光伏离网系统设计三大原则

    1、根据用户的负载类型和功率确认离网逆变器的功率。

     家用负载一般分为感性负载和阻性负载，洗衣机、空调、冰箱、水泵、抽油烟机等带有电动机的负载是感性负载，电动机启动功率是额定功率的5-7倍，在计算逆变器的功率时，要把这些负载的启动功率考虑进去。逆变器的输出功率要大于负载的功率。对于监控站，通信站等要求严格的场合，输出功率是按所以的负载功率之和。但对于一般贫困家庭而言，考虑到所有的负载不可能同时开启，为了节省成本，可以在负载功率之和乘以0.7-0.9的系数。并不是每一个客户都会对负载功率很清楚。

      2、根据用户每天的用电量确认组件功率。

    组件的设计原则是要满足平均天气条件下负载每日用电量的需求，也就是说太阳能电池组件的全年发电量要等于负载全年用电量。因为天气条件有低于和高于平均值的情况，太阳能电池组件设计的基本满足光照最差季节的需要，就是在光照最差的季节蓄电池也能够基本上天天充满电。但在有些地区，最差季节的光照度远远低于全年平均值，如果还按最差情况设计太阳能电池组件的功率，那么在一年中的其他时候发电量就会远远超过实际所需，造成浪费。这时只能考虑适当加大蓄电池的设计容量，增加电能储存，使蓄电池处于浅放电状态，弥补光照最差季节发电量的不足对蓄电浊造成的伤害。组件的发电量并不能完全转化为用电，还要考虑控制器的效率和机器的损耗以及蓄电池的损耗，太阳能控制器有PWM和MPPT两种类型，PWM控制器效率约85%，输入电压范围比较窄，但价格比较低，MPPT控制器效率约95%，价格比较高。蓄电池在充放电过程中，也会有10-15%的损耗。离网系统可用的电量=组件总功率*太阳能发电平均时数*控制器效率*蓄电池效率。

    有一些离网用户，没有装过电表，对自己的用电情况不是十分清楚，还有一些离网系统，是新建的，这时就需要去估算每天的用电量，对于灯泡、电风扇、电吹风这样的负载，用电量等于功率乘以时间；但空调，冰箱这样的负载，是间隙性工作的，电视，电脑，音响这样的负载，工作时很少在满功率状态，计算电量时，就要综合考虑了。

      空调是家用电器耗电量最大的负载，1匹空调的电功率是735W，也就是说1小时满负荷运行消耗0.735度电，空调还有一个指标“制冷量”，单位也是W，1匹空调制冷量约2300W，空调的耗电和室内外温度差，房间面积，空调的能效率有很大关系，1台1P的空调，晚上用8小时，耗电1-5度不等。

      3、根据用户晚上用电量或者期望待机时间确定蓄电池容量。

蓄电池的任务是在太阳能辐射量不足时，保证系统负载的正常用电。对于重要的负载，要能在几天内保证系统的正常工作，要考虑连续阴雨天数。对于一般的负载如太阳能路灯等可根据经验或需要在2～3天内选取。重要的负载如通信、导航、医院救治等则在3～7天内选取。另外还要考虑光伏发电系统的安装地点，如果在偏远的地方，蓄电池容量要设计得较大，因为维护人员到达现场就需要很长时间。实际应用中，有的移动通信基站由于山高路远，去一次很不方便，除了配置正常蓄电池组外，还要配备一组备用蓄电池组，对于一般贫困家庭而言，主要考虑价格，则不用考虑阴雨天，太阳好的时候多用。太阳不好的时候少用，没有太阳则不用。选择负载时，尽量使用节能设备，如LED灯，变频空调。蓄电池的设计主要包括蓄电池容量的设计计算和蓄电池组串并联组合的设计。在光伏发电系统中，大部分使用的都是铅酸蓄电池，考虑到电池的寿命，一般取放电深度为0.5-0.7之间。蓄电池设计容量=（负载日均用电量*连续阴雨天数）/蓄电池放电深度。

      离网用户的需求是多种多样的，根据用户的要求设计光伏系统。这时候就要灵活处理，不一定要按上述的原则去设计，例如有一个客户，家里有6块260W的组件，要做一套光伏离网系统，客户家里有市电，但经常会停电，总负载是10KW，一天的用电量是20-30度，如果只有这1.56KW组件，根本没有办法满足客户的用电量要求，这时候就可以考虑满足客户一部分负载的需求，经计算组件一天能发5度电，采用3.0KVA的离网逆变器，4块12V150Ah的蓄电池，输出接一个插板，平时接家里的照明灯泡，电脑，洗衣机之类的负载，晚上如果还有电，也可以单独接一台空调。

       对于针对特定人群的大项目，由于每个用户情况不一样，无法满足所有的需求，这时候就要综合考虑。一般情况下，是取一个平均值，如解决我国西部无电地区用电问题的光伏工程，一般牧民家庭，采用2块250W的组件，一个500VA的离网逆变一体机，2个12V150AH的蓄电池，每天能发2.5度电，原材料成本价约6000元左右，可满足电视机、小型电冰箱、DVD机、节能灯等电器的用电需求。重量比较轻，方便移动。在四川甘孜州某光伏扶贫项目中，采用中功率离网系统， 8块250W的组件，3KVA的离网逆变一体机，4节12V200AH的蓄电池，每天可以发8-10度电，可满足电视机、电冰箱、DVD机、电脑、1P空调，节能灯等电器的用电需求。由于系统总体发电量高，可以支持更多的家用电器设备，生活质量得到提高。

 光伏离网系统常见问题：

     设计光伏离网系统时，要灵活处理，不要拘泥于某一个固定公式。光伏离网系统不能解决所有的用电问题，遇到多个连续阴雨天，只能省着用电。离网逆变器没有统一的标准，也不需要强制认证，市面上的产品良莠不齐，产品质量和价格相差很大，大家在选购离网逆变器时，请认准品牌。碰到假货或者劣质产品要及时投诉或者报警。

     1、组件，逆变器，蓄电池设计时要匹配，任何一个都不能过大或者过小，新手设计时，经常会把用电量计算过大，如1P空调运行12小时，算成10度电，300W的冰箱运行24小时，算成7.2度电，造成蓄电池容量过大，系统成本过高。设计蓄电池容量时，最好2天时间就给能充满。

    2、光伏离网系统输出连接负载，每个逆变器输出端电压和电流相位和幅值都不一样，有些厂家逆变器不支持输出端并联，不要把逆变器输出端接在一起。

    3、负载是电梯之类的负载不能直接和逆变器输出端相连接，因为电梯在下降时，电动机反转，会产生一个反电动势，进入逆变器时，对逆变器有损坏。如果必须要用离网系统，建议在逆变器和电梯电动机之间加一个变频器。

    4、带市电互补输入的光伏微网系统，组件的绝缘要做好，如果组件对地有漏电流，会传到市电，引起市电的漏电开关跳闸。

    5、组件的电压和蓄电池的电压要匹配，PWM型控制器太阳能组件和蓄电池之间通过一个电子开关相连接，中间没有电感等装置，组件的电压是蓄电池的电压1.2-2.0倍之间，如果是24V的蓄电池，组件输入电压在30-50V之间，MPPT控制器，中间有一个功率开关管和电感等电路，组件的电压是蓄电池的电压1.2-3.5倍之间，如果是24V的蓄电池，组件输入电压在30-90V之间。

     6、组件的输出功率和控制器的功率要相近，如一个48V30A的控制器，输出功率为1440VA，组件的功率应该在1500W左右。选择控制器时，先看蓄电池的电压，再用组件功率除以蓄电池的电压，就是控制器的输出电流。

     7、蓄电池的充电电流一般为0.1C-0.2C，最大不超过0.3C，例如1节铅酸蓄电池12V200AH，充电电流一般在20A到40A之间，最大不能超过60A；蓄电池的放电电流一般为0.2C-0.5C，最大不超过1C，1节12V200AH铅酸蓄电池，输出最大功率不超过2400W，不同的厂家，不同的型号，具体的数值也不一样，设计时要向厂家索取说明书。

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.