Electrical energy past and future

I am not an expert.

My thinking is fracking has broken the monopoly of traditional oil extraction. Even 'deploited' oil fields have a new lease on life. More importantly, the production suggests methane and fossil fuel gasses have been captured more efficiently and profitable than traditional oil.

There is a role in paleo going back to when photosynthetic began depositing planetary carbon into fossil fuel feedstocks. But recognize the sun has been getting warmer than when photosynthesis began.

Bob Wilson

 

^^ I wish it said how many junctions their version has. As of April, NREL posted 3-junction concentrator samples at 44.4%, 4+ junctions at 46.0%. Back when I was still working, I was seeing a roadmap (bandgap assignments) up to 6 junctions.

Because this efficiency level still requires concentrators (focused sunlight, to far more than the unconcentrated 1 (land) or 1.36 (space) kw/m^2), it requires solar tracking. I'm not sure how well that would work with mobile land projects. It should be just fine for space based systems.

Boeing-Spectolab has been making multijunction PV for space applications for a long time. But their products were vastly too expensive to the consumer market, ambient energy harvest applications I was exploring.



https://www.nrel.gov/pv/assets/images/efficiency-chart.png

 

It has been a while since I read much about photocells so a couple of newbie questions:

• Parabolic trough reflectors? - I've wondered if a parabolic shaped, polished aluminum with air-tight coating might provide an efficient (enough) collector. Say 1-2 ft wide and 10-20 ft long, aligned to the solar track with a polished, vertical surface at each end. This would reduce the mechanical challenge of a full solar tracker as small, incremental changes, would keep the trough aligned through the year.
• Dialectic layers? - Laser reflector mirrors are made with layers tuned to the specific wave length of the laser to improve their reflection efficiency at the specific wavelength. Does the same technology work with solar cells, layers sized to optimize light capture?
• Heat recovery? - I suspect the cells require cooling. What sort of temperatures are we talking about, 100C or higher?

Thanks,
Bob Wilson

 

For terrestrial applications, it seems that the greatly reduced cost of modules over the past few decades has mostly killed off the tracking and concentrating systems. For the additional energy harvested, it is simply cheaper to add more fixed, maintenance-free panels than to build and maintain moving structures and concentrating support hardware.

For space applications, kilograms per watt is usually the controlling metric.

The single-frequency laser optics usually have multi-layer interference coatings, using constructive and destructive interference to guide the transmissions and reflections in the desired direction. This is a narrow-band approach, which falls apart at broad bands such as binoculars and PV.

Broad-band systems reduce total reflection at the boundary crossings by breaking up one big transition (index of refraction in optics, impedance in electrical lines, it all goes back to the same Maxwell equations) into multiple smaller transitions. This is what optical coatings on lenses do, applying a layer with an intermediate index of refraction. More intermediate steps are even better. For consumer PV, any topside coatings must be weather tolerant, and their small improvement increment must again compete against the already declining cost of simply adding more uncoated modules.

I seem to remember hearing something about putting a reflector on the backside of thinned PV cells, so that any transmission is reflected back for a second pass. But the etching process to thin the substrate wasn't cheap compared to the benefit.

Silicon PV is most efficient when cold, so records always involve cooled cells. I'm not remembering any other technologies that don't behave similarly. Those top-line records involved concentrations to 200X to 900X, so they must be cooled to prevent prompt destruction.

This stuff was not my specialty, so you can find vastly better and more up to date information elsewhere. I was looking into possibilities for certain affordable micro-scale consumer applications, but all the available resources were redirected to some other multi-$Billion market. As a contractor, not an FTE, the upper level management deliberations were completely opaque to me. But now that my NDAs have expired, I can be slightly more open.

At least I learned enough in the process to decide to solarize my home. And even do it myself.

 

Interesting as the Autoline After Hours program (Autoline After Hours) someone asked about comparing cylinder cells, the Tesla 2710, versus prismatic cells of the Bolt. Sandy Munro, the guest, pointed out the Tesla style cells have been very cheap to make. For fixed installations, cheap and low energy density is not a big hindrance. In contrast, efficient traction batteries need high energy density and that favors prismatic cells.

Bob Wilson

 

I think Tesla went with cylinderical cells for the same reason the first Japanese Prius and other early hybrids did; cost and availibility. Since they are branching out into stationary energy storage, sticking with cylinders gives them a cost advantage.

 

Per kWh hour, yes. The higher thermodynamic efficiency means more heat is converted to electrons so less is lost to the cooling system(s).

Bob Wilson

 

Let me suggest this excellent article: http://www.steamforum.com/pictures/ge%20turbine%20config.pdf

1- (100C / 538C) ~= 1 - ((100+273) / (538 + 273)) = 1 - (373 / 811) ~= 56%
1- (100C / 600C) ~= 1 - ((100C+273 / (600 + 273)) = 1 - (373 / 873) ~= 67%​

Back of the envelope, 67-56 ~= 11% less heat energy needed by increasing the steam inlet temperature (and pressure.)

Bob Wilson

 

Watched the 6-7min slide video. Hoping for the same timeframes, but also less optimistic here.

I wonder particularly about decarbonizing heating (homes, businesses, water heating, clothes drying, etc.), which is a significant component of total carbon emissions. Electrifying transportation and decarbonizing electricity generation have begun in earnest but will not be enough.

In the US, natural gas furnaces and dryers are common. These will need to be replaced with air or ground sourced heat pumps and heat pump or electric heating element dryers. So far there doesn't seem to be a push for this transition. So if houses/commercial/industrial buildings built in the next 20 years still have fossil fuel source furnaces, goals will not be reached by 2050. Building codes would have to change now.