The Panels

Initial Tests

Bernie and I have 7 panels from last weekend's construction course.

They are not going to be installed immediately. We want to test them, looking for any leaks, and give them a good flushing out, and see how they perform. There were tested during the construction weekend by a 3 bar pressure test connected to an air line. And they were also flushed out, but the panels may not get installed for several months, so giving them an extra long clean is a good thing to do. 


4 panels in a rowI designed 4 stands to support the panels. They're a hybrid trestle / easel / deckchair. Slightly over the top! But the panels recline beautifully.

I set the elevation to be 52. A rule of thumb says panel elevation should be the same at the local latitude. The date we started testing was the vernal equinox, so the noon sun would also be at an elevation of 52.


When is noon? We need to know the longitude; and the time of year to get the equation of time

The equation of time is the difference between the mean sun, where that big bright thing should be, and the actual sun. Our planet's orbit is a bit off, and planets get in the way and screw things up. Better descriptions elsewhere!

Bernie's house is longitude 0.2487E. On the 22nd March 2002 noon was at 12:06 PM clock time.


Our initial experiment is to test the efficiency of our lovely new panels. As any one in the UK knows, the sun will not shine when you want it, and needless to say, the day we had planned was the sunniest that week. Intermittent sunshine, with a high cirrus. No clear blue skies! 

Anyway, we could set things up, so when the sun finally obliges, we're ready!

The schematic is easy. Cold water from main, fed via hose to each of the four panels in series.

Method: adjust water flow rate. Measure how hot things get.

Measuring the amount of water flowing in a minute...Knowing the specific heat capacity of water, and the flow rate, and temperature increase, we can calculate the power received in Watts. For example, in full sunshine, with water flowing at 4l per minute, and the water temperature increasing by 8.6C that's 600W per panel.

With the dire watery sunshine, we slowed down the flow to a 300ml min-1 trickle. The contents of a fizzy drink can a minute!

Three sets of readings were taken. 

Session flow rate ml/min Air Temp C inlet C 1 C 2 C 3 C drainC Power W / Panel
1 300 17 13 18 23 25 26 68
2 300 17 15 24 33 37 39 125
3 3800 17 11 12 13 14 15 265

The main conclusion - it wasn't very sunny! I'm expecting better than 400W. (Check the design rating.)

You will see that session 3 has a high flow rate. We were flushing out the panels. Even at this high rate, and mediocre sunshine, we were able to measure a temperature difference.

One observation:  the cooler panel produced more heat; the hotter panels produced less heat. (This is due to insulation losses, besides, the garden hose we're using isn't lagged!)

Power = dt * SH * flow rate.

Temperatures were taken by a contact probe with digital readout.


Bad jointCondensationWe noticed a pressure drop.

A couple of poorly made joints were soon identified.

We just need to get hold of some bits to make the repair.


We've connected temperature logging probes. We need some thing to compare against. Nick's Thermomax panels will do as an initial reference.