Energy Storage

This blog is about how EDM can help the penetration of renewable energy sources into the electricity grid in Ireland. Another facilitator of renewable energy penetration is energy storage. For example, currently, there is significant interest in pumped hydro storage in Ireland. I have added the URL of the Electricity Storage Association to the blogroll of this site. This URL lists the many options for electricity storage and draws comparisons between them.

It would seem from the analysis that compressed air energy storage (CAES) is an option that might also deserve investigation in the Irish context. This technology uses underground mines or natural caverns to store large volumes of compressed air. During times of surplus electrical energy, air is pumped into the cavern. When electricity is required, the compressed air is used to improve the efficiency of a gas fired turbine.

Off the south coast of Cork in Ireland is the Kinsale gas field which is operated by Marathon. For full details read the following PDF.

The Kinsale field is now nearly spent and is being used as a natural gas storage facility. The Seven Heads gas field which extends further into the Atlantic uses the pipline and infrastructure of the Kinsale field to land the gas on shore. I began to wonder could the Kinsale gas field infrastructure be used to implement a CAES system. I decided to send the following email to Marathon’s press officers.


Dear Linda, Robert,

I would appreciate it if you could supply an answer to a technical question, please.

Question Background:  Ireland has a major problem with wind energy penetration due to the variable supply nature of wind generated electricity. Energy demand management (EDM) or energy storage, preferably both, are required to solve the problem. As I understand it, Ireland has 2GW of planning permissions for wind turbines for which grid connections are not possible for reasons of grid instability. I am interested in EDM and energy storage. While researching the technologies behind energy storage I grew a particular interest in the viability of compressed air energy storage (CAES). This form of energy storage is used in conjunction with natural gas to increase turbine efficiency. What is required is a large sealed natural cavern that can be used to store compressed air.

Question: I understand that the Marathon south west gas field, in Ireland, is now being used for gas storage. Could it be used for compressed air storage to help solve Ireland’s wind energy penetration problem?

I would appreciate your feedback on this issue. Please let me know if I can reprint your reply on my blog

Kindest Regards



I look forward to publishing their reply.

19th August 2007

I havn’t heard back from Marathon. I’ll try more local contacts and I will publish whatever reply I get. I think that natural gas wells may not be suitable for CAES because mixing air and natural gas makes an explosive mixture.

In the meantime I found the following two references to the two oldest CAES projects in existance.

Huntorf, Germany

McIntosh, USA

Embedded Generation Synergy Module (EGSM) test laboratory.

In my last blog I gave an outline of how I am putting the infrastructure into my home to turn it into an off peak synergy module laboratory. I am also developing a test site for embedded generation synergy module (EGSM) concepts. To get full details on the overall project please visit

The normal electrical load at the CIX data centre will be around 550kW. I am planning to put a 1.1MW multi-fuel grid synchronised generator into the CIX data centre. That generator will be controlled by an EGSM and will in effect turn the data centre into a grid stabilisation device capable of either sourcing or sinking approximately 550kW.

CIX will have a 10kV grid connect and a UPS system that will enable it to ride through any power variations that will occur moving from site power consumption to site power generation.

By running the generator on bio-diesel or PPO it is possible to make CIX a carbon neutral data centre. By using the embedded generation capacity in the data centre, CIX will be facilitating the penetartion of wind energy into the Irish electrical grid by improving grid stability.

Off Peak Synergy Module (OPSM) test laboratory.

I am planning to turn my home into a little energy test laboratory so I can experiment with Off Peak Synergy Module concepts at the domestic scale. I have installed a 500 litre insulated stainless steel tank to store hot potable water. I will install a further 1000 litre insulated tank to store central heating water. These tanks mean that I can store enough hot water for one day for both washing and central heating.

I will install a large solar panel to heat the water in both tanks. I will supplement this solar heating with a water to water heat exchanger which will be electrically operated using off peak energy. In the winter this heat exchanger will take heat from a glass covered swimming pool. In the summer, after both tanks are full of hot water any surplus heat will be transferred to the swimming pool.

Karen and I bought this house nearly two years ago and it has oil fired heating which I will now replace. Living in the country, I have access to waste timber so I bought a wood burning stove and installed it in our living room. In return for some work this will give about another 5kW of heat for evenings where the heat pump cannot cope with very cold weather.

It takes 1kW to raise 1 litre of water one degree C in one second. Therefore a 3kW output heat pump would require 167 seconds to raise the temperature of the water in the tank by 1 degree C.  This means that a 3kW energy supply would require about 2.5 hours to raise the water in the tank by 50 degrees C. Therefore this potable water tank can be seen as a 7.5kWh energy storage device. Our larger water tank for heating can be seen to store 15kWh of energy.

I drive a Toyota Prius car. I am interested in various articles that talk about plug in hybrids and I plan to purchase a kit to convert my hybrid to a plug in. I then expect my Synergy Module to charge my car each night with low cost electricity.

As Ireland has an abundance of sites for commercial wind energy exploitation, I see no ecological advantage to installing a wind turbine at my home. However if PV solar panels drop in price I am hoping that my Synergy Module may trade some high cost day time electricity for low cost night time electricity and reduce my overall energy bills.

Supply and Demand of Electricity

The following graphs contain the actual electricity demand and actual wind energy demand curves for 16th February 2007 for Ireland. The third in the series plots the percentage of the national grid that was supplied on that day by wind energy. The raw information was downloaded from the archives of, the Transmission System Operator (TSO) in Ireland.

You can see that wind production went from nearly 20% of demand to almost 0% of demand in one day and worse of all was the fact that it did so completely out of sync with the demand usage curve. Wind energy supply and electricity demand were not matched. This mismatch creates difficulties for network operators because, apart from limited pumped hydro storage capability, electricity cannot be stored and it takes time to start and stop fossil fuel burning electricity burning stations. Also, because of the unreliability of supply, it is necessary to have enough non wind based capacity to meet maximum demand.

Despite the green credentials of wind energy there are problems with its implementation. If wind energy production, in Ireland, is to rise higher than its current 4%. We will have to implement either pumped hydro storage or demand management. Demand management is cheaper and faster to implement and I believe it is the necessary option for Ireland. Perhaps there is a place for pumped hydro storage also.

Current pumped hydro storage capacity in Ireland.

As far as I am aware, there is only one pumped hydro storage facility in Ireland. This is located at Turlough Hill

Current demand management projects in Ireland.

The following pdf presentation gives an overview of current EDM schemes in Ireland.

An Irish Solution to an Irish Problem

Ireland has a unique characteristic from an energy perspective.  We have the best wind energy of any location in the world but we are unable to exploit it because of the mismatch between demand and supply. There is no flexibility in wind energy supply and to date there is very little flexibility in electricity demand. This problem is very well described in ‘Pumped Hydro Energy Storage to Support Wind Energy Penetration in Ireland’. Currently this paper is available at :

Recently there has been significant interest in and investigation of pumped hydro energy storage in Ireland. I have not heard mention of the the use of energy demand management (EDM).

There are two organisation in the USA to support professionals and companies involved in energy demand management :-

  1. The Peak Load Management Alliance
  2. Demand Response and Advanced Metering Coalition

The most publicly visible commercial organisations in the US involved in EDM are EnerNOC Inc. ( and Comverge Inc. ( Enernoc currently claim to have 650MW of customer owned diesel generator power under their control for grid stabilisation. Comverge claim to have 4.5 million demand management modules installed.

Although there is a place for both, I believe that EDM is a better solution for grid stabilisation, than pumped hydro, in Ireland for three reasons:

  1. It has very low capital cost because it uses existing resources
  2. It does not have the losses (typically 20-25%) or capacity limitation of pumped hydro
  3. It can contribute to carbon emissions reduction when combined with a bio-diesel / FAME/ PPO project