Measuring Solar’s Total Impact

solar-panel2.jpgRenewable energy generates clean power, and the fuel is often free: There’s no cost to make the wind blow or the sun shine. But just as many people advocate for considering the full cost of fossil fuels in the price of electricity (the cost of the pollution, mining, etc), so too must the full cost and impact of renewable energy be accounted for.

A new life-cycle assessment study from the Brookhaven National Laboratory in New York examined the four most common types of photovoltaic (PV) solar power cells — multicrystalline silicon, monocrystalline silicon, ribbon silicon and thin-film, if you were wondering — to find out how much energy and waste was involved in their creation.

“Emissions from Photovoltaic Life Cycles” found that even when accounting for the metals required to build PV cells, the efficiency of the cells, and the waste produced, PV cells still emit less global warming pollution throughout their life cycle than the fossil fuels needed to produce the same amount of power. Actually, most of the pollution from the solar power comes from the indirect emissions of the fossil fuels used to generate the electricity of the PV manufacturing facilities.

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The most energy-intensive type of PV cell to make — the monocrystalline silicate cells — only emits 1.8 ounces of global warming pollution per kilowatt hour, compared to 2.2 pounds by a coal-fired power plant. All told, the construction and use of PV power would cut air pollution about 90 percent if it replaced fossil fuels.

The best-case scenario, of course, would be for solar manufacturing facilities to be powered by solar. Researchers concluded that 30 percent of the energy used to make PV cells could come from solar power installed on the roofs and parking lot of facilities.

While some people point out that the study only partly takes into consideration the transportation of PV components (most of which are made in China), the researchers want to broaden their work further to include end-of-life and recycling data of the PV cells. They believe this expansion could further improve overall emissions calculations.

Scientific American


  1. Bobby B.

    I borrowed the following from one of my earlier posts:

    Does anyone ever wonder what happens to the energy that bounces off of a solar collector? Knowing its inherent inefficiency and the reflective properties of the materials used to make them, wouldn’t it stand to reason that a large amount of energy gets bounced back towards the atmosphere? Would canvassing the vast expanses of land that would be necessary to power even one city with solar collectors unintentionally accelerate global warming by reflecting heat back into what you guys believe is an atmosphere overburdened with heat collecting CO2? The land and seas act as a heat sink. If you cover the sink with mirrors, where does all that unused heat go? Why aren’t your IPCC approved scientists asking such questions, if a commoner like me can think of them?

    Reflective bounceback seems to have been omitted from the life cycle study you referenced.

  2. Joel

    Bobby, I believe most of the heat is absorbed and light that reflects would likely be sent right back out to space- granted some of it would hit clouds and turn to some heat there, but generally, the light that hits the earth now stays on the earth- if it’s reflected back out to space as light then that’s where it goes, back out to space and therefore it would actually cool the earth more to reflect it back to space. It stands to reason that on a bright sunny day when there’s a lot of light and few clouds, the reflection is able to go back up through that clear sky. Altough, I see your point, if there’s CO2 up there from burning oil and coal, it may hit that and make it warmer. Got a better solution?

    How about we cover the solar feilds with one way mirrors πŸ˜›

  3. Connie

    Bobby, Your assumption is based on the action of converting grasslands or forests into solar farms. This is not generally the case. The solar farms are being built out in deserts, or on rooftops. These are the same spaces that would otherwise absorb the heat, or reflect it back into the atmosphere as you say.

  4. Bobby B.

    Joel, please don’t take offense, but I do not think that your theory would work with either the theory of anthropogenic global warming (AGW) or with heat transfer engineering.

    AGW – or man made global warming – hinges not on cloudy or bright sunny days. In fact, the global cooling effect of clouds fails to get included in any of the accepted IPCC computer models. Google Dr. Roy Spencer (long ago tagged a denier) and check out what he has to say about clouds and atmospheric water vapor. The lynchpin in the whole AGW consensus is that man burns fuels that emit CO2 and that CO2 traps heat, thereby causing the temperature of the globe to rise. So, if man made CO2 is the problem and there is just too darn much of it and if clouds are primarily water vapor and have no effect on the global climate, then the cloudy/sunny day effects of solar panel bounceback heat retention are nil.

    The heat transfer engineering part gets much more complicated and I will admit it has been several years since I graduated from engineering school. However, the sun gives off energy in the form of heat and light. From an engineering stand point, heat is heat is heat. The light exists in both visible and invisible bandwidths, which both contain energy that is useful if converted to heat or electricity. A traditional solar collector captures heat to raise the temperature of a carrier fluid that can be used for various purposes – including making electricity. A photovoltaic converts light energy directly into electricity. However, neither technology can capture and make use of both heat and light energy. Since both types of solar collectors are made of highly reflective materials, it stands to reason that heat and light can be bounced back skyward. In fact, that is the principle behind the solar grill:


    Now, if it takes thousands of square miles of solar cells to power a mid-sized city, what happens to the light and heat that used to reach the ground? Could it be possible to get a heat retention double whammy wherein the atmospheric CO2 captures both first pass solar radiation from the sun and second pass bounceback radiation from the solar collectors? What happens if you cover enough area to really impact our dependence on traditional energy sources. One must think beyond what appears to be the solution and consider the impact of said solution, which is where I see the most shortcomings on the green energy side of the debate. The green’s equate success with making electricity without the burning of fossil fuels, but that attitude totally ignores the potential downstream consequences.

    And no, I don’t have an alternate solution to patent, although I believe ones better than solar already exist. And lastly, which way would you point the one-way mirrors? One side reflects light and the other doesn’t.

  5. Deep Patel

    “The best-case scenario, of course, would be for solar manufacturing facilities to be powered by solar. Researchers concluded that 30 percent of the energy used to make PV cells could come from solar power installed on the roofs and parking lot of facilities.”

    A couple solar manufacturing plants in germany are already doing this, they are powering the factories from the PV Panels they produce. Obvisouly they cannot power the entire factory with PV due to space limitations, but it would be really cool to see a factory running 100% off of PV, talk about carbon netural.

    -Deep Patel

  6. Michael Long

    Bobby, all of your arguments as based on the ASSUMPTION that there MAY be significant photonic bounceback, that said bounceback, if any, is significantly worse than the reflections off the sand the light would hit anyway, that any bounceback would propagate all the way back up out of the atmosphere, and that we need to cover “thousands” of square miles with solar cells.

    Considering that the portion of the earth’s surface covered by land is 57,268,900 miles, 2,000 square miles is just 0.000034% of that number. And 139,397,000 square miles are covered by water.

    BTW, one of the largest solar plants in Spain is 512,000 square meters, or just 0.19 square miles in size. Not even ONE square mile.

    So considering that we could build 2,000 of those plants and not even cover one millionth of the planets LAND mass (just 380 square miles.), I’d say your concerns are, well, overblown.

    Do some research, and stop spreading pseudo-science and FUD.

  7. Getaclue

    Bobby, are you just totally insane? Every hear about how SNOW reflects so much solar energy that the melting of that snow is going to accelerate global warming? OMG, you are beyond insane, you’re just plain nutty patootie. Sheesh!

  8. Bobby B.

    No, I am not “spreading pseudo-science” or “nutty patootie” (whatever that is). I am just asking why such things are omitted from the computer models. Maybe it’s because it is impossible to account for every possible contributing factor and some are just considered too igsignificant to include. But, does the exclusion of such possibilities make them impossibilities?

  9. Paul D.

    RE: solar reflection losses.

    Some basic assumptions for your discussion here, nutty patootie aside:

    Given the average conversion efficiency of crystalline silicon solar modules, the power density is in the range of 10 to 15 W per sqft. A government asessment done a year or so ago concluded that about 3/4 of the energy we need could come from rooftop PV alone. The balance could come from wind, geothermal, or other sustainable forms of energy.

    PV manufacturers take great pains to minimize reflection losses (no surprise here I hope) but in the end we are talking about glass, so there is some reflection. Most of the lost energy in photovoltiac conversion results in heat, which is dissapated from the module – just as it would otherwise be from the roof materials or the building/ground/sand/etc.

    The crux of the issue that Bobby B brings up is whether or not it is better for light/heat to be absorbed or reflected. From the standpoint of global warming, it is actually much better for this energy to be reflected. While some of the energy is doubtless absorbed by the atmosphere (this is the problem with GHGs by the way – they absorb reflected energy) if it is reflected from the ground at least some (most actually) will escape back into space. for example, many cities are getting hotter in part because all the concrete absorbs heat and re-emits it at night.

    As for the study, the additional reflection from PV would have to be accounted for as a good thing from a global warming perspective.

  10. Bobby B.

    Great reply Paul D., but the logic of your second-to-last paragraph leaves your argument open for some criticisms. I would ask that you please not get too angry with me by the following dissection, because we are all friends here – even though we have differences of opinion.

    Your comments imply that GHG’s only absorb reflected energy from the ground, but none of the energy that comes from the sun. How would this be possible? How would CO2 molecules floating around in the atmosphere determine which heat sources to absorb and which to ignore? You also say that most of the reflected energy actually escapes into space, which would be a good thing from a global warming perspective. What? If the already high concentration of GHG’s are absorbing only reflected heat and warming the planet, why would we want to reflect more heat and compound the problem? Seems like the wrong thing to do considering the crisis and looming doom.

    Maybe your statements should have flowed more like this:

    If we continue emitting large amounts of CO2 while we work towards converting to 3/4 solar power and survive the heating that we inadvertently speed up by reflecting more heat into an atmosphere already overburdened with reflective-heat-capturing CO2, some day in the future when the atmospheric CO2 returns to its natural percentage of 0.0300% instead of today’s extremely high 0.03811% the world will cool down to the levels that nature intended. Sure the process will take hundreds of years for the correction to occur, but the effort will have been well worth it.

    Please remember, we are all friends here.

  11. Paul D.

    Bobby, not a bad summation.

    I think you misunderstand my point about reflection vs absorbtion. Given an overly warm planet, more reflection is better than more absorbtion.

    I did not mean to imply that incoming solar radiation is not absorbed by GHG’s, only that trapping reflected light/heat energy is the bigger problem. (incoming energy that’s absorbed by the atmosphere would otherwise reach the ground anyway)

    Whether it is the ground or the atmosphere holding the heat, it is the total absorbtion of thermal energy that is the problem. Our planet was designed to absorb a certain amount of solar radiation and reflect the rest into space. We have thrown it out of balance.

  12. Kiashu

    Setting aside the babbling nonsense…

    It’s worth noting that the linked study giving us 20-55g CO2e per kWh (see here) doesn’t look at installation, maintenance and decommissioning.

    You don’t just drop the PV panels in a field and forget them, but must give them a solid base – typically concrete, with roughly 1kg CO2e emissions per kg – must empoly someone at least to polish them occasionally, and at the end of their useful life they must be removed and replaced, and their materials disposed or or recycled.

    Considering the complete lifecycle gives us figures closer to 100g CO2e per kWh. This varies quite a bit. Obviously if you put the thing in Sweden it’s going to give you less power than if you put it in the Sahara, but all the other emissions will be the same, so the emissions per kWh will be lower in Sweden than the Sahara.

    Likewise, local conditions will affect how much concrete needs to be used for foundations, and so on.

    But we can take as a good rough figure 100g CO2e/kWh. So far as I know, no-one has done complete lifecycle assessments of coal-fired stations, but just the coal makes them 1,325g CO2e/kWh.

    The lowest complete lifecycle emissions anyone’s established so far are with wind turbines, at around 50g CO2e/kWh. While they need a lot of concrete for their foundations (a 1.5MW turbine will need 200-450t), producing their materials isn’t as energy-intensive as solar photovoltaic, they don’t need purified silicon, cadmium, gallium or anything fancy like that.

    Unfortunately, concrete seems to be the weakest link in the emissions chain. In theory we could produce all the minerals and materials for the renewable generation from renewable energy itself; but concrete requires cement, which is produced by roasting limestone and driving off the carbon dioxide. Worldwide some 5-10% of our CO2 emissions are from making concrete. Since it’s a chemical process, how the stuff is roasted doesn’t matter…

  13. Bobby B.

    Yeah, maybe so. I will concede that there are forces at work that neither you nor I (nor the greatest IPCC approved scientists) fully understand. There is a balance to be maintained. That’s a given.

    The atmosphere does act as a blanket that blocks and retains heat simultaneously. The blanket allows some (but not all) heat to reach the surface during day time hours to be absorbed by the land and seas. A portion of that heat gets released skywards during the nighttime hours, but not all of it reaches outer space. Now this is a good thing, or else the planet would cook during the day and freeze during the night ultimately making it uninhabitable.

    I really find it interesting that you say that our planet was “designed to absorb a certain amount of solar radiation and reflect the rest into space”. Your use of the word “designed” indicates a belief in a Designer/Creator, as opposed to the miraculous accident that came to be via the big bang. That leads to a few additional (and possibly off topic) questions. Who designed it? Why would this creator/designer abandon his marvelous creation to let human invaders destroy it? What threw the creation out of balance so many times over millions of years before the advent of man?

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