Research on 100% renewable energy systems is a relatively recent phenomenon. It was initiated in the mid-1970s, catalyzed by skyrocketing oil prices. Since the mid-2000s, it has quickly evolved into a prominent research field encompassing an expansive and growing number of research groups and organizations across the world. The main conclusion of most of these studies is that 100% renewables is feasible worldwide at low cost. Advanced concepts and methods now enable the field to chart realistic as well as cost- or resource-optimized and efficient transition pathways to a future without the use of fossil fuels. Such proposed pathways in turn, have helped spur 100% renewable energy policy targets and actions, leading to more research. In most transition pathways, solar energy and wind power increasingly emerge as the central pillars of a sustainable energy system combined with energy efficiency measures. Cost-optimization modeling and greater resource availability tend to lead to higher solar photovoltaic shares, while emphasis on energy supply diversification tends to point to higher wind power contributions. Recent research has focused on the challenges and opportunities regarding grid congestion, energy storage, sector coupling, electrification of transport and industry implying power-to-X and hydrogen-to-X, and the inclusion of natural and technical carbon dioxide removal (CDR) approaches. The result is a holistic vision of the transition towards a net-negative greenhouse gas emissions economy that can limit global warming to 1.5°C with a clearly defined carbon budget in a sustainable and cost-effective manner based on 100% renewable energy-industry-CDR systems. Initially, the field encountered very strong skepticism. Therefore, this paper also includes a response to major critiques against 100% renewable energy systems, and also discusses the institutional inertia that hampers adoption by the International Energy Agency and the Intergovernmental Panel on Climate Change, as well as possible negative connections to community acceptance and energy justice. We conclude by discussing how this emergent research field can further progress to the benefit of society.

Some 630 million people representing two-thirds of all Africans have no access to electricity, which is identified as a key barrier towards further development. Three main electrification options are considered within our work: grid extensions, mini-grids and solar home systems (SHS). A methodology is applied to all sub-Saharan African countries to identify in high geospatial resolution which electrification option is appropriate taking into account datasets for night light imagery, population distribution and grid infrastructure. Four different scenarios are considered reflecting grid development and electrification constraints due to low population density. The results clearly indicate a dominating role of SHS for achieving a fast electrification of the not supplied people. The share of supplied people by mini-grids is found to be rather low while grid extension serves a large share of the population. The decisive factors for these distinctions are population density and distance to grid. We applied several scenarios and sensitivities to understand the influence of these key parameters. The highest trade-off happens between SHS and grid extension depending on the selected thresholds. Mini-grid deployments remain in the range of 8 to 21%.

Globally, the heat sector has a major share in energy consumption and carbon emission footprint. To provide reliable mitigation options for space heating, domestic hot water, industrial process heat and biomass for cooking for the energy transition time frame up to the year 2050, energy system modeling relies on a comprehensive and detailed heat demand database in high spatial resolution, which is not available. This study overcomes this hurdle and provides a global heat demand database for the mentioned heat demand types and in a resolution of 145 mesoscale regions up to the year 2050 based on the current heat demand and detailed elaboration of parameters influencing the future heat demand. Additionally, heat demand profiles for 145 mesoscale regions are provided. This research finds the total global heat demand will increase from about 45,400 TWh_th in 2012 up to about 56,600 TWh_th in 2050. The efficiency measures in buildings lead to a peak of space heating demand in around 2035, strong growth in standards of living leads to a steady rise of domestic hot water consumption, and a positive trend for the worldwide economic development induces a growing demand for industrial process heat, counterbalanced by the efficiency gain in already industrialised countries. For the case of biomass for cooking, a phase-out path until 2050 is presented. Literature research revealed a lack of consensus on future heat demand. This research intends to facilitate a more differentiated discussion on heat demand projections.

The idea of damming the Congo River has persisted for decades. The Grand Inga project, of up to 42 GW power generation capacity, can only be justified as part of a regional energy master plan for Africa, to bridge the energy gap on the continent. Proponents of very large dams have often exaggerated potential multiple benefits of a mega dam, marginalise environmental concerns and neglect the true risk of such projects, in particular for the fragile economies of developing countries. Studies have reported the financial risks, cost overruns and schedule spills associated with very large dams. In addition, most of the dams in the region are poorly managed. Therefore, the type and scale of Grand Inga is not the solution for millions of not yet electrified people in Sub-Saharan Africa. In this research, scenarios are defined based on announced costs and expected costs. Cost escalations in the range from 5% to 100% for the Inga project in 2030 and 2040 are considered, as average cost overruns are typically at about 70% or higher for similar mega-dams. It was found that when the cost overrun for the Grand Inga project exceeds 35% and −5% for 2030 and 2040 assumptions, respectively, the project becomes economically non-beneficial. In all scenarios, Sub-Saharan Africa can mainly be powered by solar photovoltaics to cover the electricity demand and complemented by wind energy, supported by batteries. Hydropower and biomass-based electricity can serve as complementary resources. The grid frequency stability of the power system is analysed and discussed in the paper. Benefits of the Inga hydropower project have to be increasingly questioned, in particular due to the fast cost decline of solar photovoltaics and batteries.

Faced with interrelated challenges of climate change and energy crises, Africa’s future energy system orientation could be steered toward sustainable development. In this study, we contextualized diverging fossil fuels-dominated and renewable energy-based pathways toward sustainable development in Africa. A novel and sophisticated techno-economic energy modeling tool is used to describe the scope of the pathways in high geo-spatial and full hourly resolution for Africa covering the entire energy system. This study demonstrates that a renewable energy pathway is not only climate-compatible, but also delivers a lower cost system structure than alternative pathways. Our results show that Africa can leapfrog carbonization by using its low-cost renewable electricity and green hydrogen. Furthermore, Africa can become a self-sufficient green economy and an exporter of green fuels. Notably, solar photovoltaic-battery hybrid systems and electrolyzers are instrumental in achieving carbon-neutrality in Africa. This research presents a “true-zero emission” pathway for Africa.

Sustainable energy systems form an indispensable component of sustainable development especially in developing economies. Understanding the system wide techno-economics of sustainable energy systems therefore becomes critical in shaping the energy system mix within a region or country. This paper explores progressive and optimal pathways towards a fully sustainable energy system for Cameroon by 2050 in power, heat, and transport sectors as a representative case study for the Central Africa region. Six key scenarios are modelled with the LUT Energy System Transition Model to capture key policy and sustainability constraints. Results from the study show that, the optimal least cost technology combination for a fully sustainable energy system for Cameroon with net-zero greenhouse gas emissions in 2050 is dominated by solar PV (86%), complemented by hydropower (8%) and bioenergy (5%). These results show that a fully sustainable energy system for Cameroon is feasible from both the technical and economic perspectives, if policy commitment is oriented towards these low-cost energy solutions. The results of this research provide a reliable reference for planning transitions towards a 100% renewable energy-based energy system in countries within the Central Africa region.