All right, welcome back, remind you where we are. We're talking about storage is one tool to ease grid integration of variable renewables as we just talked about storage and batteries aren't the same thing. Batteries are type of storage and the vast bulk over 90 of energy storage that's actually functioning and electricity systems today worldwide is pumped hydro, not batteries. So let's talk about pumped hydro because you may not even heard about it. It just has very low visibility. Here's what pumped hydro looks like. It's a photo of one where essentially you have a high reservoir, a low reservoir and a pipe in between. It's pretty simple conceptually. So how does that work? Here's a schematic, a pumped hydro sometimes called pump storage, but pumped hydro is a better term because it does involve hydro is the hydropower plant, hydropower power plant that can actually go both ways. It can be a pump or turban. So, here's a typical operating scenario in the daytime, when electricity is needed, water flows downhill through the turbines producing electricity the same way a regular hydropower plant would work. But at nighttime in this example, water is pumped uphill. It's usually the same turban that turns the other direction, though not always designs vary. Water is pumped uphill to the reservoir for tomorrow. In this example, the collected the example implies an electricity system with excess capacity at night, with power plants or wind turbines that producing electricity for which there isn't a need. So it's stored stored in the form of water that's moved uphill. And the Typical round trip efficiency is roughly 80 meaning of the electricity that goes into this pump type system. Overall, only 80 comes out as electricity. The other 20 is lost as he Well, why would you do that? Why would you have a device that just consumes electricity? Well, because it's storing it's time shifting the availability of that electricity. Here's a slightly more complex of schematic where you have your high reservoir and your low reservoir, you have an intake here. And when generating electricity, water flows downhill by gravity. When you're charging up this storage device, it's going uphill and you have your turban pump unit. That again, is a, is a regular turban when in in generating mode and acts as a pump, putting border uphill when you're in charging mode. So that's the schematic and here's an example Of a pump fire station near my university in the us state of Colorado was built in 1967. And in fact, many pumped hydro plant at least North America were built in the 1960s and 1970s when it was just just the thing to do. And it has a capacity of 324 megawatts, meaning it could provide that much power when called upon and generally it's charged at night. So water's pumped uphill at night. It turns out in, in this utility system, the wind blows strongly at night and the utility has a lot of wind power on their system. So they use some of that wind power to pump water uphill and during the day, particularly in the summer, when there's large air conditioning or space cooling demand, the water flows downhill round trip proficiency of this system, not exactly clear, but it's probably about 75%. It's not it's an older system with somewhat older turbines. So if you were to build that today, you could build a slightly more efficient system, though not hugely more efficient. And I've taken students on tours of this plan. It's quite interesting. When we were there, their system operator was showing us the lower reservoir which is right outside the control room and essentially we were there midday and the system operators got a call for generation. They had pumped the water uphill the night before But the system needed that 324 MW. And while we were there they essentially opened up the valves and got the turban turning And you can feel the building shake and you could, we were starting, the turbines were generating over 300 megawatts and you could actually see the water level on the lower reservoir start to rise. That's very interesting system and conceptually pretty straightforward. Mm There is a some areas of the world are building a lot of new pumped storage hydro. This shows global installations, cumulative capacity by geographic region from 2006 to 2016. And you'll notice the thick black line in the US pretty static. We have about 20 gigawatts called 22 GW and that has changed very little. The EU is by far the leader in terms Of capacity if, if you consider you as a whole with 40 some gigawatts growing slowly. But the most striking trend on this graph is china, which is rapidly building a pump storage because as you, as you probably know, their electricity demand as a country is increasing very rapidly. And one of the way they're meeting that is with pump storage because they're also building a lot of wind and solar PV. Now, pump storage like any technology as good as good and advantages and disadvantages. Some of the advantages of pumped hydro, I'll just mention here it's an established technology, this is essentially a turban. The tidal turbines have been installed and have been reliable since for at least 100 years. So there's a lot of technical, technological or technical maturity, very low technical risk. We've been doing this for 50 years, we know how to do this. Not much technological risk or operational risk. The round trip efficiency, reasonable 75, 80, maybe a little better. Maybe a little higher than 80 at best large volume storage and long storage period. So you can start a lot of electricity and you can let it all downhill rapidly if you need a lot of power or more slowly if you want to have a lot of energy, I'll talk about that distinction just a minute. It lasts a long time. As long as you maintain it, you have to ensure for example, not a lot of silting in the reservoirs, but that durability is quite good and good start stop flexibility. It can ramp up quickly. Minutes we talked about earlier hydro gramps quickly so it can play that role. But it has disadvantages they all do. Geographic is probably the largest need to find a site two areas where you could install large water reservoirs and they need to be a significant height differential. And there's just many places where that, it's just not possible large. Similar related as a large footprint. This isn't a tiny little thing. By the time you add up the size of the reservoirs, you are occupying a fair bit of land, it's high initial investment costs. It does cost a lot to build this. That's what are called Civil Works. You've got, if there's not a reservoir there, you've got to dig one out. That's a lot of work. You've got to run the pipe in between. So there's a lot of costs for then civil works pouring of concrete digging of holes laying the pipe. Environmental concerns, you're disturbing a lot of land. You're creating a reservoir where perhaps there wasn't one prior to that operationally. The environmental concerns are moderate because nothing is being consumed or burnt. You don't have deliveries of fuel, but in the installation there are definitely environmental impacts. So that's the pump tiger up story.