Method for calculating photovoltaic influence on seasonal average water temperature

Abstract

The invention relates to a method for calculating photovoltaic influence on seasonal average water temperature. The method comprises the following steps: collecting field data; calculating a comprehensive change source item; calculating a wind speed related parameter correction value; calculating a comprehensive heat dissipation coefficient; and calculating a water area water temperature change value. The invention provides a method for quantitatively calculating photovoltaic-to-seasonal average water temperature change according to seasonal average meteorological factors and photovoltaic arrangement by comparing a water area shielded by a photovoltaic facility with an adjacent non-shielded water area, correcting parameters, and taking the calculated water temperature change as a basis for evaluating the influence of a water environment.

Description

Technical Field

[0001] The invention relates to a method for calculating the effect of photovoltaics on seasonal average water temperature, which is a hydraulic calculation method and a calculation method for the effect of photovoltaic facilities on water temperature applied to a photovoltaic power plant on water. Background Art

[0002] Water photovoltaic power stations are equipped with a large number of dense photovoltaic panel arrays on the water surface. The photovoltaic panel arrays affect the radiant heat received by the water surface and the heat exchange processes such as evaporation and convection on the water surface by shielding and absorbing the short-wave solar radiation and changing the local wind field, thereby changing the water temperature. As an important environmental factor of water ecology, water temperature is an important indicator for evaluating the impact of water photovoltaic power stations on the water environment. At present, the qualitative analysis of the influence of photovoltaic power stations on water temperature is mainly based on limited observations. The numerical calculation method based on real-time changing meteorological and hydrological conditions requires a large amount of real-time data, which is not very operational when real-time data is lacking. How to quantitatively analyze the influence of water temperature in the water area of ​​photovoltaic power stations with limited data is a problem that needs to be solved. Summary of the invention

[0003] In order to overcome the problems of the prior art, the present invention proposes a method for calculating the impact of photovoltaics on seasonal average water temperature. The method proposes a method for quantitatively calculating the change of photovoltaics on seasonal average water temperature, which can quantitatively calculate the change of water temperature and accurately evaluate the impact of photovoltaic facilities on the water environment.

[0004] The object of the present invention is achieved by: a method for calculating the effect of photovoltaic power generation on seasonal average water temperature, wherein the steps of the method are as follows:

[0005] Step 1, collect on-site data: monitor various data of heat sources and cold sources on-site in the areas covered by photovoltaic facilities and areas not covered by photovoltaic facilities of the photovoltaic power plant;

[0006] Step 2, calculate the comprehensive change source term: calculate the comprehensive reduction source term Q′ of solar radiation and atmospheric radiation caused by the coverage of photovoltaic facilities:

[0007] Q′=φ s ′-φ s +φ′ a -φ a

[0008] Where: φ s ′ is the solar radiation received by the water surface when there is photovoltaic shading; φ s is the solar radiation without photovoltaic shading; φ′ a is the atmospheric radiation with photovoltaic; φ a is the atmospheric radiation when there is no photovoltaic;

[0009] Step 3, calculate the correction value of wind speed related parameters: the impact of wind speed reduction caused by coverage and shading of photovoltaic facilities on evaporation will correct the wind speed related parameters α′:

[0010] α′=22.0+12.5V w ' 2 +2.0(T s -T a ) 1 / 2 ]

[0011] Where: V w ′ is the wind speed in the photovoltaic area affected by shading; T s is the water surface temperature; T a is the temperature;

[0012] Step 4, calculate the comprehensive heat dissipation coefficient:

[0013] K′=(k+b)α′+4εσT s 3 +ΔK

[0014] in: in: α is the wind speed related parameter not blocked by photovoltaic facilities; e s For T s The corresponding saturated water vapor pressure; e a is the air vapor pressure; ε is the water body emissivity; σ is the Stefan-Boltzmann constant; b is the Bowen ratio;

[0015] Step 5, calculate the water temperature change value of the water area: calculate the water temperature change value of the water area affected by the cover and shading of the photovoltaic facilities:

[0016] ΔT s ′=Q′ / K′.

[0017] The advantages and beneficial effects of the present invention are as follows: the present invention proposes a method for quantitatively calculating the effect of photovoltaics on seasonal average water temperature changes by comparing the water area shielded by photovoltaic facilities with the adjacent water area without photovoltaic shielding, by correcting parameters and based on seasonal average meteorological factors and photovoltaic layout. The water temperature changes thus calculated are used as the basis for evaluating the impact on the water environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0019] Figure 1 is a flow chart of the method described in an embodiment of the present invention. DETAILED DESCRIPTION

[0020] Example:

[0021] This embodiment is a method for calculating the impact of photovoltaics on seasonal average water temperature.

[0022] When solving the spatiotemporal variation of natural surface water temperature, the hydrodynamic equation is solved based on the real-time meteorological parameters (temperature, humidity, wind speed, cloud cover, solar radiation, etc.) and hydrological parameters (water level, flow) to obtain the spatiotemporal distribution of water temperature. However, in the evaluation of the impact of projects (such as thermal drainage and cold drainage of power projects) on environmental water temperature, the representativeness and typicality of natural conditions need to be considered. Generally, the seasonal average meteorological and water temperature conditions are used as the evaluation benchmark. At this time, the temporal and spatial variation of natural water temperature is generally ignored, and it is regarded as a temporal and spatial uniform constant value. Only the impact of temperature changes caused by the project is concerned. Based on this requirement, the corresponding time average concept also needs to be used when evaluating the water temperature impact of photovoltaic projects.

[0023] Calculation method of water temperature impact under the influence of conventional cooling water engineering:

[0024] The heat flux φ between the water surface and the atmosphere includes solar radiation φ s , atmospheric radiation φ a , the water body radiates outward φ w , evaporative heat dissipation φ e and convection heat dissipation φ c , whose expression is:

[0025] φ=φ s +φ a -φ w -φ e -φ c (1)

[0026] where φ s and φ a is the change of solar and atmospheric radiation, and is an independent term of water temperature. w ,φ e ,φ c is the water temperature related term, and its expression is:

[0027] φ w =εσT s 4 (2)

[0028] φ e =L v f(u)(e s -e s ) (3)

[0029] φ c = bφ e (4)

[0030] b=0.66(T s -T a ) / (es -e a ) (5)

[0031] Where ε is the emissivity of water, σ is the Stefan-Boltzmann constant, σ = 5.67 × 10 -8 (J / m 2 sK 4 ), T s is the water surface temperature, L v is the latent heat of evaporation, its unit is J / kg, L v =2.5×10 6 , f(u) is the wind speed function, e s For T s Corresponding saturated water vapor pressure (hPa), e a is the air vapor pressure (hPa), b is the Bowen ratio, P is the atmospheric pressure (hPa).

[0032] When there is no artificial heat source or cold source, from the perspective of time average, it is approximately considered that the water surface heat flux φ = 0, that is, the heat flux in and out of the water body is in equilibrium. When the project causes the heat source or cold source to be discharged into the natural water body, the water body temperature changes, the natural thermal balance of the water surface is destroyed, and the water temperature must be readjusted to reach a new heat balance. After the water body is discharged due to industrial wastewater, when estimating the cooling capacity of the water surface, the net absorbed solar radiation value is set to be constant, and the atmospheric radiation value is also set to be constant. The heat flux related to the water temperature, such as water body radiation, evaporation and convection heat dissipation, changes. After the change, the new water surface heat balance equation is:

[0033] φ′=φ s ′+φ a ′-φ w ′-φ e ′-φ c ′ (6)

[0034] Where: φ w ′、φ e ′、φ c ′When solving the problem, the water temperature T caused by the engineering change is used s ′ and the corresponding water surface saturated water vapor pressure e s ′.

[0035] After adding the influence of the project, the water temperature will eventually rise until the water surface heat flux reaches a new balance, that is, φ′ = 0. For ordinary drainage projects, solar radiation and atmospheric radiation are considered unchanged, that is, φ′ s =φ s ,φ′ a =φ a, the additional heat lost or absorbed by the water surface during the temperature change is obtained by subtracting equation (6) from equation (1), and the change in surface heat flux Δφ is expressed as:

[0036] Δφ=φ w ′-φ w +φ e -φ e ′+φ c -φ c ′ (7)

[0037] When the heat source is added to the water body, the water temperature will rise. When the temperature rises to Δφ=0, the heat flux on the water surface reaches a new balance and the water temperature becomes stable. When solving the heating process, the comprehensive heat dissipation coefficient K is used to express the comprehensive heat dissipation capacity of the water surface:

[0038] K=Δφ / ΔT s (8)

[0039] Where ΔT s is the water temperature rise value.

[0040] The derivatives of water body radiation, evaporative heat dissipation, and convective heat dissipation with respect to water temperature are as follows:

[0041]

[0042] In the formula, This slope is considered to be constant when the water temperature rises within a small range.

[0043] The basic form of the comprehensive heat dissipation coefficient can be obtained from equations (8) and (9):

[0044] K=(k+b)α+4εσT s 3 +ΔK (10)

[0045] In the formula in

[0046] T s is Celsius temperature, α=[22.0+12.5V W 2 +2.0(T s -T a ) 1 / 2 ](W·m -2 ·hPa -1 ), V W —Free surface wind speed, m / s, usually the monthly average value of different seasons; T a —Air temperature, °C. Formula (10) is the water surface heat dissipation coefficient formula in the industrial cooling water engineering specification.

[0047] Assuming that the water body continuously discharges heat Q (in W), when the heat source receiving water body is a closed water body and the heat is uniformly absorbed in the entire area, the water temperature rises on average. When the water body temperature reaches a new equilibrium, the heat discharge Q = Δφ·A, where Δφ is the change in surface heat flux and A is the water area. According to formula (8), the water temperature rise value of the water area can be obtained:

[0048]

[0049] H is the water depth. When the heat source receiving water body is an open water body or a closed water body with uneven local heat absorption, it is necessary to substitute formula (8) into the temperature transport equation to solve the water temperature rise value of each part.

[0050] The method of taking the seasonal average effect of photovoltaic facilities' shading on heat flux into account in solving the water temperature problem is as follows:

[0051] The impact assessment of thermal discharge from existing power plants generally uses seasonal average air temperature, humidity, wind speed and water temperature to solve the comprehensive heat dissipation coefficient and calculate the "temperature rise" field caused by thermal discharge. In order to be consistent with previous analysis methods, when calculating the impact of photovoltaic superimposed thermal discharge on sea water temperature, the change in water surface heat flux caused by photovoltaic shading needs to be added to the temperature change solution in the same seasonal average manner.

[0052] After photovoltaics are built on the water surface, the solar radiation and atmospheric radiation heat flux entering the water body are reduced due to the photovoltaic shading, the thermal balance of the water body is destroyed, and the water temperature will drop to reach a new thermal balance. When solving the impact of water temperature changes caused by photovoltaics, the reduction in solar radiation and atmospheric radiation heat flux has nothing to do with water temperature changes. It can be regarded as a source and sink term ("heat source") similar to the industrial heat source and added to the water temperature solution equation. The difference is that the impact caused by photovoltaic shading is that the heat entering the water body is less than the natural state, that is, the "cold source". At the same time, the reduction in wind speed under the panel caused by photovoltaic shading will lead to a decrease in the evaporation capacity of the water body. This term is a function of wind speed and is reflected by wind speed reduction in the calculation of the comprehensive heat dissipation coefficient of the water surface.

[0053] For photovoltaic projects, after adding photovoltaic coverage, the change in water surface heat flux Δφ′ is obtained by subtracting equation (1) from equation (6):

[0054] Δφ′=φ s ′-φ s +φ′ a -φ a +φ w ′-φ w +φ e -φ e ′+φ c -φ c ′ (12)

[0055] The combined reduction of solar radiation and atmospheric radiation caused by photovoltaics is taken as the source term Q', and its expression is:

[0056] Q′=φ s ′-φ s +φ′ a -φ c ′ (13)

[0057] The effect of wind speed reduction caused by photovoltaic shading on evaporation is obtained by modifying the wind speed related parameters α to obtain α′.

[0058] α′=22.0+12.5V w ' 2 +2.0(T s -T a ) 1 / 2 ] (14)

[0059] Where: V w ′ is the wind speed in the photovoltaic area affected by shading.

[0060] Formula (10) becomes:

[0061] K′=(k+b)α+4εσT s 3 +ΔK (15)

[0062] Formula (11) becomes:

[0063] ΔT s ′=Q′ / K′ (16)

[0064] Thus, the temperature rise or fall caused by the shading and covering of the photovoltaic device can be obtained. The specific steps of the calculation are as follows (the process is as follows Figure 1 shown):

[0065] Step 1, collect on-site data: monitor various data on heat and cold sources on-site in the areas covered by photovoltaic facilities and those not covered by photovoltaic facilities of the photovoltaic power plant; including data on changes in solar radiation and atmospheric radiation when there is no artificial or artificial emission of heat or cold sources.

[0066] Step 2, calculate the comprehensive change source term: calculate the comprehensive reduction source term Q' of solar radiation and atmospheric radiation caused by the coverage of photovoltaic facilities:

[0067] Q′=φ s ′-φ s +φ a ′-φ a

[0068] Where: φ s′ is the change of solar radiation when there is no artificial heat source or cold source, that is, the solar radiation data detected in the area without photovoltaic facilities coverage; φ s is the change in solar radiation when there are artificial heat sources or cold sources, that is, the solar radiation data detected in the area covered by photovoltaic facilities; φ′ a is the atmospheric radiation change when there is no artificial heat source or cold source, that is, the atmospheric radiation data detected in the area without photovoltaic facilities coverage; a It is the change of solar radiation when there are artificial heat sources or cold sources, that is, the atmospheric radiation data detected in the area covered by photovoltaic facilities.

[0069] Step 3, calculate the correction value of wind speed related parameters: the impact of wind speed reduction caused by coverage and shading of photovoltaic facilities on evaporation will correct the wind speed related parameters α′:

[0070] α′=22.0+12.5V w ' 2 +2.0(T s -T a ) 1 / 2 ]

[0071] Where: V w ′ is the wind speed in the photovoltaic area affected by shading, m / s; T s is the water surface temperature, °C; T a is the air temperature, ℃.

[0072] Step 4, calculate the comprehensive heat dissipation coefficient:

[0073] K′=(k+b)α′+4εσT s 3 +ΔK

[0074] in: in: α is the wind speed related parameter not blocked by photovoltaic facilities, m / s; e s For T s Corresponding saturated water vapor pressure, hPa; e a is the air vapor pressure, hPa; ε is the water body emissivity; σ is the Stefan-Boltzmann constant, σ=5.67×10 -8 (J / m 2 sK 4 ), b is the Bowen ratio, P is the atmospheric pressure (hPa).

[0075] Step 5, calculate the water temperature change value of the water area: calculate the water temperature change value of the water area affected by the cover and shading of the photovoltaic facilities:

[0076] ΔT s ′=Q′ / K′.

[0077] Application examples:

[0078] The effect of photovoltaic power generation on the seasonal average water temperature of closed fish ponds is solved. The water temperature observation results of a photovoltaic fish pond and a control fish pond from November 4 to December 4, 2021 are selected for verification.

[0079] (1) Solution for the comprehensive heat dissipation coefficient of the photovoltaic area:

[0080] The average ambient temperature during the observation period is T a =10.1℃, average air humidity a =66%, the wind speed in the control area is 2.65m / s, the wind speed in the photovoltaic area Vwpv=1.12m / s, the water depth of the control fish pond is 1.3m, the measured average water temperature is 11.5℃, the water depth of the photovoltaic fish pond is 0.85m, and the measured average water temperature is 9.8℃. The comprehensive heat dissipation coefficient of the photovoltaic area can be calculated from formula (16) as K′=15.6W / (m 2 ℃).

[0081] (2) Seasonal average radiation flux in photovoltaic area:

[0082] During the observation period, the total monthly solar shortwave radiation on the water surface was 261 MJ / m2, and the average loss was 60.2 W / m 2 , the average increase in atmospheric long-wave radiation is 17.2W / m 2 , the total loss of water surface radiation flux in the photovoltaic area is 43.0W / m 2 .

[0083] The water temperature reduction in the photovoltaic area is calculated to be 43 / 15.6=2.8°C.

[0084] The water temperature of the control group minus the measured water temperature of the photovoltaic area = 1.7°C. The water depth of the photovoltaic area is different from that of the control group. Under the same heat loss conditions, the water temperature rise ratio is inversely proportional to the water depth. Therefore, the actual temperature reduction in the photovoltaic area converted according to the water depth ratio = 1.7*1.3 / 0.85 = 2.6°C. The calculated value of 2.8°C is close to the measured value of 2.6°C, indicating that the calculation method is reasonable.

[0085] Finally, it should be noted that the above is only used to illustrate the technical solution of the present invention and is not a limitation. Although the present invention has been described in detail with reference to the preferred arrangement scheme, a person skilled in the art should understand that the technical solution of the present invention (such as the configuration and installation form of the photovoltaic power plant, the application of various formulas, the sequence of steps, etc.) can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for calculating the impact of photovoltaics on seasonal average water temperature, characterized in that: The steps of the method described are as follows: Step 1, collect on-site data: monitor various data of heat sources and cold sources on-site in the areas covered by photovoltaic facilities and areas not covered by photovoltaic facilities of the photovoltaic power plant; Step 2, calculate the comprehensive change source term: calculate the comprehensive reduction source term Q′ of solar radiation and atmospheric radiation caused by the coverage of photovoltaic facilities: Q′=φ s ′-φ s +φ′ a -f a Where: φ s ′ is the solar radiation when there is photovoltaic cover; φ s is the solar radiation without photovoltaic cover; φ′ a is the atmospheric radiation with photovoltaic cover; φ a is the atmospheric radiation when there is no photovoltaic cover; Step 3, calculate the correction value of wind speed related parameters: the impact of wind speed reduction caused by coverage and shading of photovoltaic facilities on evaporation will correct the wind speed related parameters α′: α′=22.0+12.5V w ′2+2.0(T s -T a ) 1 / 2 ] Where: V w ′ is the wind speed in the photovoltaic area affected by shading; T s is the water surface temperature; T a is the temperature; Step 4, calculate the comprehensive heat dissipation coefficient: K′=(k+b)α'+4εσT s 3 +ΔK in: in: α is the wind speed related parameter not blocked by photovoltaic facilities; e s For T s The corresponding saturated water vapor pressure; e a is the air vapor pressure; ε is the water body emissivity; σ is the Stefan-Boltzmann constant; b is the Bowen ratio; Step 5, calculate the water temperature change value of the water area: calculate the water temperature change value of the water area affected by the cover and shading of the photovoltaic facilities: ΔT s ′=Q′ / K′。

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