30-tube panel, facing south-east, 120L tank, retro coil, short 16mm pipework.
Clear sunny morning, boiler off.
Collector | Top of tank | Bottom of tank | Time | Activity
39.2 34.9 29.8 10:15
40.8 37.3 31.3 10:44
11:00 Washing machine started, approx 13L on 40C cycle
Hand dishwashing, approx 5L
42.4 38.7 32.7 11:19
11:20 Dishwasher started, approx 14L on 55C cycle, fed from hot water only
42.5 38.6 32.8 11:29
45.8 40 34.3 12:47 Weather turned cloudy
12:51 2nd Washing machine load, 40C cycle
37.3 37.6 28.6 14:09
So it looks like the hot water used today was almost free.

There would have been some electricity used to boost the washing machine to 40C and the dishwasher to 55C. The system performed well because there were no heat loses (e.g. tank cooling overnight) and high temperatures were not necessary.
Also at 14:09 2x64 Watt UniSolar panels connected to Soladin-120 grid tied invertor produced a peak of 44 Watts into the grid, but for most of the time generated 20-30 Watts.
-Paul