Testing basin-type solar distiller prototype-2

Today, Tuesday, December 3, 2019, Perth, Western Australia, it is mid-summer and the forecast is 39 degrees C, with scattered clouds. A good day to test the second prototype basin-type solar water distiller.

This distiller is pushing the limit of low angle for the glass, aiming for the narrowest possible design. The glass angle is 10 degrees and the depth of the distiller is 140mm -- well, kind of, it is constructed with 140x12mm pine on the sides.

Some posts on design and construction of the basin-type prototype #2:

https://bkhome.org/news/201911/first-go-at-using-expanding-foam.html

https://bkhome.org/news/201911/more-planning-basin-type-prototype-2.html

So, 10 degree angle, white inside walls, how will it perform? The angle is probably going to be optimum in summer, and dismal in winter. Anyway, I set it up early this morning, around 7.30am. Initially in the shade of my garage. Orientation due North. Here it is, while still in shade:

...it is sitting on a small camping table, but could have used any old cardboard box.

By 8.30am it was about 45% still shaded and hardly even warm.

8.45am: Sun just over entire panel. Sun intensity: 890 W/m2, ambient temperature 34 degrees C (yes, already hot!). Holding the IR meter about 3 inches above the glass, about 3/4 the way up, temperature is 32 degrees C, back side of the distiller is 32 degrees C. There is a slight breeze.

Time am/pm	Sun W/m2	Ambient deg C	Top deg C	back deg C	Comments
8.45	890	34	32	32
9.00		33			Official temp., via phone. Wind 24km/h
9.35	945	35.6	49.8	44.6	Only a very tiny amount of water out
10.35	940	37.7	64	51	Still not much water out
11.35	960	39.7	74.1	57.7	Some wispy clouds
12.00		41			Official temp., via phone, wind 13km/h
12.35	960	40.2	79.8	62	Lots of puffy clouds, ait mostly still or slight breeze
1.00					Moved the still slightly, facing sun at 1.00pm
1.55	985	40.6	74.9	56.5	Cloud cover increased, puffy clouds. Slight breeze
2.00		40			Official temp. Wind 24km/h
3.00	950	40	69.1	54.2	Clouds mostly gone
4.00	910	38.2	62.2	52.2	Blue sky, no clouds
5.30	760	36.3	50.4	46.3	No water coming out

Packed up at 5.45pm. Collected distilled water: 1.85 litres

The temperature readings of the glass are very high. This is obtained by pointing my IR meter at the glass, about 3 inches away, 3/4 of the way up. So it is not the inside temperature that is being measured, only an indication, and I think inside it would be even hotter.

So, my previous thinking that the inside of the distiller would not reach 80 degrees C was wrong, and I need to think carefully about what materials are used, that will retain integrity at that temperature.

The effective surface area of the glass is 0.652*0.542 which is 0.35 metre-squared.

How does this compare with the other distillers? I have not yet tested the F-Cubed C1000 distiller in mid-summer, only in winter, when I got 3.1 litres. So I will use the claimed mid-summer output, claimed by F-Cubed, which is 6 litres. That is a 1 metre-square panel.

Here is an earlier post discussing the claimed performance of the C1000 panel:

https://bkhome.org/nomad/water-desalination.html

I am no longer going to compare by litres/hour, as the different designs work differently. The basin type is slow to get going in the morning, as it has to warm up, and internal stored heat may cause it to produce water a bit longer in the afternoon. This gives a different water output profile then the tilted wick-type, so it is simpler just to compare the total water produced in a day.

Another factor: with the sun oriented differently in the sky in mid-summer, the shade from my patio that came across the distiller late afternoon in the winter, can be avoided in mid-summer. meaning that today I got the sun on the distiller for more hours in the afternoon (albeit at an extreme angle).

Another note: I did move the distiller slightly, so as to avoid the afternoon shade from the patio, and also changed the orientation slightly, facing the sun at 1pm whereas before it was facing 12 noon. I probably should not have changed the orientation, even though only slight.

Normalizing the water output of my distiller, so as to compare with claimed output of the C1000:

1.85*(1/0.35) => 5.28 litres

That means my prototype #2 is 88% as efficient as the C1000 distiller!

I tested basin-type prototype #1 here:

https://bkhome.org/news/201911/first-test-basin-type-proto-1.html

Which produced 1.525 litres, though I did not leave it out quite so long in the afternoon, as it was not moved to avoid the afternoon shade. Prototype #1 has a larger piece of glass, 0.493 m2. Normalizing to compare with the F-Cubed:

1.525*(1/0.493) => 3.09 litres

Much less efficient. I wrote it down somewhere -- I think the glass angle was 35 degrees, rather high. Lots of side walls to loose heat. Interesting, the glass didn't get so hot.

Where to next? Enough prototypes! Basin-type prototype #2 has excellent efficiency, enough for me. The absolute efficiency of the C1000 is claimed to be 55%, so that means my prototype #2 is 0.88*55 => 48.4% -- that is very high for a basin-type.

I think that the "final design" needs a bigger glass angle, to perform better in winter, and I am thinking of 20 degrees. Also, the proportions of the glass can be changed, wider, less depth from front-to-back.

Tags: nomad