Research on the Application of Energy Storage in Photovoltaic Projects
2023.Aug
31
Regarding the current peak-valley electricity price level, the industry generally believes that the 70 cents peak-valley electricity price difference is a threshold to promote the development of the user-side energy storage industry.
This article discusses energy storage from the aspects of energy storage types, business models, and design schemes. I hope that everyone will have a preliminary understanding of energy storage after reading it.
1. Types of energy storage systems
According to different applications, solar photovoltaic energy storage power generation systems are divided into four types: off-grid power generation systems, off-grid energy storage systems, grid-connected energy storage systems, and multi-energy hybrid micro-grid systems.
1. Photovoltaic off-grid power generation system
Photovoltaic off-grid power generation system operates independently without relying on the grid. It is used in remote mountainous areas, areas without electricity, islands, communication base stations, street lights and other application places. The system consists of a photovoltaic array, a solar controller, an inverter, a battery pack, and a load. The photovoltaic array converts solar energy into electrical energy when there is light, and the solar energy controls the inverter integrated machine to supply power to the load and charge the battery pack at the same time; when there is no light, the battery supplies power to the AC load through the inverter.
Photovoltaic off-grid power generation system is specially designed for use in areas without grid or areas with frequent power outages. It is a rigid demand. The off-grid system does not depend on the grid and relies on the working mode of "storage while using" or "storage first and use later". , What I did was "send charcoal in the snow". For households in areas without grids or frequent power outages, off-grid systems are very practical. At present, the cost of photovoltaic off-grid electricity is about 1.0-1.5 yuan per kWh, which is much higher than that of grid-connected systems, but compared with fuel generators The cost of electricity per unit is 1.5-2.0 yuan, which is more economical and environmentally friendly.
2. Off-grid energy storage system
Off-grid photovoltaic power generation systems are widely used in places where there are frequent power outages, or photovoltaic self-use cannot be connected to the grid, the price of self-consumption electricity is much more expensive than the electricity price of the grid, and the peak electricity price is much more expensive than the valley electricity price.
The system consists of a photovoltaic array composed of solar cell components, a solar off-grid integrated machine, battery packs, loads, etc. The photovoltaic square array converts solar energy into electrical energy when there is light, and supplies power to the load through the solar control inverter integrated machine, and at the same time charges the battery pack; when there is no light, the battery supplies power to the solar control inverter integrated machine, and then supplies AC load power supply.
Compared with the grid-connected power generation system, the off-grid system adds charge and discharge controllers and batteries, and the system cost increases by about 30%, but the application range is wider. One is that it can be set to output at the rated power at the peak of the electricity price to reduce electricity expenses; the other is that it can be charged at the valley of the electricity price and discharged at the peak, making money by using the difference between the peak and the valley; and the third is that when the power grid fails, the photovoltaic system can be used as a backup power supply to continue work, the inverter can be switched to the off-grid working mode, and the photovoltaic and battery can supply power to the load through the inverter.
3. Photovoltaic grid-connected energy storage system
The grid-connected energy storage photovoltaic power generation system can store excess power generation and increase the proportion of self-consumption. It is used in applications where photovoltaic self-consumption cannot be used to connect the grid, self-use electricity prices are much more expensive than on-grid electricity prices, and peak electricity prices are much more expensive than wave-level electricity prices. The system consists of a photovoltaic array composed of solar cell components, a solar controller, a battery pack, a grid-connected inverter, a current detection device, and a load. When the solar power is less than the load power, the system is powered by the solar energy and the grid together. When the solar power is greater than the load power, part of the solar power supplies power to the load, and part of it is stored by the controller.
In some countries and regions, a photovoltaic system was installed before, and after the photovoltaic subsidy was cancelled, a grid-connected energy storage system can be installed to allow photovoltaic power generation to be completely self-contained. The grid-connected energy storage machine is compatible with inverters from various manufacturers, and the original system does not need to be changed. When the current sensor detects that there is current flowing to the grid, the grid-connected energy storage machine starts to work, and stores excess electric energy in the battery. If the battery is also fully charged, the electric water heater can also be turned on. When the household load increases at night, the battery can be controlled to send power to the load through the inverter.
4. Microgrid energy storage system
The micro-grid system consists of a solar cell array, a grid-connected inverter, a PCS bidirectional converter, an intelligent switch, a battery pack, a generator, and a load. The photovoltaic array converts solar energy into electrical energy when there is light, supplies power to the load through the inverter, and charges the battery pack through the PCS bidirectional converter at the same time; when there is no light, the battery supplies power to the load through the PCS bidirectional converter. powered by.
Microgrid can fully and effectively develop the potential of distributed clean energy, reduce unfavorable factors such as small capacity, unstable power generation, and low reliability of independent power supply, and ensure the safe operation of the power grid. It is a useful supplement to the large power grid. Microgrid can promote the upgrading of traditional industries, and it can play a huge role from the perspective of economy and environmental protection. Experts said that the application of micro-grids is flexible, and the scale can range from thousands of watts to tens of megawatts, as large as factories, mines, hospitals and schools, and as small as a building.
2. Several business models for energy storage development
1. Dynamic expansion
The rated capacity of the transformer is fixed from the moment it leaves the factory, and when the power user is affected by some demand in the later stage, the transformer is running at full capacity, and it is necessary to expand the capacity. It is understood that the cost of capacity expansion in general areas is very high. At this time Installing energy storage can realize dynamic expansion without spending a lot of money.
2. Demand response
Demand response, to put it simply, is the behavior of users changing the load curve according to the signals sent by the grid. my country's power load curve has a very obvious peak, and the implementation of demand-side response can effectively improve this phenomenon. After the user's energy storage facilities participate in the demand response, the grid will give a certain compensation fee, or rely on the peak-valley price difference to obtain income. One thing to note is that to participate in demand response is to accept the dispatch of the grid.
3. Demand electricity charge management
If you want to know how energy storage can participate in demand charge management, you must first understand what demand charge is. Simply put, it is the electricity charge charged by large industrial customers for transformers, regardless of whether the charge is based on the capacity of the transformer or the maximum load. , are unable to meet the user's peak and valley electricity load characteristics, and energy storage can perform peak shaving and valley filling to improve this situation and reduce demand electricity charges.
4. Supporting industrial and commercial photovoltaic
With the decline of photovoltaic subsidies, photovoltaic enterprises must find new models to increase revenue. Industrial and commercial photovoltaic + energy storage can increase the self-consumption rate, thereby reducing the pressure on users' electricity bills. At the same time, the energy storage battery can be charged during the day and discharged at night, thereby making money from the price difference.
5. Peak-to-valley price difference
I believe that many people are not unfamiliar with this profit model. At present, the source of profit for most companies is the peak-to-valley price difference. The peak-to-valley price difference refers to dividing 24 hours a day into multiple periods such as peak, flat, and trough according to the load changes of the power grid, and formulating different electricity price levels for each period to encourage customers to reasonably arrange electricity consumption time. Cut peaks and fill valleys to improve the utilization efficiency of power resources.
On July 2, the website of the National Development and Reform Commission officially released the "Opinions on Innovating and Improving the Price Mechanism for Promoting Green Development". Under the premise that the overall level of sales electricity prices remains unchanged, the department can establish a dynamic adjustment mechanism for peak and valley electricity prices, further expand the implementation scope of peak and valley electricity prices on the sales side, reasonably determine and dynamically adjust peak and valley periods, and expand peak and valley electricity price differences and floating ranges. Guide users to use electricity at staggered peaks. Encourage market entities to sign transaction contracts that include peak, valley, and normal period prices and electricity. Use market-oriented mechanisms such as peak-valley electricity price differences and auxiliary service compensation to promote the development of energy storage. Use modern information, Internet of Vehicles and other technologies, encourage electric vehicles to provide energy storage services, and obtain income through peak-valley price differences. Improve the tiered electricity price system for residents, and implement peak-valley electricity prices for residents.”
Regarding the current peak-valley electricity price level, the industry generally believes that the 70 cents peak-valley electricity price difference is a threshold to promote the development of the user-side energy storage industry.
Attached is the Jiangsu peak and valley electricity price list:
As can be seen from the figure above, the largest peak-to-valley price difference in Jiangsu is 0.9342 yuan per kWh. When the electricity difference reaches more than 70 cents, energy storage has the possibility of making a profit. Jiangsu, Beijing and other provinces and cities have large differences in peak and valley electricity prices.
3. Energy storage system design and configuration
The following takes the off-grid energy storage system as an example
1. How to design an energy storage system?
It can be seen that compared with the grid-connected system. The inverter should be changed to a hybrid inverter, that is, a machine with integrated functions of grid-connected and off-grid energy storage. At the same time to increase the energy storage battery.
2. How to choose a battery for the energy storage system?
Since the design is an off-grid integrated energy storage system, the power consumption of the load can be backed up by the grid. Then the choice of battery can be determined according to the planned stored energy. For example, if you plan to configure a battery that can store 10 kilowatt-hours of electricity, how should you choose? 10 kilowatt-hours of electricity means 10kWh, or 10000VAh.
Battery rated voltage: 48V
The battery discharge efficiency is 94%
In consideration of battery life and performance, the depth of discharge (80%) of the lithium battery is used for the calculation.
The depth of discharge of lead-acid batteries is generally 50% to 70%.
1) Select lithium battery
Calculated battery capacity
The general specification of lithium battery is 48V, 50Ah, and 6 parallel connections can be selected, with a total capacity of 300Ah.
2) Choose lead-acid battery
The discharge depth of lead-acid batteries is taken as 50%.
Requires 20 12V, 100Ah lead-acid batteries, connected in 4 series and 5 in parallel, with a total capacity of 500Ah.
At this time, you may have questions: Why is the power generation depth of lead-acid batteries only 50%?
It can be seen from the relationship curve between cycle and discharge depth that the discharge depth is 50%, when the effective capacity becomes 60%. The number of charge and discharge cycles is about 500 times. According to charging and discharging once a day, the battery life is less than two years. Therefore, appropriately increasing the battery capacity and reducing the depth of discharge can prolong the service life of the battery.
4. Cost of energy storage battery
Judging from the current market competition pattern, lithium batteries and lead batteries occupy most of the electrochemical energy storage market. Electrochemical energy storage carriers are various secondary batteries, mainly including lithium-ion batteries, lead-acid batteries, sodium-sulfur batteries, and flow batteries.
Calculate the cost first. The main equipment of the energy storage system is the energy storage two-way converter, the energy storage battery and supporting electricity bills and other equipment. At present, the price of large energy storage batteries has dropped, and the lithium battery can reach 1.6 yuan per kilowatt-hour. About 8-12 years, the charging efficiency is about 88%, the lead-carbon battery can achieve 0.7 yuan per degree, the service life is about 5-7 years, and the charging efficiency is about 85%. Despite the straightforward business model, the payback period is long.
In summary, industry veterans believe that the development of the energy storage industry still needs more industrial policy support, including taxation, social capital access, grid-connected access support, and more favorable combinations to provide the market with a benign development space. According to the industry research white paper provided by CNESA in April this year, among the main scenarios of China's energy storage market in the next three years, commercial energy saving accounts for 27.8%, peak regulation and frequency regulation account for 24.1%, and household photovoltaic accounts for 18.5%. In terms of policy, whether the peak-to-valley power price difference can be expanded in the future, in a longer investment recovery cycle, changes in power prices will have a major impact on the income of energy storage projects.
