February 2009 Temperatures

[Gixer]

Paul, do you have any other heating input to your tank apart from solar?

I have 5 20 tube panels with a 300ltr tank and I'm lucky if it gets to 20deg\C at the moment.

Regards
Darren

[Paulh_Boats]

Gixer,

Yes, but we only use the gas boiler when the tank is too cold for a shower. The pump overrun will add a degree or two if the central heating was on.

So much depends upon good sunshine and in Gloucestershire we have had a lot of sun since Saturday, which explains the good results today.

Where do you live, how was the weather recently?

-Paul

[langstroth2]

Paul

Good results. It would be usefull to know what the figures for the bottom or middle of your tank. With my system the bottom half of the tank tends to warm up first (as designed) - which if its pretty cool means its a good 2 hrs of pumping before the top moves up by any really appreciable amount. The advantage of a top coil I guess.

We had a rather cloudy day yesterday, but today looks like easily being the best day of the year so far - roll on the rest of March. By 13.00 it's already brought the bottom of the tank up to 42C from 13C, the top from 37C to 45C. This could be my first boiler free day of the year, and the first of many hopefully.

40 tubes / 140L / Direct System / South facing

Key:
Black = Panel exit temperature - temperature of water just after it has left the panel
Red = Top of hot water tank temperature
Pink = Middle of  hot water tank temperature
Blue = Bottom of hot water tank temperature
Green = Ambient outside temperature

[Gixer]

Hi Paul,

My tank has no other heating input other than solar, that is then fed to the combi.

We let rooms out here so the tank usually starts from cold most days at around 6-8 deg. I think the best day we have had so far this year was about 35deg at the top and about 25 deg at the bottom. That was after some take off with showers and washing machine. So I suppose that was quite reasonable.

Recently it's been cold, mostly cloudy with little sun. With these conditions the top of the tank will usually get to 20 deg C or so.

Biggest problems I've had with my system is the E/W 2/3 panels setup. Last year I was noticing that one side would pump hot water to the other side with little getting to the tank until both side started pumping. This is despite the pumps internal one way valves. I have since added another pair of NRV's.

The other problem is leaks. At first quite a lot of them, but with some fiddling and re-fitting it's now only weeping in a couple of places. But darn hard to cure !!
This lets the pressure drop over 4 days or so and then the system becomes quite poor, back to one side heating the other and not the tank.

After living with an E/W system for some time I have to say the next time we buy a house I would not do this again. I will make sure the house has a south facing roof or I won't buy it !!
Much simpler and less problamatic....oh, and cheaper !!

Regards
darren

[dhaslam]

February was pretty bad, only 85% of last years radiation according to the local weather station.    Something like 150 kwh from 60 tubes.   The first day of march showed 18 kwh despite being partly cloudy.     

[langstroth2]

140L Tank ended up at 52 top, 52 middle and 49 bottom. First day this year just on solar, although there's been a couple where a good portion was solar.
(Ave tank at start 27C, ave tank at end 51C - a rise of 24C. My rather crude calc says that is 0.5KW per Hr per panel - as the pump run time was 4 hrs.)

[Gixer]

How many tubes?

[langstroth2]

40 x 47mm tubes / south facing / 10m each way pipe run in 10mm.

 

[Paulh_Boats]

Gixer,

A 25C rise is pretty good for Jan/Feb and you are saving nearly 50% of the combi gas. Things improve a lot during Mar/Apr.

langstroth2

Yes middle/bottom sensors are now important, but I first want to epoxy them inside 8mm copper tube for robustness and better heat conduction.

-Paul

[Gixer]

Hi Paul, Yes, I'm not displeased with the performance I'm getting. It's just when you see people quoting tank temperatures at 50C plus at this time of year it raises questions.

Do they have a small tank, or a lot of tubes, or usually it's another heat source.

I have 100 tubes and get nowhere near 50 odd degrees at this time of year.

My temps today, should really be in a March thread but as it's a follow on I'll put it here

Time     lower tank temp     upper tank temp in deg C

10:00   8.2                       9.4
11:00   9.4                      12.1
12:00   11.2                     13.0
1:00     14.3                     15.9
2.00     17.5                     18.8
3:00     21.5                     22.9
4:00     25.3                     25.5
5:00     26.5                     26.2

It all finished around 5pm as the sun was getting very low by then.

That's 40 tubes East, 60 Tubes West and a 300 liter tank.

I make that 6.44 Kw input from 5 panels giving  1.288KW each today.
I don't think that's too bad for the 4th of March which was intermittent sun all day. I'd say about 50% sun 50% cloud cover.

Regards
Darren

[Paulh_Boats]

Gixer,

Today our panel generated a 23C rise in the 120l tank, scaling that to your 300l tank equals a 9.2C rise.  (300/120 = 2.5)

So your rise today of about 18C equates to double the power I generated with 30 tubes, which means you are in the right ball park energy wise allowing for an east/west derating. Its simply your large tank that is limiting the maximum temperature.

You either get a large amount of warm water (big tank) or a smaller amount of hot water (small tank). In the end your combi is saving the significant energy that you generate, so I would not worry much.

cheers
Paul

[langstroth2]

....small tank for the number of tubes. Early season hot water, but little scope for carry over on a cloudy day if a bath or couple of showers are had, unlike a 300L tank I imagine. Particularly true in summer when I'm guessing you will be storing more than double the amount of solar generated usable temperature hot water compared to me.

[Gixer]

Yes it seems to be working well. The water coming out the tank feels quite warm at 26C. Could just about suffer a shower in it if we had to....

300lts will carry over to the next day if we don't have any odgers in. But then they pay for the gas anyway so it's ok if they use it all up.

The suns getting stronger by the week, and longer. End of the mth should start getting interesting.

I put the system in around sept last yr with a 550ltr tank. That was just too large. I think the best it got to was around the high 40's.

Darren

[StBarnabas]

March Temp time I think? I would like some better way of comparing these. Having simultaneous weatherr data and vacuum tube performance data would be great.

[rt29781]

Hi StB, Simultaneous weather data?  What parameters do you need?  My neighbour has a weather station, literally over the fence and its hooked up to his PC.  We have our ET data and PV data.  Anything else needed?  The PV could act like a sunshine meter as I have said before.  The weather station gives wind speed and temperature and pressure I guess.