Energy Storage Solutions

Page first edition 2/12/2013.

Background

The massive advantage fossil fuels have is that their energy density is very high. They can be easily transported great distances and then stored for years at a time. People have become used to that level of convenience and for renewable energy to win in the market it needs to match it. This page is about showing that it is possible.

Battery systems

The lead acid battery is presently the dominant choice for backing up PV and wind power. However, the Edison battery is technically a much better choice. It can be left completely flat without any damage. It can be fully discharged any number of times without shortening its long life. Although the nickel in it makes it several times the price of a lead acid battery, it last many times longer. Like so many renewable energy technologies, it requires a large up-front investment, and patience is required to reap the benefits.

We can learn from the Edison battery and dramatically cut its cost. That is one of my main projects. Please contact me if you are interested to get involved.

The super-grid

One solution gaining some serious attention at last is the super-grid. The wind is always blowing and sun is always shining somewhere. Using high voltage DC (HVDC) systems there are already a number of examples around the world where power from major dams is transmitted hundreds of kilometers. It is not cheap but when agreement is reached that the need is great enough the super-grid could be built.

Pumped hydro

The dominant storage technology used today is pumped hydro. Two dams are connected so that when there is excess power the water from the lower dam is pumped to the higher dam. When there is a shortage of power the water flows the other way. These systems are 80 to 90% efficient and can respond to rapid power demand changes very quickly. The problem is that there is a shortage of sites where they can be built. The energy island (sea dam) concept could provide a huge boost to total energy storage capacity.

In areas with good hydro electric resources, the use of this power could be made more variable. There is already a move to install more generating capacity on existing dams because it can be done relatively easily. The dams will then be emptied faster when the power is need but when it is not the water will be saved.

CAES

Compressed air energy storage (CAES) is another potentially economical system. Most work has considered using old disused mines as space in which to store the high pressure air. Compressing air makes it hot so unless a good system to remove or store that heat is developed efficiency is poor. Seamus Garvey has proposed a system of putting gas bags deep under water to overcome the problems of variable pressure, and improve turnaround efficiency, possibly to 85%. Thin Red Line Aerospace have built special 20m diameter air bags that when filled 600m below the water's surface will store 70MWh of energy. The capital cost of a pumped hydro system typically comes to £50/kWh and some are claiming CAES could be about 10 times less. Batteries are currently about 10 times more, but have greater efficiency.

Flywheels

Heavy flywheels installed in below-ground bunkers are another promising idea. Their advantages are excellent short-term efficiency and sufficient speed of response to keep grid voltage and frequency completely stable. Energy density is expensive to build this way so their niche market will be supplying power while slower responding systems like gas turbines start up. Beacon Power is one example of a company pursuing this.

Fresh water

Many places are experiencing serious fresh water shortages. The supply of energy from many renewable resources is variable and hard to predict. Considering these 2 problems together reveals a solution that solves both problems. Desalinating sea water requires a large amount of energy but having produced the fresh water it can be stored for long periods until needed. Therefore, if the capacity of our renewable energy sources was increased beyond our average energy needs we could use the periods of excess energy to desalinate saline water resources that are otherwise useless to us. This, in combination with the extensive HVDC network discussed above, would ensure that we always have power when we need it.

The next essay in the main sequence is Global warming