I. System Introduction
Solar energy is a clean and environmentally friendly energy source that is inexhaustible. The wireless monitoring system uses long-distance wireless bridge networking technology, making it possible to achieve remote and uninterrupted monitoring in remote areas that cannot obtain power supply.
This system is mainly used in the field and urban areas where wiring is inconvenient, such as construction sites, reservoirs and dams, river water levels, fish farms and forest farms for monitoring, forest fire prevention, island monitoring, border defense monitoring, individual soldier reconnaissance, etc.
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II. Design Analysis of Off-Grid Photovoltaic Power Generation System:
A photovoltaic (PV) power generation system that is not connected to the external commercial power grid but can independently provide power is called an off-grid PV system, also known as a stand-alone PV system. An off-grid PV system mainly consists of solar photovoltaic (PV) power generation devices, energy storage devices, a controller, and an inverter. A brief introduction to each component is provided below. The general design principle of a PV system is to determine the minimum number of solar cell modules and battery capacity while ensuring that the load's power needs are met, in order to minimize investment; that is, to consider both reliability and economy.
Before designing a system, designers should try to do the following:
(1) Keep the design as simple as possible to improve the reliability of the system.
(2) Understand the system's efficiency and design the system efficiency appropriately. If the efficiency is unrealistically set above 99%, the cost will be high.
(3) When estimating the load, we should take it into consideration and have a certain margin.
(4) Repeatedly calculate and verify the local weather resources to obtain the solar radiation energy resources of the region. Incorrect estimates of solar radiation will greatly affect the system's performance.
(5) Before designing the system, understand the installation location and go to the local area to investigate. This will help you understand the equipment placement, wiring, protection, and regional characteristics.
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1. Determine the load power:
Determining the solar power generation capacity and configuration requires first determining the power and electricity consumption of the upstream equipment (load). Through experimental testing, we can determine the total load power P1, which mainly includes the power of the camera, its heater, wireless equipment, and the power loss from the inverter. Based on the experimentally obtained total power P1, the daily electricity consumption W1 of the load can be determined as: W1 = P1 * 24.
If the solar panels and battery bank use a 12V power supply system, then the daily battery capacity consumed by the load equipment is: Q1 = W1 / 12V = 2 * P1 (AH)
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2. Solar cell array design:
The number of solar panels is calculated based on the daily power consumption of the load equipment and the off-grid power supply method of the system. This design proposes to use solar panels with a single voltage of 12V and a single power of P2 (W). Ignoring charging losses and assuming an average daily sunshine duration of 3 hours, the daily power generation of a single solar panel is:
P2 * 3 = 3 * P2 (Wh)
Under normal circumstances, the charging loss rate is around 10%, so the actual daily power generation of a single solar panel is: 2.7 * P2.
Therefore, the minimum number of solar panels required is:
n = W/2.7P2 ≈ 9 * P1 / P2.
Note: (Rounding up was used during the design process.)
If we consider that the system is an off-grid photovoltaic power generation system, and to ensure that the system's power generation is relatively low in winter, we should consider that the sunshine duration in winter is 2.5 hours per day, then: n≈11*P1/P2.
If losses due to rainy, snowy, or other adverse conditions such as degradation, dust, charging efficiency, and smog are taken into account, and considering the need to recharge the battery after using electricity on rainy days, the number of solar panels designed should be increased accordingly based on the number of days it takes to fully charge the battery.
Note: The number of solar panels should be increased by approximately 50% based on 3 days of cloudy or rainy weather.
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3. Battery pack capacity design:
Batteries are components used to store the electrical energy (DC) generated by the photovoltaic array for use by downstream loads (inverters and AC loads). Battery life is determined by many factors such as discharge rate, depth of discharge, cycle count, and operating temperature. Battery capacity is extremely important for ensuring continuous power supply. In addition to powering the equipment, the solar array generates a portion of its daily electricity, which is stored in batteries for use at night and on cloudy days. According to the "Design Specifications," the total capacity of the battery bank configured in the design should be calculated using the following formula:
Where: Q: Battery pack capacity (Ah); K: Safety factor, taken as 1.25; I: Load current (A); T: Discharge hours (h); η: Discharge capacity coefficient; t: Minimum ambient temperature at the actual battery location; α: Battery temperature coefficient (1/℃), when the discharge hour rate ≥ 10, α = 0.006; when the discharge hour rate ≥ 1, α = 0.008; when the discharge hour rate < 1, α = 0.01. The relationship between battery capacity and temperature can be derived from the formula and is also shown in Table 1.
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If the system operates stably for 24 consecutive hours, and the daily power consumption is Q1, and the local minimum ambient temperature is -15℃, then the formula for calculating the total capacity of the battery pack over N days simplifies to:
Q=K* Q1*N*τ
N is the longest consecutive rainy days; τ is a temperature correction factor, which can be calculated at -15℃.
τ=1.32
Therefore, the battery capacity for stable system operation can be calculated:
Q≈1.65N * Q1=3.3N * P1
Where P1 is the total system load power
In off-grid photovoltaic power generation systems, during the cyclic charging and discharging process of batteries, the depth of discharge directly affects the battery life and the number of cycles. Let the depth of discharge coefficient be C, and the battery capacity formula be revised as follows:
Q=K* Q1*N*τ/C
Depth of discharge factor C: for general lead-acid batteries
Use 0.75 for alkaline nickel-cadmium batteries and 0.85 for alkaline nickel-cadmium batteries.
4. Maximize the output power of photovoltaic modules
Four factors determine the output power of a photovoltaic module: load resistance, solar irradiance, cell temperature, and photovoltaic cell efficiency.
This shows that the temperature of the components has a significant impact on their power output, so the array should be installed in a well-ventilated, unobstructed location to keep it cool;
The graph below shows the effect of temperature on power.
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5. Controller
Batteries have specific requirements for charging and discharging; frequent overcharging and over-discharging will reduce their lifespan. Therefore, battery charging and discharging control is essential, and this is the primary function of the controller. The controller selects the maximum power operating point of the solar cells based on user power consumption, battery charging and discharging, and solar radiation levels, coordinating charging and power consumption currents. The controller also performs system monitoring, protection, and data display.
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6. Inverter Selection
An inverter is a power measurement device, essential for stand-alone photovoltaic systems using AC loads. A crucial factor in inverter selection is the DC voltage you set. For AC output, in addition to output power and voltage, we must also consider its waveform and frequency. At the input, attention must be paid to variations in the inverter's required DC voltage and its surge withstand capability.
Inverter performance affects the reliability and cost of a photovoltaic system. Generally, its characteristic parameters include: output waveform, power conversion efficiency, nominal power, input voltage, voltage regulation, voltage protection, frequency, modulation power factor, and reactive current.
The following is an explanation of some parameters:
Ø Power conversion efficiency: Its value is equal to the inverter output power divided by the input power. The efficiency of the inverter will vary greatly depending on the load.
Input voltage: Determined by the power and voltage required by the AC load. Generally, the larger the load, the higher the required inverter input voltage.
Surge resistance: Most inverters can exceed their rated power for a limited time (a few seconds). Some transformers and AC motors require starting currents several times higher than normal operation. The surge requirements of these special loads should be measured.
Ø Static current: This is the current (power) used by the inverter itself when it is not under load (no power consumption). This parameter is very important when the inverter is under a small load for a long time. When the load is small, the efficiency of the inverter is extremely low.
Voltage regulation: This means a variety of output voltages. For many systems over a wide load range, the root mean square output voltage approaches a constant.
Voltage Protection: Inverters can be damaged if the DC voltage is too high. Since the inverter's upstream battery will overcharge, the inverter's DC input voltage will exceed its nominal value. Therefore, a controller to manage the battery's charging status is essential. Without a controller, the inverter must have a check and test protection circuit. When the battery voltage exceeds a set value, the protection circuit will disconnect the inverter.
III. Solar Photovoltaic Power Generation
Ground-mounted solar photovoltaic power generation systems are divided into off-grid photovoltaic power generation systems, grid-connected photovoltaic power generation systems, and distributed photovoltaic power generation systems.
Off-grid photovoltaic power generation systems mainly consist of solar cell modules, controllers, and batteries. In the field of wireless monitoring, due to objective limitations, it is impossible to use mains power, so off-grid photovoltaic power generation is generally used.
1. Distribution of Solar Energy Resources in my country
my country has abundant total solar radiation resources, which are distributed in a pattern of "high plateaus having more than plains and arid western regions having more than humid eastern regions".
2. Solar panel tilt angle
The tilt angle is the angle between the plane of the solar cell array and the horizontal ground. The design of the photovoltaic module tilt angle mainly depends on the latitude of the photovoltaic power generation system and the required power generation distribution throughout the year. Different types of solar photovoltaic power generation systems have different optimal installation tilt angles.
The optimal tilt angle is related to the local latitude; the higher the latitude, the larger the corresponding tilt angle.
3. The impact of shading on power generation
The above power generation calculations are based on the assumption of no shadows. Furthermore, if the arrays are placed horizontally, the shadows cast by the front arrays will affect the power generation of the rear arrays when the distance between them is close. Assuming the vertical height of the solar panels is L, the length of their north-south shadows is Ls, the solar altitude (elevation angle) is h, the azimuth angle is B, and the horizontal distance between the arrays...
Ls = L × coth × cosB.
At higher latitudes, the distance between the square formations increases, and the area required for their installation also increases accordingly. Typically, when arranging square formations, the structural dimensions of each square should be selected individually, and its height adjusted to an appropriate value, thereby utilizing the height difference to minimize the distance between the square formations.
IV. System Connection Diagram
The main components of an independent photovoltaic system include: photovoltaic modules (arrays), batteries, inverters, and controllers.
The solar controller has only one positive terminal. The load, solar panel, battery, and DC load all share a positive terminal, indicated by a red wire. Two solar panels are connected in parallel; the negative terminal is indicated by a blue wire and connected to the controller's blue wire. The battery's negative terminal is indicated by a black wire and connected to the controller's black wire. The load's negative terminal is indicated by a green wire. The ground wire is indicated by yellow. When setting the controller to all-day operating mode, connect the battery first for 10 minutes to allow the controller to stabilize before connecting the solar panels and load.
V. Link Design and Application
The forest fire prevention remote wireless monitoring system consists of a forest area monitoring center, a wireless transmission system, and front-end monitoring points. Since power is unavailable in the forest, the monitoring points are powered by solar energy to ensure stable transmission throughout the system. Images are transmitted to the monitoring center via the wireless transmission system. Through this remote wireless monitoring system, the forest fire prevention management center can monitor the real-time situation of forest fires, detect fires promptly, and prevent fires.
In modern reservoir monitoring, real-time, 24/7 video surveillance of key locations and water levels can be achieved, strengthening reservoir area security management, improving work efficiency, and allowing relevant management departments to understand the situation at each monitoring point in real time and handle emergencies. Since mains power cannot be used around lakes, solar-powered monitoring can meet the real-time monitoring needs.
Power is difficult to obtain around the mine, so using a combination of wireless and solar-powered monitoring can well meet the customer's needs.
VI. Solar panel installation
Install
When installing, it is best to use a compass to determine the orientation, and care should be taken to ensure that there are no tall buildings or trees blocking the sunlight in front of the array throughout the day.
Carefully check whether the anchor bolts and array brackets are sturdy and reliable. All screws and terminals should be tightened and there should be no looseness.
The battery room should be kept well-ventilated, dry, and clean. In cold northern winters, batteries should be insulated.
I. System Introduction
Solar energy is a clean and environmentally friendly energy source that is inexhaustible. The wireless monitoring system uses long-distance wireless bridge networking technology, making it possible to achieve remote and uninterrupted monitoring in remote areas that cannot obtain power supply.
This system is mainly used in the field and urban areas where wiring is inconvenient, such as construction sites, reservoirs and dams, river water levels, fish farms and forest farms for monitoring, forest fire prevention, island monitoring, border defense monitoring, individual soldier reconnaissance, etc.
Zoom in
II. Design Analysis of Off-Grid Photovoltaic Power Generation System:
A photovoltaic (PV) power generation system that is not connected to the external commercial power grid but can independently provide power is called an off-grid PV system, also known as a stand-alone PV system. An off-grid PV system mainly consists of solar photovoltaic (PV) power generation devices, energy storage devices, a controller, and an inverter. A brief introduction to each component is provided below. The general design principle of a PV system is to determine the minimum number of solar cell modules and battery capacity while ensuring that the load's power needs are met, in order to minimize investment; that is, to consider both reliability and economy.
Before designing a system, designers should try to do the following:
(1) Keep the design as simple as possible to improve the reliability of the system.
(2) Understand the system's efficiency and design the system efficiency appropriately. If the efficiency is unrealistically set above 99%, the cost will be high.
(3) When estimating the load, we should take it into consideration and have a certain margin.
(4) Repeatedly calculate and verify the local weather resources to obtain the solar radiation energy resources of the region. Incorrect estimates of solar radiation will greatly affect the system's performance.
(5) Before designing the system, understand the installation location and go to the local area to investigate. This will help you understand the equipment placement, wiring, protection, and regional characteristics.
