# The Big Picture of Solar Research

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1. Dec 6, 2014

### loginorsinup

From a top-level view, what exactly are people working on in solar these days? Efficiency? Cost? Both?

What are the parameters people really have to vary? Crystalline, polycrystalline, amorphous? Binary, ternary, quaternary compounds? Crystal structure (I have heard perovskites are a hot topic)? Substrate purity and variety? Lower dimensional structures (quantum dots, nanowires, thin films, etc.)?

What are some must read papers of the last... say 5 or 10 years? What are some seminal papers that everyone in this field must know?

What are your personal opinions of solar R&D and where it's headed? Is there money to be made? Are there known areas where there are bound to be interesting scientific things to discover?

I'm not really that familiar with any of the organic / dye-sensitized solar cells or how they work. Besides cost and maybe lower toxicity of the reactants, I don't really see why anyone would pursue them. Any ideas?

Hope to see some good discussion. Thanks in advance. :)

2. Dec 6, 2014

### phinds

Just as an aside, I think storage technology is WAY more important at this stage than incremental improvements in collection. Without better storage, the ups and downs of collection will remain a serious problem.

3. Dec 7, 2014

### loginorsinup

That's a good point. So, in your view, has solar research plateaued?

4. Dec 7, 2014

### microMRI

I have offered to do my master thesis in solar cell simulation. Sometimes i wonder whether is it a good skill to acquire? Because another Professor wants me to work in his group of packaging technology which i am also interested in and i think more relevant to industry.

5. Dec 7, 2014

### phinds

I seriously doubt it. There are very likely still cost effective improvements to be made, but unless storage catches up, they won't spread the use of solar much.

6. Dec 7, 2014

### Vanadium 50

Staff Emeritus
You seem to be thinking solar = photovoltaics. This is one option, and today is the most common one. But it's not the only one - photochemistry is another, one that attacks the energy generation and storage problems simultaneously.

7. Dec 7, 2014

### loginorsinup

Perhaps I should have said photovoltaic cells rather than solar in general. Sorry.

8. Dec 7, 2014

### omgwtfbyobbq

I think there might be a little more work in system integration. Battery costs are dropping, and with the proliferation of inexpensive bluetooth mesh networks (mostly for DSM), there's a good chance that someone will offer a complete off-grid PV system that's both easy to set up and costs less than the grid. I think the costs less than the grid part is doable now, but no one's packaged it in an easy to use way.

9. Dec 8, 2014

### elkement

I'd be interested in references re the costs argument as in middle Europe battery systems are not economical yet (no matter if Pb or Li). You'd most likely have to replace the battery before you would reach break even unless you'd just have a tiny (USV-like) battery. Batteries that would be really reliable in terms of covering, say, about 1-3 days without sun (common for plannung off-grid systems, such as for alpine huts), are expensive for home owners who just compare the costs and who don't factor in something like the value of a backup system .... which is usually not done as here we have something like 15 minutes downtime per home and year on average.

There are some European vendors of inverters who have started to offer packages including batteries, inverters and management systems that are fairly easy to setup (or are about to offer them in the near future). I am aware of solutions by: SMA (German), Nedap (Dutch), and Fronius (Austrian, will be released in 2015). As full "autonomy" is still not economically feasible these systems are typically sold with rather small batteries (covering less than a day) in order to increase the percentage of power consumed locally in relation to the fed-in power, but they can be upgraded with more cells in the futures.

I agree with all who say that storage is the challenge right now - and the much bigger investment. Since the solar panels are so cheap now also the costs of inverters and management systems do matter much more than in the past... so I think vendors try to provide "added value".

10. Dec 8, 2014

### Doug Huffman

100% efficient solar power is limited to 1350 Watts Meter^-2 for much less than 50% duty cycle time.

11. Dec 8, 2014

### loginorsinup

I see a lot of good discussion on the economic / engineering side of things.

How about on the chemistry / physics side of things? What do people in solar photovoltaic cell research do at this point? What are the problems that are being addressed? How are they tackling them? Any recent advances worth noting?

12. Dec 9, 2014

### Vagn

In terms of PV research, much of the work is aimed at getting a more efficient cell at a cost comparable to or less than silicon cells, preferably with low-toxicity chemicals, for example the main thin film technology in use at the moment is p-type cadmium telluride on n-type cadmium sulfide and a thin layer of cadmium chloride at the junction. Although CdTe and CdS are both toxic, they are not water soluble, and a s such pose little environmental risk, however CdCl2 is water soluble and toxic, which is why the discovery that MgCl2 could also be used was important, making it onto global news networks.

Perovskites are a hot topic as they have seen rapid growth in efficiency (see the NREL efficiency chart), however there are several severe issues with them: Firstly, they are unstable and it is not clear as to whether they can be made sufficiently stable to survive over the lifetime of the cell; Secondly, the known pervoskites all have lead in them which, considering that the organic components are water soluble, is also an environmental risk.

The other main thin film technology is current use is copper indium [gallium] diselenide (CI[G]S). The main issues with this are that gallium and indium are expensive and rare in the Earth's crust. One material being researched to replace this is copper zinc tin sulfide (CZTS), where the trivalent indium and gallium are replaced by bivalent zinc and IV-valent tin, however there are issues with sulfur diffusion into the back contact and the formation of other phases (e.g. ZnS, SnS, CuS etc.)

Other areas of work include looking at materials such as the III-V-bismides, for applications in thermophotovoltaics (e.g. recapturing some of the waste heat in furnaces for the glass and steel industries).

Last edited: Dec 9, 2014
13. Dec 9, 2014

### omgwtfbyobbq

Like you said, a smallish battery is pretty much required, and consistent solar generation, even if it drops in the winter. A battery pack that could handle about ~25% of daily consumption plus a backup propane or gasoline generator along with aggressive DSM via some kind of DIY "kit" would be required, since storage costs are pretty high.

My guess is that ~$.15/kWh for new Winston batteries (http://www.electricmotorsport.com/ev-parts/batteries/lithium/winston-lfp160ah.html [Broken]) is probable. It can be less than that, since I doubt the batteries will drop abruptly from 70% capacity to nothing, and packs from salvage EVs are available, but for now that's a good price floor for a new product. I imagine Tesla will undercut those prices once they get their gigafactory rolling. An offgrid PV system would run ~$3/W (http://www.wholesalesolar.com/solarpowersystems/medium-home-3-off-grid-solar-power-system.html [Broken]), which is ~$.06/kWh over 30 years. The panels should all have warrantied output at that time, and even inverters are available with ~15 year warranties these days, so that might push the cost up a smidge, but not much. The generator would be the most expensive source of electricity, at something like$.50+/kWh, but even with that, assuming the DSM system allowed a user to push ~70% of their use into the day, where the electricity didn't need to be stored, ~25% at night, and ~5% at night using the generator, their system cost would be ~$.122/kWh. That leaves ~1+c/kWh for the DSM system to reach grid parity, which works out to be ~$2500+ including profit margins to match grid prices with an offgrid system off-grid. Of course I'm leaving out the cost of a grid connection, but since that's rolled into the price of a home most people don't really think about that. In addition, someone would need to convert to solar water/space heating if their source of heat was electrical, and probably wouldn't be able to have an EV because of the high nightly energy requirements

Having said all that, I think someone could do this for less if they were to use the pack from a salvage EV (Probably Leaf), push more energy use into the day time, and build their own super efficient propane generator, probably using the 1.5L out of the Gen 2 Prius with the expansion stroke set to the maximum. I'm guessing they would seeing something like ~9c/kWh.

The system would come with the mentioned restrictions, which are mostly related to being able to push more use to the day via DSM so that most of the electricity can be used from the panels without having to store it in an expensive battery pack, but I think it would still be interesting since someone could live in the boonies with all the perks w/o the excessive cost associated with most off-grid systems.

Last edited by a moderator: May 7, 2017
14. Dec 10, 2014

### elkement

Thanks for your detailed reply - I agree, and your first parapgraph has made it clear to me. I had assumed before that you considered a battery storage systems without any sort of fossil fuel backup ... and that's why I wondered it could ever be economical in the near future given the required capacity. Typical power consumption for a home (excl. heating) in middle Europe is about 3.500kWh/year, so covering 25% of daily consumption with a battery is equivalent to a few kWh - and this is the sort of battery that might be economical also in Europe. A few years ago it had been much more "economical" here to feed in the power to the grid because of governmental subsidies - only the reduction in subsidies made home owners and system vendors consider complete energy management systems incl. batteries.

DSM and configurable kits are parts of the systems I mentioned - some take into account weather forecast or try to learn about their owners' energy usage habits.

My 2 cents on this: I believe manufacturing translucent or otherwise more "decorative" panels (at a competitive price) is an be interesting field, see e.g. http://www.extremetech.com/extreme/...d-make-every-window-and-screen-a-power-source. Then historical buildings subject to Monument Protection Laws (quite an issue in European PV projects) could also use solar panels.

15. Feb 3, 2015

### will_rl

Hmm, this thread is over a month old, but I can speak to this a bit since my graduate work was on organic photovoltaics (OPV). I think you already hit the two big pluses for the technology, that being the cost and low toxicity. There is major drawback with the stability of OPV and DSSC. To justify the cost of a PV system, you really need it to last for years if not decades. Having said that, there's a lot of research being done in the field, and it's really exciting how far efficiencies have progressed in the last 15 years (from ~1% to 11%). Also I think the neatest thing about this approach is just the shear number of different polymers and molecules you can use, and how they can be synthesized to fit your exact needs like absorbing particular wavelengths of light.

As far as research of more traditional technologies (i.e. with inorganic semiconductors), I'd say again reducing costs and improving efficiency are the biggest drivers. At least that was my experience. Outside of academic and national lab research, silicon has continued to own the industry, with very few other technologies really challenging their dominance. There are a few successful companies offering competitive thin-film cells like First Solar (CdTe) and Solar Frontier (CIS).

The seminal papers vary from each subfield (OPV, silicon, etc.), but a good place to start is the frequently updated "Solar cell efficiency tables" published in Progress in Photovoltaics: Research and Applications. When I was trying to learn about CdTe, I started by going through all the previous record efficiency citations and reading those papers.

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