Human-Powered Electricity Generation as a Renewable Resource

Abstract

Energy and human's ability to transform energy into useful work has been the cornerstone of the development of civilizations. Throughout the majority of human existence, we relied solely on metabolic energy derived from plants and animals. In only a few centuries, society has almost completely transformed, from relying on somatic energy to become almost entirely dependent on fossil fuels. The combustion of hydrocarbon energy resources has had detrimental impacts on our environment, which has initiated a push for clean energy. This research study explores the metabolic energy output of humans, specifically within an exercise facility, to evaluate the feasibility of electrical power to be sustained from human-powered energy. Two rowing workouts were evaluated and then compared to solar photovoltaic as an alternative renewable energy. The result of the study demonstrates that 40 members of various physical abilities can collaboratively provide 3–5% of the gym’s average daily electricity demand if converted at an efficiency of 64%. The cost of converting the rowing machines resulted in a 33-year payback period.

Appendix

Energy is the product of the appliance power and the estimated usage time. Energy value is needed to be calculated for every month since the usage time varied (Table 4).

Table 4 Appliance power, operating time, and daily electricity use (MacKay 2008; Almeida et al. 2011)

A stationary rower differs from the exercise machines used in previous studies by requiring an individual to engage multiple muscle groups. Figure 5 shows the rowing stroke consisting of four distinct yet interrelated movement phases; the catch, drive, finish, and recovery. The majority of the energy is exerted during the drive phase, where the rower applies force to the sprocket on the shaft of the flywheel by engaging muscles from the legs, then hips and back, ending with the arms at the finish stage. Rowers work in a transitional system, where power is produced from the force pulling the handle attached to a chain at a linear velocity. During the power stroke the rower’s exerted effort drives a flywheel via a ratchet, and the cable recoils under tension from a bungee cord during the recovery.

Fig. 5

The rowing stroke (from top left): catch, drive, finish, and recovery (Concept2 2016)

The rower’s average results for pull length [m], drive phase duration [s], and max force [N] for 20 SPM, 26 SPM, and 34 SPM from Toma and Kamnik (2011) were used to calculate the maximum power potential. Pull length is the difference between the maximum and the minimum distance of the handle pulled. Drive phase duration is the time required to achieve the pull length. Max force is the peak pull force on the handle and occurs midpoint of the drive phase duration.

The instantaneous maximum potential power (MPP) that a rower can generate is expressed (Eq. 2) with respect to the torque (τ) that the rower applies to the sprocket of the shaft and the angular velocity (ω) of the flywheel.

$${\text{MPP}}=\tau \omega$$

(2)

Torque is applied to the sprocket from the chain, which is connected to the handle that the rower exerts a pull force (F). Since the force is being applied perpendicular to the sprocket ($\sin \theta =1$), Eq. 3 can be simplified to the torque equaling the product of the force and the sprocket’s radius.

$$\tau _{~} = rF\sin \theta ~ \to ~\tau ~ = rF$$

(3)

The flywheel angular velocity can be related to the handle linear velocity (V) by the radius (r) of the sprocket (14.3 mm).

$$\omega =~\frac{{V~}}{r}$$

(4)

Table 5 displays the instantaneous MPP generated per row stroke using Eqs. 2–4. An individual's electrical power output, at a 64% conversion efficiency, could power small appliances such as a clock, cell phone charger, vacuum cleaner, or a television, but not for sustained periods. A subject rowing at 34 SPM can produce an MPP of 1520 watts, which is enough to operate a microwave, but falls short of meeting the necessary power of an industrial fan of 1800 watts (Table 6).

Table 5 Results for different rowing stroke rates measured in strokes per minute (SPM)

Table 6 Total wastage in food chain for different food commodities, with data from (Gustavsson et al. 2011)