# Scaling of Greenhouse Crop Production in Low Sunlight Environments
## Abstract
This study focuses specifically on the use of low-tech greenhouses in the event of a global catastrophe such as nuclear winter, in which sunlight and temperatures are greatly reduced across the globe.

The study used a nuclear winter climate model to determine the necessary greenhouse conditions and designed the structures to utilize global markets for materials such as timber, polymer film, construction aggregates etc.

The added cost of low-tech greenhouses is about two orders of magnitude lower than the added cost of artificial light growth, and according to the proposed scaling method, the greenhouses will provide 36% of food requirements for everyone by the end of the first year, and feed everyone after 30 months.

## Method
### Low-tech greenhouse
A-frame design was selected to maximize light transmission and enhance structural stability without bending/manipulating the wood.

### Characteristics
- Effective growing space: 80% of the ground area (Bartok, 2015a).
- Height: 3 m (permits taller crops to grow within these greenhouses and accommodates the usage of vehicles)
- Roof slope: 10 degrees (will allow rainwater to flow into the troughs without much reduction of the amount of incident sunlight) *(Bartok, 2015a)*.
- Polymer thickness: ~0.10-0.15 mm

### Considerations
- Greenhouse plants require about 12 $L/m^2/day$ of water (equivalent to 12 $mm/day$ precipitation) *(Bartok, 2015a)*. However, in nuclear winter in the tropics, water requirements are reduced. bringing the requirement for most outdoors crops to ~4 $mm/day$ *(Food and Agriculture Organization, 2019)*.
- The global reduction of daily sunlight will impact most crops.
- After three years, when the polymer begins to degrade, construction will stop, and the construction labor force will be halved to begin replacing polymer.
- By using transplanting method, there is a 39% increase in greenhouse-occupied days from each harvest.
- During first phase, materials:labor are ~ 70:30% of total cost *(Bingham, 1982; Gichuhi, 2013)*. During the polymer replacement stage, labor will be closer to 50% *(Gichuhi, 2013)*.
- Present Value formula: $P=\frac{F∗1}{(1+i)^n}$
- If interest rate (i) of 8% is used (Humbird et al., 2011) to discount the cost of polymer replacement 3 years (n) in the future (F). Then for each greenhouse, the lifetime (72 months) cost will be 1.60 $USD/m^2$. At constant expansion for 36 months, the cumulative ground coverage will equal 2.5 million $km^2$ , amounting to an annual cost of 670 billion USD.
- Environmental Control Chambers are more expensive, because of artificial light requirements. The added cost to food from the proposed greenhouses was calculated to be 2.30 USD/dry kg; whereas a closed artificial light growing system is ~600 USD/dry kg *(Denkenberger et al., 2019)*