Constant Pressure Compressed Air Storage

Reader Paul Blais sends us an interesting idea:

“I’ve been following your website for years and I like it very much. I’ve been reading your article from 2018 about off-grid compressed air energy storage and I’ve been thinking about a possible solution regarding the varying pressure problem which you mention about small scale, low pressure vessels.

What about using a constant pressure reservoir? My idea is to use a long airtight bag stored in a trench and covered with sand, that would inflate and deflate pushing the sand up and down. The height of the sand column would determine the inside pressure of the bag, which would remain constant across it’s whole inflation range. The sand would also act as a thermal mass, taking and restoring heat to the air.

I’ve read that similar storage ideas exist [1] but involve putting the bags deep underwater, which is not practical for off-grid purposes. Unlike a deep-water reservoir, a bag put under sand would not try to float, so there would be no need for complex anchors at the bottom.”

[1] http://euanmearns.com/a-review-of-underwater-compressed-air-storage/

Update. Reader Erich Wälde comments: 

> Unlike a deep-water reservoir, a bag put under sand would not try to float, so there would be no need for complex anchors at the bottom.

This is not entirely correct. The bag will work it’s way up! Around the edges some sand will always travel from “above” the bag to “below” the bag — unless the bag has considerable “flaps” around it, which will extend well into the neighboring area, i.e. complex anchoring, I’m afraid.

Other example: I bought a house several years back. In the garden there is an underground tank, which was used to store oil (heating). Heating was changed to use natural gas rather than oil, so the tank became unused. In order to fully abandon its operation, we had to get it cleaned out AND we had to show that the tank is not in the parking lot. If it were there, then it would have to be filled up with concrete or sand. Otherwise it would work it’s way up, very slowly, due to its buoyancy force. This is in Germany and local administration knows about each underground tank. Its well regulated.

So: You can’t trick physics 🙂

Battery Killers: Grid-Interactive Water Heaters

grid interactive water heatersGrid-interactive water heaters (GIWHs) add bidirectional control to electric resistance water heaters, allowing a utility or third-party aggregator to rapidly toggle them off and on. This functionality turns a fleet of water heaters into a flexible energy-storage medium, capable of increasing and decreasing the load on the grid on a second-by-second basis.

GIWHs are currently the least expensive form of energy storage available. Utilities can use fleets of grid-enabled water heaters for load shifting, demand response, arbitrage, ancillary services, or to respond to unexpected grid-stabilization events. Traditional dissemination of new water heater technology has been a painstakingly slow process, but water heater rental programs may greatly accelerate this process.

Read more: Battery Killers: How Water Heaters Have Evolved into Grid-Scale Energy-Storage Devices, David Podorson.

Related: How sustainable is stored sunlight?

Solar Powered Grain Mill

solar milling

“Graining cereal crops is a basic, century old business and it will continue to be as important as ever before for centuries to come. Before the age of oil grain milling was entirely based on renewable energy. It was either done by wind energy, hydropower, animals or manpower. For the last century the traditional grain milling has been mainly replaced by electricity and fuel driven milling.”

“The Solar PV Grain Mill works to the same principle like any conventional, electrically driven mill. The mill has a very efficient 3-phase AC motor which is directly coupled to the graining system. The main invention of the system is, and that makes it unique among PV systems, that it is a “direct drive system” without the need of batteries. The Solar PV generator converts solar radiation into electricity, and the generated electricity is directly feeding the motor drive. There are no additional conversion losses, such as energy storage losses in batteries, battery maintenance or replacement costs, which are a common problem in conventional Solar PV off-grid systems.”

Read More: Solar Milling. Via Engineering for Change.

I would like to add that the direct drive system also eliminates the high energy use caused by the production of the batteries, which can make solar PV off-grid systems everything but sustainable. Therefore, storing work instead of energy — the solar mill only operates when the sun shines — is a very interesting strategy in sunny regions.

Related:

The Energetic Implications of Energy Storage

“When renewable energy sources such as solar and wind farms generate more electricity than consumers need, storing the excess doesn’t always make sense. Large, grid-scale batteries capable of storing the extra electricity are resource-intensive and costly to manufacture and maintain — sometimes more so than the energy they’re used to store.”

The energetic implications of curtailing versus storing solar- and wind-generated electricity, Charles J. Barnhart et al, Energy & Environmental Science, Issue 10, 2013. Open access. Via Eurekalert and Yale Environment 360.

Rail Energy Storage

“ARES is a rail-based technology that stores energy by raising the elevation of mass against the force of gravity and recovering the stored energy as the mass is returned to its original location. Specifically, ARES energy storage technology employs a fleet of electric traction drive shuttle-trains, operating on a closed low-friction automated steel rail network to transport a field of heavy masses between two storage yards at different elevations.”

ares-energy-storage-3

[Read more…]

Archimedean Energy Storage

mechanical battery“Forget batteries with complex chemistries or precision-tuned flywheels. A growing number of energy storage start-ups are promoting the idea that the most economical, most expedient ways to store power revolve around harnessing the four elements of the ancient world: earth, air, water and fire.”

Read more: The most important man in energy storage? Try Archimedes.