The energy transition has now reached a significant level of maturity, driven not only by increasing attention to climate policies, but also by the falling costs of the well-established sources that are driving new installed generation capacity globally: solar photovoltaic and wind power. However, the development of the phenomenon is beginning to have a positive spillover effect on other generation technologies that are still experimental, but which are rapidly progressing in status thanks to a steadily increasing flow of green investments and growing attention to zero emission energies. Among the most promising are geothermal, bioenergy and marine energy.
Geothermal is already experiencing relative growth, with a 50 percent increase in installed capacity between 2010 and 2020 according to data from the International Renewable Energy Agency (IRENA). It is in fact a known source, with costs that are therefore already relatively low (according to the Lazard Institute, the levelized cost, the LCOE, is between USD 59 and 101 per MWh, compared to coal which ranges from 41 to 159). However, the potential is largely untapped, and the boost from the energy transition could be the key to launching it; on the one hand, growing investment in the sector could lead to the kind of evolution that could expand its exploitable areas, or increase the potential of those we already know about. Initiatives such as the Global Geothermal Alliance, launched at COP21, are now working to promote more economical ways of researching geothermal resources so that they can also be exploited in sectors beyond generation (heating for agriculture, for example) or even in small-scale electricity production. These are solutions that countries like Japan and Italy are working on. However, the contribution of large-scale geothermal will be important as capacity expands, especially in some key areas; this is the case in East Africa, where the ongoing expansion of the resource in countries such as Ethiopia and Kenya could be the key addition to solar and off-grid generation in order to achieve universal access to energy. These trends could revolutionize the contribution of renewables in the areas concerned, and are already corroborated by a growing global interest in geothermal: according to Bloomberg New Energy Finance (BNEF), between 2019 and 2020, investments in the sector have increased sixfold.
In contrast, the situation with bioenergy for electricity generation is more complex. While this source is usually mostly considered from the perspective of biofuels, its role in electricity generation is not insignificant: in 2018 it produced 546 TWh (in 2019 589), compared to just over 88 for geothermal (according to data from the International Energy Agency, the IEA, and IRENA). This is a growing figure that led the IEA itself in June 2020 to confirm its positive trend in line with the Agency’s sustainable development scenarios - the source's average growth in the last decade was around 6 percent. The most promising aspects, however, relate to the evolution of technology, driven in recent years especially by China; Beijing's goal is to increase centralized heat production in areas where agricultural waste is abundant, in order to replace the highly polluting coal-fired boilers, which are still widespread, especially in rural areas of the country. However, the country's investments also target electricity generation, which has seen substantial growth in recent decades, reaching nearly 30GW of capacity - low for China, but high for technology in general. Other countries are following a similar direction, such as Brazil and India. The flexibility of biomass generation could afford it an important role in the energy transition, especially in areas where the fuel is abundant. However, the key will be in the actual sustainability of the feedstock used: the leading players in global decarbonization will only be bioenergies with a negative contribution to emissions throughout their life cycle, a result that can be achieved only through monitoring systems and effective planning - two factors that are still insufficient in most countries focused on using this resource.
Perhaps the most interesting change is related to marine energy from the tides or motion of the waves. Until a few years ago, this resource was linked exclusively to a few plants in France and a few ongoing experiments in the North Sea - a tentative start compared to geothermal, for example, which is still reflected in the very small installed capacity worldwide, 0.56 GW in 2020 according to the IEA. While wave and tidal energy has not yet reached commercial maturity, it is perhaps one of the most dynamic in the world in terms of technological development; France, the UK, the U.S. and China are developing 1 or 2MW modules for harnessing tidal energy that are easy to install, quick to maintain and increasingly use standardized components (often taken from the wind industry) - thus breaking down the three main barriers to the source's development in previous decades. French plants from the 1960s were based on expensive and impactful artificial lagoons (such as the failed but more recent proposal for the Swansea Bay Tidal Lagoon in Wales), while these modules are anchored and can be transported without using dedicated ships (unlike the experiments of the early 2000s). In this sense, tidal technologies are growing faster than wave technologies, thanks both to the non-intermittence of generation and the possibility of complementing other components of the energy transition and the so-called blue economy, i.e. the sustainable use of marine resources. The recent boom in offshore wind in Scotland, for example, is contributing to the development of research in marine resources, which in recent years has seen the birth of the center of excellence in the Orkney archipelago - where, in fact, the largest tidal generation plant has just been tested. Marine energies could also be a key off-grid resource in general for decarbonizing islands, where diesel generators are often the only alternative for energy-intensive activities such as water desalination. A varied panorama, but one that underscores the shift in the energy transition from a phenomenon focused on a few core technologies, to a systemic change that involves and will need to involve new sectors and new sources.