Getting the Facts Straight on Solar Energy

Peter Diamandis recently wrote this in “Creating an Abundant Solar Economy”:

In 88 minutes, 470 exajoules of energy from the sun hits the Earth’s surface, as much energy as humanity consumes in a year. In 112 hours — less than five days — it provides 36 zettajoules of energy. That’s as much energy as is contained in all proven reserves of oil, coal and natural gas on the planet. If humanity could capture 1 part in 1,000 (one-tenth of one percent) of the solar energy striking the Earth — just one part in one thousand — we could have access to six times as much energy as we consume in all forms today.
These staggering numbers, in combination with an exponential decline in photovoltaic solar energy costs ($ per watt price of solar cells), put us on track to meet between 50 percent and 100 percent of the world’s energy production from solar (and other renewables) in the next 20 years. Solar is already undercutting coal and natural gas in sunny geographies.

As an environmental activist and optical physicist, I’m always alert to any argument that starts with a claim of how much solar radiant power (Watts) is intercepted by the Earth instantaneously or how much energy (Joules) is received over some stated time period. This is because writers beginning a piece on the greatness of solar energy this way usually follow it with a comparison to how phenomenally much more that energy is than the supplemental energy we humans have become accustomed to receiving from fossil fuels, nuclear reactors, geothermal sources, plus indirect solar energy in the form of wind, waves, flowing water, and biomass.

Such a comparison can be misleading — because a lot of the Earth’s surface area cannot be used by humans to collect solar without serious economic and environmental consequences and because much of the area is physically unavailable for such use.

Much of the total solar radiation intercepted by the earth is, for example, needed by ecosystems already using it on land, sea, and in fresh water lakes and rivers. The oceans comprise close to 71 percent of the Earth’s total area. Most of that is unavailable to human use because it is needed by the oceans for proper and stable functioning, physically and biologically. The shallow perimeters, perhaps, could contain large solar arrays (if protected from wayward ships and waves and storms) and if the consequences for fisheries could be mitigated. The land areas, likewise, need most of the solar radiation falling on them for forests, wilderness, and agriculture.

So let us not start with how much solar is intercepted but look at whether we could simply use the world’s available rooftop area for solar collection. Assuming world population to be 7 billion (in round numbers) and the average rooftop area per each person on Earth to be 15m², the total roof area on earth is approximately 10¹¹ square meters. The total area of the Earth is approximately 5 x 10¹⁴ m², about 5,000 times the total roof area, but only a portion of this receives solar radiation and much of it is tilted away from the sun at any one time, and still more is covered by clouds, about 60 percent.

Diamandis uses the figure of 1 part in 1,000 and I’m not sure where that came from. But that’s beside the point. There’s clearly a lot of area available for solar collectors without disrupting ecosystems and other natural life-support systems on the planet. Of course, not all rooftop area can be usefully employed for solar capture. The CaliforniaPhoton website suggests several factors that can be used in estimating how much solar can be generated from existing rooftops:

  1. A mean solar panel rooftop coverage of 40 percent
  2. A mean solar panel load factor of 20 percent
  3. A mean solar panel conversion efficiency of 50 percent (This is a bit high, but maybe we’ll get there along the way.)
  4. A mean solar flux during operating hours of 1000 watts/m² (This is also high, being the irradiance of beam solar radiation perpendicular to its propagation direction, not the average considering cloud cover and the collectors not always facing the sun, unless they are all tracking collectors.)

The conclusion of the above is positive. There truly is adequate solar radiation to power human needs for thermal and electrical energy at present and in a reasonably stable future.

I went another way in my essay “Yes, We Can! A Path to 100% Renewables,” in which I responded to a concern that we couldn’t really go all the way from using fossil fuel combustion as a source of energy to clean renewable energy. As the title indicates, the four factors that gave me concern, turned out not to be show-stoppers. I even made a crude estimate of what it might cost to do the 100% conversion. That number is very large, but not outside the realm of possibilities, considering the stakes involved and some huge enterprises pursued by human culture in its recent past.

The problem of getting to 100% renewable remains three-fold in my opinion:

1. Getting the world’s political and business leaders to recognize the need for stopping the current acceleration of climate change with its rising environmental, social, and economic costs.

2. Getting a large fraction of the world’s population to understand and support the huge changes that are needed to produce the transition.

3. Getting our political institutions to take real and timely action of a scale that can make the transition soon enough to save the future of an industrial civilization modified for true sustainability.

I take hope from an approach being pursued by Citizen’s Climate Lobby, a large U.S. organization (spreading to other countries around the world) with a few simple goals:

· Stopping fossil fuel combustion by making it sufficiently more expensive than solar that the transition can happen by simple market forces, and doing so on a scale that can make a real difference and get the job done quickly enough to save us.

· Mobilizing citizens, in their local political districts (and nationally), to lobby their political representatives for the creation of a national carbon fee and dividend program. With this approach, the fossil fuel placed into commerce will have a fee or tax placed on it (based on the carbon content of the fossil fuel) that increases over time — stimulating the needed transition away from fossil fuels sufficiently that the fee can thereafter be fixed or dropped altogether.

· Returning the proceeds of the fee collected by the national government almost completely to the citizens of that nation in monthly dividend checks which should partially or wholly compensate them for any energy price rises which might occur in the process.

I am convinced that such a program, if successful, can become a powerful stimulus toward the needed reform, even in this era of fake science, fake facts, political conservatism, and insufficient public knowledge about the problem and its remedies. }�

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