Geothermal energy technologies have differing levels of maturity. The exploitation of hot rock resources, e.g. by means of EGS which is currently in the validation phase, has particular potential for improvement

Long-term, sustained and substantially higher research, development and demonstration resources are needed to accelerate cost reductions and design, and bring novel geothermal concepts to market. These advanced technologies have to be proven in pilot plants, meaning that strong government support for innovative small plants is needed.

R&D will need to focus on understanding better how fractures open and propagate in different stress regimes and rock types, in order to be able to better assess the hot rock potential. Similarly, a common approach in identification of advanced hydrothermal resources will help assessing its potential.

Why is this gap important?

Drilling costs account for 40‑70% of the total capital costs of a geothermal power project. It is also a very time-consuming part of the project.

Technology solutions

The economical drilling of low-cost, exploration-only boreholes and drilling into deep, hard rock formations poses technical challenges that require new and innovative solutions.

Improving geophysical data inventories and geoscience exploration methods, as well as innovative geothermal resource assessment tools, would reduce exploration risks and thus diminish this investment barrier.

Two key research areas are state of stress and lost circulation events. State of stress refers to the condition of the fracture networks below the surface that permit geothermal energy to permeate and become usable for transformation into power and useful heat. This is particularly important in enhanced geothermal systems, as the stress field is measured exclusively through exploration-only drilling. Therefore, extending understanding and monitoring of fracture networks could make it easier to site wells more optimally and reduce overall exploration and drilling costs.

Lost circulation events happen when fluids are pumped into the reservoir to aid in drilling and are then lost to other underground formations and are not recoverable. Being able to better predict these events and reduce their impact would also reduce drilling costs.

What are the leading initiatives?

Bergakademie Freiberg technical university is carrying out leading research, and important research is also being done in other universities across Germany, at the University of Tokyo together with Tohuku University, and by other organisations.

The US Department of Energy (DOE) has announced it will put up to USD 7 million towards the research and development (R&D) of innovative subsurface geothermal technologies, with a component dedicated to improving geothermal drilling efficiency, focusing on state of stress and lost circulation events.

Although geothermal energy has significant technical potential globally, it receives minimal investments compared with other clean technologies, with funding provided mainly by public research programmes.

Why is this gap important?

So far, utilisation of geothermal energy has been concentrated in areas with naturally occurring water or steam, and relatively permeable rock. However, the vast majority of geothermal energy within drilling reach – up to 5 km with current technologies and economics – is in relatively dry, low-permeability rock. Heat stored in low-porosity and/or low-permeability rock is commonly referred to as a hot rock resource, and in contrast with most hydrothermal resources in use today for power generation, hot rock resources are available worldwide.

Technology solutions

Hot rock resources are characterised by limited pore space and/or minor fractures, and therefore contain insufficient water and permeability for natural exploitation. Hot rock resources can be found anywhere in the world, although they are closer to the surface in regions with an increased presence of naturally occurring radioactive isotopes (e.g. South Australia) or where tectonics have resulted in a favourable state of stress (e.g. in the western United States). In stable, old continental tectonic provinces that have low temperature gradients (7°C/km to 15°C/km) and permeability, but a less favourable state of stress, depths will be significantly greater and developing an enhanced geothermal system (EGS) resource will be less economic.

Technologies that allow energy to be tapped from hot rock resources are still in the demonstration stage and require innovation and experience to become commercially viable; the best-known such technology is EGS. Other approaches to engineering hot rock resources, which are still at the conceptual phase, experiment with methods other than fracturing the hot rock. They aim instead to create water inlet and outlet connectivity, for example by drilling a subsurface heat exchanger made of tubes underground, or by drilling a 7‑km to 10‑km vertical well of large diameter that contains water inlets and outlets at different depths.

EGS research, testing and demonstration is also under way in the United States and Australia. The United States has included large EGS RD&D components in its recent clean energy initiatives as part of a revived national geothermal programme. A global map of hot rock resources is not yet available, but some countries, including the United States, have started mapping EGS resources.

Why is this gap important?

Geological databases already exist for several parts of the world, but they could benefit from incorporating and aggregating the more complex data emerging from advanced remote sensing and monitoring of hydrothermal resources around the world. Combining these at the greatest granularity, extending them geographically, and reinterpreting, recompiling and standardising them would enable the creation of a publicly accessible, globally relevant database for use in assessing, accessing and exploiting geothermal resources.

Technology solutions

Industries and research institutes are now working towards an integrated approach for comprehensive characterisation of hot rock resources in a variety of geological settings. To better assess hot rock potential, R&D will need to focus on understanding how fractures open and propagate in different stress regimes and rock types. Similarly, a common approach to identify advanced hydrothermal resources will help to assess potential.

R&D is also required to enable exploration and assessment of hidden hydrothermal geothermal systems and hot rock resources. Rapid-reconnaissance geothermal tools will be essential to identify new prospects, especially those without surface features such as hot springs. Verification is needed on whether airborne-based hyperspectral, thermal infrared, magnetic and electromagnetic sensor tools can provide data inexpensively over large areas (TRL 10). Other tools might include ground-based verification, soil sampling and geophysical surveys (magnetotelluric, resistivity, gravity, seismic and/or heat flow measurements).

Exploration-only drilling technology is vital to enable EGS, because the in-situ stress field can only be measured in boreholes, but it needs to become much less costly to be practical

Innovation in solar power needs continued focus on increasing the performance of commercial PV systems and a shift to cell and technologies that are now only in the pipeline. At higher penetrations, innovation can enable PV to contribute to their own integration through smart grid capabilities, which can mitigate the impact of incidents on the grid. Innovation in digital technologies applied to solar PV systems can also deliver a higher share of mini- and off-grid systems and increase energy access in developing countries.

Why is this gap important?

The wide array of system designs now available – off-grid, mini-grid and on-grid – increases the number of methods available to obtain electricity access. Off-grid technologies (such as stand-alone solar home systems), mini-grids and energy-efficient appliances are complementing efforts to provide electricity access from grid expansion. Such decentralised systems can help fill the energy access gap in remote areas by delivering electricity at a level of access that is currently too expensive to be met through a grid connection, and in urban areas by providing back-up for an unreliable grid supply.

Technology solutions

So far, solar home systems, which are increasingly cost-competitive with kerosene and diesel, have been the technology most widely deployed with these new mobile platforms and pay-as-you-go (PAYG) financing. PAYG (TRL 11) helps consumers overcome the high upfront costs of the technology that traditionally has been a significant barrier to uptake in poor communities. Mobile technologies, such as cloud-based metering and software platforms (TRL 10), can also be paired with larger systems such as mini-grids, which could be used to offer households additional services and provide power for productive uses such as irrigation, for example.

Highly efficient household appliances integrated with a core solar product are being more widely deployed but could benefit from further innovation in both offerings and technology bundles. Decreasing electricity demand through the use of efficient appliances can reduce the upfront costs of a system, such as a PV panel, delivering significant cost savings even when the increased cost of the appliances is taken into account.

Beyond its use for billing and asset monitoring purposes, the wealth of data generated by many off-grid systems could be subjected to big data analytics and artificial intelligence interpretation to enable better tailoring of equipment and modular asset scale-ups, better planning, improved device management and maintenance, and wider commercial offerings.

Solutions that link to productive-use appliances and energy carriers (e.g. agricultural implements, refrigerators) have a great potential to accelerate these systems. Large suppliers of mini-grids, industrial captive power or larger stand-alone systems, and that have knowledge of the productive-use market, could benefit from collaborating with smaller-scale providers of off-grid systems that are deploying innovations to manage large numbers of households smartly.

What are the leading initiatives?

BBOXX, M-Kopa, Off-Grid Electric and Mobisol have entered the market in Africa, bringing new business models that target areas covered by mobile networks but not electricity grids.

Why is this gap important?

While dramatic scale effects have been achieved in solar PV, R&D efforts focused on efficiency and other fundamental improvements in solar PV technology need to continue to keep on pace with the SDS. Mainstream technology at present is dominated by crystalline silicon. Within it, screen-printed Al-back surface field cells (Al-BSF) holds around three quarters of the market, with the remaining quarter dominated by Passivated Emitter Rear Cell technology (PERC).  Strong global demand for higher-efficiency modules is driving a shift towards PERC and the next generation of technologies, like n-type HJT and IBC.

Technology solutions

P-type cells, built upon a positively charged silicon base (to which Al-BSF and PERC belong) are the traditional PV development pathway that has dominated the industry – to some degree because in the early days of development dominated by space applications, p-type cells proved better suited to withstand radiation.

Crystalline silicon p-type PERC technology is poised to reach 24% efficiency, a key milestone, and efforts need to continue to maximise its potential and complete the market shift. Among the barriers that remain, improved cleaning, passivated contacts, interconnection, embedding, and new metallisation pastes particularly are needed.

In n-type cells, the basis of the cell is inverted to yield a number of advantages: n‑type cells are not subject to Light-Induced Degradation (LID; degradation over time from exposure to light), are less prone to defects and impurities in the silicon, and generally have greater power output over time. A variety of designs are in development. Overall, there a pressing need to identify a means to get n‑type technologies to the market (TRL 7).

Passivated contacts promise further improvements, but production throughput, homogeneity, yields and metal paste-contacting remain challenging. TOPCon technologies (an umbrella term for passivated contacts) hold special promise as a follow-up to PERC technology. In standard contacts, which consist of pure metallisation on the wafer, losses are high. Passivated contacts reduce losses and have higher efficiencies than almost any other design structure, but they are complex to manufacture (requiring additional equipment and steps, a more expensive wafer, etc.), which is a key barrier in a traditionally conservative PV industry. Fundamentally, the metallisation paste is proving a key area of focus for scaling up.

What are the leading initiatives?

• R&D is relatively well funded, but commercialising novel n‑type technologies and improving PERC beyond 24% are challenging. While well followed, there is a need to develop commercial designs and products.
• China’s Top Runner Program has chosen some next-generation PV technologies for deployment, including TOPCon technology.
• Longi Solar/CPVT-verified 24.6% PERC cell and PV Celltech technologies are being developed.
• OECD statistics shows the most innovation within all generation technologies coming from more efficient solar PV

Why is this gap important?

Higher PV shares, particularly in distribution grids, will necessitate the development of new ways to inject power into the grid and to manage generation from solar PV systems. The inverter and the rest of the power control system is generally the gateway for smart-management measures, and while technology has been proved, systems will need to become smarter and provide a broader range of voltage, reactive power and other ancillary services to the grid. Beyond making inverters smarter, the overall balance-of-system (BOS) costs (which include inverters) should be a key area of focus, as they can take up 40‑60% of all investment costs in a PV plant, depending on the region.

Technology solutions

Solar smart inverters need to enable rooftop solar PV systems to automatically stabilise their own collective disruptions to the grid. At higher PV penetrations, they need to incorporate communication equipment that interacts in real time with utilities, increasing the visibility of the overall condition of low- and medium-voltage grids. Increasingly, they will also need to offer ancillary services such as reactive power or ramping controls.

There is currently no standard communication protocol to manage active power from large numbers of PV plants, and further work is required on interoperability and standardisation of both the ICT and PV systems.

Beyond inverters, most solutions for reducing BOS costs focus on 'soft' measures that nevertheless could benefit from increased R&D and other innovation efforts.

While hydropower is a mature power generation technology, with high energy payback ratio and conversion efficiency, there are still many areas where small but important improvements in technological development are needed. Work is underway to identify and apply new technologies, systems, approaches and innovations, including experience from other industries, that have the potential to make hydropower development more reliable, efficient, valuable and safe. Improvements along the lines of those made in the last 30 to 50 years will also need to continue, though with smaller incremental benefits: mainly in physical size, hydraulic efficiency and environmental performance.

Why is this gap important?

Dams have a high social and environmental cost, heavily disrupting ecosystems and populations where they are developed. Alternatives that do not require damming or resettlement of populations would help reach SDS levels.

Technology solutions

Zero-head or in-stream turbine technology has a lower environmental impact. No dams or head differential are necessary, they do not alter the course of a river and do not require high capital investments or large civil engineering works. The technology works best in areas where there are small water courses with discharge rates (the flow rate of water through a given cross-sectional area) of 1 m³ per second.

The recent surge of research activity and investment in technology to capture tidal energy has already produced successful prototypes. Most of these underwater devices have horizontal axis turbines, with fixed or variable pitch blades. Electrical generators tend to be direct or hydraulic drive, or have rim-mounted stators.

Relicensing dams to continue operation often involves more stringent environmental criteria that can have an impact on operations, limiting generation and impacting some of the flexibility and revenue streams of hydro plants. Complementing large installations with small-scale hydro plant such as in-stream turbines can therefore augment their generation.

Why is this gap important?

The cost of civil works associated with new hydropower project construction can be up to 70% of total project costs, and their social and environmental impacts can be considerable, so improved methods, technologies and materials for planning, design and construction have considerable potential.

Technology solutions

A roller-compacted concrete (RCC) dam is built using much drier concrete than traditional concrete gravity dams, allowing speedier and lower-cost construction. Trapezoidal cemented sand and gravel (CSG) dams (e.g. in Japan) use more local materials, reducing costs and environmental impact. Recent improvements in tunnelling technology have also reduced costs, particularly for small projects.

Some improvements in turbine technology aim directly at reducing the environmental impacts of hydropower, such as fish-friendly turbines. Aerating turbines use the low pressures created by flows through the turbines to induce additional air flow. This increases the proportion of dissolved oxygen, protecting aquatic habitats in waters below dams. Oil-free turbines use oil-free hubs and water-lubricated bearings to eliminate the possibility of oil leakage into the river. Other benefits include easy maintenance and lower friction than with the oil-filled hubs.

Extensive research to reduce mortality as fish pass downstream through the hydraulic turbines has significantly improved turbine design. In recent years, minimum gap runner (MGR) technology has achieved fish survival rates in excess of 95% for large axial flow units in the field. New designs, such as the Alden turbine, expand the range of fish-friendly units to smaller turbine applications but have not yet been widely applied.

Continuous improvements in material properties have been driven by requirements to: improve resistance to cavitation, corrosion and abrasion to extend component life and reduce outages; reduce runner weight and improve efficiency through increased strength of materials; and improve machinability to increase power output as more complex shapes can be manufactured. This has led to increased use of proven and new materials such as stainless steel and corrosion- or abrasion-resistant coatings in turbines, and lower-cost and higher-performance fiberglass and plastic materials in construction.

Recommended actions in the next five years

• Environment and energy/resource ministries should promote policy frameworks that cover the development of sustainable and appropriate hydropower projects that avoid, minimise, mitigate or compensate any legitimate and important environmental and social concerns.
• Industry should consider sustainability issues in the co-ordinated operation of hydropower plants.
• Intergovernmental organisations and multi-lateral development agencies should provide capacity building for regulatory frameworks and business models to help developing countries implement sustainable hydropower development.