SAP Calculation Spreadsheet

[solarelectrix]

I just checked the calc this morning for a quote - I dont seem to be to find the error in the calculator? May be its been fixed or something but I cant see any diffrence to the way the pv guide indicates... Can some one check this ?

 

[jason121]

I have a lovely spread sheet were you can change RPI, energy increase, and loads more. do you want a copy send me your email

 

[Telegram Sam]

I have a lovely spread sheet were you can change RPI, energy increase, and loads more. do you want a copy send me your email

Much appreciate if you could send a copy to [email protected] (I suspect that I might not be the only one on the forum to be interested!). Does what you have there calculate - for a given set of individual inputs, location, orientation, roof pitch and so on - what the "net" kwh from a 4 kw system is according to SAP?? This seems to be at the root of the discrepancies that I have encountered so far.

 

[TedM]

It looks like the RPI error has been fixed by PaperClip. It was showing 1.03 in year 1 for a 3% RPI setting (with a correct tariff of 15.44p) and then 1.06 in year 2 with the incorrect tariff of 16.4p. It now shows 1.00 in year 1 and 1.03 in year 2 with the correct 15.9p tariff. [glances over shoulder].

 

[jason121]

On its way. Based on Govt SAP.

 

[Telegram Sam]

On its way. Based on Govt SAP.

Give the man an (electrician's) medal!

 

[Telegram Sam]

It looks like the RPI error has been fixed by PaperClip. It was showing 1.03 in year 1 for a 3% RPI setting (with a correct tariff of 15.44p) and then 1.06 in year 2 with the incorrect tariff of 16.4p. It now shows 1.00 in year 1 and 1.03 in year 2 with the correct 15.9p tariff. [glances over shoulder].

Supposing I can now establish what the "correct" SAP 2009 (or 2005 or 2012) net output figure is for my location taking shading etc into account. All the installers claim that their system(s) will achieve better than SAP results in practice (surprise surprise). Are there in your experience grounds for believing that some manufacturers' panels (or panel - inverter combinations) will achieve better results than others? Two of the companies that I have spoken to swear blind that "Black Gallium" panels come in this category, whilst two others say the same of Rec and Rew. Apparently if it is your intention to emigrate to a space station, and you are not short of a penny or two, you invest in some Israeli panels. By contrast entry-level seems to be Canadian Solar plus Aurora Power One, and if all are roughly equally efficient then one might as well go for these for cost and payback reasons.

 

[Earthstore]

Can you tell us how you or your quotes have calculated your shading?

 

[Gavin A]

Supposing I can now establish what the "correct" SAP 2009 (or 2005 or 2012) net output figure is for my location taking shading etc into account. All the installers claim that their system(s) will achieve better than SAP results in practice (surprise surprise). Are there in your experience grounds for believing that some manufacturers' panels (or panel - inverter combinations) will achieve better results than others? Two of the companies that I have spoken to swear blind that "Black Gallium" panels come in this category, whilst two others say the same of Rec and Rew. Apparently if it is your intention to emigrate to a space station, and you are not short of a penny or two, you invest in some Israeli panels. By contrast entry-level seems to be Canadian Solar plus Aurora Power One, and if all are roughly equally efficient then one might as well go for these for cost and payback reasons.

Your starting point with SAP is to know that it is utter rubbish, and at least for all sap's up to the latest release, was based on average sunlight levels for the entire country (or basically Sheffield), so anywhere sunnier than that and you should definitely outperform the predictions unless your installer is fudging the figures.

SAP2005 was based on 80% inverter and cable losses, SAP 2009 was based on 15% inverter and cable losses, but modern high efficiency TL or HF inverters will have average losses of around 5-8%, so right there is the reason that the vast majority of systems seriously outperform SAP estimates even in a wet year like last year. Some companies like this because it ensures their customers are all happy that their system is overperforming, I think it's an embarrassingly unprofessional method of estimating performance.

We use detailed satellite based predictions for that specific geographic area using the actual inverter and cable loss figures for that system, and relatively accurate shading loss figures produced from analysis of a 3d model of the system and shading sources through the year, but still MCS insist that we also include the much less accurate SAP figures for some reason best known to themselves.

And to answer your question, yes of course the quality of the equipment will impact on the performance, but the quality of the design is at least as important, as for example the inverters have a range of efficiencies at different input voltages, so the same inverter could be 92% efficient or 96% efficient on average depending on the way the strings of panels are configured.

Another thing to watch for with the panels is whether they're plus rated or not tolerance or -0/+5W for example compared to -3/+3%, though for some companies they're a bit sneaky and give plus rating figures, but then state that the flash testing machine has a -/+3% tolerance, and then there are the low light performance figures, and the losses with temperature, where -0.45%/K is average, but some panels have -0.4%/K figures, and stuff like the panasonic HIT have -0.3%/k, which would basically mean the lower this figure, the more they'll produce at high temperatures / peak sunlight. Then it's down to quality control, automation and matching of the cells, and the quality of the bypass diodes, construction etc

of the panels you mention, it's worth noting that the REW lot are just ok panels, but they have a premium series that make big claims about being plus rated, having lower degradation etc but in reality are the exact same panel as the classic series they've just reduced the rated output by 20W to start with - which IMO is basically fraud as they're using them to cheat the FIT schemes into being able to claim an extra 8% of FIT.

 

[Telegram Sam]

Can you tell us how you or your quotes have calculated your shading?

I replied to this but the system seems to have logged me out prematurely while composing.
I input "none to light" in both Jason's spreadsheet (which doesn't appear to take location into account) and the PaperClip SAPview one (which does). The resulting forecast outputs from a 4 kw system varied from 2.8 to 3.8 kw which is a great confidence builder ..
I don't see why it should not be possible to
1. Agree and construct a common SAP-baseline calculator for starters taking individual factors into account.
2. By means of a spreadsheet work out by how much any given system would have to outperform 1 in order to come up with an acceptable payback period
3. Ask if there are grounds for believing that any one system can achieve 2, or come near to doing so, in practice.
Of course one can then go into all the technical complexities of system design and construction but the average Joe Soap would need a wet towel and a bottle of best Scotch to make headway, when all I want to do is establish if there is a reasoned case for putting my savings into such a system!

 

[Earthstore]

You are going around in circles.

As I have put before the are so many variables, on paper you could have whatever end result you want, please give up on your calculating.

Ask several people that have had PV for a while, they will tell you.

A customer once said to me, I have my washing machine going, my meter is stationary, and every three months my electric company dump a load of money into my account, it's great.

pv is still one of the best long term investments you can make, but your system has to be designed well for you to get the best returns.

What returns are you looking for?
10% per anum on your investment, index linked? More or less than this?

 

[Telegram Sam]

pv is still one of the best long term investments you can make, but your system has to be designed well for you to get the best returns.

What returns are you looking for?
10% per anum on your investment, index linked? More or less than this?

A payback / breakeven within as near as possible to 5 years strikes me as a reasonable target even if in my circs I am by no means convinced that it is achievable. This is the reason for the homework before taking the plunge.

 

[Earthstore]

PV is a longer term investment tax free also for domestic installs, so you are looking for a 20% return spread evenly over 5 years, as good as PV is I do not think you can realistically achieve that, the banks are retuning what, 2.5%, PV should return you around 10% year 1 then index linked from then on, also your return may rise if energy prices rise, but being realistic not to equal you 20% target.

I still believe these numbers are good for a low risk, tax free investment, but if you are aware of anything better then please share it with us all.

 

[Telegram Sam]

PV is a longer term investment tax free also for domestic installs, so you are looking for a 20% return spread evenly over 5 years, as good as PV is I do not think you can realistically achieve that, the banks are retuning what, 2.5%, PV should return you around 10% year 1 then index linked from then on, also your return may rise if energy prices rise, but being realistic not to equal you 20% target.

I still believe these numbers are good for a low risk, tax free investment, but if you are aware of anything better then please share it with us all.

The big mistake I made at the beginning was to compare PV with banks and building societies. Once you’ve put your money into PV there’s no going back – never ever. Your money’s gone and you depend entirely on the return that it generates.

No doubt your crystal ball is more advanced than mine but I won’t believe anyone’s predictions about what the situation will be in 5 + years’ time. If it’s only jam tomorrow after 10 – 15 years then thanks I’ll put my money into something more modest. If it will only start to pay for itself after (say) 8 + years then I want to be pretty convinced of the (financial and technical) fundamentals first, or I’m a real mug. Whilst doing my “research” I’m keeping an open mind – I remain to be convinced as any of the forum readers in my situation would be. I’d be keen to hear from any readers who have gone through a similar learning curve as mine.

 

[Telegram Sam]

The research that I have been able to do seems to come to a consensus that I will achieve a little over 3000 kWh p.a. from a 4 kW system in my location. I reckon that my own consumption of solar will be low due to the direct mismatch between the times of solar generation and electricity consumption - I have scaled the percentage down to 10% which is way below what most installers like to quote. On this basis and depending on the cost of the system chosen I reckon on a payback period of the order of 8 1/2 years, and 13 1/2 years before a PV installation would equal the return from investing the same amount in a savings account or ISA yielding (say) 4% after tax. These figures will obviously vary depending on the underlying assumptions made, but not the order of magnitude. Conclusion: PV's could well be a good investment for a family on the south coast, but those of us who live in the north and those with limited daytime consumption have to see through the hype and realise that these are very long term investments - to be compared against investments with much higher returns considering how long one's money is tied up.