Israel’s Arothron gets inspired by the pufferfish for a novel type of underwater energy storage system using compressed air.
Arothron was established in 2011 as an enterprise focused on underwater compressed air energy storage (UWCAES). Arothron is named after a type of pufferfish which can inflate its body into a spherical shape. This Israel-based company’s mascot helps us understand how underwater compressed air storage works. Underwater compressed air energy storage has several advantages. The first is that it can be used wherever there is a deep body of water. Some large Mideastern cities meet this criteria. The second is that because deep water is under high pressure, the containers needn’t be made of high strength steel or rock. Ordinary concrete or even plastic bladders can be used as an underwater compressed air storage tank.
But first, let me explain how electrical storage can make our grid more efficient.
The World Factbook estimates that Egypt’s per capita electrical consumption averages 154 Watts. For Saudi Arabia it is 733 and for Qatar it’s 1263. Since solar panel prices have fallen to less than $1/Watt, an investment of $150-1500 in solar panels per person should meet demand. But now we’re comparing peak solar output with average consumer demand.
What happens if a hot night raises consumption at a time when solar production is zero?
Ask any utility expert whether they prefer wind, solar or coal power and they’ll probably tell you that the first two have a lower capacity factor and are impractical for base load generation.
The output of wind, solar and other renewable energy sources varies over the course of a day and across a year. Consumption also varies in an unpredictable manner.
Energy storage can help fill the gaps between varying energy production and consumption. Many techniques have been tried. Batteries, flywheels, superconducting storage rings and other exotic methods have not yet proven themselves mature enough to compete in the real world.
Pumped storage hydro-power is promising, but it requires that a mountain and lake are conveniently located near the power plant.
Compressed air energy storage (CAES) is also a mature technology. It has been used in cities such as Paris, Dresden and Buenos Ares since the late nineteenth century. But scaling CAES to modern electricity demand is most practical when caverns, salt mines, or other large hollow geological structures are conveniently located.
Toronto based Hydrostor already has a bladder based UWCAS system under development as envisioned in this video:
[youtube http://www.youtube.com/watch?v=bWBQn7xVcwM&w=420&h=315]
Arothron intends to use ordinary concrete for the underwater pressure vessels. One advantage of UWCAS systems is that expanding air rising from the bottom of the sea should be cooler than ambient summer temperatures.
Because of this the “pollution” from a UWCAS storage plant could provide our cities with clean, cool air.
::Arothron
Image of pufferfish from Shutterstock; other schematics of underwater compressed air energy story from Arothron website
The principle of good.
You are forgetting the capacity factor of PV. If electricity is consumed at 154 Watts (for an average person), then 154 Watts of PV panels will not be able to meet this demand, since the sun is not always out. Given an average capacity factor of PV to be ~25%, you will need about 4 times the average demand to meet the installed PV capacity. Thus, you will need 600-6000 USD per person for PV panels to meet the demand. Also, you need a balance of systems (BOS) to convert the DC power of PV to AC and put it on the grid. The average BOS for large scale PV is another $1/Watt, and up to $2.5/Watt for residential. This will push up installed cost by another factor of two to three, to about 1500-15000 USD/person to meet demand. Once you have that excess PV installed, storage becomes a necessity.