[pfdietz]

> It's cheaper to size production for winter sunshine than to build a lot of storage.

Which means enormous amounts of surplus power in the summer (even with PV angled to optimize winter production.) So storage doesn't have to go far to be worthwhile, and in particular with nearly free input energy it doesn't have to be very efficient.

[bryanlarsen]

It doesn't have to be very efficient, but it is has to be cheap. Batteries aren't cheap but they discharge every night so their cost is spread out over ~365 days and their cost becomes feasible.

Pumped storage is ~10% the cost of batteries, but if used as seasonal storage so they only discharge once per year that makes them ~36X as expensive. Especially in Alberta where they're competing against Natural Gas which is also approximately free (it's often flared off as a waste gas from oil wells rather than captured and sold because the value is less than the cost of capture).

[pfdietz]

For seasonal storage, it would be either an e-fuel (like hydrogen) or bulk storage of thermal energy (basically, artificial geothermal). The latter could produce very hot rock at rather shallow depth, yet still have thermal time constants of many years.

[bryanlarsen]

Both of those are more expensive than pumped storage.

[pfdietz]

This depends on the time scale. For days or weeks? Pumped hydro is better. But for seasonal storage? The size of the reservoir becomes prohibitive.

[bryanlarsen]

A water reservoir is a heck of a lot cheaper to make large compared to a hydrogen tank.

[pfdietz]

Hydrogen on this scale would be stored underground, preferably in solution mined salt caverns. This is a well established technology, although it's more used for storing natural gas. These caverns are very inexpensive to build, which is why they are used.

Alberta, as it turns out, is underlaid by kilometers of sedimentary rock that includes salt formations.