Glass bottles with water floor for thermal storage?

Has anyone ever tried using glass bottles (beer bottle size, but with a closable lid that seals) filled with water, lying on their sides in tight rows, with cob or cement mortar to hold them in place, as a thermal mass heat storage for passive solar home design? (insulated underneath, of course)

I saw a picture of bottles in the floor and thought of this idea but am having trouble finding anything online to see if people have tried it.

At a time when I had no money and was building a small house, I used bottles instead of road base as a floor subgrade.
I just laid them out and covered them with 20mm road base and saved about   80% of the required fill.

I like John's suggestion to use them as a filler.

I feel that the water is not necessary as a thermal mass unless it is possible to use the sun as a feature to heat the water.

That is why using the bottle for walls is a good example of a thermal mass in passive solar.

I think it's an interesting idea. I haven't tried it, but would be worried about leaks over time. The bottles would need to withstand a fair amount of temperature cycling as they absorb and release heat. I suppose if you used beer bottles or similar that are designed to withstand internal pressure that might work.
thermal capacity of water is extraordinary however:
water: 4182
slate: 760
limestone: 909
brick: 840
(all J/kgdegC from engineering toolbox) The larger the number the more heat energy a material stores per unit mass. So a smaller amount of water will store more heat energy, which could be an advantage in a suspended floor I suppose.

 Instead of putting the bottled (or other moderate sized water containers) in the floor, place them up high, in a loft, supported by a bearing wall on a foundation, like the exterior wall between a sunspace or solar greenhouse, and the rest of the house.  such a wall can easily support the weight.  Warm air (from a sunspace, solar greenhouse, solar air heater, or even dark blinds at windows, that will intercept the sunlight and serve as a solar absorber) will then rise (passively) to warm the bottles, creating a thermal syphon loop.  With the heat storage located above the living space it can get quite warm without overheating the living space.  Then, when the house needs heat either a duct and fan, or even a ceiling fan can bring warm air down to living space level, so that you effectively have passive solar without needing the big heat loss through direct gain windows, and can even have thermostatic control, to avoid temperature swings.

- Retired designer of passive solar homes -

To avoid the problem of leaks, how about filling with sand?

If you leave parts of the bottles showing, stepping on an arc of glass on the floor sounds like a dangerous situation, especially if wetness is involved in any way. I dropped a cast iron skillet on the floor a while back, that would take out any glass bottles it hit, now there would be broken glass and water on the floor, and a hole when you get it cleaned up.

If you plan to cover the bottles deep enough to make the floor smooth for use they will need to be covered, at that point cob or cement are great thermal mass on their own, unless you happen to have several thousand bottles around that you are trying to use up, I'd suggest just make a decent depth of cob or cement. Much less problems.

Phil wrote:  "To avoid the problem of leaks, how about filling with sand?"

Hi Phil;

Though standing bottles upright, with the sealed opening  on top, should solve the leak problem, there are generally more problems with sand than with water, due to effectiveness.

Sand has less than a third the thermal mass of water, per volume.

Sand also weighs 60% more by volume, therefore about 5 times (or more) as much weight per thermal mass, so it generally needs to be located low.

Dry sand has an Rvalue of about 0.58 per inch, while water thermally circulates, so has virtually 0 Rvalue, though it tends to stratify, which for small containers with large surface areas, such as bottles, is generally a non-factor. ..and in big containers can be used as an advantage.

Concerns with water might be 1) freezing, 2) leakage, and 3) corrosion.   All three of these might be overcome by using recycled plastic containers, which can literally freeze solid without bursting. . However, that introduces an issue of evaporation through the surfaces of the containers, after several years. That could be reduced by a low permeability, vapor barrier paint, and/or a partial covering (around the middle) of aluminum tap, which while it would be difficult to fully cover a bottle, has a permeability that is virtually zero, and also reduces the radiant heat losses, which might be an advantage in an air convective heat storage.

As I have stated before, my recommended location of a thermal mass using small containers would be above the heat source, where air can naturally/passively convect up to it. This configuration also provides very good control of heat coming out of the heat storage to the space that is to be heated. An active fan (electric, even supplied with green electricity) can be used with a thermostat for passive solar heating with virtually full control, while avoiding the labor and/or cost and thermal uncontrollability of a heavy masonry thermal mass.  It also opens up the choices for the floor, including wood frame structures. and second story solar gain.

- Retired designer of passive solar and highly energy efficient homes -

This might help:

https://permies.com/t/74719/air-pocket-beneath-earthen-floor