基于太陽(yáng)能光伏光熱技術(shù)的灌溉水增溫系統(tǒng)試驗(yàn)

張金珠，王 欽，王振華，徐 鑫

基于太陽(yáng)能光伏光熱技術(shù)的灌溉水增溫系統(tǒng)試驗(yàn)

張金珠，王 欽，王振華，徐 鑫

（1. 石河子大學(xué)水利建筑工程學(xué)院，石河子 832000；2. 現(xiàn)代節(jié)水灌溉兵團(tuán)重點(diǎn)實(shí)驗(yàn)室，石河子大學(xué)，石河子 832000）

為減弱低溫灌溉水對(duì)中國(guó)西北地區(qū)作物帶來的不利影響，減少農(nóng)業(yè)灌溉中的能源消耗，該研究設(shè)計(jì)了一種基于太陽(yáng)能光伏光熱技術(shù)灌溉水增溫系統(tǒng)。通過搭建測(cè)試平臺(tái)，對(duì)該系統(tǒng)進(jìn)行不同流量下的性能測(cè)試研究，分析初始水溫和輻照度對(duì)系統(tǒng)性能的影響。結(jié)果顯示，出水口水溫和升溫幅度與流量呈負(fù)相關(guān)關(guān)系，固定工況下，出水口水溫及升溫幅度最高可達(dá)20.9和12.5 ℃，光電、光熱效率與流量呈正相關(guān)關(guān)系，最大分別為0.094和0.310，實(shí)際能量效率則先增后減，最大達(dá)到0.484。初始水溫越低，光伏光熱集熱器內(nèi)換熱越劇烈，升溫幅度越高，能量指標(biāo)越大，但流量增加使得不同初始水溫灌溉水升溫幅度趨于一致，出水口水溫變幅增大。輻照度越高，出水口水溫及升溫幅度越大，但流量增大會(huì)削弱輻照度對(duì)其產(chǎn)生的提升效果，光電、光熱效率均與輻照度呈負(fù)相關(guān)關(guān)系，在流量小于0.06 kg/(s·m2)時(shí)，實(shí)際能量效率與輻照度呈負(fù)相關(guān)關(guān)系，在流量大于0.07 kg/(s·m2)時(shí)則相反。研究表明該系統(tǒng)總體性能良好，為不同工況下的流量選擇提供了參考依據(jù)。

光伏光熱；灌溉；輻照度增溫；流量；初始水溫；

0 引 言

世界能源與糧食的需求日益增加，將可再生能源應(yīng)用于農(nóng)業(yè)生產(chǎn)，提高作物的產(chǎn)量及品質(zhì)，減少化石能源的消耗受到廣泛關(guān)注[1-5]。近年來，太陽(yáng)能以其分布范圍廣、環(huán)境友好等優(yōu)勢(shì)成為眾多國(guó)內(nèi)外學(xué)者的研究重點(diǎn)[6-9]。研究?jī)?nèi)容主要包括改善太陽(yáng)能的利用方式[10-13]，討論不同氣候條件下某一特定系統(tǒng)的經(jīng)濟(jì)性與可行性[14-15]等；研究方法包含模擬仿真[16-17]、建立微型試驗(yàn)系統(tǒng)進(jìn)行試驗(yàn)研究[18-19]等。通過學(xué)者們的不斷探索和研究，利用太陽(yáng)能輔助農(nóng)業(yè)生產(chǎn)的技術(shù)日益先進(jìn)。

Amaducci等[20]設(shè)計(jì)了一種名為Agrovoltaico的農(nóng)田光伏系統(tǒng)，并對(duì)該系統(tǒng)進(jìn)行模擬研究發(fā)現(xiàn)相較于全光條件下，Agrovoltaico在生產(chǎn)電能的同時(shí)可為作物生長(zhǎng)提供更有利的條件，土地當(dāng)量比始終大于1。Xu等[21]研究了一種季節(jié)性能量?jī)?chǔ)存系統(tǒng)，該系統(tǒng)將多余的太陽(yáng)能轉(zhuǎn)化為熱能儲(chǔ)存起來，應(yīng)用于冬季溫室供暖，結(jié)果發(fā)現(xiàn)該系統(tǒng)無(wú)需任何輔助增溫設(shè)備可使溫室溫度提高13 ℃。Kabalci等[22]設(shè)計(jì)了一種可遠(yuǎn)程監(jiān)控和控制的太陽(yáng)能電站及灌溉系統(tǒng)，對(duì)其進(jìn)行了大小和可行性分析，并對(duì)數(shù)據(jù)采集、遠(yuǎn)程監(jiān)控和操作系統(tǒng)進(jìn)行了優(yōu)化。李加念等[23]研制了一種基于太陽(yáng)能的微灌系統(tǒng)恒壓供水自動(dòng)控制裝置，經(jīng)過6個(gè)月的實(shí)際應(yīng)用試驗(yàn)，裝置運(yùn)行穩(wěn)定，水位誤差小于1 cm。20世紀(jì)70年代光伏光熱技術(shù)首次被提出[24]，因其較高的能量轉(zhuǎn)化效率和較廣的適用范圍，成為眾多學(xué)者的研究對(duì)象[25-29]。Barnwal等[30]利用光伏光熱技術(shù)設(shè)計(jì)了一種溫室干燥機(jī)并建立熱模型，通過試驗(yàn)得出總體熱效率在33%～37.8%，熱模型與試驗(yàn)數(shù)據(jù)吻合。但現(xiàn)有研究大多在能量轉(zhuǎn)化和改善作物生長(zhǎng)環(huán)境方面，利用太陽(yáng)能對(duì)作物必需的要素（例如水）進(jìn)行改善的探究相對(duì)缺乏。

在中國(guó)西北地區(qū)，初春時(shí)節(jié)灌溉水溫較低，作物苗期對(duì)溫度反應(yīng)極為敏感，春灌時(shí)易出現(xiàn)凍壞、死苗現(xiàn)象[31]，且灌溉時(shí)需要消耗電能。因此，本文基于光伏光熱技術(shù)設(shè)計(jì)了一套灌溉水增溫系統(tǒng)，擬通過試驗(yàn)研究的方式，對(duì)其進(jìn)行不同流量下性能測(cè)試研究，并分析初始水溫和輻照度對(duì)系統(tǒng)性能的影響，以期通過該系統(tǒng)減弱低溫灌溉水給作物帶來的不利影響，促使作物提質(zhì)增效，一定程度上填補(bǔ)農(nóng)業(yè)生產(chǎn)活動(dòng)及農(nóng)業(yè)自動(dòng)化、智能化所帶來的電能消耗。

1 基于PV/T技術(shù)灌溉水增溫試驗(yàn)系統(tǒng)

1.1 系統(tǒng)的主要部件與儀器

如圖1a所示，該試驗(yàn)?zāi)Ｐ拖到y(tǒng)主要由PV/T集熱器、保溫桶、潛水泵、變頻器和鎢鹵素?zé)舻炔考M成。系統(tǒng)關(guān)鍵部件水冷型PV/T集熱器采用管板式平板集熱器，其外框尺寸為2 550 mm×808 mm×80 mm，有效采光面積為2 m2，主要由玻璃蓋板、EVA膠膜、單晶硅電池、TPT背板、吸熱板、吸熱管和保溫材料等部件組成。單塊大光伏電池板由兩塊小光伏電池板并聯(lián)組成，單塊小光伏電池板由60塊單晶硅電池串聯(lián)組成，額定開路電壓為37.9 V，額定功率為160 W。玻璃蓋板采用透光率良好的低鐵布紋玻璃鋪設(shè)于最上方，其下是上層EVA膠膜主要用于對(duì)光伏電池的保護(hù)以及光伏電池與玻璃蓋板的連接，光伏電池與吸熱板間設(shè)有黑色TPT背板作為絕緣層，集熱板背面采用激光焊接工藝的6根平行分布的銅管，銅管的兩端嵌入集管之中。管的背面填充厚度為20 mm的巖棉和40 mm的橡塑海綿作為保溫材料。最后采用3 mm厚鋼板條將保溫材料固定。PV/T集熱器、系統(tǒng)管道、保溫桶、潛水泵的詳細(xì)材料及性能參數(shù)如表1所示。

試驗(yàn)中，使用變頻器（220-004E21，廣東東莞宇鑫科技有限公司）與潛水泵（QDX1-10-0.25，上海豐浪機(jī)電有限公司）相連，通過改變潛水泵交流電的頻率，控制水泵電機(jī)轉(zhuǎn)速，進(jìn)而實(shí)現(xiàn)灌溉水的流量控制。鎢鹵素?zé)簦≦VF137，Philips）用于模擬太陽(yáng)光，并采用TBQ-2太陽(yáng)總輻射表測(cè)量PV/T集熱器表面的太陽(yáng)輻照度，采用Pt100鉑熱電阻監(jiān)測(cè)進(jìn)出口水溫的變化，測(cè)量數(shù)據(jù)通過數(shù)據(jù)采集儀Agilent34970A進(jìn)行采集，系統(tǒng)流量采用LXSR流量計(jì)測(cè)量，光伏電池板的陽(yáng)極與陰極通過固定阻值的電阻及開關(guān)連接形成閉環(huán)環(huán)路，采用數(shù)字萬(wàn)用表檢測(cè)光伏電池板的輸出電量。所有測(cè)量均在關(guān)閉門窗并打開空調(diào)將溫度設(shè)置為20 ℃的環(huán)境中進(jìn)行。

表1 灌溉水增溫系統(tǒng)主要部件參數(shù)

1.2 系統(tǒng)運(yùn)行原理

本文探討的基于太陽(yáng)能光伏光熱技術(shù)灌溉水增溫試驗(yàn)系統(tǒng)如圖1a所示，試驗(yàn)系統(tǒng)實(shí)物圖如圖1b所示。其工作原理如下：灌溉水由外部水泵從水源進(jìn)入保溫桶1，潛水泵提供動(dòng)力使低溫灌溉水依次經(jīng)過疊片過濾器、流量計(jì)、調(diào)節(jié)閥、變徑管后進(jìn)入PV/T集熱器中，流經(jīng)背板銅管吸收熱量，對(duì)灌溉水實(shí)現(xiàn)加熱增溫，然后進(jìn)入保溫桶2，由保溫桶2中的潛水泵泵送灌溉。

1.3 試驗(yàn)設(shè)計(jì)

試驗(yàn)分別設(shè)置3種不同強(qiáng)度的輻照度[18]、3種不同的灌溉水初始水溫、8種不同的流量，共72種工況。初始水溫根據(jù)當(dāng)?shù)爻醮簳r(shí)灌溉所用河水與地下井水的平均溫度設(shè)置，由高到低分別為10、7.5（中國(guó)西北初春灌溉水平均溫度）、5 ℃。由于采用模擬太陽(yáng)光，光照不均勻，故采用太陽(yáng)輻射總表測(cè)量1/2 PV/T集熱器表面1號(hào)到60號(hào)不同位置的太陽(yáng)輻照度（由于鎢鹵素?zé)襞cPV/T集熱器左右兩側(cè)完全對(duì)稱，所以只測(cè)量1/2）如圖2a所示。測(cè)量結(jié)果如圖2b，2c，2d所示，高、中、低輻射強(qiáng)度下太陽(yáng)輻照度的變化范圍分別為499.37～795.11、311.47～600.83、198.68～445.58 W/m2，為減少試驗(yàn)中的不確定性，太陽(yáng)輻照度取所測(cè)數(shù)據(jù)的平均值，高輻照度為650 W/m2，中輻照度為465 W/m2，低輻照度為320 W/m2。試驗(yàn)中流量變化范圍為0.01～0.08 kg/(s·m2)。

圖2 PV/T集熱器表面測(cè)量點(diǎn)及太陽(yáng)輻照度

2 主要性能指標(biāo)計(jì)算方法

對(duì)所設(shè)計(jì)的基于光伏光熱技術(shù)灌溉水增溫系統(tǒng)做出以下假設(shè)[26]（所做假設(shè)僅方便計(jì)算不影響結(jié)果及結(jié)論）：

1）灌溉水在系統(tǒng)內(nèi)流動(dòng)時(shí)過流斷面上的溫度分布均勻；

2）由于在PV/T集熱器背部設(shè)有隔熱措施，故不計(jì)PV/T集熱器背面漏熱；

3）從PV/T集熱器的自身結(jié)構(gòu)來看，太陽(yáng)輻射所產(chǎn)生的能量主要集中于除去隔熱措施后的上層，上層厚度很小向四周散失的能量非常低，故認(rèn)為四周絕熱；

4）光伏電池板與集熱板之間接觸良好且集熱板厚度很小，故忽略接觸熱阻；

5）PV/T集熱器表面所受太陽(yáng)輻射是均勻的。

2.1 溫度指標(biāo)

2.2 能量效率

圖3為PV/T集熱器模型圖，其各部分能量間存在如下關(guān)系[29]：

1.光伏電池板 2.集熱板 3.銅管 4.巖棉 5.橡塑海綿 6.鋁合金外框 7. 玻璃蓋板 8.上層乙烯-醋酸乙烯共聚物膠膜 9.光伏電池片 10.下層乙烯-醋酸乙烯共聚物膠膜 11.聚氟乙烯復(fù)合膜

1.PV panel 2.Heat collecting plate 3.Copper pipe 4.Rock wool 5.Rubber plastic sponge 6.Aluminum alloy frame 7.Glass cover 8.Ethylene-vinyl acetate copolymer_up 9.PV cells 10.Ethylene-vinyl acetate copolymer_down 11. Polyfluoroethylene composite membrane

注：字母參考式（3）解釋。

Note: Letter refer to formula (3) for explanation.

圖3 PV/T集熱器模型圖

Fig.3 Model diagram of PV/T collector

2.3 應(yīng)用前景

采用全生命周期成本分析方法（Life Cycle Cost，LCC）[32-33]計(jì)算經(jīng)濟(jì)效益評(píng)估本系統(tǒng)的應(yīng)用前景。

2.4 數(shù)據(jù)分析

采用EXCEL軟件進(jìn)行平均值計(jì)算和SPSS25.0統(tǒng)計(jì)軟件進(jìn)行相關(guān)關(guān)系分析。

3 試驗(yàn)結(jié)果與分析

3.1 不同灌溉水流量對(duì)系統(tǒng)性能的影響

由試驗(yàn)結(jié)果知，不同初始水溫與輻照度，對(duì)由流量變化引起的分析指標(biāo)的變化規(guī)律無(wú)影響，因此本文對(duì)固定工況（初始水溫和輻照度分別為7.5 ℃和465 W/m2，接近中國(guó)西北初春實(shí)際工況）進(jìn)行分析。如圖4所示，出水口水溫升溫幅度隨著流量的增加呈現(xiàn)逐漸減小的趨勢(shì)，在流量為0.01 kg/(s·m2)時(shí)最高，此時(shí)出水口水溫及升溫幅度分別為20.9和12.5 ℃。流量增大，單位質(zhì)量的灌溉水流經(jīng)PV/T集熱器的時(shí)間變短，所獲得熱量減少；此外，較大的流量使得吸熱板的溫度更低，0.08 kg/(s·m2)吸熱板溫度相較于0.01 kg/(s·m2)吸熱板溫度下降了7.15 ℃，進(jìn)一步降低了系統(tǒng)的換熱效率。

由圖5可知，系統(tǒng)的光電效率和光熱效率變化規(guī)律趨于一致，均隨著流量的增加而逐漸增大，且增大趨勢(shì)逐漸減緩。分析可知這是由于流量增加，更多的熱量被灌溉水吸收，光伏組件溫度下降，光電效率和光熱效率有所增加，但灌溉水升溫幅度逐漸減少，導(dǎo)致熱量雖有所增加但增加量逐漸減少，光伏組件溫度的變化也趨于平緩，光電效率和光熱效率增長(zhǎng)幅度減小，最高光電效率和光熱效率分別為0.094和0.310。

流量對(duì)實(shí)際能量效率和水泵功率均有明顯影響，如圖6所示。試驗(yàn)結(jié)果顯示隨著流量的增加，實(shí)際綜合效率先增后減，在小流量范圍內(nèi)增加，在大流量范圍內(nèi)減小，最大達(dá)到0.484，拐點(diǎn)在流量0.03 kg/(s·m2)；水泵功率與流量為二次函數(shù)增長(zhǎng)，質(zhì)量流量越大增長(zhǎng)速度越快。在小流量范圍內(nèi)，系統(tǒng)集熱量、發(fā)電量之和遠(yuǎn)大于水泵耗電量，隨流量增加，光熱效率增幅較大，水泵功率增加速度較慢，因此系統(tǒng)實(shí)際能量效率呈上升趨勢(shì)。質(zhì)量流量增大至較大范圍后，一方面光電效率、光熱效率增長(zhǎng)已趨于平緩，系統(tǒng)收益能量增加量少，另一方面水泵功率隨流量的增加迅速變大，系統(tǒng)本身能量消耗不斷增加，二者結(jié)合綜合能量效率呈現(xiàn)明顯降低的現(xiàn)象，且流量越大綜合能量效率減少速度越快[28]。

3.2 灌溉水不同初始溫度對(duì)系統(tǒng)性能的影響

不同初始溫度灌溉水工況下出水口水溫及升溫幅度如圖7所示，可以看出在相同流量下，初始溫度為10 ℃時(shí)出水口水溫最高，7.5 ℃居中（中國(guó)西北初春灌溉水平均溫度），5 ℃最低，最高可達(dá)22.6 ℃。相較于固定工況，初始溫度為10和5 ℃的出水口水溫變幅隨著流量增加逐漸增大，分別從0.01 kg/(s·m2)的7.9%和-11.8%增大至0.08 kg/(s·m2)的23.9%和-22.7%；升溫幅度方面，初始溫度為5 ℃時(shí)灌溉水升溫幅度最高，7.5 ℃居中，10 ℃最低，隨著流量的增大，不同初始水溫的升溫幅度逐漸接近。

由圖8可以看出，灌溉水初始水溫可影響系統(tǒng)的光電效率、光熱效率和實(shí)際能量效率，3種能量指標(biāo)與初始水溫間呈負(fù)相關(guān)關(guān)系，流量為0.08 kg/(s·m2)時(shí)，5 ℃灌溉水光電效率和光熱效率較固定工況分別增加了0.024%和1.619%，10 ℃灌溉水光電效率和光熱效率較固定工況分別降低了0.048%和0.693%；流量為0.03 kg/(s·m2)時(shí)，5 ℃和10 ℃實(shí)際能量效率相較固定工況分別增加和減少了1.598%、2.058%。

綜上分析可知相同輻照度下，初始溫度相對(duì)更低的灌溉水吸收PV/T集熱器光伏組件上的熱量更多[34]，使得光伏組件溫度更低，進(jìn)而能量方面表現(xiàn)為光電效率更大，光熱效率更高、實(shí)際能量效率更大；溫度方面表現(xiàn)為升溫幅度更大，但不足以超越原本初始溫度之間的差值，因此初始水溫仍是決定出水口水溫的重要因素；隨著流量增加，單位質(zhì)量的灌溉水獲得的熱量逐漸接近，灌溉水的初始溫度成為重要因素，因而升溫幅度逐漸接近，出水口水溫變幅逐漸增大。

3.3 不同輻照度對(duì)系統(tǒng)性能的影響

由圖9可以看出，相同流量下出水口水溫和升溫幅度與輻照度呈正相關(guān)關(guān)系，流量為0.01 kg/(s·m2)時(shí)，高輻照度工況出水口水溫及升溫幅度相較于固定工況分別提高了3.38和3.47 ℃，低輻照度工況出水口水溫及升溫幅度相較于固定工況分別降低了4.42和3.6 ℃。隨著流量的增加，輻照度對(duì)出水口水溫及升溫幅度產(chǎn)生的影響逐漸減弱，流量增大至0.08 kg/(s·m2)時(shí)，出水口水溫均在10 ℃左右。這是由于較高的輻照度意味著PV/T集熱器可接收更多的太陽(yáng)能，有更多的能量轉(zhuǎn)化為灌溉水的內(nèi)能，因而在流量較小時(shí)升溫明顯；隨著流量的增加，單位質(zhì)量灌溉水流經(jīng)PV/T集熱器時(shí)間變短，換熱量趨于一致，因此對(duì)灌溉水的增溫效果也逐漸相同。

由圖10可知，系統(tǒng)光電效率、光熱效率與輻照度呈負(fù)相關(guān)關(guān)系，最大光電效率和光熱效率分別達(dá)到0.096和0.417。這是由于PV/T集熱器處于較高的輻照度工況下時(shí)，光伏組件獲得的能量更多，表面溫度相對(duì)更高，對(duì)外界環(huán)境產(chǎn)生的熱輻射和在光伏組件表面產(chǎn)生的對(duì)流更加劇烈，散失的能量更多且占比更大，造成光電效率和光熱效率更低。系統(tǒng)實(shí)際能量效率與輻照度間的關(guān)系還與灌溉水的流量有關(guān)，當(dāng)灌溉水流量較小（<0.06 kg/(s·m2)）時(shí)，實(shí)際能量效率與輻照度之間呈負(fù)相關(guān)關(guān)系；當(dāng)流量較大（>0.07 kg/(s·m2)）時(shí)，實(shí)際能量效率與輻照度之間呈正相關(guān)關(guān)系。實(shí)際能量效率方面，實(shí)際能量收益量（即產(chǎn)生的電能與灌溉水增加的內(nèi)能）與輻照度呈正相關(guān)關(guān)系，流量較小時(shí)，水泵功率較小，對(duì)實(shí)際能量收益影響不大；流量較大時(shí)，水泵功率較大，實(shí)際能量收益越小的工況受到的影響越大，因而相關(guān)關(guān)系發(fā)生變化。

3.4 應(yīng)用前景分析

系統(tǒng)初期投資根據(jù)所需各部件在當(dāng)?shù)氐钠骄鶅r(jià)格計(jì)算，首年運(yùn)行維護(hù)費(fèi)為按初期投資的2%，通脹率按5%計(jì)算，將系統(tǒng)折舊考慮到維運(yùn)總成本中。將光伏發(fā)電收益考慮到全生命周期成本中。計(jì)算結(jié)果如表 2所示。

圖10 7.5 ℃灌溉水不同輻照度下運(yùn)行的光電效率，光熱效率和實(shí)際能量效率

表2 基于光伏光熱技術(shù)的灌溉水增溫系統(tǒng)與傳統(tǒng)溫室光伏屋頂?shù)腖CC（Life Cycle Cost）分析

由表2可以看出，與傳統(tǒng)溫室光伏屋頂相比，本研究提出的基于光伏光熱技術(shù)的灌溉水增溫系統(tǒng)初期投資及生命周期維運(yùn)總成本較高，均為傳統(tǒng)溫室光伏屋頂?shù)?.11倍，然而，全生命周期成本較低，LCC減少17.6%，綜合考慮作物增產(chǎn)、提質(zhì)、增效提高的收益，應(yīng)用前景將更好。

本系統(tǒng)還尚處于研發(fā)與試驗(yàn)研究階段，其實(shí)際安裝面積還應(yīng)根據(jù)戶外實(shí)際輻照度、灌水量、灌溉時(shí)間和所需灌溉水溫度等因素進(jìn)一步討論。

4 結(jié) 論

本文以基于太陽(yáng)能光伏光熱技術(shù)灌溉水增溫系統(tǒng)為研究對(duì)象，研究分析了系統(tǒng)在不同流量運(yùn)行下的系統(tǒng)性能，以及灌溉水初始水溫和輻照度對(duì)系統(tǒng)運(yùn)行的影響。主要結(jié)論如下：

1）出水口水溫及升溫幅度與流量呈負(fù)相關(guān)關(guān)系，以中等輻照度下初始水溫為7.5 ℃灌溉水為固定工況，其出水口水溫和升溫幅度最高達(dá)20.9和12.5 ℃；光電效率和光熱效率與流量呈正相關(guān)關(guān)系；隨流量增加，實(shí)際能量效率呈先增后減的趨勢(shì)，最大達(dá)到0.484，拐點(diǎn)在0.03 kg/(s·m2)。

2）低溫灌溉水與光伏組件換熱更為劇烈，升溫幅度與初始水溫呈負(fù)相關(guān)關(guān)系，但初始水溫仍是決定出水口水溫的重要因素，具體表現(xiàn)為正相關(guān)關(guān)系，最高出水口水溫達(dá)到22.6 ℃，隨著流量的增加，升溫幅度逐漸接近，出水口水溫的變幅增大；3種能量指標(biāo)均與初始水溫呈負(fù)相關(guān)關(guān)系。

3）出水口水溫和升溫幅度均與輻照度呈正相關(guān)關(guān)系，流量增加會(huì)削弱輻照度對(duì)出水口水溫及升溫幅度產(chǎn)生的影響，流量增大到0.08 kg/(s·m2)時(shí)，出水口水溫趨于一致，均在10 ℃左右；光電效率和光熱效率與輻照度均呈負(fù)相關(guān)關(guān)系，最大分別為0.096和0.417；在流量較?。?0.06 kg/(s·m2)）時(shí)，實(shí)際能量效率與輻照度之間呈負(fù)相關(guān)關(guān)系，當(dāng)流量較大（>0.07 kg/(s·m2)）時(shí)，實(shí)際能量效率與輻照度之間呈正相關(guān)關(guān)系。

4）與傳統(tǒng)溫室光伏屋頂相比，基于太陽(yáng)能光伏光熱技術(shù)灌溉水增溫系統(tǒng)初期投資較高，但綜合電能收益，全生命周期成本較小，LCC（Life Cycle Cost）減少17.6%。本系統(tǒng)還尚處于研發(fā)與試驗(yàn)研究階段，其實(shí)際安裝面積還應(yīng)根據(jù)戶外實(shí)際輻照度、灌水量、灌溉時(shí)間和所需灌溉水溫度等因素進(jìn)一步討論。

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Experimental study on irrigation water warming system based on solar photovoltaic/thermal technology

Zhang Jinzhu, Wang Qin, Wang Zhenhua, Xu Xin

(1.,,832000,; 2.,,832000,)

The purpose of this study was to present a dedicated experimental investigation on the performance of a novel irrigation water warming system using solar photovoltaic/thermal technology. A combination was designed, including a flat-plate PV/T collector, the insulation barrels, the submerged pump, the frequency changer, the tungsten halogen lamp, and the system pipe. The cold irrigation water absorbed the heat through the flat-plate PV/T collector, where the temperature of photovoltaic modules was reduced for higher photoelectric efficiency. The experimental platform for the irrigation water warming system was built, where a series of tests were conducted under different working conditions, including the liquid mass flow rates 0.01-0.08 kg/(s·m2), initial water temperatures (5,7.5, 10 ℃), and the radiations (320, 465, and 650 W/m2). All 72 working conditions in total were conducted in the test, where the door and windows were closed in the room, and the temperature was controlled at 20 ℃ by the air conditioner. An analysis was made on the irrigation water temperature, the extent of temperature, photoelectric efficiency, solar thermal efficiency, and practical energy performance of the system. The results show that the outlet water temperature and the increasing extent of temperature reached 20.9 and 12.5 ℃, both of which were negatively correlated with the mass flow rate, particularly under the fixed condition, where the initial water temperature was 7.5 ℃, and the radiation was 465 W/m2. Nevertheless, the solar electric and thermal efficiency were positively correlated with the mass flow rate. The practical energy efficiency increased first and then decreased with the mass flow rate up rating, reaching a maximum of 0.484, where the inflection point was 0.03 kg/(s·m2). Besides, the irrigation water temperature, the extent of temperature, and energy performance of the system were compared under the middle radiation and different initial working condition of water temperatures. The heat transfer was much more intense, as the initial water temperature decreased, thereby causing the higher increasing extent of temperature. The initial water temperature was still an important factor to determine the water temperature of the outlet, indicating a positive correlation, and the maximum water temperature of the outlet of 22.6 ℃. Additionally, the solar electric efficiency, solar thermal efficiency, and practical energy efficiency were negatively correlated with the initial water temperature. Furthermore, irrigation water temperature and extent of temperature were relatively larger, when the system was under the higher solar radiation, but the increase of mass flow rate weaken the influence on the two indexes. The outlet water temperatures were maintained at about 10 ℃ when the system operated at 0.08 kg/(s·m2) with 7.5 ℃ irrigation water under different solar radiation. The solar electric efficiency and solar thermal efficiency were also negatively correlated with the solar radiation, where the maximum values were 0.096 and 0.417, respectively. Moreover, the practical energy efficiency was negatively correlated with the solar radiation, when the mass flow rate was less than 0.06 kg/(s·m2). It was just the opposite trend, when the mass flow rate was greater than 0.07 kg/(s·m2). In terms of application prospect, the initial investment of irrigation water heating system was higher using solar photovoltaic technology, compared with the traditional greenhouse photovoltaic roof, but the whole life cycle cost was smaller, and the LCC was reduced by 17.6%, considering the comprehensive energy benefits. The system was still in the stage of research and experimental study. The actual installation area can be further addressed, according to the actual outdoor irradiance, irrigation amount, irrigation time, required irrigation water temperature.

photovoltaic/thermal; irrigation; solar radiation warming; mass flow rate; initial water temperature;

張金珠，王欽，王振華，等. 基于太陽(yáng)能光伏光熱技術(shù)的灌溉水增溫系統(tǒng)試驗(yàn)[J]. 農(nóng)業(yè)工程學(xué)報(bào)，2021，37(16)：72-79.doi：10.11975/j.issn.1002-6819.2021.16.010 http://www.tcsae.org

Zhang Jinzhu, Wang Qin, Wang Zhenhua, et al. Experimental study on irrigation water warming system based on solar photovoltaic/thermal technology[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2021, 37(16): 72-79. (in Chinese with English abstract) doi：10.11975/j.issn.1002-6819.2021.16.010 http://www.tcsae.org

2021-04-10

2021-07-01

國(guó)家自然科學(xué)基金資助項(xiàng)目（51869028）

張金珠，博士，副教授，研究方向?yàn)楦珊祬^(qū)節(jié)水灌溉理論與技術(shù)。Email：xjshzzjz@sina.cn

10.11975/j.issn.1002-6819.2021.16.010

S214

A

1002-6819(2021)-16-0072-08