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Energy storage plant Print E-mail

The Hungarian grid system is striving with system regulations problems for years. One of the gravest worries is that the night demand is below of the production of the basic power stations with continuous operation (see Figure no. 1). In case of the basic power stations – first of all in case of the nuclear power plants - the interrupted operation may cause heavy expenditure together with the decreasing of the equipments` life cycle.    

 



Figure no. 1: Characteristic load curve for a summer working day (2006.)

 

The other problem besides the low night demand is the daily peak supply at system level while preserving the appropriate security reserves. Figure no. 2 shows that the peak gross reserve of the Hungarian energy system in 2006 was on more than one occasion behind the prescribed security reserve of the service.

 

 


Figure no. 2: Peak gross reserve (2006.)

 

Because of the above mentioned the solving of the energy storage, the support of the project development related to the construction of storage capacities at system level is justified. The construction of storage capacities is justified furthermore because of the obligatory taking-over of the in recent years constructed cogeneration power plants` power supply, resp. the recently issued tender invitation for the construction of wind turbines with a total capacity of 410 MW above the already licensed 330 MW wind turbines capacity where the schedule can hard be maintained while the taking-over is obligatory as well.  

 

The intermittent nature of the wind causes serious problems in the system stability. This problem can be managed with the construction of energy storage facilities; its application assists to maintain the schedule and allows that wind turbines become an appropriate alternative against the traditional base and peak power stations. 

 

In case of a 3-6 hours storage of the power produced by a wind farm planned at any location of the country while the electric energy demand is low and the utilization of the stored energy during the daily peak assists to solve the regulation troubles in case of that wind farm as the energy storage facility operates as a consumer during the storage.

 

The construction of an energy storage facility with pilot plant dimensions can already be suitable to collect experiences to manage these regulation troubles for example based on the improvement of the adaptability of the wind turbines at system level and on the improvement of holding the schedule. 6 MWh energy can be stored with a 1 MW net capacity energy storage facility after 6 hours operation during deep valley and low demand and in my opinion the operation experiences of a sample investment of this kind can be utilized in the energy system of the country as well.    

 

Taken into consideration Hungary’s geological potentialities and the likely social support 2 (two) energy storage technologies can be applied out of the different energy storage technologies applicable for power storage:

·         Hydrogen (H2) technology based on Hydrolysis, or

·         Other chemical technologies.   

 

1.) In the field of the H2 hydrolysis technology it is Norsk Hydro/Norway who undertook pioneer works. The idea of the Hydrogen (H2) storage plant is fairly new; no sample can be found at plant scale in the world yet. In case of its application the storage facility uses the power from the grid for the hydrogen production because of the hydrolysis. The produced hydrogen will be stored at 50 bars thereafter it will used in a gas turbine to produce power which shall be fed into the system during the peak period.  

 

 The security of the system increases with the application of the Hydrogen (H2) storage plant and it assists the application the renewable energy sources at system level as well. There exists a pilot plant constructed by Norsk Hydro in Utsira/Norway where the intermittent production of the wind turbines shall be smoothed out by hydrogen production in accordance with the demands and the gas engine manufacturer posses a similar reference as well. (See Figure no.3) 

 

 

 

 

Figure no. 3: Hydrogen based gas engine power and drink water production system

 

The weak point of the technology is, that the actually in energetic dimensions manufactured gas engines possessing references as well do not suit to proper hydrogen heating but only in case of mixing 15-20 mass % of natural gas to the hydrogen. In case of their application nitrogen-oxide (less, than in case of natural gas heating) and stream will be produced in small quantities only, and these do not pollute the environment, rather they can be utilized again in case of getting back to the natural water circulation of the earth.    

 

2.) In case of chemical storage using different chemical technologies the energy storage system is based on the construction of batteries taking over the power either from the wind farms or from the grid during valley, or deep valley periods and stores it in form of chemical energy then using regenerative fuel cells of different chemical elements such as vanadium phosphor, etc. converts it to power with the assistance of oxidation or reduction processes.   

 

The construction of the system is shown on Figure no. 4. This electron taking-over process generates the power, which will then be collected and transferred by the electrodes. It is natural, that the filling process is a reversed one.

 

 

Figure no. 4: Chemical storage process

 

This and similar technologies like the energy storage facilities constructed by VRB/Canada, or Xtreme Power/USA can be supplied in power station dimensions (1-10 MW) already. While planning the power storage system the fuel cell’s dimensions shall decide the production and the electrolyte tank the storage capacity.

 

Comparing the two technologies following may be said:

 

a.) the examined technologies correspond to each other in respect of electric operation and clearing of accounts, as the storage facilities shall supply the power to the 20 kV bus of the wind farms with the assistance of cable connecting transformers in both case.      

 

b.) While the hydrogen storage plant is fairly new, the other chemical storage facilities have been used in case of wind farms already.  

 

 c.) Both energy storage technologies are environment-friendly, but in case of the hydrogen technology the natural gas supply has to be secured because of the gas turbine operation.

 

d.) The electric efficiency of the hydrogen storage is about 30-35%, while in case of the other chemical storages it is worth to about 65-70%, ie. roughly the double of the hydrogen storage. 

 

e.) the starting and production changing periods are shorter in case of the other chemical storage technologies, ie the smoothing of the schedule changes, the maintaining the schedules are easier in case of the other chemical storage technologies than in case of the hydrogen based storage.  

 

Taken into consideration the above a 0” emission energy production can be realized with the application of a technology like the above mentioned should it be connected to wind turbines. It is important to know, that the investment of an energy storage facility with 1 MW net capacity and 6 MWh production takes about 31 months upon after the clarification of all questions related to the funding and the total investment cost is worth to about EUR 7,2-7,5 Million. An investment of this kind secures jobs as well, as the construction and the operation will secure 20-30 continuous jobs and they do not require special qualification.

 

Summarisation:    

 

The capacity plan elaborated by the System operator provides a picture of the shutting down of old power stations and presents when and in what mass new power station units` start-up shall be needed.

 

While elaborating it the increasing demand for the utilization of renewable energy and the support of the utilization was not known yet. For that reason it predicted only 800 MW wind turbine capacity up to 2020. Because of the obligatory taking-over of the power produced by the increasing number of cogeneration power stations and wind turbines with intermittent nature it has to find a solution for increasing the downwards regulation reserves. 

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To solve the regulation problems there are several methods. The pumping station storage principle is not new, but because of the geological and environment problems it takes a long process incl. the necessary planning and permit procedure. Similar difficulties do not come forward in case of chemical storage and their application assists to solve the deep valley regulation problems, as it operates then as a consumer.   

 

In case of combined application of wind turbines and chemical storage a 0” emission energy production can be realized, which deserves the attention because of the global climate change and assists in managing the schedule problems important because of the system stability.

 

The energy storage assists that power station of intermittent nature – like the operation of the wind turbines – supply power to the grid the same way like the operation of the traditional base and peak power stations. Their application allows that the wind turbines be appropriate alternatives to the traditional fossil power plants as the power produced by the utilization of wind energy will reach the grid the same way like in case of the traditional power plants. 

 

 

Groniewsky Erik

GEST-COM Bt.


 
 
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