Third-year university solar thermal project

[jlsouthampton]

Good day all,

Following encouragement and assurance from my supervising professor, I have spent the last few weeks researching UK-based manufacturers and suppliers of solar thermal vacuum tubes as part of my third-year undergraduate Mechanical Engineering degree project at the University of Southampton, and searching the internet has brought up endless passionate companies around the South of England catered to medium/large-scale solar thermal setups for homes and businesses. Unfortunately, none of the companies I’ve spoken to so far have been able to help with my more unusual project, which currently requires access to the rare short-form (sub-1m, often used as demo models) solar thermal vacuum tubes, and my supervisor pointed me in the direction of Navitron’s forum, which thus far appears to be a goldmine of expertise, anecdotes and contacts on the subject of renewables.

My two-semester assessed design-and-build project is something I’m delighted to be allowed to pursue as an undergraduate engineer, and I hope you guys on the forum find it as interesting as I currently do. It involves creating a small - a little less than one square metre area -  array of solar tubes fitted with reflectors and automated water circulators to provide a standalone and portable solar hot water heater/boiler suitable for use in cooking during hiking and camping. To ensure sturdy portability, the glass vacuum tubes will be fitted to a laterally-reinforced mat with interstitial reflectors doubling as padding for when the whole array is rolled up and carried inside a medium-sized tent bag. There will also be a likely theoretical add-on to this thermal solar array in the form of a small pedal-powered vapour-compression cycle heat pump which will allow the realities of heat exchanger efficiency on such a tiny scale to be investigated and perhaps only prototyped outside computer simulations if budgets and time allows.

Since the project mainly involves researching the thermodynamic feasibility of a system on such a small scale, I will require access to a small number of fairly rare components such as small-form (around 1 metre length) solar thermal vacuum tubes. The University of Southampton offers plenty of manufacturing, fabrication and design services for most elements of the project, although my supervising professor agrees that high-quality solar vacuum tubes cannot be made at the university, and therefore I am reaching out to the wealth of experience on this forum to help find a supply this necessary hardware.

I chose this project because it involves the ever-advancing field of renewable energy – something I am specialising in and immensely passionate about – and I’d love to share the progress of it with you guys.

If you think you can help or know of anyone I should contact, please reply to this post or send me a message. I can provide further contact info for myself and professor if necessary.

Best regards,

Joe the engineer

[stannn]

Welcome to the forum Joe. These are typical of the tubes which you want:-
http://www.ebay.co.uk/itm/10-Solar-Thermal-Collector-Tubes-Solar-Evacuated-Tubes-Solar-Vacuum-Tubes-/221166389832?hash=item337e8b4a48:g:R98AAOSwCypWoVpY
Navitron used to sell them in solar panel kits for a balcony. They may of course have surplus stock.
When I collected my tubes from Navitron, the agent checked the packs for tubes with a broken sealing bulb on the end. So I think that they are a bit delicate for portable use. Good luck.
Stan

[Westie]

Following up on Stans post, I notice the same supplier also has these 'mini' collectors which may be of interest to you.

http://www.ebay.co.uk/itm/Solar-Hot-Water-Thermal-Heater-Collector-Panel-for-DIY-work-Built-In-USA-e-/222040569205?hash=item33b2a63575:g:rQAAAOSw9r1V8aN4

Good luck with the project.  I suspect you principle concerns will be ruggedness and weight.

Keep us informed

[todthedog]

Hello Joe and welcome to the forum.
I would agree with the other chaps my concern would not be the effectiveness of the system, I had a system running for 8 years with no issues, but it's ruggedness .
Best of luck, remember we love pictures!!

[jlsouthampton]

Hi guys,

Big thanks for the quick replies and pointers, although I really feel as though the budget limitations of my project prohibit the high shipping cost from the USA, especially for such a small order. It's a little tricky in my situation since my project is considerably smaller and more focused on collecting data than most of the forum members here with their impressive long-term and practical solar arrays for homes and businesses, and therefore I seek people/suppliers with surplus vacuum tubes such as those used in demo models. I must be clear that my project approaches solar heating mainly from an academic perspective, and therefore top quality/new vacuum tubes won't be entirely necessary. The performance of the best hardware can then be found in published information and used alongside the data collected with this functioning prototype to put together some useful data in the various reports I'll have to submit to the university over the coming year. If the ruggedness isn't up to scratch, reasons can be given in the report. My goal is to produce DATA on this kind of system, investigate its feasibility with various add-ons (heat pumps, reflectors, etc), and hopefully get a good grade for finding out something interesting for the future of solar energy.

Of course, I will put up some pictures as things progress. You guys seem to have a keen interest.

Joe

[MR GUS]

Then don't make it short term Joe, none of the folk here adopt that approach "bodgineering"  tinkering & re-purposing is something folk thrive on here.

Any spend can likely be re-purposed or fit to applicable size, ...plenty of small cabins / sheds etc i've slept in when roughing it for instance, where a mere bowl of hot water would have made life simpler & comfortable ..or as a back up system on a moored barge etc, make something & find a purpose / re-purpose for it, otherwise you betray the first principle, only the sun is limitless (within reason) everything else is finite & energy intensive to produce only to be left to rot.. adopt that attitude & you are already halfway there.

How long is your data collection proposal?

[Westie]

Hi Joe,

There has to be a play off here between hot water output vs weight, portability and ruggedness.  The problem with using evac tubes is the water can get extremely hot and if that water is contained within a closed loop heat exchanger system the pressures can become quite high.  So you end up with copper collector headers, copper pipe, welded joints, pressure relief systems etc.. etc ... All gets very heavy.

When I installed our solar thermal system, it was a sunny day and I had the tubes set out on the lawn ready to install into the headers, after burning myself by accidentally I tested the temp at the copper tip and found it was around 250 deg C! hot enough to melt standard solder.

Have you considered other collection apparatus apart from evac tubes?

YouTube is awash with ideas here's one that caught my eye.

http://tinyurl.com/o9zre3z





 

[ringi]

What about investigating a cost effective way to connect a small air to water heat pump to a  (grid-connect) solar roof top PV system, so as to maximise the heat output, while not importing any power from the grid.

PS, in most cases just using an immersion heater with solar PV gives more useful DHW then spending the same amount on getting solar thermal installed, without any of the issues due to overheating.

[dhaslam]

It might be better  to start from scratch.   Vacuum tubes are specialised  collectors that make the most of weak sun  by retaining heat but they do take quite a lot of space.  You might be able to achieve  the same result by  making a box with a  well insulated lid, preferably vacuum.  Vacuum glass panels are made in China to use for  thinner panes in windows  but  it may be hard to  find them without anti radiation coating.  Alternatively you could use  a fresnel lens to concentrate sunlight.     There is a big requirement for this type  of device in some countries, particularly in Africa,  where  firewood  is no longer available for cooking.