I don't think this is 'cutting edge'

[rogermunns]

Has anyone rigged up reflectors to put more sunlight onto their thermal collector? I have one 20-tube setup mounted on the ground and could easily rig something up. Being at home all day I could move this every hour or so, thus crudely 'following' the Sun. Might this be worthwhile? 

[stuartiannaylor]

Yes in a big way as a hell of a lot of sun passes straight through. Problem is that your design of collector is specified to work without so it might just spend more time in stagnation. If you have direct flow collectors you could harness the extra and you will prob need to change your heat exchange liquid to something higher than glycol/water can take.

Ooooof me and my memory whats the name for the (non direct flow) collectors they will just stagnate as they are separate from the heat exchange liquid.

In fact some sheets of polished aluminium curved into a form behind the back of the collector have the possibility to almost increase output 100%.
Be carefull though as at this time of year with the snow we are having causes all sorts of problems with the design.

Reflectors without tracking provide huge gains. I am not sure about tracking in the uk as we aim south as the sun does its east-west bit. Not sure if you gains would compensate for the energy expelled and the worries from the nieghbours that your excursions are a form of stalking.

[KLD]

Roger,

You could also re-phrase the question into: what is the limiting factor in converting the solar radiation falling onto the area of the panel, into heat going into your store? The mirrors only make sense when the system isn't already in saturation. I.e. if your increase the amount of radiation falling onto the panel, can this extra energy be taken up by the panel?
I've got a few data traces (that I showed before), showing how the output power of the system changes during a day. I would have expected that the solar irradiation varies quite a lot from early morning -- midday -- late afternoon. My data don't reflect those variations, though. Don't know why. It would be nice to see data from a more controlled set-up (i.e. laboratory). 

Klaus

[billi]

I was experimenting with PV for a while  , when PV was much more pricey than it is now

My conclusion about mirrors was ( it seems mirrors are  close to a religion nowadays even they only reflect live)  : more cost effective to buy more PV, and on the solar thermal side , it is hard to belive that a mirror  can cope with this deal http://www.navitron.org.uk/product_detail.php?proID=151&catID=116


All the best froma guy who digs ponds infront of his PV panels and hopes they perform better  with the reflection (and they do marginal )

Regards Billi

[stuartiannaylor]

Your thinking about this in the wrong way if you can't do this because of saturation / stagnation.

It doesn't have to be a gylcol / water loop it could quite easily be a thermal oil which have ranges of -20 to 400°C.

Then you couple that, either a water tank or even go really esoteric and use of the top of my head, bitumen. Its phase change temp works really well with possible temps.

Also at the weekends you can earn some coin by doing peoples drives as a foreigner.

[KLD]

Stuart

Sure, if you change the rest of the system to cope with the higher irradiance, you can make it work. The question of the OP as I understood it was whether simply adding mirrors to an existing system makes much sense.

K

[stuartiannaylor]

Sorry lol, but its sounds like the man has time on his hands. A project could well satisfy that and concentrating mirrors would certainly provide much more.

A thermal oil swap is not that major if you have the right collector system (direct flow) or otherwise forget it.

PS please don't use bitumen, the tarmac business isn't funny really or heated high octane vapours.
Its a bugbear to me that I can't find a simple low cost phase change material that fits the temp range.

I have been looking as the daily storage and release of that temp could reduce storage size and provide space heating. Its a project that I have been thinking of myself but my cash is staying in my back pocket for a while.

[Ivan]

Roger, you'd be surprised just how often you have to move the mirror. It would only need small angle changes, but you'd probably find within 15-30minutes, the extra illumination would have passed completely over the panel.

Look up 'heliostat' - if you buy one, you'll probably be better off just buying an additional Navitron solar collector, but you should find DIY heliostat plans on the internet based on a satellite dish positioner (old ones on big 1m+ dishes go pretty cheap on ebay), and a timer or some electronics. DIY makes it quite affordable.

Billi - Nice thinking - I would never have thought of that.

[GavinA]

mirrors aren't going to do much for PV because they won't spread the light evenly across the array, and the array will pretty much operate at the output of the lowest cell in the array (or possibly bypass any strings of cells not affected by the mirrored light).

mirrors on solar thermal though would work fine, and unless you're talking about a massive set of mirrors a standard set up would cope fine with the mirrors particularly as they would really only be operating at times when the sun's not dead on to the panels anyway.

I keep meaning to add some to our east facing solar thermal panels as particularly in winter when the sun's really low in the sky it could make a huge difference I'd think.

[renewablejohn]

A thermal oil swap is not that major if you have the right collector system (direct flow) or otherwise forget it.



I have been looking as the daily storage and release of that temp could reduce storage size and provide space heating. Its a project that I have been thinking of myself but my cash is staying in my back pocket for a while.

Your well on the way to the solution I came up with using thermal oil and a steam evaporator to provide conventional steam and then use a Soda engine to extend your generating hours before regenerating your soda engine by using your excess solar energy to dry out the soda.  "Simples" now who will provide the finance

[stuartiannaylor]

RenewableJohn,
Is that adding caustic to water (soda) as I have done some work for a plating plant and have seen a potentially horrible accident with someone adding caustic to a heated cleaning tank too quickly. He was ok after an emergency shower but it did cause a bit of a drama
I am not saying I am doing anything revolutionary but I have been thinking of matching a panel array to provide winter heat. Then in summer the waste stagnation temps would provide generation. Its a little frustrating as collector temps and required generation temps are so near but the small difference in terms of efficiency also makes them so far.
Saying that though I have found a few products that come very close and rear mounted parabolic mirrors might just give that extra umph required.
I have been looking at :-
CoolEnergyInc's Stirling product http://www.coolenergyinc.com/
Sunpowers Stirling products http://www.sunpower.com/lib/sitefiles/pdf/productlit/Engine%20Brochure.pdf
CyclonePowers Rotary http://www.cyclonepower.com/PDF/WHE_Spec_Sheet.pdf
FreePower.co.uk ORC solutions http://www.thursbygarden.org/images/pdf/7_10.03.02_FP85_SpecDimension_Rev_2.pdf.PdfCompressor-194521.pdf
These all represent temps near to the max that you can get from a standard solar collector.
Your steam evaporator sounds a good idea and my thought path is not for microgeneration but for a term I call macrogeneration. Where small communities, districts can gain the benefits from economy of scale. Where maybe a supplier might be able to make a viable exchange for heat for FITs (roof space for heat). In the Burnley area we have a lot of terraces where the installation of linked panels to a centralised generation / heat distribution system would provide many mutual benefits.  This would suit most high density urban schemes though. CHP is amazingly efficient for small scale heating distribution and electricity is easily fed back to the grid.
I have a bit of inheritance and I am holding fire at the moment as there seems to be various products getting near to the figures I require. It even occured to be to utilise the stirling out of the whispergen and baxi CHP units as mass production always makes huge dents in cost.
The macrogeneration term is about being scalable and in a community scheme a redundent array of generators could come online when the heat is available and shrink to extend the generation period to its maximum.
As I say, I am holding fire as I haven't found a direct flow evacuated tube that really hits the mark. Well the http://srbenergy.com CERN product is perfect but it is stuck in the quagmire of the Spanish solar industry and cost. I do actually aim to setup a system at home and get my 20 years of automation skills utilised to provide concise data capture of the process.
If you think you have anything to add where the overall system will budget around £15,000 give a bit either way, then I would be most appreciative. Still fact finding and still searching the market but I am going to give it a go.

[renewablejohn]

Stuartiannaylor

If you google Honigmann fireless engine you will indeed find the beneficial effects of using Caustic Soda. The technology is still used in German chemical works shunting trains.

As for your macrogeneration scheme I will send you a PM

[stuartiannaylor]

The caustic even though nasty suff is a really good idea. Whats the energy input of drying the soda compared to energy output? Even if its less the idea of storage in this way is quite novel.

Stuart

[renewablejohn]

The caustic even though nasty suff is a really good idea. Whats the energy input of drying the soda compared to energy output? Even if its less the idea of storage in this way is quite novel.

Stuart

The energy input to dry the soda will be more than the energy output but if you use solar energy to dry the soda you can then have energy 24/7 rather than only when the sun shines and at least solar energy is "free"

[stuartiannaylor]

My wordage was of its usual quality, totally agree with you. I meant less output than input. Have you any idea on the levels as storage and peak time generation will have a premium that is much higher than base load.