Vacuum tube solar collectors.

[Andy Hall]

It seems that most people are - it's human nature to want to buy things for the lowest price with scant regard for the consequences. We see this at work even within the quite small scope of this newsgroup. People would rather buy some cheap POS tool from China in the expectation of having to replace it in 3 years rather than something made in the EU which will last for 5 - 10 times that and be far better from the outset.

So it is reasonable to say that individual motivation is not in the direction of paying more for what we buy in order to have production and distribution closer to home.

It's possible to alter import tariffs to affect prices, but this has not been the trend of the WTO.

The heavy industry ones have. It is reasonably quick and easy to implement light and high tech manufacturing in short order and add a lot of value to raw materials. The question then is whether people would be willing to pay more for a set of vacuum tube solar collectors manufactured in Hungary as opposed to China.

Little more.

However, I'm really not interested in hearing about silly little green schemes in Europe that will make scant difference to world ecology, when as Europeans we continue to want to buy cheap goods from China. Perhaps we could mandate that China manufactures goods under clean conditions and pays Western remuneration to level the playing field. However, I think that that is about as likely as a pork pie at a Bar Mitzvah.

[geoff]

In message , Andy Hall writes

Not so easy any more

The old boys are retiring and not being replaced by new blood. A lot of light engineering works (the one next to me, for example) are closing down due to lack of work. Companies are not buying new machinery

There is not much viable engineering capacity sitting waiting to spring up when someone gets the watering can out

[AJH]

I may well have missed a bit in this thread but I did follow the link and then:

directly plumbed to the main and a thermostatic blender would need little work, would it?

Now what's previously put me off fiddling with solar hot water has been the low return on the investment and altering the central heating system but this looks cheap, if it can save me the cost of heating a bath/shower each evening, say 2.5kWhr per bath heating saved then that's about 12.5p per bath . If it works 50 days a year then I get an annual return of GBP12.5 on my GBP300 investment.

A shame because I have a flat roof over my bathroom on which I could easily mount one of these and run a dedicated tap from it and the installation would be quick.

I know they use these a lot in hotter places but if they are directly attached to the main how do you prevent freezing.

AJH

[dennis]

On a good day in June a 1 sq meter panel could return about 5kWh or about

15p if you use all the hot water. In Jan you may get 3p.

So ignoring weather it would only take about 15-20 years to get pay back on a DIY solution or never on a professional one.

[David Hansen]

On Wed, 16 Jul 2008 21:13:06 +0100 someone who may be AJH wrote this:-

I wouldn't use one in the UK [1], they are far more suited to other places.

They certainly have a long simple payback period, at current fuel prices perhaps 20 years. On the other hand there are many things people install which have in infinite simple payback period, for example a new television set. Trying to put a monetary value on everything is not something humans do.

Making holes in roofs, particularly flat roofs, to mount or pass things through is not something I recommend.

I have never looked at one. Presumably a combination of insulation and sun during the day, perhaps an air gap at the top, is enough to counter freezing.

[1] other than a few specialised uses, they may be suitable for things like outdoor showers at festivals.

[The Natural Philosopher]

There you go again. A television set ahs a perceived value beyond saving or making money.

Now what possble value dies a useless solar panel on your roof have?

A fashion statement?.

As a sop to your greenie neighbours?

If its not saving money or carbon over its lifetime, I'd say it was a worthless piece of junk, frankly.

[David Hansen]

On Thu, 17 Jul 2008 10:51:50 +0100 someone who may be The Natural Philosopher wrote this:-

You let emotion get in the way of your point.

[Andy Hall]

Assigned to Alt_Shift_F7

[Tim S]

David Hansen coughed up some electrons that declared:

Some of the tubes I've seen are guaranteed for 10 years, with an "expected" life of 15-20. Doing a very rough calculation based on the average expected kWh per year of useful collection in the UK (vendor's figures) suggested that I'd get a payback period of 15 years approx based on mains gas prices today.

That rather put me off - as the only sensible location (from a solar POV) for me is atop two dormer flat roofs. The pipes could be looped under and up the soffits, but the main frame mounts would be hard. Roofs have been refelted recently and have bugger all slope (ie felt integrity is paramount, even more than usual) so I don't really want to go messing them up.

Given the wind force potential on a 1.5x2.5m panel with reflectors at 30 degrees angle to a flat roof at the highest level of the entire roof and a force 8 wind, they are going to want to be pretty well anchored right through to the roof timbers.

Drain down is an option (designed-inherent or manual)

My overall assessment is I'm not convinced it's worth the effort, yet... Probably better to upgrade as much insulation round the house as possible first, but I'm not the first to say that.

Even allowing for the fact I'm putting in a heatbank, so the solar coil and system elements are minimal extra cost.

Pity. It's a technology that is almost useful - but not quite yet IMO.

Cheers

Tim

[Andy Dingley]

Baths cost more than that. Don't estimate their cost from a theoretical basis on lossless heating of water, take your heating bill, split it appropriately by use and divide it by your number of baths. This is closer to what you're actually paying, and it'll be more than half a crown.

It's modern vacuum tube tech, not a flat plate. You'll see far more than 50 days use out of it.

[David Hansen]

On Thu, 17 Jul 2008 04:19:14 -0700 (PDT) someone who may be Andy Dingley wrote this:-

Indeed. It will gather sunlight on all but the most overcast days. It does not need direct sunlight to work.

[The Natural Philosopher]

What emotion?

once again, you refuse to answer the basic question and resort to add hominem attacks.

Of what value is a useless solar energy panel on your roof?

Or is it a religious issue with you, like having a crucifix up there?

[David Hansen]

On Thu, 17 Jul 2008 11:36:29 +0100 someone who may be Tim S wrote this:-

It sounds like there are two possibilities, both relatively difficult. One is to build a U shaped set of supports connected to the walls either side of the roof, which would support the panel over the roof. The second is to peel back the covering, put in a support connected to the roof timbers and then put the felt back to the upstand and finish it off with new felt or some other covering. Some other covering might be ideal as it will be penetrated by the panel fixings.

Of course solar panels don't have to go on the roof. They can also go on walls or the ground. The sunlight has made it all the way from the sun, a few extra metres makes no measurable difference. Although mounting them at an angle is ideal, they can be mounted vertically on walls.

It is always best to reduce energy consumption, rather than install some gadget to "make" it. However, there comes a point where a gadget is worthwhile, but where that point is depends on one's ideas.

[The Natural Philosopher]

I see. basic overall energy in versus enregy out, and other objective factors like cost are simply not an issue when it comes to installing energy efficient devices?

And you claim to be a scientist? phew.

[Andy Dingley]

What's this thing _for_? Why do they offer a number of panels with integral hot header tanks? Even though they're insulated, this seems like a strange place to install the tank.

Mind you, I wouldn't mind one on wheels for the festival season. Portable solar showers!

[AJH]

I imagine in a warm climate you simply don't need any other DHW system, so this can be plumbed to the mains just like a combi would be.

AJH

[AJH]

I agree with you, I was just seeing if others would comment! I shall monitor gas use for the next week to see what we use for DHW in the summer, including losses.

We'll see.

AJH

[AJH]

I was thinking of plastic pipe to the header, hep20 (OK I know it's not recommended out doors) from the hot water header/thermal store down the side of the bathroom to the height of the shower and a hole through the cavity wall, essentially a dedicated shower/bath supply.

I seldom used hot water downstairs and the dishwasher heats itself, so I could stop using the gas in the summer when the panel is hot.

I was thinking of a felt pad and then fixed to some concrete slabs with the panel guyed by wires to the walls.

The trouble with that is that the vacuum tubes need a heat dump or they can pop.

AJH

[David Hansen]

On Thu, 17 Jul 2008 13:38:19 +0100 someone who may be The Natural Philosopher wrote this:-

Feel free to search the archives for any post where I make such a claim.

You are not a party politician by any chance? Inventing what others have said is a mark of one of them.

[David Hansen]

On Thu, 17 Jul 2008 07:50:49 -0700 (PDT) someone who may be Andy Dingley wrote this:-

Simplicity. No pumps and other gadgets.

Though Navitron used their ordinary panels for the solar powered showers .

I see they also have a page on solar powered cooking .