CN106059494A - Irradiance calculation method based on voltage at two ends of load of photovoltaic cell - Google Patents

Abstract

The invention discloses an irradiance calculation method based on a voltage at two ends of a load of a photovoltaic cell. A relationship between a voltage at two ends of the load and a short circuit current is obtained according to output features of a solar cell, through combination of a relationship between the voltage and current at two ends of the load, and the fact that a photo-generated current is approximately considered to be equal to the short circuit current; performance parameters in a formula are determined by employing performance parameters of the solar cell; calculation is carried out by employing open circuit voltages exposed to sunlight and environment temperature, thereby obtaining the temperature of a silicon wafer cell piece; and a relationship between the voltage at two ends of the load and irradiance is obtained through combination of the irradiance and the voltage at two ends of the load. According to the method, the accurate irradiance can be obtained by employing the voltage at two ends of the load through calculation; and the generating capacity can be predicted accurately.

Description

A kind of method calculating irradiance based on photovoltaic cell load both end voltage

Technical field

The present invention relates to a kind of method calculating irradiance based on photovoltaic cell load both end voltage, belong to photovoltaic system skill Art field.

Background technology

Day by day exhausted along with non-renewable energy resources, the regenerative resource such as water energy, wind energy, solar energy receives much concern.With light The development of volt system, the key factor as calculating solar cell performance of measuring of system effectiveness is widely studied, irradiance meter Calculating precision is one of its influence factor.Existing irradiance computation model think photovoltaic cell operating current and irradiance linearly Relation, calculates irradiance after all utilizing the photovoltaic cell output performance relation derivation short circuit current ignoring series resistors inside.Thing In reality, operating current and irradiance are the most linear when high irradiation, ignore series resistance simultaneously and make model when low irradiation Calculating error is big.The error that existing model is bigger in the case of high and low irradiation, causes component efficiency assessment error, thus predicts There is error in generated energy；The most existing computation model is basic for calculating to export electric current, and it gathers, and difficulty is big, precision is the highest.

Summary of the invention

The technical problem to be solved is the defect overcoming prior art, it is provided that a kind of based on photovoltaic cell load Both end voltage calculates the method for irradiance, solves irradiance linear model and calculates the bigger problem of error, thus precisely predicts generating Amount.

For solving above-mentioned technical problem, the present invention provides the side calculating irradiance based on photovoltaic cell load both end voltage Method, comprises the following steps:

1) a load resistance R is terminated at photovoltaic cell two_L, photovoltaic cell output characteristic meets:

$I=I_{ph}-I_0\[e^{\frac{q(U+{\mathrm{IR}}_s)}{AkT}}-1\]-\frac{U+{\mathrm{IR}}_s}{R_{sh}}---\left(5\right)$

Wherein, I represents the electric current flowing through load resistance, I_phFor photogenerated current, I₀For new index prefactor, q is single light Charge of the electron number, U represents load resistance both end voltage, R_shRepresent bypass resistance, R_sRepresent series resistance, A be P-N junction ideal because of Son, k is Boltzmann constant, and T is cell piece surface temperature；

2) load resistance both end voltage U, flows through the electric current I and load resistance R of load resistance_LBetween meet:

U=I × R_L (6)

Then, formula (5) is converted to load both end voltage U and photogenerated current I_phRelation:

$I_{ph}=\frac{U}{R_L}+\frac{U(R_s+R_L)}{R_{sh}\·R_L}+I_0\[e^{\frac{qU(R_L+R_s)}{AkT\·R_L}}-1\]---\left(7\right)$

3) as load resistance R_LDuring short circuit, U=0, I=I_sc, then formula (5) is changed into:

$I_{ph}=I_{sc}+I_0(e^{\frac{{\mathrm{qI}}_{sc}{R}_s}{{\mathrm{AkT}}_{sc}}}-1)+\frac{I_{sc}{R}_s}{R_{sh}}---\left(8\right)$

Wherein, T_scRepresent load R_LCell panel surface temperature during short circuit；I_scRepresent short circuit current；

Assume I_ph=I_sc, formula (8) becomes:

$I_0(e^{\frac{{\mathrm{qI}}_{sc}{R}_s}{{\mathrm{AkT}}_{sc}}}-1)=-\frac{I_{sc}{R}_s}{R_{sh}}---\left(10\right)$

SelectIn the range of load resistance, obtain performance parameter R of photovoltaic cell under standard conditions_s、 R_sh、I_sc、T_sc, substitute into and formula (10) calculate acquisition new index prefactor I₀；

4) I is also assumed that_ph=I_sc, according to the IV characteristic curve analysis of photovoltaic cell under different irradiance, short circuit electricity Stream I_scPositive correlation, corresponding photogenerated current I is become with incident irradiance degree H_phAlso positive correlation is become with incident irradiance degree H, because of This, make I_ph=k_HH, then formula (7) becomes:

$k_{H}H=U\frac{R_s+R_L+R_{sh}}{R_{sh}\·R_L}+I_0\[e^{\frac{q(R_L+R_s)}{AkT\·R_L}\·U}-1\]---\left(11\right)$

In formula, k_HFor the coefficient of relationship between load both end voltage and incident irradiance degree, k_HIt is to load both end voltage to be The formula of independent variable；

5) utilizing the difference of the open-circuit voltage of the photovoltaic cell being exposed under sunlight and being under ambient temperature, calculating obtains Cell piece surface temperature:

T represents cell piece surface temperature, T_EnvironmentRepresent ambient temperature, U_ocRepresent photovoltaic cell open-circuit voltage under ambient temperature, U_oc-TRepresent the photovoltaic cell open-circuit voltage being exposed under the sun；

6) choose different time points, record under the irradiance H of this time point, load resistance both end voltage U, ambient temperature Photovoltaic cell open-circuit voltage U_oc, the photovoltaic cell open-circuit voltage U that is exposed under the sun_oc-T, ambient temperature T_Environment, by collect Data substitute into formula (11) and calculate k_H, utilize linear regression method to calculate k_HAnd the relation between U, thus derive photovoltaic electric Relation between pond load resistance both end voltage U and irradiance H.

The beneficial effect that the present invention is reached:

The present invention makes up the error that the linear computation model of existing irradiance is bigger in the case of high and low irradiation, by load Both end voltage calculates irradiance accurately, it was predicted that the generating efficiency of assembly, thus Accurate Prediction generated energy.

Accompanying drawing explanation

Fig. 1 is the flow chart of the inventive method；

Fig. 2 is the internal equivalent circuit diagram of solar cell；

Fig. 3 is the IV characteristic curve of photovoltaic cell under different irradiance.

Detailed description of the invention

The invention will be further described below in conjunction with the accompanying drawings.Following example are only used for clearly illustrating the present invention Technical scheme, and can not limit the scope of the invention with this.

As it is shown in figure 1, the inventive method first passes through solar cell output characteristics, close with electric current in conjunction with load both end voltage System and be approximately considered photogenerated current equal to short circuit current, obtains the relation loading both end voltage with short circuit current, utilizes sun electricity The performance parameter in pond determines the performance parameter in formula.Further with the open circuit voltage meter being exposed under the sun and ambient temperature Calculate the temperature obtaining silicon wafer cell piece, in conjunction with irradiance, load both end voltage, obtain the pass loading both end voltage with irradiance System, concrete calculation process is as follows:

1. photovoltaic cell calculates

A load resistance R is terminated at photovoltaic cell two_L, think at it when photovoltaic cell receives the irradiation of sunlight In duty, its equivalent circuit is as shown in Figure 2.Photovoltaic cell forms photogenerated current I after receiving sunlight_ph, the biggest portion Shunting is through load resistance R_L, terminal voltage U is formed at load resistance two ends, this voltage forward bias in turn is in the P-of photovoltaic cell N junction diode, forms the dark current I in opposite direction with photogenerated current at diode two ends_D, it is recombination current, tunnel current And injection current three's sum, ignore tunnel current in the ordinary course of things.Utopian photovoltaic cell is equivalent to an electric current I_phConstant-current source in parallel with internal body diodes, but actually used during photovoltaic cell self there is also bypass resistance R_sh, series connection Resistance R_s。

Assuming that resistance both end voltage is U, the electric current flowing through resistance is I, then be carried in bypass resistance R_shBoth end voltage is U+ IR_s, therefore flow through bypass resistance R_shElectric current be:

I_sh=(U+IR_s)/R_sh (1)

In conjunction with photogenerated current:

I_ph=I_D+I_sh+I (2)

Can obtain:

$I(1+\frac{R_s}{R_{sh}})=I_{ph}-\frac{U}{R_{sh}}-I_D---\left(3\right)$

In order to utilize equivalent circuit to calculate the output performance of photovoltaic cell, dark current is reduced to exponential form:

$I_D=I_0\[e^{\frac{q(U+{\mathrm{IR}}_s)}{AkT}}-1\]---\left(4\right)$

In formula, q is single Photo charge number, q=1.6 × 10^-19, I₀For new index prefactor, A is P-N junction ideal factor (typically taking 1), k is Boltzmann constant, k=1.38 × 10^-23J/K, T are cell panel surface temperature (K).Composite type (3), (4) Can obtain photovoltaic cell output characteristic:

$I=I_{ph}-I_0\[e^{\frac{q(U+{\mathrm{IR}}_s)}{AkT}}-1\]-\frac{U+{\mathrm{IR}}_s}{R_{sh}}---\left(5\right)$

2. irradiation intensity Mathematical Models

Owing to short circuit current is the most linear with irradiance, the most existing method is substantially and records electric current Calculate irradiance by formula afterwards, but the current value in circuit is difficult to obtain, and a/d converter on the market is all by voltage Signal is converted to irradiation signal, and therefore this method is the relation trying to achieve between voltage and irradiation based on outer meeting resistance.Specific as follows:

Assume to connect a load resistance R at the positive and negative interpolar of photovoltaic cell_L:

U=I × R_L (6)

Then formula (5) can be changed into load both end voltage U and photogenerated current I_phRelation:

$I_{ph}=\frac{U}{R_L}+\frac{U(R_s+R_L)}{R_{sh}\·R_L}+I_0\[e^{\frac{qU(R_L+R_s)}{AkT\·R_L}}-1\]---\left(7\right)$

From formula (5), as load R_LDuring short circuit, i.e. U=0 in formula, I=I_sc, then formula (5) is changed into:

$I_{ph}=I_{sc}+I_0(e^{\frac{{\mathrm{qI}}_{sc}{R}_s}{{\mathrm{AkT}}_{sc}}}-1)+\frac{I_{sc}{R}_s}{R_{sh}}---\left(8\right)$

T_scRepresent load R_LCell panel surface temperature during short circuit；I_scRepresent short circuit current；

As load R_LWhen tending to infinite, then U=U_oc, I=0, then formula (5) becomes:

$I_{ph}=I_0(e^{\frac{{\mathrm{qU}}_{oc}}{{\mathrm{AkT}}_{oc}}}-1)+\frac{U_{oc}}{R_{sh}}---\left(9\right)$

T_ocRepresent load R_LCell panel surface temperature when tending to infinite；U_ocRepresent open-circuit voltage；

Here it is considered that in circuit, the resistance of series connection should ensure that photovoltaic cell works near power maximum point left end, if light Lying prostrate the battery operated right-hand member at maximum power point, the change that this section of voltage is small can cause electric current significantly to decline, and there is peace Total failure hidden danger.And if photovoltaic cell is operated in the left end of maximum power point, electric current approximation is uncorrelated with voltage, therefore recognizes here Determine the photogenerated current I of photovoltaic cell_ph=I_sc, then formula (8) is changed into:

$I_0(e^{\frac{{\mathrm{qI}}_{sc}{R}_s}{{\mathrm{AkT}}_{sc}}}-1)=-\frac{I_{sc}{R}_s}{R_{sh}}---\left(10\right)$

As can be drawn from Figure 3, when the irradiance of incident illumination increases and decreases, and corresponding short circuit current increases and decreases, therefore the most accordingly Short circuit current I can be obtained_scPositive correlation, corresponding photogenerated current I is become with incident irradiance degree H_phAlso become with incident irradiance degree H Positive correlation, makes I_ph=k_HH, then the relation between load resistance both end voltage U and incident irradiance degree H is:

$k_{H}H=U\frac{R_s+R_L+R_{sh}}{R_{sh}\·R_L}+I_0\[e^{\frac{q(R_L+R_s)}{AkT\·R_L}\·U}-1\]---\left(11\right)$

In formula, k_HFor the coefficient of relationship between load both end voltage and incident irradiance degree, T is silicon wafer cell panel surface temperature Degree (K).

3. irradiance coefficient of relationship determines

(1) performance parameter determines

As load resistor value R_LMeet:Time, just can ensure that surveyed irradiation precision is at 10W/m²In, therefore select Select the external load resistance of suitable resistance in the range of this, obtain performance parameter R of photovoltaic cell under standard conditions_s、R_sh、I_sc、 T_sc, substitute into and formula (10) calculate acquisition new index prefactor I₀。

(2) silicon wafer battery temperature determines

Usually, cell piece temperature and open-circuit voltage are negative correlation, as follows:

$\frac{U_{oc}-U_{oc-T}}{U_{oc}}=-0.4\%\mathrm{\Δ}T---\left(13\right)$

U_oc-TRepresent the photovoltaic cell open-circuit voltage that is exposed under the sun, Δ T represent cell piece temperature and ambient temperature it Difference, Δ T=T-T_Environment。

The present invention utilizes the difference of the open-circuit voltage of the photovoltaic cell being exposed under sunlight and being under ambient temperature, meter Calculate and obtain cell piece temperature:

T represents cell piece temperature, T_EnvironmentRepresent ambient temperature.

(3) voltage-radiation factor determines

Utilize irradiatometer test irradiance, circuit tester test photovoltaic cell load both end voltage value, be exposed under the sun and Photovoltaic cell open-circuit voltage values under ambient temperature.The present invention chooses different time points, record this time point irradiance H, Photovoltaic cell open-circuit voltage U under external load both end voltage U, ambient temperature_oc, the photovoltaic cell open-circuit voltage that is exposed under the sun U_oc-T, ambient temperature T_Environment, it is ensured that under different irradiance, corresponding data can collect.The data collected are substituted into formula (11) k is calculated_H, coefficient k here_HIt is to load the both end voltage formula as independent variable, hence with methods such as linear regressions Calculate k_HAnd the relation between U, thus derive the relation between photovoltaic cell load both end voltage and irradiance.

The above is only the preferred embodiment of the present invention, it is noted that for the ordinary skill people of the art For Yuan, on the premise of without departing from the technology of the present invention principle, it is also possible to make some improvement and deformation, these improve and deformation Also should be regarded as protection scope of the present invention.

Claims (1)

1. the method calculating irradiance based on photovoltaic cell load both end voltage, it is characterised in that comprise the following steps:

1) a load resistance R is terminated at photovoltaic cell two_L, photovoltaic cell output characteristic meets:

$I=I_{ph}-I_0\[e^{\frac{q(U+{\mathrm{IR}}_s)}{AkT}}-1\]-\frac{U+{\mathrm{IR}}_s}{R_{sh}}---\left(5\right)$

Wherein, I represents the electric current flowing through load resistance, I_phFor photogenerated current, I₀For new index prefactor, q is single photon electricity Lotus number, U represents load resistance both end voltage, R_shRepresent bypass resistance, R_sRepresenting series resistance, A is P-N junction ideal factor, and k is Boltzmann constant, T is cell piece surface temperature；

2) load resistance both end voltage U, flows through the electric current I and load resistance R of load resistance_LBetween meet:

U=I × R_L (6)

Then, formula (5) is converted to load both end voltage U and photogenerated current I_phRelation:

$I_{ph}=\frac{U}{R_L}+\frac{U(R_s+R_L)}{R_{sh}\·R_L}+I_0\[e^{\frac{qU(R_L+R_s)}{AkT\·R_L}}-1\]---\left(7\right)$

3) as load resistance R_LDuring short circuit, U=0, I=I_sc, then formula (5) is changed into:

$I_{ph}=I_{sc}+I_0(e^{\frac{{\mathrm{qI}}_{sc}{R}_s}{{\mathrm{AkT}}_{sc}}}-1)+\frac{I_{sc}{R}_s}{R_{sh}}---\left(8\right)$

Wherein, T_scRepresent load R_LCell panel surface temperature during short circuit；I_scRepresent short circuit current；

Assume I_ph=I_sc, formula (8) becomes:

$I_0(e^{\frac{{\mathrm{qI}}_{sc}{R}_s}{{\mathrm{AkT}}_{sc}}}-1)=-\frac{I_{sc}{R}_s}{R_{sh}}---\left(10\right)$

SelectIn the range of load resistance, obtain performance parameter R of photovoltaic cell under standard conditions_s、R_sh、I_sc、 T_sc, substitute into and formula (10) calculate acquisition new index prefactor I₀；

4) I is also assumed that_ph=I_sc, according to the IV characteristic curve analysis of photovoltaic cell, short circuit current I under different irradiance_sc Positive correlation, corresponding photogenerated current I is become with incident irradiance degree H_phAlso positive correlation is become with incident irradiance degree H, therefore, order I_ph=k_HH, then formula (7) becomes:

$k_{H}H=U\frac{R_s+R_L+R_{sh}}{R_{sh}\·R_L}+I_0\[e^{\frac{q(R_L+R_s)}{AkT\·R_L}\·U}-1\]---\left(11\right)$

In formula, k_HFor the coefficient of relationship between load both end voltage and incident irradiance degree；k_HIt is to load both end voltage for from becoming The formula of amount；

5) utilize the difference of the open-circuit voltage of the photovoltaic cell being exposed under sunlight and being under ambient temperature, calculate and obtain electricity Pond sheet surface temperature:

T represents cell piece surface temperature, T_EnvironmentRepresent ambient temperature, U_ocRepresent photovoltaic cell open-circuit voltage under ambient temperature, U_oc-T Represent the photovoltaic cell open-circuit voltage being exposed under the sun；

6) choose different time points, record photovoltaic under the irradiance H of this time point, load resistance both end voltage U, ambient temperature Battery open circuit voltage U_oc, the photovoltaic cell open-circuit voltage U that is exposed under the sun_oc-T, ambient temperature T_Environment, the data that will collect Substitution formula (11) calculates k_H, utilize linear regression method to calculate k_HAnd the relation between U, thus derive photovoltaic cell and bear Carry the relation between resistance both end voltage U and irradiance H.