MCS Guide to the installation of Photovoltaic systems (shading analysis)

[SolarRoofSols]

I've been testing it out on a couple of projects and would appreciate a sense check by someone on a calculation for an aerial.

4kWp
Location 11
pitch - 40 d
Azu - 40 d
Angle above horizon 45 d
Aerial Sited at 20 d west of South

= 4 (kWp) x 849 (Kk) x 0.69 (SF) = 2343kWh

Is this right??

 

[Ian-LS]

:thinking:.....there is no way a tv aerial would cause 31 % shading losses. Is the tv aerial coming into 31 of the boxes for the shading horizon? If so then if using this method (which I for one am not) then I'd suspect that shading losses would be moe like 10% probably a bit less.

Another reason why the shading analysis is at best a draft version for an undergraduate degree thesis, maybe even A level project maybe even GCSE project.

 

[SRE]

PVsol for my Sharp NU180E & SMA 400tl reckon I should be getting 2800ish kwh/pa using SAP 2012 for NW England. Strange that with a phone line running diagonally across the whole of the array I've had 7685kwh in 29 months, the first ones of which were Nov, Dec & Jan .........

 

[Gavin A]

I've been testing it out on a couple of projects and would appreciate a sense check by someone on a calculation for an aerial.

4kWp
Location 11
pitch - 40 d
Azu - 40 d
Angle above horizon 45 d
Aerial Sited at 20 d west of South

= 4 (kWp) x 849 (Kk) x 0.69 (SF) = 2343kWh

Is this right??

have you worked this out as if the aerial is a solid object?

Obviously it's wrong in reality, I'm just checking how you've worked it out using the new / already badly outdated methodology to see if it really is that bad or not.

 

[SolarRoofSols]

How have I worked it out...?

The aerial is about 1 ft from the bottom of the array and the top of the aerial is at a 45 degrees from the bottom of the array.

I have plotted a line from the bottom of the chart to the 45 degrees line and then drawn a circle to see which areas the path of shading will hit - 31 squares in total through out the course of the day.

:willy_nilly:

 

[Ian-LS]

could the aerial not be moved to a position on the roof where its doesnt shade the system?

Also do you not see that just because the aerial hits 31 of the boxes it won't actually cause 31% shading losses? As its only shading one part of the roof where you did the shading survey.

Another case for modelling properties as its quite easy to stick a tv aerial on the roof then model the shading to design the system best to mitigate the shading.

 

[SolarRoofSols]

In this case we are moving the aerial but I am trying to get my head round this method if we have to demonstrate its use.

 

[Ian-LS]

You'll be at it a long time if you are trying to get your head round the method. I'm still baffled by its basic flaws

 

[The Solar King]

Here is Martin Cotterell's (The main author of the ECA/MCS Guide) latest blog on shading etc.

Shade assessment guidance |*Solar Power Portal

Both myself and Gavin have left comments. I would encourage others to do the same. The more people who tell him this whole methodology is pants the better. May be we can get some movement on this.

 

[Ian-LS]

I've commented on it as well. I would urge others to as well.

 

[The Solar King]

There is yet another blog from Martin Cotterell on this here:

How the MCS shade procedure was developed | Solar Power Portal

Please feel free to comment as I have done.

 

[Worcester]

Here's the key phrase:

After all, installers are free to use modelling software and present an alternative estimate to the customer if they wish.

The MIS 3002 says

Solar PV Microgeneration systems shall be designed and installed in accordance with the MCS/ECA publication: Guide to the Installation of Photovoltaic Systems (ISBN 978-0-9574827-0-8– Hard Copy / ISBN 978-0-9574827-1-5– Electronic PDF) – hereafter referred to as The Guide, and paragraph 4.4 below

4.3 System Performance
An estimate of annual energy performance shall be made using the methodology detailed in section 3.7 of The Guide taking account of the actual orientation, pitch, location and over shading conditions.
This estimate shall be communicated with the client at or before the point that the contract is awarded and shall be accompanied by the relevant disclaimers detailed in clause 3.7 of The Guide.

and

"Additional estimates may be provided using an alternative methodology, including proprietary software packages, but any such estimates must clearly describe and justify the approach taken and factors used and must not be given greater prominence than the standard MCS estimate. In addition, it must be accompanied by warning stating that it should be treated with caution if it is significantly greater than the result given by the standard method."

So it's good to know that one of the authors of the guide actually reckons it is more of a guide than a 'regulation'

Time to print that blog post for when the MCS inspection comes around

 

[The Solar King]

Received an email from Gemserve today, as most of you will with these attachments:

http://www.microgenerationcertification.org/images/MCS Shading 1 FINAL.pdf
http://www.microgenerationcertification.org/images/MCS Shading 2 FINAL.pdf
http://www.microgenerationcertification.org/images/FINAL FAQs for MIS 3002 3.1.pdf

Here is the reply I sent to Gemserve:

"I am sorry that you are persisting in your support of this deeply flawed procedure.

First and foremost, it ignores the very first rule of Safe Working at Height procedures that states avoid work at height where you can. This takes precedence over any other consideration you may have within the MCS Guidelines. Failure to follow advice given under the Health & Safety at Work Act and the Work at Height Regulations 2005 can lead to very substantial fines. You state in on slide 33 of the first presentation there is no need to go on the roof, this being the case, why are you even promoting a methodology where in many cases this is the assumed course necessary to undertake a shading survey?

This means a different method of assessment will be used in which drawing a sunpath diagram is unnecessary as more accurate results will be obtained without it.

Our preferred method is 3D modelling in PVSol simulation software. Contrary to what is eroniously stated on slide 25 of the second presentation, it is a measurement method in its own right and considerably more accurate than the sunpath method. Having used this correctly, drawing a sunpath is a complete and utter waste of time. It is of no benefit to anyone except those attempting to defend a methodology over which there was no consultation during its development.

In using this method, we use the identical source of irradiance data as that for the MCS method. It should also be noted that there can be considerable variation within the defined regions set out in the MCS method. Accessing the PVGIS-SAF database by postcode gives a far more accurate dataset.

The software can cope with arrays located on different roof faces and at different inclinations. It can deal with the use of optimisers such as Solar Edge. To suggest modelling every single panel or string using the sunpath method is quite frankly laughable. Should we then present the prospective customer with 16 sunpath diagrams?

Those who intelligently use the software also use it to optimise panel position on the roof and also look at other design considerations to provide the customer with the best possible outcome. The software produces output estimations that are far more accurate including the percentage reduction due to shading. Why then waste time drawing a sunpath diagram to duplicate what is already shown?

Another couple of questions: How would you present a sunpath diagram to a prospective customer where you had suggested lopping the top of conifers in the garden and restricting their height to 6m? I note that within the presentations it states only shading objects within 10m of the array need to be considered. So a proposed south facing array on a single story building on the oppositie side of the street from a twenty story office block is OK?

It is a little cheap to have used 3D screen captures from PVSOL in the presentations to demonstrate the MCS which by comparison is clearly so deeply flawed.

Of vital importance the MCS method takes no account of the equipment specified. All it does is take account of panel location on a roof and possible shading objects. In theory if six companies assess a customers property, all propose the same location of panels of a similar size, all output estimates should be the same. How does the customer then differentiate between the six proposals? The only thing left is price. Is Gemserve really wishing to promote a race to the bottom encouraging installers to fit the cheapest and nastiest equipment?

Different combinations of equipment give different outputs. Some equipment is specifically designed to help mitigate the effects of shade. Different panels of the same rating have different outputs. Different inverters have differing efficiencies. None of this is taken into consideration in the MCS output estimation method. This is verging on farce.

By comparison, the draft MIS3001 standard for Solar Thermal will specifically require the specifications of proposed collector panels to be used in the output calculation, not the generic numbers given in SAP.

Some degree of shading is a fact of life. It doesn't mean an installation shouldn't go ahead, but should be fully accounted for, which is what we do in an intelligent and professional manner.

It should be noted that that MCS/ECA document is a guide. As such how can you justify making guidance mandatory? Guidance is about providing a framework of minimum standards which can be exceeded by those working with them should they so wish. It is not about preventing those wishing to exceed them from doing so. Your current approach is hardly professional. In all of the approach to this issue, you are tackling the effects, not the causes of poor installations and dissatisfied customers. Mis-selling is mis-selling, what ever the reason. A new output estimation procedure will not prevent it. MCS should be about promoting and encouraging best practice not forcing the better parts of the industry to dumb down and double up their processes because of problems elsewhere not being dealt with.

I would urge you to immediately drop your insistence on use of the MCS procedure if an organisation can demonstrate to their MCS assessor that they are using a method equal or better (and safer) to it.

I appreciate that two leading members of my own trade body gave a lot of time to compiling the new MCS/ECA guide, most of which is excellent. This however is one aspect that has fallen short. If I can help to take this forward to resolve the issue in a positive manner, I am happy to do so.

I look forward to hearing from you.

Regards"

I will post any response should I get one.

 

[jason121]

PVSOL is exceptable

 

[Gavin A]

I was just writing something similar and debating whether to send it but if you're going to stick your neck out, then so will I.

Just need to send an email to NAPIT now to ensure they're aware that it would amount to illegal restraint of trade to attempt to enforce the MCS mandatory guidelines now, and request that they don't attempt to enforce illegal regulations.

To the MCS PV working group,

RE your updated shading guidelines, and FAQs.

While I acknowledge the amount of work that must have gone into producing this shading performance method in the first place, unfortunately it doesn't matter how many times you explain it, this shading estimation method is still dangerous and still not fit for purpose.

Please scrap it and go back to the drawing board, consult with companies who really know what we're doing and come up with a method that actually works please as this is just embarrassingly bad. It also breaches HSE guidelines in forcing surveyors to go on the roof when far more accurate alternatives exist that involve no roof work at all - ie 3d modelling and analysis that we've carried out on every quote since 2010.

As a minimum, until a more accurate, safer method can be adopted, I would urge MCS to drop your insistence on the use of the flawed MCS procedure as long as a company can demonstrate to their MCS assessor that they are using a method that is equal to or better than the MCS method in terms of both accuracy and safety.

HSE working at height guidance

As your FAQ's state...

. In such situations, it is important for your assessment to be as accurate as possible, this therefore may require climbing on to the roof, in which case all working at heights regulations shall be complied with in full.
​

The most important working at height guidance is for the duty holder (ie the employing company, us, and advisory budy - MCS) to

'avoid working at height where they can'. ​

In line with HSE regulations we will be avoiding working at height where we can, by not complying with this unnecessary and unsafe piece of mandatory guidance MCS have produced. It remains for MCS to explain why it thinks it appropriate for MCS to issue mandatory guidance that is contrary to the first principle of HSE working at height regulations.

I'd seriously advise MCS / Gemserve to consult with a specialist employment / health and safety law lawyer as well, as I'd expect you will be jointly liable for any injuries or deaths resulting from your mandatory guidance that surveyors should survey close up shading from the roof regardless of whether they have a safer and more accurate desktop method they can use instead. (I also run a consultancy with an expert in health and safety law - MCS is leaving itself wide open to prosecution by HSE, or lawsuits from the grieving family of a dead surveyor here).

Accuracy
Please put the crayons away and start treating the industry like the professionals we all should be by now. We're in the computer age, let us use computers to produce accurate performance estimates rather than crayons and tables that only even vaguely apply to south facing roofs in the middle of the country to produce hopelessly inaccurate estimates that make no allowance for the technology used to mitigate the shading (I'm talking about Optitrac Global Peak and similar full scan functions, combined with the orientation of panels bypass diaodes that can more than halve shading losses from properly designed systems with near shading, that the MCS method makes no allowance for).

In our company we have 1 x 3 year masters in solar PV (including a dissertation on the impact of shading) + 5 years electrical engineering degree, 1 x masters in energy and environment, 1 x BSc hons in Environmental Management, on top of the usual electrical and renewables qualifications, and work closely with Leeds University energy research institute supervising 2-3 masters students a year for dissertations on solar PV. I'd strongly suspect that we have more relevant qualifications and expertise in this specific field within our company than MCS does on this steering group, I did offer to assist with this issue last year, but got the feeling you were already too far down the line with this method to listen to reason. I'd hope you'll take the opportunity now to seek expertise from outside your steering group, given the reaction your method has provoked within the industry.

As a company, we've guaranteed our performance estimates to within 5% since 2010 including in shaded conditions (allowing for variations in sunlight levels) and have yet to need to pay out on this, yet we're being forced to use such a hopelessly inaccurate method as well as our far more accurate methods as MCS seeks to drag the rest of the industry down to the lowest common denominator. MCS should be about the complete opposite of this, it should be about raising standards, spreading best practice, encouraging the use of the latest technology to improve yield forecast accuracy, and the best technology and techniques to maximise yields in shaded conditions rather than treating all designs, and all equipment as if it will perform to exactly the same level.

Many in the industry are absolutely fuming about this, and most I've discussed this with are refusing to participate in it if they have a better method already in place. You don't have a leg to stand on legally anyway if you try to enforce this rule as you didn't consult on it and it breaches HSE guidelines, so please at least change the wording to allow more accurate methods to be used instead of the MCS method, not as well as it.

The question here really boils down to whether MCS wants to encourage excellence within a professional industry staffed by people who really know what they're doing and who customers can have real confidence in, or does it want an industry that's staffed by largely clueless sales people who think that a rough guestimate about performance is adequate, and force everyone else down to their level? Your call I guess, but we won't be participating in your enforced race to the bottom this time, and certainly won't be endangering our staff in the process.

There are several other aspects of your latest guide that we disagree with, but this really is the worst offender and needs to be sorted our rapidly before someone gets badly hurt and customers get too badly misled please.

I would be more than happy to work constructively with the MCS working group and other companies who've taken the same view as us to come up with a workable compromise here for the immediate future, and a more accurate method in the longer term. We previously worked constructively behind the scenes with Ofgem to amend the G83/2 close geographic area definitions during that consultation, so are more than capable of engaging constructively in such processes for the wider good of the industry.

I will try to find time to send a more reasoned point by point report to explain the failings of the MCS method as I see it alongside a method statement for our alternative method, and suggestions for improvements / compromise - I'd actually be willing to update and offer our spreadsheets and method statement for free if it would help the industry to clean up its act and sort this mess out.

ps Please ensure you consult properly on any significant changes in future to avoid this sort of situation occurring.