The two most environmentally popular alternatives for generating electricity are solar power and wind power.
A European Union study of externalities, via Daily Kos diarist NNadir, suggests that solar power is much more harmful environmentally than wind power, hydroelectric power, or nuclear power, per kilowatt-hour.
The study found that the harms to human health from various electricity generation methods, and global warming impacts, overwhelmed all other negative impacts of electricity generation, such as noise, crop damage, and harm to ecosystems.
In terms of harm to human health, photovoltaic cells were rated more of a problem than natural gas (primarily air pollution), nuclear power (primary risk of nuclear accidents), wind power, and hydroelectric power, although not as great as coal (with lignite coal being the worst), which is a great producer of air pollution.
Also, while, as expected, wind, hydro and nuclear have very little global warming impact, while fossil fuels have a great deal of global warming impact, solar power is rated at a decidedly intermediate level, about ten times a bad the low low impact sources, half the impact of natural gas, and about a fifth the impact of non-lignite coal.
Environmental Harms Associated With Solar Power
The European Union source is obscure regarding the reason for this distinction saying only: "Photovoltaics is a very clean technology at the use stage, but has considerable life cycle impacts." Presumably, this means that making and/or disposing of solar panels has associated health risks to people. The global warming impact is presumably related to the energy costs involved in making solar cells.
The Union of Concerned Scientists goes into greater depth:
Energy is required to manufacture and install solar components, and any fossil fuels used for this purpose will generate emissions. Thus, an important question is how much fossil energy input is required for solar systems compared to the fossil energy consumed by comparable conventional energy systems. Although this varies depending upon the technology and climate, the energy balance is generally favorable to solar systems in applications where they are cost effective, and it is improving with each successive generation of technology. . . .
[T]he manufacturing of photovoltaic cells often requires hazardous materials such as arsenic and cadmium. Even relatively inert silicon, a major material used in solar cells, can be hazardous to workers if it is breathed in as dust. Workers involved in manufacturing photovoltaic modules and components must consequently be protected from exposure to these materials. . . .
The large amount of land required for utility-scale solar power plants-approximately one square kilometer for every 20-60 megawatts (MW) generated-poses an additional problem, especially where wildlife protection is a concern. But this problem is not unique to solar power plants. Generating electricity from coal actually requires as much or more land per unit of energy delivered if the land used in strip mining is taken into account. Solar-thermal plants (like most conventional power plants) also require cooling water, which may be costly or scarce in desert areas. [Land use is even less of a concern when panels are on rooftops.]
Thus, the big concerns seem to be moderately high energy costs to build solar panels, and considerable toxic waste exposure issues in making and disposing of solar panels. By the European Union's estimate, these are greater concerns than nuclear waste or nuclear accidents. Wind farms, in contrast, involve non-toxic materials that take less energy to produce.
All this matters a great deal, because solar and wind power are basically chasing after the same clean electricity market. If solar power is environmentally much worse than wind power, the incentive is to use wind power instead of solar power.
This depends both on the efficiency of the respective power production mechanisms, and on the externalities they impose. Thus, if solar power were more efficient, it would also per less harmful per kilowatt-hour.
While the harm associated with making and eventually disposing of a solar cell is not site specific, the harm per kilowatt-hour may be very site specific.
The figures in the European source, which are based on harm per kilowatt hour produced, may partially reflect the fact that Germany, which is the site evaluated, is not a great place to build photovoltaic power stations.
The United States Get More Sun
If the power generation per photovoltaic cell is low in Germany, than the harm per kilowatt-hour will be articially high.
The Southern tip of Germany is at about the same latitude as Maine. Northern Germany's latitude is about the same as Ketchikan, near the Southern boundary of Alaska. Berlin's summer temperatures are cooler than Duluth, Minnesota (mean high in July of 76 degrees Farenheit), with a mean high in July of 73.6 degrees Farenheit. Denver is South of Lisbon, and at similar latitudes to Sicily and Athens, Greece, locations at the very Southern limit of Europe. Phoenix is at about the same latitude as Casblanca and Beruit, and the high temperature on an average day in Phoenix, Arizona in July is 104 degrees.
Phoenix has 50% to 100% more solar radiation per year than Berlin, which might immediately cut by a third to a half, the environmental impact of photovoltaic systems per kilowatt-hour there.
The United States Is Relatively Hot
Berlin isn't the only place in the world without hot summers. London's summer days are even cooler, and Dublin, Ireland's summers have a mean high of a chilly 66 degrees Farenheit (no wonder the Irish make good sweaters). Down under, summer days (i.e. January) in Auckland, New Zealand are similar in temperature to those in Berlin in the summer. Paris is just a wee bit warmer than Berlin in the summer with mean July highs of 75.2 degrees Farenheit. Mexico City, due largely to its high elevation, is cooler in the summer than Berlin.
Denver has a mean July high temperature of 88 degrees Farenheit. This is about the same as Athens, Greece, Rome, Italy, Havanna, Cuba, or Shanghai, China, cooler than Hawaii or Jerusalem or Tokoyo, and cooler than the year round mean temperature in sweltering Bombay. Yet, many homeowners in Denver have found it tolerable to not install air conditioning.
Some of the major world cities with summers warmer than Denver are Bangkok, Thailand, Cairo, Egypt, Damasacus, Syria, and Tehran, Iran.
Very few places in the United States, outside Maine, the West Coast and the Great Lakes have mean July temperatures below 80 degrees, and in much of the South, temperatures in the 90s in July are the norm. San Francisco is the only major city in the Continental United States where summers are cooler, on average than in Berlin.
The United States Needs More Air Conditioning
As a result of warmer summer tempeartures, the United States needs far more air conditioning than the Europeans, or the Japanese, for instance.
Berlin's mean temperature (average high plus average low, divided by two) in July, the warmest month of the year, is 64.4 degrees Farenheit. Cooling degree days, a measure of air conditioning demand, are the number of day that the mean temperature is above 65 degees Farenheit, times the number of degrees the temperature exceeds 65 degrees on each respective day. Thus, it needs has only a few cooling degree days a year. Denver's mean temperature, in contrast, exceeds 65 degrees for June, July and August producing roughly 540 cooling degree days per year. In Phoenix, mean temperatures exceed 65 degrees seven months a year, while February and November are almost as warm as a Berlin summer.
Where Does Solar Power Make The Most Sense?
The biggest virtue of power from photovoltaics is timing. Solar power generation is greatest precisely on the hot sunny summer days when air conditioning demand is greatest. Winds don't match air conditioning demand nearly so well. And, places with lots of available solar energy (due to clear skies and the more direct sunlight recieved in low latitudes), often coincide with places which have a great need for air conditioning.
This suggests that solar electricity may be best reserved for places with high air conditioning demand and reliable sunlight, but may be undesirable, where air conditioning is a relatively minor part of electricity demand, and where the energy available from sunlight is considerably less. The Northern U.S. and the West Coast of the United States tend to have cool summers. And, it turns out the the Southeast United States, for example, gets significantly less sunlight than the Southwest.
Thus, while most of heavily populated areas of the world, and a good share of the United States, may be ill suited to solar power, it may be ideal for a sizeable chunk of the Southern United States, particular in the Southwest, which both recieves a great deal of sunlight, and has a great many cooling degree days, as a way to provide peak power for air conditioning.