A novel approach is presented to reduce the moisture content of biomass by employing a solar dryer. The impact of decreasing moisture contents on the key parameters of the system is investigated . Also , the effect of air mass flux on drying rate of biomass is evalu ated and discussed considering three alternative air mass flux rates as well as two different time period s for drying and discharging biomass , namely 15 and 30 minutes . Results demonstrate that by reducing the moisture of biomass, power output and efficien cy of the hybrid system have been improved from 265 kW and 30% efficiency up to 295 kW and 57.6% respectiv ely. The best efficiency performance of system is achieved by the 15 minutes drain time and air mass flux of 0.011 kgm−2s−1, while the best powe r generation of the system will be obtained by the 30 minutes drain time and air mass flux of 0.011 kg m−2s−1. Keywords : Biomass, Gasifier, Solar dryer, SOFC -GT, Performance analysis 1. Introduction Biomass has been considered a vit al energy resource on the earth . Based on sustainable development approaches, not only has it significant potential to enhance energy supplies in the world also it has a vast potential to be applied as an effective alternative strategy for supplying fuel and power generatio n [1]. Solid Oxide Fuel Cell (SOFC) is one of the most promising technologies for power production due to its great efficiency compared to rival technologies and its environmentally friendly energy production aspect. For d ecades, one of the most popular ideas in energy systems integration in the literature was the idea of SOFC and Gas Turbine (GT) integration . These integrated systems have been widely examined for Combined Heat and Power (CHP) applications because of their higher efficiency [2-6]. Several researches have studied biomass integration into SOFC -GT systems [7-13] and a variety of other novel biomass gasification systems have been integrated with SOFCs systems [14-18]. In addition, performance evaluation of an integrated biomass gasiﬁer and SOFC -GT system has been comprehensively studied in the literature [19-24]. The integration of SOFC -GT with a gasifier is modelled numerically [19] in order to investigate the effects of gas components such as H 2, CH 4 and CO on the overall system’s performance. The findings revealed that the concentration of H 2 has the most pivotal influence on both the power and efficiency of the syst em, followed by CH 4 then CO in the order of impact . Different gasification agents like air, oxygen and steam have been taken into consideration by Coplan et al. , [21] and Shayan et al ., [23]. The results of both stu dies show that employing steam as gasification agent will improve overall performance of the integrated system significantly . A small -scale integration of a gasifier with SOFC -MGT have been studied by Perna et al. , [25] where the effect of some influential operating parameters like Micro Gas Turbine (MGT) pressure ratio and the steam to carbon ratio have been e xamined to achieve the best electrical and thermal power generation of the system. The Results show that the best performances of the system will be obtained by the MGT pressu re ratio of 4.5 and the steam to carbon ratio of 0. At the mentioned operation co ndition s, the corresponding electric power generation is 262 kW while the thermal power is 405 kW . A variety of operating conditions impact, such as the effect of H2 utilizati on and moisture content in biomass on the gasifier -SOFC system's performance have been analyze d by Campitelli et al., [26]. Also, the effects of some influential parameters such as equivalence ratio and mass ﬂow rate of dry biomass as well as its moisture content on the overall performance of an integrated SOFC -MGT system have been investigated by Junxi Jia et al. ,[27]. According to recent studies, one of the key factors affecting the performance of biomass integrated system is th e moisture component in biomass. High moisture content in the biomass gasification of SOFC -GT is not desirable and will have negative effects on the system performance. Therefore, the moisture content has to be reduced to a certain level before biomass enters gasifi er. As discussed earlier, this energy cannot be retrieved from the system [28]. One of the current methods of reducing the moisture of biomas s is using fossil fuels dryer, where the moisture content in biomass is reduced by burning fossil fuel, that will pose some significant environmental issues . To the best of authors knowledge, t here is no previous research using a semi- continues solar dryer to later the moisture content of biomass . Therefore, to provide solution to this problem, the present study purposes a new idea to reduce the moisture of input biomass by employing the active mixed semi -continuous solar dryer . After this dry biomass is lo gged into the gasifier system , the synthesis gas generated by the gasifier enters the SOFC -GT hybrid system that generates electricity. Furthermore, a parameter study regarding the initial and fi nal moisture content will be obtained from the products. The main objective of this study is to investigate the moisture influence on the temperature of gasifier and fuel cell, fuel calorific value, the output power of the system and the impact of using the solar dryer on both efficiency and output power of the hy brid system. Significance and advantage of the present work is employing environmentally friendly approach to enhance a totally renewable energy hybrid system overall performance to avoid d etrimental effects of burning fossil fuels for drying biomass. Another practical advantage of th is method is it can be used in rural areas where plenty of biomass resources are available. In order to make renewable energy technologies more competitive in t he current energy market, the proposed system could have significan t privileges due to using conventional power generators along with alternative fuel resources. 2. Material and methods 2.1. System description The proposed system is divided into three subsystems in which the core technology is a biomass gasification pl ant. A down -draft gasifier is studied with steam as the gasification agent. The second unit is a SOFC -GT hybrid system which is fed by the syngas generated by the gasifier. Besides, the proposed plant includes a “Semi -Continuous Solar Dryer” to reduce the moisture content of biomass to an acceptable level before entering the gasifier. Other auxiliary pieces of equipment like a pump, Heat Recovery Steam Generator (HRS G) and a heat exchanger are used to enhance the system's performance. The schematic diagra m of the proposed plant is depicted in Figure 1. Firstly, wet biomass enters the solar dryer and its moisture content will be reduced, then dried biomass is introduce d to the gasification plant to be turned into syngas. Presumably, the syngas produced by down-draft gasifier contains some contaminants such as tar, sulfur, etc. which has harmful technical effects when used in SOFC module. Consequently, a gas filtration s ystem is facilitated to separate impurities and supply clean syngas to the SOFC. The pur ified combustible raw syngas will be introduced to the anode side of the SOFC, while the compressed air initially heated by the gas turbine exhausts will enter the cathode side of the SOFC where electricity will be generate d by means of some electrochemica l reactions. The off -fuel and the off -air which came from the anod e and cathode sides of the SOFC are introduced to a combustor to be burnt to acquire additional el ectric power by expanding through the GT. Eventually, the stream of burned gas supplies heat to the HRSG to produce steam and then let to the environment . Figure 1. The Schematic block diagram of plant. 2.2. Numerical modeling The simulation model is described here to determine the key components of the designed layout. A comprehensive model was developed in MATLAB to accurately evaluate the system’s performance under a variety of operating conditions. 2.2.1 Solar dryer The solar dryer used in our simulation was designed and built by the department of agricultural engineering of Shiraz University [29]. This dryer is a cross flow and an active mixed -mode type that works semi -continuously and is able to adapt to the workload. The Solar dryer equations is presented in Table 1. [29] Table 1. The solar dryer equations [29] 𝐪𝐜=𝐦̇𝐜𝐩(𝐓𝟐−𝐓𝟏) (1) 𝛈𝐜=𝐪𝐜 𝐆𝐓 (2) 𝐪𝐥𝐨𝐬𝐬=𝐦̇𝐂𝐩(𝐓𝟑−𝐓𝟐) (3) 𝐖=𝟎.𝟔𝟐𝟐𝛗𝐏𝐕𝐒 𝐏−𝛗𝐏𝐕𝐒 (4) 𝐡=𝟏𝟎𝟎𝟔 .𝟗𝐭+𝐖[𝟐𝟓𝟏𝟐𝟏𝟑𝟏 .𝟎+𝟏𝟓𝟓𝟐 .𝟒𝐭] (5) 𝛈𝐝𝐫𝐲𝐢𝐧𝐠 =(𝐡𝟏−𝐡𝟐) 𝐡𝟏 (6) 𝐪𝐝𝐫𝐲𝐢𝐧𝐠 =𝛈𝐝𝐫𝐲𝐢𝐧𝐠 (𝐀𝐂𝐪𝐜+𝐪𝐡𝐞𝐚𝐭𝐞𝐫 −𝐪𝐥𝐨𝐬𝐬) (7) 𝛈𝐧𝐞𝐭=𝐪𝐝𝐫𝐲𝐢𝐧𝐠 (𝐪𝐜+𝐪𝐟𝐚𝐧+𝐪𝐡𝐞𝐚𝐭𝐞𝐫 ) (8) More details about the calculation process and solar dryer specificati ons may be found in [29]. 2.2.2 Down - draft gasifier Numerical modeling is applied to simulate the processes of a down -draft gasifier. A simple structure of a downdraf t gasifier is illustrated in F igure 2. As shown, the gasifier consists of two principal parts, including the pyrolysis -oxidation zone and the reduction zone, where the pyrolysis and oxidation reactions wil l take place in succession followed by the reduction reactions [27]. Ash collectorPyrolysis zone Oxidation zone Reduction zone Figure 2. Schematic diagram of a down -draft gasifier [27] The down -draft gasifier equations are listed in Table 2. To determine the pyrolysis -oxidation zone reactions , the global reaction formula is written as equation (9) . Further, the impact of biomass moisture content (MC) as well as supplied air to the gasifi cation process, are evaluated by equations ( 10,11) [27] Then, two equilibrium reactions named, methane formation and the shift reaction in t he pyrolysis -oxidant zone (12,13) are employed to solve the equations [27]. Equilibrium constants for these reactions are presented by equatio ns (14) and (15) , respectively also, the energy balance can be obtained by equation (16) [27] . The pyro-oxidation zone calculation results w ill be introduced as input parameters to the reduction zone. The reduction reactions can be written as equations (17 -20) while the volumetric reaction rate of each chemical reaction can be written as equations (21 -24) [27]. Furthermore, the C old Gas Efficiency (CGE) metric is used to assess the progress of gasification defined as equation (25) [30]. Table 2: The down -draft gasifier [27]. CH aObNc+wH 2O+m(O2+3.76N2) →x1H2+x2CO+x3CO 2+x4H2O+x5CH 4+x6N2+x7C (9) MC =Mw MBio+Mw=18w (12+a+16b +14p )+18w (10) ER=Air Actual Air Stoichiometric=m (1+0.25a −0.5b) (11) C+2H 2↔CH 4 (12) CO+H2O↔H2+CO 2 (13) K1=x5nT x12P0 (14) K2=x1x3 x2x4 (15) HBiomass +wHH2O+m(HO2+3.76HN 2) =x1HH2+x2HCO+x3HCO 2+x4HH2O+x5HCH 4+x6HN2+x7HC (16) R1: C+CO 2↔2CO (17) R2: C+H2O↔CO+H2 (18) R3: C+2H 2↔CH 4 (19) R4: CH 4+H2O↔3H 2+CO (20) rR1= CRFAR1exp (−ER1 RmT)(yCO 2−yCO 22 kR1) (21) rR2= CRFAR2exp (−ER2 RmT)(yH2O−yH2yCO kR2) (22) rR3= CRFAR3exp (−ER3 RmT)(yH22−yCH 4 kR3) (23) rR4= CRFAR4exp (−ER4 RmT)(yH2𝑂2yCH 4−yCOyH23 kR4) (24) CGE =GYf ×HHV PG HHV f×Heat aer (25) Where the unknown parameters x1, x2, x3, x14, x5, x6, x7and T (the react ion temperature ) will be determined . By using energy and mass balance equations and bisection approach, above equations and reaction temperature will be calculated. M ore detail s about the calculation process as well as the thermodynamic properties values m ay be found in [27, 28] . 2.2.3 SOFC numerical model To investigate the SOFC performance , it is crucial to consider a model that is capable of predicting the performance based on its operating condition. The schem atic diagram of the electrochemical processes occurring in a planar SOFC system is illustrated in Figure 3. Electric Current Oxygen Hydrogen 𝐇𝟐𝐎 𝐇𝟐𝐎 𝐇𝟐𝐎 𝐞− 𝐞− 𝐞− 𝐞− 𝐎𝟐− 𝐎𝟐− 𝐎𝟐− 𝐎𝟐− 𝐎𝟐 𝐎𝟐 𝐎𝟐 𝐎𝟐 𝐎𝟐 𝐎𝟐 𝐎𝟐 𝐇𝟐 𝐇𝟐 𝐇𝟐 𝐇𝟐 𝐇𝟐 Anode Fuel ChannelBipolar Interconnect Bipolar Interconnect Electrolyte Oxidant ChannelCathode Figure 3. The Schematic of a planar SOFC system. The SOFC electrochemical equations are prese nted in T ables 3 - 6. The operating cell voltage is calculated by equation (26) . Table 3. Lists the voltage equations [31]. Table 3. Voltage equatio ns [31] 𝐕𝐂𝐞𝐥𝐥=𝐕𝐎𝐂𝐕−(∑𝛈𝐨𝐡𝐦 ,𝐣+𝛈𝐜𝐨𝐧𝐜 ,𝟑 𝐣 +𝛈𝐜𝐨𝐧𝐜 ,𝟓+𝛈𝐚𝐜𝐭,𝟑+𝛈𝐚𝐜𝐭,𝟓), 𝐣= 𝟏,𝟑,𝟒,𝟓 (26) 𝐕𝐎𝐂𝐕 =−𝟏 𝟐𝐅(𝐇𝐇𝟐𝐎−𝐇𝐇𝟐−𝟏 𝟐𝐇𝟐𝐎)+𝐓 𝟐𝐅(𝐒𝐇𝟐𝐎𝟎−𝐒𝐇𝟐𝟎−𝟏 𝟐𝐒𝐎𝟐𝟎)+ 𝐑𝐓 𝟐𝐅𝐥𝐧(𝐏𝐇𝟐𝐎 𝐏𝐇𝟐(𝐏𝐎𝟐)𝟏𝟐⁄) (27) The materials resistance, involved in terconnector anode, cathode, electrolyte , and the ohmic losses will be calculated f rom equations (28 -32) listed in T able 4 [31] . Table 4. Ohmic los ses equations [31]. 𝛈𝐎𝐡𝐦 ,𝐣=𝐈𝛃𝐣, 𝐣=𝟏,𝟒 (28) 𝛈𝐎𝐡𝐦 ,𝐣=𝐈(𝐀𝐣,𝐨𝐩𝐭−𝐋𝐲𝐋𝐙)𝐋𝐣,𝐨𝐩𝐭 𝟐𝐀𝐣,𝐨𝐩𝐭𝐋𝐲𝐋𝐙(𝟏−𝛗𝐣)𝛔𝟒+𝐈(𝐋𝐣−𝐋𝐣,𝐨𝐩𝐭) 𝐋𝐲𝐋𝐙(𝟏−𝟏.𝟖𝛗𝐣)𝛔𝐢 𝐣=𝟑,𝟓 (29) 𝛃𝟏=𝐋𝟏 𝐋𝐲𝐋𝐙𝛔𝟏+𝐋𝟐 (𝟏+𝐧𝐂𝐇)𝐋𝐭𝐋𝐲𝛔𝟏+𝐋𝟔 (𝟏+𝐧𝐂𝐇)𝐋𝐭𝐋𝐙𝛔𝟏 (30) 𝛃𝟒=𝐋𝟒 𝐋𝐲𝐋𝐙𝛔𝟒 (31) 𝐀𝐣,𝐨𝐩𝐭=(𝟏+𝟐𝐋𝐣,𝐨𝐩𝐭𝛗𝐣 𝐃𝐏,𝐣)𝐋𝐲𝐋𝐙 (32) Following the d iffusion losses will be determined using equations listed in Table 5 [31]. Table 5. Diffusion losses equations [31]. 𝐃𝐏,𝐣=𝐃𝐖,𝐣𝛗𝐣 (𝟏−𝛗𝐣) (33) 𝐏𝐇𝟐𝐎,𝐓𝐏𝐁 =𝐩𝐟𝐱𝐇𝟐𝐎+𝐑𝐓 𝛙𝟑 𝟐𝐅𝐃𝟑𝛙𝟑 𝐋𝟑𝐈 𝐋𝐲𝐋𝐳 (34) 𝐏𝐇𝟐,𝐓𝐏𝐁 =𝐩𝐟𝐱𝐇𝟐−𝐑𝐓 𝛙𝟑 𝟐𝐅𝐃𝟑𝛙𝟑 𝐋𝟑𝐈 𝐋𝐲𝐋𝐳 (35) 𝐏𝐎𝟐,𝐓𝐏𝐁 =𝐩𝐚𝐢𝐫−(𝐩𝐚𝐢𝐫−𝐱𝐎𝟐𝐩𝐚𝐢𝐫)𝐞𝐱𝐩 (𝐑𝐓 𝛙𝟓𝐋𝟓𝐈 𝟒𝐅𝐃𝟓𝛙𝟓𝐩𝐚𝐢𝐫𝐋𝐲𝐋𝐳) (36) 𝐃𝟑=𝟏.𝟒𝟑×𝟏𝟎−𝟕𝐓𝟏.𝟕𝟓(𝐌𝐇𝟐+𝐌𝐇𝟐𝟎)𝟏𝟐⁄ 𝐏𝐟(𝟐𝐌𝐇𝟐+𝐌𝐇𝟐𝟎)𝟏𝟐⁄(𝛖𝐇𝟐𝟏𝟑⁄+𝛖𝐇𝟐𝐨𝟏𝟑⁄)𝟐 (37) 𝐃𝟓=𝟏.𝟒𝟑×𝟏𝟎−𝟕𝐓𝟏.𝟕𝟓(𝐌𝐎𝟐+𝐌𝐍𝟐)𝟏𝟐⁄ 𝐏𝐚𝐢𝐫(𝟐𝐌𝐎𝟐+𝐌𝐍𝟐)𝟏𝟐⁄(𝛖𝐎𝟐𝟏𝟑⁄+𝛖𝐍𝟐𝟏𝟑⁄)𝟐 (38) 𝛈𝐝𝐢𝐟𝐟 ,𝐜=𝐑𝐓 𝟒𝐅𝐋𝐧(𝐩𝐎𝟐 𝐩𝐎𝟐,𝐓𝐏𝐁) (39) 𝛈𝐝𝐢𝐟𝐟 ,𝐚=𝐑𝐓 𝟒𝐅𝐋𝐧(𝐩𝐇𝟐𝐩𝐇𝟐𝐎,𝐓𝐏𝐁 𝐩𝐇𝟐,𝐓𝐏𝐁𝐩𝐇𝟐𝐎) (40) Later the activation loss, which is related to the irreversibility of the electrochemical reaction, can be examined by the equation s listed in Table 6. Table 6. Activation losses equations [31] 𝐢=𝐢𝐨,𝐣 [𝐞𝐱𝐩 (𝛂𝐧𝐅 𝐑𝐓𝛈𝐚𝐜𝐭,𝐣)−𝐞𝐱𝐩 (−(𝟏−𝛂)𝐧𝐅 𝐑𝐓𝛈𝐚𝐜𝐭,𝐣),𝐣=𝟑,𝟓] (41) 𝛈𝐚𝐜𝐭,𝐣=𝐑𝐓 𝛂𝐧𝐅𝐬𝐢𝐧𝐡−𝟏(𝐢 𝐢𝐨,𝐣) (42) 𝐢𝐨,𝐣=𝐑𝐓 𝐧𝐅𝛅𝐣𝐞𝐱𝐩 (−𝐄𝐣 𝐑𝐓),𝐣=𝟑,𝟓 (43) The electri cal power generated by the SOFC can be calculated by (44,45) as follow [32]: ẆSOFC =N .VCell .j.AC (44) ẆSOFC ,net=ẆSOFC .Ƞinv (45) Where Ƞinv is the inverter efficiency that is considered to be 0.98 [32]. The heat generated and the overall eﬃciency of SOFC can be determined as follows [32] Q̇ SOFC =(ṁf∗Uf∗LHV ) (46) ηHS=Ẇ net Q̇ tot (47) Mass balance of SOFC considering in put and output flows may be written as [32]: ∑ṁi=∑ṁe (48) ṁ4+ṁ8=ṁ5+ṁ9=ṁ8+(ṁ4Uf)+ṁ4(1−Uf) (49) Where, ṁ4 is the fuel mass rate injected to the SOFC and ṁ8 is the air mass rate injected to SOFC. Alternatively, applying the first law of thermodynamic equation (49) can be rewritten as [32]: ṁ8h8+(ṁ4Uf)LHV +ṁ4(1−Uf)h4−ṁ5h5−ṁ9h9=0 (50) where LHV stands for the lower heating value of biomass. It should be noted that all products are considered to be adiabatic. 2.2.4. Other auxiliary equipment The proposed design consists of other auxiliary pieces of equi pment including Air Compressor, Gas turbine, Combustion chamber , Heat exchanger and Heat recovery steam generator (HRSG). The governing equations on them are listed in Table 7 [32]. Table 7. Other auxiliary pieces equipment equations [29]. 𝛈𝐀𝐂=𝐖𝐒 𝐖𝐚=𝐡̅𝟕𝐬−𝐡̅𝟔 𝐡̅𝟕−𝐡̅𝟔 (51) 𝐓𝟕𝐒 𝐓𝟔=(𝐏𝟕 𝐏𝟔)𝛄−𝟏𝛄⁄ (52) 𝐖̇𝐀𝐂=𝐦̇𝟔(𝐡̅𝟕−𝐡̅𝟔) (53) 𝛈𝐭𝐢𝐬=𝐖𝐚 𝐖𝐬−𝐡̅𝟏𝟎−𝐡̅𝟏𝟏 𝐡̅𝟏𝟎−𝐡̅𝟏𝟏𝐬 (54) 𝐏𝐫𝐭=𝐏𝟏𝟎 𝐏𝟏𝟏 (55) 𝐖̇𝐓=∑(𝐦̇𝟏𝟎𝐡̅𝟏𝟎)𝐢𝐧 𝐢−∑(𝐦̇𝟏𝟏𝐡̅𝟏𝟏)𝐨𝐮𝐭 𝐢 (56) 𝐖̇ 𝐆𝐓=(𝐖̇𝐓−𝐖𝐀𝐂̇)𝛍𝐦.𝛍𝐠 (57) ∑𝐦𝐢𝐢𝐧𝟕 𝐢=𝟏(∆𝐇𝐟𝟎+∫ 𝐂𝐩𝐝𝐓𝐓𝐢𝐧 𝟐𝟗𝟖)=∑𝐦𝐢𝐨𝐮𝐭𝟒 𝐢=𝟏(∆𝐇𝐟𝟎+∫ 𝐂𝐩𝐝𝐓𝐓𝐨𝐮𝐭 𝟐𝟗𝟖) (58) 𝛆𝐀𝐏𝐇 =𝐓𝟏𝟐−𝐓𝟖 𝐓𝟏𝟏−𝐓𝟕 (59) 𝐦̇𝟕(𝐡𝟏𝟐−𝐡𝟕)=𝐦̇𝟏𝟏(𝐡𝟏𝟏−𝐡𝟏𝟐)𝛆𝐀𝐏𝐇 (60) 𝐦̇𝐠=𝐦̇𝐚+𝐦̇𝐟 (61) 𝐦̇𝐬(𝐡𝟏𝟔−𝐡𝟏𝟓)=𝐦̇𝐠(𝐡𝟏𝟐−𝐡𝟏𝟑) (62) 𝐦̇𝐬(𝐡𝟏𝟔−𝐡𝟏𝟓𝐏)=𝐦̇𝐠(𝐡𝟏𝟐−𝐡𝟏𝟑𝐏) (63) 𝐏𝟎=𝐏𝟏𝟐(𝟏−∆𝐏𝐇𝐑𝐒𝐆 ) (64) Further ẆT can be determined by equation (56) following the ẆGT can be obtained by (57) [32]. Where μm is assumed 0.80 and μg is assumed 0.98 [33]. Also, the energy balance of the combustor is expressed by equation (58) [32]. The isentropic efficiency of the air preheater can be defined by equation (59) follow ed by the energy conservation th at can be calculated by equation (60), where εAPH is the isentropic efficiency of air preheater [34]. The HRSG is employed to recover energy from the exhausts gas of turbine as well as gener ating some auxiliary steam to be utilized in an internal reformer where water is pumped to the HRSG. The steam flow rate generated by the HRSG, ṁs, can be determined by considering the equations (61-64) simultaneously [34]. 2.2.5. Power and eff iciency The energy balance for the proposed hybrid system can be written as [32, 34] : ṁ1h1+ṁ16h16+ṁ4UfLHV +Q̇CC−ṁ17h17−Q̇Loss −ẆP−ẆGT=0 (65) The total energy efficie ncy and net power output of the proposed hybrid system including the SOFC and GT hybrid cycle is determined as [32, 34] Ẇ net=(ẆSOFC +ẆGT−ẆWP) (66) Q̇ tot=(ṁbiomass ∗Uf∗LHV ) (67) ηHS=Ẇ net Q̇ tot (68) 2.3 Simulation and validation The model input data of the considered integrated down -draft gasifier SOFC/GT system are selected from [27, 29 -31, 33] . Input parameters for simulation of the solar dryer is derived from [27]. The values of the operation parameters in modelling of the down -draft gasifier are selected from [29]. The properties and cons tant values used in the plana r SOFC model may be found in [31, 33] Table 8: Gas composition comparison by experimental results for moisture content 10% [27]. Gas Composition (%) Hydrogen Carbon monoxide Carbon dioxide Methane Present study 16.99 17.51 11.41 1.26 Experimental results 16.81 19.70 12.30 1.90 Our results are in a reasonable agreement w ith counterparts in literature. 3. Solution methodology In this work, we have used a solution methodology that conducts the performance analysis of operation conditions . The main objective of proposed methodology is providing the operation solutions base d on techn ical model for engineering applications. The technical proposed model will be solved in six consecutive steps by employing all required equations in a structured way as illustrated in Fig ure. 3. To solve the technical model, constant parameters a re selected initially followed by modelling solar dryer , down -draft gasifier , SOFC, GT, HRSG , and energy balance. Later, power and efficiency will be calculated as the dependent variables . Input constant parameter Down -draft Gasifier SOFC Model Combustion ChamberEnergy Balance ModelGas Turbine Model HRSGTemperatureSolar dryerMoisture content Turbine Inlet Temperature Gas composition Gas composition & TemperatureAir Compressor Pressure & Temperature Power generation / consumption & Efficiency Figure 4. The model structure for integrated Gasifier SOFC/GT system. 4. Results and discussion In this section, the impact of decreasing moisture content by employing solar dryer on different kinds of parameters have been studied . The parameters include syngas compo sition, gasifier temperature, SOFC temperature, fuel calorific value, efficiency and power output of the hybrid system. The effect of moisture content on gas composition is given in Figure 5. The gas composition is highly dependent to the moisture content such that as moisture content is increased from 0 % to 40 %, the molar fraction of generated gases will be affected sign ificantly. It should be noted that although in practice achieving a 0% moisture content might be impossible, the objective of this study is to determine the maximum possible efficiency . Figure 5: Gas composition versus Moisture Content As shown in Figu re 5. by increasing the biomass moisture amount, the mole fraction of H 2 gradually increased until 25% moisture and starts decreasing af terwards while the mole fraction of CO is decreased dramatically and linearly . It is noteworthy that as moisture content increased from 10% to 20% , the CO molar fraction experiences a 4% drop, i.e. from 0.16 % to 0.12 %, while at the same moisture, the H2o molar fraction increased from 0.075 % to 0.1 %. Also, the CH4 which consists a sma ll fraction of produced gas undergoes a slight boost, like CO2 with the same trend when the moisture content increases . Our findings on moisture content amount variatio n on syngas composition hint that although lower moisture content is favored to provide high-quality syngas, maintaining the moisture content of about 20% - 25% is desirable to produce a better combustible syngas considering all syngas components . In Figure 6. the variation of moisture content amount versus gasifier temperature is illustrated . It can be seen that by increasing moisture content the gasifier temperature declines significantly. Figure 6. Temperature changes relative to moisture It is illustr ated that on average there is a temperature drop of approximately 30 K when moisture content increases every 10%. For example, when moisture content increases from 10% to 20% the correspond gasifier temperature drop s from 133 0 K to 1300 K. It is confirmed that the temperature drops as the moisture content increases , in either case. This is mainly according to the fact that, by assuming constant inlet air, as biomass moisture content increases, more heat is required to evaporate its moisture, hence the process equilibrium temperature is reduced. In Figure 7. A parametric study is conducted to determine the eﬀects of gasifier temperature on generated gas composition to assess the best working temperature of gasifier with the aim to achieve better syngas compo sition. Figure 7: Gas composition versus Gasifier t emperature As expected, concentration of H2O is highly correlated to gasifier working temperature where on average by every 10 K reduction in gasifier temperature , H2O concentration in the generate d gas will be decreased approximately 7%. The molar fraction of CH4 is considerably less than other species in the gas composition and this is mainly since most of carbon content is converted into CO. It is observed that by increasing temperature , the concentration of CH4 and CO2 declin e while concentration of CO increas es remarkably . It can be understood that the highest concentration of H2 amount is achieved when gasifier working temperature lay between 1300 K to 1320 K. This operation condi tion happens when the hydrogen concentration in the syngas is about 18 %. Figure 8. Calorific value changes of produced gas versus moisture content In Figure 8. the gas High Heating Value behavior versus moisture content amount is presented. It can be observed that the gas calorific value decreas es considerably as moisture content increase s. It is displayed that, by raising the moisture content from 10% to 30% the gas calorific value declines from 4.01×105 to 3.95×105 MJm−3; this reduction is mainly due to vapor content increase in the gas composition. Since the cold gas efficiency is considered a crucial factor in biomass gasification, the impact of moisture content on the cold gas efficiency is studied as depicted in Figure 9. Figure 9: The cold gas efficiency variation versus moisture content The result reveal s that as moisture content is increased, the cold gas efficiency is decreased. It is observed that for moisture content of 10% , the corresponding cold gas efficiency is approximately 84.5% while by increasing the moisture content up to 30% the cold gas efficiency declines to 82.7%. Figure 10., displays the effect of SOFC temperature varia tion on power and efficiency of the system. As illustrated, the higher temperature of the SOFC lead s to more output power of the system, whilst by increasing temperature from 1200 K to 1400 K the corresponding power of the system is considerably enhanced f rom 305 kW to 360 kW. Figure 10: Power and Efficiency versus SOFC temperature variation A similar trend is depicted for the efficiency of the system, where the efficiency will be improved about 7% when the operation temperature is boosted from 1200 K to 1400 K. Figure1 1., demonstrates the SOFC temperature variation effect on the e fficiency and heat generation of the integrated system. The results prove that, since a lower operating temperature leads to more polarization losses in SOFC system, conseque ntly, heat generation of the system will be increased significantly. Figure 1 1: Efficiency and heat generation versus SOFC temperature variation The heat generated by the system declines while the temperature raises to approximately 1470 K, where it starts a slight enhancement. In essence, the entropy -generated heat will be greater than the polarization -induced heat that will lead to a slight increment in the generated heat. As it is indicated the maximum efficiency of the system is gained at corresp onding SOFC working temperature of about 1450 K. It can be seen that by raising SOFC temperature from 1200 K to 1400 K, the efficiency improves about 19% while at similar SOFC temperature, the heat generation of the system decreases significantly. This imp lies that SOFC temperature has contradictory effects on system efficiency and heat generation. From above analysis it can be concluded that two vital parameters on the performance of an integrated gasifier SOFC/GT system are biomass moisture content and w orking temperature . In the proceeding section , the effect of employing a solar dryer on the power and effi ciency of the system will be discussed employing two different scenarios. B ased on the results and tables obtained from air flow and time interval of product drain, it is concluded that these two factors have a significant effect on the reduc tion of moistu re content leaving the solar dryer. It should be noted that the input biomass moisture content is assumed to be about 27-30 (Vol.%) when entering the dryer . Other influential factors such as the Environment Initial Relative (EIR), and the inlet air temper ature to the dryer are almost identical . Therefore , the initial velocity of air flow (air flow mass) is the only highly influential operation paramete r on the drying rate. At the first scenario two factors are consider ed; first, the air mass flux to the so lar dryer is considered to take three values of 0.011, 0.0066, and 0.0048 kg m−2s−1, whereas the second factor , that is the drying and discharging time of biomass , is assumed to be 15 minutes. Briefly in the Table 9, the result of combination of three air mass flux and the drain time of 15 minutes is illustrated on the resultant output moisture content of biomass from sola r dryer . At the first scenario t 1 = 15 min while Q1=0.011 kg m−2s−1, Q2=0.0066 kg m−2s−1, Q3=0.0048 kg m−2s−1. Table 9. The combination of drain time and air mass flow and corresponding moisture content Alternatives Moisture Content (%) Q1t1 14.2 Q2t1 17 Q3t1 20 According to Table 9. it can be found that the higher the air flow mass , the faster the input biomass dries. The main reason behind it is, by increasing the flow of drying air, pressure difference of water between biomass and drying air will be increased. As a result, the moisture transmission rate of biomass to drying air will be increased consequently the biomass will be dried in faster rate. Figure 1 2., depicts the variations of the first scenario impact on the entire system ’s efficiency . Figure 1 2. The effect of output moisture content of dryer regards to first scenario on the efficiency From Figure 1 2., it can be seen that the rate of moisture loss for biomass at the first ste ps of the drying process is faster, individually at higher mass flow rates of Q 1=0.011 kg 𝑚−2𝑠−1 and consequently the system efficiency is proved higher performance regarding the l ower moisture content of biomass. The second scenario employs the same three air flow mass to the solar dryer as of the first scenario, i.e. 0.011, 0.0066, 0.0 048 kg 𝑚−2𝑠−1 while using a longer drain time of biomass, i.e. 30 minutes. In the Table 10, the effect of combination of three air mass flux and the drain time of 30 minutes is presented on the resultant output moisture content of biomass from solar dryer . Table 10. The combination of drain time of 30 min and air mass flow and corresponding moisture content Alternatives Moisture Content (%) Q1t2 13 Q2t2 16 Q3t2 20 Figure 1 3., represents the entire system’s efficiency in response to three flow rates and drain time of 30 minutes employed for the second scenario. By comparing these results, it can be observed that however by increasing drain time from 15 to 30 minutes at the same air mass flow rate of Q 1=0.011 kg m−2s−1 the moisture content of output biomass is decreased down to 13 %, the overall efficiency of the system is diminished from 57.6% to 51%. The results demonstrated in this section are gone beyond previous findings and approved that the moisture content of lower than about 15% is not desirable for the system. Figure 13. The effect of output moisture content of dryer regards to second scenario on the efficiency Figure 14. The effect of moisture content of dryer regards to two scenarios on the power In Figure 1 4., the effect of output moisture content of both scenarios on the output power of system is investigated. The results suggest that by decreasing moisture content, the output power of the system will be increased. For instance, by declining moi sture content from 20% to 14.2% output power generation of the system improves from 265 kW to 290 kW. Moreover, the maximum power of the whole system under studied conditions is 295 kW when the mass flow rate is 0.0011 kg/m−2s−1 and the drain time is 30 minutes . Interestingly, the maximum efficiency of the system is achieved at mass flow rate of 0.0011 kg/ m−2s−1 and the drain time of 15 minutes. The results indicate that by decreasing approximately 6% in moisture content of biomass, the overall power generation of the proposed system will be enhanced about 8.5 % which is a desirable result for decision makers. 5. Conclusion In this study, a performance analysis of an integrated solar dryer with a Gasifier -SOFC -GT system has been studied. Since b iomass moisture content plays a key factor on the hybrid system performance , the effect of alternating moisture content on the key parameters such as the gasifier temperature, the SOFC temperature, fuel calorific value as well as the efficiency and power o utput of the overall hybrid system have been examined and discussed . In summary s ome key ﬁndings of this paper can be concluded as: (1) The higher reaction temperature result s in more H 2 and CO concentration in generated syngas hence, the cold gas eff icien cy and the HHV are enhance d significantly. (2) Employing solar dryer to reduce moisture content of bio mass leads to an improvement of efficiency up to 27.6%. (3) Reducing the moisture of biomass, improves the power output and efficiency of the hybrid syste m from 265kW and 30% up to 295 kW and 57.6% , respectively. (4) The best efficiency performance of system under investigated conditions is achieved by the 15 minutes drain time and the air mass flow rate of 0.011 kg m−2s−1, while the best power generation of the system is obtained employing the 30 minutes drain time and the air mass flow r ate of 0.011 kg m−2s−1. (5) It can be concluded that a solar dryer as a sustainable approach proposes a practical and envir onmentally friendly technic to enhance such a hybrid systems performance. For future work s, it is suggested to conduct the exergy -econ omic evaluations of the designed system considering different biomass feeding s into the system. 6. Acknowledgement This r esearch did not receive any specific grant from funding agencies in the public, commercial, or not -for-profit sectors. 7. Nomenclature Solar Dryer C Coefficient of discharge (𝐦) Aa Collector surface area 𝐂𝐩 Specific heat of air (J/kgK) h Enthalpy (kj/kg) 𝐡𝟏 Enthalpy of hot air in dryer chamber (kj/kg) 𝐡𝟐 Enthalpy of dryer outlet air chamber (kj/kg) GT Incident solar radiation (W/m2) M Air mass flow ra te (kg/s) 𝐦̇ Air mass flow rate (kg/s m2) P Atmospheric pressure (bar) 𝐏𝐯𝐬 Partial vapor pressure (bar) 𝐪𝐜 Useful collected heat (W/ m2) 𝐪𝐥𝐨𝐬𝐬 Total heat losses (W/ m2) 𝐪𝐝𝐫𝐲𝐢𝐧𝐠 Heat consumed for drying process (W) 𝐪𝐡𝐞𝐚𝐭𝐞𝐫 Heat provided by heating channel (W) 𝐪𝐟𝐚𝐧 Heat consumed by fan (W) 𝛈𝐜 Efficiency (%) 𝛗 Relative humidity, decimal 𝐰 Humidity ratio, decimal Down -Draft Gasifier 𝐧𝐇𝟐 Hydrogen moles ( 𝐤𝐦𝐨𝐥 ) 𝐧𝐂𝐎 Carbon monoxide moles (kmol ) 𝐧𝐂𝐎𝟐 Carbon dioxide moles (kmol ) 𝐧𝐇𝐎 𝟐 Water moles (kmol ) 𝐧𝐂𝐇𝟒 Methane moles (kmol ) 𝐧𝐍𝟐 Nitrogen moles (kmol ) 𝐧𝐎𝟐 Oxygen moles (kmol ) 𝐧𝐂 Carbon moles (kmol ) C Carbon c ontent in biomass (w%) H Hydrogen content in biomass (w%) O Oxygen content in biomass (w%) K Equilibrium constant ΔG Change in Gibbs function h Enthalpy ( kJ kmol−1K−1) LHV Lower heating value ( kJ kg−1) n kmol of oxygen per kmol of biomass w kmol of water per kmol of biomass m kmol of steam per kmol of biomass T Temperature (K) P Pressure (bar) MC Mass of water per mass of wet biomass 𝐡̅𝐢 Specific enthalpy of species 𝑖 𝐓𝐠𝐬̅°𝐢 Temperature of species 𝑖 𝐆𝐲𝐟𝐮𝐞𝐥 Gas yield (Nm3kg−1fuel) 𝐇𝐇𝐕𝐏𝐆 HHV of product gas (MJNm−3) 𝐇𝐞𝐚𝐭𝐚𝐞𝐫 Endothermic reaction heat (MJKg−1) CGE Cold Gas Efficiency Solid Oxide Fuel Cell A )2m Area ( 𝐀𝐎𝐩𝐭 )2m( Area of active TPB D )s−1 2(mity Mass diffusiv 𝐃𝐰 Width of a corrugation (m) 𝐃𝐩 Average diameter of pores E Activation energy (kJ kmol−1) F Faraday’s constant ( kmol−1) L Length (m) 𝐋𝐨𝐩𝐭 )1-Activation energy (Jmol 𝒊 )2-Current density (Am 𝒊𝒐 Exchange current density (A m−2) 𝐣𝐋 Limiting current density (A m−2) M Molecular weight (kg kmol−1) n Molar ﬂow rates ( kmol−1) ne Number of electrons 𝐩𝐓𝐏𝐁 Partial pressure (bar) P Operating pressure (bar) 𝐐𝐂𝐞𝐥𝐥 Heat generation r ate (W) r Ohmic resistance (Ω) R Universal gas constant ( 8.134Jmol−1𝑘−1) k Fuel cell components T Cell temperature (K) 𝐔𝐟 Fuel utilization factor 𝐕𝐨𝐜𝐯 Open circuit voltage (V) 𝐕𝐧𝐞𝐫𝐬𝐭 Nernst potential (V) 𝛈𝐚𝐜𝐭 Activation polarization (V) 𝛈𝐂𝐨𝐧𝐜 Concentration polarization (V) 𝐕𝑳𝒐𝒔𝒔 Voltage losses (V) 𝛈𝑶𝒉𝒎 Ohmic polarization (V) 𝐖̇𝐞𝐥 Electrical power (W) z Reacted hydrogen molar follow rate ( 𝑘𝑚𝑜𝑙𝑠−1) 𝜶 Charge transfer coeffi cient β Ohmic resistance ( Ω) δ )2-m1-(Ω Pre exponential factor 𝝋 Porosity γ Pre-exponential coeﬃcient η Over potential (V) 𝝀𝒂𝒊𝒓 Stoichiometric ratio σ )1-m1-(Ω Electrical conductivity ψ Tortuosity Gas Turbine 𝐖̇𝐓 Turbine power 𝐖̇𝐂 Consumed power from the air compressor 𝐖̇𝐆𝐓 Gas turbine net electrical power 𝛍𝐠 Generator efficiency 𝛍𝐦 Mechanical efficiency TIT Turbine inlet temperature Subscript and Superscript an Anode ca Cathode e Exit 𝐢 Inlet f fuel OCV Open circuit voltage TPB Three -Phase boundary 1