UWE Bristol Engineering showcase 2015

George Close
Beng Electrical and Electronic Engineering
Project Supervisor
Rohitha Weerasinghe
Can Exercise Equipment Be Used To Help Fuel Britain’s Growing
Electricity Demand?
Introduction
This project is an investigation into the feasibility of taking an
existing concept of attaching a small generator system to a
stationary exercise bike. The concept is a simple one, people are
using these machines voluntarily to get fitter, yet all their energy
they output into the machine is dissipated as heat through
resistance. So why not try and capture back some of that energy?
The project started with a literature review of related areas of
research, as well as looking at existing products available and in
use today. There were some past research papers that also looked
the feasibility of this concept, yet after calculations of energy
produced against costs to build new systems or retrofit existing
bikes , it was found that the cost-efficiency of the idea made it
unreasonable.
The market leading existing product in terms of claimed standard
power produced was the Human Dynamo. It utilises both the
arms and the legs via two pedaling crankshafts, thus increasing
the power input to the system from the user and therefore
increasing the electrical output to around 200W for a standard
workout. The company also claims the generator is 70% efficient.
My Design and Calculations
My design of the generator system was based on researching the
main individual components that make up the system, and then
selecting the best one available. I finalised on a DC generator, of
individual efficiency of 85%, followed by a Lead-Acid battery, of
individual efficiency 90% and finally an inverter to turn the DC
electricity stored in the batteries into the correct AC form of 230V
at 50Hz, which had an individual efficiency of 82%. The combine
rating came together to give the system an overall efficiency
rating of 63%.
Next I had to calculate what the average use of an exercise bike
at the gym was each day. Data showing there is 6112 gyms
currently in the UK, with a membership base of 8.3 million. This
gave 1357 members per gym. Research suggested that 67% of
people with a membership don’t go, and those that do go, only
31.5% like to use a stationary bike. This gave
((1357 x 0.67) x 0.315) = 140 people use a bike at each gym
Data also showed that they attend on average twice a week.
Assumptions were made that all 140 people worked out an hour
on a bike both times they visit the gym a week. This gives 280
hours of bike use a week, averaged out at 40 hours a day, with an
assumption made that each gym had 10 bikes, so each bike was in
use for 4 hours a day. Combined bike use of 40 hours a day across
the UK gives 40 x 6112 = 244,480 hours of power production a
day.
Data was found to show the average human can sustain 233W
pedaling output for one hour. Combing my system efficiency,
hours of power production a day and the average human pedaling
output, the following calculation of possible energy produced can
be made:
233 x 0.63 x 244.480 = 35.9 kWh produced a day
Project summary
The project was set out to determine whether an
existing concept of attaching small dynamos to
stationary exercise bikes to generate electricity was
viable enough to be scaled up nationally across all
gyms and try and offset the power-hungry nature of
them, and if possible, supply excess power to the
grid.
Project Objectives
Objectives of the project were:
• Determine the effectiveness of existing systems,
and take this forward to outline a design proposal
for a generator system to use for this project
• Theoretically calculate the efficiency of said
design proposal
• Calculate the average use a stationary bike gets a
day in any gym in the UK
• Research the theoretical mechanical energy
outputs of an average person pedaling
• Combine the results from the three previous
points to attain the possible national daily
production of electricity purely from stationary
bikes
Project Conclusion
The results of the objectives were found as follows:
• Theoretical DC generator system had efficiency of
63%
• If there were 10 of these bikes in each gym across
the UK, calculated use would be 4 hours a day =
40 hours total
• Theoretical 1 hour maximum-effort mechanical
energy output via pedaling for average human
found to be 0.299 hp = 233W
• Combined numbers across UK’s 6112 gyms:
233W output x 63% efficiency = 147W electrical
output
6112 gyms x 40 hrs use = 244,480 hours a day
production
244,480 hrs x 147W = 35.9 kWh produced a day
• Not a large enough amount of energy produced