Good question, it doesn't really need to be, those numbers are partly just to visualize it. But we do have some reasons to keep it with more surface area:
- less digging
- less reinforcing needed - it's more stable
- In some cases we're interested in floating solar on top of the reservoir which wouldn't work well if the reservoir was too deep.
But it's certainly not out of the question to go deeper instead.
yup! More fun facts about a 1 km head height... Off-the-shelf turbines are actually spec'd for a max head height of something closer to .5 km. So the design calls for a double-drop. This design approach is taken from the DOE research linked on our website.
Hmm, I think what you're alluding to is that pumped hydro is about 70-85% efficient and Li-ion is sometimes quoted at 100% efficient (in theory). But here are some more details.
In reality, when Li-ion batteries are installed in a large system, I believe the round-trip efficiency is quoted much closer to PHS. Sorry, i can't find the best research to cite right now, but here are a couple sources i found with a quick search.
I've heard that Li-ion installations can get up to 90-95% round trip, which is fantastic, and better than PHS for sure. But it's not the most important detail in the equation. Here's why:
One thing to remember is that power is lost all over the system in conversion and transmission. So raw efficiency can be less important than getting the right capacity to the right place on the grid. And that brings us to cost.
Even though PHS is a little less efficient than Li-ion, 85% for PHS is still really good. (see other my other comment below about 70% vs 85%) And the math shows that investing in PHS is simply cheaper -- even after assuming that Li-ion will drop in price by 3x in the coming decades. This is partly because Li-ion has a much shorter life span and needs to be replaced about every decade.
Li-ion is still great and super important! But it's not looking like the best contender right now for grid-scale storage.
Thanks to the commenter below who posted the link to the paper. Yes please! If you want to email me I'd love to see how we could work together. eric at terramenthq.com or syllablehq.com
If we attach our installation to an existing reservoir, we'll take up nearly zero land above ground. If we build a new self-contained upper reservoir it will be about 0.5 miles on each side and 40 feet deep. It can be built with material excavated from the lower reservoir. This may seem large, but it's for a huge amount of storage 20GWh - enough to balance the load of a large city. And keep in mind that it's about the same size of the many large reservoirs that are scattered around a large city.
Again, the most promising option would be to simply attach our installation to an existing reservoir. We don't use any additional water, we just borrow it. For an ample sized reservoir, each cycle would just raise and lower the water level by an inch or so. Another promising option is that we can even use the ocean as an upper reservoir. Salt water can be accommodated -- See our notes about the Okinawa Yanbaru Station.
There are more details in our white paper posted on the website.
I love this quote:
Hydro pumped storage is “astoundingly efficient…In this future world where we want renewables to get 20%, 30%, or 50% of our electricity generation, you need pumped hydro storage. It’s an incredible opportunity.”
– U.S. Energy Secretary Dr. Steven Chu in 2009. Still true today.
And actually, we think that 80-85% round trip is more accurate for our projects because we'll use the latest/greatest tech (variable-speed reversible francis style pump/generator turbines). I think the 70% from these figures is citing older projects with pump/turbines that were not quite as efficient.
Thanks! Yes, and our research agrees that the short-life of Li-ion is a problem, and it's one of the reasons why we believe our solution has so much more promise than Li-ion for grid scale storage.
The pump/turbine technology we use is the same that's been used for a hundred plus years for traditional pumped hydro dams, and the maintenance cost is very low. The life of a project is 40+ years. And in reality it can be 100 years with relatively low amount of maintenance. The San Diego County research posted on our website has good figures on this. thanks!
If you want to send me research supporting some of your thoughts here then I'd love to see it. I do know for example that it's a very valid debate whether or not nuclear has a place in our climate fight.
I'll try to re-work the language in my materials to make sure I'm not excluding other valid viewpoints. Thanks!
Solving the world's trillion-dollar energy storage crisis. (multi-trillion, actually.)
https://www.terramenthq.com/
About a year ago, I started spending more time researching about climate change. I learned how important energy storage will be to enable renewable energy to displace fossil fuels. The more I read, the more fascinated I became with the idea of building underground pumped hydro energy storage. I found a research paper from the U.S. DOE written in 1984 showing that the idea was perfectly feasible and affordable, but it seems that nearly everyone has forgotten about it since. (they didn't build it at the time because the demand wasn't there yet. Now energy storage demand is growing exponentially)
A year later, I'm applying for grant funding to get it built. I know that nearly everyone will tell me I can't do it because this or that reason. Because people don't like change and they're scared of big things even if the research shows it makes perfect sense. But I'm doing it anyways because no one else is getting it done. The idea is too compelling and too important to ignore. So here goes nothing!
There is so much important and inspiring work to do in the world. It might take some energy to find it, but I think it will be rewarding if you do. It sounds like you have an amazing opportunity to find this work because you have a financial cushion to fall back on. So good luck in finding it! You could start by just seeking out people to talk to who you think are doing important work. Maybe don't worry about whether there's a job in it or if it even feels related to technology. Chances are those conversations could inspire you to do something you can't picture yet. Maybe an entrepreneurial opportunity. Everything needs technology these days after all. Good luck!
But it's certainly not out of the question to go deeper instead.