solar energy

In an October article Will Demand for Solar Homes Pick Up? Business Week reporter Adam Aston discovers that houses with built in solar energy collectors are bucking the general downward trend in the market.

Consumers recognize that green homes “save money month in, month out,” says Rick Andreen, president of Shea Homes Active Lifestyles Communities in Scottsdale, Ariz.

The combination of the renewal of the investment tax credits for solar installations, the ascendance of “green” lifestyles, and to some degree the target demographic of these homes, the number of solar houses in the U.S. is set to spike from 40,000 units. Several of the big home builders in Arizona, California, and other states are ramping up their plans for solar houses. Especially after the experience of Standard Pacific Homes in their Whitney Ranch, a development south of Sacramento. Sales had been soft, but when Standard Pacific put solar systems on a group of new models in the development, they sold out. Now they’re putting solar panels on all 304 of the homes.

Image via Wikipedia

Do you ever wonder about that claim that the energy flux of sunshine on the Earth is 10,000 times the projected energy use of civilization? Well, I do. I decided to drill down a bit into this number, to find out what the real bottom line potential of solar energy is. There are a lot of caveats to that number:

• 3/4 of the Earth’s surface is ocean, so the energy flux on land, right off, is on 2,500 times the projected energy use of civilization. I’m not saying we can’t collect solar energy off the ocean, but to the layperson, “Earth’s surface” means “land surface,” and that should be clarified
• The sun’s energy is not just going to waste as it hits the Earth - it drives climate, for example. Most importantly, it drives photosynthesis. How much of the sunlight dropping on the earth used for photosynthesis? Interesting question.
• The amount of solar energy hitting one square meter at noon is about one kilowatt, which is a handy metric to remember
• For a roof-mounted solar photovoltaic system today, you can expect to get 20% or less efficiency - meaning that you need 5 square meters for one kilowatt

But, as it turns out, there’s actually a cool map (shown above) that shows not only where the sun shines across the Earth on average, but also provides a visual clue about how much area it would take to provide all the energy demand of the entire world using solar power. The map is presented in this paper from Matthias Loster, and has been shown in various places around the web.

Solar power systems installed in the areas defined by the dark disks could provide a little more than the world’s current total primary energy demand (assuming a conversion efficiency of 8%, [and for the year 2006]).

Now all we have to do is string some (big) wires over to those desert-y places with the big black dots, and we’re made in the shade … er… sun.

By the way, while researching this post, I came across one from Robert Rapier at R-Squared Energy blog, focusing on the insolation just in the United States, and comparing it to Germany’s. Interesting reading.

What questions do you have about solar energy and its potential either in the US or around the world? Let me know what you’re wondering about in the comments section and I’ll do some more research.

A laundromat in California with rooftop solar collectors (Image via Wikipedia)

As we contemplate the future of energy, and the combination of utility-level and distributed energy, and of different types - solar PV, solar thermal (heat your own hot water for showers), wind, etc., one question I have asked myself is how much energy can realistically be produced by the solar collectors on the roofs of our houses and office buildings in the U.S.?

It turns out the United States government has done some research on this! There’s a very interesting set of Department Of Energy reports, including one (PDF) on the market opportunities for grid-tied distributed solar PV. It figures out, state by state, how much roof surface is available, how attractive the incentives and infrastructure are (e.g., is there net metering?) and uses some simple algorithms to come up with an expected market penetration for solar PV on commercial and residential roofs. The resulting amount of electricity generated in this distributed fashion is amazingly high. Their best case scenario has installed MWs of rooftop solar PVs rising from about 2,000 in 2008 to almost 25,000 in 2015, more than a factor of ten increase over seven years.

Influence of system pricing, net metering policy, federal tax credits, and interconnection policy on cumulative installations

The report uses conservative numbers for solar PV cost improvements - breakthoughs and innovations like the ones mentioned in Technology Review every week (like this one), will make the market penetration even faster (and higher) as they come to market.

I was pleased to see that our government has done this kind of research. Think what could be done if funding for renewable energy research and development was an order of magnitude higher!

Windmills Along the M6, photo by Bob Cox Photography

Saw this news item about the growth of green energy investment last week, which tends to correlate with the idea that the growth rate of renewable energy is not linear, but geometric (that is, doubling every n years, like Moore’s Law).

The UN Environment Programme (UNEP) reports that investments in renewable energy in 2007, at $148 billion, were 60 percent above 2006, with 2008 growth continuing. Achim Steiner, head of UNEP, said:

“The clean energy industry is maturing and its backers remain bullish. These findings should empower governments both North and South to reach a deep and meaningful new agreement by the crucial climate convention meeting in Copenhagen in late 2009. It is increasingly obvious to the public and investors alike that the transition to a low-carbon society is both a global imperative and an inevitability. This is attracting an enormous inflow of capital, talent and technology. But it is only inevitable if creative market mechanisms and public policy continue to evolve to liberate rather than frustrate this clean energy dawn. What is unfolding is nothing less than a fundamental transformation of the world’s energy infrastructure.”

There was similar news recently about the growth of both solar energy generation and wind energy generation.

Thanks to blow-hard winds, the United States has just become the world’s largest generator of wind energy.

Germany previously held this distinction, though since the United States has about 26 times more land than Germany, the milestone isn’t a huge surprise. Nonetheless, we weren’t expected to reach this point until late 2009. [Emphasis added - npd]

The key point is that we’re ahead of schedule on renewables, because the schedule was based on linear growth projections. The big question that remains is not whether the growth is exponential, but what’s the time period for doubling? Is it two years? Three years? One year? What do you think?

Image via Wikipedia

I wrote on Monday about why I am optimistic that we will come out of this energy mess in excellent shape. But, my optimism is not unalloyed - there are a lot of questions still to answer.

• Is there truly enough capturable solar energy streaming down on the Earth to power a good lifestyle for all 9 billion of us in 2050? Clearly not, at least at the U.S.’s current per capita energy intensity. What about at 50% of our current energy use? That’s a target that many think we can accomplish here in the U.S., so why not around the world?
• What about all the C02 we’ve stuck up there already? Can we do something about it that won’t end up causing as many problems as it solves? Certainly sensible steps like reversing deforestation will help a lot, but do we have time, and do we know how? Can we grow a rainforest from a burned-out meadow, even if it use to be a rainforest? This is not clear - but we should figure it out.
• Can we do any of this fast enough? I’ve argued that the technology and knowledge are here for reducing our energy footprint in the U.S. by 50% and replacing all of the remaining energy needs with renewables, but is there time and will to do it? The sheer manpower that it will take? Even if owners of commercial real estate were willing to do the necessary retrofits to achieve the goals, because they are cost effective? More importantly, if every one agreed to do it, are there enough architects, contractors, HVAC installers, and electricians to do the work?
• There’s a similar question for residences - most residences get enough solar energy flux on the roof to offset a good portion of their electricity use - but even if the cost were free, after first year saving, who would do the 100 million installations? Even if spread over ten years, that would keep 25,000 installers busy every day.

There are many more such questions - can we successfully combine distributed power generation (e.g., on residences) with utility energy on a gigantic scale? Where do all the materials to do these installations come from?

I’d love to hear your questions and comments about whether you’re optimistic, the obstacles you see in the road ahead, and your ideas on how to overcome the roadblocks.