The cheapest option-solar thermal- is not even considered?
Here the EU project COMBISOL:
Interesting reading promised!
Here some samples of hydraulic arrangements at page 25, all tried and tested:
Since all homes must include a certain 'renewable' coverage of their thermal energy demand trav's research is not very usefull. Rather useless, no insult intended!
According to EU legislation ALL DHW systems must be rated from the 1st of June this year, i.e. the primary energy input must be compared to the output. At the tap that is.
Shown in clear numbers to the consumer (home owner).
And the combination of clear energy labeling/rating with the fact of the renewable energy mandate leaves only 1 option to be most cost effective.
And that is the usage of ST energy.
Modern (combi-) boilers modulate, are fully suitable to use pre-warmed water topping up only what is necessary at the point of draw.
From ca. 1.5 kW upwards. So using a 26 kW boiler to provide 3-9 liters of warm water per minute (sink or shower)is technical and economical non-sense, insult intended (smiley).
If using electricity in the DHW system then for the solar pump. 4-12 Watts per hour of sunshine, not more. So called 'A-rated circulation pumps'.
These A-rated circulation pumps are soon to become mandatory anyhow (January 2013?).
And if still insisting on electric resistance then a direct flow module. No storage loss. And of course: solar compatible, ready to use pre-warmed water, see above.