As some put it, energy storage may be the holy grail of clean energy technology. It is the glue that can bind sustainability to everyday life. It is the sought after hope that if we lose power, proven battery technology could quite literally shed light to get us through the dark.
Forms of Energy Stored
Energy storage is any medium that can store various forms of energy over controlled periods of time. Energy comes in multiple forms including: radiation, chemical, gravitational potential, electrical potential, electricity, elevated temperature, latent heat and kinetic.
Energy is a highly volatile resource and very tricky to package into an economical storage vessel. Science has begun catching up with this concept. The advances in our research and development of energy storage technologies have become less science fiction and more of a business case for the energy services industry. Now that the key energy storage technologies are out of their beta testing sites and available to the public, the gap between feasibility and probability could be bridged. Energy storage systems are designed to be charged from on-site sources of power generation such as solar panels or wind turbines, but can also be charged by the grid during off peak hours when rates are lower.
Energy Storage Technologies
Lead acid batteries have been a common form of energy storage and remain the most economical. To form a good pitch for lead acid batteries would be to focus on charging time, simplicity in design, long lifecycle in deep discharge applications, fast module replacement, and proven safety record.
Lithium ion is a storage medium that can reliably handle energy produced from solar panels, among other sources of on-site power. The actual output of lithium ion batteries is slightly lower than the rating. The kilowatt (kW) output is affected by usage and design. Multiple lithium ion batteries can also be installed together to increase storage capacity. The design provides an advantage of being wall hung as opposed to displacing the weight on the floor. Available in 7 kW and 10 kW models, these batteries are designed for large homes or small commercial applications.
Sodium ion batteries have a similar capacity rating to lithium, but are slightly heavier. They also need adequate floor space for installation, a 30.6 kW battery module takes up about 5 cubic feet of space. Sodium ion batteries perform best when equal portions of stored energy are discharged over a span of a few hours or more. They are available for purchase in 2.6 kW and 30.6 kW models.
Utilizing Energy Storage
Demand response is an available program for utility customers used to reduce peak electrical loads. A customer who enters into a demand response contract will be under obligation to shed a portion of their building’s electrical load at certain times per year. There could be up to four demand response events annually, normally occurring during the summer months when electrical usage peaks. For more information about demand response programs, you would need to speak with a Curtailment Service Provider (CSP) who works directly with an Independent System Operator (ISO).
Frequency regulation is implemented when a utility customer wants to clean up the power at their facility by installing ancillary services to balance the electrical transmission from the grid. You can identify where frequency regulation is applied by locating the power factor on your electric bill. You may find a power factor of .8, which represents an electrical inefficiency of 20%. Installing ancillary services (ex. energy storage), can help reduce your power factor closer to a value of 1.
In terms of technology, lithium ion has an advantage because it can perform acceptably well for both frequency regulation and demand response. The batteries operate effectively for the shorter, quicker burst of energy needed for frequency regulation or can be spread out for longer durations during demand response events. However, lithium ion batteries have limitations. It’s important to be clear on the minimum percentage to which lithium ion batteries can be discharged before having a negative effect on performance and lifespan. Some can only discharge energy down to 60% while others may perform better.
Sodium ion batteries function well for demand response but not frequency regulation. Available models are designed to discharge from 4-6 hours, but can operate up to 20 hours per cycle. Sodium ion batteries can discharge close to 90% of the useful energy per cycle having minimal impact on lifespan or performance.
Lead acid batteries are the most well adapted form of energy storage and commonly used for Uninterruptable Power Supply Systems (UPS) to prevent failures of critical infrastructure such as Data Centers. In comparison, lithium ion and sodium ion have yet to be approved for installation in strict metropolitan areas such as New York City where lead acid are already code compliant.
Energy Storage for Micro Grids
Down the road, implementing building infrastructure with a combination of smart meters, on-site power sources, energy storage systems and demand response would create a smart grid. During brownouts or blackouts, a utility company could reduce strain on the centralized grid by using a smart grid to safely shed loads in one place while diverting electricity to another, opening the door to a decentralized approach to power generation by forming micro grids.
Having on-site generating capabilities is becoming a more relevant conversation as time progresses and our needs are dependent on utility convenience. Many on-site distributed generation resources are sold based on payback with the economic feasibility proven by the savings. This is where energy storage by itself can be tricky.
Combining multiple forms of on-site generation with smart grid technology, ultimately making a micro grid, can provide the greatest performance in terms of return on investment while making your building more resistant to power loses (grid resiliency).