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In regards to this question: How to determine the efficacy and potential energy of hydro power energy storage?.

I'm searching for a cheap liquid that I can use for a small scale pumped hydro storage. Obviously water came to mind but that has a freezing point of 0C. The average winter temperatures here are min -6C and max +7C. With some extreme days of -24C (a century ago) and more recently (a decade ago) about -18C.

I'm thinking to simply use a water mixture to lower the freezing point.

I'm intending to eighter make saline water at NaCl, wt% 23.3, lowering the freezing point to −21C, which should be more than sufficient. https://en.wikipedia.org/wiki/Saline_water.

Or making a water ethanol mixture to lower the freezing point. But in order to get roughly the same freezing point (-21C) with a 23.3% water ethanol mixture I need to used about 40% ethanol which is much more expensive than salt. https://www.engineeringtoolbox.com/ethanol-water-d_989.html.

  • Are there any other cheap liquid solutions or mixtures I could consider for volumes of 200 to 1000L?
  • Would (the viscosity of) saline water or an ethanol-water mixture affect the systems performance or degradation? As water alone has a viscosity of 1.002Cp and the 23.2% saline mixture a viscosity above 1.557 Cp.
  • Would the ambient temperature (further) affect the behavior's of the liquid?

Probably related: Pump power and fluid viscosity

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    $\begingroup$ As per my comments on your other question check out the effects of density and viscosity on the power calculation. $\endgroup$
    – Solar Mike
    Jan 12 at 10:33
  • $\begingroup$ A reasonable power bank stores a few hundred kJ. Do the math how high you need to pump those 200 or 1000l to approach this. $\endgroup$
    – mart
    Jan 12 at 13:38
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    $\begingroup$ @mart What does that matter? It's a test bed and learning opportunity regardless of the performance. $\endgroup$
    – Drew
    Jan 12 at 14:55
  • $\begingroup$ Exactly what @Drew said is the reason for this project. It's clear that chemical storage is most and much more efficient. Moreover, doing the math of this is exactly what my questions are about. $\endgroup$
    – Bob Ortiz
    Jan 12 at 17:19

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NOT a hydroelectric engineer, but I have spent a lot of years developing fluid systems using saline and related liquids.

To answer the basic question: yes saline works for hydro storage systems.

But there are issues.

  • Saline produces much worse corrosion than fresh water. Not just those parts immersed in the water, but anything that the salt gets on to which will mean anything even near your system.
  • When water evaporates you'll get salt deposits, which can clog things up.
  • Depending on where you have this system located, you face the risk of spilling a lot of salt water into an environment where this would be damaging to the plants and wildlife.

The water will be a bit more dense, which gives you MORE energy storage for the same volume and head height.

The water will be a bit more viscous... but I suspect that the effects this makes to a small hydro generator system would be buried in the noise.

Alternative methods of lowering the freezing point? Well the standard one is ethylene glycol type chemicals. AKA Antifreeze. As the name suggests, it stops water freezing.

It's also not corrosive. Indeed it's available in bulk amounts with corrosion inhibitors, and so would make life easy for the machinery you run it in.

Note that this is now a toxic liquid, and one that is sadly sweet, causing many tragedies with both children and pets. So that's NOT a good idea for any open system. And any large scale system would now face environmental regulations about the risk of spills etc.

If I had to deal with this issue I'd be leaning towards the saline, and use suitable marine quality materials to deal with the corrosion issues.

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