Link: https://interestingengineering.com/energy/store-summer-solar-power-winter

A Norwegian startup has secured USD 17.5 million (EUR 15 million) in a Series A funding to develop a new seasonal energy storage system aimed to help homes store excess amounts of solar energy in summer for use during the winter.

Designed by Oslo-based energy storage scaleup Photoncycle, the seasonal solid-state hydrogen energy storage system is set to roll out commercially in Denmark and the Netherlands. It aims to tackle long-duration storage across seasons, one of the greatest challenges facing renewable energy systems.

That article is light on details about what exactly a "solid-state hydrogen energy storage system" is? How does it work?

Likely a metal hydride based system. It is at present the only geniuinely mature way of storing hydrogen in a solid state form.

Solid state hydrogen storage is essentially a sponge made from a metallic hydride (NaAlH4, MgH2, LaNi5H6, etc) or some other material which either absorbs or releases hydrogen depending on its temperature.

Advantages: low pressure operation (reduced losses during extended storage), controllable and predictable release rates, much less risk of explosion vs pressurized hydrogen.

Disadvantages: larger, more expensive, and more than 10x heavier than a compressed liquid hydrogen container of equivalent capacity, plus chemical degredation over time can limit the lifetime charge/discharge cycle count of certain mediums.