Batteries for large scale systems are usually either lead acid batteries dating back to around 1800, or lithium batteries from this century:
~1800 lead acid batteries
lead and sulfuric acid
3 year lifespan
shorter if used more
only 40% of capacity is usable
slow discharge and recharge
about $300 for each kWh stored
Example: our overnight campus use is about 100 kW for 20 hours or 2000 kWh (or 2 mWh). At $300/kWh this would cost us $600,000 and would last 3-5 years at max capacity, but in actuality it would be 2.5 times this because these batteries cannot be discharged all the way, so $1.5M.
~2010 lithium batteries (LiPO, Lithium iron phosphate, etc.)
Used in Prius, Leaf and other cars
fast discharge and recharge (good for regenerative braking in cars)
20 year lifespan at 80% capacity
expensive ($1300 per kWh)
Tesla's Power Wall is one example, so is the blue box in the student union and IT office. Kauai island is using these to move that island to complete energy neutrality in the next few years.
The same example above costs more, last longer, and requires fewer batteries. It also discharges faster to maintain our microgrid, and recharges faster when used as backup power for the IT building, protecting our computers from multiple outages we face with HELCO.
Pumped storage hydro:
Water tanks low on campus have a pump and a generator. When we have extra energy, we pump this water uphill to a similar tank where it is stored for use later on. When needed, the system activates the generator, which provides power for the campus. This is green, cheap, renewable, lasts 50 years or more and can be safely integrated into other water systems (e.g. fire suppression) as needed.
Check out the lead acid battery bank in the elab.
Check out the lithium storage system in the student union.