As a research area, grid integration of variable renewable energy resources touches all areas of electrical power engineering. It stretches into areas as diverse as economics and social science, is both applied and fundamental, and has aspects that require technology development and others that require analysis. It is topical and fast moving, has longevity, and involves stakeholders as diverse as policy makers, equipment manufacturers, and system operators. Grid integration is, in my view, the most interesting and exciting area of research in the world today. In addition to experiencing increasing levels of renewable energy sources, electricity grids are undergoing other significant changes including the deployment of smart meters, more active demand-side participation, and increasing levels of energy efficiency. Electricity is also increasingly moving into the transport (electric vehicles) and heat (heat pumps) markets. Hence electricity grids are set to become even more central in energy systems, and the future is truly “electric.”
Fastest Growing Resources
The fastest growing renewable energy sources are wind and solar photovoltaic (PV), both geographically distributed, variable, and difficult to predict accurately in advance. These characteristics make variable renewable resources challenging to integrate into electricity grids and are the key drivers of the research needs and opportunities.
The best variable energy resources, in particular wind, are typically remote from the load and existing generation and therefore require the development of new transmission. Public opposition to overhead transmission in particular is very strong. One of the solutions to this opposition is to bury transmission, but at scale this can be costly. It requires different planning and operating approaches that require research to further develop technologies [e.g., high voltage direct current (HVDC)], grid architectures, and planning and operating methodologies.
Research and understanding in the social science aspects of public opposition and the development of new approaches to the siting and permitting of transmission may help mitigate the opposition. For example, anecdotal evidence would suggest that many of the same people who object to transmission are also favorably disposed to the development of renewable energy resources. Maximizing the capability of existing transmission capacity, physically or operationally, requires research into, for example, the development of improved conductors and development of techniques to exploit dynamic line ratings.
Offshore wind resources are particularly attractive as they are very good resources, can be close to load, and are suited to larger, and more efficient, wind turbine designs. However, there are significant cost and technical barriers to large-scale deployment, e.g., the development of cost-effective, high-voltage power electronic devices such as breakers that would allow HVDC meshed grids. Lower voltage applications of power electronics, in particular the trend toward connecting the variable renewable resources to the electricity grids via power electronics, underpin the research importance of this fast growing research area. With increasing levels of power electronic interfaced generation, load and transmission on the electricity grid, the fundamental underlying nature of the grid will change. If the penetration levels go far enough, then what was a synchronous power system with some asynchronous generation connected will become an asynchronous electricity grid with some synchronous generation connected. The dynamics of these grids are not well understood, and research is needed to improve our understanding and develop mitigation measures to counter any negative implications.
In many regions the distributed nature of the variable renewable energy resource is such that much of the resource is not connecting to the transmission system (e.g., wind in Ireland is 50% connected to the distribution system, and solar PV in Germany is largely connected at the individual building level). Distribution systems present their own particular variation on the transmission research challenges, for example, voltage control with a large amount of distributed resources.
All of these electricity grid developments are bookended by the requirement to maintain or indeed improve system reliability. With increasing demand-side participation and the need to maximize the use of transmission capacity, the reliability metrics may need to be revisited. For example, the N-1 criteria is a deterministic criteria that has served the industry well, but it may be possible to develop probabilistic approaches that deliver the same level of reliability while minimizing transmission investment.
Variable renewable energy resources require more ancillary services, and, with almost zero incremental cost, they depress energy market prices. Research into new electricity market designs that reward capacity and the ability to provide ancillary services is needed. Done properly, these new market designs should incentivize the evolution of optimal generation portfolios with large renewable energy penetrations. There is a desire from many stakeholders to know what this future portfolio will be. With an almost infinite number of possible scenarios (e.g., future carbon/gas prices, technology improvements, etc.) and unknowns (e.g., how would we operate such as system), this is a significant computational, optimization, and modeling challenge and a fruitful research area. The existing generating portfolio and any near-future systems will continue to have very large penetrations of thermal generation.
With increased levels of variability and uncertainty and the need to maintain supply–demand balance, it is likely that these thermal plants will be experiencing more starts and more cycling. This cycling is potentially very costly, and research is needed to quantify the costs and impacts and develop and implement mitigation strategies. One example is new operational paradigms and/or new materials that can withstand heavier cycling duty. A potential new operating paradigm, requiring more research, is to optimize the system in a stochastic manner, using a range of possible variable renewable energy forecasts. Variable renewable energy forecasting technology is an area that requires further research, in particular to better forecast extreme and ramping events and to identify the forecast information format and content required to get the best operational performance from the portfolio of generation.
Capacity Needs to Be Built
As a university-based researcher with an interest in education, I cannot avoid making some mention of the all-important research/education interface. The need to grow human capacity for research, development, design, and deployment in the area of grid integration of variable renewable energy is well recognized. Power engineering programs, after years of decline in many parts of the world (such as in the United States), are now seeing a welcome increase in student enrollment, driven in large part by the student interest in renewable energy. However, there is a limited faculty capacity, ironically made worse by research opportunities.
Capacity can be built by attracting researchers into this area, and much can be learned from the experience and knowledge of others. For example, Denmark, Spain, Germany, Ireland, South Australia, and Texas all have high wind and/or solar PV penetrations, and there is extensive real-world experience, in industry in particular, of the research challenges and opportunities. It would be advisable for motivated researchers entering this area to look to these sources of experience for guidance, insight, and potential fruitful collaborations.