You'd think water would be easier to exchange heat with since it can slosh around the heat exchanger elements in the tank more easily. Which should translate to lower costs since you don't need as many exchanger structures in the medium.
Any guesses for the motivation in using sand? Maybe it's that you can heat it over 100C? But then big heat differences to the environment mean high conductive/radiation losses or heavier insulation requirements.
"Rock, sand and concrete has a heat capacity about one third of water's. On the other hand, concrete can be heated to much higher temperatures (1200 °C) by for example electrical heating and therefore has a much higher overall volumetric capacity."
and
"Polar Night Energy installed a thermal battery in Finland that stores heat in a mass of sand. It was expected to reduce carbon emissions from the local heating network by as much as 70%. It is about 42 ft (13 m) tall and 50 ft (15 m) wide. It can store 100 MWh, with a round trip efficiency of 90%. Temperatures reach 1,112 ºF (600 ºC). The heat transfer medium is air, which can reach temperatures of 752 ºF (400 ºC) – can produce steam for industrial processes, or it can supply district heating using a heat exchanger."
It is essential to study these tactics in this website... if only because they are the only "ground truth" known about Go. But for rapid improvement, the only real way forward is to play lots and lots of games to learn how the early game flows. Direction of play, which side of the board is most important and other such details.
Seems like a reasonably good tutorial in terms of layout. But just pointing out: joseki and direction of play is "more important" in terms of winning. Its just damn near impossible to teach so maybe its best for beginners to ignore this incredibly important (and difficult) subject.
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To put it in perhaps more concrete terms: playing a "tactic" position may net you +10 points across a sequence of 5 moves or so. (IE: One well placed tactical move, and ~4 followup moves may capture 5 enemy stones + 5 territory simultaneously from your opponent). However, every single early-game move is worth nearly +20 points of territory if played correctly. I'm serious.
That's why when you watch top-level Go play, there's a lot of "teleporting" across the 19x19 board, searching for the most important positions. And there is also very, very loose play and possible sacrifices / aji. (Maybe its not a true sacrifice, but you'd be willing to sacrifice if the opponent over-extends).
A couple of things I love about go is that you don't need to memorize fuseki, and that applying joseki correctly is as much a matter of judgment as it is of memory.
(I am a 1 dan go player but haven't played much in the last 15 years.)