光伏離網(wǎng)系統(tǒng)設(shè)計三大原則

    1、根據(jù)用戶的負(fù)載類型和功率確認(rèn)離網(wǎng)逆變器的功率。

     家用負(fù)載一般分為感性負(fù)載和阻性負(fù)載，洗衣機、空調(diào)、冰箱、水泵、抽油煙機等帶有電動機的負(fù)載是感性負(fù)載，電動機啟動功率是額定功率的5-7倍，在計算逆變器的功率時，要把這些負(fù)載的啟動功率考慮進去。逆變器的輸出功率要大于負(fù)載的功率。對于監(jiān)控站，通信站等要求嚴(yán)格的場合，輸出功率是按所以的負(fù)載功率之和。但對于一般貧困家庭而言，考慮到所有的負(fù)載不可能同時開啟，為了節(jié)省成本，可以在負(fù)載功率之和乘以0.7-0.9的系數(shù)。并不是每一個客戶都會對負(fù)載功率很清楚。

      2、根據(jù)用戶每天的用電量確認(rèn)組件功率。

    組件的設(shè)計原則是要滿足平均天氣條件下負(fù)載每日用電量的需求，也就是說太陽能電池組件的全年發(fā)電量要等于負(fù)載全年用電量。因為天氣條件有低于和高于平均值的情況，太陽能電池組件設(shè)計的基本滿足光照最差季節(jié)的需要，就是在光照最差的季節(jié)蓄電池也能夠基本上天天充滿電。但在有些地區(qū)，最差季節(jié)的光照度遠(yuǎn)遠(yuǎn)低于全年平均值，如果還按最差情況設(shè)計太陽能電池組件的功率，那么在一年中的其他時候發(fā)電量就會遠(yuǎn)遠(yuǎn)超過實際所需，造成浪費。這時只能考慮適當(dāng)加大蓄電池的設(shè)計容量，增加電能儲存，使蓄電池處于淺放電狀態(tài)，彌補光照最差季節(jié)發(fā)電量的不足對蓄電濁造成的傷害。組件的發(fā)電量并不能完全轉(zhuǎn)化為用電，還要考慮控制器的效率和機器的損耗以及蓄電池的損耗，太陽能控制器有PWM和MPPT兩種類型，PWM控制器效率約85%，輸入電壓范圍比較窄，但價格比較低，MPPT控制器效率約95%，價格比較高。蓄電池在充放電過程中，也會有10-15%的損耗。離網(wǎng)系統(tǒng)可用的電量=組件總功率*太陽能發(fā)電平均時數(shù)*控制器效率*蓄電池效率。

    有一些離網(wǎng)用戶，沒有裝過電表，對自己的用電情況不是十分清楚，還有一些離網(wǎng)系統(tǒng)，是新建的，這時就需要去估算每天的用電量，對于燈泡、電風(fēng)扇、電吹風(fēng)這樣的負(fù)載，用電量等于功率乘以時間；但空調(diào)，冰箱這樣的負(fù)載，是間隙性工作的，電視，電腦，音響這樣的負(fù)載，工作時很少在滿功率狀態(tài)，計算電量時，就要綜合考慮了。

      空調(diào)是家用電器耗電量最大的負(fù)載，1匹空調(diào)的電功率是735W，也就是說1小時滿負(fù)荷運行消耗0.735度電，空調(diào)還有一個指標(biāo)“制冷量”，單位也是W，1匹空調(diào)制冷量約2300W，空調(diào)的耗電和室內(nèi)外溫度差，房間面積，空調(diào)的能效率有很大關(guān)系，1臺1P的空調(diào)，晚上用8小時，耗電1-5度不等。

      3、根據(jù)用戶晚上用電量或者期望待機時間確定蓄電池容量。

蓄電池的任務(wù)是在太陽能輻射量不足時，保證系統(tǒng)負(fù)載的正常用電。對于重要的負(fù)載，要能在幾天內(nèi)保證系統(tǒng)的正常工作，要考慮連續(xù)陰雨天數(shù)。對于一般的負(fù)載如太陽能路燈等可根據(jù)經(jīng)驗或需要在2～3天內(nèi)選取。重要的負(fù)載如通信、導(dǎo)航、醫(yī)院救治等則在3～7天內(nèi)選取。另外還要考慮光伏發(fā)電系統(tǒng)的安裝地點，如果在偏遠(yuǎn)的地方，蓄電池容量要設(shè)計得較大，因為維護人員到達(dá)現(xiàn)場就需要很長時間。實際應(yīng)用中，有的移動通信基站由于山高路遠(yuǎn)，去一次很不方便，除了配置正常蓄電池組外，還要配備一組備用蓄電池組，對于一般貧困家庭而言，主要考慮價格，則不用考慮陰雨天，太陽好的時候多用。太陽不好的時候少用，沒有太陽則不用。選擇負(fù)載時，盡量使用節(jié)能設(shè)備，如LED燈，變頻空調(diào)。蓄電池的設(shè)計主要包括蓄電池容量的設(shè)計計算和蓄電池組串并聯(lián)組合的設(shè)計。在光伏發(fā)電系統(tǒng)中，大部分使用的都是鉛酸蓄電池，考慮到電池的壽命，一般取放電深度為0.5-0.7之間。蓄電池設(shè)計容量=（負(fù)載日均用電量*連續(xù)陰雨天數(shù)）/蓄電池放電深度。

      離網(wǎng)用戶的需求是多種多樣的，根據(jù)用戶的要求設(shè)計光伏系統(tǒng)。這時候就要靈活處理，不一定要按上述的原則去設(shè)計，例如有一個客戶，家里有6塊260W的組件，要做一套光伏離網(wǎng)系統(tǒng)，客戶家里有市電，但經(jīng)常會停電，總負(fù)載是10KW，一天的用電量是20-30度，如果只有這1.56KW組件，根本沒有辦法滿足客戶的用電量要求，這時候就可以考慮滿足客戶一部分負(fù)載的需求，經(jīng)計算組件一天能發(fā)5度電，采用3.0KVA的離網(wǎng)逆變器，4塊12V150Ah的蓄電池，輸出接一個插板，平時接家里的照明燈泡，電腦，洗衣機之類的負(fù)載，晚上如果還有電，也可以單獨接一臺空調(diào)。

       對于針對特定人群的大項目，由于每個用戶情況不一樣，無法滿足所有的需求，這時候就要綜合考慮。一般情況下，是取一個平均值，如解決我國西部無電地區(qū)用電問題的光伏工程，一般牧民家庭，采用2塊250W的組件，一個500VA的離網(wǎng)逆變一體機，2個12V150AH的蓄電池，每天能發(fā)2.5度電，原材料成本價約6000元左右，可滿足電視機、小型電冰箱、DVD機、節(jié)能燈等電器的用電需求。重量比較輕，方便移動。在四川甘孜州某光伏扶貧項目中，采用中功率離網(wǎng)系統(tǒng)， 8塊250W的組件，3KVA的離網(wǎng)逆變一體機，4節(jié)12V200AH的蓄電池，每天可以發(fā)8-10度電，可滿足電視機、電冰箱、DVD機、電腦、1P空調(diào)，節(jié)能燈等電器的用電需求。由于系統(tǒng)總體發(fā)電量高，可以支持更多的家用電器設(shè)備，生活質(zhì)量得到提高。

 光伏離網(wǎng)系統(tǒng)常見問題：

     設(shè)計光伏離網(wǎng)系統(tǒng)時，要靈活處理，不要拘泥于某一個固定公式。光伏離網(wǎng)系統(tǒng)不能解決所有的用電問題，遇到多個連續(xù)陰雨天，只能省著用電。離網(wǎng)逆變器沒有統(tǒng)一的標(biāo)準(zhǔn)，也不需要強制認(rèn)證，市面上的產(chǎn)品良莠不齊，產(chǎn)品質(zhì)量和價格相差很大，大家在選購離網(wǎng)逆變器時，請認(rèn)準(zhǔn)品牌。碰到假貨或者劣質(zhì)產(chǎn)品要及時投訴或者報警。

     1、組件，逆變器，蓄電池設(shè)計時要匹配，任何一個都不能過大或者過小，新手設(shè)計時，經(jīng)常會把用電量計算過大，如1P空調(diào)運行12小時，算成10度電，300W的冰箱運行24小時，算成7.2度電，造成蓄電池容量過大，系統(tǒng)成本過高。設(shè)計蓄電池容量時，最好2天時間就給能充滿。

    2、光伏離網(wǎng)系統(tǒng)輸出連接負(fù)載，每個逆變器輸出端電壓和電流相位和幅值都不一樣，有些廠家逆變器不支持輸出端并聯(lián)，不要把逆變器輸出端接在一起。

    3、負(fù)載是電梯之類的負(fù)載不能直接和逆變器輸出端相連接，因為電梯在下降時，電動機反轉(zhuǎn)，會產(chǎn)生一個反電動勢，進入逆變器時，對逆變器有損壞。如果必須要用離網(wǎng)系統(tǒng)，建議在逆變器和電梯電動機之間加一個變頻器。

    4、帶市電互補輸入的光伏微網(wǎng)系統(tǒng)，組件的絕緣要做好，如果組件對地有漏電流，會傳到市電，引起市電的漏電開關(guān)跳閘。

    5、組件的電壓和蓄電池的電壓要匹配，PWM型控制器太陽能組件和蓄電池之間通過一個電子開關(guān)相連接，中間沒有電感等裝置，組件的電壓是蓄電池的電壓1.2-2.0倍之間，如果是24V的蓄電池，組件輸入電壓在30-50V之間，MPPT控制器，中間有一個功率開關(guān)管和電感等電路，組件的電壓是蓄電池的電壓1.2-3.5倍之間，如果是24V的蓄電池，組件輸入電壓在30-90V之間。

     6、組件的輸出功率和控制器的功率要相近，如一個48V30A的控制器，輸出功率為1440VA，組件的功率應(yīng)該在1500W左右。選擇控制器時，先看蓄電池的電壓，再用組件功率除以蓄電池的電壓，就是控制器的輸出電流。

     7、蓄電池的充電電流一般為0.1C-0.2C，最大不超過0.3C，例如1節(jié)鉛酸蓄電池12V200AH，充電電流一般在20A到40A之間，最大不能超過60A；蓄電池的放電電流一般為0.2C-0.5C，最大不超過1C，1節(jié)12V200AH鉛酸蓄電池，輸出最大功率不超過2400W，不同的廠家，不同的型號，具體的數(shù)值也不一樣，設(shè)計時要向廠家索取說明書。

Three principles of photovoltaic off-grid system design  

 

1. Confirm the power of the off-grid inverter according to the user's load type and power.  

 

 

 

Household load is generally divided into inductive load and resistive load, washing machine, air conditioner, refrigerator, water pump, range hood with motor load is inductive load, motor starting power is 5-7 times the rated power, in the calculation of the power of the inverter, to take these load starting power into account.   The output power of the inverter is greater than that of the load.  For monitoring station, communication station and other occasions with strict requirements, the output power is the sum of all the load power.  However, for general poor families, considering that all the loads can not be turned on at the same time, in order to save costs, the sum of the load power can be multiplied by the coefficient of 0.7-0.9.  Not every customer will be clear about the load power.  

 

 

2. Confirm the power of the component according to the daily power consumption of the user.  

 

 

 

The modules are designed to meet the load's daily demand for electricity under average weather conditions, which means that the solar modules need to generate as much electricity as the load does in a year.   Because the weather conditions are lower than or above the average, the solar cell module design basically meets the needs of the worst season of light, even in the worst season of light the battery can be fully charged every day.  But in some areas, the worst season is far below the annual average, and designing solar modules for the worst can waste much more electricity than is needed at other times of the year.  At this time, we can only consider appropriately increasing the design capacity of the battery, increasing the storage of electric energy, so that the battery is in a shallow discharge state, to make up for the damage caused by the lack of power generation in the worst lighting season.  Component power generation can not be completely converted to electricity, but also consider the efficiency of the controller and the loss of the machine and the loss of the battery, the solar controller has TWO types of PWM and MPPT, PWM controller efficiency of about 85%, the input voltage range is relatively narrow, but the price is low, MPPT controller efficiency of about 95%, the price is relatively high.  Battery in the process of charging and discharging, there will be 10-15% loss.  Available power of the off-grid system = total power of the module * average hours of solar power generation * controller efficiency * battery efficiency.  

 

There are some off-grid users, not installed electricity meter, is not very clear about their electricity consumption, and some off-grid system, is a new, then it is necessary to estimate the daily electricity consumption, for light bulbs, electric fans, hair dryers such a load, electricity consumption is equal to power times time;   But air conditioning, refrigerator such load, it is gap sex work, TV, computer, acoustics such load, working rarely in full power state, when calculating electric quantity, it is necessary to consider comprehensively.  

 

Air conditioning is one of the biggest household appliances power consumption load, air conditioning of electric power is 735 W, 1 that is 1 hour at full capacity operation consumes 0.735 KWH, air conditioning and a index "capacity", the unit is W, 1 air conditioning refrigerating capacity of about 2300 W, the power consumption of air conditioning and indoor and outdoor temperature difference, room area, air conditioning can efficiency has a lot to do,   A 1P air conditioner, 8 hours in the evening, power consumption 1-5 degrees.  

 

 

3. Determine the battery capacity according to the user's evening power consumption or expected standby time.  

 

 

 

The task of the battery is to ensure the normal power consumption of the system load when the solar radiation is insufficient.  For critical loads, to be able to maintain the normal operation of the system within a few days, consider consecutive rainy days.  For general loads such as solar street lamps, it can be selected in 2 ~ 3 days according to experience or need.  Important loads such as communications, navigation and hospital treatment are selected within 3 to 7 days.  Also consider the location of the photovoltaic system installation, if in a remote location, the battery capacity should be designed to be large, because maintenance personnel can take a long time to reach the site.  In practical application, some mobile communication base station because of the high mountain road far, to a very inconvenient, in addition to the normal configuration of battery, but also equipped with a group of backup battery, for the general poor families, the main consideration of the price, do not have to consider the rainy day, the sun is good when multi-purpose.  Use less when the sun is bad, not when there is no sun.  When choosing the load, try to use energy-saving equipment, such as LED lights, frequency conversion air conditioning.  The design of battery mainly includes the design and calculation of battery capacity and the design of battery series and parallel combination.  In the photovoltaic power generation system, most of the lead acid batteries are used. Considering the life of the battery, the discharge depth is generally between 0.5-0.7.  Battery design capacity = (Load daily power consumption x Consecutive rainy days)/Battery discharge depth.  

 

 

Off-grid users' needs are diverse, and photovoltaic systems are designed according to users' requirements.  For example, there is a customer who has six 260W modules in his home and wants to make a set of photovoltaic off-grid system. The customer has mains electricity in his home, but there are frequent power outages. The total load is 10KW, and the daily electricity consumption is 20-30 degrees.  There is no way to satisfy clients' demand for electricity use, can consider to meet the needs of customer part load, by calculating the component can send a day 5 degrees, use 3.0 KVA off-grid inverter, 4 pieces of 12 v150ah battery, flashboard output by one, at ordinary times take home lighting bulbs, computer, washing machine, such as load at night if there is electricity,  You can also connect a separate air conditioner.  

 

 

For large projects aimed at specific groups of people, due to the different situation of each user, can not meet all the needs, at this time to consider comprehensively.   Under normal circumstances, it is to take an average value, such as the photovoltaic project to solve the problem of electricity consumption in the western regions of China. The average herdsman family uses two 250W components, a 500VA off-grid inverter integrated machine, and two 12V150AH batteries, which can generate 2.5 KWH of electricity every day. The cost of raw materials is about 6000 yuan.  It can meet the electricity demand of TV sets, small refrigerators, DVD players, energy saving lamps and other electrical appliances.  Relatively light weight, easy to move.  In a photovoltaic poverty alleviation project in Ganzi Prefecture, Sichuan province, medium power off-grid system is adopted, including 8 250W components, 3KVA off-grid inverter integrated machine, and 4 batteries of 12V200AH, which can generate 8-10 KWH of electricity every day and meet the electricity demand of TV sets, refrigerators, DVD players, computers, 1P air conditioners, energy-saving lamps and other electrical appliances.  Due to the high overall power generation, the system can support more household appliances and improve the quality of life.  

 

 

Common problems of photovoltaic off-grid system:  

 

 

When designing photovoltaic off-grid system, we should be flexible and not stick to a fixed formula.  Photovoltaic off-grid system can not solve all the electricity problems, encounter a number of continuous cloudy and rainy days, can only save electricity.  There is no unified standard for off-grid inverters, and there is no compulsory certification. The products on the market are uneven, and the quality and price of products differ greatly. Please look for the brand when choosing off-grid inverters.   If you encounter fake or inferior products, you should complain or report to the police in time.  

 

1, components, inverter, battery design to match, any one can not be too large or too small, novice design, often calculate the power consumption is too large, such as 1P air conditioning 12 hours, calculated as 10 KWH electricity, 300W refrigerator 24 hours, calculated as 7.2 KWH electricity, resulting in battery capacity is too large, the system cost is too high.   When designing battery capacity, it is best to give 2 days to be able to fill.  

 

2, photovoltaic off-grid system output connection load, each inverter output voltage and current phase and amplitude are not the same, some inverter manufacturers do not support the output end parallel, do not connect the inverter output end together.  

 

 

3, the load is such as the elevator load can not be directly connected to the inverter output end, because when the elevator is down, the motor reverses, will produce a back electromotive force, into the inverter, the inverter is damaged.   If off-grid system must be used, it is recommended to add a frequency converter between the inverter and the elevator motor.  

 

4. For photovoltaic microgrid system with complementary input of municipal power, the insulation of the components should be done well. If there is leakage current of the components to the ground, it will be transmitted to the municipal power and cause the leakage switch of the municipal power to trip.  

 

5, the voltage of the component and the voltage of the battery to match, PWM controller between the solar module and the battery through an electronic switch connected, there is no inductive device in the middle, the voltage of the component is between 1.2-2.0 times the voltage of the battery, if it is 24V battery, the input voltage of the component is between 30-50V, MPPT controller,   There is a power switch tube and inductor circuit in the middle, the voltage of the component is between 1.2-3.5 times of the voltage of the battery, if it is a 24V battery, the input voltage of the component is between 30-90V.  

 

6, the output power of the component and the power of the controller should be similar, such as a 48V30A controller, the output power is 1440VA, the power of the component should be about 1500W.   When selecting the controller, first look at the battery voltage, and then divide the component power by the battery voltage, is the output current of the controller.  

 

7, battery charging current is generally 0.1C-0.2C, the maximum is not more than 0.3c, for example, 1 lead-acid battery 12V200AH, charging current is generally between 20A and 40A, the maximum can not exceed 60A;   The discharge current of batteries is generally 0.2C-0.5C, and the maximum is not more than 1C. The maximum output power of one 12V200AH lead-acid battery is not more than 2400W. Different manufacturers, different models, and specific values are different.