Japanese company develops a solar cell with record-breaking efficiency

It's not that.

The 95% is the limit. You can't extract solar power with a higher efficiency. (Funny thing that you can extract energy from Earth, radiating it away, with ~99% efficiency.)

86.8% and and 40% are theoretical limits to some current technologies. The others are people debating what is the best available on the market (with varying definitions of "available").

Admittedly, there still a lot of room for solar panel research for the upcoming years which is pretty exciting!

The discrepancies is often due to fact we're defining "solar panels" quite different for each application and also the definition of input energy is different.

A great example is engines. The theoretical (Carnot) efficiency is limited by the heat difference between the source and the sink. You can burn fuel at a higher temperature and pressure which will give you great efficiency, but it's not realistically possibly due to physical constraints (usually the steel that houses the explosions). That's why steel engines are often said to have a maximum fuel efficiency of 37%.

This same idea applies to solar panel but it's even more convoluted. What is input energy? Is it all the energy from the sun or is it only the energy within the energy band that the panel can "see"? What is efficiency? The efficiency for different energy band is different for each solar panel as well. Worst of all, this efficiency changes for different temperature and is effected by hysteresis! By the time you store the energy, you also lose efficiency depending on the internal resistance of the energy storage (That's why MPPT exist and fun fact of the day, from what I know, there is still no reliable analytical method to account for this. Most MPPT trackers are done empirically).

Sorry for the long rant, but yeah, solar panels are confusing and there is a surprising about of research that still needs to be done!

When talking about solar cells, the efficiency is defined as electrical power produced divided by the solar irradiance on the panel (~1000 W/m^s without concentration). In this situation, the theoretical limit for a single junction solar cell on Earth is ~34% as shown by Shockley-Queisser in their detailed balance calculations. Multijunction cells can be more efficient than single junction cells and can theoretically reach ~70-80% efficiency if >30 junctions are used and concentrated sunlight is used. In practice it is prohibitively difficult and expensive to make a device with more than 4 or 5 junctions, so you will not see one sun efficiency greater than 70% in real life. The 95% number is for a Carnot engine and doesn't apply to an operating solar cell. In order to extract power from a solar cell, you need to operate it in forward bias (typically at the maximum power point). When at the maximum power point, the solar cell emits radiation and therefore has irreversible losses. This is why the real limit for a single junction cell is 34% and not 95%.

I often wonder how good/cost effective optics would be, given the price of glass is cheap and that could be used to focus a larger area upon a small, more costly and yet efficient material.

But as you highlight, cost and with that a balance of cost/return is a huge factor and whilst scale can help in many area's. It gets more detrimental with more expensive materials.

There are already 46% efficient solar cells, the 33.7% limit is for a specific type of solar cell (single p-n junction) which are cheaper to manufacture.

The maximum theoretical limit is ~86.8% for solar panels.

If you "lack the skill to install" it yourself, then you don't get to complain about "very greedy middlemen." If labor really WERE super expensive and they were greedy, then you could afford to learn the skills and install yourself. Nah, don't expect labor costs to be free or expect labor to be paid below a livable wage. Or heck, don't expect labor which is more skilled than you are to be paid less than you are.

But this is an important point: residential solar will always be fairly expensive due to labor costs. As module and other hardware costs reduce, it'll make sense to use the very highest efficiency cells, tracking systems (provided they're simple to install), etc.

But I think utility and commercial scale solar will dominate. Someone will eventually get really good at installing solar farms a gigawatt at a time with a highly automated system. Think of the harvesting and planting machines we use in agriculture. Or the machines used to lay railroads automatically. When this happens, utility solar at the interconnection point will drop well below 1 cent per kWh in sunny locations, and transport costs will dominate. Which has some interesting implications.

You're only considering grid tie when you say that a system won't really pay for itself in ten years. For off grid solar there are a number of places (example: very rural parts of ID and WA) where it might cost $40,000 to extend code compliant grid electricity from the nearest road to a new bare land property. And that is before you pay any monthly bills for ten years. Versus spending $35,000 one time on a big ground mounted solar system, charge controllers and a set of Tesla power wall 2 for battery storage.

Cost and efficiency also hugely impacts developing nation solar (most of rural Africa) where no grid whatsoever currently exists.

Why?

AFAICT, there are three ways to double the output of a solar cell: Double the area, double the efficiency, and move the cell to somewhere with twice as bright sunlight and install a cable. That one option presents intractable problems doesn't seem to matter very much when either of the two others are available.

I don't know if we're already at diminishing returns, but to estimate that you need to compute the economic returns, not just the conversion efficiency.

As yearly production escalates, even small increases to the "conversion efficiency"/"production cost" can yield high total returns on the investment.

Cheap lenses can provide far less concentrated light than similarly cheap mirrors, since the latter are not constrained by having to sit atop a solar cell. As long as space is not a major constraint, controllable mirrors in array should handsomely beat lenses.

This is the current version of that chart: https://www.nrel.gov/pv/assets/images/efficiency-chart.png

This cell is the blue dot "Kaneka".

Multijunction cells are very expensive to make. The reason the multijunction cells in that chart all have concentrators is that without them, the cost is ridiculously too much to even consider.

This particular cell is noteworthy because it is cheap enough that you can eschew the added cost and complexity of the concentrator and just use more cells and potentially still be cheaper.

Insolight is a startup commercializing cheap plastic lens, that both focus and track the sun(hard to do with fixed lens, requires some optics magic). Panels made from those will have 36.5% efficiency, with only a 30% increase in total installation costs - that's their goal at launch.

> I'm not sure I like this. It seems that we're very clearly in the area of diminishing returns when it comes to solar panels.

I don't follow this argument. The median panels used in actual installations have increased in efficiency from about 16% to about 18% over the last 10 years (while the prices have more than halved).

First, the chart you link to is for 'hero' cells, using expensive technology to test the limits of a particular material, it is only tenuously linked to industrial production. There's lots of leeway for improvement in industrial production, which is what matters to the economy.

Second, improvements in efficiency are only one part of cost reductions. In the time that the cost of panels has dropped perhaps 50 fold you're only talking about a 1/3 to 1/2 increase in efficiency.

Third, there's always potential for other materials or structures to come to the fore. If we could find a cheap way of producing multi-junction cells then the ~30% theoretical efficiency limit disappears.

So, there's plenty of scope for continued improvements.

A fundamental limitation of concentrating systems is they only work well with direct solar irradiance - it's very hard to concentrate diffuse solar rays coming from random directions, as you have on any overcast day. This dramatically reduces the potential generated power in locations that don't have consistently clear skys (i.e. most places). So a high efficiency flat panel with a promising route to commercialization and built by a reputable company is a great step.

Efficiency isn't quite the important thing for solar as it is for fuel burning engines since all the sunlight is used up at the same rate no matter how much power you capture from it. We could get much cheaper panels with no better efficiency and that would still be excellent.

More important than energy efficiency is price per unit energy. You could have an inefficient but cheap solar cell that's more economical than an expensive efficient one (eg. active tracker vs fixed - the less efficient option is usually more economical). Though when installation costs dominate, then you really do want smaller panels so you can spend fewer man-hours nailing them up.

Isn't the conversion efficiency basically irrelevant except for specialized applications like spaceflight where every gram counts? 8% thin film solar cells will be the market winner if their marketplace ROI is superior - $ per Watt and lifetime.

Aren't we at the stage where "balance of system" costs are starting to dominate: wiring, mountings, inverters, installation labour and so on? Or is that only true for house-scale systems?

Or very, very large arrays in space!

I think your comment is the first use of "breakthrough," to be fair. The article title and body refer to it as "breaking" the record. You are correct about the (vastly more expensive) multi-junction concentrating cells having higher efficiency, of course.

You're also correct that not all improvements make it to market. Without research and continuing efforts to improve, nothing makes it to market. What's the point of your second paragraph? The article makes it _very_ clear that this is not in production, and speaks specifically to concerns about whether the process is suitable for industrialization.

Yes

(for more https://en.wikipedia.org/wiki/Solar_cell_efficiency)

For reference, in https://en.wikipedia.org/wiki/Photosynthetic_efficiency there is mention that photosynthesis has a nominal efficiency of about 30%, but in practice the absorbed energy stays in the 3-6% range, with sugar cane being exceptionally efficient at 8%.

No - because 2.7% (or 0.7 efficiency difference) increase is not insignificant when you scale up. As an analogy, think of what 0.7% tax saving would mean to you annually.

In reality solar-cells and batteries are not at all cheap to install and maintain. We can scale up the solar cells and collect more energy. However, that needs more surface area to be covered with these panels. We still need better ways to store the energy efficiently.

DC-AC losses are small (<5% I think), and the majority of solar systems aren't connected to storage at the moment.

Google ran a prize project to build a better inverter a while ago: https://blog.google/topics/environment/and-winner-of-1-milli...

"It had to have an efficiency greater than 95 percent and handle loads of 2 kVA. It also had to fit in a metal enclosure of no more than 40 cubic inches."

Yes. However:

> If a story has had significant attention in the last year or so, we kill reposts as duplicates. If not, a small number of reposts is ok.

This submission got traction, the other one was posted 12hrs ago and didn't really get anywhere.