Calculating the Energy of Sun’s Radiation on Vegetation for Preparing Goat Meat: Answer in Joules

Understanding the energy transfer from the sun to our plates is a fascinating journey that involves multiple steps. This process is not only crucial for our survival but also plays a significant role in maintaining the balance of our ecosystem. In this article, we will explore how the energy of the sun’s radiation on vegetation is calculated to prepare goat meat, and how this energy is then consumed by a family of five. This topic was inspired by a question that asked how much energy from the sun had fallen on vegetation to prepare food for a goat, which was then consumed by a family of five to meet their average energy need of 2700 kcal per person.

Understanding the Energy Transfer

The energy transfer from the sun to our plates involves several steps. First, the sun’s energy is absorbed by plants through a process called photosynthesis. This energy is then transferred to animals when they consume these plants. Finally, when we consume animal products, we receive this energy. In this case, the goat consumes the vegetation, and then the family consumes the goat meat.

Calculating the Energy in Joules

To calculate the energy in joules, we first need to convert the energy need of the family from kilocalories to joules. Given that 1 calorie is equivalent to 4.2 joules, the total energy need of the family is 2700 kcal * 5 (members of the family) * 1000 (to convert kcal to cal) * 4.2 (to convert cal to J) = 56,700,000 J.

Estimating the Energy from the Sun

Estimating the energy from the sun that has fallen on the vegetation to prepare food for the goat is a bit more complex. This is because only a small fraction of the sun’s energy is actually absorbed by plants. According to the 10% rule in ecology, only about 10% of the energy from one trophic level is transferred to the next. This means that if the goat needs to consume 56,700,000 J of energy, the vegetation it consumes must have absorbed about 10 times this amount from the sun, or 567,000,000 J.


Understanding the energy transfer from the sun to our plates helps us appreciate the intricate balance of our ecosystem. It also highlights the importance of sustainable farming practices, as the energy efficiency of this process is quite low. By making conscious choices about our food, we can help ensure that this energy transfer continues to sustain life on our planet.