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Climate Progress

Climate Progress

Joe Romm is a Fellow at American Progress and is the editor of Climate Progress, which New York Times columnist Tom Friedman called "the indispensable…

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How A Solar Revolution Could Be Near

How A Solar Revolution Could Be Near

Solar Installation

Credit: Shutterstock

Can we build enough carbon-free energy fast enough to avert catastrophic climate change without having to power this energy transition with fossil fuels that would undermine the whole transition? The answer is “yes,” and here’s why.

The “global solar photovoltaic industry is likely now a net energy producer,” concluded a Stanford study released last year. That was followed by a very detailed analysis, Energy Balance of the Global Photovoltaic (PV) Industry, by post-doc Michael Dale and Global Climate & Energy Project director Sally Benson. They examined how much energy is consumed during the entire lifecycle of the production process for every major kind of PV system.

Perhaps their most important conclusion was this:

If current rapid growth rates persist, by 2020 about 10 percent of the world’s electricity could be produced by PV systems … if the energy intensity of PV systems continues to drop at its current learning rate, then by 2020 less than 2 percent of global electricity will be needed to sustain growth of the industry.

Related: Renewable Energy Stocks that are Already Paying Out

As we’ll see below, the energy intensity of solar PV systems has continued to drop in recent years — and is all but certain to continue doing so. That means the solar industry will be generating a vast surplus of carbon free power in the coming years and decades.

Dale and Benson found that the electricity generated by all of the world’s installed solar PV panels in the year 2012 “probably surpassed the amount of energy going into fabricating more modules.” In the figure below, that means 2012 was the “breakeven” year.

Inputs and outputs for whole industry

Energy inputs and outputs for an energy production industry growing asymptotically to some upper limit. Gross output is shown as a bold line; net output is shown with the dashed line.

They projected that “the payback year has a 50 percent likelihood of occurring between 2012 and 2015.” In other words, there’s a good chance the cumulative solar energy generated by every PV system in use as of today equals the cumulative electricity consumed in producing those system to date.

This is “largely due to steadily declining energy inputs required to manufacture and install PV systems.” That is, just as the PV industry has seen a stunning drop in total cost of production — 99 percent in the last quarter century — it has also seen the stunning drop in “energy payback time” (EPBT) for PV systems. The EPBT is the “time necessary for an energy technology to generate the equivalent amount of primary energy used to produce it.”

This Stanford chart shows that, as of 2010, the energy payback time for PV systems as a whole had dropped to under two years.

Energy Balance Of PV Energy

For reasons that are discussed below, the EPBT for PV systems in regions with high amounts of sunlight (high solar insolation), such as the U.S. Southwest, is now under one year.

This year, Dale was lead author on a study that extended the analysis of PV out to 2012 and also examined the wind industry.

Dale et al note that global wind and PV “installed capacities are growing at very high rates (20 percent per year and 60 percent per year, respectively).” Therefore, they “require large, ‘up-front’ energetic investments. Conceptually, as these industries grow, some proportion of their electrical output is ‘re-invested’ to support manufacture and deployment of new generation capacity.”

Here is their chart for the wind industry:

Cumulative Electricity Demand - Wind

Net energy trajectory for the wind industry. The red region represents a net energy deficit and the green region a net energy surplus. Diagonal sloping lines represent the fractional re-investment, i.e. how much of the gross output from the industry is consumed by the growth of the industry.

The red region (a fractional re-investment of greater than 100 percent) “means that the industry consumes more electricity than it produces on an annual basis, i.e. running an energy deficit. The green region represents an energy surplus.”

The wind industry has been in energy surplus for decades. That’s because, relative to PV, wind has had a slower growth rate and a faster energy payback time. Onshore wind has a fractional re-investment of under 10 percent, which means that over 90 percent of the electrical output of the onshore wind industry is available to society.

The capacity factor is “the average power output [in Watts] of a technology relative to its nameplate capacity [Wavg/Wp].” The wind doesn’t blow all the time, and when it does, it doesn’t always blow as strongly as a turbine is capable of handling. So, the average capacity factor across all wind turbines installed globally is roughly 25 percent. That means each 1 Wp capacity of wind will generate 2.2 kWhe per year. (8760 hours in a year times 0.25 capacity factor = 2200 hours. So 1 Wp capacity generations 2200 W-hours = 2.2 Kwh)

Here is the chart for the solar industry:

Cumulative Electricity Demand - Solar

Cumulative electricity demand (CEeD) trajectory for the solar PV industry. The red region represents a net electricity deficit and the green region a net electricity surplus. Diagonal sloping lines represent the fractional re-investment. Solar PV has been disaggregated by the major technologies: single crystal silicon (sc-Si), multicrystalline silicon (mc-Si), amorphous silicon (a-Si), ribbon silicon, cadmium telluride (CdTe), and copper indium gallium diselenide (CIGS).

This graph shows that all of the major solar PV technologies were in electricity surplus by 2012, except copper indium gallium diselenide (CIGS) and single crystal silicon (sc-Si), which were getting close.


But here is a crucial point about this PV chart and the earlier one. They assume an average capacity factor for solar PV of about 11.5 percent — where 1 Wp of installed capacity will generate 1 kWh per year.

In many parts of the world, such as the U.S. Southwest and Mideast, the actual capacity factor for PV is double that average, over 20 percent. Why do the authors use such a low capacity factor then? They are taking the global average of what is installed. As Dale explains in the news release:

“At the moment, Germany makes up about 40 percent of the installed market, but sunshine in Germany isn’t that great. So from a system perspective, it may be better to deploy PV systems where there is more sunshine.”

The energy payback time of solar systems can be reduced in two ways. First, the world can continue improving the technology and cutting costs as it has for decades. Second, the world can install a larger fraction of PV panels “in locations with high quality solar resources, like the desert Southwest in the United States and the Middle East.

Related: Big Oil And Renewables: Not So Strange Bedfellows

In fact, as Climate Progress reported last week, the price of utility-scale solar power is 59 percent lower than analysts projected it would be just four years ago, according to a report from two U.S. national labs. Indeed, the price of a roof-top solar system dropped 12 to 15 percent between 2012 and 2013 alone.

This means the astonishing growth in solar capacity in the United States since 2010 is very likely occurring with systems that have an energy payback of under one year.

Bottom Line: We can certainly build enough carbon-free power systems fast enough to avert catastrophic warming without having to power that energy transition with fossil fuels that would undermine the transition.

By Joe Romm

Source: www.thinkprogress.org

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