Energy is used in the delivery of many functions of humanitarian aid, from shelter, lighting and transport, to clean water, sanitation, and medical assistance. This Focus issue explores how thinking around energy is changing as the need for sustainable energy solutions in refugee camps intensifies and as humanitarian crises become more protracted.

The stability of tin–lead perovskite solar cells has been falling behind that of pure lead perovskite devices despite recent advancements. Prasanna et al. now redesign the device architecture, extending the retention of the initial solar cell performance from a few hours to a thousand hours under light, heat or humidity.

Prasanna et al.

A German government commission recently proposed to phase out coal by 2038, a goal not in line with the country’s climate targets. Rinscheid and Wüstenhagen find that German citizens prefer to phase out coal by 2025 instead, suggesting that voters want more aggressive climate action than political decision makers.

Rinscheid and Wüstenhagen

In 2016, the Government of India launched a massive subsidies and small loans program to promote replacement of unclean fuels with liquefied petroleum gas. Analysing gas sales data, Kar et al. find that the program succeeded in creating rapid initial uptake but more work will be needed for rural consumers to fully transition away from the use of solid fuels.

See Kar et al.

Building façades, windows or solar panel installations are stationary and typically do not respond to changing heat or sunlight. Svetozarevic et al. demonstrate the prototype of an adaptive solar façade where each photovoltaic module is individually adjusted by a soft-hard-material actuator to optimize heating, cooling, lighting and solar electricity generation.

See Svetozarevic et al.

Harder to reach fossil fuels such as shale oil and gas, tar sands or offshore reserves require much more energy to extract than conventional oil and gas. Using extraction to end-use energy input estimates, Brockway et al. show that fossil fuel net energy might be close to that of renewables and to a theorized precipitous decline.

See Brockway et al.

The addition of selenium to cadmium telluride solar cells has led to record energy conversion efficiencies. While it is generally assumed that the selenium improves the optoelectronic properties of the material, Fiducia et al. show that selenium (distributed across the device, as shown in blue) also deactivates detrimental defects allowing the cells to absorb more light.

See Fiducia et al.

Predicting the lifetime of lithium-ion batteries is a challenging yet essential task. Severson et al. develop a machine-learning-based approach that can accurately predict battery lifetime before degradation has taken place, using only early-cycle data.

See Severson et al.

Energy systems planning in conflict-affected and fragile countries has appeared futile in the past because of ever-changing socioeconomic and political conditions and violent disruptions. To help overcome this, Spyrou et al. present a planning framework that takes into account uncertainty from multiple sources including conflict and apply it to South Sudan.

See Spyrou et al.

Shade from buildings and other obstructions in the city makes it difficult to estimate the potential yield from solar panels accurately. To help overcome this, Calcabrini et al. develop and validate a simplified model to calculate solar energy yield at any location based on irradiance and the shape of the urban skyline profile.

See Calcabrini et al.

The complexity of distributed energy systems with decentralized energy sources such as wind and solar could be simplified by distributed management. Thomas et al. present a basic template for a smart contract between entities such as grids that will allow for automated decentralized energy trading and that can be built upon for more complex transactions.

See Thomas et al.

Knowing the energy being used during an energy-intensive activity may encourage behaviour that reduces consumption. Tiefenbeck et al. now show that randomly chosen hotel guests in rooms where a smart shower meter provided real-time feedback on energy and water consumption used 11.4% less energy while showering, demonstrating the effectiveness of this easy-to-implement, scalable conservation intervention.

See Tiefenbeck et al.