Solar fuels and photosynthesis

Sunlight stored as chemical energy, in crops and forests or in fuels made by artificial photosynthesis.

Capture · Solar · No. 25

• Capture
• Output: Fuel / chemicals

Every crop on Earth runs on sunlight, yet a soybean field stores only about 1.6% of it as chemical energy.

Chart: Illustration: Solar fuels and photosynthesis

Where it comes from

Chart: Map of where it comes from

Sunlight arrives spread thin, so leaves and machines must gather a lot of it. The thermochemical route focuses it about 2,500 times to heat ceria to roughly 1,500 C.

Three things to know

1. Plants hit a hard ceiling: at most 4.6% of sunlight ends up stored in wheat, rice and trees, and 6% in maize or sugar cane.
2. Colour is half the problem: about 51% of incoming sunlight lies outside the band that chlorophyll can use at all.
3. In Spain, a 50 kW solar tower with 169 mirrors has run the whole chain from sunlight, water and CO₂ to kerosene.

The journey

1. 1 SunlightPlants use only the 400-700 nm band
2. 2 Light captureChlorophyll, semiconductor or mirror field
3. 3 Water splittingOxygen released, hydrogen freed
4. 4 Carbon fixingCO2 built into sugars or syngas
5. 5 Food and fuelCrops, wood, hydrogen, solar kerosene

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