Energy-Generating Desks

Introduction

Fig. 1: A stationary bicycle. (Source: Wikimedia Commons).

What is the potential energy output if all desks in American corporate offices were replaced by energy-generating bicycles? This analysis critically evaluates the plausibility of this notion, taking into account factors such as human performance, physical work capacity, and efficiency rates, among other elements constituting this unique energy paradigm.

Cogs in the Machine

First, we need to collect some variables: the number of white-collar workers in the U.S., their daily hours at work, the wattage output of an average American during a cycling session, and the efficiency of mechanical-to-electrical energy conversion.

Firstly, we must consider several variables: the total number of white-collar workers in the U.S., their daily work hours, the average wattage output of an American during a cycling exercise, and the conversion efficiency of mechanical energy to electrical energy.

There are approximately 166.8 million full-time employees in the United States, based on approximately 80% of the working-age population of 208 million. In 2020, 59.8% of the total workforce were professionals. [1] Let's assume an average workday of 8 hours--subtracting time for breaks and lunch means that 6 hours could be spent on these energy-generating bicycles (Fig. 1). Research indicates that an average person can generate about 100 watts on a stationary bicycle, but this is difficult to sustain over a long period of time. [2] An average human would rest for approximately half of that time, pedaling for only 3 hours in the workday. Additionally, to convert mechanical energy to electrical energy via a generator, there is inefficiency in the friction drive between the bike wheel and the motor, inefficiency in the motor itself converting rotational motion into electricity, energy lost in the voltage regulator, inefficiency of energy going into the battery, and inefficiency in the inverter. Each step in that sequence compounds for a loss of power. Cumulatively, The conversion of human foot motion into usable energy has an overall efficiency of about 65%. [3]

In summary, the resultant energy generation potential would be:

An Exercise in Realism

Fig. 2: An office interior. (Source: Wikimedia Commons)

In practical terms, stationary bicycles equipped with generators are recognized for their high energy consumption. In the pre-LED era, these units were charged with illuminating 100 Watt incandescent bulbs, a task challenging for an average individual to sustain over extended periods. This demands significant exertion with relatively insufficient luminosity as an outcome.

Moreover, it must be taken into account that the energy generated by office employees working at energy-generating bicycle desks (Fig. 2) cannot surpass the energy they consume as food. They are limited by such a "donuts to electricity" conversion. To establish an estimate of the energy office workers glean from their food intake, we need to draw upon dietary guidelines and caloric intake averages for adults. According to the U.S. Department of Agriculture, the recommended daily caloric intake for adult men and women are 2,500 and 2,000 kilocalories, respectively. [4] Let's use 2,250 kilocalories for an average person. These recommended amounts may vary based on factors such as age, physical activity level, and metabolic rate, but given the sedentary nature of most office jobs, we'll assume that office workers are less likely to deviate significantly from these averages.

For one person we have

For all white-collar workers we have

Conclusion

For reference, commercial buildings consumed 16,419 trillion BTU of energy in 2022. [5] This is equal to 16419 × 10¹² BTU/year = 13174 GWh/day.

Since 16.1 GWh/day / 13174 GWh/day = 0.0012, even if all white-collar workers used a generator bike at their desks it would provide less than 0.2% of the energy needed to power America's commercial buildings.

Also, 210.3 GWh/day / 13174 GWh/day = 0.0159. Thus if everything the employees ate was perfectly converted into powering buildings (and nothing else) it would only provide 1.59% of the energy needed to power America's commercial buildings.

The concept of energy-generating desks is whimsical, but given logistical implications, this proposal falls short as we contemplate various innovative approaches to address global energy crises.

© Raymond Zhen. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

References

[1] K. Barrows, "The Professional and Technical Workforce: By the Numbers," AFL-CIO, 2021.

[2] T. Gibson, "These Exercise Machines Turn Your Sweat Into Electricity," IEEE Spectrum, 21 Jun 2011.

[3] R. Riemer and A. Shapiro, "Biomechanical Energy Harvesting From Human Motion: Theory, State of the Art, Design Guidelines, and Future Firections," J Neuroeng. Rehabilitation 8, 22 (2011).

[4] S. E. Gebhardt and R. G. Thomas, "Nutritive Value of Foods," U.S. Department of Agriculture, October 2002, p. 9.

[5] "Monthly Energy Review October 2023," U.S. Energy Information Administration, DOE/EIA-0035(2023/10), October 2023, Table 2.1.a.