Photovoltaic power plants as a renewable energy source have been receiving rapidly growing attention in the Czech Republic and in the other EU countries. This rapid development of photovoltaic sources is having a negative effect on the electricity power system control, because they depend on the weather conditions and provide a variable and unreliable supply of electric power. One way to reduce this effect is by accumulating electricity in hydrogen. The aim of this paper is to introduce hydrogen as a tool for regulating photovoltaic energy in island mode. A configuration has been designed for connecting households with the photovoltaic hybrid system, and a simulation model has been made in order to check the validity of this system. The simulation results provide energy flows and have been used for optimal sizing of real devices. An appropriate system can deliver energy in a stand-alone installation

Doucek, Aleš

Polák, Lukáš

Čermáková, Jiřina

Acta Polytechnica

English

Jiřina Čermáková

Aleš Doucek

Lukáš Polák

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Energy Accumulation by Hydrogen Technologies

CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)

Acta Polytechnica Vol. 52 No. 4/2012Energy Accumulation by Hydrogen TechnologiesJiˇrina Cˇerma´kova´1,2, Alesˇ Doucek1,2, Luka´sˇ Pola´k1,21Nuclear Research Institute, Department of Hydrogen Technologies, Husinec – Rˇezˇ 130, 250 68 Rˇezˇ, Czech Republic2Institute of Chemical Technology, Department of Gas, Coke and Air Protection,Technicka´ 5, 168 48 Praha, Czech RepublicCorrespondence to: cea@ujv.czAbstractPhotovoltaic power plants as a renewable energy source have been receiving rapidly growing attention in the CzechRepublic and in the other EU countries. This rapid development of photovoltaic sources is having a negative eﬀect onthe electricity power system control, because they depend on the weather conditions and provide a variable and unreliablesupply of electric power. One way to reduce this eﬀect is by accumulating electricity in hydrogen. The aim of this paperis to introduce hydrogen as a tool for regulating photovoltaic energy in island mode. A conﬁguration has been designedfor connecting households with the photovoltaic hybrid system, and a simulation model has been made in order to checkthe validity of this system. The simulation results provide energy ﬂows and have been used for optimal sizing of realdevices. An appropriate system can deliver energy in a stand-alone installation.Keywords: hydrogen, accumulation, photovoltaic.1 IntroductionThe main reasons for higher utilization of renew-able electricity sources are the ﬂuctuation of crudeoil prices and the limited supply of fossil resources,and also global warming, local pollution and con-tamination, geopolitical pressure, and the growth inpower consumption. Photovoltaic (PV) power plantsare one type of renewable electricity source. Photo-voltaic power plants produce practically zero emis-sions, but the amount of electricity that is produceddepends on the sunlight falling on the earth’s sur-face. PV power plants provide a variable and un-reliable supply of electric power over time, and thishas a negative impact on the operation of the electricpower system [1]. There are two ways to overcomethe variability in the output of photovoltaic powerplants. One is by transposing consumption into thetime when energy is available, while the other wayis accumulation. The only way to accumulate elec-tricity is by transforming it into another type of en-ergy, e.g. into hydrogen. Hydrogen as an energy car-rier enables photovoltaic energy produced in timesof excess power in the grid to be stored, and thensupplied to the grid when it is required, i.e., duringpeak periods in the daily load curve [2]. Anotherpossible way to use the hydrogen that is producedis as a fuel for vehicles. Hydrogen-fuelled vehicleshave several advantages over vehicles equipped withpetrol or diesel engines, especially ecological advan-tages.2 Solar energy storage byhydrogenFor obvious reasons, the production of electricityfrom PV panels is linked to the weather conditions,and is variable in the course of a day, a month, anda year. It is also unpredictable. An example of thedaily PV power proﬁle is shown in Figure 1. Thisload proﬁle does not correspond closely with the en-ergy requirements of an average household, which arerepresented in Figure 2. Energy requirements are un-stable, and they diﬀer between weekdays and week-ends. This discordance between energy productionand energy utilization can be dealt with by hydrogenaccumulation.The conﬁguration of the proposed PV layout andhydrogen equipment is shown in Figure 3. It consistsof the following components: PV panels, an elec-trolyzer, a fuel cell (FC), a hydrogen storage tank,and a battery [5]. The components represent the cur-rent state-of-the-art, and their parameters are pre-sented in Table 1. The photovoltaic power plant con-tains 56 polycrystalline PV panels with a total area ofabout 90 m2. A PEM (proton exchange membrane)electrolyte made by Hogen R© Company is used as theelectrolyzer. The electrolyzer is a fully integratedsystem that includes power supply, a hydrogen gasdryer and a heat exchanger, and it generates hydro-gen (0–1 m3/hr) at 13 bars. The hydrogen is storedin a low pressure tank. A PEM fuel cell made by39Acta Polytechnica Vol. 52 No. 4/2012Figure 1: Load proﬁle of electrical energy generated from PV panels, providing a power output of 12 kWp [3]Figure 2: Average household electricity use over the day for detached houses [4]Figure 3: Conﬁguration layoutTable 1: Parameters of the devicesDevice Characteristic ParametersPhotovoltaic power plant polycrystalline PV cell 12 kWp (230 W)Battery capacity Li-ion battery 45 Ah (2.2 kWh)Electrolyzer power PEM electrolyte 6.3 kWFuel cell PEM cell 4 kWH2 storage volume Low pressure tank 10 kg (5–15 bar)40Acta Polytechnica Vol. 52 No. 4/2012Fronius will be used as the fuel cell. A lithium-ionbattery has been chosen.The PV panels produce electrical power from thesolar source. Some the power that is produced isdirectly consumed by the electrolyzer that produceshydrogen. Hydrogen is stored in the low pressuretank for short-term or long-term storage. The dura-tion of storage depends on the requirements of thetargeted application, and on the amount of powerthat is generated. The stored hydrogen is used byFC to generate electricity, or can be utilized as a fuelfor cars. In our case, we will use the hydrogen fora hydrogen bus that we built and operate. The re-maining part of the power that is produced is storedin a Li-ion battery, which enables a rapid responseto ﬂuctuations in renewable energy generation, as itreleases power directly in response to a request fromend devices.A simulation model has been made in order tocheck the validity of the connection of the householdwith the photovoltaic hybrid system. The model,based on realistic photovoltaic production over thecourse of half a year (1. 4.–29. 9. 2011), and the con-sumption of a household, enabled the energy ﬂow tobe observed. The model is intended for a long-termevaluation of energy ﬂow, and batteries are thereforenot taken into consideration. The simulation resultshave been used for optimal sizing of each device, andwill be veriﬁed by an experimental system.The model was developed using Matlab/Simulink,and worked on the assumption that the photovoltaichybrid system covers the entire energy consumptionof the household, and in addition, it permits the saleof excess energy to the local electricity grid. Thefollowing input quantities are used:• Immediate power of the photovoltaic plant [kWe]• Immediate energy consumption of a household[kWe].The output data includes• Immediate fuel cell power [kWe]• Immediate hydrogen consumption [kg/hr]• Immediate electrolyzer power [kWe]• Immediate hydrogen production [kg/hr].3 ResultsThe simulation model addresses the optimum designof an integrated power system, when weather vari-ations co-exist with varying eﬃciency in the perfor-mance of the electrolyzer and the fuel cell. The aim isto meet the power demands for a targeted applicationunder a variable load schedule. The results obtainedfrom the simulation model are shown in Figures 4and 5. The data shows that the energy producedfrom the PV panels ﬁrst covers the household con-sumption, and then the rest of energy is used by theelectrolyzer, until the pressure in the hydrogen stor-age tank reaches a pre-speciﬁed pressure limit. Whenthe pressure in the storage tank is below this limit,hydrogen production is initiated in the electrolyzer inorder to ﬁll the tanks. When the pressure in the tankreaches the pre-speciﬁed limit, the excess of energyis sold to the local grid. The hydrogen production islimited to the pressure limit and the maximum powerof the electrolyzer (7 kW). The energy deﬁcit that isgenerated from lack of energy from the PV panelsis compensated by the use of hydrogen stored in thefuel cell, which produces electrical energy again.Figure 4: Results obtained from the simulation model41Acta Polytechnica Vol. 52 No. 4/2012Figure 5: Results obtained from the simulation modelOn the basis of an analysis of the energy ﬂowpatterns was made the following characteristic situa-tions:• Daily ordinary disproportion of the energy pro-duction from PV panels and the household en-ergy consumption; basically higher energy pro-duction around midday, and lack of energy pro-duction in the evening. This disproportionis covered by using hydrogen from the stor-age tank. Figures 4 and 5 show that thereis a requirement for about 0.3 kg of H2 perday.• Longer-term lack of energy production dueto unfavourable weather conditions; basicallythis period is not longer than 7–10 days.In this case, the required amount of storedH2 is higher, and is assessed at 2 kg ofH2. This amount of H2 proceeds from real-istic PV panel power data, which was mea-sured in the time period from 1. 4.–29. 9. 2011.We estimate that the required amount of H2will increase to 4 kg H2 in the winter pe-riod.Irrespective of our results, the experimental fa-cility constructed at the Nuclear Research Instituteis designed with a storage tank for 10 m3 of H2 un-der a working pressure of 5–15 bar. This volumeis equal to approximately 10 kg of usable hydrogen.This relatively large volume of hydrogen allows goodexperimental ﬂexibility. The parameters of the powerelectrolyzer and the fuel cell remain at the same level,7 kW for the power electrolyzer and 4 kW for the fuelcell.4 ConclusionThis paper has described a hybrid RES-based sys-tem, consisting of PV panels, an electrolyzer, a fuelcell and a hydrogen storage tank. In order the checkthe validity of this system, a simulation model wasmade, which is based on realistic photovoltaic pro-duction over a period of half a year. The results showtwo major discrepancies between energy productionand energy utilization: the daily ordinary dispropor-tion between energy is covered by 0.3 kg of H2, andthe long-term lack of energy is covered by 2 kg ofH2. The results indicate that this hybrid RES-basedsystem can deliver energy in a stand-alone installa-tion.AcknowledgementThis work received ﬁnancial support from MPOTIP FR-TI2/442.References[1] Giannakoudis, G., Papadopoulos, A. I., Se-ferlis, P., Voutetakis, S.: Optimum Design andOperation under Uncertainty of Power SystemsUsing Renewable Energy Sources and HydrogenStorage. In International Journal of HydrogenEnergy, 2010, Vol. 35, p. 872–891.[2] Moldrˇ´ık, P., Cva´lek, R.: Akumulace energie z fo-tovoltaiky do vod´ıku. In Elektrorevue, 2011. ISSN1213-1539.42Acta Polytechnica Vol. 52 No. 4/2012[3] Doucek, A.: Na´vrh technicke´ho rˇesˇen´ı pro vy´robuvod´ıku ze sola´rn´ı energie. Studie cˇ. U´JV-FR-TI2-442-2012-3, 2011, U´JV Rˇezˇ.[4] Wide´n, J., Lundh, M., Vassileva, I., Dahlquist, E.,Ellega, K., Wackelga, E.: Constructing LoadProﬁles for Household Electricity and Hot Wa-ter from Time-use Data — Modelling Approachand Validation. In Energy and Buildings, 2009,Vol. 41, p. 753–768.[5] Lagorsea, J., Simoesm, M. G., Miraouia, A.,Costergc, P.: Energy Cost Analysis of a Solar-hydrogen Hybrid Energy System for Stand-aloneApplications. In International Journal of Hydro-gen Energy, 2008, Vol. 33, p. 2 871–2879.43

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