Solar energy is effectively infinite. The Sun’s energy is so abundant that more energy is transferred to our planet in an hour’s sunlight than the entire global electricity consumption for a year (https://books.wwnorton.com/books/The-Great-Transition/). It is also one of the fastest expanding renewable energy sources. With quicker technical gains and stronger policy support, the price of solar power is dropping rapidly.

Figure. Annual photovoltaic addition history versus International Energy Agency (IEA) World Energy Outlook (WEO) predictions from 2002 to 2016. The graph shows exponential growth in solar energy capacity and a continuous underestimation by WEO.

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Figure. In the Evolving Transition scenario (ET scenario), which is premised on a demand for fossil fuels that vastly exceeds the carbon budget for limiting temperature rises to 1.5-2C, solar cost continues following its learning curve. The module cost falls by around 24% with every doubling of cumulative capacity. The rate of decline slows down in the BP 2018 Outlook, as it takes longer to double the cumulative capacity later on the learning curve.

However, there are still unsolved issues in using solar power. We are currently only capable of harvesting a small part of the light spectrum. We harvest the visual light spectrum while the IR and UV sunlight comprise, respectively, 47% and 46% of the light spectrum. The problem now is that how to open up from the current 7% through more efficient solar panel materials and mechanisms.

Solar energy is intermittent, and so are wind and tidal power. We could not get 24/7 access to these kinds of renewable energy. Without a cost-effective large-scale energy storage system, renewables will never take over oil and gas in market share. Although researchers and companies have been working on developing stationary energy storage, there are no existing solutions, which is low cost, reliable, environment-friendly, well-developed with a proven track record, to this problem.