Flexibility of Smart Hybrid Grids
What are two-way smart hybrid grids
Electric grids are becoming hybrid, with an increasing contribution of renewables (RE) to the energy mix. In addition to RE generation plants, in some countries distributed energy resources (solar panels on rooftops, small turbines, etc) also feed their power networks, in a two-way energy flow. Due to the variable nature of weather-dependant-renewables (RE), managing this fluctuating energy supply is becoming more challenging for grid operators, who however are learning how to deal with an ever increasing RE generation, as in the case of Denmark, South Australia, etc. Use of smart technology, tracking closely supply from all sources and also user demand, can help too (Taskin and Sayedus 2020). Storing excess energy to be used during low generation periods is also a new need derived from using RE. Storage technology is a fast-developing field. This technology is needed for seamless power integration in the grid – storage needs to be flexible and respond fast to peaks of demand or low generation. Power demand is ‘communicated’ to generation plants, typically via power markets, that can fine-tune their management. This process allows to balance supply and demand. In addition to a two-way energy flow, there could also be a two-way information flow where energy users can be informed of different electricity rates/availability according to peak load and generation output. As the energy mix becomes more weather-dependent, voltage swings can cause the voltage to go out of regulation limits. Grids are becoming more reliant on storage to stabilise the system and to provide energy when there is little generation. In this respect, energy users could play a key role, as they could store energy during energy surplus/low energy rates, and sell it back to the system at the time when is needed (Taskin and Sayedus, 2020).
Figure 1: Schematic overview of the electricity system, Source: EPRS
There is a need to improve grid flexibility to cope with a fluctuating energy flow that can range from seconds (PV installations and Wind farms) to seasonal (Hydro-electric dams). Hybrid grids face several challenges because the energy mix is ever-changing (for instance, there can be sunny days and no wind but also overcast days with no wind). Also, grid assets can be exposed to quite different local weather conditions and hazards over their, typically wide, extent. A variety of events can disrupt grid operation across all timescales, from seconds (heavy machinery turning on or off, failure of a generator or transmission line) through hours, days, and months (power plant shutdown, routine maintenance). To minimize these vulnerabilities, the operator of a power grid takes into account specific features of each generator, such as its size, its start-up time, the maximum rates at which it can increase and decrease its output (its ramping rates), and its costs for electricity production. The grid operator also considers transmission constraints (USDE 2017).
As distributed energy mix becomes more complex, there is an increasing threat to the stability of the grid, there can be a cascading effect if generators simultaneously disconnect during a grid disruption, which can be weather related (e.g. during a heavy storm). For instance, the wind industry realized that wind turbines needed to be modified and actively managed, in accordance with grid operators, to account for variations in wind conditions.
Current grids form a complex system of systems, that are becoming ever more complex as new RE technologies get added, new assets get connected to grids, grid expansion reach out to remote locations or to neighbouring countries (including via underwater cables), while serving billions of end user’s devices and appliances, in addition to changing the type of energy demand (e.g. for e-commerce, home office, electrified transport, etc). New methods which recognise the complexity of energy systems in relation to social, technological, economic and environmental aspects including its emergent properties and adaptive and learning processes therefore need to be developed and implemented (Bale et al., 2015).
Overall, the electricity sector is confronting a complex set of changes and challenges. In particular for W&CSs, climate change is increasing the volatility of weather causing wide voltage fluctuations and damages to infrastructure. How these changes are managed is critical and could fundamentally transform the electricity system’s structure, operations, customer base, and jurisdictional framework (USDE, 2017).
References
- Bale, C, Vergara, L., Foxon, T. 2015. Energy and complexity: New ways forward, Applied Energy, Vol. 138, pp150-159
- Bandi, M.M.; Apt, J. Variability of the Wind Turbine Power Curve. Appl. Sci. 2016, 6, 262. https://doi.org/10.3390/app6090262
- Ruilong, D. Zaiyue, Y., Mo-Yuen, Ch and, Jiming, Ch. 2015. A Survey on Demand Response in Smart Grids: Mathematical Models and Approaches. IEEE Transactions on Industrial Informatics. 11. 1-1. 10.1109/TII.2015.2414719.
- Taskin, J., and Sayedus, S. 2020. Hybrid renewable energy sources power systems. In: Hybrid Renewable Energy Systems and Microgrids (pp.179-21, Academic Press. DOI:10.1016/B978-0-12-821724-5.00010-6
- USDE. 2017. Transforming the Nation’s Electricity System: The Second Instalment of the Quadrennial Energy Review Summary for Policymakers. United States, Department of Energy (USDE) https://www.hsdl.org/?abstract&did=797992
- Sohoni V, S. C. Gupta, R. K. Nema, A Critical Review on Wind Turbine Power Curve Modelling Techniques and Their Applications in Wind Based Energy Systems, Journal of Energy, vol. 2016, Article ID 8519785, 2016. https://doi.org/10.1155/2016/8519785
- WMO SG-Ene. 2022. Weather and Climate Services in the context of the global Energy transformation, In: Guidelines of the WMO Commission for Weather, Climate, Water and Related Environmental Services and Applications- Study Group on Integrated Energy Services, Integrated weather & climate services in support to net zero energy transition.