Credit: Abengoa’s IST Thermal Trough
About half the energy burned in the U.S. is used to make hot water and heat (most of which is below the boiling point), yet PV solar and wind energy do little to provide it aside from electric water tanks and inefficient baseboard heaters.
Does that mean natural gas is here to stay? Solar thermal, as the term is generally used, is a bit of a misnomer, since the thermal output is used to make electricity. It becomes part of the same process as a conventional steam or gas turbine plant, but instead of burning natural gas, or coal, the steam comes from a liquid heated by concentrated sunlight.
In the case of troughs, the so-called concentration ratio is about 60 to 1. Three to five ‘suns’ from a magnifying glass will start a fire. Sixty suns will produce enough high quality steam to run a power plant. (PV power comes from one-sun, i.e. what you see is what you get). Concentrated sunlight is no trifling matter. […]
You do not need to boil water to obtain useful heat from the sun. In my house, that is not heated by solar, but by burning natural gas, the downstairs is heated by passing hot water through copper tubes embedded in the slab upon which my house is built.
Notice that the temperature of that hot water is automatically adjusted depending on the outdoor temperature. When it is over 50F outside, I put 80F water into the slab to maintain a temperature of 69F inside the house. As it gets colder outside, I must raise the temperature of the water so that when it is 14F outside, I need 116F. 95% of the time it is over 14F outside. Were the outside temperature to get all the way to 0F outside (I have never seen it that cold), I would need a water temperature of 130F.
Heating water to 80F, 116F, or even 130F is a lot easier than boiling it.
The reason I have not converted to solar hot water is the lack of financial capital to buy and inwstall the solar panels, and finding a suitable place to put them. The house is oriented in just about the worst way for collecting solar hat.
I lived in an apartment if Florida in which a large hot water tank on the roof had supplied great hot water for over forty years at that point in time which was in the 1970’s. Solar hot water has been around along time and worked well. Now they seldom build with the same that they did in the 1940’s, apparently. Are we loosing our wisdom in the USA?