ENERGY MATTERS

[Pluggy]

I don't know about the solar panels behind glass, it would depend on how much of the ultra violet spectrum they use (window glass is opaque to UV). The old incandescent bulbs were something like 90% heat and 10% light. I made a photographic developing tray heater out of a 100 watt bulb inside an old biscuit tin once.

Shading is a big issue with PV panels, even a small part of them being shaded can cut down the power dramatically. They are made up of hundreds of little cells all wired in series, the ones in shade have a high resistance so it affects all the others. They put diode by passes on groups of cells to reduce the effect, put they can't do it on a single cells because the voltage of a single cell isn't enough to 'open' the diode. One bird sitting on one of one of say 10 panels can cut down the power generated by half.

There is much up in arms about 'rent a roof' schemes (somebody else buys the panels and takes the FIT payments whilst giving the householder the 'free' electric) its a 25 year contract with 3rd parties that really screws up the legal process of selling a house. Some estate agents are refusing to deal with properties fitted with PV panels because of this (irrespective of whose panels they are). There are also doubts about them improving the value of properties because some buyers don't like the look of them despite the payback they'd be getting if they owned them. They do change the appearance of the property somewhat.

[Pluggy]

The delights of cameras with high ratio zoom lenses, the barrel distortion on that photo is appalling.......

[Pluggy]

Having done some research on solar PV panels, they aren't very sensitive to UV light (they are sensitive to IF to a larger extent) so putting panels behind glass won't have too much effect other than the losses introduced by having extra reflective surfaces in the equation. Most panels are made of glass on their top surface anyhow. I can't find any figures but I'd hazard a guess that you've get 30% less out of them behind double glazing provided they don't introduce any extra shading.

[Tardis]

Funny that, I have a 100 watt bulb in an mdf box that I use for curing rubber.

Just allows that little extra temperature in a small area to allow the stuff to set slowly enough to allow the majority of the air bubbles to be released.

The new Green Bank stuff will mean that home owners can buy the panels or other stuff but the loan will remain with the house and not with the original purchaser. It is a possibility that this opportunity might deliver community street schemes.

As to driving down house value, I can only think that some people are barking mad because extra insulation and renewable technologies mean that you are less dependant upon imported energy prices, but could encourage real bargains for those people who do believe in the technology.

But that brings me to another point which has been niggling for a bit. When I went to the renewables presentation one of the Town Cllr's (I won't name her) said she didn't know how much electricity the panels installed by Housing Pendle on her Council House had generated because she hadn't had a bill (installed before Christmas). So is that a lack of engagement by her or a failure by Housing Pendle to communicate the value of this "freebie" to the tenant? After all, if you don't check it, how do you know if it is working, and exactly what value has this tenant placed on this investment and what commitment is there to ensure that the investment continues to do its supposed role? Then why are the Town Council supporting this Low Carbon/Renewables study if they haven't already engaged?

[Pluggy]

Some people just never look at their meters........

[Tizer]

Thanks for all that info Pluggy. My reason for asking about PV behind glass is that you can now buy windows which have a PV coating that generates heat. The sellers claim that you can use such windows to help heat rooms in your house but there is a great argument going on with others claiming foul play, saying that much of the heat would be lost directly through to the cold outside of the window. That seems to make sense when you first consider it but after further thought you realise that it's not quite so simple, e.g. which pane has the PV coating? (presumably the inner facing pane) ...and what sort of coatings are on the outer pane to reflect back heat? How effective is the gas insulator within the glazing (krypton is better than argon)? Is it used in the inner pane of triple glazing? All a bit complicated and easy for the snake oil solar salesmen to baffle the poor consumer.

It did make me wonder if you could use such heat-generating glass inside a house where all the heat would be useful, for instance if you had a glass dividing partition that received light from a window. The heat-generating glass is also said to be useful for bathroom windows to prevent condensation but I suppose it depends on whether you shower in day or night time!

[Pluggy]

Can you give a link Tiz ?

I found electrically heated glass but its nothing to do with PV except perhaps you could use the output from seperate panels to heat the glass. But mounting PV panels which are normally opaque inside windows seems a little counter productive, or am I missing the point ?

Photo voltaic panels work on light, if you were going to use the sun for heating, you'd be better off with a solar thermal system which use the heat from the sun directly. PV panels actually work better when they are cold, I get more out of mine on cold sunny days than warm sunny days.

Heating a room via the glass in the windows seems like a stupid idea to me, especially with electricity. Theres a reason next to the window is the coldest part of the room ,even on double and triple gazed windows, its because glazing is a relatively good conductor of heat in comparison to even badly insulated walls, putting the heating element there is probably the worst place you could put it.

[Whyperion]

If you shower then condensation will normally occur ,assuming no extractor fan running or trickle vent in window , so if its not appearing on the windows , its on the walls or ceilings , hello mould home.
I thought all new d/g windows had to have the solar glass in (Pilkingtons K glass was the original trade name I think ). I got in before this was a legal requirment , I did not want to be roasted during the summer , ( in winter I can pull the curtains to reduce heat loss )

[Bodger]

Am i missing a major point in this forum ?, are we totally concerned with power costs , i know it's part of our lives, but i still prefer to live comfortable, at a reasonable cost, as i type the room temp is 24.9, yes it costs me, but i'd rather sit here in comfort than brag about how i can live at 20.1 C. in comfort if i wear my cardigan, Whats the point in spending your old age at a temperature that you endured as a child, or is it the old Yorkshire thing i can live cheaper than you, WHY ?,spend a few bob relax and enjoy life instead of worrying i spent a £ 1.00 extra last month, youre only propagating the image of the miserly Yorkshire man

[Stanley]

You're right Bodge in a way. My front room gets to around 25C in an evening but we have enquiring minds and enjoy getting those sorts of levels cheaper. I couldn't afford it on gas CH but the stove is fine.
At the end of WW2 there was a bed warmer on tha market that was simply an insulated case with a 60 watt bulb inside. If you left it in the bed for more than 30 minutes it scorched the sheets!
Dead right about being a singleton, no complaints about heat levels and no hot water in kitchen.
Best cure for condensation in a bathroom is to wallpaper it with paper that has an absorbent surface. In the 1940s high gloss paint was popular for house decoration if you could get it and condensation ran down the walls in streams on a wet washing day when washing was drying in front of the fire. Absorbent wallpaper soaks up the excess and releases it slowly when the source goes away.

[Tizer]

Pluggy, perhaps I've added 2 + 2 to make 5! I read in a chemical industry magazine last year about windows being tested (on skyscrapers) which incorporate PV material and generate electricity which would be used in the building (not necessarily for heating in this case) and the window glass was almost as transparent as the normal glass. Then the boss of a British company (Glazing Vision) is quoted in the current issue of a self-build magazine (in an article on rooflights) as saying "PV cells can be laminated to the outer pane of a double-glazed unit and produce a rooflight with multiple benefits which ticks several boxes with regard to compliance with Part L". So I assume these produce electricity. The quote then continues with a discussion of the functions of heated glass and saying there are no visible wires. On re-reading I suspect that something has been left out here and that he had switched to talking about electrically heated windows rather than the PV heating the glass....yes, down at the very end of the article there is a mention of cable management. The big debate about the value of heated glass is on The Green Building Forum and 16 pages long but seems to be referring to ordinary, wired electric heating.

But the question about whether or not a PV panel would work `indoors' from light passing through a window is still interesting to an anorak like me!

[Pluggy]

Ahh

http://green.blogs.nytimes.com/2011/04/ ... ar-panels/

Sounds like its experimental with results in the decade. They'd need to last better than standard double glazing units if they were at all costly, I only get around 8 or 10 years out of double glazed units at the front of house before they fog up or look dirty on the inside. Using electric for space heating doesn't sit nicely with me, PV cells built into windows - fine but I wouldn't waste what they generate on space heating, particularly a dubious technology like heated glass.

Bodge - you're missing most of the point, saving money is only a small part of saving energy, I like it because its geeky, and you can use the environment as a nice built in excuse.........

(well that's me labelled as a heretic)

[Whyperion]

For keeping warm is putting ones feet in shredded newspaper better than wearing cotton or wool socks ( the air gaps in the shredings warm up from body temp and the paper acts as an insulator. ( Its why I feel warm when sitting still and I fall off to sleep reading the newspaper , when I wake up to move it off my knees my upper legs can feel distinctly cold )

[Stanley]

Tiz, it looks to me as though you have found another instance of our favourite bugbear; bad writing! Some journo somewhere was given the job of editing an article and mangled it. Of this is the case, how did it get past the author? The dreaded deadline has struck again! If there is an explanatory article I hope they get it right the second time.
Time for my favourite apocryphal typo. This retraction appeared in a paper. " We apologise for referring to General ***** as a 'Battle Scared veteran". This should of course have read 'Bottle scarred veteran'.

[Sunray10]

Talking of energy matters, lights flickering and dipping in Nelson this evening. Is it happening elsewhere ?

[Tardis]

I believe Anglian are selling those kinds of window unit

[Pluggy]

http://www.anglianhome.co.uk/windows/ecogain_windows/

These are just passive coated glass, not the active embedded solar cells that Tiz was talking about.

[Tizer]

Anglian's Ecogain is just a brand name for windows with a pane made from low-iron glass. Lowering the iron content of glass selectively raises its transmittance of solar (i.e. incoming) radiation but not of the outgoing radiation. Nothing very new, you can have low-iron glass - but be prepared to pay a premium for it. It would be interesting to see an independent comparison between Ecogain and triple glazing in performance and price (triple won't let in more of the sun's heat but it will let out less of your room's heat). They claim the Ecogain window `heats your house' - it does this by letting in more of the sun's heat. I haven't seen Anglian explain yet what happens on a hot summer's day when your Ecogain house is hotter than your neighbour's! I notice they claim on the web site to be offering Ecogain windows`at half price'. That makes me wonder what staggering price they were at before!

[Whyperion]

So I think the room/s would get too hot if its over sunny , maybe the K glass , which supposedly reflects energy back into the room is better.

[Stanley]

I once rang Pilkington's to ask how I could be sure I had got the more expensive 'K' glass I had paid for. The lady told me to wait till it was dark and hold a candle about 2" from the glass and view the reflection from the side. If it was genuine there would be a faint secondary reflection next to one of the two primary reflections. It works. The reason I had to ask was that the windows were 'K' glass as standard so there was nothing in the documentation to confirm the fact.

[Tizer]

Pilkington K glass has a coating that helps trap the heat inside your room. Technically speaking, it selectively lowers the transmission of infrared radiation of the type (wavelength) that is trying to escape from your room. It's not the only coating that does this and they are divided into `hard' and `soft' coatings. The hard coating used on K glass has an unwanted side-effect of making the glass look hazy under some lighting conditions - it looks as if the glass needs cleaning, rather like on a car windscreen when it gets a thin coating of oily stuff. Not very pronounced but it's there and if you are fussy about the clarity of your windows it can be a nuisance (we had a couple of windows replaced with K glass and noticed the difference). The other side effect is that white net curtains on a K glass window look slightly grey. Companies selling double glazing incorporating Pilkington K glass were reluctant to admit to these side-effects but Pilkington itself now admits they occur. In comparison, St Gobain's soft coat glass has the same ability to trap heat but doesn't have the side-effects - but it's more expensive and you need to decide how much you values clarity of vision through your windows and whiteness of net curtains if you have them.

I had a big argument with the company that put in our two replacement K glass windows. At first they claimed I was making it all up, then they put me in contact with the company who made the double-glazed units. Their salesman admitted to me that these effects existed and were well-known in the trade, and he knew it well because he had K glass windows in his house - he didn't like the problems either and agreed that St Gobain glass didn't have the problem but he got the K windows cheap because of his job! The DG fitting company also claimed that they had to give us K glass because `the regulations demanded it K glass'. I had to point out to them that regulators never specify products or brands, only performance and quality, and that the regs demanded only that the window should be below a specific U value (heat loss value).

[Whyperion]

I dont mind if my nets look grey to me , but do they look grey to the outside world ( and I spend sooo much on glo-white as it is.

[Tizer]

Good question Whippy and I don't have an answer - we don't have net curtains on those windows. Another important aspect of saving heat by careful choice of windows is to choose double glazing units filled with argon gas instead of air. They are becoming standard now because argon (a chemically inert gas) is a better insulator than air. For those who are able to shell out more cash, units filled with another inert gas, krypton, are even better. For millionaires, a further inert gas, xenon, beats even krypton.

Stanley mentioned above that he was concerned about how to tell whether his K glass units really were fitted with K glass. Units filled with inert gas are even trickier - how do you know they really put in argon and not just air? Inert gases are difficult to detect and measure and you'd probably have to get Professor Brian Cox to use one of his astronomy spectroscopes on your window, the type he uses to see what stars are made of. Just imagine if you paid a fortune for xenon and they had filled the units with air. Trouble is, the units leak inert gas out and air in over time so you eventually end up with a mixture. The industry has been told to take this into account when calculating the effectiveness of their units. If you buy any units filled with argon, ask the salesman how you can be sure they have 100% argon in them at the start, then ask what percentage argon they will be after 5, 10 and 20 years. Then ask for a big discount!

[Whyperion]

So if the difference in price of the D/G units is greater than the expected fuel (cost in £ or cost in saving the earth over a 20 year time period ) it could be as effective to go for the cheapest unit ?

[Stanley]

Bugger what colour the net curtains look from the outside. As long as I know they are clean that's all that matters! This all, reminds me of the old story about the man who took all his window glass out, inverted it and refitted. When asked he said that he'd found out that glass was fluid and slowly thinned out at the top and got thicker at the bottom so he was compensating for this. He was right of course but didn't realise the time scale under low shear conditions was so long he didn't need to worry! (LINK)