I'm a little embarrassed that in all of the discussions I've heard about ways to store solar energy for dark periods, I never noticed that this kind of solution was omitted.
I wonder how it stacks up against the more commonly discussed approaches.
I wonder how it stacks up against the more commonly discussed approaches.
A previous discussion mentioned a heavy train being hoisted up and down a slope for the same effect - same problem. In addition to the weight you can shift being a fraction of a hydroelectric dam, you also have to deal with material maintenance and wear and tear, security, etc.
Water you can get it perfectly load matched. Here you get one concrete block lowered worth of energy and stopping midway has its own share of problems. Look at the mere 100MWh Tesla bank in Australia. They made millions per day and reduced power prices for consumers by millions as well. They did it by not only utterly cornered the power service market but managed to outrun the problem so well they weren't getting paid for all of them until the grid upped their sampling rate to deal with the unprecedented speed for a system that expected dispatched natrual gas turbines to be the fastest thing it would ever deal with.
I may be wrong and it may have a legitimate use but it would clearly need complimentary components to cover its flaws.
The problem is the linear relationship between the mass, the height, and the stored energy: energy = mass * height * gravitational-acceleration.
gravitational-acceleration is fixed at the earth's surface to ~10m/s2
So taking an example of 1,000,000 tons lifted up 100 meters:
energy = 1,000,000,000 (mass) * 100 (height) * 10 (gravity) = 1,000,000,000,000 Joules
This looks like a lot, but really isn't. It's equal to ~278 MWh (megawatt hours), which means it can supply 278 MWs for one hour. 278 MWs is equivalent to one small power station.
Note that the largest pumped-storage power station in the UK, which is of course constrained by exactly the same E = mgh formula, Dinorwig (https://en.wikipedia.org/wiki/Dinorwig_Power_Station) stores ~9,000 MWh.
Another way to consider this is to calculate how much mass needs lifting 100m to supply the whole of a country for a day.
As a very crude estimate the UK requires an average of about 30,000MW of electrical energy. Over a day this equals 30,000,000,000 * 24 3,600,000 Joules = 2.510^18 Joules per day.
The mass required to be lifted up 100m to store this is 2.510^18 / (100 10) = 2.510^15 Kg = 2.510^12 tons = 2,500,000,000,000 tons.
Which is many times more than the current global annual concrete production of 10,000,000,000 tons (ref: http://www.columbia.edu/cu/civileng/meyer/publications/publi...)
So... where do I sign up?
Why would the stresses be any greater than burying a turbine electric generator at the bottom of a hydroelectric dam? The forces would be similar, right? That's the whole point: it's just a crap load of "pressure" due to a bunch of stuff piled up on top.
Also concrete is not exactly environmentally friendly to make.
Anything heavy will work. I wonder about bags of stones & rubble, or earth itself. The challenge would be making such bags not break apart due to fall.
If they're falling and there's an impact at the end, something has already gone wrong.
When operating correctly, the descent is a smooth glide.
Think that through.
A dam probably holds 100 or 1000 tons of water for every ton of dam material.
A concrete weight holds exactly on ton of concrete for one ton of concrete weight material.
And "amount of weight helt", be it water or concrete, is Exactly what matters here.
You don't necessarily need a river to be involved at all for pumped storage. Just build two reservoirs at different heights.
Charge the cars during the day, and park them at the top at dusk. Then drive one downhill every hour at night, using regenerative braking to pull some of the potential-turned-kinetic energy into the battery as electricity. Then discharge the car into the grid. Descending the hills in east Auburn and Kent in WA State usually regenerate 400-500 Wh into my hybrid.
Gravitational potential batteries have less vampiric effects than chemical batteries, but still some possibility to suddenly discharge, in a landslide or similar event. And they are less efficient than hydroelectric, as another poster has pointed out.