Back to the Garden

Inna Godda da Vida

    -Iron Butterfly

You can have it all

My empire of dirt

     -Nine Inch Nails

Greetings

       I've been spending the last few days shoveling dirt.  Which is pretty elemental.  This dirt has a lot of cow poop in it, so, there is no avoiding  the basics of the basic biological realities of life on the planet.   Which has got me thinking about sustainability   My garden is far from it!  

       I suppose we all want "the good life" and the long-term sustainability of the ecosystem, (which is to say -  the Holocene, but without the 6th extinction ).

      We continue to argue about whether it is, in fact, an oxymoron - a contradiction, that lets us paper over the fact that we really want two contradictory things.

      One data point emerged last month.   A study of the sustainability of various countries and their ability to provide the basis to their population. .  Study here

      

"Their answer is uncomfortable. After looking at data on quality of life and use of resources from some 150 countries, they found that no nation currently meets the basic needs of its citizens in a sustainable way. The nations of the world either don’t provide the basics of a good life or they do it at excessive cost in resources, or they fail at both.

To Dr. O’Neill, an economist, this was something of a surprise. “When we started, we kind of thought, ‘surely, out of 150 different countries, there will be some shining star’” with a high quality of life and moderate resource use. “We really didn’t find that,” he said, pointing only to Vietnam as coming close to meeting both measures.

He did not say, however, that these findings doom humanity to poverty or environmental ruin. “It doesn’t tell us what’s theoretically possible,” he said, noting that the study only projects the results of continuing with business as usual. 

      

 So, it may possible, but we really have no existing  model to point to.

So, what about theoretically?   For instance what about CO2,?  Is  100% renewable power possible?.

There seems to be some disagreement on that question

Here's a good summary of the controversy comes from radio Ecoshock.

MIT Professor Mark Z. Jacobson published a paper in December 2015, outlining how the United States could power up with just wind, water, and solar. The title is “Low-cost solution to the grid reliability problem with 100% penetration of intermittent wind, water, and solar for all purposes“, PNAS.

Two years later, Caldeira along with others, including lead author Christopher Clack, issued a very negative rebuttal paper, also in the Proceedings of the National Academy of Sciences. That paper is “Evaluation of a proposal for reliable low-cost grid power with 100% wind, water, and solar”, PNAS, February 24, 2017. You can read the full text here.

Mark Jacobson pushed back with this article, published in the same issue of PNAS: “The United States can keep the grid stable at low cost with 100% clean, renewable energy in all sectors despite inaccurate claims”

Jacobson appears to have taken criticism of his model as an insult to his science. In a move very unusual for debate in science, Jacobson sued C. Clack and the National AAcademy.That suit was dropped this year. You can read Mark’s Tweet about the lawsuit ending here, and his full statement here. To dig into this further, Mark says “a total of 30 peer-reviewed scientific papers located at [here at Stanford] support the contention that the grid can stay stable with 100% or near 100% renewable energy.”

This Jacobson lawsuit sent a too some scientists wanting to add to this debate. You can read all about these “fisticuffs” here in the New York Times. It came to the point where one article rebutting Jacobson was passed on to Ken Caldi because the author worried about being sued. Caldeira published that articles blog.

In November of 2014, Mark Jacobson described his plan for all-green power here on Radio Ecoshock. But he did not talk about his heavy reliance on a projected renaissance of hydroelectric power. The problem is that Jacobson’s plan assumed nearly ten-fold increase in hydropower much of it by adding more generators to existing dams. You can find Ken Caldeira’s criticism of that hydro reliance here.

     

                Here is an interview with Ken Caldera, where he explains his view.  Basically, he finds that there are certain times when the wind doesn't blow and the sun doesn't shine.  Jacobson assumed that more hydro could be developed to provide backup during those times.  Caldera and his co authors concluded that most of the good hydro sites had already been developed and further expansion would be minimal.  They conclude that 100% renewable power is not achievable, and that only 80% could be supplied reliably.   Calderra notes in the interview that the batteries currently used by TESLA, and used in Australia and Puerto Rico are useful to make up for short term power losses, including overnight , but that they are not able to handle  other   longer term events (several weeks).  Arguably these could be handles by massively overbuilding the wind and solar facilities, but in Caldera's view,  it would be cost prohibitive.

          Here is the paper, Geophysical constraints on the reliability of solar and wind power in the United States

'We analyze 36 years of global, hourly weather data (1980–2015) to quantify the covariability of solar and wind resources as a function of time and location, over multi-decadal time scales and up to continental length scales. Assuming minimal excess generation, lossless transmission, and no other generation sources, the analysis indicates that wind-heavy or solar-heavy U.S.-scale power generation portfolios could in principle provide ∼80% of recent total annual U.S. electricity demand. However, to reliably meet 100% of total annual electricity demand, seasonal cycles and unpredictable weather events require several weeks’ worth of energy storage and/or the installation of much more capacity of solar and wind power than is routinely necessary to meet peak demand. To obtain ∼80% reliability, solar-heavy wind/solar generation mixes require sufficient energy storage to overcome the daily solar cycle, whereas wind-heavy wind/solar generation mixes require continental-scale transmission to exploit the geographic diversity of wind. Policy and planning aimed at providing a reliable electricity supply must therefore rigorously consider constraints associated with the geophysical variability of the solar and wind resource—even over continental scales.

Of course, there are many ways to be unsustainable.   At least seven according to the study mentioned above    One way, is to emit carbon dioxide.   Any carbon dioxide

       Basically, we have already emitted all the CO2 that we can afford.   The nations of the world agreed in Paris that 1.5 degrees was too dangerous .   And there is no budget left for that .  in fact it is likely that we have used up the budget for 2 degrees.   As discussed here,   recent studies indicate that ,  thanks to   reflective sulphate pollutants (aerosols) produced from the dirty burning of coal,   2 degrees is basically "baked in" , even if we stopped all CO2 tomorrow

In other words, going to zero emissions with CO2 at ~420ppm would result in a warming of around 2°C at equilibrium, if the level of short-lived gases was constant. Not going to zero emissions would be worse in the short term: other recent work shows warming would be 2.2-2.4°C by 2050 if we continue on the current high-emissions path.

And there is a consensus that 2 degrees is no longer a global warming guard rail. see here

“Limiting global warming to two degrees Celsius will not prevent destructive and deadly climate impacts, as once hoped, dozens of experts concluded in a score of scientific studies released Monday…With only one degree of warming so far, Earth has seen a crescendo of droughts, heatwaves, and storms ramped up by rising seas. Voluntary national pledges made under the Paris pact to cut CO2 emissions, if fulfilled, would yield a 3C world at best.

       

  It's hard to grasp how quickly things a re changing. An interesting article from. Eric Holthaus, notes that the last official report of the IPCC came out in 2013, and its already out of date.

The climate models used in these reports grow old in a hurry. Since the 1970s, they’ve routinely underestimated the rate of global warming. Some of the most recent comprehensive assessments of climate science, including last year’s congressionally-mandated, White House-approved, Climate Science Special Report, include scary new sections on “climate surprises” like simultaneous droughts and hurricanes, that have wide-reaching consequences. .....

“Positive feedbacks (self-reinforcing cycles) within the climate system have the potential to accelerate human-induced climate change,” says a section from that Climate Science Special report, “and even shift the Earth’s climate system, in part or in whole, into new states that are very different from those experienced in the recent past.” None of this was included in the last IPCC report."

"Actually, a helluva lot has changed in our understanding of the Earth’s climate system since the 2013 IPCC report. Here are some of the highlights:

1. Sea-level rise is going to be much worse than we thought. Like, potentially a lot worse. In the last IPCC assessment, the worst case scenario for sea-level rise this century was about three feet. That’s now about the midpoint of what’s expected; the worst-case has ballooned to about eight feet. That’s largely because …
2. Antarctica’s massive ice sheets could collapse much more quickly than we thought. Newly discovered mechanisms of collapse in some of the planet’s largest and most vulnerable glaciers in the West Antarctic Ice Sheet are beginning to capture the attention of the scientific community. Should these mechanisms kick in over the next few decades, they’d unleash enough meltwater to flood every coastal city on Earth.
3. Extreme weather is here and can now be linked to climate change in real time.From the Arctic to the tropics, wildfires, intense storms and other extreme weather events have been increasingly fierce in recent years, and climate change has played a measurable role. A 2016 report from the National Academies of Sciences opened the floodgates, so to speak, of the burgeoning field of extreme weather attribution. From last year’s Hurricane Harvey to last month’s nor’easter-linked floods in Massachusetts, nearly every weather event now bears a traceable connection to human-caused climate change.
4. Global warming of 1.5 degrees Celsius is pretty much locked in. A forthcoming special report of the IPCC will say that meeting the 1.5-degree target — one of the most ambitious commitments of the Paris Agreement — looks “extremely unlikely.” Humanity’s shift to zero-carbon energy sources is moving about 10 times too slowly. At this point, it would probably take geoengineering to prevent it. Researchers have started testing ways to do that.
5. We’ve already lost entire ecosystems, most notably coral reefs. During a record-breaking El Niño event in 2015, the world lost massive swaths of coral in a global bleaching event “unlike anything we’ve ever seen before.” More than 90 percent of the world’s coral will surely die by 2050 without rapid emissions reductions. That means one of the richest stores of biodiversity on the planet is already in jeopardy.

So, where does that leave us?

Professor Jem Bendell suggests that we have moved into a new world.   In the old world, one could hope that if we were to just live "sustainably"  we could hope to stop dangerous climate change.  Now, that appraoch is no longer an option.  Sustainability, whatever its beefits, will not stop dangerous climate change.  Bendell pulls no punchs in describing what the future looks like  " we are set for disruptive and uncontrollable levels of climate change, bringing starvation, destruction, migration, disease and war."

     He suggest a new approach is needed, one he calls "deep adaptation"

A deep adaption agenda will involve increasing resilience, relinquishment and restoration Resilience involves people and communities better coping with disruptions. Examples include how river catchments can better cope with rains, or how buildings can better cope with floods. What I’m calling relinquishment, involves people and communities letting go of certain assets, behaviours and beliefs where retaining them could make matters worse. Examples include withdrawing from coastlines or giving up expectations for certain types of consumption. Restoration involves people and communities rediscovering attitudes and approaches to life and organisation that the hydrocarbon-fuelled civilisation eroded. Examples include re-wilding landscapes so they provide more ecological benefits and require less management, or increased community-level productivity and support.

See also The End of Sustainability

The difference between a sustainability approach and one based on resilience can be seen this way.

Sustainability starts with a functioning system, and then looks at how long that system can operate without wearing down. It also takes into consideration how a system’s component functions can be improved so that the system can run continuously on its own.

Resilience starts with a disaster, and then looks at how to clean up afterward. It then considers how to prevent or minimize a future disaster, or at least minimize the negative effects of the disaster. The end result may or may not be sustainable, although a sustainable outcome is ideal.

Generally, many of us take the implicit view that  we can "have it all" - material progress for billions, as well as an intact ecosystem, perhaps through "sustainable development", perhaps through some other mechanism (degrowth?)     But is it a hope, a dogma, or merely an assumption?  An illusion? What happens if we come to the conclusion that it isn't so? 

Here is some interesting food for thought.

Paris: Optimism, Pessimism, and Realism

Towards Deep Hope

   As for me, I find I do my best thinking with my hands dirty.  Back to the garden!

Devilish Details

I'm seeing

Puzzling evidence

     -Talking Heads

Who would have thought...?

It figures

     _Alanis Morissette

Greetings 

     Tip O'Neil once is said "All politics is local."  Perhaps the same might be said of energy.  For instance , it is well recognized that any benefits of driving an eletric car will depend on the fuel used to generate the electricity.  See PNAS study : here.   So, if if you fill up in a state that relies mainly on coal, driving your EV may be worse than your old  ICE.  On the other hand if you live in hydro heavy northwest, you will see some environmental benefit.

       How about the environmental benefits of solar panels?   The article below  here (h/t Ben) , provides an interesting analysis of pv panels.  The author reasons that  there are several factors that need to be considered :  The energy that goes into the panels. the energy required to transport it to where it is used, and the solar influx of the location where it is used .  

     Most  PV panels are made in China  (87%!), which has a notoriously dirty energy system.  They are shipped around the world, and may end up in a country with less than optimal sunny-ness.  Like Germany  (or Oregon).  The author  suggest that in such a scenario, you would still get some benefit - but much lower than advertised.   Here, he calculates the impacts , without transportation.

 "If solar modules manufactured in China are installed in Germany, then the carbon footprint increases to about 120 gCO2e/kWh for both mono- and multi-si -- which makes solar PV only 3.75 times less carbon-intensive than natural gas, not 15 times."  

     The author takes the analysis one step further, by analyzing the growth rate of the PV systems.  As we know, the carbon impact of a PV system is "front loaded" in the early years.  Thus there is a "burp" of CO2 at the beginning,  and the system is in carbon "debt" for a number of years while it is off setting grid power.  With an individual panel, the debt is paid off in the later years.  However in a growing industry, the payback from the early panel is swamped by the debt of  manufacture of the later panels.    The author attempts to look at this factor across the industry using "dynamic life cycle analysis"    He notes:

"This means that the net CO2 balance of solar PV was negative for the period 1998-2008. Solar PV power was growing too fast to be sustainable, and the aggregate of solar panels actually increased GHG emissions and energy use. According to the paper, the net CO2 emissions of the solar PV industry during those 10 years accounted to 800,000 tonnes of CO2. [16] These figures take into account the fact that, as a consequence of a cleaner grid and better manufacturing processes, the production of solar PV panels becomes more energy efficient and less carbon-intensive over time.

       This is kind of an odd result.   For now, we may actually be digging the hole deeper, while we think we are making things better.  Do we ever get out of carbon debt?    Presumably, once all the needed PV's are installed.  But , pretty soon we have start doing it all over, as the current PV's degrade and we have to replace them.  

       He does suggest  one possible way out.

"By carefully selecting the locations for production and installation we could improve the sustainability of solar PV power in a spectacular way. For PV modules produced in countries with low-carbon energy grids -- such as France, Norway, Canada or Belgium -- and installed in countries with high insolation and carbon-intensive grids -- such as China, India, the Middle East or Australia -- greenhouse gas emissions can be as low as 6-9 gCO2/kWh of generated electricity. [16] [20] [14-15] That's 13 to 20 times less CO2 per kWh than solar PV cells manufactured in China and installed in Germany. [25]

            When we consider "green power" it is easy to forget the industrial economy that is needed for its development, manufacture, installations, and operation.  For an interesting tour of the various industries behind PV panels - Take a look here

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How Sustainable is PV Solar Power?

Solar photovoltaic (PV) systems generate "free" electricity from sunlight, but manufacturing them is an energy-intensive process.

It's generally assumed that it only takes a few years before solar panels have generated as much energy as it took to make them, resulting in very low greenhouse gas emissions compared to conventional grid electricity.

However, the studies upon which this assumption is based are written by a handful of researchers who arguably have a positive bias towards solar PV. A more critical analysis shows that the cumulative energy and CO2 balance of the industry is negative, meaning that solar PV has actually increased energy use and greenhouse gas emissions instead of lowering them.

This doesn't mean that the technology is useless. It's just that our approach is wrong. By carefully selecting the location of the manufacturing and the installation of solar panels, the potential of solar power could be huge. We have to rethink the way we use and produce solar energy systems on a global scale.

Picture: Jonathan Potts.

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There's nothing but good news about solar energy these days. The average global price of PV panels has plummeted by more than 75% since 2008, and this trend is expected to continue in the coming years, though at a lower rate. [1-2] According to the 2015 solar outlook by investment bank Deutsche Bank, solar systems will be at grid parity in up to 80% of the global market by the end of 2017, meaning that PV electricity will be cost-effective compared to electricity from the grid. [3-4]

Lower costs have spurred an increase in solar PV installments. According to the Renewables 2014 Global Status Report, a record of more than 39 gigawatt (GW) of solar PV capacity was added in 2013, which brings total (peak) capacity worldwide to 139 GW at the end of 2013. While this is not even enough to generate 1% of global electricity demand, the growth is impressive. Almost half of all PV capacity in operation today was added in the past two years (2012-2013). [5] In 2014, an estimated 45 GW was added, bringing the total to 184 GW. [6] [4].

Solar PV total global capacity, 2004-2013. Source: Renewables 2014 Global Status Report.

Meanwhile, solar cells are becoming more energy efficient, and the same goes for the technology used to manufacture them. For example, the polysilicon content in solar cells -- the most energy-intensive component -- has come down to 5.5-6.0 grams per watt peak (g/wp), a number that will further decrease to 4.5-5.0 g/wp in 2017. [2] Both trends have a positive effect on the sustainability of solar PV systems. According to the latest life cycle analyses, which measure the environmental impact of solar panels from production to decommission, greenhouse gas emissions have come down to around 30 grams of CO2-equivalents per kilwatt-hour of electricity generated (gCO2e/kWh), compared to 40-50 grams of CO2-equivalents ten years ago. [7-11] [12]

According to these numbers, electricity generated by photovoltaic systems is 15 times less carbon-intensive than electricity generated by a natural gas plant (450 gCO2e/kWh), and at least 30 times less carbon-intensive than electricity generated by a coal plant (+1,000 gCO2e/kWh). The most-cited energy payback times (EPBT) for solar PV systems are between one and two years. It seems that photovoltaic power, around since the 1970s, is finally ready to take over the role of fossil fuels.

Manufacturing has Moved to China

Unfortunately, a critical review of the PV solar industry paints a very different picture. Many commenters attribute the plummeting cost of solar PV to more efficient manufacturing processes and scale economies. However, if we look at the graph below, we see that the decline in costs accelerates sharply from 2009 onwards. This acceleration has nothing to do with more efficient manufacturing processes or a technological breakthrough. Instead, it's the consequence of moving almost the entire PV manufacturing industry from western countries to Asian countries, where labour and energy are cheaper and where environmental restrictions are more loose.

Less than 10 years ago, almost all solar panels were produced in Europe, Japan, and the USA. In 2013, Asia accounted for 87% of global production (up from 85% in 2012), with China producing 67% of the world total (62% in 2012). Europe's share continued to fall, to 9% in 2013 (11% in 2012), while Japan's share remained at 5% and the US share was only 2.6%. [5]

Compared to Europe, Japan and the USA, the electric grid in China is about twice as carbon-intensive and about 50% less energy efficient. [13-15] Because the manufacture of solar PV cells relies heavily on the use of electricity (for more than 95%) [16], this means that in spite of the lower prices and the increasing efficiency, the production of solar cells has become more energy-intensive, resulting in longer energy payback times and higher greenhouse gas emissions. The geographical shift in manufacturing has made almost all life cycle analyses of solar PV panels obsolete, because they are based on a scenario of domestic manufacturing, either in Europe or in the United States.

LCA of Solar Panels Manufactured in China

We could find only one study that investigates the manufacturing of solar panels in China, and it's very recent. In 2014, a team of researchers performed a comparative life cycle analysis between domestic and overseas manufacturing scenarios, taking into account geographic diversity by utilizing localized inventory data for processes and materials. [13] In the domestic manufacturing scenario, silicon PV modules (mono-si with 14% efficiency and multi-si with 13.2% efficiency) are made and installed in Spain. In the overseas manufacturing scenario, the panels are made in China and installed in Spain.

For solar panels manufactured in China, the carbon footprint and the energy payback time are almost doubled

Compared to the domestic manufacturing scenario, the carbon footprint and the energy payback time are almost doubled in the overseas manufacturing scenario. The carbon footprint of the modules made in Spain (which has a cleaner grid than the average in Europe) is 37.3 and 31.8 gCO2e/kWh for mono-si and multi-si, respectively, while the energy payback times are 1.9 and 1.6 years. However, for the modules made in China, the carbon footprint is72.2 and 69.2 gCO2e/kWh for mono-si and multi-si, respectively, while the energy payback times are 2.4 and 2.3 years. [13]

At least as important as the place of manufacturing is the place of installation. Almost all LCAs -- including the one that deals with manufacturing in China -- assume a solar insolation of 1,700 kilowatt-hour per square meter per year (kWh/m2/yr), typical of Southern Europe and the southwestern USA. If solar modules manufactured in China are installed in Germany, then the carbon footprint increases to about 120 gCO2e/kWh for both mono- and multi-si -- which makes solar PV only 3.75 times less carbon-intensive than natural gas, not 15 times.

Considering that at the end of 2014, Germany had more solar PV installed than all Southern European nations combined, and twice as much as the entire United States, this number is not a worst-case scenario. It reflects the carbon intensity of most solar PV systems installed between 2009 and 2014. More critical researchers had already anticipated these results. A 2010 study refers to the 2008 consensus figure of 50 gCO2e/kWh mentioned above, and adds that "in less sunny locations, or in carbon-intensive economies, these emissions can be up to 2-4 times higher". [17] Taking the more recent figure of 30 gCO2e/kWh as a starting point, which reflects improvements in solar cell and manufacturing efficiency, this would be 60-120 gCO2e/kWh, which corresponds neatly with the numbers of the 2014 study.

Solar insolation in Europe and the USA. Source: SolarGIS.

These results don't include the energy required to ship the solar panels from China to Europe. Transportation is usually ignored in LCAs of solar panels that assume domestic production, which would make comparisons difficult. Furthermore, energy requirements for transportation are very case-specific. It should also be kept in mind that these results are based on a solar PV lifespan of 30 years. This might be over-optimistic, because the relocation of manufacturing to China has been associated with a decrease in the quality of PV solar panels. [18] Research has shown that the percentage of defective or under-performing PV cells has risen substantially in recent years, which could have a negative influence on the lifespan of the average solar panel, decreasing its sustainability.

Energy Cannibalism

Solar PV electricity remains less carbon-intensive than conventional grid electricity, even when solar cells are manufactured in China and installed in countries with relatively low solar insolation. This seems to suggest that solar PV remains a good choice no matter where the panels are produced or installed. However, if we take into account the growth of the industry, the energy and carbon balance can quickly turn negative. That's because at high growth rates, the energy and CO2 savings made by the cumulative installed capacity of solar PV systems can be cancelled out by the energy use and CO2 emissions from the production of new installed capacity. [16] [19-20]

At high growth rates, the energy and CO2 savings made by the cumulative installed capacity of solar PV systems can be cancelled out by the energy use and CO2 emissions from the production of new installed capacity

A life cycle analysis that takes into account the growth rate of solar PV is called a "dynamic" life cycle analysis, as opposed to a "static" LCA, which looks only at an individual solar PV system. The two factors that determine the outcome of a dynamic life cycle analysis are the growth rate on the one hand, and the embodied energy and carbon of the PV system on the other hand. If the growth rate or the embodied energy or carbon increases, so does the "erosion" or "cannibalization" of the energy and CO2 savings made due to the production of newly installed capacity. [16]

For the deployment of solar PV systems to grow while remaining net greenhouse gas mitigators, they must grow at a rate slower than the inverse of their CO2 payback time. [19] For example, if the average energy and CO2 payback times of a solar PV system are four years and the industry grows at a rate of 25%, no net energy is produced and no greenhouse gas emissions are offset. [19] If the growth rate is higher than 25%, the aggregate of solar PV systems actually becomes a net CO2 and energy sink. In this scenario, the industry expands so fast that the energy savings and GHG emissions prevented by solar PV systems are negated to fabricate the next wave of solar PV systems. [20]

The CO2 Balance of Solar PV

Several studies have undertaken a dynamic life cycle analysis of renewable energy technologies. The results -- which are valid for the period between 1998 and 2008 -- are very sobering for those that have put their hopes on the carbon mitigation potential of solar PV power. A 2009 paper, which takes into account the geographical distribution of global solar PV installations, sets the maximum sustainable annual growth rate at 23%, while the actual average annual growth rate of solar PV between 1998 and 2008 was 40%. [16] [21]

This means that the net CO2 balance of solar PV was negative for the period 1998-2008. Solar PV power was growing too fast to be sustainable, and the aggregate of solar panels actually increased GHG emissions and energy use. According to the paper, the net CO2 emissions of the solar PV industry during those 10 years accounted to 800,000 tonnes of CO2. [16] These figures take into account the fact that, as a consequence of a cleaner grid and better manufacturing processes, the production of solar PV panels becomes more energy efficient and less carbon-intensive over time.

Between 2009 and 2014, solar PV grew four times too fast to be sustainable

The sustainability of solar PV has further deteriorated since 2008. On the one hand, industry growth rates have accelerated. Solar PV grew on average by 59% per year between 2008 and 2014, compared to an annual growth rate of 40% between 1998 and 2008 . [5] On the other hand, manufacturing has become more carbon-intensive. For its calculations of the CO2 balance in 2008, the study discussed above considers the carbon intensity of production worldwide to be 500 gCO2e/kWh. In 2013, with 87% of the production in Asia, this number had risen to about 950 gCO2e/kWh, which halves the maximum sustainable growth rate to about 12%.

If we also take into account the changes in geographic distribution of solar panels, with an increasing percentage installed in regions with higher solar insolation, the maximum sustainable growth rate increases to about 16%. [23-24] Although more recent research is not available, it's obvious that the CO2 emissions of the solar PV industry have further increased during the period 2009-2014. If we would consider all solar panels in the world as one large energy generating plant, it would not have generated any net energy or CO2-savings.

The Solution: Rethink the Manufacture and Use of Solar PV

Obviously, the net CO2 balance of solar PV could be improved by limiting the growth of the industry, but that would be undesirable. If we want solar PV to become important, it has to grow fast. Therefore, it's much more interesting to focus on lowering the embodied energy of solar PV power systems, which automatically results in higher sustainable growth rates. The shorter the energy and CO2 payback times, the faster the industry can grow without becoming a net producer of CO2.

Annual net CO2 balance of the crystalline silicon PV industry at different growth rates for different combinations of countries of production and installation. Source: Briner 2009.

Embodied energy and CO2 will gradually decrease because of technological advances such as higher solar cell efficiencies and more efficient manufacturing techniques, and also as a consequence of the recycling of solar panels, which is not yet a reality. However, what matters most is where solar panels are manufactured, and where they are installed. The location of production and installation is a decisive factor because there are three parameters in a life cycle analysis that are location dependent: the carbon intensity of the electricity used in production, the carbon intensity of the displaced electricity mix at the place of installation, and the solar insolation in the place of installation. [16]

By carefully selecting the locations for production and installation we could improve the sustainability of solar PV power in a spectacular way. For PV modules produced in countries with low-carbon energy grids -- such as France, Norway, Canada or Belgium -- and installed in countries with high insolation and carbon-intensive grids -- such as China, India, the Middle East or Australia -- greenhouse gas emissions can be as low as 6-9 gCO2/kWh of generated electricity. [16] [20] [14-15] That's 13 to 20 times less CO2 per kWh than solar PV cells manufactured in China and installed in Germany. [25]

Sustainable growth rates of 300-460% are possible when PV modules are produced in countries with low-carbon energy grids and installed in countries with high insolation and carbon-intensive grids

This would allow sustainable growth rates of up to 300-460%, far above what's even necessary. If solar PV would grow on average at a rate of 100% per year, it would take less than 10 years to meet today's electricity's demand. If it would grow at the 16% maximum sustainable growth rate we calculated above, meeting today's electricity demand would take until 2045 -- with no net CO2 savings. By that time, according to the forecasts, total global electricity demand will have more than doubled. [26]

Of course, producing and installing solar panels in the right places implies international cooperation and a sound economic system, none of which exist. Manufacturing solar panels in Europe or the USA would also make them more expensive again, while many countries with the right conditions for solar don't have the money to install them in large amounts.

CO2 mitigation potential for crystalline silicon PV modules produced in China and installed in different countries. Source: Briner 2009.

An alternative solution is using on-site generation from renewables to meet a greater proportion of the electricity demand of PV manufacturing facilities -- which can also happen in a country with a carbon-intensive grid. For example, if the electricity for the manufacturing of solar cells would be supplied by other solar cells, then the greenhouse emissions of solar PV systems could be reduced by 50-70%, depending on where they are produced (Europe or the USA). [7] In China, this decrease in CO2 emissions would even be greater.

In yet another scenario, we could dedicate nuclear plants exclusively to the manufacture of solar cells. Because nuclear is less carbon-intensive than PV solar, this sounds like the fastest, cheapest and easiest way to start producing a massive amount of solar cells without raising energy use and greenhouse emissions. But don't underestimate the task ahead. A 1 GW nuclear power plant can produce about 11 million square metres of solar panels per year, which corresponds to 1.66 GWp of solar power (based on the often cited average number of 150 w/m2). We would have needed 24 nuclear plants -- or 1 in 20 atomic plants worldwide -- working full-time to produce the solar panels manufactured in 2013. [27]

What About Storage?

Why does the production of solar PV requires so much energy? Because the low power density -- several orders of magnitude below fossil fuels -- and the intermittency of solar power require a much larger energy infrastructure than fossil fuels do. It's important to realize that the intermittency of solar power is not taken into account in our analysis. Solar power is not always available, which means that we need a backup-source of power or a storage system to jump in when the need is there. This component is usually not considered in LCAs of solar PV, even though it has a large influence on the sustainability of solar power.

Storage is no longer an academic question because several manufacturers -- most notably Tesla -- are pushing lithium-ion battery storage as an alternative for a grid-connected solar PV system. Lithium-ion batteries are more compact and technically superior to the lead-acid batteries commonly used in off-grid solar systems. Furthermore, the disincentivation of  grid-connected solar systems in a growing number of countries makes off-grid systems more attractive.

In the next article, we investigate the sustainability of a PV-system with a lithium-ion battery. Meanwhile, enjoy the sun and stay tuned.

Kris De Decker (edited by Aaron Vansintjan)