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?

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…

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.

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.

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.

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.