HARVESTING ENERGY FROM RAINFALL
III-Electrical and Electronics Engineering
Sri Shakthi Institute of Engineering and Technology
Abstract: The goal of this project is to utilize
energy stored in rain water to provide power to the
buildings, which are situated in the regions,
affected by power cuts during summer. This can be
achieved by making use of a structured disposal
pipeline system, use of individual small scale
generator turbine, and use of piezoelectric
generators to harness the kinetic energy of falling
water. This project deals with the required piping
design needed for maximum power output. This
project also highlights the advantages and the
shortcomings of the proposed design.
Keywords: Renewable, Piezoelectric, Inelastic, PVDF
Fast production demands fast utilization of
resources. One such major resource is electricity.
Electricity is the lifeline for all the industrial work.
Rising standard of living and development of
technology has made use of appliances imperative
in our day to day life. Thus there is also a vast rise
in power consumption in residential areas. In order
to suffice the growing power demands, we are now
largely dependent on the extraction of power from
non-conventional, renewable sources of energy.
This paper focuses largely on the areas receiving
moderate to heavy rainfall. Solar and wind energy
are the major forms of renewable energy our
mankind look forward to.
Apart from these, high rainfall regions can also
utilize the rain to generate power on residential
basis. This work could be considered as a good
alternative to power systems in raining outdoor
environments where solar energy is difficult to
exploit . Following figure shows the brief block
diagram of this project.
This system converts the energy of falling rain
drops in two ways.
A. Utilizing the potential head available at
Multi-storey buildings having large terrace
areas act can act as water reservoirs. The water
accumulated can be made to pass through a
turbine situated at result in generation of
B. Utilizing the kinetic energy of falling
raindrops These consist of using piezoelectric
materials to convert the mechanical energy of
falling drops into electricity.
Piezoelectric materials exhibit the unique
property known as the piezoelectric effect.
When these materials are subjected to a
compressive or tensile stress, an electric field is
generated across the material creating the
voltage difference resulting in current flow. This
effect asymmetric nature of their unit cell when
a stress As seen in Figure, the unit cell contains
a small positive charges particle in the centre.
When a stress is applied this particle becomes
shifted in one direction which creates a charge
distribution, and subsequent electric field. These
materials come in several different forms. The
most common is crystals, but they are also found
as plastics and ceramics.
Figure 2: Lattice structure of piezoelectric crystals
The power generated from above methods are then
stored in storage batteries. This power can be used
during summer when there are large power cuts.
2. COMPONENTS AND DESIGN
For utilization of the potential head of the
accumulated water, the water is channeled through
pipes and made to pass through turbine situated at
the ground level. The dis-charge out from the
guiding pipe will be in the range of several liters/
This is a low discharge condition and hence
Pelton wheel will result in higher efficiencies. For
multi-storey buildings ‘H’ m tall. The potential
energy of volume V m3 of water accumulated will
be equal to
Potential energy= d*V*g H
Where, d= density of rain water
g= acceleration due to gravity (9.81 m/s2)
For regions receiving heavy rainfall during
monsoon of about 100mm per day, the potential
energy available per day for the buildings with
terrace area of 100m2 is
The accumulated water is made to pass through
a nozzle on the turbine blades. The power
generated per day with an overall
efficiency of ‘no’is
Considering density of water=1000kg/m3,
Head H=50m with no =0.7. The total power
output from the turbine will be P=3.4 MJ/ day.
Thus power generated in the entire rainy season
will be about 340MJ for a building of 50m
height and roof area of 100m2.
2.2. Piezoelectric Generators
This method aims at utilizing the kinetic
energy of the falling drop, to generate electricity.
Scientists from CEA/Leti-Minatec, an R&D
institute in Grenoble, France, specializing in
microelectronics, have recently developed a
system that recovers the vibration energy from a
piezoelectric structure impacted by a falling
The raindrop falling from the sky is
accelerated along its motion. This tends to
increase its velocity. At the same time the Drag
force offered by the air increases as its velocity
increase. At a certain point the drop experiences
equilibrium and the drop continues to fall with a
constant speed called as terminal velocity. It is
this kinetic energy of the drop which gets
converted into electricity due to piezoelectric
Figure 4: Piezoelectric effect in quartz
When a raindrop impacts a surface, it produces a
perfectly inelastic shock.  For application in
our rain drop scenario we have to consider a
membrane material sensitive to surface impacts.
Refer to diagram below for a simplified
representation of our system. To capture the
raindrops’ mechanical energy, we can use a
PVDF (polyvinylidene fluoride) polymer, a
piezoelectric material that converts mechanical
energy into electrical energy. When a raindrop
impacts the 25-micrometer-thick PVDF, the
polymer starts to vibrate. Electrodes embedded in
the PVDF are used to recover the electrical
charges generated by the vibrations .
Figure 5: Schematic diagram of vibration – electrical
Various tests conducted by the various researches
showed that, the instantaneous power converted
per rain drop for a converter area of few sq.cms
ranges from few micro watts and goes up to 12mW
The recoverable energy depends directly on the
size of the piezoelectric membrane, the size of
raindrops, and their frequency.The available
energy per drop varies between 2 µJ from 1 MJ
depending on its size . Following table shows
the variation in power generated for various drop
sizes. Table 1. Variation in power generated for various
drop sizes 
Based on data available, energy generated for a
span of 4 months in a region having rainfall of
100mm per day will be approximately 21.6 kJ
per sq.m of converter area. Thus for a converter
area of 100 sq.m, the energy generated will be
nearly 2.16MJ for the entire season.
2.3. Design of Rooftops
The important factor to be considered in
implementation of this project is the design of
rooftops. Rain water making contact with the
roof tops will be used to generate electricity in
above mentioned two ways.
Power generated by the turbine is due to the
flow of water accumulated on the rooftops of
buildings. For maximum power generation,
majority of the rain water from the roof top
must be channeled down the pipe. For this, the
roof surface must be provided with 5-10
degrees of inclination with the horizontal.
Also, multiple outlets must be provided for
large terraces so that there is maximum
outflow of water and minimum water logging.
Also for maximum power output from
piezoelectric generators, rain drops need to
strike the surface every single time. Water
accumulation results in piezoelectric sensors
getting submerged thus rendering them
useless. Hence proper inclination of 5-10
degrees must be provided.
3. BENEFITS AND DRAWBACKS
1. This system can be considered an
alternative to power systems in rainy outdoor
environments where solar energy is difficult to
2. This is a clean source of energy with
zero pollutant emissions.
3. This energy generation method is
independent of time of the day. It is fully
functional during day as well as night.
4. Use of new renewable sources of
electricity is the need of the day and
advancement in piezo sensor industry will
improve the output capacity.
1. Electricity produced by these means, at
present would cost more than electricity generated
from fossil fuels at their current costs.
2. The Piezoelectric sensors and turbine that
is needed to be installed are costly components.
3. Power generated is very low for direct use.
For effective utilization in needed times, the
energy generated must be stored in batteries which
also increase the system cost.
4. Such system is only operational during
rainy season. Thus the payback period of this plan
is quite large.
The current power output of this project is very less
with respect to the power consumption. The
investment cost is high and returns are low, thus
currently it can’t be implemented. Piezoelectric
technology can also be used to empower mobile
objects like cars and busses. Constant research in
the field piezoelectric materials assures the
potential of this project.
 “Rainfall as an Energy source”, Curt Harting,
Physics 240, Stanford university, November
 “Harvesting Rainfall”, Askel Bode, Project 1,
Phys575, 14th February 2012,
 “Residential Piezoelectric Energy Sources”,
Andrew Katz, delta smart house, 21st July
 “Rain power: Harvesting Energy from sky”,
Lisa Zyga, January 2008.
 Micka¨el Lallart,_ Shashank Priya, Scott
Bressers and Daniel Inman, “small scale
piezoelectric energy harvesting devices using
low energy density sources”, Journal of Korean
Physical society, vol 57, no 4, pp. 947-951,