Shading analysis for East facing roof

[balbecdaze]

I've tried a search, read through the MCS powerpoints, hope I've not missed anything obvious ...

How do I fill in the sunpath diagram for an unshaded East facing roof?

Thanks.

 

[whinmoor]

Just write: "No shading" on a blank sunpath diagram and give it to your customer. That's my interpretation of the MCS guidance anyway.

Customer will probably think you're either very thorough or a bit mad.

 

[balbecdaze]

Yeah, I guess I'm going to end up doing that, it isn't exactly following the MCS methodology though. I asked ELECSA too, they said they'll get back to me ...

 

[Gavin A]

as above.

it's the same method for all roofs no matter what the oriention, just point your sun path tool south, and draw on any shading onto the sun path diagram. It ain't going to be massively accurate for east or west facing roofs, but that is currently the only MCS approved method, and they are aware of the inaccuracies and consider that the statement about them being accurate to within +/-10% is adequate.

I and many others disagree with this situation, but that's the way it currently stands... see the thread in the sun lounge for more discussion about this.

 

[Ian-LS]

Erm you can't as the shading methodology is only intended for south facing roofs.....

 

[Gavin A]

Yeah, I guess I'm going to end up doing that, it isn't exactly following the MCS methodology though. I asked ELECSA too, they said they'll get back to me ...

actually that is exactly the MCS method that Whinmoor gave you for situations with no shading.

- - - Updated - - -

Erm you can't as the shading methodology is only intended for south facing roofs.....

the shading method is intended to cover all roofs, it just gets less accurate the further off south it goes.

 

[SolarRoofSols]

it also gets less accurate the further away from Germany you get....according to our MCS assessor!

 

[balbecdaze]

Ok, Thanks for the replies, If I point my sun path tool (or take measurements from the ground with my inclinometer south then the roof becomes a source of shade. So my unshaded panels suddenly get a spurious shading factor. That can't be right surely, what am I missing, do I just ignore the roof?

 

[balbecdaze]

I've over-thought this haven't I? I'm just going to ignore the roof.

 

[Worcester]

What's this brothers in arms .... :82::57:

 

[balbecdaze]

Right, this is still niggling at me. If I want to do a shade analysis for a roof that faces due east, then assuming that nothing protrudes over the ridge, I can just ignore the RHS of the sunpath diagram (from South to West)?

Thanks.

 

[Worcester]

Presumably you have read these documents : Microgeneration Certification Scheme - Solar PV Reference Materials

Reading the above documents it's clear that the Sunpath diagram was developed by using PV*Sol, so long as you can show competence at using that, I don't see how any MCS assessor can say that what you are doing is non-compliant, the above documents say:

The background (you don’t need to know this, but it may help) …
a)The chart was developed by first modelling a series of different shade scenarios using proprietary software. The shade factor for each case was recorded. The initial model assumed a 3kWp system, pitched at 30°, facing due south, located in Birmingham.
b)Shade factors from various different iterations of an MCS chart design were then compared to the model results
c)Once a draft design was established, more modelling was done to see how the chart coped with arrays of different pitches and orientations, and also for other geographic locations The resulting chart is clearly a compromise … as stated in the PV guide it “yields results within 10% for most systems”.
.....
After all, installers are free to use modelling software and present an alternative estimate to the customer if they wish.


and later on:
It is recognised that installers may want to present an alternative estimate of system performance to the client – particularly where they are concerned that the MCS method is not as accurate as they would like.

In such circumstances, the PV Guide states:

“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 a warning stating that it should be treated with caution if it is significantly greater than the result given by the standard method.”