KR102521695B1 - Integrated management device for solar power facilities - Google Patents

Abstract

The present invention relates to a device for integrated management of photovoltaic power generation facilities, and more particularly, to a device for integrating and managing maintenance/repair/replacement of photovoltaic modules.
The present invention can provide clear criteria for replacement of solar modules, guide replacement of solar modules based on profitability analysis of solar modules, and guide scheduled replacement timing. At the same time, the present invention can provide an integrated solution for maintenance/repair/replacement of solar modules.

Description

Integrated management device for solar power facilities}

The present invention relates to a device for integrated management of photovoltaic power generation facilities, and more particularly, to a device for integrating and managing maintenance/repair/replacement of photovoltaic modules.

A photovoltaic power generation system constructs a photovoltaic module string by connecting a plurality of photovoltaic modules including a plurality of photovoltaic cells in series to obtain a desired voltage. Then, in order to obtain a desired large current, a plurality of solar module strings are connected in parallel in the connection terminal box. In addition, the inverter performs MPPT (Maximum Power Point Tracking) control to output maximum power through voltage and current received through a plurality of strings.

There are various techniques for monitoring the photovoltaic power generation system for maintenance and repair of the photovoltaic power generation system having the above structure.

Korean Patent Registration No. 10-1911334 includes a unique identification number and includes one or more photovoltaic modules; a connection panel that receives power output from the solar module; A connecting module connected to an output terminal of each photovoltaic module to measure power information output from the photovoltaic module and transmit it together with an identification number; And it is connected to the connecting module to receive and store the power information of the photovoltaic module transmitted from the individual photovoltaic module, display the power information on the individual photovoltaic module, and compare and analyze the power information to determine whether or not the individual photovoltaic module has a problem. Including, a monitoring server for determining a; and configuring a plurality of photovoltaic modules to configure a unit photovoltaic string, but selecting one of the connecting modules connected to each photovoltaic module in one unit photovoltaic string. While setting as the main transmission module, the remaining connecting modules are set as sub-transmission modules, and the main transmission module has the power information and identification number measured from the connected photovoltaic module and the power information and identification number measured by the sub-transmission module. After collecting for a set time, it is configured to transmit data in batches through one solar module on one unit photovoltaic string, and the photovoltaic module has a support structure, but the The support structure includes a pedestal and a support mounted on the pedestal, wherein the lower surface of the support forms a convex curved surface toward the lower side and the upper surface of the pedestal forms a concave curved surface toward the upper side corresponding to the lower surface of the support, so that when an impact due to an earthquake occurs The support and the pedestal are capable of sliding in all directions along a curved surface, and the inner periphery of the spring is tightly wrapped around the outer periphery of the connection portion between the support and the pedestal, and the spring is applied to the lower surface of the support and the pedestal. It is configured to have a length longer than the upper and lower ranges of the curved surface formed on the upper surface of the curved surface, so that the upper and lower ranges in which the curved surface is formed are included, so that the support and the support act as a buffer when sliding, and are configured to prevent complete separation from each other. , Accommodating grooves facing each other are formed on the lower surface and the upper surface, and a receiving space communicating with each other is formed by the combination of the lower surface and the upper surface, and an elastic column forming a hollow in the receiving space and a hollow of the elastic column A face lift including a firing bar interposed therein is placed, and a head is formed at both ends of the firing bar, and a body having a smaller diameter while connecting the head is formed, and a plastic deformation space is formed at the inner periphery of the body and the hollow. Disclosed is a solar module monitoring system characterized in that formed.

Korean Patent Publication No. 10-2018-0080599 discloses a voltage measurement unit for measuring individual voltage values of a plurality of solar panels connected in series; a current measuring unit measuring a common current value flowing through the plurality of solar panels connected in series; a central processing unit which digitally converts the individual voltage values and the common current value; and a communication unit for transmitting the digitally converted individual voltage values and common current value to a data collection device.

Existing photovoltaic power generation monitoring systems only provide an alarm when an abnormality occurs passively.

Solar power generation system operators basically build solar power generation systems on their own land through profitability analysis in order to make profits by using the energy resource called solar light irradiated on the land they own.

Therefore, in the photovoltaic power generation system, maintenance/repair/replacement of the photovoltaic power generation facility must be performed from the operator's point of view of profitability.

However, the existing technology simply monitors the solar module only in terms of voltage/current/efficiency of the solar module or array and performs maintenance/repair according to the monitoring result. In addition, only from a technical point of view, the status of solar power generation facilities was diagnosed and guidance for maintenance/repair was provided, but no guidance was provided for replacement from a profit point of view.

Korean Patent Registration No. 10-1911334 (Publication date: 2018.12.28, solar module monitoring system) Korean Patent Publication No. 10-2018-0080599 (published date: 2018.07.12, solar panel monitoring device and method)

Therefore, the present invention is to provide a device capable of providing a clear standard for replacing a solar module, guiding solar module replacement based on profitability analysis of a solar module, and guiding a scheduled replacement time for the purpose of providing do.

In addition, an object of the present invention is to provide a device capable of integrating and managing maintenance/repair/replacement of a solar module.

An integrated management device for photovoltaic power generation facilities according to a preferred embodiment of the present invention includes a revenue curve generation unit for generating an actual revenue curve; Yield analysis unit for calculating the revenue deduction rate of the photovoltaic power generation system according to the following equation;

[mathematical expression]

here,

x = percentage of revenue deduction from solar power system

Pvirtual = total return over the warranty life of the solar module according to the hypothetical return curve

Preal = total return over the warranty life of the solar module according to the actual return curve

Mnow = amount invested so far

a simulation unit for predicting a replacement time point of a solar module and the number of photovoltaic modules to be replaced when the revenue deduction rate calculated by the yield analysis unit is less than a preset standard revenue deduction rate; and the virtual MPPT unit calculates the difference between the virtual output value of the inverter calculated in real time and the actual output value of the inverter measured through the real-time watt-hour meter using the information collected through the sensing value collection unit, and between the real-time virtual output value of the inverter and the real-time actual output value of the inverter. A maintenance information unit providing a maintenance/repair alarm to the outside when the difference is greater than or equal to a preset standard output difference is included.

Here, the simulation unit calculates the future profit deduction rate at predetermined time intervals according to the following equation,

[mathematical expression]

here,

Pnv = return at any point in time according to the hypothetical return curve

Pnr = the return at any point in time of the PV system according to the actual return curve

The simulation unit determines whether or not there is a future revenue reduction rate in which a future revenue reduction rate enters a predetermined unit standard or higher among future revenue reduction rates calculated at a predetermined time interval, and the simulation unit determines whether or not there is a future revenue reduction rate based on a predetermined unit standard. If there is a future profit deduction rate that enters more than the profit deduction rate, the point at which the profit deduction rate exceeds the predetermined unit standard can be predicted as the replacement time point.

The present invention can guide the replacement of solar modules so that the yield of solar modules can be secured within an error range of a standard revenue deduction rate.

And, in the present invention, the yield of the solar module is secured within the error range of the standard revenue deduction rate, but the replacement of the solar module is selected in a form that minimizes the number of solar modules to be replaced. Additional costs for replacement can be minimized.

In addition, the present invention can facilitate the management of assets called solar modules by providing prediction information on the estimated time when the solar modules should be replaced and the number of solar modules to be replaced.

The present invention may provide maintenance/repair guidance for a solar module using a difference between an inverter output through virtual MPPT control and an actual inverter output.

1 is a schematic diagram of a photovoltaic power generation system to which an integrated photovoltaic facility management device according to a preferred embodiment of the present invention is applied.
2 is a diagram for explaining the profitability of the photovoltaic power generation system in the present invention.
FIG. 3 is a functional block diagram of the solar power facility integrated management device of FIG. 1 .

Since the present invention can make various changes and have various embodiments, specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Like reference numerals have been used for like elements throughout the description of each figure. In describing the present invention, if it is determined that a detailed description of related known technologies may obscure the gist of the present invention, the detailed description will be omitted.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. These terms are only used for the purpose of distinguishing one component from another.

For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the scope of the present invention.

The terms and/or include any combination of a plurality of related recited items or any of a plurality of related recited items.

It is understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, but other elements may exist in the middle. It should be.

On the other hand, when an element is referred to as “directly connected” or “directly connected” to another element, it should be understood that no other element exists in the middle.

Terms used in this application are only used to describe specific embodiments, and are not intended to limit the present invention.

Singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, the terms "include" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that the presence or addition of numbers, steps, operations, components, parts, or combinations thereof is not precluded.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and unless explicitly defined in this application, it should not be interpreted in an ideal or excessively formal meaning. don't

Hereinafter, a photovoltaic facility integrated management device (hereinafter referred to as a 'management device') according to a preferred embodiment of the present invention will be described with reference to FIGS. 1 to 3. In order to clarify the gist of the present invention, descriptions of conventionally known matters are omitted or simplified.

Referring to FIG. 1, the photovoltaic power generation system includes a plurality of photovoltaic arrays (10-1, 10-2, ..., hereinafter collectively referred to as '10'), an array connection board 20, an inverter 30, management Device 40 may be included. Each of the plurality of photovoltaic arrays 10 may include a plurality of photovoltaic modules 11 . 1 illustrates a case where solar modules are installed 3 by 4. A plurality of photovoltaic arrays 10 may be connected in parallel through the array connection board 20 . The inverter 10 may receive DC power generated from the photovoltaic array through the array connection board 20, convert it into AC, and output it. At this time, DC may be converted to AC through the MPPT control scheme.

In FIG. 2, the virtual revenue curve shows the output characteristics of the photovoltaic array, the annual amount of sunlight at the location where the photovoltaic power generation system is installed, and the average temperature during the generation time (eg, 9:00 am to 6:00 pm), and the MPPT control result. can be created by integrating Specifically, when the solar array is installed at a predetermined angle, the solar array output according to the real-time amount of sunlight and average temperature for one year may be calculated. In addition, by applying MPPT control to the output (voltage and current) of the photovoltaic array, the amount of electricity sold by the photovoltaic power generation facility can be calculated in real time for one year. At this time, the output characteristics of the solar array may be provided by the solar array manufacturer. In addition, the output characteristics of the photovoltaic array may be set to have performance degradation by, for example, 1%, for example, whenever the number of years of operation increases by 1 year, in consideration of the lifespan of the photovoltaic array (tmax, for example, 20 years). there is. In addition, the MPPT control result may be calculated by modeling an inverter installed in the photovoltaic power generation system and setting the input as the photovoltaic array output (voltage, current) in the corresponding inverter model. And, by multiplying the sales amount according to the unit sales amount by the MPPT control result, the profit according to the electricity sale can be calculated. Alternatively, the virtual revenue curve may be a seasonal or monthly revenue curve arbitrarily calculated by a solar power generation system installer in consideration of power generation capacity. The present invention does not place any restrictions on the manner in which the virtual yield curve is generated, and it suffices to provide some reliable information about the yield of the photovoltaic system over the lifetime of the photovoltaic module.

The actual yield curve can be calculated by the following process.

Step 1) Operation of the photovoltaic power generation system based on the output (voltage, current) of the photovoltaic module from the start of operation of the photovoltaic power generation system to the present time (t1) and the output power of the inverter reflecting virtual MPPT control on the output Calculate the revenue of the photovoltaic power generation system at a preset period from the start time to the present time (t1)

Step ii) Generating an actual return curve by curve approximating the calculated return for the photovoltaic power generation system at a preset cycle

In FIG. 2 , a dotted line area in the actual revenue curve means revenue predicted from t1 to the life of the solar module through curve approximation at time t1. In the case of a solar power generation system that has been installed for at least one year, the standard actual profit curve prepared by the solar power system diagnosis company is applied as the profit curve to date (the solid line area in the actual profit curve in FIG. 2) After that, the actual yield curve can be updated by applying the value calculated in step 1) above.

Referring to FIG. 2, the total virtual revenue of the solar power generation system can be calculated by the lower area of the virtual revenue curve during the lifetime of the solar module (the lifetime of the solar module guaranteed by the solar module manufacturer, tmax). . In addition, the total actual revenue of the photovoltaic power generation system can be calculated by the area under the actual revenue curve. At this time, a difference between the total virtual return and the total actual return may occur. This may be due to deterioration of the photovoltaic power generation system in an environment in which the photovoltaic power generation system is operated, a difference according to the actual amount of sunlight and temperature compared to the predicted amount of sunlight and temperature, and the like.

A solar power generation system operator builds a solar power generation system by considering the return on investment. For example, when the investment amount is 200 million, the rate of return (return to investment amount) for 20 years is 300% (600 million), and the solar power generation system can be invested. Of course, there may be risks associated with investing. However, it is preferable that the decrease in profit due to the risk is less than a predetermined value, for example, 10%.

Accordingly, an object of the present invention is to provide a management device capable of guiding replacement of a solar module so as to secure the rate of return of the solar power generation system considering the risk. That is, according to the present invention, the standard for determining whether to replace a solar module is the rate of return of the photovoltaic power generation system, and guides replacement of the photovoltaic module so as to secure the rate of return.

Specifically, referring to FIG. 3 , the management device 40 includes a sensing value collection unit 41, a virtual MPPT unit 42, a yield curve generator 43, a yield analysis unit 44, a simulation unit 45, A module replacement guide 46 and a maintenance guide 47 may be included.

The sensing value collection unit 41 includes the output current of the photovoltaic module in real time from the current sensor 1 installed at the output end of the photovoltaic module, the output voltage of the photovoltaic module in real time from the voltage sensor 2 installed at the output end of the photovoltaic module, and sunlight Real-time solar radiation irradiated to the solar module from the solar radiation sensor 3 installed on the module side and real-time temperature of the solar module can be collected from the temperature sensor 4 installed on the solar module. Also, the sensed value collection unit 41 may collect the actual output power amount of the inverter 30 from the watt-hour meter 5 installed at the output terminal of the inverter 30 in real time.

The virtual MPPT unit 42 inputs input values (input voltage value, input current value) from the solar panel to the inverter according to the output (voltage, current) of the solar module collected through the sensing value collection unit 41. By calculating and applying the MPPT control algorithm to this input value, the inverter output value can be calculated. Here, the MPPT control algorithm may be the same as the MPPT control algorithm of the inverter installed in the solar power generation system. Accordingly, the amount of power sold by the real-time photovoltaic power generation system to the power system can be calculated. The virtual MPPT unit 42 may have an inverter model to which MPPT is applied.

The revenue curve generating unit 43 may calculate real-time revenue by applying the electricity sales price to the amount of electricity sold by the real-time photovoltaic power generation system to the power system. And, the yield curve generation unit 43 may generate an actual yield curve by curve approximating the accumulated yield values with respect to the t-axis. In this case, the actual yield curve may be a yield curve for a guaranteed lifetime (eg, 20 years) of the photovoltaic module.

The yield analysis unit 44 may calculate the yield deduction rate of the solar power generation system by the following equation.

[Equation 1]

here,

x = percentage of revenue deduction from solar power system

Pvirtual = total return over the warranty life of the solar module according to the hypothetical return curve

Preal = total return over the warranty life of the solar module according to the actual return curve

Mnow = investment amount to date (all costs to date for building a solar power generation system)

The simulation unit 45 may determine the replacement of the solar module when the profit reduction rate calculated by the yield analysis unit 44 is greater than or equal to the predetermined reference revenue reduction rate. At this time, the simulation unit 45 may determine the solar module replacement through the following process.

Step 1) Calculate the output power when the simulation unit 45 replaces the solar module with the lowest output power among all the modules of the solar power generation system based on the current time point (At this time, the simulation unit 45 collects the sensed value After replacing the solar module using solar radiation and temperature from the solar module collected through the unit 41, the output (voltage, current) of the replaced solar module is calculated and reflected to the same method as the virtual MPPT unit 42. Calculate the total output power of the inverter by performing MPPT control with

Step 2) The simulation unit 45 calculates revenue at the current point on the assumption that the solar module is replaced in the same way as the yield curve generator 43

Step 3) The simulation unit 45 extracts the difference between the current revenue calculated on the premise of replacing the solar module and the actual revenue calculated on the premise that there is no replacement of the solar module

Step 4) Estimated value from the actual revenue curve by the difference between the current revenue calculated by the simulation unit 45 on the premise of replacing the solar module and the current revenue calculated on the premise that there is no replacement of the solar module move up

Step 5) Calculate the profit deduction rate after replacing the solar module according to the following equation on the assumption that the simulation unit 45 has moved the estimate upwards

[Equation 2]

here,

x' = percentage of revenue deduction of solar module solar power system

Pvirtual = total return over the warranty life of the solar module according to the hypothetical return curve

Preal' = total return over the guaranteed lifetime of the solar module according to the actual yield curve calculated on the premise of solar module replacement

Mnow = investment amount to date (all costs to date for building a solar power generation system)

Madd = replacement cost of solar modules

Step 6) The simulation unit 45 sequentially adds the number of photovoltaic modules to be replaced in the order of output power from the photovoltaic module with the lowest output power until the revenue deduction rate is less than the standard revenue deduction rate, while step 1 to 5 is repeated, and if the revenue reduction rate is less than the standard revenue reduction rate, the above steps 1 to 5 are stopped and the module replacement guidance unit 46 returns the solar module to be replaced so that the revenue reduction rate is less than the standard revenue reduction rate. Notification of replacement (At this time, the module replacement guide 46 provides information on the solar module to be replaced)

The simulation unit 45 may predict the replacement time of the solar module if the profit reduction rate calculated by the return analysis unit 44 is less than the preset reference profit reduction rate. At this time, the simulation unit 45 may predict the solar module replacement time through the following process.

Step 1) The simulation unit 45 may calculate the future profit deduction rate at a preset time interval (eg, one month). The future revenue deduction rate may be calculated at predetermined time intervals from the present time until 20 years from the installation time. Unlike Equation 1, the future profit deduction rate may be calculated according to the following equation at a predetermined time period.

[Equation 3]

here,

Pnv = return at a point in time according to the hypothetical return curve according to Fig. 2

Pnr = the return at a point in time of the PV system according to the actual return curve according to Fig. 2

The future profit deduction rate may be calculated at intervals of one month.

Step 2) The simulation unit 45 may determine whether or not there is a future revenue deduction rate in which the future revenue deduction rate is greater than or equal to the predetermined unit standard revenue deduction rate among the future revenue deduction rates calculated at a predetermined time interval. . At this time, if there is no future revenue reduction rate entering the preset unit standard revenue reduction rate or higher, it is possible to stop predicting the replacement time of the photovoltaic module. On the other hand, if there is a future revenue reduction rate that enters the preset unit-based revenue reduction rate or higher, a time point that enters the preset unit-based revenue reduction rate or higher can be predicted as the replacement time point.

Step 3) And, the simulation unit 45 can predict the number of photovoltaic modules to be replaced. In this case, the simulation unit 45 may regard a photovoltaic module whose degree of deterioration exceeds a reference degree of deterioration by more than a standard excess value as a photovoltaic module to be replaced, based on the current time point. The degree of deterioration according to the usage period of the solar module may be provided by the solar module manufacturer. For example, deterioration may progress by 1% whenever the period of use increases by one year. Therefore, the standard degree of deterioration can be calculated according to the following equation. The degree of degradation of the photovoltaic module at the current time point may be ((actual output power of the photovoltaic module at the current temperature and solar radiation/virtual output of the solar module at the current temperature and solar radiation) * 100). The virtual output of the photovoltaic module at the current temperature and solar radiation may be specification information provided by a photovoltaic module manufacturer.

[Equation 4]

Standard degree of deterioration = number of years of use * degree of deterioration that progresses each time the period of use increases by 1 year

And, the value exceeding the standard may be preset information, for example, 3%.

At this time, the module replacement guidance unit 46 may inform the outside of prediction information about the replacement time of the solar module and the number of solar modules to be replaced.

In addition, the maintenance information unit 47 measures the virtual output value of the inverter 30 calculated in real time using the information collected by the virtual MPPT unit 42 through the sensing value collection unit 41 and the real-time power meter 5. The difference between the actual output values of the inverter 30 may be calculated. Here, the virtual MPPT unit 42 is an input value (input voltage value) input from the solar panel to the inverter 30 according to the output (voltage, current) of the solar module collected through the sensing value collection unit 41. , the input current value), and by applying the MPPT control algorithm to the input value, the virtual output value of the inverter 30 can be calculated. Here, the MPPT control algorithm may be the same as the MPPT control algorithm of the inverter 30 installed in the solar power generation system. In addition, the maintenance guidance unit 47 may provide a maintenance/repair alarm to the outside when a difference between a real-time virtual output value of the inverter 30 and a real-time actual output value of the inverter 30 is greater than or equal to a preset reference output difference. In addition to deterioration, photovoltaic power generation may decrease in output due to damage and contamination. In the case of deterioration and damage, the photovoltaic module must be managed in terms of replacement, and in the case of contamination, the photovoltaic module must be managed in terms of cleaning. If the difference between the real-time virtual output value of the inverter 30 and the real-time actual output value of the inverter 30 is equal to or greater than a preset reference output difference, it is preferable to first determine whether it corresponds to contamination or damage. In addition, in a state in which the effects of contamination and damage are removed, that is, in a state in which the cause of the decrease in the amount of photovoltaic power generation is removed in addition to the external circumstance condition in the photovoltaic power generation facility, the simulation unit 46 calculates the solar power based on the profitability of solar power generation. It is desirable to determine whether or not to replace the optical module.

In this way, the present invention can facilitate asset management by an operator of a photovoltaic power generation system by providing prediction information on the replacement time and number of photovoltaic modules. In addition, since maintenance and repair are performed concurrently based on the amount of photovoltaic power generation, the reliability of prediction information on the replacement time and number of photovoltaic modules may be increased.

In this way, the management device of the present invention may guide the replacement of the solar module so that the yield of the solar module can be secured within the error range of the standard revenue deduction rate. In addition, the rate of return of the solar module is secured within the error range of the standard revenue deduction rate, but by selecting the replacement of the solar module in a form that minimizes the number of solar modules to be replaced, Additional costs can be minimized.

10-1, 10-2: solar array
11: solar module
20: array access panel
30: Inverter
40: solar power facility integrated management device

Claims (2)

a yield curve generation unit that generates an actual yield curve;
Yield analysis unit for calculating a revenue deduction rate of the photovoltaic system according to Equation 1 below;
[Equation 1]

here,
x = percentage of revenue deduction from solar power system
Pvirtual = total return over the warranty life of the solar module according to the hypothetical return curve
Preal = total return over the warranty life of the solar module according to the actual return curve
Mnow = Amount invested so far
a simulation unit for predicting a replacement time point of a solar module and the number of photovoltaic modules to be replaced when the revenue deduction rate calculated by the yield analysis unit is less than a preset standard revenue deduction rate; and
The virtual MPPT unit collects real-time photovoltaic module output current, real-time photovoltaic module output voltage, real-time solar radiation irradiated to the photovoltaic module, real-time temperature of the photovoltaic module, and real-time inverter actual output power information collected through the sensing value collection unit. If the difference between the virtual output value of the inverter calculated in real time and the actual output value of the inverter measured through the real-time watt-hour meter is calculated using Including a maintenance guide that provides an alarm,
The simulation unit calculates the future profit deduction rate at a predetermined time interval according to Equation 2 below,
[Equation 2]

here,
Pnv = return at any point in time according to the hypothetical return curve
Pnr = the return at any point in time of the PV system according to the actual return curve
The simulation unit determines whether there is a future revenue deduction rate that enters a predetermined unit-based revenue deduction rate or more among the future revenue deduction rates calculated at a predetermined time interval,
The simulation unit predicts, as a replacement time point, a point in time at which the unit-based rate of profit deduction or higher is entered when a future rate of profit deduction that enters the preset unit-based rate of deduction or higher exists,
The simulation unit regards a photovoltaic module whose deterioration degree according to the period of use provided by the photovoltaic module manufacturer exceeds the standard deterioration degree of Equation 3 by more than the standard excess value as a photovoltaic module to be replaced, based on the current time point. An integrated management device for photovoltaic power generation facilities, characterized in that for doing.
[Equation 3]
Standard degree of deterioration = number of years of use * degree of deterioration that progresses each time the period of use increases by 1 year
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