Question

One way of generating electricity from solar energy involves the collection and storage of solar energy in large artificial lakes a few meters deep, called solar ponds. Solar energy is stored at the bottom part of the pond at temperatures close to boiling, and the rise of hot water to the top is prevented by planting salt in the bottom of the pond. Write an essay on the operation of solar pond power plants, and find out how much salt is used per year per \(\mathrm{m}^{2}\). If the cost is not a factor, can sugar be used instead of salt to maintain the concentration gradient? Explain.

Short answer

Answer: Solar pond power plants are a method of capturing solar energy through large, shallow bodies of water with a high salt content, utilizing the salt concentration gradient to trap and store heat. Solar energy heats the bottom water layers, and the heat can then be converted into electricity through a turbine-generator system. Replacing salt with sugar for maintaining the concentration gradient is unlikely to be effective, as sugar is less soluble in water, potentially more expensive, and its presence could encourage bacterial growth and destabilize the concentration gradient.

Step-by-step solution

Explain the operation of solar pond power plants

A solar pond power plant is a method of capturing and storing solar energy through large, shallow bodies of water with a high salt content. The bottom of the pond contains a high concentration of salt, which serves to create a stable density gradient, preventing heat from escaping the lower layers. When sunlight penetrates the upper layers of the pond, it reaches the bottom and is absorbed by the black lining, heating the water. The high salt concentration at the bottom prevents hot water from rising to the surface through convection, effectively trapping the heat. Heat from the bottom layers can then be used to generate electricity by transferring it to a working fluid, which drives a turbine-generator system.

Calculate the amount of salt used per square meter per year

To calculate the amount of salt used per square meter per year, we need to make assumptions on the evaporation rate, water depth, and the salt concentration gradient. Let's assume an evaporation rate of 2 meters per year, a depth of 1 meter, and a salt concentration gradient of 30% at the bottom and 0% at the top. The average salt concentration in the pond would be 15%. If we assume that the evaporation rate is constant and that the salt stays in the pond, then we can set up a proportion calculation: Salt used per year = Depth * Area * (Final salt concentration - Initial salt concentration) Salt used per square meter per year = 1000 \,kg \cdot 0.15 = 150 \,\text{kg/year} So, in this solar pond power plant, about 150 kg of salt is used per square meter per year.

Can sugar replace salt for maintaining the concentration gradient?

In principle, any material that can dissolve in water to create a density gradient could be used instead of salt in a solar pond power plant. However, there are several reasons why sugar might not be a suitable replacement for salt: 1. Solubility: Sugar is less soluble in water than salt. Therefore, a much larger amount of sugar would be required to create a similar density gradient. 2. Cost: Although the prompt mentions that cost is not a factor, it is worth noting that replacing salt with sugar would likely result in significantly higher costs due to increased material requirements and potentially lower energy output. 3. Stability: Sugar is an organic compound, and its presence in the pond could encourage the growth of bacteria and fungi, leading to the breakdown of the sugar and a decrease in concentration gradient stability. Based on these factors, it is unlikely that sugar would be a suitable replacement for salt in solar pond power plants.