Contemporary comparison between photovoltaic solar panels and large solar collector installations

• It seems that the most readily visible form of energy comes from the sun.

• The amount of energy received from the sun is about 174.7 W/m^2, taking into account the roughly 30% of the flux being scattered, and the roughly 19% being absorbed by the atmosphere and clouds. [1]

• P= (intensity) x (area)=(174.7 W/m^2)*(4π · r^2)= (174.7 W/m2 ) · 4π · (6,378 km) 2 · (106 m^2 /km^2 ) · (10^-12 TW/W) = 89,300 TW !!

• How can we tap into this energy?

• Photovoltaic and Solar thermal

Photovoltaic• In the year of 1954, Bell Labs made the first photovoltaic technology that

was able to actually provide power to basic electrical equipment. Providing only a 4% efficiency at about $300 per watt to manufacture [2].

• In the 70’s a solar cell was produced at 20$ a watt vs. the previous $100’s a watt [3]. Vast improvement. [3]

• Now we’ve come to the time where for the residential sector the price is about (5kW) $3.71 a watt, and commercially about (223kW) $2.61 a watt(2013),$1.80 a watt [4],[8].

Concentrated Solar Power

• Uses mirrors to concentrate light from the sun to transfer heat, that transferred heat can then be used as a source of heat, think heating your water tank, or to run a heat engine to turn a generator by driving a heat cycle for example Sterling engine. There are 3 main methods of accomplishing this.

A parabolic trough

• Uses a long parabolic trough mirror to reflect the concentrated line receiver at its focus.

Concentrated Tower System

• Gathers the thermal energy of the sun by using a surrounding field of large flat mirrors (heliostats) to reflect the rays to a focal point.

Parabolic Solar Dish System

• This system uses discrete reflective dishes, (think radio towers) to take the thermal energy of the sun

Solar Thermal

• Notice how this seems to be very similar to the process in which fossil fuels are used for carbon combustion, Transforming heat energy into electricity by means of using a vapor to drive a turbine. It may in time be used to add to the power production of fossil fuels, as well as expand the life of coal power plants.

Energy storage• The sun is more than enough to power consumer homes during the day,

but at night the solar energy being ceases to be made when the suns intensity is not enough to overcome the minimum voltage. One solution for photovoltaic's is the use of batteries.

• Concentrated Solar thermal systems have the benefit of using heat as its primary energy source. This heat which was gathered through out the sunlight hours can still be used by storing the thermal energy of molten salts into thermal tanks which can retain its thermal energy output for about 10-15 hours in storage [6].

Costs

• As of 2009, the cost of making a Large Scale concentrated solar power facility is roughly $2.50/W to $4/W [7], this would make a PowerStation of about 250 MW on the order of $600-100 million to build. Because of this even Google themselves have decided to not further invest in them due to the costs of photovoltaic's declining very quickly. This can be seen in the following graphs.

Costs

• U.S. Department of Energy [4]

Costs

• The economist [10]

Market Shares

• U.S DOE [9]

Thoughts

• Photovoltaics relied on solar modals that were not cheap and not very common in power plants, but it seems a couple of factors swung in Photovoltaics favor.

• Market size and Technology getting better and cheaper

• PV’s hindrances.

• [1] Wallace 1977. J.W. Wallace and P.V. Hobbs, Atmospheric Science: An Introductory Survey (Academic Press, San Diego, 1977).

• [2] APS News (American Physical Society) 18 (4). April 2009• [3] "The History of Solar," U.S. Department of Energy, 2004.• [4] David Feldman, et al., Photovoltaic System pricing trends, U.S. Department of Energy, 2014. • [5] Trimarchi, Maria. “How Solar Thermal Power Works.” HowStuffWorks. N.p., n.d. Web. Sept. 2012.• [6] “Concentrated Solar Thermal Plant with Energy Storage: How It Works.” Planet Forward. N.p., Feb.

2012. Web. Sept. 2012.• [7] Poornima Gupta “Google Plans New Mirror For Cheaper Solar Power “

http://www.reuters.com/article/2009/09/11/us-summit-google-idUSTRE58867I20090911 (11 September 2009).

• [8] http://www.nrel.gov/news/press/2014/15405.html• [9] US. Department of Energy. Energy Efficiency and Renewable Energy. 2010 Solar Technologies Market

Report.• [10] Geoffrey Carr, “Sunny uplands “www.economist.com” Nov 21st 2012