An iconoclastic Canadian startup just raised a landmark investment from Goldman Sachs to build massive storage for clean energy. Hydrostor stores surplus electricity by compressing air into underground caverns. It updates a long-standing technology that never took off for electrical storage. Hydrostor thinks the tweaks it has made will allow underground storage to work in more places — just as grids increasingly need help turning wind and solar production into reliable 24/7 electricity. Goldman Sachs agreed and invested $250 million from its private equity division. That’s unusual for the long-duration energy storage sector, which typically draws riskier venture-capital investment.