Wednesday, June 4, 2014

Climate Change & Renewables - 8:Solar

Science of Solar Power

(If the science/technology of solar power is not of interest, skip this and go to the Development  part below) 

Solar mostly means Photovoltaic (PV) cells.  There are other forms of drawing energy from the sun but they have insignificant market share.  PV cells are the first really new way to generate electricity.  All the other ways involve turning a shaft which turns wires inside powerful magnets to generate electrical current.  This was first conceived in the early 1800's by Michael Faraday and others.

To turn the wires one can direct running water (from hydro-electric dams), or wind, over a turbine to turn a shaft which turns the wires between electromagnets.  One can also boil water with coal, wood, oil, gas or controlled nuclear reaction and use the steam jet to turn a turbine which turns the wires. In the diagram below I've highlighted the steam generator and turbines in a typical nuclear reactor.  A nuclear power power plant is really just a big steam generator.  Click on the diagram to enlarge.

PV differs from all these other ways of making electricity.  PV uses light falling on atoms to give electrons enough energy to leave their atoms and move to a positively charged area.  That flow of electrons is electricity.  The photoelectric effect was discovered by Heinrich Hertz in 1887.

Einstein explained what happens in 1905 and won the Nobel prize for it. The basic idea is that energy, in the form of visible light, (or X-rays, or microwaves, or infra-red radiation, or etc.) travels in little packets.  An electron that absorbs a packet with enough energy will break free of it's atom and travel freely in the space between atoms.  If a single packet has not enough energy the electron cannot break free.  This is important because it is irrelevant how much energy you shine on a PV cell if the frequency is too low.  So one packet (= "quantum") of energy of the right frequency will free an electron.  A million packets, each with too little energy (= "frequency") will do nothing.  The "light" falling on the PV that dislodges the electrons is most commonly infra-red (invisible to humans) so clouds do not get in the way.
The Red Wave has too little energy to free a Potassium electron.  The Green and Purple rays have enough energy.  The energy above the minimum needed gives the electron more speed (velocity "v").
The most popular types of PV cells at the moment are using the same technology we use for integrated circuits - Silicon with impurities like Boron and Phosphorus added in very small amounts (1 Boron or Phosphorus atom for every million or so Silicon atoms) to provide the extra electrons and positive "holes" needed for current.  There are other novel ways of making solar cells but they are not yet a market reality.  A pretty decent explanation of silicon solar cells is here:

Two other types of solar power generation are worth mentioning although they are currently too costly to gain much market share.  One is Concentrated Solar Power (CSP) where a set of mirrors concentrates the sun at a container of salt raising it to a high enough temperature to melt the salt.  The molten salt boils water to turn a turbine and make electricity.  This is not yet economical on its own but can be important as a large energy storage device when wind and solar are not up to the demand for electricity.

One CSP installation (in photo above in Spain) is discussed here:

The other form of solar power is Concentrating Photovoltaics (CPV) where small optical magnifier and concentrator lenses are embedded around solar cells.  This is more complicated to make and does not yet yield enough advantage in electricity generation to make up for the added manufacturing cost.  That will change over time as experience is gained and steady incremental cost savings are realized.


Photovoltaic solar cells have been around for quite a while but only started showing up in electrical generation data the last 3-4 years as anything other than rounding errors.  Recent price drops seem to have crossed some threshold and solar is quickly growing in many countries.  I have included only Germany and Italy in the following graph because those two countries alone represented over 50% of the world-wide installed Solar Cell capacity in 2011. By 2012 those two had almost doubled their installed capacity.  Other countries like the US are growing fast as well but from such a small installed base that they wouldn't be visible on the graph compared to Germany and Italy.  Examining German and European PV development is of interest because they are far ahead in solar and renewables so give insight to the future for the rest of the world.
The most recent data from the USEIA (US Energy Information Agency) only goes to 2011-2012 for most countries.  The growth of solar is so explosive that 2011 is ancient history,    If the total worldwide PV Solar Cell growth continues at it's current 56% annual growth rate, PV Cells will overtake Hydroelectric generation world-wide by roughly 2026.  PV overtook Hydroelectic in Germany in 2011.  See chart below from

PV installation in Germany and Italy slowed in 2013.  In Italy, because the austerity program imposed on the EU by the European Central Bank and other lenders caused Italy to stop it's tax breaks and subsidies for PV.  PV installation slowed in Germany because the traditional centralized power companies stock price sank to very low values, so the German govt. instituted a number of tax measures to slow the spread of PV installation.  In addition, the high number of PV installed generation lowered the cost of electricity during the day and raised it at night thereby lengthening the payback time of PV systems.  There are also statutory limits on the percentage of solar power allowed in the grid.  From previous document link.

One projection is that improved storage systems (batteries) will make PV installation viable again as it enables PV installations to store energy and sell it at peak rates, thereby decreasing payback time and leveling price fluctuations during the day.

The traditional German power generation cos. pay a surcharge on the electricity they sell to help pay for renewable installation.  An indirect subsidy designed to attain aggressive goals of 80% renewable energy by 2050 (chart below from previous link).

The following shows the current cost of energy in Germany as of 11/2013.  Clearly coal is cheapest (the dirtiest coal is the cheapest coal) but onshore wind is now competitive and PV at the utility level is nearly competitive.  (From:
In the future, economies of scale and experience will gradually decrease the cost of Concentrated PV (CPV - see Science part above).  The following graph shows the cost of coal going up because of carbon taxes in the EU and the cost of PV and offshore wind declining into a range competitive with coal. (from Fraunhofer, op. cit.)

Over the same time frame, CPV and CSP (Concentrated Solar Power - see "Science" section above) will decline in price as well to a point where different situations may enable different technologies.(from European Photovoltaic Industry Association (EPIA) (Click image to enlarge)

The key issue with solar power is that the sun doesn't shine all the time, particularly in the Winter, and away from the equator.  The European Photovoltaic Industry Association chart has an optimistic projection of Wind and PV into 2030 for different latitudes (UK, Germany, and Italy) shows overcapacity in energy generation during the day and the need for other forms of energy generation in the evening. Wind is expected to comprise 30% of energy generation in 2030 vs. US projections of 35% for 2050. Wind power is more consistent over a day by season. Click on chart to enlarge. (from "EPIA", op. cit.)

You can see the same effect in California in May 2014 below (from

Former US Energy Secretary Chu said in March that "as the cost of PV modules plummets and battery prices falls, it was possible to envisage a situation in five to 10 years where homeowners could be 80% ‘self-sufficient’ and off-grid with a US$10,000 to US$12,000 solar-plus-battery system."

The most optimistic scenario of the EPIA is 25% of electricity demand being met by PV in Europe.  More realistic estimates are for 10%-15%.

Another problem is seasonal.  The northern hemisphere gets much less sun in the Winter. and this shows up dramatically in PV electricity production on a monthly basis (below). The ratio in irradiation (available sunlight) between Spain and Sweden is two to one  (from "EPIA", op. cit.)

This could be mitigated by placing more PV generation in the South and selling it to the Northern countries.  In the chart below, the darker regions get more sunlight and could export solar power to the northern regions. See below:(EPIA, op. cit.)

The difficulty is that about 50% of electricity is lost in transmission and in trying to send a lot of electricity north, the grid capacity would need to be greatly upgraded so overall there would be no advantage to shipping energy vast distances.  The real effect of less irradiation is to push out the year at which PV becomes economically viable for northern countries.

One problem with exporting electricity is that Europe does still not have a EU-wide grid so it is simply not yet possible to move electricity generated freely to every country that needs it - some countries can, but not all.  Storage systems are needed to absorb the mid-day peaks and use the energy later.  They have not been implemented on sufficient scale yet. Click below to enlarge (EPIA, ibid)
The above chart shows "pumped hydroelectric storage" as the most technologically proven followed by compressed air, lead-acid, Nickel-Cadmium, and NiMH, and other batteries.  Pumping water up a tower and later releasing it to draw energy from it like a mini-hydroelectric dam (currently the most viable storage) is obvious and easy, but the higher you need to pump the water, the more power it takes.  A simple flywheel for mechanical storage is also a possibility.

Interesting is the very high tech SMES - Superconducting Magnetic Energy Storage which uses inductor coils at very, VERY low temperatures (20 degrees Kelvin = -424 degrees Fahrenheit) to store a circulating current which can then be drawn on for power.  It is an ideal way to store energy since there is very little energy loss in storing, or drawing energy.  It is currently used in Wisconsin to even the loads from lumbermills which have many sharp peaks and troughs in energy use.
Above from:

Another problem with generating more electricity than can be used during peak sunlight is that the grids were not designed to handle a reverse flow of electricity and voltages can overload and burn out parts of the grid.  Grids need to be re-designed.  All this costs money and is an impediment to maximum use of solar power.

Still, solar power is growing, particularly in Japan and China in 2013  The chart below also shows Saudi Arabia.  Why would Saudi Arabia invest in Solar?  Like many other oil-rich areas it subsidizes electricity for its citizens.  It currently burns its own oil to generate electricity which at today's prices is far more expensive than PV electricity, particularly given the much greater direct irradiation it gets being so near the equator.  Solar doesn't have to be cheaper than coal in Saudi Arabia, just cheaper than oil, which it already is.

After Fukushima, Japan shut down all it's nuclear reactors.  That was a lot of electricity generation so to encourage solar replacement of the lost power, "net metering"  was introduced in 2012 so roof top solar generators are paid by the utility companies for the electricity they generate.  As a result, solar cells are becoming extremely popular on Japanese roofs.  Japanese pay high rates for electricity and even the high cost of solar panels in the protected Japanese market make it very cost-effective.  The Japanese electronics companies are aggressively marketing solar panels and lowering costs to be ready for the imminent removal of import barriers.

Worldwide, "renewables accounted for more than 56% of net additions to global power capacity last year. Renewable energy provided 19% of global final energy consumption in 2012, and continued to grow in 2013. Of this total share in 2012, modern renewables accounted for 10%, with the remaining 9% coming from traditional biomass, the share of which is declining."

Above from:

The Rocky Mountain Institute has a study forecasting when various parts of the country could find battery-plus-PV ("Utility in a box") a viable alternative to being hooked up to the grid.  They find it is viable for Hawaii now, NY in 2025, and CA in 2031.  See chart below (from

Here is an article about a home battery installation from Solar City, made by Tesla.
A sunny future for renewable energy.