An energy storage configuration planning strategy considering photovoltaic consumption

The extensive access to new energy resources will influence the grid’s economic operation and reliable power supply. This text considers the planning problem of the power company’s configuration in the energy-storage system. And the planning goal is to maximize the comprehensive benefits of the power company. The comprehensive benefit model of new energy resource costs and related revenue of power companies, as well as the operational characteristics of photovoltaic and energy-storage equipments, is analyzed, and a comprehensive operational strategy for energy storage systems is constructed. Optimizing energy storage configuration plans and operational strategies for power companies can improve the operations’ economic benefits and the utilization level of new energy generation.


Introduction
With the growth and prevalence of green energy power generation technology, the proportion of green energy power generation formed by photovoltaic power generation (PV, Photovoltaic) and wind power generation in power grids is gradually raising.The massive grid connection of these clean and green energy sources can effectively decline carbon release in the power system, which is good at environmental protection and sustainable development.However, these new energy power generation forms are different from traditional thermal power generation, etc., which are greatly affected by photovoltaic, wind power, and other energy forms, and different lighting conditions, wind speed conditions, etc., have a direct influence on the output of these new energy sources, resulting in the fluctuation, randomness and unpredictability of production, the integration of massive green energy power generation can lead to the uncertainty of the voltage, frequency, power angle and harmonics in power grids, and the power quality of the power supply and the reliability of power grid operation.Other indicators will be reduced to some extent, and the cost of power system operation, maintenance, and upgrading will also increase to a certain extent.
As an emerging energy management measure, a battery energy-storage system (BESS) is involved in the operation of power grids.It has the characteristic of changing the time-space relationship of energy, which can promote the reliability of the energy in the power grid.It can also discharge during peak charging periods to achieve peak shaving.Meanwhile, energy storage equipment, as an effective form of energy storage, can serve as an emergency power source in the event of a power system malfunction, reducing the influence of the malfunction.Due to these operating characteristics of energy storage systems, many appear in power system planning and play a significant role in power system operation [1][2].
Given that energy storage systems are involved in the research of power system operation planning, some scholars have constructed energy storage capacity configuration models on a multi-cycle scale based on the flexible application of energy storage [3].From this point of view, a generation side shared energy-storage planning strategy model considering the decay characteristics of retired power batteries is proposed [4]; some scholars suggest a two-level planning model for energy storage power plants, which considers the uncertainty of sources and loads and solves the fluctuation problem of frequency, voltage, and other indicators under the conditions of a high ratio of green new energy connected to the distribution network [5]; some scholars consider different planning scenarios, The decision-making preference of decision-makers and other uncertain factors, establish a decision-making approach for energy-storage planning strategy based on dual uncertainty to better the productiveness of energy-storage applications [6], controlled hybrid energy storage stabilization and constant volume bi-level programming model.From the perspective of the practical problems solved by energy storage, the above literature conducts research based on the characteristics of energy-storage equipments operation.However, there are a few of studies on the construction of operation strategies with power companies as the main benefit of the operation and considering the costs related to the energy-storage equipment system.
From the view of benefiting power companies due to their actual operation conditions, this paper analyzes the typical annual operating days as a reference.It considers the operating costs and related operating benefits in normal operation.The company's complete operation benefit model, with the best comprehensive operation benefit as the planning and analysis goal, makes use of the operation characteristics of new energy resource generation and energy-storage equipment system to set up a comprehensive operation strategy of energy storage system to materialize optimal economic operation of the power company and improve the use of new energy resources in the area.

Running indicators
This article analyses the application scenarios of configuring energy-storage equipment systems in power-related companies.Due to energy storage systems to improve distribution network reliability, delay distribution network upgrades, and absorb photovoltaic output benefits, a comprehensive operation revenue model is established.Meanwhile, a specific scale of the energy-storage equipment system can absorb the output of green energy and better the utilization level of new energy.In this article, photovoltaic is chosen as the new energy power generation.

PV utilization
The utilization rate of photovoltaic energy represents the utilization level of photovoltaic energy in one region, which is related to the output of solar power generation, the absorption of photovoltaic power by loads, and the absorption of energy storage systems.Since photovoltaics often use the local consumption mode, the default photovoltaic power generation loss is ignored in this paper.The photovoltaic utilization rate is: ( )

Comprehensive operating income of the power company
This article takes the maximization of the daily average comprehensive operating revenue of power companies as the planning objective and establishes an objective function.
Where: V is the comprehensive daily operating income of the power company; 1 V is the daily average revenue of the power company; 2 V is the daily operational cost of the power company; rel V refers to the benefit brought by the join of energy-storage systems in operation to improve system's reliability; del V cites the benefit obtained by the delayed upgrade and renovation of the power grids by the energy-storage equipment systems; lpv V refers to the benefits brought by the participation of energy-storage equipment systems in operation and absorption from photovoltaic output; PV V cites the average yearly circulating and maintenance cost of photovoltaic power generation system equivalent to each operating day; BESS V refers to the average annual installation cost and circulating and maintenance cost of the energy-storage equipment equal to each operating day.

Average daily circulating and maintenance cost of the solar system
During the regular operation of photovoltaic output devices, certain operating losses and maintenance costs may be incurred during maintenance due to environmental factors such as light.

( ) (
) Where: 0 r is the benchmark yield; PV n is the service life of the solar power generation device; PV,n v is the circulating and maintenance cost of per-unit capacity solar device; PV,n E is the installed capacity of solar power generation devices; PVW N is the annual operating days of the solar power generation equipment.

Energy-storage device installation and maintenance costs
Where: BESS,n

S
is the specified capacity of the energy-storage equipment; BESS,n P is the specified power of energy-storage equipment; s,n v is the installation cost per-unit capacity of energy-storage equipments; BESS n is the service life of energy-storage equipments; BESS,n v is the unit-power of circulating and maintenance cost of energy-storage equipments; BESSW N is the annual operating days of energy-storage equipments.

Energy storage devices improve system reliability benefits
The participation of energy-storage equipments in operation could change the tome-space correlation of energy, adjust the energy distribution in power systems, and thus improve the reliability level of the power system to some extent.In the article, Expected Unsupplied Energy (EENS) is used to measure the reliability norm of the system.
( ) Where: is the EENS difference of the power-system front and after the configuration of energy-storage equipment systems; sell f is the average unit price of electric power sold by power grids; comp f is the power generation ratio per unit of power shortage; IEA R is the specified user evaluation coefficient; 0 i is the benchmark rate of return.

Energy storage delays the benefits of power grid upgrades
The energy-storage equipment system has the characteristics of fast response and sensitive adjustment.It can bear a portion of the load during peak load periods in the power system, thereby reducing the power supply burden on substation nodes and delaying grid upgrades to a certain extent [7].
( ) Where: del N is the number of years delaying upgrading; del v is the cost of upgrading the substation; BESS,rel P is the trusted capacity of the energy-storage equipments; max P is system's max load value before deploying energy storage systems; λ is the growth rate of load.

Energy storage consumes photovoltaic output income
Due to the ability of energy storage systems to charge during low periods and release during peak periods of the power system, they can absorb part of the photovoltaic output by their operating characteristics to use the peak-valley transaction price to obtain the photovoltaic production and reduce the abandonment rate.

E
is the output of the photovoltaic-power generation equipment during the current period; load U

E
is the load usage of photovoltaic power generation during the current period; pv r is the on-grid price of photovoltaic-power generation; PVR N is the period of time when surplus electricity of the photovoltaic is stored into the energy-storage equipment.

Constraints
The regular running of the power system ought to meet the component constraints and other constraints.
Where: i U and j U are the voltage of panel-nodes i, j; i P and i Q are the active and reactive power of panel-node i; ij G and ij B are the line conductivity and admittance between panel-nodes i and j in the system; ij δ is the difference of the panel-node voltage's phase angle.

Node Voltage Constraints.
,min ,max Where: ,min i U and ,max i U are the lowest and highest limit of the node i voltage amplitude.

Photovoltaic output constraints.
PV PV-MPPT 0 ( ) Where: PV ( ) P t is the active power output by the photovoltaic output equipment at time t; PV-MPPT P is the upper limit of the active power output of the photovoltaic output device by MPPT operation mode.

State-of-charge constraints of energy-storage equipment.
( ) ( ) BESS,m P t is the charging and discharging power of the m-th energy-storage equipment at time t, which is positive charging and negative discharging; BESS N P − is the rated charging and discharging power of the energy-storage equipment.

Energy storage operation strategy
This article uses the typical annual operation days as a reference for the analysis.A cost-benefit model for energy-storage equipments invested and constructed by the power company is established.Energy system integrated operation strategy.By comparing the regional load curve and photovoltaic output curve, photovoltaic power generation is prioritized for transmission to the load.If there is still surplus electricity in photovoltaic-power generation, the energy-storage equipments will consume it; When energy-storage equipments are charged, photovoltaic-power generation will be prioritized for consumption.If the energy-storage equipments still have backup capacity, they will purchase electricity from the main grid.

Case analysis
The article uses a local distribution network in Northwest China as an example.A revised genetic-evolution algorithm is aimed to analyze and validate the optimal operating strategy of photovoltaic grid-connected energy storage system proposed in this article [8].
The regional system structure is as follows, displayed in Figure 1.The voltage level of the chosen distribution network is 10 kV, including three photovoltaic power generation systems: PV1, PV2, and PV3, and the output rated power is 0.25 MW.The scheduling period on the selected typical operating day is 1 h, and the system power factor is 0.9.The energy storage system adopts a ternary lithium-ion structure battery, and the benchmark rate of return of the system is set as 0.8.The specific data of the circulating and maintenance cost of photovoltaic installations per-unit capacity are represented in Table 2. Considering the structure and operational characteristics of the distribution network in the region, a typical node connected to the energy storage system is selected as node 2 or node 3. Based on the established model and operational strategy, the optimal configured capacity and comprehensive benefits of energy-storage system are obtained through simulation.The endings are represented in Table 3. the total benefits of node 2 are higher compared with node 3, but the photovoltaic utilization rate is lower compared with node 3. The configuration of node 2's energy storage system could efficaciously reduce peak-valley load, alleviate the operational pressure of grids, and delay the upgrading and transformation of grids to a certain extent to obtain this part of the income.And node 2, as the regional hub node, is equipped with an energy storage system.Compared with that end node, the improvement in operational reliability is also more apparent.Due to the photovoltaic access of node 3, configuring energy storage system at that node could absorb the photovoltaic output of that node on the spot, which has a significant impression on the consumption of photovoltaic output.However, due to the influence of grid operation scale and photovoltaic access capacity, the photovoltaic consumption benefit of node 3 is not significantly different from that of node 2, so the comprehensive benefit of node 2 is better than that of node 3. Therefore, arranging the battery energy storage system at node 2 can maximize the comprehensive operating benefits of the power company and, at the same time, ensure the utilization level of photovoltaic energy to some great extent.

Conclusion
This article considers the scenario of a huge amount of scattered photovoltaic power generation attached to the distribution network, and the power company builds energy storage power stations.It establishes relevant cost models for energy storage power stations and photovoltaic power stations.It constructs energy storage systems to facilitate the distribution network's reliability and delay grid upgrades.The benefit model for upgrading, transforming, and absorbing photovoltaic output has formed a comprehensive benefit model for the power company to invest in constructing energy storage power stations.Take the optimal comprehensive benefits as the planning goal, absorb the output of photovoltaic power stations, and develop a comprehensive operation strategy for energy storage power stations.And according to the actual power grid in a specific region, the best energy storage access point is obtained.The results indicate that the energy storage operation strategy proposed in this article can achieve the effect of absorbing photovoltaic output and bring certain benefits to the power company.It has good economic benefits and practical value.
In the future, based on the research conclusions in this article, a comprehensive operational strategy will be established, taking into account the joint grid-connection planning of green new energy power generation.

Table 2 .
Parameters of energy-storage device.

Table 3 .
Scheme comparison.According to the simulation results, comparing the comprehensive benefit and photovoltaic utilization rate of the two typical node energy storage system access schemes, it can be concluded that