I have done my own solar hot water
And have been playing with boosting a bit.
After I gave up on the idiocy of the controller I bought, and built my own, I moved the booster over to running on a timeclock.
Here's the theory.
The booster is contolled by the timeclock AND the thermostat (set to 55c).
The termostat senses the bottom of the tank, and the tank tends to remain stratified from use. Solar heating circulation is all at the bottom - so that de-stratifies it during solar days. The booster is at the bottom, so that de-stratifies is during boosting.
At 4pm - the booster kicks in. If the thermostat (bottom of tank) is not at 55c, the booster will run until either 5:15PM, or it hits 55c.
I chose these times as at about 5:30, we throw the kids in the bath, and this pulls cold water into the bottom of the tank, possibly tripping the thermostat again.
So this way, we ensure that at the end of each day, we have a full tank of hot water, enough for our next 24hrs.
BUT - I have been thinking.
Say I set the thermostat to 85C and ran the booster 24/7 without the timeclock.
Solar would take that up further. Now assuming that it doens't open the releif valve and waste water / heat (it didn't when I tried this last week) - I have a tank of very hot water.
I would only need to use 1/2 the hot water i was before, and mix it down with more cold in the shower (my safety valve would do that automatically).
SO I would be using the same number of JOULES as before, it's jsut the tank has a higher standing temperature.
My use of X Joules of heat / day is constant.
The input of Y solar Joules / day is out of my control
I have to add electricity to ger from Y to X - regardless of tank temperature or the time it is added.
SO really, timing the boosting time, makes no difference the number of Joules needed / day.
THe higher the tank standing temperature, the greater the parasitic heat loss.
Every time you use hot water you pull about 3-5L into the pipes, that stays there when you turn off the tap, and then cools and the heat is lost. The higher standing temp will increase that loss (4L*50C vs 4L*90C)
So - after that huge explanation
Would this parasitic and pipe loss matter? Are we talking 1% of total HWS energy, or 50%.
It's worth thinking on.
I'm googling for info atm - but anyone with thoughts - I'm interested to hear them.