When you set up a water tank, you just pump water into it to get the storage medium, and when you need to extract heat, you can pump out actual storage medium and do the heat exchange directly. With a rock storage, you either need pipes in them or move air through the rocks, which requires a much beefier overall system since it's harder to extract the heat. Does that make sense?
Rusting tanks sounds like a problem with either badly engineered mismatched piping, or badly engineered tanks. Ideally, you'd have a well-engineered tank as a closed system with a heat exchange unit next to it.
By the way, I live in a town with a wide district heating system, and there's no storage at all in the individual houses here, only a small heat exchange unit. They are building a 200.000 cubic meter water storage system in the other end, though. I don't know about this particular project, but there are other projects where the water storage is large enough and insulated well enough that they actually do store cheap solar heat from the summer through the winter - and it's cheaper than using gas, even before the current price spikes.
Hot water heaters are always rusting and then leaking. Corrosion is always a problem with water and metal, along with sedimentation and the growth of slime.
With the box of rocks, yes you'll need to duct hot air in to heat them, and duct cool air in to extract the heat and blow it through the house. I don't know that this needs a beefy system, if you've got central air there is already most of the duct work in place.
https://www.stiesdal.com/storage/
for some time, and water tanks are simpler.
When you set up a water tank, you just pump water into it to get the storage medium, and when you need to extract heat, you can pump out actual storage medium and do the heat exchange directly. With a rock storage, you either need pipes in them or move air through the rocks, which requires a much beefier overall system since it's harder to extract the heat. Does that make sense?
Rusting tanks sounds like a problem with either badly engineered mismatched piping, or badly engineered tanks. Ideally, you'd have a well-engineered tank as a closed system with a heat exchange unit next to it.
By the way, I live in a town with a wide district heating system, and there's no storage at all in the individual houses here, only a small heat exchange unit. They are building a 200.000 cubic meter water storage system in the other end, though. I don't know about this particular project, but there are other projects where the water storage is large enough and insulated well enough that they actually do store cheap solar heat from the summer through the winter - and it's cheaper than using gas, even before the current price spikes.