Solar Thermal and Solar PV Differences

I could write on this topic for days.  However, let’s try and stay out of the research lab and give you the information that can make a practical impact.  Can you go off the grid altogether?  The answer is “Yes, if you live out of the city limits” because you will need your own well for water and a septic system.  You will also need a backup source of electrical generation because there may be dark brooding overcast days during the winter unless you live close to the equator.   Let’s look at history.  Near the end of the 19th century, improvements in the provision of commercial electrical production coincided with an increased demand for electricity in the home. Still electricity in homes and businesses was something that could be found only in large cities.   At this time, residents in rural settings found themselves totally off of the grid.  In fact, I remember the home that my grandfather built deep in the woods.  After my grandfather died, my grandmother continued to live in this isolated cabin where she chopped wood to heat her home, had a cooking stove that used propane, a deep well that she lowered a big bucket down into in order to bring up fresh spring water, a cast iron wash tub fitted with a scrub board, and an unceremonious outhouse.  She had electricity that powered her refrigerator and one small bulb that was part of a light fixture in the middle of each room.  However, with every storm high winds took down the electric lines and she would have no electricity for days.  But in all of time that I stayed with her, I never missed the electricity.  Our world did not center around electricity and we were self-sufficient in countless ways.  In fact, during the time before the last century people lived off of the grid for two thousand years.   But bringing us into the present let me share with you the practical value of solar thermal.  You ask what is the difference between solar thermal and PV?   The practical answer can be found in water.  If Grandmother had used solar thermal the water in her cast iron washtub would have been warm.  There are various maximum temperatures that different forms of solar thermal can deliver ranging from low to very high.  But most often we use a low temperature solar thermal in our homes as a way to heat our swimming pools on the outside and our water heaters on the inside.  In fact, almost all heated swimming pools worldwide use solar thermal as their heating source.  Most solar pool heating systems include the following:

  • A solar collector — the device through which pool water is circulated to be heated by the sun
  • A filter — removes debris before water is pumped through the collector
  • A pump — circulates water through the filter and collector and back to the pool
  • A flow control valve — automatic or manual device that diverts pool water through the solar collector.

In solar thermal, pool water is pumped through the filter and then through the solar collector, where it is heated before it is returned to the pool. In hot climates, the collector can also be used to cool the pool during peak summer months by circulating the water through the collector at night. In this article we went from Grandmother’s washtub in yesteryear to today’s heated pools.

See You Next Time!  Dr. Stripling