SAP Calculation Spreadsheet

[Telegram Sam]

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Chose wisely, and you will probably make the best investment of your life.

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I see the thing in 3 stages:
1. Decide if the project is viable in my circs and whether the approximate payback period makes sense. For this the SAP guidelines are presumably the best starting point - except that I am confused by what inputs different installers have used which have led to differing projections.
2. Decide on an installer. I wish it was a simple matter. Without your experience I can only go by gut feeling and the content of various discussions.
3. Decide on the system - make of panel and inverter - if it is possible to draw any distinctions in practice between them, otherwise go for the cheapest "reputable" one - Canadian Solar seems to be one of these. Micro inverters and Solar Edge have not figured in the discussions so far though Aurora Power One seems to be the benchmark.
As a starter for 1 it would be nice if VMan could let me have a copy of his spreadsheet!!

 

[The Solar King]

Have a look at the draft for SAP2102. The irrandiance figures are regionalised and any roof angle can be put in. I have this as a working model and it does improve the accuracy. Sums are quite complex. Shading is still a bit naff.

PVGIS is also good.

An installer who uses PVSol and can properly use the economic model could provide useful projections. It is based on a discounted cashflow model producing a Net Present value for a given investment taking on to account differing inflation rates, the value of money, plus the kind of factors Earthstore mentions.

 

[Telegram Sam]

Is there something somewhere like the spreadsheet which I as a consumer can download myself and at least come to some initial conclusions even if it doesn't provide the complete answer? I hadn't intended to progress to DCF calculations - a simple payback period would be sufficient!

 

[Ian-LS]

Is there something somewhere like the spreadsheet which I as a consumer can download myself and at least come to some initial conclusions even if it doesn't provide the complete answer? I hadn't intended to progress to DCF calculations - a simple payback period would be sufficient!

This is probably what you are after Solar PV (Photovoltaic) Feed-In Tariff Calculator - Discover how much a Solar PV System costs to install and the payback profits from the Feed In Tariff. You can alter the assumptions, put how much you pay per kWh etc. Its a good place to start but obviously won't accurately predict the annual output given you have shading issues.

 

[Telegram Sam]

Great, many thanks. This is not the Excel spreadsheet (each row representing a year in the future) that I have seen a printout of but perhaps this is not universally used. Either way what you have sent is a very useful step forward for someone that takes an interest in these things!

 

[Telegram Sam]

This is probably what you are after Solar PV (Photovoltaic) Feed-In Tariff Calculator - Discover how much a Solar PV System costs to install and the payback profits from the Feed In Tariff. You can alter the assumptions, put how much you pay per kWh etc. Its a good place to start but obviously won't accurately predict the annual output given you have shading issues.

If you dig around in this system it does allow you to change the key variables to correspond to alternative scenarios but apparently not the shading factor and the effect this has on the "net" kwp generated from a nominal 4 kwp installation. Am I missing something?

 

[Earthstore]

To calculate the effects of shading is very difficult, and to be 100% accurate is nigh on impossible.

This is where good system design comes into play,
Depending on how the shading falls on your roof, do you mount the panels portrait or landscape? this depends on which way the panels are divided with the bypass diodes, Which inverter do you choose? SMA with optitrac enabled, micro inverters, solar edge?

If shading is caused by a tree, this will change over 20 years as it grows, Shading is normally(not always) worse in the winter when the sun is lower in the sky, but then systems produce much less in the winter so the financial effects can be much lower.

Or do you install a smaller system to keep the panels out of the shade altogether?

These are just some of the options, and yes there is professional software out there to simulate a years shading and the effects it has, but just using common sense and good system design you can reap the rewards.

Do not be put off by all of this, but choose an installer that designs the best system for you, if they use SMA for example, do the know how optitrac works, (it constantly searches for the highest power curve).

What you do not want is " we have installed lots of ABC inverters and they work great...

PS pleased you have taken notice of the effects of shading, you will reap the rewards.

 

[Telegram Sam]

Thanks for all of this. It obviously goes beyond the ken of the average Joe Soap and into the expertise of a "good" installer, assuming the consumer (me) can identify one or more. I will relay your comments to one or two who I have spoken to who seem to be more clued up than others. In my case now I am simply trying to replicate the "formulas" that SAP uses (I believe) as a first step towards taking into account shading, location and orientation so that I can construct my own payback spreadsheet as a basis for negotiations. If successful this might for a start shed some light on why different installers have quoted different net outputs for nominal 4 kwp system in my location - without which any subsequent comparisons strike me as pretty meaningless.

In my case shading would only be a factor first thing in the morning and last thing in the evening, and there is not much I can do about it whilst staying within reasonable limits of activity (!)

 

[solarelectrix]

I found this new 'zoned SAP caluculator' on the Paper Clip web site which is the new standard in the MCS PV Guide
PaperClip :: SAP Calculator

 

[Telegram Sam]

I found this new 'zoned SAP caluculator' on the Paper Clip web site which is the new standard in the MCS PV Guide
PaperClip :: SAP Calculator

Great, I think this is it at last! It shows my SAP net output as 2278 kwh* and payback as 10 years, and on these assumptions I'd have live to a good old age to achieve anywhere near the £17,000 return that is commonly kicked around in the blurb. Good basis for negotiations with the installers (who now have to prove to me that their system / recommendations can do better!). Many thanks.
*compared with the 3063, 3190, 3314, 3364, 3433 and 3540 kwh's that I have been quoted to date!

 

[Earthstore]

I would have said, judging by the information given, some of your SAP estimates given would be nearer the mark than your calculation, at a guess, around 3190-3314 would be the figure that you would really achieve, maybe a little higher.

Have a look on PVOutput and see if you can find some systems in your area, this will give you an idea of what systems are really producing.
Have a look at several though to get a general idea, as some of the information on this site is not totally accurate.

I hope this helps.

Added, Also try not to screw your installer into the ground on price, they are all running on tight margins at the moment, so to save money corners would need to be cut, something that is not a good idea if you want a good system.

 

[Telegram Sam]

I wish I could understand the discrepancy between the results of what I have input and the figures quoted from installers.

Unfortunately there seems to be little if anything on PVOutput that is comparable to my location and situation - seems that from this one could generate any outputs you want (by equating e.g. Israel with Co Durham!)

 

[TedM]

I think there is an error in the way that PaperClip software calculates the RPI uplifted tariff. With RPI set to 3% is adds 6% in year 2 rather than just the 3%. The tariff is then too high for all remaining years.

 

[Earthstore]

I wish I could understand the discrepancy between the results of what I have input and the figures quoted from installers.

Unfortunately there seems to be little if anything on PVOutput that is comparable to my location and situation - seems that from this one could generate any outputs you want (by equating e.g. Israel with Co Durham!)

Sorry about that, I just had a look too and can not seem to find any, maybe I was not searching correctly, but the site seemed terrible...

Also listen to TedM, he is the father of information on this site.

 

[Telegram Sam]

I think there is an error in the way that PaperClip software calculates the RPI uplifted tariff. With RPI set to 3% is adds 6% in year 2 rather than just the 3%. The tariff is then too high for all remaining years.

I could probably clone the spreadsheet myself hopefully without the mistake - provided that I/we had confidence in the net kwh output as a starting point. I input postcode DH2 1NA (Co Durham), south facing, light to moderate shading [then 10% own consumption, £5500 installation cost, 12 p / kwh] and it came up with the 2870 kwh which you experts (along with "my installers" no doubt) would query. If there is a bug here also I would need to correct it before proceeding.