The Sunsharing Concept

©John Wood 1974

Re-invented in Japan in 2017

• Japanese farmers produce crops with solar energy

The background

(from notes compiled in 1975)

• Although it takes a little less than 5 Watt/hours of sunshine to grow a gramme of food, less than half of the available solar spectrum is necessary for plant growth.
• Indeed, the short (ultra-violet) wavelengths can even burn the surface tissue of leaves, especially now that the Ozone layer is becoming dangerously thin.
• However, these ultra-violet wavelengths contain proportionately more energy than any other part of the sunlight spectrum and, although they are damaging, they are also potentially useful to a society addicted to wasting energy.
• In plant growth terms this means that even for a total annual yield of, say, 1700 kilogrammes/hectare the total year's sunlight need not exceed 700 Watt/hours for each square metre of land - roughly what you would expect from a single Summer's day in the UK !
• Basically, this is because the growth-efficiency of plants is better at low light-levels than it is in strong sunshine.
• When the sunshine is brighter than about 6 Watt/hours per square metre, the plants are receiving more energy than they can make use of for photosyntesis and growth.
• If crops could ever be developed to utilize all the available sunlight, then the world would receive more than a hundred fold increase in food from the area of land presently being farmed.
• Technologies of genetic engineering are being developed to re-design features of photosynthesis in food crops.
• This approach has uncertain, perhaps even dangerous, consequences in the long term.

What Might it Look Like?

• Imagine it as a large double glazed window on the South facing side of your house, or as a greenhouse covering the whole garden.
• Between the two panes of glass there are vertical shutters - like electronically controlled Venetian blinds - which adjust themselves automatically to moderate the intake of Sunlight.

• When the shutters present their edges to the sunlight there is a maximum intake of solar energy received by the plants.
• When the shutters close, they absorb maximum energy because of their special black coating. This is ducted away by forced air flowing upwards to the heat pump.

How Might It Work?

• The Sunsharer system does not attempt to improve the intrinsic design of cereal plants, but is a method of absorbing the sunshine energy which is surplus to their requirements for normal growth.
• The Sunsharer's outer window is made from special iron-free glass which is transparent to 98% of the wavelengths in the solar spectrum.
• The inner glass, however, is opaque to Ultra-violet wavelengths and ensures that this energy-rich bandwidth is made available for domestic purposes.
• The Sunsharer controls the amount and quality of light reaching the plants to a level at which their growth rate is optimal.
• When sunlight intake exceeds this level, the shutters between the double-glazing are automatically turned to absorb the extra light.
• Heat generated on the shutters can be stored in insulated tanks below the green house and released in cold periods (at night, for instance), or used for domestic purposes such as space heating or water-heating.

References

1. Penman, H., L., (1968), "The Earth's Potential" by Science Journal May 1968 Vol. 4 no. 5
2. James, W. O. (1963). An introduction to plant physiology. Fourth Edition.
3. Bjorkman, O., and Berry, J., (1973), "High Efficiency Photosynthesis", Scientific American; October 1973