The effects of global pollution on solar power efficiency

Tom Hanley April 19, 2004

Solar cells will be playing a large part in providing the world’s

energy in the next twenty years.• The world’s energy demands continue to grow at a rate

that fossil fuel production cannot keep up with.• Production of photovoltaic cells and modules has grown

exponentially over the past twenty years.• Some estimate that solar power could provide at much as

20% of the world’s power by 2020.• Advancing technology and lowered cost will eventually

allow solar power to be of comparable price with power from fossil fuels.

The Source: The Sun

• Free and virtually unlimited resource that is available (in various intensities) all over the world.

• Solar spectrum matches well with current semiconductor absorption properties.

Solar Cell Materials and Properties

• Silicon - relatively cheap, abundant and easily manufacturable. Can absorb photons with wavelengths less than 1.1m and has a top efficiency around 25%.

• Gallium Arsenide - more expensive and rare, but can absorb photons with wavelengths less than 1.85m and has a top efficiency around 40%.

Accounting for the sun’s energy• Solar radiation is 35%

stronger before it enters earth’s atmosphere.– Primary absorbers of this

energy are: O3, O2, H2O, NO2

– Other atmospheric gases absorb in the visible region, but their concentrations are too low to make significant contributions

• Scattering and absorption by aerosols also accounts for a loss of photons available at the surface for conversion to electricity.

Light Degradation

• Power available from a solar cell is directly proportional to the intensity of the light incident upon it.

• When atmospheric conditions are continually less than optimal, total available solar power, especially in urban areas where it is needed most, is significantly reduced.

Some Economics...

• With the current growth trend in solar cell production, solar power could be providing as much as 88 GW of power by 2020, about a fifth of that in the US.

• At the current US price of about $.08/kWh and about twice that in the rest of the world, total solar power generated in 2020 could be upwards of $14 billion in the US and $95 billion in the rest of the world per year.

The effective loss of usable light• Average aerosol concentrations can reduce

the total light flux by as much as 10%, mostly by scattering and more so in urban areas.

• Higher surface ozone and nitrogen dioxide concentrations would also decrease the flux of incoming photons.

The Result…

• A drop in total annual sunlight reaching the surface by even as small as 1% could mean over a billion dollars in lost revenues worldwide every year!

Other Considerations

• Solar cells, like computers and other electronic equipment perform better when the temperatures are lower.

• For every average temperature rise of 2º C the efficiency of a solar cell is decreased by 1%, thus translating into another possible billion dollars in lost revenue.

• Global warming must also be considered.

Possible Solutions

• Place more solar power plants in remote areas less subject to localized pollution.– Power would have to be transferred greater

distances and much of the benefit of incorporating solar cells into houses and buildings would be lost.

• Invest the money that would be lost otherwise into reducing pollutant and aerosol levels on a global basis.

Conclusions

• The pollutants from fossil fuels that solar power is aiming on reducing are fighting back to hurt the effectiveness of solar power through reducing the total amount of light reaching the earth’s surface and by raising the average surface temperature.

• Through continued efforts at reducing pollution and curbing global warming, the efficiency of solar power generation can be improved.