Wednesday, 30 December 2015

Lesson 10: generating power

First I asked how power could be generated, which elicited a long list, including the methods below that I had prepared earlier.

The first electric power was probably generated by water, just as water mills were probably the first regular power sources to be harnessed, long before the discovery of electricity or the scientific understanding of energy and power. In 1868 a hydroelectric power station was built at Cragside, a country house in Northumberland, UK. The first modern power station was built at Niagara Falls, 1895, producing alternating current that was sent over power lines to a town several miles away. Coal was first used to generate power in 1882, in Pearl Street, Manhattan. The first electricity was generated from wind in 1887 in Glasgow. The first commercial wind farm was commissioned in 1980 in Crotched Mountain, New Hampshire. Geothermal power began on a small scale in 1904 in Lardello, Italy, and was commercialised in 1911. Oil and gas are also used to generated electricity, using similar steam turbines to coal power stations.

More recently,  nuclear power was first generated in 1954 in Obninsk USSR. Silicon solar cells were first made in the same year, and the first large-scale solar power station was built in the Mojave desert, California, in 1984. Other forms of generation include biomass, tide and wave.

Which of these is zero carbon?

None of them!

Why not?

In each case, fossil fuels are used, and carbon is emitted at some stage in the construction process. Once solar cells have been installed or hydroelectric dams have been built, electricity can be produced without carbon cost, but we need to take account of the whole lifecycle when estimating carbon footprint. Radioactive decay does not produce any carbon, but the mining, transportation and purification of nuclear fuel do, and these must be taken into consideration. 
The more pertinent questions are: which is lowest carbon? which is cheapest? and which is best? I gave this question a little bit more depth by asking which is the best way to make energy if you're an electricity company; if you're a government; if you're a city; if you're a business or if you're a home owner.

There are at least three factors to take into consideration when we're looking at cost analysis. First is $ per kWh. Second is kilograms of carbon per kWh. Third is energy return on energy invested (EROI, or EROEI), kWh out per kWh in. You can see some comparisons in the table below from two different studies.

Murphy and Hall
Scientific American
Natural gas
Oil 1970
Oil 2007

If you are a homeowner, you would not want to live under a coal power station or a nuclear reactor, and most locations would not suit hydroelectric turbines or windmills, but living under solar panels seems like a good idea in most places.

The current economics of solar power  see costs falling, year on year, and the cost of the competition rising. Fossil fuels are finite, and the situation can be likened to hiding ten thousand yen in hundred yen coins around the room. The first few coins will be really easy to find, but as more are found, the time and effort taken to find each one will increase. You can see in Murphy and Hall's data above that oil in 2007 takes almost three times more energy to extract than it did in 1970.

Grid parity is the point at which solar power costs the same as other electricity available on the grid. Of course this will be different at the point of production to the point of use. If you are an electricity company considering building a new power station, the cost of solar electricity will need to be cheaper than other options such as nuclear, coal or hydroelectric. If you are a homeowner, then you are comparing the generation cost with the market value of the electricity, which includes the transmission costs as well as other overheads and profits of the electricity companies. In many places grid parity has been reached at the point of use. This depends greatly on the local cost of electricity, and local sunlight conditions, as well as local cost of solar panels and fees for installation. Conditions are skewed by grants and feed-in tariffs.

The advantages of solar power generation include no fuel, no pollution, no noise and a long lifetime. Solar power is modular so an array can be any size from a few watts to a few megawatts, to meet supply or demand, while other forms of electricity generation need to be on a large scale. The disadvantages and challenges include the high cost and relatively large area. Orientation must be carefully considered. Solar power is unreliable and varying: nothing will be generated at night time and clouds and weather make a difference. Sunny days produce a predictably high level. Overcast days produce a predictably low level. The worst days are partly cloudy, when generation will go up and down with each passing shadow.

This is a particular challenge for the electricity companies, who have long been working on the balance between electricity supply and demand. Unlike other areas of supply and demand, electricity must be immediately available when people turn the switch on. Usually the various users in the grid will average out, but George Monbiot, in his book Heat, writes about the FA cup final. When this is on, most TVs in England are tuned to the game. This is not such a big problem, but when half time comes, somebody sitting in front of each of those TVs gets up, goes into the kitchen and puts on the kettle. This creates a surge in demand bigger than the largest power station in the country. To cope with fluctuations in demand, there are hydroelectric facilities which pump water up the hill when there is too much electricity on the grid, and send it down again when more is needed.

I have an image of guy somewhere in Wales in front of a portable TV, glued to the first half of the game and ready to flick a switch as soon as the ref reaches for his whistle.

Storage may be needed to cover the unreliability of solar, but the extra cost of the storage, especially in terms of energy, may make an already marginal source of power unsustainable.

Will solar panels save us? Are they good for the environment? Until now more energy has gone in to making solar panels than has been generated from them, but that changed around this year, and as production becomes cheaper, the return on energy invested will improve. They may save us in the future.

I didn't properly have time to cover the installation of solar panels, the best orientation, angle to the horizontal and other conditions such as the avoidance of obstacles.

Also I didn't have time to talk about solar thermal collectors, which can make a difference to the energy use of a building. There are flat plate collectors and vacuum tubes, circuits and drain back systems. Challenges include overheating, freezing, hygiene, and once again we face unreliability and the need for backup

I also didn't have time to talk about PV-T hybrid systems that combine electricity generation and collection. In the process of collecting heat, the photovoltaic elements are cooled, which makes generation more efficient, and overall these kinds of panels can reach efficiencies of something like 80%.

Murphy, D.J. & Hall, C.A.S. (2010). "Year in review EROI or energy return on (energy) invested". Annals of the New York Academy of Sciences 1185: 102–118.