Solar energy resources belong to renewable and clean resources. Solar photovoltaic power generation systems can be used wherever there is light, and they are not limited by geographical or altitude factors. Solar cells also have the characteristics of simple operation, maintenance, and long service life. At the same time, the solar photovoltaic power generation system has a simple structure, is easy to install and transport, and is extremely easy to combine and expand. The above characteristics determine the promising development prospects of solar photovoltaic power generation technology in household environments.
1. The characteristics of household solar photovoltaic power supply systems
The current household solar photovoltaic power supply system generally refers to off grid solar photovoltaic power supply systems, consisting of solar cell arrays, battery packs, controllers, DC/AC inverters, circuit protection, and other components.
Common terms include “solar household power supply”, “portable photovoltaic power supply”, etc.
Solar photovoltaic power sources are widely applicable in various environments. In areas with high rates of conventional energy and electricity consumption, small and portable solar photovoltaic power sources are mainly used for mobile work. In remote areas with low power rates and frequent power shortages, household solar photovoltaic power systems have become the main power source for daily life.
The Yunnan region has abundant solar energy resources. This article will introduce how to build a solar photovoltaic power generation system based on the characteristics of ordinary household users, and reduce carbon emissions by using clean energy. At the same time, it provides reference for how to establish solar photovoltaic power supply systems in remote areas with low power rates and frequent power shortages.
2. Basic requirements for the main components of household solar photovoltaic power supply systems
The main components that make up a household solar photovoltaic power supply system are: solar cell modules, batteries, controllers, and DC/AC inverters.
2.1 Solar cell modules
The core of a solar photovoltaic power generation system is solar cells, but solar cells cannot be directly used in the system. Mainly due to the low mechanical strength, thinness, and fragility of individual solar cells; Direct exposure to air is prone to corrosion; Due to the size limitation of silicon wafer materials, the power of individual batteries is very small. Therefore, we need to package the individual solar cells in series and parallel to form the smallest and indivisible solar cell module with internal connections that can provide separate DC power output.
To meet household needs, solar cell modules should have the following characteristics: ① sufficient mechanical strength to withstand the stress of impacts and vibrations that occur during installation and use; ② Having sufficient mechanical strength to withstand hail strikes; ③ Has good electrical insulation performance; ④ Strong resistance to ultraviolet radiation; ⑤ Long working life, should be able to use for more than 20 years under natural conditions; ⑥ Can provide different wiring methods for working voltage and output power; ⑦ Reliable connection between solar cells; The efficiency loss caused by series parallel combination is small; ⑧ Under the above conditions, the packaging cost should be as low as possible.
2.2 Battery
In a solar photovoltaic power generation system, the solar cell array converts solar radiation into direct current energy, which is then converted into chemical energy and stored through a battery. For solar photovoltaic power systems, energy storage devices play a role in providing stable electricity to the load at any time, as well as storing and regulating the electricity generated by solar cells.
To meet the particularity of solar energy system operation, as the energy storage battery of the system, it needs to be frequently in the process of charging and discharging, and adverse working conditions such as overcharging or deep discharge often occur. Therefore, it is required that the batteries used in household solar photovoltaic systems should have the following characteristics: ① have deep cycle discharge performance; ② Long cycle life; ③ Strong tolerance to overcharging and discharging; ④ Has maintenance free or low maintenance performance; ⑤ Has good charging and discharging characteristics at low temperatures; ⑥ The charging and discharging characteristics are not sensitive to high temperatures; ⑦ Has high energy efficiency; ⑧ No need for initial charging operation; ⑨ Has high cost-effectiveness.
2.3 Controller
The charge and discharge controller is a device that automatically prevents overcharging and over discharging of energy storage batteries in solar photovoltaic power systems. It is one of the core components of solar photovoltaic power generation systems. The controller is mainly responsible for the distribution of output voltage and current, and can play an important role in managing the energy of solar photovoltaic systems, protecting batteries, and ensuring the normal operation of the entire solar photovoltaic system.
The charging and discharging controller of household solar photovoltaic power supply systems should have the following protection functions: ① load short circuit protection; ② Internal short circuit protection; ③ Reverse discharge protection; ④ Polarity reverse protection; ⑤ Lightning protection; ⑥ Display the state of charge of the battery. At the same time, the controller should be able to withstand 1.25 times the nominal voltage applied to both ends of the solar cell for 1 hour without damage, or be able to withstand 1.25 times the nominal current in the charging circuit for 1 hour without damage.
2.4 Inverter
DC/AC inverter is a device that converts direct current into alternating current. In China, most commonly used household appliances and other electrical equipment use 220V, 50Hz AC power. However, batteries can generally only provide low-voltage DC power of 12V, 24V, or 48V, and the 220V AC power output through inverter conversion has a wide range of usage environments.
For inverters in household solar photovoltaic power generation systems, in addition to considering basic technical indicators such as output voltage variation range, output frequency, output voltage waveform distortion, efficiency, static current, etc. The load capacity, protection capacity, and insulation capacity of the inverter should also be considered. Among them, it is required that when the input voltage and output power are at the rated value and the ambient temperature is 25 ℃, the inverter should be able to work continuously for no less than 4 hours. It should also have undervoltage protection, overcurrent protection, short circuit protection, polarity reversal protection, and lightning protection. In addition, to ensure the safety of users, the insulation resistance between the DC input and AC output of the inverter and the casing should not be less than 50M Ω.
3. Design of household solar photovoltaic power supply system
Although solar photovoltaic systems have fewer components, in order to maximize the efficiency of solar photovoltaic power generation systems, it is necessary to fully grasp the solar radiation parameters and user electricity demand in the location, and fully analyze the load characteristics, solar cell module capacity, inverter conversion efficiency, battery capacity and other parameters before achieving the optimal design as much as possible.
3.1 System Configuration Principles
The solar photovoltaic power generation system in ordinary households is generally designed for fixed use, but due to the low popularity of solar photovoltaic power generation products, when configuring a solar photovoltaic power generation system, the overall stability and durability of the system should be considered to reduce the possibility of external damage. In addition, for the convenience of maintenance and repair, products with simple assembly and strong universality should be selected as much as possible.
3.2 Electricity demand analysis
This section mainly needs to consider the size of the electricity load, the nature of the load, the duration of use, and the power supply guarantee rate.
3.2.1 User Type
However, due to the current impact of the cost of solar photovoltaic power generation systems, the cost of power generation is still relatively high, so large margins are generally not considered when configuring the system. It is necessary to classify the electricity demand based on the duration of use and the power supply guarantee rate, in order to select targeted design solutions.
| Electricity demand | Main load | Usage time | Guarantee rate/day |
| Low power | Lighting | 4 | 2 |
| General power | Lighting, laptops | ≥ 6 | 3 |
| High power | Lighting, desktop computers, color televisions | ≥ 10 | 3 |
| High power | Handheld tools such as lighting, desktop computers, color televisions, refrigerators, hair dryers, etc | 24 | 3 |
3.2.2 Load characteristics
Before designing a solar photovoltaic power generation system and selecting system equipment, it is necessary to fully understand the load characteristics. Is the most important load among all loads DC load or AC load, impact load or non impact load, important load or general load.
Resistive load: Generally, there are incandescent lamps, electronic energy-saving lamps, water dispensers, etc., with the same current and voltage, and no surge current.
Inductive load: Generally, there are refrigerators and water pumps, with voltage leading current and impulse current.
Power electronic loads: fluorescent lamps (with electronic ballasts), televisions, computers, etc., with impulse currents.
The surge current of inductive loads: The motor is generally 5-8 times the rated current and lasts for 50-150ms; Refrigerators are generally 5-10 times the rated current and last for 50-150ms; The demagnetization coil and display of color televisions are generally 2-5 times the rated current, lasting for 20-100ms.
3.2.3 Calculation of solar radiation energy resources
Overall, solar radiation varies with seasons, with the highest in summer and the lowest in winter. But there are changes in weather conditions, such as sunny, cloudy, rainy, and foggy, and the solar radiation energy varies at different times in the same time zone. Household solar photovoltaic power generation systems should generally refer to the radiation situation of previous years as the design basis, but the solar radiation throughout the year is variable, and the radiation value of the worst month of the year cannot be used, otherwise the designed system will inevitably be too large, causing cost waste; We cannot consider the supply-demand balance of the system based on the best sunshine time, as such a system will be small and result in a long period of time when the power generation cannot meet the electricity demand.
3.3 Capacity calculation
For the design of household solar photovoltaic power generation systems, it is necessary to calculate and determine the capacity of solar cell components, batteries, and inverters in the system. Among them, the solar cell components determine the possible power generation of the system, the capacity of the inverter is determined based on the total power of the load and the type of load, and the capacity of the battery is determined by the daily charging and discharging amount, the self-sufficiency days to be guaranteed, and the maximum allowable discharge depth.
When designing capacity, the following design principles are generally followed: ① Consider load demand and local meteorological and geographical conditions; ② Balancing reliability and economy, while fully meeting user requirements, minimize the capacity of solar cells and batteries as much as possible; ③ Avoid blindly increasing or decreasing the capacity of solar cells and batteries in pursuit of high reliability or economy.
3.3.1 Calculation of solar cell module capacity
When designing the capacity of solar cell modules, consideration should be given to climate and environmental conditions as well as user electricity needs. The climate and environmental conditions determine the system’s ability to generate electricity, and the electricity demand determines the amount of electricity the system needs to provide. The two should strive for balance as much as possible.
The solar radiation data obtained during design is generally the annual total radiation on the horizontal plane. When calculating, it should be converted into units using kW. h/m ^ 2. Similarly, the annual electricity consumption is also taken as the calculation value for the convenience of calculation. Due to the fact that users cannot use it daily in actual use, a simultaneous coefficient of 0.9 is taken.
Considering the impact of dust and scratches on solar panels, combined with practical experience, a dust scratch impact value of 10% is taken. The impact of temperature on solar energy, combined with practical experience, takes a temperature loss impact value of 10%. The situation of energy loss caused by batteries in terms of energy storage and the loss caused by improper arrangement of solar panels also need to be considered.
Based on high-quality inverters, the conversion efficiency can generally reach over 90%. Therefore, after considering the above factors comprehensively, the calculation formula for AC household solar energy systems can be listed as follows:
Formula:
δ—— The annual electricity consumption rate is generally set at 0.9;
H – Annual theoretical total electricity consumption, kW. h;
W0- Calculation value of solar cell capacity, kWp;
Q – Annual total solar radiation energy on the horizontal plane, kW. h/m2;
R – The wallpaper of the total solar radiation received on the surface of the solar cell module and the annual total radiation on the horizontal plane, generally taken as 1.2.
η—— Total system efficiency;
F – Efficiency loss caused by improper user use, generally set at 0.9;
η 1- Battery charging and discharging efficiency, taken as 0.85;
η 2- Temperature loss coefficient, taken as 0.9;
η 3- Dust scratch shielding loss coefficient, taken as 0.9;
η 4- Inverter efficiency, generally 0.92 can be taken as the design value.
To ensure power supply reliability, W0 should also be corrected, usually by expanding the capacity by 5% -15%.
3.3.2 Calculation of battery capacity
The capacity calculation of a battery is determined based on the system’s daily electricity consumption, self-sufficiency days, and the depth of battery discharge. The self-sufficiency days represent the user’s requirements for power supply guarantee rate in solar photovoltaic power systems, and are artificially set values. In the design, comprehensive consideration should be given to local meteorological conditions, the number of rainy and cloudy days over the years, user requirements for power supply guarantee rate, system cost, and other aspects. In addition, the discharge depth of batteries also varies depending on the type of battery. The discharge depth of lead-acid batteries is set at 80%, and the maximum discharge depth of alkaline batteries can reach 100%.
The correct selection of battery capacity is crucial for the successful design of household solar photovoltaic power generation systems. Due to the fact that batteries are the most expensive part of maintenance in solar photovoltaic power generation technology, improper design and configuration of batteries can increase the construction and maintenance costs of solar photovoltaic power generation systems. So, usually after determining the daily electricity consumption and self-sufficiency time, the following formula can be used to calculate:
In the formula:
C – Battery energy, W.h;
E0- Average daily load electricity consumption, W.h;
D – days of battery self-sufficiency;
D0D – Battery discharge depth;
η—— Inverter efficiency
It should be pointed out that when the temperature is low in winter, the charging and discharging efficiency of the battery will decrease. Therefore, in order to avoid excessive discharge and accelerated aging of the battery at low temperatures, appropriate adjustments can be made when selecting the capacity, usually by expanding the capacity by 5% -10%.
3.3.3 Capacity calculation of inverters
Inverters are essential in communication household solar photovoltaic power supply systems, and the determination of their capacity should pay attention to the following points: the rated power of the inverter should be slightly greater than the calculated power in the system, that is, a safety factor should be taken, and its value can be taken as 1.2-1.5. For pure resistive loads, the power of the inverter is the sum of the loads in the system; For systems with inductive loads, the inverter capacity should be increased based on the surge current during the start-up of the inductive load.
According to the above principles, the following calculation formula can be used:
In the formula:
CN – inverter capacity;
K – safety factor, generally taken as 1.2-1.5;
N – The surge current at the start of the inductive load is a multiple of the rated current;
PG – Power of inductive load in the system;
PC – The power of a pure resistive load in the system.
4. Conclusion
With the continuous improvement of solar photovoltaic power generation efficiency and the continuous reduction of power generation costs, solar photovoltaic power generation technology will inevitably enter thousands of households. Yunnan region belongs to the moderate type of solar energy resources in China, with relatively abundant solar energy resources. In the era of advocating energy conservation, emission reduction, and low-carbon economy, this article provides a shallow analysis and introduction of the application of household solar photovoltaic power generation technology, hoping to provide reference for the application of household solar photovoltaic power generation technology.