離網(wǎng)運行光伏發(fā)電系統(tǒng)，一般都要配置蓄電池組作為儲能裝置。蓄電池的作用是將太電池方陣在有日照時發(fā)出的多余電能儲存起來，以供晚間或陰雨天時負載使用。蓄電池容量是指其蓄電的能力，通常用該蓄電池放電至終了電壓所放出的電量大小來度。鉛蓄電池的使用容量是在一定的工作條件下所放出的電量，鉛蓄電池使用容量與廠家造質(zhì)量及電池工作條件有關(guān)。確定離網(wǎng)光伏系統(tǒng)蓄電池容量最佳值，必須綜合考慮太陽電方陣發(fā)電量、負荷容量及直交變換裝置（逆變器）的效率等。蓄電池容量的計算方法有種，一般可通過下式求出。

C－蓄電池容量，kW·h（Ah）；D－最長無日期間用電時數(shù)，h；F—蓄電池放電效率的修正系數(shù)，（通常取1.05）；PO－平均負荷容量，kW；Ｌ為蓄電池的維修保養(yǎng)率，（通常取0.8）；U為蓄電池的放電深度（通常取0.5）；Ｋα為包括逆變器等交流回路的損耗率（通常取0.7～0.8）。上式可簡化為：

 
      這就是由平均負荷容量和最長連續(xù)無日照時間（用電使用時間）求出蓄電池容量的簡計算公式。應(yīng)當注意到，無日照時間取多長為恰當。若取得過長，計算出的蓄電池容量大，不必要地加大投資。而且，若蓄電池容量增大，必須使太陽電池的容量相應(yīng)加大，使者容量相匹配才合適；否則相對的蓄電池充電速率減小，蓄電池總是充不滿也會影響使用命，因為蓄電池在接近滿充電的狀態(tài)下使用較好。因此，過長預(yù)估無日照時間以為安全，實際并不恰當。一般地說，取3倍于太陽電池出力的蓄電池出力認為是比較適當?shù)?。由于蓄電池容量一般以安時數(shù)表示，故蓄電池容量應(yīng)該為：

       為蓄電池容量，A·ｈ；V為光伏系統(tǒng)的電壓等級（系統(tǒng)電壓），通常為12V、24V、48V、110V或220V。
         案例1：按廣東星火太陽能電源有限公司提供的晶體電池組件，對廣東耐普電池股份有限公司的閥控式密封鉛酸蓄電池進行選型?；疽鬄椋嚎蔀?00W的負載連續(xù)5天陰雨天的情況下供電；蓄電池能放電到其額定容量的75%-80%，性能正常，并保證具有5年使用壽命。

耐普AGM電池放電容量如表4-3所示。

      表1 AGM電池的放電容量/Ah。 

  逆變器的轉(zhuǎn)換效率為0.75，負載為400W,故實際所需功率為400/0.75=533W。功率400W太陽能電池方陣用蓄電池選型容量計算如下：電壓為24V，則電流I=533/24=22.2A。  如果連續(xù)使用5天，即120h，則放電容量為22.2*120=2664Ah。如果按電池的80%利用率計算，

則對電池的額定容量要求為：容量C=2664/0.8=3330(Ah)

正常使用情況下，按照此設(shè)計，正常白天充電，晚上蓄電池放電（以放電12h為例）的情況下（負載工作6-12h），逆變器轉(zhuǎn)換效率按75%進行計算，該蓄電池的放電深度為：U=22.2*12/3330=8.0%
       方案1：用2組1500Ah電池并聯(lián)使用。上述測試數(shù)據(jù)可以看出，1500Ah的電池容量比較富余，其10h容量平均可以達到1700Ah，如果采用2組并聯(lián)，容量可以達到3330Ah以上，可以滿足要求。這一方面的優(yōu)點是容量可以達到要求并有點富余，同時只需要2組電池，維護相應(yīng)較少，電池占的空間要少。
       方案2：用4組800Ah電池并聯(lián)使用。800Ah電池10h的放電平均容量為880Ah，如果采用4組并聯(lián)，其容量可以達到3500Ah，足以達到3330Ah，容量比較富余。這一方案優(yōu)點是使用4組為800Ah的電池并聯(lián)，容量更充分、富余；其缺點是要并聯(lián)使用4組電池，相對于1500Ah的電池，成本要增加，所占用的場地或則體積和空間要增加，維護工作也要大些。

Off-grid operation of photovoltaic power generation system, generally to configure battery pack as energy storage device.  The role of the battery is to store the excess energy generated by the battery array in sunlight for use at night or in rainy days.  Battery capacity refers to its capacity to store electricity, usually with the battery discharge to the terminal voltage of the amount of electricity released.  The service capacity of lead battery is the amount of electricity released under certain working conditions. The service capacity of lead battery is related to the quality of the manufacturer and the working conditions of the battery.   To determine the optimal capacity of battery in off-grid photovoltaic system, the solar array generation, load capacity and efficiency of DC converter (inverter) must be considered comprehensively.   Battery capacity calculation method, generally can be obtained by the following formula.   

C- Battery capacity, kW·h (Ah);  D- Maximum number of hours of electricity consumption without a day, h;  F -- Correction coefficient of battery discharge efficiency, (usually 1.05);  PO- Average load capacity, kW;  L is the maintenance rate of the battery (usually 0.8);  U is the discharge depth of the battery (usually 0.5).   Kα is the loss rate of ac circuit including inverter (usually 0.7 ~ 0.8).  The above equation can be simplified as:   

This is the average load capacity and the longest continuous sunshine (use time) to calculate the battery capacity simple formula.  It should be noted that the length of time without sunshine is appropriate.  If obtained too long, the calculated battery capacity is large, unnecessarily increase investment.  Moreover, if the capacity of the battery increases, the capacity of the solar cell must be increased accordingly, and the capacity of the messenger is appropriate to match;  Otherwise the relative battery charging rate is reduced, the battery is always dissatisfied will also affect the use of life, because the battery in close to the state of full charge is better used.  Therefore, it is not appropriate to estimate the time without sunshine for too long as it is safe.  Generally speaking, take 3 times the output of the solar battery output is considered to be more appropriate.  As the battery capacity is generally expressed in ampere hours, the battery capacity should be:   

Is battery capacity, A·h;  V is the voltage level of the photovoltaic system (system voltage), usually 12V, 24V, 48V, 110V or 220V.  

Case 1: The valve-controlled sealed lead-acid battery of Guangdong Knapp Battery Co., LTD was selected according to the crystal battery module provided by Guangdong Spark Solar Power Supply Co., LTD.   The basic requirements are: can supply power for the load of 400W for 5 consecutive days under cloudy and rainy conditions;   The battery can discharge up to 75% to 80% of its rated capacity, with normal performance and guaranteed service life of 5 years.   

Table 4-3 lists the discharge capacity of the KNap AGM battery.  

Table 1 Discharge capacity of the AGM battery /Ah.   

The conversion efficiency of the inverter is 0.75, and the load is 400W, so the actual power required is 400/0.75=533W.  The selection capacity of battery for solar cell square array with 400W power is calculated as follows: voltage is 24V, current I=533/24= 22.2a.   If it is used continuously for 5 days, i.e. 120h, the discharge capacity is 22.2*120=2664Ah.  If you use 80% of the battery,       

The rated capacity of the battery is: Capacity C=2664/0.8=3330(Ah)   

In normal use, according to this design, when the battery is normally charged during the day and discharged at night (for example, the battery is discharged for 12h) (the load is 6-12h), the inverter conversion efficiency is calculated as 75%, and the discharge depth of the battery is: U=22.2*12/3330=8.0%  

Solution 1: use two 1500Ah batteries in parallel.  As can be seen from the above test data, the battery capacity of 1500Ah is relatively surplus, and its 10h capacity can reach 1700Ah on average. If two groups are used in parallel, the capacity can reach more than 3330Ah, which can meet the requirements.   The advantage of this aspect is that the capacity can meet the requirements and a little surplus, at the same time, only two batteries are needed, so the maintenance is correspondingly less, the battery takes up less space.  

Scheme 2: Use four 800Ah batteries in parallel.  The average discharging capacity of an 800Ah battery in 10h is 880Ah. If four groups are used in parallel, the capacity can reach 3500Ah, which is enough to reach 3330Ah.  The advantage of this scheme is that four groups of 800Ah batteries are used in parallel, and the capacity is more sufficient and surplus.  Its disadvantage is to use four groups of batteries in parallel. Compared with the 1500Ah battery, the cost should be increased, the site or volume and space occupied should be increased, and the maintenance work should be larger.