Hacker News

77 Comments:
jsingleton said 13 days ago:

This is a great long read (if you like log graphs) on how solar prices have dropped more than anyone predicted: https://rameznaam.com/2020/05/14/solars-future-is-insanely-c...

> This incredible pace of solar cost decline, with average prices in sunny parts of the world down to a penny or two by 2030 or 2035, is just remarkable. Building new solar would routinely be cheaper than operating already built fossil fuel plants, even in the world of ultra-cheap natural gas we live in now. This is what I’ve called the third phase of clean energy, where building new clean energy is cheaper than keeping fossil fuel plants running. Even in places like Northern Europe, by the later 2030s we’d see solar costs below the operating cost of fossil fuels, providing cheap electricity in summer months with their very long days in the high latitudes. These prices would be disruptive to a large fraction of already operating fossil fuel power plants – particularly coal power plants, that are far less able to ramp their power flexibly...

(hat tip to the Forge the Future newsletter: https://forgethefuture.substack.com/?no_cover=true)

I predict a lot of fossil plants will convert to simply providing inertia for grid stabilisation and charge for the service. They won't burn anything any more and may even demolish their stacks and cooling towers. They will just keep their generators and turbines connected to the grid as a big virtual flywheel to dampen spikes in demand / supply and maintain the AC frequency within tolerance.

jiofih said 13 days ago:

Seems like that role will also be moved over to battery installations, as they have an instant response time vs long minutes for a plant.

akjssdk said 13 days ago:

Battery installations are still relatively expensive right for the capacity they offer right?

ZeroGravitas said 13 days ago:

That's a very general statement, but solar plus lithium battery storage is now competitive with gas peaker plants and those can grid balance as an extra service.

woodandsteel said 12 days ago:

That is true, but prices have been dropping rapidly.

jsingleton said 9 days ago:

Inertia is slightly different to supply response and most inverters use grid coupling for frequency and phase synchronisation so are not suitable. The slow response of old plants is an asset in this case and only a problem if they are generating rather than just providing inertia, which is instant.

DarkGodErebus said 12 days ago:

Currently it would probably be better to generate hydrogen if there is excess power in the gridit would probably be a lot more economical than batteries though roughly 66% is lost in conversion

henearkr said 13 days ago:

IIRC, there are some nasty heavy metals in some perovskites. Does anybody know which type is used in these projects? I'm 3000% in favor of solar, but still it bothers me if they use Pb etc...

borkt said 13 days ago:

I focused on PV in college and the fact is solar is dirty and they haven't planned for end of life recycling. The potential is great and we will get there im sure, but I always thought it was irresponsible to subsidize and widely roll out especially the early stuff in the 90s that was very inefficient and filled with heavy metals and REE. I'm not up to date now but the only thing I can say is at least the efficiency is better even if they are using similarly toxic elements.

iamthemonster said 13 days ago:

I'm probably much less well-informed than you, but I can't understand the arguments about the disposal of the panels at the end of their life. I throw away a wheelie-bin worth of trash every single week, that's 1040 wheelie bins over a 20-year panel lifetime, yet those panels are probably equivalent to about two wheelie bins. It's a microscopic volume. What is in solar panels that is such a disaster compared to household trash? In 20 years I also expect to go through ten phones and five computers (although admittedly I'd chuck them into the local electronics recycling bin).

nimish said 13 days ago:

Heavy metals in thin film, mostly. Cadmium isn't great. They can be highly recycled though. Nevertheless, if a storm destroys a bunch of panels lots of cadmium will be dispersed

henearkr said 13 days ago:

Cadmium telluride is not the prefered technology for solar cells. Silicon is still the major player, and it is free of any pollutants. I checked the wikipedia page for "solar cell". Given these informations, any consumer or technologist can adopt solar without compromising on pollutants.

gibolt said 13 days ago:

The amount of oil or natural gas for the equivalent amount of energy that will be saved is worth it.

Old panels were bad, but without it we wouldn't have today's cheap and efficient panels, with more drops to come.

Just like with batteries, recycling will become more profitable and thus researched as we march forward

drcross said 13 days ago:

Batteries being made today will last 30 years, the first 15 will most likely be in a car and after that in a house battery. In 30 years we'll have drastically different ways of coping with waste so this concern about recycling is such a red herring.

alacombe said 13 days ago:

If "recycling details" can be figured out later, then the same argument can be used to justify a massive investment in nuclear power, ie. 4th generation reactor, LFTR, you name it. It would generate more energy over its lifetime than PV ever would.

woodandsteel said 12 days ago:

Nuclear has been around for 70 years and it is still extremely expensive to dissemble nuclear plants and dispose of their wastes. In fact, in the US we still don't have a permanent solution to nuclear waste storage. And a lot of the radioactive materials in them are vastly more dangerous than what you find in solar cells.

wlll said 13 days ago:

One key difference between solar and nuclear is that when solar goes wrong it goes wrong in a pretty small way.

Nuclear’s failure states are pretty awful, see Chernobyl, Fukushima for disasters, but just (something I learned as a kid) the Irish Sea being quite significantly radioactively polluted through normal operation of plants in the area.

alacombe said 12 days ago:

The cost to dismantle millions, if not billions of tons of PV cell in 30 years is gonna be pretty higher, both in term of cost AND ecological impact than a localized power plant.

Also, Chernobyl is not a Gen4 reactor, the core design of RBMK reactor was highly unstable, and that the problem with anti-nuclear lobbying: we're stuck with old design we have since learned a lot from.

wlll said 12 days ago:

>The cost to dismantle millions, if not billions of tons of PV cell in 30 years is gonna be pretty higher, both in term of cost AND ecological impact than a localized power plant.

Got any figures for that? Higher than the ecological cost of dumping radioactive stuff into the pacific, or polluting the Irish sea?

As someone who might last another 40 years, but is hoping his kids last another 60 to 80, I'm OK if the cost is monetary in 30 years, as opposed to ecologically over that time.

> Also, Chernobyl is not a Gen4 reactor

Was Fukushima though?

alacombe said 11 days ago:

> Got any figures for that?

Assuming a 15W per sqft, and an average weight of 3lb per sqft, and assuming the output of a nuclear power plant is around 1GW, you'll need about 9e+4T of solar panel that you're gonna need to recycle over a lifespan of 40 years. Just the volume of this waste is 4.5e+3 truck load, and I'm not even getting started about recycling the silicon cells themselves (ie. very nasty chemicals), and all this is just about 1 equivalent plants. US wide, you'd probably need 200x this (to be significant), plus a 5x extra capacity to deal with fluctuation and non-peak production, that's another 3 order of magnitude. You also need to factor into account a redesign of the grid to accomodate with the mesh production, and the extra battery on each site.

Compare this to burying a few hundreds tons per year of low volume wastes for ~eternity in a cave in the middle of nowhere.

> Was Fukushima though?

No, Fukushima used BWR design from the 1060's, so geneneration 2.

henearkr said 11 days ago:

> No, Fukushima used BWR design from the 1060's, so geneneration 2.

Wow, animal-powered nuclear fission? These Heian period horse-drawn neutron beams were pretty ahead of their time though.

gibolt said 13 days ago:

I'm totally happy if Nuclear becomes the major source that gets us off fossil fuels. But I'm also realistic. The cost, timeline, and red tape holding it back isn't moving fast enough.

henearkr said 13 days ago:

Sorry, I checked and you are probably wrong, in the sense that silicon based solar panels (the vast majority) is free of heavy metals. The one you are maybe thinking about is cadmium telluride, and it's far from being widely adopted, precisely because of toxicity concerns.

catmanjan said 13 days ago:

Do solar panels eventually stop producing any power?

I have some second hand panels that are around 10 years old, I'm sure they are less efficient and I have had to replace diodes etc - but it seems to me that if you have lots of space (as we do in Aus) you could just keep adding new panels without getting rid of old ones

fyfy18 said 13 days ago:

Solar panels you buy today just go down in efficiency - if you are installing them on say a house, they will continue producing good power output for the lifetime of the house (bar physical damage). Typically they will come with a waranty that after 25 years, they produce at least 80% of their rated output.

(You will probably need to replace the inverter during that time, but the panels will be fine)

WrtCdEvrydy said 13 days ago:

Would it be viable to create a business to take the old panels and basically just mount them out in the desert to provide nearly free power (assuming you just do morning loads)?

ZeroGravitas said 13 days ago:

The progress of PV technology over 3 decades means it's probably cheaper to recycle them for raw material and build out new PV.

henearkr said 13 days ago:

Is there nasty heavy metals in current silicon panels? Have you more details? I'm (badly) surprised, I thought that would be merely the lead solder, solved by using lead-free one... Last I checked, I was under the impression that current technology was clean.

numpad0 said 13 days ago:

Photovoltaic is a fucking photodiode in the size of doors and windows right?

Unbelievable people think piles of huge diode in backyards is “green” somehow. I’m all in nukes since I realized that.

woodandsteel said 12 days ago:

Why is a big photodiode not green?

kitotik said 13 days ago:

So is part of the bet here that future potential efficiency numbers will continue to increase at a rate faster than silicon can? Or is strictly a low cost play?

ResearchAtPlay said 13 days ago:

Efficiency improvements amplify cost reduction per kWh electricity: An ever growing share of PV system costs stems from every item that is not a a module (inverter, cables, labour etc). Modules are becoming cheaper faster than other components, so reducing module costs further has diminishing returns.

In contrast, taking your module efficiency from 20% to 21% increases electricity generation by 5% and thus reduces costs per kWh by 5%.

einpoklum said 13 days ago:

We should always remember additional factors to the equation, including:

* The materials involved in production of such cells and of power-stations/fields based on them - in particular, their rarity and/or their toxicity.

* The sustainability and environmental impact of procuring the materials.

* Longevity of the cells.

* Recyclability / decomposability of the cells at end-of-life.

* Logistical considerations in setting up and operating solar cell fields, specifically of this type.

* Ease/cost/frequency of maintenance on these cells, individually and in a solar-field, when in operation.

and perhaps other factors I'm forgetting. Still, the materials science achievement is to be lauded.

m463 said 13 days ago:

Your comment seems very general.

It would be better to address perovskite cells specifically.

BiteCode_dev said 13 days ago:

Anything using fossil energy also has such hidden issues.

And you have to consider the ecosystem:

- fossil fuel engines require much more maintenance than electrical engines, and now vehicules always embed heavy electronics anyway.

- fuel need to be transported at a heavy cost, which is now hidden by the massive demand. The day we use more solar than fossil, the whole fossil infra will suddenly feels very expensive

- most countries are not like the US and don't have oil on their soil. Countries don't like to be dependant on others for critical things. You may buy solar panels (or fuel engine) from a friendly country, but if things turn out badly, people can't cut sunlight from you one the initial setup is there.

Nothing is perfect of course, but I like the solar future we are hinted at.

einpoklum said 13 days ago:

I didn't suggest fossil-fuel-based energy production is superior.

Having said that - maintenance of cars using fossil fuels is not a relevant comparison, since we're talking about power plants.

Personally, I doubt that we can just -whoosh- swap the coal and petroleum for solar-based electricity and have our problems solved. It's likely that a lot of social effort to conserve more and waste less energy will be necessary to reach some sort of long-term-sustainable state of affairs.

xiphias2 said 13 days ago:

The article talks about these things:

- Increasing the longevity of the cells is the main achievement of the research.

- Gas-spectromenty should help in understanding the toxicity as well

- Something that's 200 cheaper than the current material and scalable can't be rare at the same time.

LockAndLol said 12 days ago:

So encasing the cells in glass stopped decomposition? There was no pressure buildup in the cells? No gasses released?

The test says it's 1800 hours of stressful conditions for the cells. Assuming 10h of sunlight per day, that's 180 days of stability. I guess time will tell how long they really last, but it's good news that they surpassed test requirements.

And having a 25% conversion rate baseline compared to a ~26% assumed max for silicon is also impressive. I wonder how much they can boost that.

kumarski said 13 days ago:

Gonna chime in here, have a weak materials engineering background.

The material economics go wild if you try to solve for stability of perovskite. You really don't know how much this thing is going to cost.

With perovskite, from what I remember, you get the nice efficiencies with lead based perovskites.

This increases the price of electricity as you layer it on top and you get an extra 2% efficiency.

darksaints said 13 days ago:

I've passively followed the perovskite revolution for a while now, and the constant claim is that they're cheaper. But how cheap? Nobody can ever seem to quantify it.

kragen said 13 days ago:

If you're making something in a laboratory, it's not cheap, even if it could conceivably be cheap in mass production. Even once something is in mass production — like silicon PV has been for the last 40 years — it can take a long time to bring the cost down. Silicon PV cells have fallen in cost by a factor of 10 in the last 10 years, in part due to much higher volumes, in part because the production lines no longer need to be staffed by Ph.D.s. Who could have predicted in 1980 that that would take until 2015?

In a lab you can demonstrate how much material something uses, how long it lasts under given conditions, and, say, how sensitive it is to contamination. But you can't predict, you know, the late-oughties polysilicon price bubble, the ensuing long-term purchase agreements made by companies like Evergreen, and the subsequent polysilicon price collapse that sunk those companies. (I'm still not sure where modern PV cell companies source their silicon! Is it UMG?)

"How cheap?" is a question about international trade, mining, and management, not a question about materials science. Don't expect materials scientists to be able to answer it.

philipkglass said 13 days ago:

The raw materials for perovskite cells are cheap, but so are the raw materials for silicon cells. There won't be hard cost numbers on perovskite PV modules until they go into volume manufacturing. They won't go into volume manufacturing until they can be stabilized enough to last years in the field.

My personal guess is that single-junction perovskite cells will not ever overtake single-junction silicon cells for rooftop or utility scale solar. Single junction perovskite cells may be used in applications where light weight and flexibility are advantageous, like charging portable electronics, if they can be stabilized.

Perovskite cells may compete in rooftop/utility solar with conventional silicon when incorporated into tandem cell designs -- either perovskite on silicon or a stack of different perovskites with different band gaps. That gives them the potential to exceed conventional crystalline silicon module efficiency rather than merely play catch-up. The company that seems to be furthest along with this approach is Oxford PV, which is pursuing a perovskite/silicon tandem design:

https://www.oxfordpv.com/perovskite-silicon-tandem

powerslacker said 13 days ago:

Full disclosure, I know next to nothing about solar markets. What about putting panels on vehicles? Couldn't the market for cells on vehicles overtake the existing solar market?

mkl said 13 days ago:

If your goal is to power the car while driving, even 100% efficient solar cells wouldn't be enough, as there simply isn't enough surface area to gather enough energy to power a normal car doing normal driving. If your goal is to leave the car sitting charging in the sun all day, that's a bit more practical, but I believe there aren't yet any production vehicles like that yet: https://en.wikipedia.org/wiki/Solar_car

hnick said 13 days ago:

Solar trees could help for the parking, but I don't know how the economics of that plays out.

ctdonath said 13 days ago:

All factors considered, solar panels average 10-20 watts/m^2. A Tesla uses ~325Wh/mile, Leaf ~250, Cybertruck ~500.

Putting PV panels on a vehicle can give you a few miles per day - enough to get you to a plug if battery drains too low. More an emergency tool than viable power source.

robotbikes said 13 days ago:

I think you meant to say 100-200 watts a square meter average output as a 300 watt solar panel isn't much larger than a square meter. Either way, you are right that it is unlikely that solar charging via a car roof will be anything aside from a backup/gimmick. But it is possible to get a good charge from solar panels on a rooftop with not a huge amount of panels.

ResearchAtPlay said 13 days ago:

OP is probably correct, maybe even high in their 10 to 20 W/m^2 estimated average output for car mounted PV systems.

Rooftop mounted, optimally oriented PV systems at Seattle latitude have an annual capacity factor of ~ 14%. That means a 1 kW system will average 140 W output over a year. That system has a module area of about 4-7 m^2, equivalent to the area available on a sedan.

On a car that has suboptimal module orientation and solar exposure, "power density" (RE: Smil) is really low.

robotbikes said 13 days ago:

Ok, that makes sense if you average over a year considering night time etc. Yeah, car mounted solar isn't a great idea unless we were in a mars rover type of situation which is not how we use cars.

ctdonath said 12 days ago:

I meant what I wrote. Sure you get 100W/m^2 when the sun is shining perpendicular to the surface, but divide by night, clouds, angles, dust/snow, latitude, air transmissiviness, line/battery/conversion loss, etc and you’re well under 20W long-term average.

ncmncm said 13 days ago:

Most of the time the panel is at a sharp angle to the sun, or in shade. Fully half the time it is entirely in the dark.

elihu said 13 days ago:

It's probably worthwhile to put solar on cars, but it doesn't really do much to improve range.

A way to think of it is to imagine a gas-powered car with a gas tank that magically refilled at a rate of one gallon per week. That would be a great feature, but it wouldn't really change what you do with the car. It would mostly just mean spending less on gas over the lifetime of the car.

In the end, a car costs a lot of money and provides a couple square meters of usable space. Roofs of houses are a lot bigger and can supply the needs of a household, but if you're in the business of energy production and want to generate energy on the scale of a major power plant, it makes far more sense to use cheap land in sunny places away from cities.

philipkglass said 13 days ago:

There isn't enough surface area on vehicles for that to happen.

The world installed about 117 gigawatts (peak) of solar PV last year [1]. If the average panel is 17% efficient that's more than 680 million square meters of panels being manufactured per year. World motor vehicle production in 2018 was 96 million [2]. To put more solar panels on vehicles than we already put in fields and on rooftops, the average vehicle would need more than 7 square meters of surface covered with panels. That's neglecting that most vehicles are still internal combustion vehicles that couldn't do much with the electricity those panels would generate.

[1] https://en.wikipedia.org/wiki/Growth_of_photovoltaics

[2] https://en.wikipedia.org/wiki/List_of_countries_by_motor_veh...

woodandsteel said 12 days ago:

>There isn't enough surface area on vehicles for that to happen.

Yeah, it's the old square-cube law in action.

nimos said 13 days ago:

Just not enough room really. Maybe(read: no) you could get 5m^2 of panels on a car. With 100% efficient panels the energy would be 5 * 1000 W m^2 = 5000 watts which is about 7 horse power.

That is a bit below what a very aerodynamic car needs to maintain highway speed so sort of relevant from a range extension perspective but 100% efficient panels and 5m^2 being fully illuminated at once are not very realistic assumptions.

I could see electric trucks(non commuting) + tiny home on wheel with big arrays potentially being viable though. That + starlink would make a pretty cool working remote combo.

Gibbon1 said 13 days ago:

I tried estimating the range per day if you put solar panels on top of an RV. I think it was ~10 miles day. That's a tantalizing number since a lot of RV's sit for long periods of time.

jayrot said 13 days ago:

No idea if it applies here or not, but a general rule of thumb is if they don't how say how much cheaper...it's not that much cheaper.

"new solar cells are 94% of the price than existing mono-crystalline cells"

econcon said 13 days ago:

Last time I was installing panels, panel were fairly cheap.

More expensive were inverter, controller, batteries.

said 13 days ago:
[deleted]
bufferoverflow said 13 days ago:

TL;DR: 500 times thinner, much cheaper, 25.2% efficiency, but not durable at all.

phkahler said 13 days ago:

Now they have a coating that protects them. TFA did not say how much that changed efficiency, if at all.

Fielddisturb said 13 days ago:

Low cost energy? Think twice, the population is controlled by this expense mostly! It's a nice utopian dream, scientifically achievable, but politically not viable.

roenxi said 13 days ago:

The uncertainties here are demonstrated by the fact that the article is quoting 25.2% efficiencies. Solar panel efficiency wouldn't matter as much as the ratio of energy/m2/$ ratio.

Nobody cares if a solar panel is 2% efficient if it costs 100 times less to fabricate and install. Just build more of them. Still, it is good news to see this sort of energy research bearing fruit.

yardie said 13 days ago:

When we kitted our boat with solar panels the cheapest part of the entire system were the panels, ~$1/W. Half of the budget went into mounting and the fabrication of the mounting hardware and 1/3, or the remainder, went to wiring and controllers. This nearly lines up with domestic solar. 1/3 to panles, 1/3 to frames and mounting, and 1/3 towards electrical.

Panels at 2% efficiency would be wildly uneconomical at practical any price.

woodandsteel said 12 days ago:

Ok, good points. But I am thinking some of that could be saved if perovskites, or silicon plus perovskites became more efficient than silocon alone.

roenxi said 13 days ago:

> Panels at 2% efficiency would be wildly uneconomical at practical any price.

I guarantee that is wrong, if the price got low enough it would be economical. Wikipedia suggests to me [0] plants operate at 3-6%, and plants are extremely economical. Even starving African children can afford access to plants. If solar panels were as cheap and easy to produce/distribute as plants but could be plugged in to a grid then 2% efficiency would be wildly economical - it would be the greatest energy revolution in human history.

[0] https://en.wikipedia.org/wiki/Photosynthetic_efficiency

anoncareer0212 said 13 days ago:

Lots to unpack here - is there a more straightforward way to word your argument here? To put GP's post in terms of yours, the planters and water cost much more than the plant, so even if "starving kids in Africa can afford access to plants", it doesn't mean greenhouses are free

roenxi said 13 days ago:

It isn't an analogy. Plants are literal solar systems. The only reasons they can't be plugged into the grid is they deal with energy chemically instead of electrically.

It doesn't require that much imagination to say that solar cells might one day be work in an extremely similar fashion to plants. Not likely, but not an outrageous thought.

Nature has produced a cheaper, more ubiquitous and more self-replicating solar system using efficiencies in the 5% range with a theoretical cap of 11%. That suggests we don't need 25% efficiency to accomplish amazing things. It isn't a critical metric.

perl4ever said 13 days ago:

I'm fine with your equation of plants with solar power. But it's not cheaper; look at the price of biofuels. Aren't they in fact more expensive than fossil fuels and solar panels?

robotbikes said 13 days ago:

I think most biofuel is currently more expensive because it is diverting high input monoculture crops that are typically grown for feed like say corn ethanol or soybean oil. I believe ethanol from sugar cane in Brazil was cheap but only because the humans laboring to harvest it and process it were paid very little. But yeah the current choice of using industrially farmed high input crops to source biofuel does make it expensive. I think ultimately heavily refined energy dense fuel does require lots of time or energy input to produce.

roenxi said 13 days ago:

The energy that a plant captures doesn't go in to biofuels; it goes into growing the plant. Pushing roots through rock, extracting minerals from the earth or whatever it is plants do. Pushing water from the soil up trunks or through stems.

The biofuel is burning what amounts to the plant's surplus energy that it wasn't using for anything, and recovering some of the energy that went growing the mass of the plant. It isn't comparable.

The point here is plants are covered with tiny green solar panels that are grossly inefficient compared to what humans produce. However, they are beyond cheap to produce (in fact they grow themselves) and suggest that we are not even close to pushing the limits on what we can do with solar energy design wise.

Efficiency of the solar panels really isn't all that important compared to making something with the flexibility and weight of a leaf. Comparing efficiency between solar panels is a waste of time outside the research community; all that matters is total cost to install vs. watts produced.

pengaru said 13 days ago:

> Nobody cares if a solar panel is 2% efficient if it costs 100 times less to fabricate and install

I use a modern portable solar panel that's in the realm of ~25% efficiency when camping, and I certainly wish it were smaller for the same output. I'd be willing to pay more for that.

There's obviously segments that care more about efficiency than cost, not all solar applications have unlimited space.

nimos said 13 days ago:

At 2% efficient and 0 cost they would probably be more expensive than current when looking at total installed cost for commercial/residential, maybe even utility.

You can see even at utility scale the panel prices are generally less than 50%.[1] I think 2018 increase was tariff related. Been out of the industry ~5 years so don't follow stuff that closely. Many of the other costs are basically a multiple of # of panels which would be 10x at 2% efficiency.

[1]https://www.nrel.gov/docs/fy19osti/72399.pdf

roenxi said 13 days ago:

I did say fabricate and install you'll notice. If they came up with something really light and cheap to produce installation costs would plummet. Compare the cost of installing windows to installing solar panels - windows don't even have a rate of return but everyone has windows. It is a no-brainer to install windows. Solar panels are not a no brainer decision (yet, hopefully).

And that was the point - weight and difficulty of transporting the final system is a very important variable. Probably more important than efficiency when orders of magnitude are concerned. From a 25% base efficiency can double and double then it stops improving. Weights and installation costs due to the panel technology can halve and halve and halve and so on - and each halving reduces the cost of transporting the panels. There are more gains to be made there. It would be worth trading efficiency away to make big gains there.

Gravityloss said 13 days ago:

Solar cells have been getting quite cheap. At some point covering materials and installation cost start to have an effect - and those are smaller with better efficiency.

Gibbon1 said 13 days ago:

I think what's happening is bare processed silicon wafers are cheap enough that that other costs of a panel are starting to dominate. That pushes you towards using high efficiency cells in order to reduce number of panels needed.

I think Perovskites are interesting because they are cheap and can get you 25% efficiency in a single layer cell.

AYBABTME said 13 days ago:

It matters for mobile applications where space and weight are limited.