Predicted yield from non-south facing roofs.

[Martin Dawes]

Having been messing around with a few calculations, I was surprised by the estimated yield that I can get from a PV System that isn't South facing.

Being East or West facing still gives me impressive results. I was under the impression that going past SE or SW would not be worth it - Was I wrong? Or are my calculations wrong?

 

[Markc]

East and West can produce good yields but if there's shading issues then the yield drops harder than being south. One system we have designed but didn't get was a E -W we planned to use two inverters one for the E and one for the W so as the east array fell into shade and the west came out the yield was maximised. Pity we didn't get it would of been good to see the out come.

 

[Martin Dawes]

That is interesting. We are heading down to Cornwall on Friday to look at a potential installation on a school. Judging from Google Earth, their best possible roof is at a 70 degree azimuth. I was ready to dismiss it but it might be worth it after all.

Incidentally, the figures on a north facing roof don't seem that bad either. That can't possibly be right, can it?

By my calcs, using http://projects.bre.co.uk/sap2005/pdf/SAP2005_9-83.pdf, a typical 3kW system would produce 2500.8 kWh per year on a SOUTH facing roof. On a NORTH facing roof, my result is 1701.4 kWh per year.

The south facing roof would make around £1,357 a year and the north facing roof would still make around £925 (assuming that all electricity generated was used by the customer) which is surprisingly good in my opinion.

Am I missing something?

 

[sherbert]

Remember that the sun only rises in the east and sets in the west on 2 days in the year. In the summer the sun is higher in the sky and will shine on north facing roof especially if they are not too steep. Also the sun sets and rises anything up to +/- 120 degrees from due south allowing north facing walls to get some sun although the sun will be low in the sky.

simon
www.http://southwestfreeenergy.co.uk

 

[SRE]

We regularly quote for E/W orientations as long as the customer is aware of the reduced income from Fit there isn't a problem and 12 year paybacks are common. Just a word of caution it's highly unlikely that the customer will use 50% of the electricity produced never mind 100%, this is especially true with anything over 2kwp. We always quote 25% to be on the safe side and our customers are delighted when the system over achieves.

 

[robbobnbill]

we installed a system last year with a south facing array and an west facing array with 2 inverters, the south facing roof already had thermal on it so to get the best returns the west face needed to be used. from feedback we've had from the client the west array is doing great

 

[SolarCity]

7 Just a word of caution it's highly unlikely that the customer will use 50% of the electricity produced never mind 100%, this is especially true with anything over 2kwp. We always quote 25% to be on the safe side and our customers are delighted when the system over achieves.

Our firm advises homeowners to make the most of the electricity that is generated - using washing machines, tumble dryers, showers, dishwashers etc. sequentially rather than all at the same time. I'd say that 50% is on the low side in these kind of circumstances.

 

[SRE]

Highly unlikely that you'll use a tumble dryer during peak production periods. I've been providing advice on energy efficiency atr senior level for nearly 20 yerars and we advise our customers that it's much more realistic to quote 25% for systems over 2kwp and 50% can be achieved with a lot behavioural changes for systems under 2kwp.

 

[SolarCity]

Highly unlikely that you'll use a tumble dryer during peak production periods. I've been providing advice on energy efficiency atr senior level for nearly 20 yerars and we advise our customers that it's much more realistic to quote 25% for systems over 2kwp and 50% can be achieved with a lot behavioural changes for systems under 2kwp.

With that kind of experience, I'm sure you know what you're talking about. However, surely devices that swallow up most of the array electricty (showers, tumble driers, showers, dishwashers) are therefore using ALL of the electricity?

 

[SRE]

Set up and ran an energy efficiency advice centre with £2 million turnover. My team gave advice to around 40k people a year Your washing machine and dishwasher is really only using about .5 to 1 kw for a full cycle. Your right about running the appliances one after the other but even then if you're generating 2kwh/hour and using 1/2kwh for your washing machine you're not going to be using anything like 50% and how often are you running the washing machine? Even doing 2 or 3 loads a day with a large family you'd need to be in when the sun's shining to maximise it. It's up to individual installers really what they quote but after 14 years of free and impartial advice we take the view that pv is a great buy anyway so better to be conservative with the estimates and have the customer delighted if/when it over achieves.

In case you're wondering why we switched sides - money!!!

 

[SolarCity]

Set up and ran an energy efficiency advice centre with £2 million turnover. My team gave advice to around 40k people a year Your washing machine and dishwasher is really only using about .5 to 1 kw for a full cycle. Your right about running the appliances one after the other but even then if you're generating 2kwh/hour and using 1/2kwh for your washing machine you're not going to be using anything like 50% and how often are you running the washing machine? Even doing 2 or 3 loads a day with a large family you'd need to be in when the sun's shining to maximise it. It's up to individual installers really what they quote but after 14 years of free and impartial advice we take the view that pv is a great buy anyway so better to be conservative with the estimates and have the customer delighted if/when it over achieves.

In case you're wondering why we switched sides - money!!!

That's a fair point, well made. We're going to follow up on each of our installs to see how the arrays are getting on and it will be interesting to see how much savings on electricity use are actually made.

And fair point about being conservative with the results. A happy customer is going to recommend - a disappointed customer isn't. Best to err on the side of caution.

 

[renewablerob]

SRE your advice is really helpful. Just setting up a renewables/energy efficiency business and agree with your conservative / considered approach. The last thing the industry needs is over promising and under delivering. Did you have much to do with GSHPs ASHPs/ MVHR when you were advising?!

 

[SRE]

Installed the first public sector ashp's in 2004/5 - all failed over Christmas and we ran round the diy stores buying up oil filled radiators to keep customers happy!! BUT it was mostly all our fault, lack of understanding about sizing systems properly and pretty average back up from the manufacturers. It's all quite different now although you still need to be careful with sizing and predictions. The biggest mistake that I see is the suggestion from installers and manufacturers that the COP is 3.5 - it is at 7 degrees but significantly less in lower temperatures and I've heard recently about a load of ashps that failed at -3. My advice would be research very careful your products and again don't over promise. They have a place in the marketplace for smaller well insulated home off the gas grid otherwise I wouldn't bother. GSHPs are different altogether because you've got a relatively constant core temperature. Didn't get into MVHR much kept getting dragged back into the boring insulation/heating stuff. Another reason for leaving ..

 

[renewablerob]

SRE... used to be a marketing manager for a large distributor of building materials so did a lot of research into renewables before jumping ship... have spent 7 odd months getting my plumbing and sparky qualifications and doing all the BPEC cetificates in unvented / GSHP/ part L/ ASHP / solar thermal / solar pv. Excited about getting going but wary of the risks of relying on manufacturers' claims. The devil is in the detail! Thinking of going with NIBE/Dimplex on GSHP and ASHP. what firm do you work for now?!

 

[SRE]

My own, set up with other half, just doing pv though. Be careful with Dimplex, heard quite a few bad stories recently about their performance. Nebe seem to be ok and Mitsubishi after sales service is v good. They had a problem with one ashp and recalled and replaced all 5,000 that had been installed in the UK within 4 weeks.