2.03.
Or put the other way, £1.00 invested returns 0.599 Kwh/year and 0.492Kwh/year respectively.

So what factor could make the more expensive system beter value?

tunnel

Instead of playing the mathematician a better idea would be to post the cost of the quotes in £k's, what sort of kit you get for that quote, where your situated, is your roof south facing, any shading issues and probably roof pitch(someone else will be along to say if I've missed something). Then you may get a little bit more help. I'm sorry to be blunt but babbling on about figures when we don't have any of the information above means absolutely nothing


Tunnel

[Deleted User]

Mirrors could definitely help with generation but smoke... no way.

Joking aside best read the sticky...

https://forums.moneysavingexpert.com/discussion/3872445

Cheers

patmanrob

OK. Here goes.


Site.
Orientation 0 degrees from South
Inclination 30 degrees
Zone 6
Shading factor 0.99


Quote 1
16x Canadian Solar CS6P-250M-AB Panels
1x Samil Solar River 3680TL inverter
Schueco Roof Mounting System
DC & AC isolators & Electric cabling
Installation & Scaffolding
Generation meter & Connection
Part P Cert
Snow/Wind Calc report
EPC
MCS registration & Cert
10 yr workmanship waranty
Insurance Backed waranty

£6140 inc.
Expected output 3679 Kwh/year
(£1.67 per Kwh per year by my calculation)


Quote 2

17x Panasonic VBHN235se51 Panels
1x Samil Solar River 4000TL-D inverter
Schueco Roof Mounting System
DC & AC isolators & Electric cabling
Installation & Scaffolding
Generation meter & Connection
Part P Cert
Snow/Wind Calc report
EPC
MCS registration & Cert
10 yr workmanship waranty
Insurance Backed waranty

£7460 inc.
Expected output 3674 Kwh/year
(£2.03 per Kwh per year by my calculation)

So which is "Better"?

To my methematical mind it looks like an extra £1320 buys 5 fewer Kwh. Am I missing something really obvious? Or are there hidden factors that now need to be taken into consideration.

Thanks, by the way, for all the replies so far. :j

tunnel

Got to say the first quote looks quite impressive and if pushed I'd opt for that one, Canadian solar are a decent brand as are Panasonic, both will probably carry a 10 year warranty.


You could check the site WestonDave gave to see which would perform better but my gut feeling would be pretty much the same.


Do you need anything that's aesthetically pleasing, ie all black panels for front facing rooves or is the south facing roof at the back where no-one can see them


As for which is better, only you can decide that. Panasonic are a big name which you'd expect to be around in a good few years, can you say the same for the Canadians? How much do you value your warranties?


You are looking at £633 generation with whatever electric savings you can make, as Martyn will say, about £120 a year average. That's a pretty good return on either system

ed110220

A lot of these salespeople will try and confuse you (or not understand themselves) about what higher efficiency panels really mean for you.

The reason for choosing higher efficiency panels is usually because you don't have enough space for the lower/standard efficiency ones.

For example I could only fit a 4kW system on my roof if I went for the highest efficiency 333W panels as I'd only have room for 12. If I had more room, I could achieve the same thing more cheaply with 16 standard efficiency 250W panels.

Ed

patmanrob

Just thought of a way of explaining how stupidly complicated the way of working out the feed in tarrif is.

I shall use an analogy.

Counting sheep's legs. (As if they were Kwh)
1. count the sheep.
2. There are 3 (THREE) legs on each sheep.
3 it is "deemed" that there are additional legs. to calculate the extra legs, count the number of nostrils the sheep has. The number of additional legs is 50% of the number of nostrils.
4. Add the number of legs to the number of additional legs. That is your FIT number of legs.

A Worked example.

I have 8 sheep.
8 sheep x 3 legs = 24 legs.
Each sheep has 2 nostrils.
8 sheep x 2 nostrils = 16 nostrils.
Additional legs = 16 nostrils /2 = 8
Add the aditional legs to the legs
8+24 = 32legs
QED.

The combined feed in and export tarrif is 17.22p.
Sheep have 4 legs.

Martyn1981

patmanrob wrote: »

The combined feed in and export tarrif is 17.22p.

Just in case you thought you'd got your head around this, and that FiT and export were 'locked' together, here's some fun numbers for you:

An install that was registered on 31/12/13 currently receives a combined total of 17.22p/kWh generated* and an install registered on 1/1/14 currently receives the same.*

On the 1/4/14 the older system will receive a combined total of 17.685p/kWh, whilst the newer system will receive 17.285p/kWh. Whilst an install on that date will receive 16.765p/kWh.

Hope this helps.

[*Assuming no export meter, nor the installation of a smart meter, if it's decided to monitor export too.]

patmanrob wrote: »

Sheep have 4 legs.

Not after Sunday lunch in Wales.

Mart.