tube performance on shortest day of year 2006

[Ivan]

The 21st December is the shortest day of the year, and it receives the lowest intensity of sunshine. This year, at my location (S.Wales), we had hazy sunshine, having partially burnt through a thick fog which persisted into mid-morning. As there was some sunshine available, it seemed like a good opportunity to demonstrate the power of vacuum tube solar technology.

The following photo shows a 58mm Navitron solar tube reaching 104°C. I tested a 47mm tube also, which reached 95°C. The ambient air temperature was 7°C.

Ivan


58mm tube on 21st December

[KenB]

Ivan,

Thanks for the picture.

It should be remembered that it's not the temperature but the wattage thats important.

A 15W soldering iron can heat it's tip to 300C, but it's still only 15W.

The only thing that's getting hot here is the copper "finger" and perhaps 20W of power could do this quite easily.

However it's good to hear that you have had some sun in South Wales,   I landed into a very cold, foggy, Heathrow yesterday after two weeks in delightfully sunny Southern China, where I had an opprotunity to catch up with some of the alternative technology on display down there.

Happy Christmas Everyone,


Ken

[Ivan]

Hi Ken,

Good to hear from you - you are absolutely right - but 20x20W =400W of free solar heating! The main reason for illustrating this  is that most people assume that solar-powered hot water is not able to heat above 40C on the best of days - this photo shows that the water temperature is a function of the number of tubes and the amount of water you are trying to heat - a far cry from traditional flat plate solar tubes. This type of photo really helps Joe Public appreciate that solar water heating can really make a difference, even in the UK!

[ecogeorge]

Nice to see at Monmouth you had sunshine !!  here at Forest of Dean (only 15 miles east) I have only had .3KwH produced per day from 1Kw of PV panels during the last 14 days!
I know its not solar thermal but is slightly relevant.
rgds George.

[Amaterasu]

Since I have added the Time clock to my Resol I can now accurately log pump time.
In sunny weymouth - and I mean really sunny on some days recently on the 21st I recorded the following readings.

I take readings at 08:00 and again at 18:00 (or therabouts)

I have a 30 panel SW facing array heating a 210 litre cylinder.
The boiler tops up the upper half of the cylinder for 30 mins between 06:30 and 07:00 (this will be a winter only practice, in the summer i intend to dispense with this and only top up late evening.

Lower cylinder temp reading
08:00 - 12.8C
18:00 - 24.4

Thats a gain of 11.6 degrees

Pump run time 0.86 of an hour

DTO = 6
DTF = 4

The 21st was not my best day recently.
On the 19th I managed a gain of 19.3 degrees for a pump run time of 1.95 hours

During both periods no HW was drawn off between 08:00 and 18:00.

Also worth noting is on the night of the 20th - 21st I recorded 0.04 hours of frost protection running.

[Ivan]

I think solar PV is much more dependant on direct sunshine. Solar thermal systems perform relatively well in overcast or hazy conditions, whereas solar PV tends to suffer quite dramatically. Having said that on a heavily overcast day at this time of year, you can expect only a small amount of heat from your solar water heating system