You raise an important topic with somewhat unhelpful framing: "viable" is a boolean label for a continuous variable, the value of storage, which is context-depe

You raise an important topic with somewhat unhelpful framing: "viable" is a boolean label for a continuous variable, the value of storage, which is context-dependent today and an important feedback element in ever-shifting complex systems. Here's the frame I'd suggest: batteries, demand-response (to which efficiency contributes), grid management, and rate schedules are mutually supporting tools which allow us to continually improve our use of power along several axes, including GHG emissions, efficiency, end-user price, and reliability. There isn't one accurate and stable perspective from which to consider the "value" or "viability" of, say, compressed-air storage. Instead we have a web of complex local, regional, and global situations and concerns, and varying sets of goals to pursue within those situations.