- Trying to figure out why Norway's plant failed eventually led me here.

Here we are, the junkiest possible version of this setup.

But I had to start simple.

Two beakers of water at the same temperature, 18.2.

But when I pour one into the other, I was expecting to see a small temperature increase here because one of these beakers had salt water in it.

What are we getting?

Instead I saw nothing, at least not on this thermometer.

Anything?

But there is energy to be harvested here.

In theory where a river meets the ocean, you could get as much energy out of that fresh water and salt water mixing.

It went down.

As you could from a 200-meter waterfall.

In fact, in the early 2000s, Norway built a plant to try and harness that energy of mixing using osmosis.

And honestly, when I first heard about this, I thought it was kind of scammy.

But this is not the story of a large publicly owned company falling for a hoax energy technology.

It's the story of how sometimes the transition from chemistry to chemical engineering just fails.

Oh (beep).

This is dialysis tubing.

It's made of cellulose.

And if you throw it under the microscope, we can see lots of little pores.

Water, and lots of other ions, and small molecules can pass through this.

Ah, gloves.

But proteins and sugar molecules cannot.

This thing I'm holding is called a thistle tube, and I covered up one end with dialysis tubing, flipped it over and filled it up with a two molar sucrose solution and some food coloring just so it's easier to see.

And then I dunked the whole thing into a beaker of distilled water.

Sure looks like nothing is happening.

And now, we wait.

(chimes tinkling) This is osmosis.

Water is flowing from an area with nothing dissolved in it to an area with lots of stuff dissolved in it.

And all that water moving across the membrane raises the water level higher and higher up the tube.

And it's important to note the water is doing work.

Look how far it has lifted all this weight of water above the waterline.

This is a good probably five, six centimeters from where it started.

And now, unlike making mercury imperceptibly rise in a thermometer, this work we might actually be able to do something with.

And now, I wanna take a stab at generating power using osmosis, kind of the same way the Statkraft plant did.

Spinning a turbine by mixing fresh water and salt water.

Dialysis tubing does not prevent salt from passing through it.

So we need a membrane that does.

This is DuPont FilmTec SW30.

And no, this video is not sponsored.

I paid $20 for this.

$20.

This expensive membrane blocks salt.

So now, I just need an osmosis test cell to put it in.

I could buy one.

You know what?

I'm gonna make my own.

(grunting) I made this out of food service and toilet parts.

(bright upbeat music) So step one is to just confirm that I can even do osmosis with this thing.

This is my test cell.

It saved me about $1,500.

This is leaking.

No, this is leaking.

- No.

That's leaking.

- How's that leaking?

Take two, using different food service and toilet parts.

Wow.

So this is my osmosis test rig, and it might save me $1,500 if it actually works.

(bright upbeat music continues) Now, theoretically, water should move from here to here, which should increase the level in this tube and decrease the level in this tube.

And now, again, we wait.

I'll know for certain if the water level goes past the L on this (laughs) printed tube.

Oh wait, yeah, no, this is actually, this is...

Okay, now I can actually say this is working.

I know it doesn't seem like much, (laughs) but it is working.

Here we are 45 minutes later, a full centimeter I think (laughs) of salt water, sea water up our tube.

That sounds wrong.

Though obviously this is very slow.

But just because it's slow doesn't mean we can't get power out of this.

Now the question is, can I get enough power to push a very small piston?

(bright upbeat music continues) We've got distilled water in the beaker.

We have got salt water in this section right here and in the syringe.

And theoretically, the distilled water should push through the membrane and push our syringe, AKA our piston upwards.

And now, we wait some more.

(slide whistle whistling) Wow, that actually worked.

And you know what?

Even better than I thought it would.

Low bar, but it worked.

Now, I wanna see how much pressure the water is exerting here.

I know the osmotic pressure of seawater is up there in the hundreds of PSI.

So we should have been getting somewhere in there.

So now I'm confused.

Take two, using a different pressure gauge.

Whoa, hey!

Wow.

I was getting somewhere around 350 kilopascals, which is impressive, but only a little over 10% of the actual osmotic pressure of seawater.

Which raises the question, where does all that pressure come from?

Every textbook says that osmosis is just diffusion across a membrane.

But some experiments in the 1950s showed that diffusion alone is not nearly enough to explain the pressures you get out of osmosis.

But we've actually had the correct explanation since 1923, which is this.

Because the membrane is impermeable to salt, salt ions bounce off of it, which ends up creating lower pressure here.

And the higher pressure pure water on the other side rushes in through the membrane to relieve that imbalance.

The membrane is the key here.

So can I use all that pressure to generate some power in my creepy basement?

I bought the smallest turbine I could find.

This converts water flow to electricity.

(inhales deeply) (air hissing) Oh, yeah.

In theory, the pressure I get from my test rig should be plenty to spin this turbine, but unfortunately, the rig doesn't produce nearly enough flow rate to spin the turbine.

So I need to supplement it.

I've got a five gallon bucket of water up here that is connected up to the line from my osmosis rig from here, and then both of them flow through the turbine.

You might think this is cheating, but it's actually very similar to the design used in the Statkraft plant.

I'm using gravity.

The plant in Norway used a pressure exchanger to help keep the turbine spinning.

And in theory, you should get more power out of the turbine than you put into the pressure exchanger or then I exerted lifting this bucket on top of the ladder.

(grunting) But when you factor in the energy of filtering all the junk out of river water and sea water, pumping both into your facility, constantly cleaning and eventually replacing kilometers of membrane, inefficiency in your turbine, and who knows what else, you are very likely to be using up more energy than you produced.

And while Statkraft was developing their plant, wind and solar were becoming so much cheaper that maybe it didn't make financial sense for them to keep trying anymore.

Of course, I asked them why they shut down and they declined to answer, which is a shame because what they learned could be very useful for, say making desalination plants more efficient.

So I'm gonna keep developing this technology right here with my food service and toilet parts.

Hmm.

And my first attempt went about as well as you would expect.

This turbine is not moving.

So take two, using a different pressure source.

Here we are, the junkiest possible version of this setup.

And we are getting four volts.

Now, let's add osmosis to the mix.

Here we go.

On.

There's not a substantial additional voltage.

In fact, now we're dropping.

Now we're just dropping.

We're going down.

Shockingly, amazingly, stunningly, this junkiest thing I've ever built did not work.

What a surprise.

Still working on it.

It's coming.

It's gonna happen one day.

Every Earth Month, PBS releases a slate of new episodes celebrating our planet, and we wanted to tell you about the latest episode of Weathered, which explores what has been called the most important unanswered question in climate science.

Wanna find out what it is?

Links to their latest episode and the full Earth Month playlist are in the description.