Maximizing the Renewable Power of Batteries

Energy Storage Systems (ESS) are a crucial component to improving energy resilience for residential, commercial/industrial and government sectors. We are looking for the highest level of innovative and efficient approach to how we use energy in various applications.

What is Energy Storage? 

“Energy storage” refers to any device (usually a battery or an “accumulator”) used for storing electric energy for later release and use. The effectiveness of an energy storage device is determined by how quickly it can react to changes in demand, the rate of energy lost in the storage process, its overall energy storage capacity, and how quickly it can be recharged. A key factor in assessing the viability of an energy storage device is its “energy density.”

What is energy density? 

Energy density generally is defined as the measure of how much energy a battery contains in proportion to its weight.  It typically is measured in watt-hours per kilogram (Wh/kg). A watt-hour is a measure of electrical energy that is equivalent to the consumption of one watt for one hour. Energy density in batteries generally refers to their available power when fully charged (again, as compared to their weight).

What are the different energy storage technologies or devices current in use in the industry?

Energy storage devices and technologies include the following:

Lead-acid Batteries: Lead-acid batteries were among the first and best-known energy storage devices.  They are not popular for energy storage at the “grid”-level because of their low-energy density and short cycle and calendar life.  They were commonly used for electric cars, but increasingly are being replaced with longer-lasting lithium-ion batteries.

Lithium-ion batteries: A lithium-ion (or Li-ion) battery is a rechargeable battery in which lithium ions move from the negative electrode through an electrolyte to the positive electrode during discharge, and back when charging.  They have high energy density, and generally favorable size and weight compared to other battery technologies, such that they have become prevalent in portable electronics (smart phones and laptops) and electric vehicles, and they have been expanding into aerospace and military applications.

Flow Batteries: Flow batteries are an alternative to lithium-ion batteries.  Though still far less popular than lithium-ion batteries (accounting for less than 5 percent of the battery market), flow batteries can be used in energy storage projects that require longer energy storage durations.  Flow batteries have relatively low energy densities and have long life cycles, which makes them well-suited for supplying continuous power. 

Solid State Batteries: Solid state batteries have multiple advantages over lithium-ion batteries in large-scale grid storage. Solid-state batteries contain solid electrolytes which have higher energy densities and are much less prone to fires than liquid electrolytes.  These factors make solid-state batteries well suited for large-scale grid applications. However, solid state battery technology has remained more expensive than lithium-ion battery technology (among other things, because growing lithium-ion production has led to economies of scale for that technology). One company, QuantumScape, recently (December 2020) released test results showing breakthrough performance in solid state batteries.  (According to the company’s press release, their “anode-less” design and ceramic separator create a battery where an anode of metallic lithium is formed in situ when the finished cell is charged – which apparently allowed a 15-minute charge to 80% capacity, significantly beyond what any type of EV battery is capable of delivering.) 

Hydrogen: Hydrogen fuel cells, which generate electricity by combining hydrogen and oxygen, offer several favorable qualities: they are reliable and quiet (no moving parts); they have a small footprint and high energy density; and they produce no harmful emissions (their only byproduct is water).  In addition, the process also can be reversed, making it useful for energy storage: electrolysis of water produces oxygen and hydrogen.  Fuel cell facilities thus can produce hydrogen when electricity is cheap, and later use that hydrogen to generate electricity when it is needed (in most cases, the hydrogen is produced in one location, and used in another).  Though hydrogen fuel cells remain expensive (primarily because of their need for platinum, an expensive metal), they are being used as primary and backup power for many critical facilities (such as data centers, credit card processing facilities, etc.).

Flywheels: Flywheels are mechanical storage devices. They are not suitable for long-term energy storage, but are very effective for load-leveling and load-shifting applications.  Flywheels are known for their long-life cycle, high-energy density, low maintenance costs, and quick response speeds.  Motors store energy into flywheels by accelerating their spins to very high rates (up to 50,000 rpm).  The motor can later use that stored kinetic energy to generate electricity by going into reverse. 

What is the relationship between Electric Vehicles and Energy Storage?

Energy storage is particularly important for electric vehicles (EVs). As EVs become more widespread, they will increase electricity demand at peak times (such as early evening, as users arrive home from work and plug in their cars for a nightly recharge).  To handle this demand without necessarily building new power plants, electricity will need to be stored during off-peak times. Storage also is important for households that generate their own renewable electricity (i.e., a car cannot be charged overnight by solar energy without a storage system). Notably, electric vehicles themselves also can be used as back-up storage during periods of grid failure or spikes in demand.  Although most EVs today are not designed to supply energy back into the grid, vehicle-to-grid (V2G) cars can store electricity in car batteries and then transfer that energy back into the grid later.  EV batteries can still be used in grid storage even after they are taken off the road (some utilities are using the batteries from retired EVs as second-hand energy storage). 

The importance of energy storage device technology in fields such as renewable energy generation and hybrid automobile systems continues to grow.  In the past decade, the cost of energy storage, solar and wind energy have all dramatically decreased, making solutions that pair storage with renewable energy more competitive. Energy storage can help address the intermittency of solar and wind power (and it also can respond rapidly to large fluctuations in demand, making the grid more responsive and reducing the need to build backup power plants).

Global venture capital investment in energy storage technology continues to boom, with over a billion dollars flowing into the sector annually. According to Wood Mackenzie and the U.S. Energy Storage Association’s (ESA) latest “US Energy Storage Monitor” report, 476 megawatts (MW) of storage were deployed in Q3 2020, an increase of 240% over the previous high, set in the prior quarter.  The U.S. battery energy storage market is set to grow from 1.2 GW in 2020 to nearly 7.5 GW (and 26.5 GWh) in in 2025, driven primarily by large-scale utility procurements. Solar-paired storage will account for a large majority of these installations, and potentially the vast majority, as developers aim to capture value from the Investment Tax Credit.  Other key findings from the report: 736.6 MWh of energy storage was deployed in the United States in Q3 2020, rising 179% year over year from Q3 2019, and 475.9 MW of storage was brought online in the United States in Q3 2020, rising 373% year over year.