Implementation of electrolysers in the power system as a load management mechanism

• Main Author: Troncoso, Enrique
• Published: Heriot-Watt University 2008
• Subjects: 621.31
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491294

A future power system with a large installed capacity of intermittent renewable power sources (RE) relative to its maximum system demand, also requires large capacities of controllable thermal power plant to cover periods of low RE generation. The most prominent example of intermittency is wind power, where natural fluctuations are challenging to achieve high penetrations, especially in islanded power systems. If high wind penetrations are to be realised, two carbon emissions problems associated with managing intermittency need to be addressed. Firstly, the requirement for flexible operation of back-up fossil-fuelled power plant increases with wind penetration in order to balance the intermittent supply with the time-varying demand. This results in a carbon penalty that increases with wind penetration. Secondly, if at any time wind power plant generation exceeds that which can be safely absorbed by the power system, some of the available RE input needs to be curtailed. The curtailment of wind generation inhibits the production of low-carbon electricity and penalizes efforts to achieve high wind penetrations. The value of wind penetration at which such measures need to be taken depends on the characteristics ofthe specific power system, but an islanded power system without significant interconnections is the most challenging to manage. Solutions are therefore required for regions of high wind resource to facilitate the achievement of high wind penetrations. The solution presented in this thesis is to deploy water electrolysers as controllable loads for load management exclusively in case of 'valley filling'. In combination with hydrogen storage systems, electrolysers can thus be used for hydrogen production both in the case of a fluctuating excess supply (e.g. during prolonged and rising RE generation) and during periods of low electricity demand. The supply of electricity becomes effectively decoupled from the demand in such a way that the operation of power plant depends less on consumer demand. An analysis is carried out to assess the mass implementation and operation of a stock of .electrolysers in combination with wind power plant (WPP) and zero-carbon thermal power plant (ZPP, e.g. nuclear, CO2-sequestered). Three electrolyser implementation cases were simulated for increasing WPP and ZPP penetrations and periods of different · d availability. The key objectives are: (i) increasing the penetrations of RE in the power system (by reducing wind energy curtailment); (ii) maximizing the efficiency of utilization of FPP (by maximizing the load factor of the aggregate FPP load profile, LFTH); and (iii) creating a source of zero/low-carbon hydrogen. A generic simulation tool, namely the AELM model, has been developed for implementing and controlling a large stock of electrolysers for an islanded power system. From power plant availability, demand and RE forecast profiles, the AELM model generates utilization strategies for the electrolyser stock, ZPP, WPP and FPP. Preferred capacity levels are obtained for the required stock of electrolysers as a function of the penetration of WPP and ZPP in the power system. Other general outputs are energy balances, hydrogen yields and carbon intensities for electricity and hydrogen for the time period analyzed. Results are presented for an isolated power system based on wind generation and demand data for Eastern Denmark. It is found that load management via electrolysers is an attractive option with the view of optimizing the operation of the power system. LFTH of up to 100% can be achieved (a virtually flat FPP load profile) at wind penetrations::::: 50% of system maximum demand (SMD). For high wind penetrations the electrolyser stock must include implementations close to WPP if wind curtailment is to be avoided. Results also indicate that the deployment of ZPP in addition to WPP is a considerable benefit. In particular much greater hydrogen yields and electrolyser utilization factors can be obtained especially on days of low wind availability, thus solving the main drawbacks of a pure wind-hydrogen (or more generally renewables-hydrogen) implementation. The key parameters of the analysis presented are system-specific, and the outcomes for different energy/power systems will be different. The intention is to establish a generic methodology and the boundary conditions for the deployment of a large electrolyser stock in any given power system. The approach presented could be a valuable tool in the decision-making processes towards more sustainable energy systems and eventually towards a prospective hydrogen economy.