A Paint-Based Solution to Capturing Sunlight

published: 2012-02-14 15:48 | editor: | category: Analysis

By Dr Dino R Ponnampalam

There has been a considerable push to restructure the energy mix to favor non-finite energy resources due to traditional energy resources being finite.  Examples of non-finite energy resources include solar energy, wind power, and marine energy.  This shift to less-polluting sources of energy will no doubt be of benefit to the environment, but for the economy to benefit, current technological barriers will need to be scaled.

Solar energy, for example, is one such energy technology that has immense potential but is currently hampered by the technology in use.  Considering that more sunlight reaches the Earth in a single sixty-minute period than what is required to power our energy intensive lifestyles for three hundred and sixty five days, the potential of solar energy technology is clear.

Multi-Generational Progressions in Solar Energy Technology

As mentioned, barriers exist.  For solar energy, and certainly for most energy technologies, the two main barriers are manufacturing costs and the electrical energy conversion efficiency rate.  In a general sense, the manufacturing costs are high and the electrical energy conversion rates are low; this relationship requires change in order for solar energy technology to become widespread and for society to fully harness this natural energy resource.

Solar energy technology focuses mainly on first-generation solar cells and, more recently, second-generation solar cells.  First generation solar cells are conventional in nature, with silicon being the main component.  With an electrical energy efficiency conversion rate of around 20%, these solar cells and modules have become the backbone of the solar energy industry.

Second-generation solar cells advanced the solar industry by reducing the manufacturing costs of producing solar cells, specifically by using thin slices of refined silicon or non-silicon material.  Examples of second-generation solar cells include cadmium telluride (CdTe) solar cells, copper indium gallium selenide (CIGS) solar cells, and silicon thin films such as amorphous silicon solar cells.  Typical electrical energy efficiency conversion rates range from 10% to 15%, which are not as high as first generation solar cells.  However, due to the advances made in manufacturing and in the amount of material used, in addition to its flexibility that allowed for integration into the architecture of a building, thin film solar cells became very popular as a cost-effective way to generate electricity from sunlight.    

Third-generation and fourth-generation solar cells offer the prospect of correcting this inverted relationship by reducing the associated manufacturing costs of producing solar cells and module.  Furthermore, these third and fourth generation solar cells offer the prospect of improving on the electrical energy conversion rates by exceeding the theoretical Shockley–Queisser limit.  This limit states the maximum electrical energy conversion rate is roughly 32%. 

Innovative Ways to Incorporate Solar Energy Technology through Paint

There is no doubt that an inexpensive and highly efficient solar cell will be deployed in the near future; advances are being made on a monthly basis so there is a strong indication that this cost-effective and barrier-breaking solar cell is not too far away in the distant future.  However, while society waits for this arrival, alternatives to conventional solar energy technology – where a solar cell, module, or an array is fitted to the roof of a property - could be explored.

When buildings are refurbished, an opportunity to shape the internal layout and external façade arises.  In addition to the possibility of implementing energy efficient measures to reduce the energy profile of a building, homeowners and building owners might also repaint the property.  This common occurrence, where the home or building is repainted, is where a creative use of solar energy technology has found use.  In late 2011, academics at the University of Notre Dame (Indiana, USA) put forward just how paint could be used in a creative way. 

Prashant V Kamat, Professor of Science in the Department of Chemistry and Biochemistry Radiation Laboratory and Department of Chemical & Biomolecular Engineering at the University of Notre Dame (Indiana, USA), recently released details on paint that generated electricity by harvesting sunlight.  Kamat’s research group, advancing the work done by a research group in the United Kingdom, modified the chemical constituents of paint to create essentially a quantum dot solar cell.

A quantum dot is capable of absorbing a greater degree of incident sunlight.  This is achieved by its relatively small cross-section and very high absorption ability.  By possessing small cross-sections, only a fraction of semiconducting material is required, thus reducing manufacturing costs considerably.  

Using Chemically Altered Paint in Generating Electricity

The concept of using paint to generate electricity is relatively new.  Professor David Worsley and his research team at the University of Swansea (Wales, UK) were investigating the idea of turning steel found in building frameworks into usable individual “power stations”.  In 2007, this area of research resulted in an inventive approach that took advantage of the natural degradation of paint on steel. 

One major constituent of paint for external coatings is titanium dioxide.  This compound degrades in sunlight.  Professor Worsley and his team realized this natural change could, under the right circumstances, be used for generating electricity in the form of a dye-sensitized solar cell (DSSC). 

This proposal saw steel beams coated with a layer of unaltered paint.  Then, the electrolyte and dye layers are applied.  To protect the innovative solar cell from the elements, a protective layer was then added.  As light strikes the modified coating, molecules are excited that release electrons.  These electrons, released into the titanium dioxide layer, act to form a circuit and eventually move back into the dye due to the attraction of the positively charged ions in the electrolyte solution.  This movement, in a simplistic way, accounts for the generation of electricity.      

At the time, the multinational steel firm Corus (now Tata Steel) commercialized this pioneering approach to using steel architecture, stating that the chemically altered paint had an electrical energy conversion efficiency rate of 11%.

Quantum Dot Solar Paint to Generate Electricity

Utilizing a different approach, Professor Kamat and his research team from the University of Notre Dame (Indiana, USA) aimed for a similar result: paint that could be applied to a structure in order to generate electricity. 

Treating the titanium dioxide, found as a pigment in paint, with either cadmium selenide (CdSe) or cadmium sulfide (CdS), and then mixing the compound in a water-alcohol solvent resulted in the formation of a paste.  Figure 1 is a photograph of the chemically modified paste.

Figure 1: Photograph showing the chemical paste caused by mixing titanium dioxide particles with either cadmium sulfide or cadmium selenide particles.  Credit: University of Notre Dame Center for Nano Sciene and Technology

This chemically altered paste was then applied to a conductive surface.  The research team discovered that the paint generated electricity but not very efficiently.  As a first step though, it was quite an achievement.  With an electrical energy conversion efficiency rate of 1%, this solar paint cannot match the efficiency rates of conventional solar cells, which can reach up to 20%.  What solar paint lacks in terms of electrical efficiency it makes up for in cost savings, making solar paint an appealing technology.    

The Promise of Solar Paint as a Source of Power

As stated, with an efficiency rate of 1%, solar paint cannot compete with traditional solar cells or modules.  As such, this significant drawback indicates that the solar paint is not quite ready for commercialization.  However, with time, the efficiency rate of solar paint is predicted to improve to around 10%, at which point this paint becomes suitable for low-power applications or even as an ancillary source of power. 

Regardless of the disadvantage of a low efficiency rating, this creative use of paint is packed with promise.  Once the efficiency rating reaches double digits, solar paint could be applied to the outer structures of a building or to any surface that receives sunlight.  This would effectively turn that surface into a power-generating surface providing power for low-level applications such as indoor or outdoor lighting, and acting as a secondary power source that could help to reduce the primary power source usage. 

In addition to being used as a way to reduce main electricity usage, solar paint has an extremely attractive feature in its favor: cost.  Manufacturing solar paint requires neither specialized equipment nor specialized areas such as clean rooms commonly found in the manufacture of first-generation solar modules.  Therefore, the manufacturing costs for solar paint are negligible.

A Creative Wayto Use Sunlight through Solar Paint

Paint manufacturers would require no significant investment plans to produce solar paint, as there is very little alteration to the current methodology to manufacture paint.  What will change is the mindset: paint manufacturers can now offer their customers an opportunity to generate a small but nonetheless appreciable amount of electricity from a clean source of energy next time a property refurbishment commences. 

As there is always a battle between cost effectiveness and electrical energy conversion efficiency ratings, solar paint would probably be unattractive as it stands now.  However, once the 1% efficiency rating creeps over 10%, the cost effectiveness–electrical efficiency relationship will tolerate the lower rating for low-power applications.  The inference from this is that solar paint does indeed have a future as a niche product.  

The ability to generate electricity from sunlight is an opportunity to move our energy-intensive lifestyles to one that is less destructive and polluting.  While society cannot rely on a single method or technology to effect such a change, adopting wholesale changes with complementary initiatives could be adopted to further reduce the damaging reach of society.  Harvesting sunlight through a single coat of paint is certainly a step in the right direction, a step towards generating clean, environmentally friendly energy.

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