Well that was my attempt at a pun.
I havent written for a while, real life has gotten in the way, kids, houses, work. On the bright side, we we will probably have our first industrial product shipped this year. On the bad side, less blogging, less time to point the skeptical eye at events and announcements. And less time to bring out the first update for Skeptic's Bingo. Sad.
So today we are talking about Pokeberries! Woohoo! Did you know that the dark dye that can be extracted from these berries can improve solar cells output by 2x? Did you know the pokeberries are from a weed that grows almost everywhere in the world and therefore are very cheap? Did you know that this method could " double the energy production of today’s flat cells at a fraction of the cost"? Does this sound familiar? Did you know that universities and companies like to hype up technologies long before they have even begun to be proven out?
If you were to read the many many websites that parroted the press release from Wake Forest, you would think a major breakthrough has occurred!
Perhaps it has, but none of the available information delineates this. Lets take a closer look. First the background.
The actual idea is as follows: There is a solar cell technology that is a bit different than what is commonly used. Most solar panels are made from silicon slices that have been doped in a way that lets them convert incident light into electrons. Alternatively, but similarly, some solar cells are made on a flexible substrate by laying down a thin film of material that can perform the same function. Other proposals for solar cells are wide and varied. One common theme is to create a three dimensional surface so that more light get absorbed.
So this new technology incorporates these same ideas, flexible substrate, larger surface area for incident light, and other features, but the places that actually trap the light are made from a polymer. I don't see a reason why this wouldn't work. Other incarnations of the same idea provide some improvement.
What are the key claims?
- This solar cell is cheaper than other technologies, so much cheaper that is enables deployment in scenarios unavailable to normal solar cells.
- This solar cell produces 2x the power than a "normal" solar cell.
- This solar cell can collect more light at oblique angles than a "normal" solar cell.
I quoted "normal" because its hard to say what is normal these days. On houses, the most common type is the silicon based flat panels. But solar farms can use other technologies, like focused light with stirling engines, or even photovoltaics that are2x to 4x more efficient than a residential solar cell (these are known as full spectrum cells and are far more expensive, but you need less becuase you can concentrate the light).
So, the first question is, could these really be cheap enough to provide a boon to the solar industry? Well, when you have a panel installed, how much of the cost is associated with the cell and how much for the rest of the installation? Well let's do an example.
A typical solar installation is around 2000 watts. That means that you put enough panels up to make 2000 watts on on average on sunny days. During the day, you may get more than this depending on the sun, sky and time of year. But often you get less, like when its cloudy or night time. Most families don't use a full 2000 watts all the time, so the extra gets sold to the power company (or charges batteries), and then when power is needed but there is no sun, the power is returned from the power company.
Prices for silicon solar cells is as low as $1.75/watt. But when placed into modules for a large installation, when multiple cells are strung together and modules (generally 125 watts each) are electrically tied together, the price increases to about $4.23/watt. Then, in order to send the extra power to the power company you need an inverter which costs about $0.72/watt (or charge batteries which cost about 20 cents per watt, but you will require a charge controller also for extra cost).
So, then you have to get it installed which adds about 100% of the panel costs, so the cost of an installation is about $9.00/watt. The point of throwing all these numbers out there is that, even if the cost of the solar cell dropped to $0.00 the cost of an installation would still be quite expensive. The cells are a big part of the cost, but not even close to a majority of the cost.
The next claim is that it can create 2x the power of a normal cell. Can it? Well let's go to the source. The technology (which interestingly, does not seem to have US patent protection), was licensed to Fibercell inc (who really should buy a mac and use iweb to get just a basically decent website made). They have only one single performance graph on their website and it is shown to the right. This graph shows cumulative power over time (otherwise known as energy). It's true, there are times during the day where the slope of the Fibercell curve is 2x that of a normal silicon cell. But that hardly matters, what is important is how much energy it supplies over the whole day. If the 2x power could be sustained, then it would end up with 2x the energy over the whole day. Clearly this is not the case. The very graph they present to show how good it is, shows that in fact, it performs exactly as well as conventional solar cells.
One final question on that graph, for which I do not have an answer, why is the power maximized between 10:00AM and noon? Why does the power almost go to zero shortly after noon, and provide no extra energy after 3:00 PM?
The final claim is that this technology works better when the sun is at oblique angles. Well, the graph above shows that may be true at some angles and not other, but the problem is that it doesn't matter that much if it performs slightly better at oblique angles. There is something called the cosine problem for solar cells. If the sun hits the panel at an angle, there is less overall light on it than if it hits it straight on. It doesn't matter how cool the panel is, what cool features are on the panel, it simply can not get away from the fact that there is less light on the panel itself when the sun shines light on to the panel at an angle. The best/cheapest solution for this problem is to have a tracker, but in general people don't like these on their houses, plus it adds cost, but it can double the energy output from a panel. So, based on their own data and basic fundamental issues with non-tracking panels, this claim seems sketchy.
It's good to keep an open mind on this, perhaps this device can reduce the cost of panels by some amount, perhaps, as they show to some small degree, the performance is better than a normal solar cell. But there doesn't seem to be any actual data out there to support these claims in a way that is different than any other new solar technology.
Look for it for any new solar technology... If they hit these three things, then it is being promoted like every other new solar technology:
- 1) <$1/watt
- 2) reel-to-reel manufacturing
- 3) 2x-4x better than "normal" solar cells
Here is an example, can you see any relevant difference in the boasts between the Fibercell technology and say, this one? Solar technology is improving on many front. There has not been a breakthrough that will lead to the benefits that this PR extolls. There probably never will be because the costs of a solar implementation is multifaceted, its simply not just the cost of the cell itself.
But, where are the pokeberries?
Funny how most of the articles about this technology focuses on the pokeberry angle. I guess it makes good news. What do the pokeberries do? They used a dye from pokeberries that gets spread on top of the cells. It promotes the absorption of light, like it could do for any solar cell. Really, that's it. Silly, huh?
