The goal of the course is to give students awareness of the largest alternative form of energy and how organic / polymer solar cells can harvest this energy. The course provides an insight into the theory behind organic solar cells and describes the three main research areas within the field i.e. materials, stability and processing. NOTE: This course is a specialized course on organic solar cells. If you are looking for a more general solar cell course, we strongly recommend Introduction to solar cells (https://www.coursera.org/learn/solar-cells).
Recorded Live Session V
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From the course by Technical University of Denmark (DTU)
Organic Solar Cells - Theory and Practice
644 ratings
From the lesson
Wrapping Up
This is the final module of the course and it is almost time to sit back and congratulate yourself! You just have two more videos and an exam to complete.
Meet the Instructors
Eva BundgaardPhD, Senior Scientist
DTU Energy
Frederik C. KrebsPhD, Professor
DTU Energy
Mikkel JørgensenPhD, Senior Scientist
DTU Energy
Morten Vesterager MadsenResearcher
DTU Energy
Okay and so, now we are online and, as usual,
I'm sitting over here and going through
the chat box and forwarding your questions.
And so, can you hear us, first and foremost?
Yes, okay, so we are ready.
Okay, so today we have both Edith, Frederick and
[INAUDIBLE] here and we're ready for our last live session.
This is the last session since we're in the last week now.
And I put down some questions, I think I'll start out with those.
And actually, I think one of the questions I wrote down is so
similar to one that's just here now, so we'll start with that.
And we've seen that we can use many different types of electrodes,
can we use as an electrode?
>> In principal, yes and I would say judging by the number of papers that
are published, absolutely yes, both as a electrode and a [INAUDIBLE].
If you mean that you want to use it as the only transparent electrode or
semi-transparent electrode,
I think the question is a little more difficult to answer.
At the moment the transparency that you can achieve while still
attaining good with pure is not good enough.
So you would need to use it as a composite with for
instance a highly conducting grid or a deep grided metal grid, or
another then this is certainly.
On its own, it's not, I would say,
technically possible at today on large scale to do with that.
>> Okay, thank you.
Okay, it says, no sound here, are there other people having issues with sound?
Okay, we see how that turns up.
I think there is sound.
Okay, a question that we had was specific to this last week of video,
this week's video is you talk Frederick about that you can
surely connect OPDs and you also did that for silicon cells.
Then you said that when you shadow just one silicon cell
you lose a lot of current.
And you did the same experiment where you did it for three weeks.
And here you didn't see the same loss of current and
that's the main reason we can do the solar power.
So can you explain a little bit what is the reason that this is possible?
>> Well, I think it is also also [CROSSTALK]
well I think that cause we did describe it in the compendium.
>> Yeah.
>> Yeah. >> And the thing is that the organic solar
cell when used as a diode is actually a pretty [INAUDIBLE] and
perhaps the semi-conductor that works so
well for silicon and that we have
on the organic junction is perhaps not fully correct to use.
You could use it, but in this particular case the shadowing starts
acting like simply more like resistive element and
that means that you can actually pass a large current through even when it's not
generating the same current as the neighboring sets.
So I think that explains it the best way.
Had the access has been exceptionally high for
the organic solar cell and the fine behavior extreme,
we would have been in exactly the same situation as junction.
Does that answer it?
>> I think so, yeah.
Okay, we have a little bit of an interesting question here coming
from the chat.
So the question is, we know we can do multi-junction cells, for example tandem
cells, but are there any options to do them with next generations of solar cells?
For example, could you do a tandem solar cell out of silicon device,
and then a OPV device on top of it.
>> Yes this has been done, people have tried making [INAUDIBLE] on top of silicon
solar cells, organically as on top of silicon solar cells.
And in all the cases, we are having an acquired performing silicon solar cells
that gives you maybe on that leak more than 20% and
you end up with something significant, inferior to the silicon solar cell, but
significantly better than the organic or [INAUDIBLE] solar cell.
So I think it's technically, yes you could stack whatever.
Not without limits, but if you think about if you admit enough light
through the front cell then the tandem concept works regardless of technology.
This has been, there's quite a few examples.
>> I guess one thing you could say is you probably end up stacking many of
the disadvantages while not keeping the advantages.
So the main advantage of OPV is you can fabricate it on both roadways.
If you had to do it on top of a silicon cell, you'd lose that advantage.
And you'll probably also gain the full stability, and
the poor performance of the organic cell.
I think it is the it is the lowest
denominator that always wins.
>> You could say it's a huge effort to make tandem solar cells.
>> The reason for doing it is to increase the efficiency lots of
to where we good and the bad, so it's.
>> Yeah, and you would expect it to be better than single cell.
>> Yes.
>> Even if it was only marginal, say, a 5% organic on top of a 25%
silicon solar cell so instead, expect 30 rather than 12 or
something which as I recall the majority of cases are on the order of 12 to 15 for
silicon cells stacked with either [CROSSTALK].
>> One of the problems is that you have to have the same count.
>> Yes. [CROSSTALK] In both cells, so
if you have a very good silicon cell that generates a huge
current of current for OPV that they're strong.
>> Okay sort of a related question that I have from the forums, here it is and
will OPV ever reach the same level of performance as for
example a silicon device or other types of PV technology?
>> Well I suppose, database mining paper which shows this pretty well.
I think there's no scientific argument for not seeing or
going beyond silicon or something else, but
practice has shown that OPV's probably limited to the lower
range of efficiencies when [INAUDIBLE] takes as a whole.
And probably, you look at the current density that you can achieve with organic
sources, it's typically low, typically significantly less then 20 milligrams.
Where as many of the inorganic solar cells,
the high polymer are way in excess of 20 milligrams twice a week.
So the organic solar cells the quantities are low, current density technology.
It may have caused a tandem geometry yield to make up for
some of this, but I still think the practically the organic solar
cells is limited to the low range of efficiencies.
But then they have certain other advantages like Bunch of high processed
speed being possible with low thermal objects shortening the play back time.
Low cost.
So you loose a little on the efficiency but
I'm sure that it will be by far outweighed by the advantages.
Yeah, and I can see that it's not so many questions coming in on the chat today, so
if you want us to keep online for a while, then you need to ask more questions.
Of course I have more listed here, but please just type in your questions.
There's one here about a specific material used.
[INAUDIBLE] Have you ever used?
Polyvinyl cabesol or any derivatives of this?
>> [INAUDIBLE] Unit has been used.
A series of polymers, maybe [INAUDIBLE] >> It's not very stable
>> No polyvinyl cabesol has been used in
the past as an electron transport layers [INAUDIBLE].
In principle it could be used as a transport layer but we haven't used it.
>> [INAUDIBLE] Limits it because
it doesn't absorb [INAUDIBLE].
>> It might be useful as a carrier, blocker, or a transport base.
>> So it's a good question.
I think it could possibly be useful.
It's a low cost material.
And it is a carrier, transporting some.
Technically yes, we have not tried with a [INAUDIBLE].
Okay, another specific question: can
sodium silicate be used as an oxygen barrier?
I suppose the question goes with whether you could precipitate it or.
>> I guess so, yeah.
And would it work?
>> It's a good question.
[CROSSTALK] yeah, in principle, you could coat it,
but I don't think he has impervious as
a caught up and then fully [INAUDIBLE].
But I mean it shouldn't be a solution.
It's a good point.
There are people working
at the moment at making
solution processes.
It's a good idea, it's at least worth a try.
>> [LAUGH] >> Okay, then there's
a question here that's more related to the commercialization aspect I guess of this,
so have we licensed any of our processes?
>> A process no, but some machinery has been licensed.
Some equipment and destology has not been process itself.
>> And I guess the followup question could be what is the patent situation on this?
Just briefly.
>> Time over here in general?
>> Yeah.
>> Honestly, there's a lot of patents on [INAUDIBLE]
are several thousand that are direct.
And there are maybe at least ten times as many, and today many times as more.
So maybe on the order of 40, or
30 to 40 thousand that somehow has implications that could become relevant.
Could be semitransparent electrodes would
be methods of treating the surface or
coating the surface [INAUDIBLE] for instance.
There are several [INAUDIBLE] >> [INAUDIBLE]
>> Yes, and
many of those are difficult to find if you do a search.
It's difficult to find those patents that could actually be quite relevant to your
particular device.
For instance, if you add a device and you wanted to or
you had an IP [INAUDIBLE] invention and you wanted to patent it.
It's likely and some other people already have a patent in a not related field that.
They actually have the claim.
A good example is when in the old days you could be in the solar huts.
You actually try to claim the geometry, which is circular, so
it was concentric rings.
And this idea of making connections through having a series of concentric
rings that are the same area, we thought.
And we actually found an old shipment on not the same idea, but
where the had described the invention in such a way that it actually.
We found it by accident, and it shows that a lot of inventions have been made, except
that you don't know it, and the other inventors, they don't know it either.
So it's only if you accidentally meet and
the guys who already have the patent realizes that they already have it and
you realize that you already had it, that there isn't one.
So the patent situation's probably decides that if you put this aside,
this dark cloud of unknownness, then there's is this tall mountain of papers
of maybe 3000 of nuclear, which is my guess is there's not that money that are.
Generic [INAUDIBLE] also the generic patterns were lost
during the [INAUDIBLE] had been captured by other companies.
But I think in the majority of cases also since the [INAUDIBLE] at the [INAUDIBLE]
What was a good valuable idea five years ago is of little value today.
An answer of we becomes widely commercialized in a particular form.
We don't know what is relevant and it would be that,
I don't know which one if it's a data, so
it's a tricky situation, patenting, the patenting game is has many facets.
>> Okay, there's a followup question on our discussion here.
So it says, can grapheme be part of the exit layer, or do we use it mostly for
its transport properties?
>> Well, grapheme has little absorption and,
I suppose, well I'm sure, I have read somewhere,
mixed in with the different lectures and [INAUDIBLE].
But I think the main grammar of the graphics is the very thing layer
can use it either, both as a barrier and as a transport lead.
The transport [INAUDIBLE].
So I think its main interest is in this interface material has [INAUDIBLE].
A fusion barrier.
Yeah.
>> I have a question, and it takes a little bit of explaining to do.
But we have a question on the phone from Darren Scott Wilson.
I don't know if he's online, but let me try and show you what the question is.
So, I think you can now see his profile picture.
This is from the video, and it shows the quick structure that you're using for
the solar park.
And in the video, it was explained that a hexagonal structure was used previously,
and then this wasn't good because you have a lot of crossings off the nature and
then you introduced this slanted grid instead And then his question is,
since we can see this line of grid here,we see there are some overlaps still.
There's one, maximally two overlaps.
>> Yeah. >> We must decide such that there are one
and rarely, but maximally two crossings.
>> Let me just show you this, he did [CROSSTALK]
>> It's a very, Darren, was his name,
yeah?
I think it's a brilliant question.
It's of course one.
So it really shows that they are at least a really unsecured recourse.
At least this part of it.
>> Yeah, yeah. [LAUGH]
>> So congratulations there of course.
This is the most obvious thing to do.
So you put the hammers on the nails head and
of course we would want to do this but.
What is a challenge when you work with tin foil that is not firmly stable.
That means that you would do a multi-step process,
so we use eight closing steps to make infinity.
And for every passage through the machine, you have a drying step.
For every heating step of course, so it wouldn't be soaked either by driven.
For every hidden step the foil shrinks or stretches a little.
That means the next time you print on top of it registration is getting to maintain.
And even if it shrinks, it typically shrinks about two millimeters
over the motif, which is a foot or twelve inches.
So it can easily, in the worst case, or
over the entire process you're talking differences of a few millimeters.
And that is more than the grid lines.
[COUGH] And that means if you look at the Moire Effect that you have on having two
overlapped grids, for with a periodicity of like here of like one and
a half millimeter, that means that it is completely
impossible to predict where the crosses will be.
If you don't know what the shrinkage is.
And the shrinkage is predictable in the sense that we know that it will shrink or
stretch for given batches of polymer a foil in a given direction.
But we don't always know by how much.
And certainly over a length of a kilometer it's not the same throughout
the length of the.
So we needed to invent this other grid where we have to deviate from this ideal.
A condition where, you can say that the image here would require that we have
a registration, and that is leaving aside any stretching or shrinkage.
We did a registration accuracy of about half a million in the length direction.
Which is already pretty challenging when you are operating this at 20 or
15 meters a minute.
Bring us up to speed.
>> Four kilometers.
>> Or during the kilometer where it all leads to what?
You can't screw up the 5 meters because then all this is likely to then be shun.
It has to be predictably wrong or we have to be able to know that we
have one matching the two crosses for every unit setup this grid stops.
And that's why we came up with this kind of grid.
If we have a different device geometry or the printed direction was different,
it would be an easy case to realize this structure that's on the screen now.
[NOISE] That the- We have
an emergency here in our lab.
[NOISE] Not our building it doesn't seem to be in this building.
[LAUGH] Okay,
we will wait two
seconds until
this is over.
>> [INAUDIBLE] >> Okay, so
apparently we had a fire alarm and it wasn't in this building so
we'll continue on until the fire spreads up here.
[LAUGH] Okay, I think the next question I see in here is can you give
a little bit more explanation about what a hole is in the solar cell?
>> So, a hole is a carrier or a hole is a- >> Is a carrier.
Yeah.
>> Well, I think we had the question earlier, in one of the earlier,
where you don't have an electron.
>> Yeah. >> As opposed to-
>> And I guess the
>> What he asks is,
in a material sense what is a hole.
And I guess the answer is.
If you want a chemical explanation it's a keri.
>> So if you remove an electron from an organic material you have a radical keri.
And this is what a hole is.
>> It's a little special in this case because normally the host
fixed up the hands and in this case the host can actually move.
But generally the whole moves by a movement of electrons.
So there's a hole and there's an electron next to it
on the keri that drops in there and the hole's somewhere else.
So, you always have- and that's how the hole moves.
And it is I suppose the whole electron picture is an extraction.
And it makes it easier to rationalize how the demise works.
>> Okay, the next question here is related to PIDA PSS and
what happens when it's in a humid area.
So will there be a difference in lifetime whereas for seashore or
dry conditions for example?
Good question and it also depends a lot on the PIDA.
PIDA does not own PIDA.
PIDA is a chain from two commercial sources today.
[FOREIGN] And they have several different brands, visitors,
types of PIDA and aside from the PIDA PSS there's a lot of other stuff and
this other stuff is actually worn in different ways.
There are some facts and there are cross figures.
There's a lot of different things and so the answer is a clear yes.
There is certainly an interaction between water PIDA.
And it has certainly affected, affecting the performance.
Sometimes a very dry PIDA in some case and
that is what we deliberately explore is not good.
PIDA likes to have a little residual water.
And that's an advantage in some cases that there is a little water.
So it can actually tolerate some more presence of water.
Of course we are not talking liquid.
We are talking to very low degrees.
And what we observed is using a PIDA reading.
Actually a humid environment is not, if it's packaged and
you are allowed to equilibrate the humid surrounding.
It's actually a situation for this.
Continuities affect the water.
There's a lot of things water affects.
Adhesion, and certainly if water gets into the cell, it will be destroyed.
This is the case for
this carbon based feed that you will receive throughout this course.
That has a PIDA lakeshore leading up to the main contact.
And if water gets in here the PIDA will absorb more water and the cell will
suck basically water into itself and it will be animated into itself.
Of course there's humidity and then there's liquid water.
Humidity to certain levels, so dissolved water molecules didn't work.
So you have this tolerable to a certain level.
>> I guess a follow up question could be what are good and
bad environments for opds in general?
So I guess if you have them by the seaside you'd see corrosion of the contacts of
the salt in the air and >> We are close to sea here and
we don't see any effect of sea spray on the context and
in the case if Fred didn't finish it where everything is sea.
You might see something at the very quite context but
it don't matter whether the source.
But we had in a past made experiments also corroborated in the Netherlands,
also close to the sea.
There we see that we had a proper contact error.
So we see in grace of providers.
Over here we see growth of copper chloride or the hydroxy carbonate.
[NOISE] [INAUDIBLE].
>> Yeah.
>> What happened?
[INAUDIBLE] >> Okay, so no file.
>> [INAUDIBLE] >> [LAUGH]
>> [INAUDIBLE]
>> Okay, so we are safe again.
>> Sorry for the interruption.
>> Did I finish that one up?
>> Yeah, at least for that part.
I guess we can broaden it a little bit more.
Maybe we can go through, what a bad environment.
>> The contact points, where the electron.
>> An electronic connection is made into the.
This is always a tricky point.
Because you normally have a path for ingress of water and
the necessary components at this point.
And this is really a weak spot.
And that is what in the infinity concept,
this is completely soft because we have no contact.
All the connections are made in Tyramid.
It's only at the ends that we make the contact, and
this is a pretty sealed contact over a large area around its bot.
And for small liquid water is a bad environment around the contact especially.
And generally or
otherwise on the surface of the cell we would not seem to present such a problem.
Then another environment is cause temperature.
The higher the temperature, the more stability [INAUDIBLE].
So above 65 degrees they start to gain an appreciable degradation at.
And I guess temperature swings would also be a problem.
>> Yes, mechanically,
mechanical isolation and the [INAUDIBLE] yeah,
okay there's a question, directly related to this, what about dust particles?
So I guess a layer on.
>> Yeah, I mean of course that will shadow,
harshly shadow a scattering of see.
>> In the infinity pack,
we would have a bird colony [INAUDIBLE] large particles that it drops off birds.
They have cause, they are in surface.
But we also have dust on columns.
That sort of thing.
And there we actually see up to a ten percent loss from this dust and
column stock, and then when it's rain, it washes off and
we can see the problems coming back.
And then you have a new layer of dust that you need.
So there's always this going up and down for dust, and
this is not only [INAUDIBLE].
It's also well known for that big installation.
That's [INAUDIBLE] seems to be that dust is really a killer for your phones.
>> Out of the question, yes, actually, how does it compare to.
>> For example so you can tell us.
>> Except that perhaps the organic
is better.
[INAUDIBLE]
Generally, of course.
[INAUDIBLE] >> [INAUDIBLE]
>> [INAUDIBLE]
>> Applied to the entire service.
>> [CROSSTALK] Yeah.
>> I guess the most optimum issue would even have sort
of a after effect of coding.
>> It does.
[CROSSTALK] [INAUDIBLE] >> [INAUDIBLE] particles and so on.
>> [INAUDIBLE] >> It does become quite complicated.
>> It is something you have to accept if you put things,
something outside that is subject to the environment.
Yeah, exactly, and.
>> This part of, they said it would be extreme dust.
In a country like Denmark, you would be happy that it rained sometimes.
Or it would get washed.
>> Yeah, okay.
We have a few more questions here on my piece of paper,
and you are still welcome to write questions in.
Let's take the broad one I have here.
Do you see a future for OPV and energy production or the grid?
So of course we have to sort of a demonstration of this but
of course it's still just a demonstration.
What is missing and so on.
>> I mean I'm starting to think that they, future is.
The question is how big does your power plant
have to be to make it a profitable business?
you know that goes beyond wind energy and hydro power,
and nuclear power, and natural gas.
Its also a question right now could you imagine
if you made a power plant based you would be replacing natural gas or
carbon based all plants.
And this is a good deal.
But later on when if you are replacing some already renewable source,
then you are starting to compare the impact of.
We don't actually know yet
the impact as compared to many of your other, [INAUDIBLE.
And here I'm talking not only the just the impact but
during processing and decommissioning.
Could be that the area is a to get rid of
I don't think it is the case, but even if it were, then he wouldn't be a good
idea in [INAUDIBLE], but it might be a decent idea today.
Because we can place this up even worse.
Something on sight it was [INAUDIBLE].
>> Okay. There is a question here
that's a little bit specific, but it's that's a good question.
So when we have the solar part, we have this huge [molecule
with] hundred cells, thousands of connected cells.
[CROSSTALK] >> Yeah.
>> Exactly.
So what happens, first of all, do cells degrade at different rates and
what would happen if a single cell degraded?
That's a very good question.
We've seen where due to mechanical things,
some cells have been destroyed [INAUDIBLE] and nothing happens.
We lose [INAUDIBLE] but it's not something.
We can not measure that losing one of [INAUDIBLE] as long as it sill conducts.
What is catastrophic is if you break the connection.
You have to remember that you are looking at,
you have an overall field of ten kilowatts and you are trying to break this circuit.
We will have ten kilowatts develop over that spot when we break it.
Depends on where you break it and
it's like a Christmas tree with all the lights off so you couldn't see it.
And a big large truck is in the biggest spot, so
normally observe is that abduction is forced through such and such.
So what's the [INAUDIBLE] falls.
We have observed for instance that they simply became [INAUDIBLE].
So the current simply flowing by burning the soap.
And then the whole module works.
And then happy ever after without you could say
that the fact that the organic sources we have built in
that is inherently included in the But
in city councils, the modules can only employ
eye cast eyes to counteract the standard model.
And that's not the way to answer the earlier question on why.
>> Yeah, what you actually do with the, with the city.
Okay, another part of the same question was,
when you have a bad or degraded cell, can you then see it?
Does it change color?
Is there anything you can visually see to identify it?
>> We're talking the solar part.
We're actually not seeing anything.
This changes in the.
Normally generally what you see with the cell that has
for instance.
Basically see the color has become less [INAUDIBLE].
Some of you have had paint stuff, color stuff,
that doesn't look so good on the side that is [INAUDIBLE] by the sun.
Maybe you even knew [INAUDIBLE].
>> Okay, next question here I think we might have touched upon this
in a previous live session, but let's just take it once again.
So the question is, do you have any experience of using biological
systems, and the example here is bacterial [INAUDIBLE] mobilized
[INAUDIBLE] polymers to manufacture [INAUDIBLE].
So can we have something that's I mean I think we, I understand the motivation.
>> It's inspiration from nature that demonstratively works well.
For millions of years or billions.
But in this case we would like a stable cell.
That is sustaining itself and if the biological system.
What at least biology found out was that organic
materials are not suited to exposure to sun for long periods of time.
So instead of solving this degradations issue they maintained the diversity of
the molecules, and they solved the problem of degradation by
repair mechanisms where they can simply replace the molecules after the turnover.
A good example is leaves on trees,
they stay green all summer because they are repaired all the time.
And the moment the tree reaches ultimate size,
that now it no longer wants to repairing the leaf, they go brown and fall off.
So many of these dye materials that are available, each are for.
There are a few that could be generally.
They don't have for solar cells.
>> Okay. I think the next question here really
comes well into, as an extension of this,
so it goes around what do we do with the old we had?
Can they be absolved by nature, are they biologically degradable?
Do we have to separate the materials, can we incinerate them?
What do we do with them?
>> Well, at the moment we, the ones we have that works we ship as we [INAUDIBLE].
And then if you are looking at the recycling efforts
where we have a project where we actually taking down solar cells,
and then we are trying to recover a special silicon inside the cell.
And so basically by shredding them
we've done this experiment several times already.
Now the solar cell module of a [INAUDIBLE] we let it reduce the amount of energy that
we put into its making pile.
At least once sometimes up to effective two we've done.
So paid itself back twice and then we take it down.
We shred it, we re extract [INAUDIBLE] and this will give you away.
High yield is [INAUDIBLE] around 95% of the we can extract [INAUDIBLE] and
the rest is more or less, we get a fraction of plastic,
which is 99 more than 99.9% of the weight.
That increasing could be burned.
It is unlikely that it can be used for solar cells.
Pure pt is might be used for clothing or something like that.
I'm sure the quality has degraded so it will not be a reusable source.
And there's also this, from the various.
So I think the majority of single basic and incinerate the rest.
>> [CROSSTALK] Yeah, and
then if you can elaborate we also have the carbon based cells.
>> I sent to you all course their they're [INAUDIBLE].
So they are simply- >> [INAUDIBLE] [CROSSTALK]
>> But it says.
>> Yeah. >> [INAUDIBLE].
>> The clear majority is the carbon based ones.
>> Yeah.
>> There's a few generations that we should.
But anyway the carbon versions is, of course, it can just be incinerated or
[INAUDIBLE].
>> There is a follow-up question here, can we use, I guess, carbon instead of silver?
>> Yes, but I don't then I don't.
I'd rather go [INAUDIBLE] than just use carbon instead of-
>> Yeah.
>> Because copper is marginally poorer conductor than silver.
Silver is the best metallic conductor.
Copper isn't nearly as good.
Copper has the problem that it oxidizes more readily.
It is not conducting oxide.
[INAUDIBLE].
So I don't see any advantages of using copper.
[INAUDIBLE].
And I would rather just use carbon.
We have too many compromising [INAUDIBLE].
>> Okay, I think we are almost running out of questions, so
you have a last chance now to type them in.
And in the mean time we'll talk a little bit about energy storage, because of
course when we have new technology we cannot produce energy on demand.
So energy storage will be a major issue in the future.
Do you have any comments on this?
>> The storage is an issue and I think they are many ideas for storage.
A good example is hydropower.
Where you have electricity you pump water up into a much taller, much higher.
Where you can re extract it, where you are simply water.
That's a very good way of storage.
And even though the technology is not is also imagine
turn it into solar electricity into a chemical.
And then there's batteries.
And batteries today.
I think the scale that is required for batteries,
today's batteries are not a solution.
As we see in our energy needs.
>> Yeah, it could be used,
of course, if we get [INAUDIBLE] being more available than this.
A lot of energy could be placed there.
>> Yes.
>> But yeah, of course, what we can say is that this
is something that needs to be developed along the energy-producing technologies.
>> Okay. I don't see anymore questions coming in so
that means will be rounding off, and I think will just go out with you,
and you can say what you have for feelings for this course.
Start from [INAUDIBLE] >> I think it's been a great experience.
>> Thank you all for having.
So whether you participated and follow this course,
I think we've had a lot of good questions on and also.
And I think it really shows we have a motivated audience and
set of participants so it's been a great experience for us at.
And we'll certainly do it again.
And we also learned a lot.
And we will improve.
We can see a lot of places where maybe some of the topics we found very
difficult, more difficult than others.
Some of it was as expected, but both we were surprised.
Both respect to what you found easy and what you found difficult.
In this of course we will readjust.
And this is bound to develop this further [INAUDIBLE].
I think I will add onto this is that people have many different issues.
So what some people find really easy will be hard for others.
And this course is quite general, so
there will be parts that are not easy to everybody and
parts that will be really hard to some and we will try and optimize this.
We'll go through the forums, look at all your comments, and try and
do improvements based on all of this.
Again, it's handed over to me.
>> [INAUDIBLE]
>> I think about 10,000 have participated
in this, 20,000 in this study and this is mind boggling that
so many people have invested time in this and I'm grateful for that.
>> Yeah we can see that the statistics we have we had people from 179 countries
sign up so we're covering >> A lot more than 90% of
all the countries in the world so at this we are really proud of.
I don't know if you have some closing remarks Eva.
>> Yeah, I'd like to thank you all for
joining our course, it's been nice to have you here.
And also for the We say.
>> And the application assignment?
>> Application assignment, yes.
Thank you [INAUDIBLE].
And it's a lot of great ideas [INAUDIBLE].
Well go through them and perhaps [INAUDIBLE].
>> Okay.
Okay. So
I can see a lot of people are writing thank you, so thank you again.
>> Have a nice summer.
>> Thanks. Yeah.
Bye.
>> Bye.
[INAUDIBLE]
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