# Would it be realistic to store energy using gravity by elevating buildings?

The basic idea is that a building (house, business, etc...) would be on a type of foundation that would allow it to be lifted into the air (not by a lot, I'm thinking inches at most) to store energy that is created by a renewable source. The building would slowly and very minutely raise as energy is created. When the energy needs to be used it would then be lowered and use a flywheel or another method to power a generator and convert the energy into electricity.

Would this be possible with current technology? What reasons would prevent this from being possible/practical (money, materials, design, legality, ect...)?

• If you have a fly wheel why bother with moving the house, just make the flywheel bigger. – user25818 Jan 10 '17 at 23:16
• Or, take your idea but instead of elevating the house, elevate a large tank of water. That would remove all the challenges in John Feltz' answer. Pump the water to an upper tank with energy as it is generated, and let it flow to the lower tank as it is needed. Oops we have just re-invented hydro power which was patented 136 years ago. I like your thinking but it's just completely unnecessary complexity – Darren H Jan 11 '17 at 4:32
• FYI there is deconstruction method for buildings that generate part of the electricity they need by moving down the materials. – Antzi Jan 11 '17 at 6:01
• Gravity is commonly used, but its usually water that is pumped into a reservoir on a mountain/hill. This water is then used to drive a turbine when it flows downhill when energy is needed. You could use it in a building as well, by adding a large tank on the top of the building. But engineering is much simpler when doing it on a mountain... – Polygnome Jan 11 '17 at 13:06
• @notstoreboughtdirt that's the issue you cannot simply upscale flywheels (neither diameter nor its rpm - both are relevant for the energy stored). It's limited by the structural strength of the materials available. – Ghanima Jan 11 '17 at 22:37

We have done experiments with gravity energy storage using trains loaded with rocks in the southwest US.

I can see several drawbacks to your suggestion.

## Plumbing and other utilities

You'd need to make all your utility connections flexible enough to deal with this change in elevation.

## Walking in and out of the house

The last step into the house is now going to be different, and people are going to misjudge the distance, fall, and break bones.

## System failure

What if one corner of the building sticks in the high position and the other corners drop? Now the entire thing is crooked.

## Fatigue

All this up and down means something is going to wear out sooner or later, and then break. Fixing the foundation of a building is hard, expensive, and disruptive work.

## Capacity

I don't think you're going to get enough work out of the system to justify manufacturing and maintaining all the mechanical parts to do this. Lifting 20 tons by 6 inches (15 cm) gives you a potential energy of 7.4 Watt-hours. Not KILOWATT-hours, Watt-hours. That's only enough to run a really efficient LED light bulb for a couple of hours.

• Yup, gravity storage is only really practical if you can raise a lot of weight - and in this context, "a lot" is preferably measured in millions of tons, e.g. it works if you can raise a full lake (as in pumped hydro stations), but a mere house is too tiny and light. – Peteris Jan 10 '17 at 22:59
• @Peteris also a lot of height – Chris H Jan 11 '17 at 8:52
• – Mołot Jan 11 '17 at 10:36
• @Cakchas maybe it's just me but I would assume being featured on something called "Grand Designs" implies it's actually much harder than you would think. – Devsman Jan 11 '17 at 13:39
• @Devsman Grand Designs is a UK TV show, they are looking at things people do with houses with an emphasis on "cool" or "unusual" rather than "technically difficult". en.wikipedia.org/wiki/Grand_Designs – Tim B Jan 11 '17 at 15:17

This idea is an application of Compress Air Energy Storage. CAES provides a reasonable method to store energy, but the idea of using buildings to provide the weight has associated challenges which would be less than ideal.

## Insufficient Pressure

In short, a house weighs too little. Solutions involving mines will typically store air at up to 1100PSI. By comparison, the ground that a house lays on typically has a maximum bearing pressure of 43.51PSI (300kN/m^2). That represents a huge discrepancy is capacity and efficiency. Building on bedrock would increase capability, but the logistics of building a compressible air chamber on top of bedrock AND constructing a large building on top of it would be extreme.

## It Would Destroy the Building

In this situation the building is effectively sitting on a large, inflatable balloon. Since the balloon must be collapsable, it means that load shifting within the building would impact which side of the building pushes further into the balloon. At worst (which is very realistic) this could lead to a catastrophic failure, with the building tipping over. At best the building will experience constant re-settling, which would destroy the foundation and all stiff components of the building.

## Other Problems

There would be other logistic issues with such a building, like plumbing, electrical wiring, transpiration of goods and people, etc. I think that those challenges could be overcome with some careful thought, but the cost of installing the highly specialized solutions would vastly outstrip any potential cost savings associated with energy storage.

The cost of building such a building could be high. In general, buildings don't move, so we can make some assumptions about what sort of structure is needed. For example, if your slab cracks, you don't have to worry about your house falling. You just have to worry about termintes.

However, the general idea of lifting things for power is reasonable. Pumped Storage Hydroelectricity is being used in several places. In this system, you store energy by pumping water uphill, and then release it by letting the pump run backwards and generating electricity. In areas where there's no convenient hill, there has been exploration into storing the water in a plastic bag-like container and putting that container under a large volume of sand. Sand is easy to come by, and as you store power, you fill the bag, lifting the sand. That sounds similar to your building solution. The only difference is that sand doesn't really mind being lifted up and down, while lifting a building comes with all sorts of challenges.

Both impractical and stores surprisingly little energy.

The energy stored is given as mgh where m is the mass of the house, h is the height and g is the gravitational acceleration of 9.8 m/s^2.

You can see from this expression that if you double the height, you can get the same energy with half the mass. Lets work through an example:

250 metric tons is a guesstimate for the weight of a house and the question calls for lifting it something like 5 inches or 13 cm. With these numbers we arrive at:

250 tons * 13 cm * 9.8 m/s^2 = 289 kiloJoule.


This is enough to light an old-fashioned 60watt lightbulb for 1.3 hours:

60 watt * 1.3 hours = 281 kiloJoule


How about alternative methods? A standard water tower is about 40 metres high. To get the same potential energy in the water you'd need:

0.8 tons * 40 m * 9.8 m/s^2 = 284 kilo Joule.


0.8 tons of water is 726 litres, equal in volume to a cube with sides of length 90cm (35inches). This is more of a water "mast" than a "tower". Far simpler than lifting a house, but still only a tiny bit of energy.

Conclusion: We think of "lifting a house" as a gigantic effort, but cooking your dinner takes more energy!

It would be possible

I am certain that this would be possible but what you should be asking is "Why would we use this method instead of pumped hydro?".

Really the only reason for this is when there is no other water/material/substance nearby which you could use to store gravitational potential energy.

The only reason I can see for this would be Ecumenopolis. So in answer to your questions

Would this be possible with current technology? What reasons would prevent this from being possible/practical (money, materials, design, legality, ect...)?

I would say the only thing stopping it is the fact that there are nicer, safer and easier options for those of us on planet Earth. If you lived on Ecumenopolis then it might well be a viable energy storage solution.

• Or you could do this: aresnorthamerica.com Fill trains full of concrete and run them up a mountain during off peak, then when power is needed let them go down the hill and use the brakes as generators. Useful if you have no water. – Ben Jan 12 '17 at 12:21
• @Ben My scenario requires there to be no to be very limited space. I think this would take up too much room. Did you mean to comment on the question? – josh Jan 12 '17 at 12:55

This would be possible, but pointless.

Houses have relatively low density, but can have sensitive structural integrity, so you would have to have cleverly placed supporters to prevent their foundations from bending and crashing from the weight. They are also connected to the ground with many pipes and cables, including water, GAS, electricity and internet.

So it's much more practical, to use water fore gravity based energy storage, wich is an alreadsy existing technology.

Yes we can - we just have to think big, big, BIG!

As other answers have already pointed out, lifting a puny house for only a few inches or so allows to save only a very limited amount of energy. So think bigger, don't go for houses, go for a whole town. Heindl's Gravity Storage has already sorted it out for us.

The fundamental idea of the hydraulic potential energy store is based on the hydraulic lifting of a very large rock mass using water pumps. The rock mass acquires potential energy and can release this energy when the water that is under pressure is discharged back through a turbine.

The decisive variable with such energy storage lies in the storage capacity. If a piston is selected for the Gravity Storage having a radius r and a length l=2r, then the piston can be lifted to the height h=r. The height h=r results from the consideration that the seal must lie somewhat above the center of gravity, thus at a distance r above the bottom of the cylinder so that the cylinder is hydrostatically stable while floating.

The storage capacity E is given by the density ρr of the rock and the density ρw of water, and the gravitational acceleration g:

E = (2ρr - 3/2ρw)πgr^4


Key is the r to the fourth here. The larger the radius of the piston the absurdly higher the storage capacity gets (double the radius, increase the capacity by 16 times)... and at the same time construction effort is expected to increase only with a lower power of radius.

This has two important consequences. First, the storage capacity can increase 16-fold by doubling the radius, and second, the construction costs only increase by approximately the square of the radius. Therefore due to geometrical rules, the relative cost per energy unit decreases proportionally to 1/r².

Multiple GWh for diameters of a few hundred meters are easily achievable.

Bonus: You get yourself a fine tourist attraction too.

• Sloppy math. If the piston has radius r and length proportional to radius then material cost alone will scale with r^3. – Taemyr Jan 12 '17 at 8:58
• @Taemyr you misunderstood. The material is the existing rock itself. Thus there is no such thing as material cost scaling with the volume. They assume construction cost mainly necessary to cut that rock "in-place" and for the infrastructure (water supply, pumps, generators, seals, ...). I know it's a back-of-an-envelope calculation only but hey, as part of a story or so it is certainly believable enough ;) – Ghanima Jan 12 '17 at 9:04
• The key being r of "a few hundred meters". This means a cylinder with a height of 2 x 'a few hundred meters' has to be cut from the rock ... in one piece ... with a gap underneath to pump the water into ... and the size of the cut cannot be too large, so how are you going to get all that plant machinery down under the cylinder? – Evil Dog Pie Jan 12 '17 at 11:03
• @MikeofSST, yes. I think that this is very well "science based". The author of that original article outlines that this idea (albeit somewhat megalomaniac) is very well within realistic engineering approaches and technologies we have available. The Gravity Storage will be built using methods and techniques already known from the mining and tunneling industry.. You know, drilling tunnels, mining, and putting heavy machinery beneath the surface of the earth is a real thing... and this is Worldbuilding not Physics.SE ;) – Ghanima Jan 12 '17 at 11:30
• @Ghanima The largest tunnel boring machine has a diameter of 17.4 m and bores a hole, rather than taking a core. In addition to the practicality of cutting the cylinder, the pressure exerted by 100 m of grantite (r = 50 m) is approximate 27.5 bar (400 psi). The block would need a seal all the way around its 314 m circumference, capable of withstanding this pressure. We do not have the mining or tunnelling technology to do this, let alone the mechanical sealing technology. Not by a very long way. – Evil Dog Pie Jan 12 '17 at 12:00

Since the purpose is to create energy, I assume the flywheel is designed to be attached to an electric generator. Using the flywheel means the axel will generate resistance at the connection points that hold the flywheel in place. How about instead, generate the electricity using magnetism directly on the poles that the house slides down? (By the way, if someone actually develops this, I want credit)

Electricity can be generated by moving a metal past a magnet. This is how a generator works...a wheel of magnets circle around a metal case(or vice versa) and the magnetic field causes the metal case to generate electricity.

In my idea, as the house' magnetic base slides down the metal poles, it would generate electricity on the metal poles. By removing the resistance of a flywheel, you eliminate moving parts that can wear out quickly, and also eliminate a source of wasted energy. As an added benefit, as the house is returned to the upper position, it would also generate electricity.