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The new thinking in energy storage – creating a solar bank

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What if households could deposit excess solar output in an “energy bank”, and use it to drawn down when needed or loan energy to others.

There is no doubt that rooftop solar systems are seen as a threat to incumbent utilities – be they they generators suffering from lower demand or network operators finding their business model under threat.

Most of the scenarios generated for the development of rooftop solar, such as that by the CSIRO Future Grid forum, suggest the development of in-home battery storage that could enable householders to shift their peaks, store energy for night-time or even, one day, go off grid.

But another proposal involves a different way of thinking about this – using storage, in this case compressed air, to create a sort of “solar bank” that would allow householders to deposit surplus electricity, and either draw down for their own use or lend it out to others.

solar bank

Just connect them to the bank.

The proposal comes from General Compression, a Boston-based company which is developing and trialling technology that allows excess output to be stored as compressed air in large caverns.

General Compression argues that its proposal avoids the pitfalls of rooftop solar created when too much strain in put on the network when the sun goes down, or from too much electricity being sent back to the grid.

But what if a single bulk energy storage facility could act like a bank for thousands of distributed solar system owners, suggests Peter Rood, the development manager from General Compression.

A network connected storage project would allow multiple customers to “deposit” energy into the bank during the day when they have excess generation and later “withdraw” that energy when the sun goes down.

He says that low cost of bulk storage – estimated at around one quarter of the megawatt hour cost of batteries, combined with a pay-for-use model would allow easy access to storage for customers – and allow the network to benefit from the fast responding ancillary services provided by the storage system.

Like a bank, not every customer would demand their stored energy be withdrawn at the same time and unused energy from the storage facility could be “loaned” during peak periods and later repaid during off-peak periods. This would further off-sett the cost of the facility and increasing the benefits to the network.

Rood says this would help networks because it would maintain their relationship with customers – which others have pointed out is under threat from rising network costs, falling solar and battery prices, and unchanging and inflexible business models.

And it would provide access to low cost storage to distributed solar owners and avoid individual households having excess capacity at each location. As mentioned before, general Compression sees CAES at one quarter the cost of batteries.

If such a system were introduced, it would probably require the rules of the market to be re-written, and the roles and responsibility of the storage facility operator, the network operator and the electricity retailer would need to be defined.

Note: Certain market rules and regulations may require revision to allow for the creation of the business model described in this section. In particular the roles and responsibilities of the storage facility operator, network operator, and retailer need to be defined.

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  • Rob

    An energy storage bank is definitely an idea with potential! ( Sorry, that was an unintentional pun! ) It gives people who generate their own electricity, in most cases from solar PV, a number of reasons to stay connected to the grid. Something which the electricity grid owner/operators should be extremely interested in, if they wish to remain relevant to energy users into the future. In the not too distant future people will have the choice of leaving the grid altogether, assuming they have enough space for the storage system. This could be devastating for those with an interest in keeping the grid going. An energy storage bank on the other hand could result in a win/win situation for both users and suppliers. Assuming the terms are fair and reasonable! Why bother getting home energy storage, which would be limited in its capacity, when you can just bank your excess. ( once again, assuming the terms are fair and reasonable! ) Our home has a 1.48 kW solar PV system on the roof. We have had it for just over 3 years and in that time it has generated just under 1400 kWhs more than what we have used. Admittedly we have been paid for this surplus ( which could be banked to pay for future electricity ) but it might have been better value to have it stored for the future. Say for when we get an electric car that needs charging overnight. Home storage systems will be limited in their capacity to store your excess energy whereas community energy storage banks would be able to account for all your excess energy. There would no doubt be advantages for the grid overall to have that large amount of energy stored and standing by, as well as enabling renewables to more easily mesh with the existing system.

  • Motorshack

    According to Wikipedia, a practical CAES system might have an energy density of about 100 kJoules per KG, which is equivalent to 27 watt-hours per KG, so the storage of one KWH will take about 40 KG of equipment, give or take. To store 5 KWH would take a facility roughly on the order of a small closet full of SCUBA tanks – assuming I have not made any math errors.

    The article also points out that one of the main engineering challenges is that the pressure drops as the container empties, so a generator would have to be able to accommodate that change, which adds significant complexity to the design.

    Another challenge is that compressing air heats it, and decompressing cools it, and that behavior needs to be managed carefully also.

    Still, the costs are reportedly on a par with lead acid battery systems, and are potentially lower over the long term.

    My point is that it might also be worth exploring CAES systems sized for individual households, even though a centralized facility for a whole neighborhood might be a more efficient proposition.

  • Ian

    To make the electricity grid relevant in the future this idea of the grid providing energy banking services could be extended to providing transmission services. A fee could be charged for transmitting energy from a persons point of production such as the home to their point of storage or consumption such as the electric vehicle parked at work . Renters could generate electricity at a community solar garden and then store this on the grid for use at a convenient time at some distant point to their rented accommodation. An farmer could set up a reasonably large solar farm inland and sell the electricity to an industrial user in a city. In this situation the grid operator could provide a transmission and storage service at a fee to either the farmer or the industrial user. Generators large and small could sell electricity on the grid and storage operators could do the same. Community storage facilities in a warehousing situation could house individual’s battery systems under this scenario. There are many opportunities with this kind of exchange. Consumers could take advantage of very cheap electricity during peak production times for heating and cooling with thermal storage, or charge their battery systems for later sale of electricity when generation of power is reduced and electricty prices are high.