一、了解太阳能光伏 (PV) 发电
了解并网和离网光伏系统配置以及每种类型涉及的基本组件。
太阳能光伏发电是使用太阳能电池板将来自太阳的能量转换为电能的过程。太阳能电池板，也称为光伏电池板，在光伏系统中组合成阵列。光伏系统也可以安装在并网或离网(独立)配置中。这两种光伏系统配置的基本组件包括太阳能电池板、汇流箱、逆变器、优化器和断开器。并网光伏系统还可能包括仪表、电池、充电控制器和电池断开器。太阳能光伏发电有几个优点和缺点(见表 1)。
1、太阳能光伏 (PV) 发电优点缺点
•阳光是免费的，在该国的许多地区很容易获得。•光伏系统初始投资高。
•光伏系统不会产生有毒气体排放、温室气体或噪音。•光伏系统需要大面积发电。
•光伏系统没有活动部件。•日照量可能会有所不同。
•光伏系统减少对石油的依赖。•当系统无法提供全部容量时，光伏系统需要额外的能量存储或访问其他资源，如公用电网。
•光伏系统能够在未连接到电网的偏远地区发电。
•并网光伏系统可以减少电费。
表 1.太阳能光伏发电有优缺点。
2、并网光伏系统
光伏系统最常采用并网配置，因为与依赖电池的离网光伏系统相比，它更易于设计且通常更便宜。并网光伏系统允许房主从电网消耗更少的电力，并将未使用或多余的电力提供回公用电网(见图 2)。系统的应用将决定系统的配置和规模。例如，住宅并网光伏系统的额定功率小于 20 kW，商业系统的额定功率为 20 kW 至 1MW，而公用事业储能系统的额定功率大于 1MW。
图 2.光伏系统的常见配置是没有备用电池的并网光伏系统。
3、离网(独立)光伏系统
离网(独立)光伏系统在白天使用太阳能电池板阵列为可充电电池组充电，以便在无法获得太阳能的夜间使用。使用离网光伏系统的原因包括降低能源成本和停电、生产清洁能源和能源独立。离网光伏系统包括电池组、逆变器、充电控制器、电池断开器和可选发电机。
4、太阳能板
光伏系统中使用的太阳能电池板是太阳能电池的组件，通常由硅组成，通常安装在刚性平面框架中。太阳能电池板串联在一起形成串，太阳能电池板串并联形成阵列。太阳能电池板按其产生的直流电量进行评级。应定期检查太阳能电池板以清除污垢、碎屑或雪，并检查电气连接。
由于光伏受到阴影的不利影响，任何阴影都会显着降低太阳能电池板的功率输出。太阳能电池板的性能会有所不同，但在大多数情况下，保证的功率输出预期寿命在 10 年到 25 年之间。太阳能电池板的功率输出以瓦特为单位。在理想的阳光和温度条件下，额定功率输出范围为 200 W 至 350 W。
5、太阳能电池阵列的构造和安装
当太阳能电池板安装在物业上时，它们必须以一定角度安装以最好地接收阳光。典型的太阳能电池阵列支架包括屋顶、独立式和定向跟踪支架(参见图 4)。屋顶安装的太阳能电池板可以与住宅的建筑融为一体，并将节省院子空间。
图 4.典型的太阳能电池阵列支架包括屋顶、独立式和屋顶或地面上的定向跟踪支架。图片由格林沙捞越提供
安装在屋顶的太阳能电池阵列连接到屋顶椽子上，旨在处理与屋顶相同的力和气候条件。复合瓦被认为是最容易安装太阳能电池板的屋顶材料，而板岩和瓷砖屋顶材料通常被认为是最困难的。屋顶安装的太阳能电池板的主要缺点是它们需要进行维护。
独立式太阳能电池阵列可以设置在便于维护的高度。然而，独立式太阳能电池阵列通常需要大量空间。此外，独立式太阳能电池板不应安装在积雪较多的地区的地面上。
太阳能阵列支架也可以是固定的或跟踪的。固定式太阳能电池板通常安装在屋顶或独立式上，预先设置了高度和角度，不会随太阳移动。定向跟踪太阳能电池阵列随太阳从东向西移动，并在太阳移动时调整其角度以保持最大曝光。定向跟踪太阳能阵列可以将光伏系统的每日能量输出从 25% 提高到 40%。然而，尽管增加了功率输出，但由于安装系统的复杂性，定向跟踪阵列可能无法证明增加的成本是合理的。
6、光伏汇流箱
光伏汇流箱接收多个太阳能电池板串的输出，并将该输出合并到一个连接到逆变器的主电源中。光伏汇流箱通常安装在太阳能电池板附近和逆变器之前。光伏汇流箱可以包括过流保护、浪涌保护、预接线保险丝座和预配置连接器，以便于安装到逆变器。使用预接线连接器可以节省连接到逆变器的电线。光伏汇流箱应定期检查是否有泄漏或连接松动。
并非每个光伏系统安装都需要光伏汇流箱。例如，当只有两串或三串太阳能电池板时，可能不需要汇流箱。在这些情况下，太阳能电池板串直接连接到逆变器。
7、光伏逆变器
逆变器是一种接收直流电并将其转换为交流电的设备。光伏逆变器具有三个基本功能：将光伏面板的直流电转换为交流电，确保产生的交流频率保持在每秒 60 个周期，并将电压波动降至最低。最常见的光伏逆变器是微型逆变器、组串式逆变器和功率优化器(见图 5)。
图 5.微型逆变器连接到每个并联的太阳能电池板，并将直流电直接转换为交流电。串式逆变器与多个串联的太阳能电池板一起使用。功率优化器安装在每个并联的太阳能电池板上。图片由Letsgosolar提供
微型逆变器是将直流电转换为交流电并直接安装在单个太阳能电池板上的设备。因为直流到交流的转换发生在每个太阳能电池板上，微型逆变器最大限度地提高了系统的潜在输出。例如，如果一个太阳能电池板被一棵树遮蔽，它不会影响任何其他太阳能电池板的输出。微型逆变器还消除了对潜在危险的高压直流接线的需求。
串式逆变器是一种将多个串联太阳能电池板的直流电转换为交流电的设备。然而，在串联配置中，如果其中一个太阳能电池板停止发电，即使是由于临时遮蔽，也会降低整个系统的性能。组串式逆变器处于高压范围(600 V 至 1000 V)，用于大型光伏系统，没有阴影问题。通常，住宅应用只需要一个组串式逆变器。
功率优化器(最大化器)是一种混合微型逆变器系统，可在将直流电发送到集中式逆变器之前对其进行调节，而不是将太阳能电池板的直流电直接转换为交流电。当一个或多个面板被遮蔽或面板面向不同方向安装时，功率优化器(如微型逆变器)仍然表现良好。功率优化器系统的成本往往高于串式逆变器系统，但低于微型逆变器系统。
8、光伏断开器
自动和手动安全断开器可保护光伏系统的接线和组件免受电涌和其他设备故障的影响。断开连接确保光伏系统可以安全关闭，并且可以移除系统组件进行维护或维修。对于并网光伏系统，安全断开装置可确保发电设备与电网隔离，以确保公用事业人员的安全。光伏系统中的每个电源或储能设备都需要断开连接。交流断开器通常安装在主配电板之前的家中。公用事业通常需要一个可锁定并安装在公用事业仪表旁边的外部交流断开器，以便公用事业人员可以访问它。
英文翻译：
Learn about grid-connected and off-grid PV system configurations and the basic components involved in each kind.
Solar photovoltaic (PV) power generation is the process of converting energy from the sun into electricity using solar panels. Solar panels, also called PV panels, are combined into arrays in a PV system. PV systems can also be installed in grid-connected or off-grid (stand-alone) configurations. The basic components of these two configurations of PV systems include solar panels, combiner boxes, inverters, optimizers, and disconnects. Grid-connected PV systems also may include meters, batteries, charge controllers, and battery disconnects. There are several advantages and disadvantages to solar PV power generation (see Table 1).
| Advantages | Disadvantages |
•Sunlight is free and readily available in many areas of the country. | •PV systems have a high initial investment. |
•PV systems do not produce toxic gas emissions, greenhouse gases, or noise. | •PV systems require large surface areas for electricity generation. |
•PV systems do not have moving parts. | •The amount of sunlight can vary. |
•PV systems reduce dependence on oil. | •PV systems require excess storage of energy or access to other sources, like the utility grid, when systems cannot provide full capacity. |
•PV systems have the ability to generate electricity in remote locations that are not linked to a grid. | |
•Grid-connected PV systems can reduce electric bills. |
Table 1. There are advantages and disadvantages to solar PV power generation.
Grid-Connected PV Systems
PV systems are most commonly in the grid-connected configuration because it is easier to design and typically less expensive compared to off-grid PV systems, which rely on batteries. Grid-connected PV systems allow homeowners to consume less power from the grid and supply unused or excess power back to the utility grid (see Figure 2). The application of the system will determine the system configuration and size. For example, residential grid-connected PV systems are rated less than 20 kW, commercial systems are rated from 20 kW to 1MW, and utility energy-storage systems are rated at more than 1MW.
Off-Grid (Stand-Alone) PV Systems
Off-grid (stand-alone) PV systems use arrays of solar panels to charge banks of rechargeable batteries during the day for use at night when energy from the sun is not available. The reasons for using an off-grid PV system include reduced energy costs and power outages, production of clean energy, and energy independence. Off-grid PV systems include battery banks, inverters, charge controllers, battery disconnects, and optional generators.
Solar Panels
Solar panels used in PV systems are assemblies of solar cells, typically composed of silicon and commonly mounted in a rigid flat frame. Solar panels are wired together in series to form strings, and strings of solar panels are wired in parallel to form arrays. Solar panels are rated by the amount of DC that they produce. Solar panels should be inspected periodically to remove dirt, debris, or snow, as well as to check electrical connections.
Since photovoltaics are adversely affected by shade, any shadow can significantly reduce the power output of a solar panel. The performance of a solar panel will vary, but in most cases, guaranteed power output life expectancy is between 10 years and 25 years. Solar panel power output is measured in watts. Power output ratings range from 200 W to 350 W under ideal sunlight and temperature conditions.
Solar Arrays Construction and Mounting
When solar arrays are installed on a property, they must be mounted at an angle to best receive sunlight. Typical solar array mounts include roof, freestanding, and directional tracking mounts (see Figure 4). Roof-mounted solar arrays can blend in with the architecture of a dwelling and will save yard space.
Roof-mounted solar arrays attach to the roof rafters and are engineered to handle the same forces and climate conditions as the rooftop. Composition shingles are considered the easiest roofing on which to mount solar arrays, while slate and tile roofing materials are often considered the most difficult. The main drawback of roof-mounted solar arrays is that they require access for maintenance.
Freestanding solar arrays can be set at heights that allow convenient maintenance. However, freestanding solar arrays usually require a lot of space. Also, freestanding solar arrays should not be mounted on the ground in areas that receive a lot of snow.
Solar array mounts can also be either fixed or tracking. Fixed solar arrays, which are often roof-mounted or freestanding, are preset for height and angle and do not move with the sun. Directional tracking solar arrays move with the sun from east to west and adjust their angle to maintain the maximum exposure as the sun moves. Directional tracking solar arrays can increase the daily energy output of a PV system from 25% to 40%. However, despite the increased power output, directional tracking arrays may not justify the increased cost due to the complexity of the mounting system.
PV Combiner Boxes
A PV combiner box receives the output of several solar panel strings and consolidates this output into one main power feed that connects to an inverter. PV combiner boxes are normally installed close to solar panels and before inverters. PV combiner boxes can include overcurrent protection, surge protection, pre-wired fuse holders, and preconfigured connectors for ease of installation to the inverter. The use of pre-wired connectors saves running wires to the inverter. PV combiner boxes should be inspected periodically for leaks or loose connections.
PV combiner boxes are not required for every PV system installation. For example, when there are only two or three strings of solar panels, a combiner box may not be required. In these cases, the strings of solar panels are connected directly to the inverter.
PV Inverters
An inverter is a device that receives DC power and converts it to AC power. PV inverters serve three basic functions: they convert DC power from the PV panels to AC power, they ensure that the AC frequency produced remains at 60 cycles per second, and they minimize voltage fluctuations. The most common PV inverters are micro-inverters, string inverters, and power optimizers (See Figure 5).
A microinverter is a device that converts DC power to AC power and is mounted directly to individual solar panels. Because the DC to AC conversion happens at each solar panel, the microinverters maximize the potential output of a system. For example, if one solar panel is shaded by a tree, it will not affect the output of any other solar panels. Microinverters also eliminate the need for potentially hazardous high-voltage DC wiring.
A string inverter is a device that converts DC power to AC power from several solar panels that are connected in series. However, in a series configuration, if one of the solar panels stops producing electricity, even due to temporary shading, it can decrease the performance of the whole system. String inverters are in the high-voltage range (600 V to 1000 V) and are used with large PV systems with no shading concerns. Usually, only one string inverter is needed for a residential application.
A power optimizer (maximizer) is a hybrid microinverter system that conditions the DC power before sending it to a centralized inverter instead of converting the DC power from the solar panels directly into AC power. Power optimizers, like microinverters, still perform well when one or more panels are shaded or when panels are installed facing different directions. Power optimizer systems tend to cost more than string inverter systems but less than microinverter systems.
PV Disconnects
Automatic and manual safety disconnects protect the wiring and components of PV systems from power surges and other equipment malfunctions. Disconnects ensure that the PV system can be safely shut down and system components can be removed for maintenance or repair. With grid-connected PV systems, safety disconnects ensure that the generating equipment is isolated from the grid for the safety of utility personnel. A disconnect is needed for each source of power or energy storage device in the PV system. An AC disconnect is typically installed inside the home before the main electrical panel. Utilities commonly require an exterior AC disconnect that is lockable and mounted next to the utility meter so that it is accessible to utility personnel.
