test: The Future of Solar: DSC! or DSC?

A relative newcomer, DSC looks to many like a complete replacement for silicon

Technology Comparison: Silicon Solar Cells vs Dye-sensitized Solar Cells (DSC)

In my previous article I outlined a bit of the history of solar and how DSC fits into this timeline. It is attracting a lot of attention, and for good reason. Let's take a look at a number of reasons why many scientists worldwide believe this is the future of solar.

	Silicon Solar	DSC
Cost	Expensive	Inexpensive
Production	Has a complicated and energy intensive production process	Very simple to produce using little energy
Materials	Needs large amounts of very pure silicon	Needs only trace amounts of rare materials
Application	Rigid structure and opacity limits applications	Flexible structure and transparency makes them widely applicable (covering buildings, tinting windows, etc)
Lifetime	40+ years	1-2 years
Theoretical efficiency limit	23%	39%
Indoor light efficiency	?	12%
Direct sunlight	15%	11%

DSC: A few snags

-Currently have a lower efficiency than silicon (~11% vs ~15%)

-Can be flexible, but these are a bit more expensive and less efficient (around 6%)

-Lifetime is limited (1-2 years indoors, a few months outdoors)

DSC: The Breakdown

So you can see that this technology, while promising, is still in the works. Even with silicon’s long hiatus in the 80’s and 90’s, DSC is not nearly as mature of a technology. It has great potential to become the first renewable technology that can truly reach grid parity (where people pay as much for energy as it costs to produce, aka no government subsidies needed) because of its low cost.

Low Cost

The low cost of DSC and its environmental cleanliness go hand in hand. Silicon extraction is not cheap and purification to the level necessary to make solar cells uses an enormous amount of energy, costing money and creating pollution before it ever leaves the factory.

If you look carefully at 2008 you can see the drop Chinese
price dumping caused

The cost of decent silicon panels has decreased exorbitantly in the past few years and is now at about $0.70 per watt. This is partially because of increasing scale of production, but really mostly because of cheap heavily-subsidized solar panels flooding the market from China.^[1] With tariffs from the US already in place and the EU finally initiating its plan to investigate price-dumping by Chinese panel manufacturers, the price will probably return to its natural price of about $3/w.

DSC cost about $6/w right now. This may seem expensive, but this is because DSC is pre-industrialized, meaning they are still made by hand (see the $76.67/w price of silicon solar in 1977 for a reasonable comparison).

Three steps will follow solving the electrolyte leakage problem discussed farther down:

1. Industrialization via a simple automated process will immediately drop the cost down to ~$0.30/w (1/10 the cost of silicon).

2. Once the materials used in production are also streamlined, the cost could drop down to ~$0.25/w (1/12 the cost of silicon).

3. The final step in cost cutting would be to make the entire product printable, which is nearly possible now with the flexible versions, bringing the cost down to ~$0.15/w (1/20 the cost of silicon).

Keep in mind that many applications of DSC don't need fancy
installation (about $4.50/w ^[2]), making the price for pasting them on windows and
tacking them onto phones incredibly low^[3]

These figures are estimates of course, but even being off by a factor of 2 (unlikely according to engineers working with DSC) would still make these significantly cheaper than silicon cells, and even be able to compete with fossil fuels like coal. The importance of this cannot be overstated.

The energy you use to make silicon pure enough to be used in solar panels explains most of the difference in price, but material cost come into play as well. Silicon cells, by their very nature as silicon-based, have high material costs. DSC also use a number of relatively expensive materials in construction, such as platinum and titanium, but these are in very low quantity. To further drop the cost of DSC, researchers are working on finding replacements for both of these with varying degrees of success. Through basic knowledge of the period table and a bit of trial and error, cheap equivalently effective replacements have already been found to act as a catalyst in the cell instead of platinum, and scientists expect that even more effective replacements will be found as time goes on.

Clean


DSC's production uses much less energy than silicon's

Because of the large amount of energy needed for purification, silicon takes about 10 years to repay its energy costs (produce as much energy as it used being made). DSC requires very small amounts of titanium and platinum, requiring much less processing, and therefore DSC has an energy payback time of about 3 years. Much better!

The Rand Carbide silicon smelting
plant in South Africa is a great example
of how silicon solar often just transfers
pollution from the 1st to the 3rd world

The chemicals used in the cell will also naturally break down in nature, so the waste created won’t do a lot of harm to the environment. At the end of the lifetime of a cell (when sealed properly to last 15-20 years), the chemicals have already broken down into inert and naturally occurring forms. Before they break down, however, you would not want these in your water supply, so a good recycling program would be the best solution. It is possible that this could naturally occur in the market because companies would be able to cut their costs by reacquiring and reusing materials and chemicals from old panels.

Everywhereable

DSC window tint covering Dubai’s latest monstrosity
would make it a 4.2 megawatt powerplant. ^[4]

Silicon panels can be stuck on many types of surfaces, but it comes nowhere near DSC’s multitude of uses. DSC can be both flexible (more expensive, but they’re working on it) and transparent. Where silicon panels are starting to be attached to the back of a phone to absorb sunlight, DSC’s can cover the screen, absorbing the light from the screen itself as well as sunlight and ambient indoor light. Silicon panels are opaque, so they’re fine for roofs and empty spaces, but DSC can be the tint on every window of an 80-story office building.

Covering handheld electronics, clothing, Google glasses, buildings, indoor surfaces, screens, vehicles, and everything else under or away from the sun cheaply and cleanly is the true genius of this technology.

discrete

DSC can be flexible

and colorful

But…

Unfortunately step 4 historically hasn't worked very well

Here it comes. There are two reasons why we can’t do this yesterday; one more important than the other.

DSC efficiency has not yet reached that of silicon cells, making them less space efficient, but because of their low cost they are still much more cost efficient.

However, the real reason why DSC’s can’t be spread across the earth like so many locusts gone green is their grasshopper-like lifetime. It is just unimaginable that people will keep pasting new layers of DSC on everything and buying new cell phones every few months (well maybe the second one). The source of this problem does offers some hope: it is simply a practical matter of sealing the liquid electrolyte properly; currently it leaks (non-toxic!) materials slowly, decaying efficiency from 11% down to almost nothing within about a year. By solving the problem of sealing cells properly, much longer lifetimes of 15-20 years will be instantly possible, making it into the final product within a few years.

Cells made by Dyesol in 2011 survived the equivalent of
3 years in a harsh environment with little performance drop

The Good News

The leakage problem HAS already been solved using solid-state DSCs (no liquid electrolyte) by the initial inventor himself, Dr. Michael Gratzel, but so recently that nothing has been officially published about the solution yet. There are also new ways of sealing liquid-state cells that has also solved this problem, also still unpublished. This could be either for reasons of simple time constraints or secrecy. This is a very competitive industry with many companies (my internship included) waiting in the wings, and the first person out the gate with a stable cell will make a killing!

Tacky and completely useless

The Future

This technology is not quite there yet, but wow is it close! After some seemingly inevitable improvement in lifetime it will begin to be mass produced and we’ll start seeing these pop up all over the place in the next few years. Based on what they’re doing at my internship and at competitors, they’ll start out as small trinkets and glowing novelty items, some useful, some not, and take a few more years to develop into a more effective and larger scale energy source.

Tasteful(ish), and actually marginally useful

Summary
This could be not only the cleaner, cheaper replacement for silicon, but could also go a long way in curbing our reliance on fossil fuels. The one major issue that this technology doesn't confront at all is intermittency: the sun doesn't shine ALL day! Because of this, DSC can still not be a real alternative to fossil fuels; merely a supplement. Storage devices that can cheaply store lots of energy for long periods of time are still a ways off, and until they come to market it looks like we're going to keep churning out plenty of carbon to keep our skies ever greyer and our climate changing. That said, in the meantime it seems we can soon begin the large chore of covering every man-made surface on Earth, indoor and out, with DSC to cut our oil, gas, and coal use significantly.