Solar PV installation advice please...

2 As and a B · Post by **2 As and a B** » 18 May 2011, 08:56

I have someone from HomeSun coming soon to do a survey for solar PV on the roof.

The roof faces just north of SW, I think, so wouldn't qualify for their rented roof schemes. However, the survey will be free. This started through EAGA, now Carillion.

The roof is rectangular, unshaded except for the very south end early in the morning (next door is slightly higher and briefly casts a shadow and there is also a raised vent pipe), the pitch is about 30 degrees and the area about 35msq (7m wide by 5m rise). The width is free of all the above-mentioned shadows but the rise, which I have estimated anyway, is the total from gutter edge to ridge tile edge - I appreciate that the usable rise will be less.

What sort of solar PV msq size and kWp output could I expect from such an area and orientation? Is it worth leaving a bit of space (by the partially shaded end, which is above the bathroom) for solar thermal?

Any advice or questions to ask the surveyor would be greatly appreciated!

Post by **adam2** » 18 May 2011, 09:15

Even a little shade drasticly reduces the output of PV modules and should therefore be avoided. An exception could reasonably be made IF the shading occurs ONLY in the very early morning or very late evening, since output is very limited at these times anyway.

Solar thermal is much more tolerant, a thermal collecter that is 10% shaded will still produce about 90% of the full heat output.

Any proper solar installation firm should be able to produce a computer simulation of any shading and advise what the impact on output would be.

Presuming that this is a grid tied installation, you may wish to consider the installation of a single additional module for a stand alone battery charging system.
It might be cheaper to do this at the same time, and should result in neater install.
Partial shading of a battery charging module for part of the day, in Summer only is less of a concern. Completly unshaded access to to the winter sun is more important for battery charging.

2 As and a B · Post by **2 As and a B** » 18 May 2011, 09:31

Thanks Adam.

The total roof width is 8.8m (approx - this is calculated from the paving slab size on the patio), so I have discounted the 1.8m at the south end where any shadows would be.

Would 1.8m width by 5m rise (excluding an area around the vent pipe of about 90cm by 90cm at the top right/south of the roof) be sufficient for any useful solar thermal, or should I allow more?

An additional module or two for battery charging sounds interesting. What is involved in getting it to work? And could key electricals in the house (fridge, freezer and my wife's airbed, feed pump and suction pump) be run on both the grid and the battery?

I am not an electrical expert. I got lost around the time of designing traffic light systems at school!

Post by **adam2** » 18 May 2011, 11:48

foodimista wrote:Thanks Adam.

An additional module or two for battery charging sounds interesting. What is involved in getting it to work? And could key electricals in the house (fridge, freezer and my wife's airbed, feed pump and suction pump) be run on both the grid and the battery?

Rather than take this thread away from the proposed grid tied PV array, I will start another on this subject.

New thread here
http://www.powerswitch.org.uk/forum/vie ... 973#176973

emordnilap · Post by **emordnilap** » 18 May 2011, 12:08

Not wishing to derail the thread but wouldn't solar DHW be a better investment first? What do people think? Or do you already have that, foodi?

2 As and a B · Post by **2 As and a B** » 18 May 2011, 14:35

emordnilap wrote:Not wishing to derail the thread but wouldn't solar DHW be a better investment first? What do people think? Or do you already have that, foodi?

No. Start a thread on it if you want to know. No.

Did you read what I had written?

I am considering leaving space on the roof for solar thermal - so I'd like to know how the two can go together on the same roof (area requirements, roof strength, etc) - but for now I'm concentrating on the solar PV surveyor's visit next week.

RenewableCandy · Post by **RenewableCandy** » 18 May 2011, 15:52

It sounds as if the most sensible thing to do is put the solar thermal nearest to the sometime-shady part of the roof, and save the rest for the PV.

What type of tiles has your roof got? Sometimes slates have been replaced by (much-heavier) slabs and the roof's straining even before the extra weight of the PV and/or water goes on top. In this case, putting in an extra beam is quite straightforward but very necessary.

Typical panel efficiency these days is about 16%, giving 6 m^2 of panel for a 1 kWpeak system (which will give just shy of 1000 kWh per year in sunny Sussex), so it sounds as if you have plenty of room to play with anyway.

JohnB · Post by **JohnB** » 18 May 2011, 16:36

foodimista wrote:I am considering leaving space on the roof for solar thermal - so I'd like to know how the two can go together on the same roof (area requirements, roof strength, etc) - but for now I'm concentrating on the solar PV surveyor's visit next week.

The only PV installation I was involved with had a flat plate solar thermal collector fitted. The roof was being re-slated at the same time, so it was all integrated into the roof. The plan was to built it into the PV framing so it all matched. I can't quite remember how it worked out, and can't find the photos at the moment.

emordnilap · Post by **emordnilap** » 18 May 2011, 17:20

foodimista wrote:
emordnilap wrote:Not wishing to derail the thread but wouldn't solar DHW be a better investment first? What do people think? Or do you already have that, foodi?
No. Start a thread on it if you want to know. No.

Did you read what I had written?

Gah, missed that little bit...sorry.

If you do get solar thermal at some point, as far as weight is concerned, get a flashing kit and set it into the roof rather than mounting it above the tiles/slates, thereby saving a bit of weight.

I suppose the ideal would be re-slate with solar slates plus a dhw panel!

2 As and a B · Post by **2 As and a B** » 18 May 2011, 19:32

Thanks for your comments. Here's a bit more info.

The house is early 1970s and the roof, an original, is made from flat slab tiles (i.e. not slate, not ridged).

Electricity consumption...

5 July 2006 to 14 Mar 2011: 3090kWh per year
4 Sep 2009 to 14 Mar 2011: 4025kWh per year

The consumption increased since 2008 because of equipment on 24/7, boiling of full kettles and, more lately, an electric oil-filled radiator on 24/7 over the winters. If allowed to conserve electricity use, I would say the consumption is something like 2000kWh per year but would it be worth doing the installation based on 4000kWh per year?

JohnB · Post by **JohnB** » 18 May 2011, 22:21

Found the photos I mentioned earlier. The plan was to integrate the solar thermal so the whole lot formed a rectangle, but it didn't work out like that. This was done in 2004, so products have probably changed since then

Post by **kenneal - lagger** » 19 May 2011, 02:24

One of these would fit in (1500 wide) or possibly two if your hot water consumption is high -

http://www.navitron.org.uk/product_deta ... &catID=115

The Navitron forum shows fitters or I suspect Navitron will help directly. I've got one that I fitted myself and I'm happy with it. It's a lot more efficient than the Solartwin system I had previously.

From your description of your tiles they are either a Marley Modern or a Redland Stonewold concrete interlocking pantile.

Have you got cavity wall insulation and 450mm in your loft, Foodi? If you've got central heating and you need an oil filled rad as well sounds like something is lacking in the comfort stakes and extra insulation is cheaper than renewables.

2 As and a B · Post by **2 As and a B** » 19 May 2011, 08:45

Thanks both. Glad to hear that solar thermal is so compact. Can definitely leave room for one or two panels.

I've been out checking the roof this morning (those would be the type of tile Ken). The sun was on it by 7.30 and the shadows were as predicted - for this time of year. No idea where they will be in mid-winter but I would expect the survey to tell me that.

Yes, we have cavity wall insulation and are getting 450mm loft insulation. We have the radiator because the winter before last had some very cold spells and the nurses, especially the ones from Africa, were cold with just the central heating radiators in the living room. They are not very efficient - a small one by the nurse and a long low one down the far end. (Also, I can't turn the radiator off in my bedroom! - it was snowing when the gas and plumbing service was done last year but will get it fixed this year.) The nurses are inactive during the night so feel the cold more than someone who is up and around. And, of course, as the radiator is on in the morning, the day nurses just leave it on or, if it has been turned off, switch it on just because it is there (NHS training). We've had some disagreements about how high the thermostat on it needs to be set - they always turn it to full and leave it there even when the room is 20+ degrees. [/gripe]

caspian · Post by **caspian** » 19 May 2011, 09:01

Just wanted to add something to this thread that might be worth considering. We've just put down a deposit for a solar PV array (due to be installed this summer). Our roof currently has some late afternoon shading issues caused by a chimney. Based on what we've learned, the traditional string inverters used with PV arrays can mean that shading over one or two panels brings down the overall efficiency of the array. However, a company called Enecsys have developed a 'micro' inverter that sits behind each panel and controls only that panel. This means that if some panels are shaded, it won't affect the others in the array. Clever stuff, although you have to pay extra for them. Another advantage is that micro inverters supposedly last longer than string inverters. Apparently, string inverters last about 10 years on average, whereas the micro inverters are reckoned to last 20 years.

One downside of micro inverters is that they can't be fitted to all solar panels, because (I think) there needs to be enough room behind the panel for them. Also, they are harder to get to if any of the inverters need to be replaced.

Post by **kenneal - lagger** » 19 May 2011, 16:07

foodimista wrote: No idea where they will be in mid-winter but I would expect the survey to tell me that.

That won't be a problem really as the output is so low anyway at that time of year.

Yes, we have cavity wall insulation and are getting 450mm loft insulation. We have the radiator because the winter before last had some very cold spells and the nurses, especially the ones from Africa, were cold with just the central heating radiators in the living room. They are not very efficient - a small one by the nurse and a long low one down the far end. (Also, I can't turn the radiator off in my bedroom! - it was snowing when the gas and plumbing service was done last year but will get it fixed this year.) The nurses are inactive during the night so feel the cold more than someone who is up and around. And, of course, as the radiator is on in the morning, the day nurses just leave it on or, if it has been turned off, switch it on just because it is there (NHS training). We've had some disagreements about how high the thermostat on it needs to be set - they always turn it to full and leave it there even when the room is 20+ degrees. [/gripe]

Set it to what you want and then put a load of tape around it to stop it moving. Be careful not to cover the ventilation gaps though. Could you supply the nurse with one of those "snuggle blankets" that were talked about on another thread for use when they are inactive?

This highlights one of the problems with the NHS. They just don't think about costs for anything, apart from, perhaps, new drugs! Hospitals are horrendously inefficient structures, in the main, and waste heat on a monumental scale with large windows and bad insulation. They could save a large proportion of their energy bills if they just put room stats on their 24/7/365 heating systems.