Are current Solar PV Panels ready for Mass Deployment?

PV panels are a waste of time in any situation other than off-the-grid tropics. The amount of energy to produce them makes them an unrealistic option for a reduced energy future. Trees are the world’s most efficient solar collectors, having developed over millions of years to transform solar energy into usable energy, for fuel and so on, far more effectively than any solar panel we could ever make. 

- David Homgren, Cofounder of Permaculture

The Question of Toxicity

SVTC White Paper: Towards a Just and Sustainable Solar Energy Industry

There is no simple answer to this question as there is such a wide variety of PV panels. Furthermore, their current manufacture may be from plants powered by coal powered plants or other fossil fuel sources. It is important to decouple this in the analysis so we know what the potential ecological footprint is. The groundbreaking white paper from the Silicon Valley Toxic Coalition has produced a white paper that points the industry in the right direction:

 

The SVTC Rating System

The SVTC releases a rating system each year to determine which PV manufacturers meet the conditions of environmental and human health well being. Purchasing agents are encouraged to use this rating system to help establish meaningful standards in the industry.

Figure 1: Silicon Valley Toxics Coalition 2012 PV manufacturers scorecard (Source: svtc.org)

SVTC Types of PV Panels

Figure 2: Production Toxins (Source: SVTC white paper: Towards a Just and Sustainable Solar Industry)

SVTC Current Toxins in Manufacturing and at End of Life

It will become apparent from looking at the chemicals used in the manufacturing of the enormous variety of PV panels, that the industry has a lot of environmental challenges to face. The solar PV industry finds itself in a transitional period which all technology companies are entering as cradle-to-cradle methodology begins to gain traction in industry. Cradle-to-cradle design methodology has enormous implications for high technology in general. It is an added constraint that will be imposed upon all scientific research that is on a concrete trajectory towards market commercialization. It will no longer be acceptable to manufacture technology in a way that presents production and disposal problems. This new environmental constraint will fundamentally alter applied research as cradle-to-cradle techniques will determine the fundamental physics used to port pure research to useful technology. Many techniques previously used in the past will simply be unacceptable in light of the new requirements.

Production Toxins

The diagrams below illustrate the processes for the common PV panels currently manufactured, along with the associated toxic outputs at each stage of production.

Figure 3: Production Toxins of Crystalline Silicon PV Panels (Source: SVTC white paper: Towards a Just and Sustainable Solar Industry)

Figure 4: Production Toxins Amorphous Silicon PV Panels(Source: SVTC white paper: Towards a Just and Sustainable Solar Industry)

Figure 5: Production Toxins Cadmium Tulleride PV Panels (Source: SVTC white paper: Towards a Just and Sustainable Solar Industry)

Figure 6: Production Toxins Copper Indium Selenide (CIS) and Copper Indium Gallium Selenide (CIGS) PV Panels (Source: SVTC white paper: Towards a Just and Sustainable Solar Industry)

Figure 7: Production Toxins Galium Arsenide and Multijunction Panels (Source: SVTC white paper: Towards a Just and Sustainable Solar Industry)

Additional toxic materials used to produce GaAs PV cells include the following:

• Arsenic is a metalloid used to produce gallium arsenide crystals. Arsenic is highly toxic and carcinogenic,65 and extreme caution will be required to avoid occupational hazards as the use of this technology expands.
• Phosphine and arsine are highly toxic gases used to dope GaAs crystals, but they are not found in the final PV cells. Less toxic alternatives are being developed (including tertiary butyl arsine and tertiary butyl phosphine) and researchers are looking into substituting hydrogen with non-explosive (inert) nitrogen.
• Trichloroethylene, a known carcinogen, is a solvent used for cleaning. Other chemicals used or produced in the manufacturing process include hydrochloric acid, methane, triethyl gallium, and trimethyl gallium

Emerging Technologies:

• Dye-sensitized solar cells release electrons from (in one particular case) titanium dioxide covered in a pigment that effectively absorbs sunlight.
• Organic (living or dead carbon-based) solar cells are made of biodegradable materials. At this point, many of these organic technologies degrade during operation, making them very unstable and far from commercial viability.
• Hybrid cells that combine various technologies and therefore present all the production hazards associated with their constituent semiconductors.
• Emerging solar cell technologies are also rapidly incorporating advanced techniques in nanotechnology which have unknown hazards. Applications include:
• deposition of nanocrystals
• nanoparticles suspended in ink, quantum dots, nanowires, and silver cells.
• very stable laminate layers to protect solar cells

STVC Disposal Toxins and Health Effects

At the End of Life of the Solar PV (approx. 25 years), many of the toxins within the variety of PV panels can be released to the environment if not properly recycled. There are currently no commercial facilities to recycle the wide variety of hazardous ingredients that make up solar PV panels.

Figure 8: Effects of e-waste on human body (Source: Silicon Valley Toxics Coalition)

The Question of Embodied Energy

Photovoltaic panels, like integrated circuits are a high tech product which currently uses energy-intensive processes that are powered by carbon-based fuels:

1. Raw materials have to be mined: quartz sand for silicon cells, metal ore for thin film cells
2. Materials have to be treated. For silicon cells: purification, crystallization and wafering
3. Upgraded materials have to be manufactured into solar cells, and assembled into modules

All these processes produce air pollution, heavy metal emissions, and they consume energy. So unless we do a complete Life Cycle Analysis, we will not their real Cradle-to-Grave cost.

There are a number of researchers working to determine embodied energy of Solar Panels with conflicting answers:

1. Green Illusions, a book on solar PV as a viable solution written by Ozzie Zehner
2. National Renewable Energy Laboratory (NREL)
3. The Ugly Side of Solar Panels, Kris De Decker of Low Tech Magazine
4. Nathan Lewis of Lewis Research Center at the California Institute of Technology

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1. Green Illusions – Ozzie Zehner, Visiting Scholar, U of C, Berkeley

Ozzie Zehner is the author of the book Green Illusions: The Dirty Secrets of Clean Energy. Watch his eye-opening talk as he describes the personal and surprising discoveries he has made with Solar PV

 Main Points

•  United Emerates Study Findings: Humidity and Haze disperses suns rays
• Debris such as dust or leaves, etc must be cleared off continuously
• At midday, the heat can halve the efficiency / output
• Output fades 1% per year, newer technologies can degrade even rapidly
• After 5 or 10 years, inverter will fail. They need to be replaced 2 to 5 times in the lifetime of the panel
• Each inverter costs about a new furnace
• Solar panels theft on the rise
• Cost: most expensive options of dealing with CO2 will become cost effective long before solar panels: why mitigate 1 ton CO2 when 5 or 10 ton CO2 elsewhere for same cost?
• Solar PV Plants are largest emitters of: Hexafluroethane, Nitrogen Trifluoride & Sulfur Hexafluoride: 10,000 to 25,000 more virulent than CO2. PV industry is one of the growing and leading emitters of these gases
• At End of Life, solar cells are not Cradle-to-Cradle and have to be buried in special sealed toxic waste plot
• Trees will produce far more benefits than solar PV cells
• Our energy appetite is a leaky bucket which keeps growing
• What’s causing the bucket to grow? Consumption, overpopulation
• The Boomerang Effect: Hydropower and Nuclear power was suppose to decrease our demand for coal, however, they did not reduce the demand for coal. Extra capacity simply caused demand to increase and the result was more coal powered plants were built, not fewer
• Solar Cells add to the Boomerang Effect; another attempt to fill the expanding leaky bucket of energy by making more energy
• How do we stop the Boomerang effect? More “clean tech” is not the answer
• Plugging the huge leaks will do far more
• And addressing consumption and overpopulation will do the most
• If we increased solar cell production by 100x, it would bankrupt the US government and would still only supply a very small percentage of our current energy needs
• Clean technology is a deity which we do not question

 

  

Ozzie Zehner’s Main Conclusion: Throwing More Energy to the Problem won’t solve the Problem

The Jevon’s Paradox implies that efficiency alone will not reduce our requirements for energy either. It has the same effect as the Boomerang Effect; improving efficiency will cause consumers to demand more energy for other things.

The solution is really a social one, not a technological one; education and a paradigm shift to a lower energy consuming society & reducing population growth

2. National Renewable Energy Laboratory

The NREL has released a pamphlet entitled PV FAQs in which it addresses the question of Energy Payback for PV.

Energy payback estimates for rooftop PV systems are 4, 3, 2, and 1 years:

• 4 years for systems using current multicrystalline-silicon PV modules
• 3 years for current thin-film modules
• 2 years for anticipated multicrystalline modules
• 1 year for anticipated thin-film modules

With energy paybacks of 1 to 4 years and assumed life expectancies of 30 years, 87% to 97% of the energy that PV systems generate won’t be plagued by pollution, greenhouse gases, and depletion of resources. Based on models and real data, the idea that PV cannot pay back its energy investment is simply a myth. Indeed, researchers Dones and Frischknecht found that PV-systems fabrication and fossil fuel energy production have similar energy payback periods (including costs for mining, transportation, refining, andconstruction) 

- NREL PV FAQs

 Crystalline-Silicon PV Payback Calculations

Most solar cells and modules sold today are of the crystalline silicon type. Both single-crystal and multicrystalline silicon use large wafers of purified silicon which has been recrystallized from any number of “off-grade” silicon from the microelectronics industry. Estimates for the energy used to purify and crystallize silicon vary widely. Because of these factors, energy payback calculations are not straightforward. Until the PV industry begins to make its own silicon, which it could do in the near future, calculating payback for crystalline PV requires that we make certain assumptions.

Solar-cell manufacturing process includes the following components:

• purifying and crystallizing the silicon (most energy-intensive part)
• cutting the silicon into wafers
• processing the wafers into cells
• assembling the cells into modules (including encapsulation)
• manufacturing  facility overhead energy use

To calculate payback, Dutch researcher Alsema reviewed
previous energy analyses and did not include the energy
that originally went into crystallizing microelectronics
scrap. His best estimates of electricity used to make nearfuture,
frameless PV were 600 kWh/m2 for single-crystalsilicon
modules and 420 kWh/m2 for multicrystalline
silicon. Assuming 12% conversion efficiency (standard
conditions) and 1,700 kWh/m2 per year of available sunlight
energy (the U.S. average is 1,800), Alsema calculated
a payback of about 4 years for current multicrystallinesilicon
PV systems. Projecting 10 years into the future, he
assumes a solar-grade silicon feedstock and 14% efficiency,
dropping energy payback to about 2 years.

NREL References:

E. Alsema, “Energy Requirements and CO2 Mitigation Potential of PV Systems,” Photovoltaics and the Environment, Keystone, CO. Workshop Proceedings, July 1998.

R. Dones; R. Frischknecht, “Life Cycle Assessment of Photovoltaic Systems: Results of Swiss Studies on Energy Chains.” Appendix B-9. Environmental Aspects of PV Power Systems. Utrecht, The Netherlands: Utrecht University, Report Number 97072, 1997.

K. Kato; A. Murata; K. Sakuta, “Energy Payback Time and Life-Cycle CO2 Emission of Residential PV Power System with Silicon PV Module.” Appendix B-8. Environmental Aspects of PV Power Systems. Utrecht, The Netherlands: Utrecht University, Report Number 97072, 1997.

K. Knapp; T.L. Jester, “An Empirical Perspective on the Energy Payback Time for PV Modules.” Solar 2000 Conference, Madison, WI, June 16–21, 2000.

W. Palz.; H. Zibetta, “Energy Payback Time of Photovoltaic Modules.” International Journal of Solar Energy. Volume 10, Number 3-4, pp. 211–216, 1991.

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3. Low Tech Magazine

In March 2008, Kris De Decker, a contributor to Low Tech Magazine wrote a revealing article entitled The Ugly Side of Solar Panels which argued that generating electricity with solar panels can be a very bad idea. In fact, in some cases, Decker reaches a surprising conclusion: producing electricity by solar panels releases more greenhouse gases than producing electricity by gas or even coal. Decker’s claim is based on his review of a research paper which made the claim that producing electricity from solar cells reduces air pollutants and greenhouse gases by about 90 percent in comparison to using conventional fossil fuel technologies (“Emissions from Photovoltaic Life Cycles” published in “Environmental Science & Technology”. The researchers of that paper appeared to have come up with a solid set of figures. However, Decker found that they interpret them in a rather optimistic way. Deckers recalculations  are the basis for his surprising conclusions.

Energy mix

For this study, the researchers investigated 3 geographic scenarios and 4 types of solar cells:

Scenarios:

1. Average European energy mix
2. Average American energy mix (about 45% more CO2-intensive)
3. “CrystalClear” European Commission project

(Note: The CrystalClear project investigated the real energy mix used by 11 European and American silicon and PV module manufacturing factories. They used comparatively more gas and hydropower, so this is the best case scenario.)

Types of solar cells:

1. multi-crystalline silicon (with an efficiency of 13%)
2. mono-crystalline silicon (14%)
3. ribbon silicon (11.5%)
4. thin-film cadmium telluride (9%)

Assumptions

• Solar insolation (the amount of sunlight that the cells receive) = 1,700 kWh per m² per year (average of sunlight in Southern Europe)
• Lifetime expectancy = 30 years

Results

In the study, the scientists calculate the amount of greenhouses gasses emitted per kilowatt-hour of electricity delivered by one square meter of solar cells. This was done by:

1. Calculating the total lifetime electricity generation of one square meter of solar cells using the above assumptions
2. Dividing the amount of CO2 emitted for the production of one square meter of solar panels by this lifetime electricity generation

The conclusions of the researchers are based on rather optimistic life expectancy of 30 years and solar insolation in the Mediterranean.

Thin film solar cells got the best score:

• 20.5 grams of CO2 per KWh in the European energy mix
• 25 grams of CO2 per KWh  in the American energy mix

In spite of their lower efficiency, they are more eco-friendly because they need less material and no aluminium frame.

Surprisingly, the most efficient mono-crystalline silicon cells  got the worst score

• 43 grams of CO2 per KWh  in the EU
• 55 gram of CO2 per KWh  in the US

Surprisingly, Decker found that the key data of the calculation (the amount of CO2 emitted per square meter of solar panels) were not found in the report.  Even so, Decker easily calculated them by:

Kg GHG emitted per meter squared of PV panel = (Gram CO2 emitted per kilowatt-hour of generated electricity)   x   (Lifetime electricity generation)

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Carbon Footprint 

Once Decker calculated these, he said that he could see why the researchers choose not to publish these figures.

Optimistic Assumptions

• Best case scenario: one square meter of solar cells emits 75 kilograms of CO2
• Worst case scenario: one square meter of solar cells emits 314 kilograms of CO2
• If solar insolation = 1,700 kWh/m²/yr an average household needs 8 to 10 square meters of solar panels or 600 to 3,140 kilograms of CO2
• If solar insolation = 900 kWh/m²/yr  an average household needs 16 to 20 square meters of solar panels or 1,200 to 6,280 kilograms of CO2

Realistic Assumptions for Western Europe and North Eastern USA

In Western Europe and North Eastern US, solar insolation is 900 kWh/m²

• Using mono-crystalline silicon and 900 KWh/m2, CO2 emissions rise to 104 gram CO2 per kilowatt-hour of solar generated electricity, which makes solar panels only 4 times cleaner than gas.
• Assume expected lifetime of only 15 years, the worst case scenario now becomes 207 grams of CO2 per kilowatt-hour – just 2 times better than gas.

In this worst case, solar panels are still a better choice than fossil fuels but it is not truthful to describe them as a “clean” source of fuel.

Other Factors

The scientists in the study note that the environmental score of solar panels will improve as technological advancement improves their efficiency, reduce their embodied energy, carbon footprint and will probably be cheaper.  If the evolution in efficiency improves as projected, in about 10 to 20 years, we will see panels with 20 % or greater efficiency. However, one fact that the researchers did not take into account is that solar cells degrade in time. The typical manufacturers warranty covers just 80 percent of power output. Hence it may make economic sense to substitute older panels with newer panels before they are 30 years old. Solar PV cell ecological score will probably still be better than fossil fuel, but not by much.

Rooftop installation vs PV for Gadgets

While PV’s can be considered for rooftop usage, the following calculation shows that it’s just a bad idea for using with gadgets like mobile phones, tablets or laptops.

• Average Gadget PV life expectancy = 3 years
• Solar insolation of 900 kWh/m² (since they are not lying on the roof in the best orientation)
• Mono-crystalline cells
• Result = 1,038 gram CO2 per kWh/m²

Conclusion: It is better for the environment to power a gadget with coal-generated electricity than by solar!

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4. Lewis Research Center, California Institute of Technology Analysis of Solar PV Technology

Dr. Nathan S Lewis of the California Institute of Technology has done extensive research on this subject. In his 2006 paper Powering the Planet: Chemical challenges in Solar Utilization, Lewis writes:

Solar energy utilization requires solar (i) capture and conversion and (ii) storage. Solar capture and conversion may be accomplished by photovoltaics (PVs). The challenge here is to dramatically reduce the cost per W of delivered solar electricity. Compared with fossil energy, solar energy is diffuse, and hence materials costs must be very inexpensive to make a solar-based process economical. Knowing the insolation striking an area of the earth for a 30-yr period, it is relatively simple to calculate the sale price of the converted energy that is needed to pay back at least the initial cost that is required to cover that area with the solar energy conversion system.

At 10% efficiency, and a cost of $300 m2, both typical of current Si-based solar electricity modules, along with a balance of systems cost of $3 Wp 1 (peak W), an electricity price of $0.35 [kW-hr]1 is required to cover the initial system costs (13). By comparison, fossil-derived electricity (high-value energy) now costs approximately $0.02–0.05 [kW-hr]1, and that cost includes storage and distribution costs. To reach a cost point near that of fossil derived energy will thus require improvements in efficiency but additionally will require large decreases in cost, into a range below $100 m2. For comparison, the cost of paint is about $1 m2, so the solar energy conversion system can cost 10 times more than the cost of paint, but not much primary energy. In the absence of cost-effective storage, solar electricity can never be a primary energy source for society, because of the diurnal variation in local insolation. In principle, storage of electricity could be obtained using batteries, but at present no battery is inexpensive enough, when amortized over the 30-yr lifetime of a solar device, to satisfy the needed cost per W targets for the whole system.

Conclusion

1. In order to deploy Solar PV technology on a global and massive scale, not only does cost have to decrease orders of magnitude, but their embodied energy costs must be dramatically reduced and any pollution or waste associated with their manufacture or End of Life must be satisfactorily addressed
2. Current generations of solar PV cells are NOT a zero emission technology. Their usage must be carefully evaluated and their improvements over fossil fuels may only be incremental in many cases
3. Solar panels can be a doubtful choice in less sunny regions
4. Solar panels mounted on gadgets are unsustainable
5. Solar cells should be manufactured to be recyclable
6. Life expectancy must be increased to a minimum of 30 years
7. Solar Thermal power should have priority over solar PV power
8. If the world embarked on a giant deployment of solar energy, the first result would be massive spike of greenhouse gasses, due to the production of the cells. This is due to their high embodied energy
9. Use existing solar panels to provide power to solar PV manufacturing plants. The researchers showed that the CO2 impact of solar panels can be halved if this were done.
10. Unless the next generation of solar PV technology address the issues covered here, they will not be a true cradle-to-cradle solution

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