Here, the experts at Power Control highlight the value of UPS systems when it comes to energy storage and renewables.
Developments within the power industry are happening at accelerated rates. Technological advancements in other sectors are having a domino effect on the power grid, resulting in increased pressures being put on the electricity industry to transition to a ‘smart grid’. Variable renewable energy (VRE), such as wind and solar, are being utilised to form decarbonised electric power generation.
For VRE to be successfully integrated into the grid, the future availability and cost of energy storage technologies are critical. Until recent years, the price of lithium-ion has made the technology seem unattainable. However, over the past decade, these prices have dropped significantly and the potential economic value that energy storage could bring to the industry has surpassed any preconceptions.
With that said, there are still many hurdles to consider before VRE gains prevalence. For example, without firming the production in a cost-effective way, the industry would not be able to compete with fossil fuels.
Options for energy storage
Although the concept of storing energy is not new, batteries have been storing energy since the early 1800s, innovative technologies have led to the diversification of now utilising them as storage devices. They are evolving into being used to store energy from on-peak renewable sources, ready to be released when there is a greater need, such as in central, de-central and off-grid solutions.
Lead acid was among the first battery technologies to be used for storing electricity. However, these batteries have a limited energy density and a working life that is not long to be economically viable for use as a grid storage device.
The rise in electric vehicles (EV) has contributed to the drop in price of lithium-ion. This technology is now 85% cheaper than it was ten years ago, and is expected to continue to become more accessible in the future. Li-ion batteries have one of the highest energy densities of any battery technology today, they have a longer working life and are capable of increased lifecycles.
Additionally, because they can be easily sized, lithium-ion batteries are more likely to be used to solve curtailment issues, particularly behind the meter and off grid sites.
What are the benefits of energy storage?
Maximise time of use rates
Batteries can store energy produced during low price periods and discharge it during high value periods. It is also beneficial for mitigating the shift in peak demand periods. For example, peak demand periods shift to the evening when there is no sun or wind to generate electricity.
Improve reliability and resilience
Just as a company invests in backup power on individual bases for specific devices or critical systems, the same concept applies for scaling up to an energy storage system at mains grid level.
Batteries are charged during low demand and discharged during high demand to help with balancing the voltage and frequency. The risk of unexpected VRE disconnection is also substantially reduced. Power outages can be costly for the operator and so having reliability measures in place is key to business continuity.
Integrate diverse resources
Energy storage systems not only smooth out the delivery of variable resources but can also support the efficient delivery of electricity for inflexible baseload resources. When demand shifts and baseload resources cannot react quickly enough, an energy storage system will inject or extract electricity to match.
With the UK’s target to bring all greenhouse gas emissions to net-zero by 2050, government initiatives are in place to encourage the switch to renewables by businesses and consumers.
Energy storage sits at the heart of increasing renewable energy uptake, it accelerates the broader adoption of renewable energy by improving the overall efficiency of the power grid. On a more local level, an energy storage system has no emissions so it can be placed anywhere within a facility and have no immediate impact on the environment.
Peak looping for high demand and EVs
Energy storage configured for peak looping is an ideal solution for applications that demand more power than what is available from the supply. A typical example of this would include EVs.
With the increasing popularity and a shift towards EVs, there is an increased demand for shorter charging times. EVs now require larger chargers, some of which consume 250kW to ensure rapid charging.
However, some charging stations with multiple rapid chargers are restricted by the maximum available supply. For example, if the local supply is only 200kW, the capacity isn’t large enough to supply ten chargers with a maximum capacity of 50kW at peak demand.
Battery storage systems resolve this problem by enabling batteries to charge from a smaller supply whilst enabling higher peak power outputs directly connected to the EV charging infrastructure. When there isn’t enough supply to meet the demand, this can prove to be a cost effective and environmentally-friendly solution.
Additionally, the batteries can be used as an uninterruptible power supply (UPS), keeping the EV charging throughout a mains failure and preventing some chargers from having to be reset or locked when power is lost.
Participation in demand response programmes
Energy storage opens up demand response programmes. Unlike the traditional demand response, this emerging technology allows consumers to shift from an event-based demand response, where utility requests the shedding of a load, towards programmed utility price signals. A 24/7 demand response where consumers see incentives for controlling their load.
Demand response will also help the grid to maintain stability during periods of high supply and low demand, giving financial incentives for grid operators too.
Where do uninterruptible power supplies (UPS) fit?
“As lithium-ion technology becomes more commonplace among UPS specialists, a UPS’ usage as an energy storage system will increase. Existing UPS topology can be modified effectively to grid tie and charge and discharge without the need for separate inverter and charger systems. UPS’ inherently have advanced battery management that can be used to ensure balanced charging and safety cut-outs in the event of thermal runaway,” comments Graeme Tucker, director at Power Control.
As with typical energy storage systems, the modified UPS is connected to the grid. The batteries are charged during low electricity price periods, storing that power and discharging it back to the grid when necessary. The reasons for which may be to smooth out the delivery of variable or intermittent resources (renewables) or to support the efficient delivery of electricity for inflexible baseload resources, injecting electricity as and when required.
The amount of power that can be stored/pushed back on to the grid is dependent on several variables. One of which is the number of batteries used. It is possible to configure the bespoke energy storage system with a large UPS system and a few battery strings or a small UPS system and many battery strings. The variations affect power availability and runtimes.
A modified UPS can also be used to manage battery storage, discharge and charge in applications requiring peak load looping. In this instance, the UPS charges the batteries at a constant rate while having the capacity to supply higher peak demand. Some UPS’ can also be used in conjunction with solar, hydrogen or other green energy sources to balance the peak load between the energy source, batteries and mains connection.