There's definitely politics involved, but also the prices of solar, wind and batteries are and have been steadily falling.
One mental blindspot when comparing storage is to assume you need X amount of stored energy, but of course no-one wants stored energy, they just want energy.
Storing it only makes sense if you can't generate it for less so you need to compare against a portfolio of generation and short term storage. If you can't beat that on economics then you're useless, even if no other tech can beat you at your specific task of long duration storage.
At least as of a year ago, pumped hydro was cost competitive with lithium ion batteries and filled the 10 hour niche. The other benefits are longer lifespan and domestic construction.
Lithium ion batteries filled the sub-10 hour niche.
But lithium ion battery costs will keep falling and pumped hydro costs won't fall or will increase alongside rising labour costs and gutted state capacity. So there could be a crossover point if it hasn't already happened.
Remember that energy and power are distinct quantities. A battery can easily match the power output of pumped hydro, but pumped hydro can exceed the energy storage of even the largest battery. The energy storage of pumped hydro is only limited by the size of the lakes, and lake size is only loosely linked to cost since the lake will potentially already exist. If a lake is artificial, volume increases non-linearly as a dam gets higher.
For example, the largest batteries can currently store about 3GWh of energy, but Snowy 2.0 will store abut 350GWh. Smaller pumped hydro schemes are typically 8GWh up.
Pumped hydro is suited for wind storage, and lithium ion is suited for solar storage, is a good approximation.
Snowy 2.0 with 2.2GW power and 350GWh energy will be great for multi-day wind surplus followed by multi-day dunkelflaute. But not as useful for solar, which is more stable, and where the droughts are seasonal in nature rather than weekly.
The opposite may happen. Batteries follow a learning curve where the price drops exponentially in volume. High demand means a larger industry which means more scale benefits and cheaper prices.
Solar panels could be a comparison. Demand has been growing exponentially but this has actually pushed prices down because this demand drive the learning curve.
Or maybe the prices are being pushed down by the chinese government? I remember reading some news about how european governments are upset over this.
In general, I wonder how much do we really know when we talk about cause and effect in economics. We see prices going down. We attribute it to something. But without experiments, how can we be sure?
We see it in other goods like lightbulbs. Economies of scale is understood. The learning curve for solar/batteries has been stable for almost 50 years.
A small part of the price declines is due to subsidies from the Chinese government but I don't believe it's the best explanation for the 97% price drop.
But if you can answer the question "how much would batteries go up in price next year if China removed subsidies", I'd genuinely like to know the answer to that because it is important.
One risk is a war between the US and China, regardless of the subsidy question. So we should get good at domestic alternatives like compressed air and pumped hydro, and work towards our own manufacturing of batteries.
Most pumped hydro is short-ish term storage and at full capacity runs from full to empty within 10-20 hours. And in a new development there's nothing really stopping you from putting in more pipes and generators so you can get the full energy out in half the time if that makes more economic sense.
Conceptually they are like batteries, just with the ability to scale max discharge rate and max capacity somewhat independently, a much lower cost per MWh stored, but high engineering complexity because each site needs a bespoke solution.
Of course there are some projects that just go for huge storage and few generators. Sometimes they serve another purpose and just have generators as a side benefit. And sometimes they don't make a lot of sense and seem to just be built that way to be more impressive
One mental blindspot when comparing storage is to assume you need X amount of stored energy, but of course no-one wants stored energy, they just want energy.
Storing it only makes sense if you can't generate it for less so you need to compare against a portfolio of generation and short term storage. If you can't beat that on economics then you're useless, even if no other tech can beat you at your specific task of long duration storage.