To achieve a more sustainable future, cities are rapidly adopting smart grid technologies. The integration of renewable energy sources, such as wind and photovoltaics, is increasing and resulting in power supply uncertainty. As a result, meeting energy system demands is more difficult. Rolling blackouts can occur due to an imbalance between supply and demand, prompting energy providers to keep turbines running at a few offline plants in order to increase production in the event of a sudden increase in consumption. Coal-fired backup generators can also be activated quickly in case of an emergency. However, these methods are either expensive or polluting, if not both.

Moreover, the penetration of renewable energy sources via power converters decreases the system’s inertia. In any power system, the frequency must be constant to balance the demand and supply. Rapid changes in generation or demand will have a greater impact on frequency stability in a system with a low inertia power. As a result, a more rapid reaction to variations in frequency is necessary.

One solution to the above-discussed issues is to use a battery to maintain supply and demand balance, but current energy storage technologies do not offer any financial benefits over power production. However, smart flexible loads in homes and offices that can be controlled remotely, and electric vehicles interfaced with the power grid could serve as virtual energy storage systems (VESS). Thereby, these alternatives to grid backup power generation are less expensive and emit less pollution.

The technology

A VESS integrates multiple controllable elements of energy systems, such as traditional energy storage systems, flexible loads, microgrids, distributed generators, multi-vector energy systems and local DC networks. It is able to respond to external signals by varying its energy exchange with the power network and is incorporated with power network operations. This means that flexible loads, small-capacity electric storage systems and distributed renewable energy sources can access the marketplace and offer power system services, such as transmission and distribution. While the virtual power plant aggregates distributed energy resources to function as a solitary power plant, VESS seeks to accumulate surplus electricity and discharge it as needed.

[See also: Introduction to virtual power plants]

Currently, there are a significant number of flexible loads but they are dispersed, small and diverse throughout the facilities. They are not a well-understood commodity at the moment, highlighting the need to develop control systems for scheduling their power consumption in a way that meets all the requirements of the system and also serves as virtual batteries, capable of holding and discharging a certain amount of energy, and doing so at a predetermined rate. In a fascinating conceptual leap, many scientists are considering making use of the power demand from electric vehicles and HVAC systems to function as a "virtual storage system."

Features

The promising features of VESS are outlined below:

• The system can integrate renewable energy sources into distribution networks more easily. Fluctuations in renewable energy generation output can be smoothed by the charging or discharging of a VESS. Increased distribution network capacity for renewable energy sources can also help alleviate voltage and thermal constraints on renewable energy sources integration.

• It makes it easy for developers to control the charging and battery condition of every virtual machine, irrespective of the host system's battery. The virtual batteries are discharged in accordance with the resource usage of their virtual machine, simulating the battery's behavior in the process. VESS can serve as battery resource containers thanks to this feature.

• This approach can defer the need for the construction of new transmission lines. Following a system contingency, a VESS can greatly boost the utilization of transmission systems by supplying immediate responses. As an added benefit, a VESS can delay the need for transmission reinforcements by reducing the likelihood of network congestion.

• The technology allows for a narrower gap between generation units, as the loading capacity of generators can be increased by using a VESS to decrease spinning reserve capacity. System operators can be informed of VESS capacity ahead of time as well as every second thanks to smart grid technologies.

• It can also provide value-added services. For instance, it can offer frequency and voltage support under emergency or system contingencies conditions. Additional primary frequency response specifications, which are currently met primarily by expensive frequency sensitive generation, are projected to rise over the next years in different power systems. For these services, VESS are technically feasible because they can respond faster, ramp up more quickly and have greater flexibility than traditional power sources.

[Discover more about power generation technologies and equipment suppliers on GlobalSpec]

Conclusion

The use of renewable energy sources is growing rapidly, but this also means that there are more unknown variables and fluctuations in power and voltage. Virtual energy storage systems can help in solving these issues and their effective management and integration with the power grid will lead to cleaner energy and a cleaner transportation future.

To contact the author of this article, email engineering360editors@globalspec.com