In just the end of 2015 Germany INERSOLAR exhibition, many large manufacturers (Tesla, BMS, Mercedes Benz, LG, Samsung, etc.) were launched the families of their own, commercial storage system, indicating that this area has received more and more attention.
With respect to has become more and more mature household / commercial PV grid connected system, household / commercial optical storage hybrid system (referred to in this paper storage can system are assumed to be design based on energy storage battery) to more complex, and due to the large number of its field of application and easy to cause confusion leads to the unreasonable design of the system. In this paper Shanghai Xu of GMDE in this field by virtue of years of work experience, of mixed optical storage system need to be considered in the practical application system design elements are brief analysis for your reference and discuss.
1 system installation purpose:
Why should you install the optical energy storage (or pure energy storage) system, what is the purpose of installing the system? This is a problem that must be clearly defined before the design of a reasonable optical storage hybrid system. According to the design of different systems, the results of the system design are very different.
At this stage, different countries have different requirements for the installation of optical storage and mixing system, but can be determined in the following categories:
A. to improve the solar energy (including wind, etc.) spontaneous self use rate: this application is currently in Europe, Australia, the United Kingdom has a wide range of demand. The main background is due in such areas, now grid connected solar power subsidies gradually decreased, while household, commercial electricity prices increased year by year, also because of new energy, especially solar energy, generating power curve and the load of electrical curve does not match, for home users, generally only 20% - 30% of new energy power generation amount is to use their own, while the remaining power are fed back into the grid, so under the above background, user terminal hope solar electricity as much as possible by their own consumed rather than feedback to the grid. In this case, the installation of optical storage system, through the system control to improve the spontaneous self - use rate, so that the solar system as the main purpose of the user service system.
B. energy dissipation peak fill in the valley: the main focus of this kind of application in the peak and valley electricity price difference of some industries or countries, generally only need to install a pure energy storage system can be. The user to install the purpose of this system is to load is light, electricity price is relatively low on storage can charging system in heavy load, a higher price when the energy storage system discharge, using peak valley electricity price difference to achieve the goal of reducing the users of electricity.
UPS C. work mode: this kind of application is mainly concentrated in the area of poor reliability of the power grid, the country, such as Africa, Southeast Asia, etc.. The installation of such a system is that when the grid work normal, by the power grid to the user for power supply, at the same time, the solar power to charge the battery, the battery in the normal operation of the grid as far as possible to maintain the filled state. When the power grid faults, the power supply of the user is transferred by the optical energy storage hybrid (or pure energy storage) system, in order to ensure the continuity of the user's power supply.
In the above three modes, the mode A and B are the main operation mode of the grid connected and the network is the main way of the network. Mode C is mainly from the network, and the network is supplemented. (on the application of the network function in the optical storage and mixing system, the author will analyze the future of the paper.
In addition to the above three kind of main patterns, in the grid application level storage can system and adjust the frequency of power grid requirements. This paper mainly analyses the household, commercial light hybrid energy storage system, so for this kind of application mode no longer are discussed.
2 system configuration
The main configuration of the system can be designed for the purpose of the system installation. In the design of the hybrid energy storage system configuration, the core part of is for the storage battery can be part of the design, the key is to also take into account the power balance and energy balance to optimize the system cost. Frankly, the design and calculation of this area is very complex (especially in the field of providing solar energy), and it is a good result to consider many factors. This article is only for a brief analysis of different installation purposes for your reference discussion:
A. improve the spontaneous self occupied rate of solar energy:
In such applications, in fact, should be divided into two cases to consider: installed solar energy users and users are not installed solar.
(1) for the user has installed solar energy: because the existing solar power system, so the exchange coupling scheme to form a light storage hybrid system more appropriate: the original solar panels and solar inverter constitute solar power system, installed at the same time bidirectional battery charge and discharge inverter and storage battery, wherein a battery energy storage system, the power of both in the measured AC coupling.
Due to solar power, daily generation capacity and user load peak power and power consumption can be predicted, so the design of a storage battery can system mainly from two aspects of power balance and energy balance be considered:
Power balance: the purpose is to select the appropriate power (KW) of the battery inverter through solar energy generation power curve, the user's daily load power curve. Inverter battery power should not be chosen too large, over the General Assembly lead to increased cost and not practical, because the solar energy does not necessarily provide enough charging power; if the battery inverter power is too small, will lead to solar spontaneously occupied rate decreased, too much power is fed back to the power grid and did not reach the objective of system design, at the same time, energy storage battery may not be able to fill. Generally speaking, the power of the battery inverter for photovoltaic power of 60%-80% is a more appropriate choice range.
Energy balance: the purpose is to determine the capacity of the energy storage battery (KWH) by the solar energy, the daily electricity consumption, the daily consumption of the load and the expected rate of spontaneous use of solar energy. With power balance is similar, the storage battery capacity over the General Assembly lead battery cannot be filled with due to the high cost of the system, the capacity is too small will lead storage batteries are easy to be filled, and solar energy emitted by the electricity had to be feedback to the grid and the solar spontaneously with rate is too low. Combined with the design experience of the author for many years, the battery capacity (KWH) is 1-1.5 times (numerical) of the battery power (KW) is appropriate.
(2) for users is not installed on the solar energy, the DC coupling scheme is appropriate, namely solar with MPP tracker and storage can (with a bi-directional DC-DC converter) battery energy in the DC link coupling, and the two share a DC-AC inverter. The design of solar energy can be directly referred to the design of the grid connected photovoltaic system. The design method of the battery is the same as that of the solar energy.
B. elimination peak filling:
For this kind of application, because no need to consider solar energy, so the system design is clear. According to the customer's requirement, the charging and discharging power of the energy storage system is determined, and the capacity of the storage battery can be determined according to the different time periods of peak and valley. But need to pay attention to is, because the day may have a plurality of peak and valley, usually, so will lead to energy storage cells in repeated charge and deep deep discharge cycles, the reservoir to the service life of the battery is a problem that must be considered.
UPS C. working mode:
In this mode, the optical energy storage system is designed, which can be considered directly from two angles of the power balance and energy balance:
Power balance: as long as the maximum power of the optical storage system is greater than the maximum instantaneous power.
Energy balance: according to the worst case no solar energy considerations, according to customer requirements of the electrical time can determine the storage battery capacity.
3 system running time evaluation
The hybrid energy storage system for energy is cost is the highest, the most easily damaged part of the storage battery, so the whole system running life basically is by storage battery cycles, use fixed number of year to decide. (Note: the inverter general warranty period is 5 years, basically can be used to 7 years or so. Generally if the service life of the direct replacement)
In the operation of the system, energy storage battery operating life of the main factors is the DOD (depth of discharge) and the charge and discharge current, also a have a good balance of the battery management system of reservoir can influence the service life of batteries, especially lithium batteries a huge. How to prolong the service life of the battery is in the field of optical storage of hybrid system also a very important technical issues here without too much discussion here only appear on the market some specifically for applications in solar energy to improve the storage occupied rate of spontaneous to battery warranty period for your reference:
In the use of certain DOD and charge and discharge current:
General lead acid battery: 1 years
Colloid lead acid battery: 2-3
Lead carbon battery: 5-7
Lithium energy storage battery: 7-10
In addition, now the market has been a number of 20 years of the battery, but the price has not become the mainstream of the market.
After taking into account the above three system elements, the design of a hybrid system can be roughly determined. But in addition to the above three design elements, system the key communication integration, system on-site installation and debugging, etc. factors must to be considered in. All these require on-site installation experience, here in this paper, we will not repeat them. Hope through the description of some design elements of the optical storage hybrid system analysis, let users more deeper understanding of optical storage hybrid system, more conducive to promoting the development of the storage industry.
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