Terawatt Photovoltaic Energy Scenario, Dreams and Realities
The photovoltaic (PV) industry is promoting the idea of scaling-up photovoltaic technologies to produce deca-Terrawatts, some are even talking about hundreds of TWs. In many ways, they are right; but are these extreme ideas doable? If so, how to achieve them? Will these goals be met by only relying on silicon PV technologies? Realistically, how much could be achieved by 2050?
We believe that scaling PV production to TWs, using current technologies, will hit various materials shortage issues. These will start to appear beyond few hundreds of gigawatt production. Many in the industrial arena and the PV business think that scaling is going to be done based on today’s most dominant technology, which is silicon (Si) crystalline solar cells. Obviously, this is giving false hopes and leads to miscalculations that could be detrimental for PV industry. In the contrary, diversification of PV technologies will prevent using-up all essential materials by one dominant technology, and will allow PV to thrive and may well secure the path towards hundreds TW goal. Many strategists think that 30 GW PV /year is most likely the trend for at least the next 5 to 10 years. They argue that even the production of solar grade silicon would require a large volume of high quality graphite crucibles that, practically, can not exceed a certain threshold, given economic and material availability constrains.
80MW Lieberose Photovoltaic Park, Germany, Courtesy Wikipedia
If the TW PV scaling is done in the US, as promoted by many companies, it would mean tens to hundred TWs across the globe are installed. That would be a good achievement for humanity, but fundamental questions remain: will these be really achievable? Can they be done with the dominant silicon technology and with current cell design?
As far as we know, there are no serious economic and PV material availability studies determining whether scarce materials will be exhausted or not, when scaling-up PV cell production to terrawatts. The luck of such studies led PV industry to promote the idea of scaling-up photovoltaics based mostly on silicon technology performances in a hope to reassure investors and consumers about the future and the resolve of the photovoltaic industry to attain such goal.
US based PV companies have been all the time optimistic about the future of PV. No doubt, there is no industrial sector that has suffered as much as PV, since its launch in mid-seventies, and yet, it survived all tides coming from all over. However, for reaching the TW scale the given picture is very simplistic. Some say we could cover an area of only 86 miles in diameter with PV to power America. Others infer that silicon technology is largely capable to cover the US energy needs. The number looks small, but in fact, the area is also 245km x 245km, which is rather huge, and the energy produced is about 12 TW (accounting for the PV system output, not the cell efficiency). But PV industry omitted that several needed materials for making silicon solar cells will surpass the PV share of existing natural resources. Other industry sectors will not give-up their shares. That will cause inflation of the prices when production is cranked-up, which will suddenly hinder PV production and the TW goal, and the industry will find itself unprepared. They also omitted that capital investment takes risk only if governments provide incentives and guarantees. Hence, the pace of scaling will remain constrained by the investment, and most likely will continue to be slow. The emergence of PV has been like a miracle, a very difficult one, after so much labor. No PV project has been accomplished before creating a need for it, and without oil and gas stakeholders leaving a spot for the PV project. More recently, installation of PV went from 1 GW to 100 GW in about 15 years. PV could grow 30% every year, along with all the raw material required without creating any repeat of poly silicon shortage. That 30% could be reached thanks to the guarantee that silicon technology has brought after 2000, and thanks to the increase of pressure for environmental and global warming problems. These driving forces are still, but the technology needs further development.
One of the primary issues in promoting the TW scaling is the omission of the way to reach that goal, in particular the material availability. As those ideas are mainly from PV cell manufacturers satisfied with silicon cell technology, they are inferring that Si type of technology will be capable, alone, to bring us to the TW goal. Many doubt this assertion, which is neither because of the incapacity of silicon, nor for the luck of such material, but it is rather because the current technology is not mature enough and the fact that PV Si technology is stuck with some not-abundant materials, which is even more problematic. When scaling-up production to some TW(s), positive and negative things will arise, and some will be detrimental to the progress of PV modules deployment. PV industry will attest at least the following:
1) a SURPRISING drastic increase of the scarcity and the cost of some materials needed to make silicon PV cells, possible shortage of silicon, … all which will hit badly the progress towards the TW scaling,
2) a reduction of the labor through more automation, which is a good trend that will increase the solar cell quality and will reduce the manufacturing cost, and
3) a reduction of the cost of some materials, in particular those used in making the PV module, but not so much for those making the solar cell.
The first must worry TW PV promoters who extrapolate the currently favorable costs to support the idea of building trillion watt PV industry. While Si is very abundant, its production is limited by materials used in the casting. Other essential elements for making Si PV cells are rather scarce in a context of extreme mass-production, including: Silver (Ag), Tin (Sn), Boron (B),... Si is 50% abundant in earth crust (relative to O, the most abundant), B is 0.002%, Sn is 0.0005%, and Ag is 0.00002%. Moreover, not all natural resources are minable, not all mines are profitable, and there is not effective abundance of such materials on the market for all applications. These facts mean that the scarce materials, will not suffice for the hundreds of TW PV production.
To overcome this major problem scarce materials must be substituted by others and subsequently new fabrication technologies must be developed. For instance, B could be substituted with Ga or Al. However, that will not be enough; so, to prevent depletion of materials (by the dominant Si technology), PV industry must be diversified (e.g., further developing thin film technologies, integration of perovskite onto Si, CPV,… novel PV materials, novel solar cell design,...).
Powering the US and the world with PV is a nice dream, indeed, and the we believe it is doable if various materials and technology routes are used, but never with a single material and a single technology. Technology variation is inherently healthy from various standpoints. In addition to the stabilization of a diversified PV industry; benefits of that diversification include materials availability, maintaining accessible pricing of scarce materials, reducing regional conflicts, and well serving the environment. It also allows a better business dynamics, and prevents business monopoly within a country, as well as globally.
Briefly, using several PV materials and technologies is the only way to fulfill that 10 to 100 TW PV dream, that is to avoid shortage of the non-abundant materials used in making solar cells. For the US, if we could cover with PV 1/4 of the area claimed by industry, it would be more realistic, as PV alone is incomplete. In that case, we would only need to cover 43mile diam. area. As mentioned above, PV alone (with no grid) will not work as it needs back-up systems, which could be fulfilled with Wind, CSP, Kinetic energy storage… Electric batteries are less fitted for large scale back-up, as batteries are extremely pollutant, non-reliable, and use rare materials that could hinder the TW scaling.
In addition, for reaching the hundred TW PV goal, recycling PV modules must be also done in order not to hurt the environment. Obviously, recycling will reduce the overall cost of PV systems, and will delay materials shortage.
As far as the practical use of PV, even though solar technologies, in general, and PV in particular, have huge energy potentials, it is necessary to have an energy mix, where various alternative technologies are employed, including Wind, Solar thermal water heating, CSP, Hydro,… The main idea of using these various routes, is to create a complementarity that enables persistence of energy production, as well as storage potentials. The obvious benefit is avoiding shortage of scarce materials.
In closing, in order not to run out of materials, to achieve the TW scale PV ambitious goal, scientists and engineers must find alternative materials and new solar cells. This will lead to developing the necessary fabrication technologies or altering existing processes. Focus should be on using abundant materials. To illustrate, let’s look at this example: magnesium (Mg) is the 5th most abundant material on earth, and magnesium chloride can be used in new type of solar cells. Moreover, other Mg compounds are very likely to be good since you can make oxides, conductors, and semiconductors with Mg, all you need to make new solar cells with this abundant material (note that forms of Mg are biologically friendly for humans and other species). Therefore, to enable the TW scaling, R&D agencies must promote new research programs with large funding support. As of today, the need for alternative materials is not spelled out by industry. Unfortunately, PV companies got busy with competition (this does not constitute in any way a blame) and their bottom line, which is understandable as they need to keep their PV companies afloat after the successive economic strains they just came out of. Undeniably, these circumstnaces have been keeping PV companies thinking only on using currently available technologies, and at best they have been doing only small incremental improvements; a linear evolution that will not lead photovotlaics to TW production. Industry must cooperate with universities and research centers, as well as governmental agencies, for finding alternative PV materials and for developing future PV processing technologies. They have to invest in "Bottom-UP PV TW scaling", that is investing in R&D and technology transfer, instead of extrapolating current performances to create a "TW PV vision".