2.6 bar is approx. 40 psi, so the tank won't take a lot of pressure (most of us have a 20-40/30-50/40-60 pressure switch and most city water I have come across is at least 40 psi or more). What I don't see are expansion tank and temperature/pressure relief valve which stops an enclosed pressure vessel from becoming a missle when the water inside is heated up and expands.
I have solar thermal on my roof and my system has both T&P valve and potable water expansion tank to keep explosion from happening. Solar thermal can be very efficient on a sunny day for sure.