There was a great talk given here last Thursday by Tom Hansen of Tucson Electric Power.

He first showed an image taken from the WBGU (German Advisory Council on Global Change), shown below (originally from WBGU.

As can be seen, the Germans think that fossil fuels use as primary sources of energy will increase until the year 2030. Right now, solar and other renewable energy sources consitute only a small percentage of our energy supply. However, by the year 2100 they expect that the majority of primary energy will come from renewables - specifically solor power.

Mr. Hansen talked a little about the Energy Policy Act of 2005. He stated that in the law there are incentives given to power companies to build solar power plants. The Wikipedia article for this law does not mention this though. I’m not going to go digging through the original language to try to decipher lawyerese, but I’ll trust Mr. Hansen. He said that the incentives given in the 2005 law are starting to be phased out. That is, the incentives given under the law were very short term (2-3 years). As will be seen, this is not good enough.

Arizona also has a law called the Arizona Renewable Energy Standard and Tariff which calls on utilities to generate at least 15% of their energy by renewables by the year 2025. There is no law that says they must produce 15% renewable energy though. Right now, TEP only produces 0.6% of its energy from renewable resources. They use several methods including solar photovoltaic, solar heat (not sure of the technical term for this is, but it’s the technology they use at their Springerville plant), and methane from landfill gas.

Arizona uses several renewable primary energy sources. However, there are only a few that are viable for long-term growth. Biomass burning, besides producing CO2 and other pollutants, is not sustainable. Only 100-300MW of power can sustainably be obtained from burning wood. Geothermal is a great energy source. It’s both clean and renewable. However, there is little to no geothermal potential in Arizona. Other areas of the world, such as Iceland, have great geothermal sources, and they should be encouraged to use them. Hydro power currently produces about 12% of Arizona power. This is all from dammed rivers. Since there are no plans to build new dams, due mostly to environmental reasons, hydro power is not expected to increase at all in Arizona. Wind power is great. It too is clean and renewable. However, there have been some concerns expressed about their impacts on migratory birds. Wind power has the potential of producing 25,000MW for Arizona. This is a huge amount compared to other sources of renewable energy. However, it is nothing compared to solar.

Here in Arizona we have many sunny days due to the general circulation of the atmosphere. There is a general sinking motion that occurs at 30N and 30S latitude. See here for a brief introduction. The sunny days and relatively low latitude means Arizona is a perfect spot for solar power. It is estimated that solar power plants covering 20% of the land surface of Arizona could support 2,260,00MW at 15-20% “annual capacity factor”.

I’m not sure what exactly “annual capacity factor” means, but he stated that this amount could “feed” the US. I’m not so sure about this as my back of the envelope calculation showed that it would require much more land area than that. Of course, he may have been assuming that solar photovoltaic efficiency would increase before the system was implemented. The major problem with both solar and wind power is their cost and intermitancy. Cost is something that can be handled with subsidies and advances in technology. But we’ll never be able to get the sun to shine for 24 hours at every location on the Earth. (Talk about a global warming!) Therefore, if solar power is going to be a viable energy solution, we need some way to store the power produced during the day to use it at night. Longer-term power storage would also be good, so that excess power produced during one part of the year could be used in subsequent seasons, but that would constitute a huge leap in technology.

Mr. Hansen gave some advantages and disadvantages of the several renewable energy sources. Since I think that wind and solar are the most important for Arizona, only those will be discussed here.

Wind Generation:
- medium capital costs
- uses little water
- reliable ( > 99% )
- low fixed operating costs
- will produce less than 10% of AZ energy without storage
- cost heavily related to capacity factor
– $0.035 - $0.1 / kWh
- average wind must be greater than 16 mph to be a viable source of energy

Solar Generation:
- reliable, but intermittent
- expected to be highly stable
- low to medium fixed operation costs
- very high initial capital costs
- need a storage system, preferably long-tem
- $0.18 - $0.50 / kWh - EXPENSIVE!

At the end of his talk, Mr. Hansen gaves several important facts about solar power.

500 square miles of solar power could produce all of the energy required by the state of Arizona.
The efficiency of the solar cells is related to the temperature. The higher the air temperature, the lower the efficiency.
If all 200,000 single family homes in Tucson has solar photovoltaic cells on their roofs, it would produce approximately 600MW, or roughly 10% of TEPs annual needs.

He finished by saying that “maintaining the energy status quo is not an option“.
I strongly agree.

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