PDS APES 8th Period 2009-10

Today we took a brief look at solar power.  Solar makes up a tiny fraction (<1%) of the commercial energy market, but it is doubling every two years.  I tried to distinguish between solar electricity technologies and solar thermal (heat) technologies.

When considering solar electricity, it can be done on a small scale (homes/buildings) and a large scale (solar tower power plants).  Most folks are familiar with solar panels, or photovoltaic panels, made from two layers of silicon and divide into solar “cells.”  These panels can be bolted on existing structures or built into the roof (as shingles).  When light hits the panels, electrons are freed from silicon and flow in wiring for immediate use or storage in batteries.  Battery storage is critical, since solar incidence (amount of sunlight energy) varies by season and location and of course, since there is no sunlight at night.   Small bolt-on systems are a great solution for homes that are off an electrical grid.  A good basic explanation of PV technology is in your text, or at HowStuffWorks.com:
http://www.howstuffworks.com/solar-cell.htm

Folks are less familiar with large-scale solar-thermal power plants, like the one seen in the video below from Spain:

A huge field of mirrors follows the sun and focuses the sunlight on a central tower where water is heated to make steam, to turn a turbine, to turn a generator, to make electricity.  There are a quite a few of these in the US and other countries.

As for solar thermal technologies, they focus on capturing the sun’s heat (infrared radiation).  Unfortunately this year we will not get to tour a local home that incorporates both these techniques.  In years past, I’ve taken APES classes to the home of Jeff Martin up at Lake Norman.  From the front, Jeff’s home looks like a normal house, but if you walk around back you can see his huge solar roof:

Local Solar Home

Jeff designed the home, not just to produce electricity (the lower 3/5 of that roof) by PV cells, but also to take advantage of passive and active solar thermal technologies.

• Passive techniques: The rear of the home (and the panels) faces south to maximize the sun’s light and heat.  Also, the amount of window space is maximized on the south face of the home.  A large overhang blocks the more intense, higher sun in the summer but is designed to let the lower winter sun in completely.  The home also has concrete floors (with nice wood on top) to absorb the sun’s heat to heat the structure.  Finally, the house is super-insulated to retain all this warmth.
• Active techniques. The top 2/5 of the roof (see picture above) has copper sheets with water piped through them via a pump in the basement. The water is heated by the sun, then piped back down to the basement for storage in a huge insulated water tank.  This heated water not only provides almost unlimited hot showers, but it can also be circulated through tubing in the concrete floors to provide radiant heating for the structure.

Between all these technologies, Jeff and his family have a house that is heated and lighted in a super efficient fashion.  He further works to maximize energy efficiency with Energy Star rated appliances, super insulation, and CFL bulbs.  Of course, one of the downsides is the cost–not everyone can afford the technology on this scale.  Regardless, solar technologies are becoming more and more prevalent in the USA and enjoy even greater popularity in Japan and Germany.