The nascent energy storage sector is often described in terms of how fast it’s currently expanding — and its potential for explosive growth in the near future. But across San Diego County decades-old deployments such as ice storage are still in use just as cutting-edge technologies such as lithium-ion storage grab so many headlines. At the sprawling Mission City office complex in Mission Valley not far from Qualcomm Stadium, 29 ice thermal storage tanks help slash the energy costs for the owners of three office towers who retro-fitted the facility in 1999.