There is sufficient energy arriving in the form of sunshine on the earth every day to power humanity for a whole year. If 2% of the earth’s land surface were covered in solar panels, that would be sufficient. These simple facts are cause for optimism and drives much of the technological measures to avoid irreversible climate change.

Most energy is used for domestic heating and cooling, lighting, powering machinery or appliances, industrial processes and transport. In addition to alternative energy sources, there are opportunities to cut consumption or improve efficiency. This includes change of lifestyles to uses less power – such as energy hungry pursuits like flying, motoring, skiing or arbitrary consumption of goods. Efficiency can also be enhanced, with the use of LED lighting and improved thermal insulation to buildings. Such measures typically deliver most rapid payback on investment.

In supply of energy, the primary technologies are solar power and wind power, driving greater electrification in the distribution of energy. Hydroelectricity is great, but most viable schemes have been exploited already. Biofuels can be useful, but only at the margins and not at large scale, as the consumption of land and resources is simply too great to be viable. Nuclear fission is attractive to some, as it effective in producing large amounts of electricity – but is expensive and controversial, given the long-lasting waste and perceived operational risks.

Solar power, primarily using photovoltaic panels, is now cost competitive with new build fossil fuel electricity generation. The most effective schemes are at scale and in sunnier areas. Manufacturing costs continue to fall as production expands. The major brake in ramp up of capacity is that coal and gas are cheap, so generating plants have been run until they drop. The UK, France and Scandinavia lead in the exit from coal having started winding down 30 years ago. The USA is a laggard. China and India, in their industrialisation have been building new plants. Nevertheless, the switch over progresses.

Wind power is a useful additional resource, especially in less sunny areas or areas with windy coastal waters. The UK is now advancing in the use of offshore wind.

There are two issues with solar and wind. Periodicity (i.e. the variation in generation depending on time of day, weather and season) and mobility. The solution to both lies in storage. Battery technology is advancing and scaling, and now practical in road vehicles. Of other technologies to store and transport energy, hydrogen looks the most promising. Hydrogen can be produced by electrolysis using solar or wind power, and then distributed via a grid in place of methane for carbon free heating. With development hydrogen, or compounds based on it like ammonia, can be used as a transport fuel in cars, trains, ships and probably last: in aircraft.

You can see the variation in use of different types of energy over time by countries by looking at the IEA Sankey charts.