Green Engineering Products,IES NUS Student Branch

Engineering Paper Writing Competition 2009

Particulars

Name: Ng Joe HoongCourse: 2nd year, Engineering Science ProgrammeE-mail: ng_joehoong@nus.edu.sgTel: 8263 1132

Title: ”Piezoelectricity: 100% Free Energy?”No. of words: 1471 words

Piezoelectricity – 100% Free Energy?By: Ng Joe Hoong

Introduction

Surging energy demand is a driving motivator for obtaining new sources of energy which are clean and renewable. Huge initiatives have been taken to further research efforts and commercialization of well-known sources of renewable energy such as solar, wind, hydroelectricity and biofuels. However, in addition to the above sources, there is a lesser known technique which converts energy which would be wasted otherwise, into electricity, namely piezoelectricity. In this paper, we will study current and future applications of piezoelectricity. I will also introduce my proposed concept of the Submerged Piezo (SP).

Background on piezoelectricity

Piezoelectricity can be defined as the generation of an electric potential due to the application of mechanical stress to a crystal or ceramic which is asymmetrical (Wikipedia, 2009). A similarity piezoelectricity shares with the dynamo is that they both convert mechanical energy to electricity. The difference is that the dynamo generally requires rotational motion to generate electricity while piezoelectricity relies solely on force applied normally to the surface of the material, thus opening up new avenues where electricity can be harvested from mechanical motion impossible to harvest using the dynamo. Examples of materials which exhibit piezoelectricity are quartz, barium titanate, and polyvinylidene fluoride (Wikipedia, 2009).

Large scale application of piezoelectricity

I will now discuss current applications of piezoelectricity. A major example is the pioneering work done by Innowattech, an Israeli company affiliated with Technion Institute, which is the first company to demonstrate large scale generation of electricity using piezoelectricity (Innowattech Ltd., 2008). The material they have developed, Innowattech Piezo Electric Generators (IPEG), can be deployed under roads, rails, runways and pedestrian walkways. Electricity will be generated when vehicles or pedestrians move over and compress the IPEG. The IPEG material is definitely commercially viable as the cost per kWh is 3 – 10 cents, which is much less compared to solar, which costs 10 – 20 cents per kWh and oil and gas, which costs 8 – 16 cents per kWh. The payback period, assuming an income of 10 cents per kWh, is between 6 to 12 years using the IPEG technology. Besides that, the IPEG system is low maintenance and will only have to be changed once in 30 years. Innowattech also estimates that if all roads in Israel were equipped with the IPEG, 250 MWh’s of energy could be generated annually.

However, many critics argue that vehicles would have to burn more fuel when driving over the piezoelectric material (The Huffington Post, 2008). I disagreed with this criticism. When cars drive over roads, they are already causing a deflection in the roads surface. Thus, why should additional energy be consumed when cars drive over the IPEG? This was backed up by Innowattech (Innowattech Ltd., 2008). In fact, they

claim that in the worst case, the miles per gallon (MPG) of a particular vehicle would be unaffected, but it is possible that the MPG of the vehicle could actually decrease, as the addition of the piezoelectric material would increase the Young’s modulus of the road, reducing the deflection of the road and the loss of potential energy of the vehicle.

Small scale/portable application of piezoelectricity

In addition to large scale electricity generation, piezoelectricity can also be used on a small scale to power portable devices. A good example would be the Energy Harvesting program by SRI International and DARPA (Paul Eng, 2009). By inserting a piezoelectric polymer in the sole of boots, about half a watt of electricity can be generated while walking, which is sufficient to power a handphone. It is hoped that the output power could be raised to 2 watts. Another possible application according to Paul Eng is the production of a gas-powered generator which generates electricity by flexing a piezoelectric polymer, rather than cranking the conventional magnet-and-metal based generator. The advantages are a lighter and quieter generator.

Similarly to the above large scale application of piezoelectricity above, the electricity generated comes from energy which would be wasted if not harvested, and is a clean energy source which is non-polluting. Another major benefit of having portable power sources is the reduction in the number of batteries manufactured and discarded. For example, every year, over 15 billion batteries are produced worldwide and 98% are discarded after a single use (It Must Be Green, 2008). This is not only a waste of natural resources, but also results in the harmful release of chemicals such as cadmium, which is harmful to aquatic invertebrates (Waste Online, 2005). By using piezoelectric generators to phase out single-use batteries, we can avoid the growing problem of wastage disposal.

Revolutionary application of piezoelectricity in the harvesting of energy from ocean waves

The previous applications relied on man-made sources of energy, namely the engines of vehicles and footsteps. Now, I will analyse attempts to harness energy from nature as well as propose my own system for generating piezoelectricity. SRI International, previously mentioned above, has created a prototype buoy, which can convert the motion of ocean waves into electricity (SRI International, 2007). They absorb the vertical force of waves, compressing a piezoelectric material, and siphoning off the additional voltage induced to generate electrical current. Although the prototype only generates miniscule amounts of electricity, it is forecasted that this technology would be able to rival wind and solar energy in the future. Another example is the Pelamis Wave Energy Converter, which uses hydraulic motors to generate electricity (Pelamis Wave Power, 2007).

There is a problem I predict if this technology is applied on a large scale. The buoy would be extracting energy from the waves, thus reducing the energy of waves exiting from the generator, limiting the potential for this technology to be applied on a large scale. My proposed solution, the Submerged Piezo (SP), is to place the

piezoelectric material horizontally below sea level, and the pressure applied would be due to the change in the wave height as waves propagate over the piezoelectric material. Thus, instead of absorbing the vertical force of waves on the surface, I will absorb force which would otherwise be applied on deeper water or the seabed. In a sense, this method is similar to Innowattech’s IPEG, which absorbs the force vehicles exert on the road, which would be wasted if not harnessed.

I will now illustrate the feasibility of the SP. To make my approximations, I set the wave height at 3 m and the wave period at 8 s (Wikipedia, 2009). I would also take the wave speed to be 5 m/s (David Raymond, 2006). The piezoelectric material which I would use is the Innowattech Piezo Electric Generators (IPEG) (Innowattech Ltd., 2008). I will use the results of a pilot test performed by Innowattech. Using a 17 ton truck, which was driven at an average speed of 72 km/h, over a 10 m length of piezoelectric material of width 1.0 m (0.5 m per wheel), and assuming a frequency of 1000 trucks per hour, 1 kWh of electricity was generated.

To estimate the power generated by the SP, we will assume a wave is the approximate equivalent to a truck. Assuming that ocean waves are a sinusoidal function, by integrating the sine function to obtain the area under the curve, we obtained an estimate the volume of each wave, and by multiplying it with the density of sea water, 1025 g/ml (Wikipedia, 2009), we obtain a mass of 123,000 kg per wave. Next, by assuming that the power generated is directly proportional to the weight of the object and the frequency of the objects moving over it, we estimate the power generated would be 3.6 kWh. To be conservative, we decided to round it down to 3 kWh. Thus, using the estimates from Innowattech (Innowattech Ltd., 2008), we can conclude that it would be theoretically possible to generate electricity at a cost of 1 – 3 cents per kWh, and have a payback period of 2 – 4 years. In addition to that, the power generated is assumed to be more constant and predictable, available 24 hours a day, and as it is powered by a natural source, could be used as a sole power source for a nation, unlike the original IPEGs which require vehicles powered by fossil fuel to function.

Conclusion - Improving piezoelectricity using nanotechnology

In summary, I would like to iterate that the potential of piezoelectricity is due to its ability to harness energy which would be wasted otherwise. Piezoelectricity is already being applied to harness energy from roads, pedestrian walkways, walking and the ocean, and they are certainly economically viable in addition to being beneficial to the environment. The Submerged Piezo is a possible method to harvest energy from ocean waves with the potential to be scaled up as it has minimal impact on wave motion. To conclude, piezoelectricity has its niche and would play an integral role in powering the world.

References

David Raymond. (2006). Group Velocity. Retrieved March 27th, 2009, from http://physics.nmt.edu/~raymond/classes/ph13xbook/node16.html

Geek.com Team. (2000). The power of walking. Retrieved March 22nd, 2009, from http://www.geek.com/articles/news/the-power-of-walking-20000629/

Innowattech Ltd. (2008). Innowattech Energy Harvesting Systems. Retrieved March 20th, 2009, from http://www.innowattech.co.il/index.aspx

It Must Be Green. (2008). Batteries and Chargers. Retrieved March 27th, 2009, from http://www.itmustbegreen.co.uk/acatalog/Batteries___Chargers.html

Paul Eng. (2009). Boots Made for Power Walking. Retrieved March 21st, 2009, from http://www.waikato.ac.nz/library/learning/g_apaguide.shtml#gene

Pelamis Wave Power. (2007). The Pelamis Wave Energy Converter. Retrieved March 27th, 2009, from http://www.pelamiswave.com/content.php?id=161

SRI International. (2007). Novel Wave-Powered Generators Deployed in Sea Trials off Florida Coast. Retrieved March 27th, 2009, from http://www.sri.com/news/releases/080307.html

The Huffington Post. (2008). Piezoelectricity: Would Highway Power Be Stealing From Drivers? Retrieved March 27th, 2009, from http://www.huffingtonpost.com/2008/12/17/piezoelectricity-would-hi_n_151816.html

Waste Online. (2005). Battery recycling information sheet. Retrieved March 27th, 2009, from http://www.wasteonline.org.uk/resources/InformationSheets/Batteries.htm

Wikipedia. (2009). Piezoelectricity. Retrieved March 27th, 2009, from http://en.wikipedia.org/wiki/Seawater

Wikipedia. (2009). Seawater. Retrieved March 27th, 2009, from http://en.wikipedia.org/wiki/Seawater

Wikipedia. (2009). Wave power. Retrieved March 27th, 2009, from http://en.wikipedia.org/wiki/Wave_power