Tuesday, June 19, 2012

Solar-thermal / low-temp boiler / turbine power generation?

(Apparently this is a ridiculously obscure technology discussion so this post is going to sit dormant. Maybe people searching for this topic will find this post and respond.)



I am looking for a low-power high-efficiency electricity generation system using heat from solar collectors.

In general this is the same as how a huge multiple-megawatt coal plant operates, except on a tiny scale using lower temperatures.

Heat pipe evacuated tube solar collectors are very efficient and extract a large amount of thermal energy from sunlight. They basically don't turn off however so when your thermal storage has reached the rated temperature you need (140F say), the heat pipes continue to collect heat anyway.

Some systems actually suggest using a "heat dump" to blow off the excess collected heat in the summer vs winter operation. It seems more rational to use that excess heat in some manner such as power generation.



Coal power is real simple. You burn coal, make heat, heat water, boil it, keep on heating it until it is "dry superheated steam" and use that to drive a turbine. Then cool the steam and run it through the cycle again.

Problem is, the temperatures are very high, and the turbines are monstrous million-watt critters that no homeowner could ever hope to afford for themselves.

But turbine power generation doesn't have to be huge and the temperatures don't have to be ridiculously high. Small high-effiency turbines can exist.



Turbine power can also be done using "low-temperature boiling point" liquids like alcohol or substances normally called refrigerants since their usual application is in cooling.

Rather than superheating steam, you can superheat other gases with lower boiling points, and achieve high turbine power energy conversion efficiency with lower temperature differentials between "hot" and "cold", and also do this with smaller energy inputs.



Though apparently, this is "uncommon". Probably it's more accurate to say that nobody does this on the small scale, and solar-thermal turbine power technology is mostly undeveloped for the 0.5 kw to 10 kw scale.

The most logical term for what this is, would be a "solar turbine" but that name is already being used as a trademark by a company that makes megawatt-sized turbines for the fossil fuel power plant industry, and they don't have anything smaller that a 1 megawatt turbine.

 
- Dale Mahalko