Solar energy, as a widely used clean, efficient, and never-ending resource, is increasingly valued and loved by countries around the world. The solar photovoltaic power generation system mainly utilizes the effect of sunlight shining on semiconductor materials to convert light energy into electrical energy (photovoltaic effect) for power generation. Once upon a time, we found that there were already many products around us that utilized the solar photovoltaic effect to generate electricity, such as solar powered small fans, solar powered mobile phone charging power supplies, solar powered calculators, and so on. Most of these solar photovoltaic power generation products are small in size and easy to carry, which not only saves energy but also facilitates our daily needs, and are deeply loved by people. With the increasing attention paid by countries around the world to utilizing solar energy resources to establish a low-carbon economy and society, many countries around the world have formulated preferential policies for household utilization of solar photovoltaic power generation. For example, the federal government in the United States provides a 30% tax credit discount for the installation of solar photovoltaic systems in households; China provides preferential electricity prices and installation subsidies for households using solar photovoltaic power generation systems to generate electricity and connect to the national power grid.
The use of solar energy for photovoltaic power generation in urban households has certain peculiarities in our daily lives. This article analyzes the characteristics of urban residential buildings and explores the selection and configuration of solar photovoltaic power generation systems for household use in urban residential areas, for your reference.
1. Choose the installation location of solar photovoltaic panels based on the characteristics of urban residential buildings
In cities, the main living environment for families includes multi story or high-rise unit residential buildings, single story or multi story villa residential buildings, etc. For single story or multi story villa residential buildings, when the roof and surrounding areas are the property of each household, solar photovoltaic panels can be installed on the roof or in the best direction of the open space in front of the house. For multi story or high-rise residential buildings, as many residents do not have the right to use the building roof, solar photovoltaic panels can be installed on balconies, external windows, exterior walls, etc. in the best direction.
To improve the efficiency of solar photovoltaic power generation, the installation of solar photovoltaic panels should
The best direction selection based on local latitude includes azimuth angle (the angle between the vertical plane of the solar photovoltaic panel and the due south direction) and tilt angle (the angle between the solar photovoltaic panel and the horizontal ground at the installation site).
For households in residential buildings in cities in China (Northern Hemisphere), it is recommended to make the orientation angle of solar photovoltaic panels as close to the south as possible as the initial optimal direction for solar photovoltaic panels. After installing the solar photovoltaic power generation system, the azimuth angle of the solar photovoltaic panel can be adjusted slightly through measuring instruments. The tilt angle of the solar photovoltaic panel should be adjusted to the optimal tilt angle when the solar photovoltaic panel generates maximum power. This angle is related to the geographical latitude of the residence. After actual testing and calculation, the recommended values for the optimal installation angle of solar photovoltaic panels in major cities across the country have been published in national standards. For example, in Beijing, the latitude is 39.80 degrees, and the optimal angle is 39.80+4=43.80 degrees; The latitude of Chengdu is 30.67 degrees, and the optimal inclination angle is 30.67+2=32.67 degrees. During installation, adjustments can be made based on the measured maximum power generation of the photovoltaic panel.
1.2 Several precautions for selecting the installation position of solar photovoltaic panels
(1) When considering the installation location, it is also necessary to consider the impact of nearby buildings, trees, and other shadows on the photovoltaic panels receiving solar energy.
(2) When there is frequent snowfall, rainfall, and strong winds in the local area, solar photovoltaic panels should be installed firmly and measures should be taken to allow rainwater and snow water to flow automatically.
(3) The solar photovoltaic panels installed on the roof or outdoors should have lightning protection measures and can be reliably connected to the lightning protection and grounding devices on the roof or ground through metal conductors.
2. Reasonably select household solar photovoltaic power generation system schemes based on the characteristics of urban residential areas
2.1 Precautions when selecting a household solar photovoltaic power generation system scheme in urban residential buildings
(1) The impact of household solar photovoltaic power generation systems on personal safety. Due to the complexity of the household environment, the voltage of the selected photovoltaic panel combination should be as safe as possible. The current regulations in our country stipulate that the safe voltage is 50V and below. When a person comes into contact with this voltage, it may not cause direct death or disability. The wires in the system should be laid through pipes.
(2) The impact of household solar photovoltaic power generation systems on the safety of household living environment. Household solar photovoltaic power generation systems are composed of various electrical equipment, and the gases emitted by batteries, as well as some low-quality electrical equipment and wires that generate heat, have a certain impact on the household living environment. Therefore, the batteries and electrical equipment of household solar photovoltaic power generation systems should be installed outdoors, on the roof, or in ventilated independent rooms and spaces as much as possible. Please choose qualified and environmentally friendly electrical equipment and wires.
(3) The household solar photovoltaic power generation system should have complete electrical protection measures. The household solar photovoltaic power generation system should have protective measures such as circuit breakers, fuses, etc. from the generation of photovoltaic panels to the final output to the electrical equipment, to prevent safety issues such as electrical fires and electric shock accidents caused by faults in electrical equipment and wires.
2.2 Selection of schemes for household solar photovoltaic power generation systems in urban residential buildings
Household solar photovoltaic power generation systems are divided into the following two categories based on whether they output power to the outside:
The first type is systems without energy storage devices (usually batteries). The commonly used form is: during the sunshine period, the load is supplied by the photovoltaic power generation system, the excess electricity is connected to the grid and sold to the public grid, and during the insufficient sunshine period, the public grid supplies power to household users. This system, without energy storage devices, can significantly reduce the investment cost of the system. It is recommended to use this system for areas with longer annual average sunshine time and higher daily radiation levels.
The second type is systems with energy storage devices. The commonly used form is: during the sunshine period, the load is powered by the electricity generated by the photovoltaic power generation system, and the excess electricity is stored in the energy storage device. After the energy storage device is fully charged, the remaining electricity is connected to the grid and sold to the public grid. When the electricity generated by the photovoltaic power generation system cannot meet the electricity requirements, it is supplied by the public grid. This system can be called a photovoltaic power generation grid connected system with energy storage devices. It is recommended to mainly use this system for areas with short annual average sunshine time and low daily radiation.
When such systems are unable or inconvenient to connect to the public grid of residential buildings due to limited conditions, independent solar photovoltaic power generation systems can be used for power supply. According to the regulations in our country, “places with an average annual sunshine time greater than 1800 hours can independently use solar photovoltaic power supply.” The calculation is based on 365 days per year, which means that when the average annual sunshine time is greater than 4.93 hours, an independent solar photovoltaic power generation system can be used for power supply. When the average annual sunshine time is small, an independent power supply system with photovoltaic backup power supply complementarity can be adopted. The system composition diagram is shown in Figure 1.
According to the current situation of the power supply public grid for urban modular residential buildings, the power supply grid has been fully installed when the houses are delivered for occupancy, and there is no reserved grid connection interface for residential users to install solar photovoltaic power generation systems. Users of modular residential buildings are advised to adopt an independent photovoltaic backup complementary photovoltaic power generation system. For villa buildings, due to the relatively easy renovation of the existing power supply system, a photovoltaic power generation grid connected system with energy storage devices can be adopted.
3. Selection of main equipment for solar photovoltaic power generation systems in urban residential buildings
3.1 Composition of photovoltaic panel components
The main components include: photovoltaic cells, brackets, bypass diodes, and corresponding pipelines.
At present, photovoltaic cells mainly include: monocrystalline silicon photovoltaic cells, polycrystalline silicon photovoltaic cells, amorphous silicon (flexible thin film) photovoltaic cells, etc.
The production process of polycrystalline silicon photovoltaic cells is relatively simple and the price is relatively low. Polycrystalline silicon photovoltaic cells can be used in places with sufficient sunlight to save investment costs.
The photovoltaic conversion efficiency of monocrystalline silicon photovoltaic cells is higher than that of polycrystalline silicon. Due to the fewer impurities in monocrystalline silicon photovoltaic cells and the relatively stable electrical performance parameters, monocrystalline silicon photovoltaic cells should be used in areas with more cloudy and rainy days and relatively less sunlight.
The conversion efficiency of amorphous silicon photovoltaic cells is generally lower than that of monocrystalline silicon and polycrystalline silicon photovoltaic cells, but amorphous silicon cells can absorb a wider wavelength of sunlight and have better operating efficiency even in cloudy or weak sunlight. Amorphous silicon photovoltaic cells have relatively low requirements for solar illumination conditions and good weak light properties. They can be made into flexible thin film photovoltaic cells and used in places with limited position and direction. For modular residential buildings, due to limitations in conditions, household users can flexibly install amorphous silicon photovoltaic panels on multiple locations such as exterior walls, roofs, curtain walls, canopies, balconies, etc.
The photovoltaic panel bracket is used to support the solar panel, ensuring that the connection between the solar panel and the bracket is firm and reliable, and that the solar cell can be easily replaced.
3.2 Selection of battery packs
The energy storage equipment of solar photovoltaic power generation systems mainly consists of batteries. For a small photovoltaic power generation system in a household, the battery pack can be composed of multiple batteries in series or parallel.
The types of batteries suitable for photovoltaic power generation systems include ordinary lead-acid batteries, sealed maintenance free lead-acid batteries, colloidal batteries, nickel hydrogen batteries, etc. Taking into account system performance, cost, and other factors, deep cycle sealed maintenance free lead-acid batteries are the preferred product for home solar photovoltaic power generation systems.
3.3 Selection of solar power generation system controller
The solar controller is an automatic control device that controls the charging of the battery by the solar panel and the power supply of the battery to the load, and makes the solar photovoltaic power generation system in the optimal power generation state as much as possible to achieve high power generation efficiency.
The controller can be an independent device or can be integrated with an inverter. Some controllers are equipped with automatic switching function for backup power supply, which can automatically switch to backup power supply in case of insufficient power generation in the photovoltaic power system (backup power supply can be public utility power supply, wind power, generator power supply, etc.).
In small photovoltaic power generation systems used in residential buildings, it is recommended to use solar controllers with the following functions to save costs and reduce the complexity of system composition: circuit protection with grounded load short circuit; Circuit protection that can withstand loads, solar cell components, or battery polarity reversal; Has circuit protection to withstand internal short circuits in controllers, inverters, and other equipment; Capable of withstanding breakdown protection caused by lightning strikes; A protection that can prevent the battery from discharging in the opposite direction to the solar cell module through the controller.
3.4 Selection of inverters
In a photovoltaic power generation system, an inverter is a device that converts direct current into alternating current for use by AC power equipment. It is recommended to use inverters with an output waveform of pure sine wave in residential buildings.
3.5 Backup Power Converter
In residential building photovoltaic backup power complementary photovoltaic power generation systems, in order to ensure continuous power supply under poor sunlight conditions, when the photovoltaic power generation capacity is small and cannot meet the load needs, the backup power converter is used to automatically switch the photovoltaic power supply system power supply to the backup power supply to meet the continuous power supply requirements of the load.
4. Examples of solar photovoltaic power generation systems for urban modular residential buildings
Taking the household solar photovoltaic power generation system of a single unit residential building in Chengdu as an example:
4.1 Determination of installation location for solar photovoltaic power generation system
According to the installation environment conditions of this household, the photovoltaic panels and brackets in this example can be fixed on the terrace and installed facing south. The solar controller, inverter, and battery pack are all installed below the bracket. The installation angle of photovoltaic panels is tentatively set at 32.67 degrees according to the latitude of Chengdu and the recommended value by the country.
4.2 Determine the composition structure of photovoltaic power generation system and the functions to be achieved
According to the needs of the household, this example adopts an independent photovoltaic backup power generation system with a battery. When there is sufficient sunlight, the electricity generated by the photovoltaic power generation system supplies power to the electrical equipment and stores excess electricity in the battery. When the electricity consumption of the photovoltaic power generation system cannot meet the load electricity requirements, it will automatically switch to a backup power source (mains power supply) for power supply.
4.3 Estimation during the design of household solar photovoltaic power generation systems
The solar photovoltaic power generation system needs to calculate the power and current of each electrical circuit; Calculate the capacity of solar panels; Battery capacity, etc. In large-scale engineering design, professional software is generally used for calculation.
When designing small household solar photovoltaic power generation systems, estimates can be made based on actual electricity consumption and adjustments can be made according to actual usage.
4.3.1 Calculate the required solar panel power
This system actually has three power sources: solar photovoltaic power supply, battery power supply, and mains power supply. When the battery power supply capacity is insufficient due to various reasons, it can be switched to the mains power supply through the controller. When calculating the system of an instance, the impact of continuous rainy days on the system calculation can be temporarily ignored.
The battery voltage is temporarily selected as 60Ah, 12V maintenance free lead-acid battery, and the discharge depth of the battery is considered to be 70%.
The total daily power consumption is: 12X40+72X5+16X5=920 (Wh).
The required battery panel power=(safety factor * daily total power consumption * continuous rainy days+daily total power consumption * battery charging days)/battery charging days (/sunshine factor * correction factor).
Among them, the safety factor is set to 1.1; Take 1 as the number of consecutive rainy days; The battery needs to be charged for 10 days; The sunshine coefficient in Chengdu is 2.87; The correction factor is taken as 0.88~0.9.
The required solar panel power for this example is (1.1 * 920 * 1+920 * 10)/10/(2.87 * 0.88)=273 (W), so a 300W monocrystalline silicon solar photovoltaic panel with a voltage of approximately 18V can be selected for this example.
4.3.2 Determine the required battery capacity
The required capacity of a battery is 100 * safety factor * total daily power consumption * continuous rainy days * environmental temperature correction factor/discharge depth/working voltage. Among them: environmental temperature correction coefficient: 1 for temperatures above 0 degrees, 1.1 for temperatures above -10 degrees, and 1.2 for temperatures below -10 degrees.
The required capacity of the battery in this example is 100 * 1.1 * 920 * 1 * 1/70%/12=120 (Ah).
From this, it can be seen that the battery we choose should be at least 2 60Ah batteries. Considering the partial impact of continuous cloudy and rainy days, the impact of partially used batteries at night when the battery capacity is not fully charged or there is a power outage, and the impact of converting the DC power supply of the batteries into AC power supply through inverters and power loss on the line, this example selected three maintenance free lead-acid batteries with a capacity of 60Ah and 12V to form a 180Ah and 12V battery pack.
4.3.3 Selection of other main equipment for solar photovoltaic power generation systems
According to the calculation in this example, one solar controller with a wide input DC voltage of 12V~24V and a 30A output voltage was used, and it comes with a backup power automatic converter. We used one 500W pure sine wave inverter to convert DC 12V into AC 220V.
5. Conclusion
With the improvement of photovoltaic cell conversion efficiency and the continuous development of photovoltaic power generation system equipment performance, solar energy as a green and clean energy will be widely used. If solar photovoltaic power generation systems are widely used as the main or auxiliary energy source in urban residential buildings, it will greatly save energy and non renewable resources, reduce CO2 emissions, and provide an energy-saving, environmentally friendly, and comfortable living environment for the whole society.