EP3701201A1

EP3701201A1 - Solar power plant provided with a device for measuring direct normal insolation

Info

Publication number: EP3701201A1
Application number: EP18827183.7A
Authority: EP
Inventors: Sylvain RODAT; Adrien CAMUS
Original assignee: Commissariat a lEnergie Atomique CEA; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2017-11-28
Filing date: 2018-11-26
Publication date: 2020-09-02
Also published as: WO2019106267A1; FR3074269A1; FR3074269B1; MA50847A

Abstract

The invention relates to a solar power plant, in particular a concentrated solar power plant, provided with a device for measuring direct normal insolation (DNI), comprising: - a mirror (4) intended to reflect direct solar radiation and disposed on a movable support, - a light sensor (2) arranged with respect to the mirror so as to detect solar radiation reflected by the mirror, - a solar tracker designed to orient the mirror towards the sun, the solar tracker being provided with means for actuating the support that are able to move the mirror (4).

Description

SOLAR POWER PLANT WITH DIRECT SUNSET MEASUREMENT DEVICE

NORMAL

DESCRIPTION

TECHNICAL FIELD AND PRIOR ART

The present application relates to the field of solar power plants having means for measuring the available solar resource.

One method for determining a solar resource is to perform a normal direct irradiation measurement also called normal direct irradiance (DNI).

Normal direct sunlight is defined in the document "Direct normal irradiance related definitions and applications" of Blanc et al. Solar Energy 110 (2014) 561-577 as the direct irradiance received on a plane normal to the sun.

Different devices can provide a DNI measurement.

Such a measurement can be implemented for example using several pyranometers, a first measuring the global radiation and another pyranometer performing a diffuse radiation measurement by the use of a mask associated with a specific solar tracking device. .

As a variant, it is known to carry out a DNI measurement using a pyrheliometer, that is to say a device that permanently targets the sun by means of a specific solar tracking device associated with the photosensitive sensor.

Document IN201127410 presents another example of a device for measuring DNI whose measuring principle is similar to that of a pyrheliometer.

For some solar installations such as solar power plants, the measurement of DNI can be particularly important because it is representative of the solar resource likely to be used and because the variations of solar resource, in particular related to periods of cover cloud, affect the reliability of power generation plants. To obtain a measure of available solar resource in a concentrating solar power station, the document "Validation of spatially resolved sky imager derived DNI nowcasts" by Kuhn et al., AIP conference Proceedings 2017 presents for example a device for measuring DNI comprising several pyranometers as well as several pyrheliometers and a system image acquisition device taken from a high point to evaluate the effects of shading on the power station caused by clouds. Such a device therefore applies mainly to the implementation of measurement on solar power plants with a tower serving as a high point.

There is the problem of finding a new type of DNI measuring device for a solar power station, which can in particular adapt to a concentrating solar power station and allow precise measurement to be made.

STATEMENT OF THE INVENTION

An embodiment of the present invention provides for integrating in a solar installation a device for measuring normal direct sunlight (DNI) comprising:

at least one first mirror capable of reflecting direct solar radiation and disposed on a first mobile support,

at least one first photosensitive sensor arranged with respect to the first mirror so as to detect the solar radiation reflected by the first mirror,

at least one solar tracker adapted to orient the first mirror towards the sun, the first solar tracker being provided with first means for actuating the first support able to move the first mirror.

With such a device, a specific solar tracker to move the sensor is not necessary since it operates rather a movement of the mirror or mirrors with respect to the sky. It is therefore possible to use a mirror actuation device of a solar installation already equipped with solar trackers to produce such a measuring device, which represents an advantage, particularly in terms of cost.

Compared to a device with a sensor positioned horizontally on the ground and receiving all the diffuse radiation of the celestial measurement device as defined above alone can detect essentially direct radiation from a limited portion of the celestial vault.

The photosensitive sensor is advantageously fixed or is arranged on a support element displaceable independently of the first support.

According to an advantageous embodiment, the photosensitive sensor is fixed and the solar tracker is adapted to move the first mirror along two axes, the measuring device further comprising a means such as a tube for limiting to a predetermined solid angle a flow incident light on said first photosensitive sensor.

A measuring device as defined above can be used to evaluate the state of the first mirror, in particular its degree of soiling or the state of its reflecting surface. The presence of dirt or a defective condition can result in a decrease in DNI compared to a reference value.

According to one aspect, the present invention relates to a solar power plant, in particular at a concentration, provided with a device for measuring normal direct sunlight (DNI) as described above.

An advantage of a DNI measuring device is that it can be deployed at a lower cost on a concentrating solar installation. Indeed, one can use pre-existing solar trackers and mirrors in the solar power station to realize it. Thus, a shadow band mobile system or a specific solar tracking device is not necessary.

In particular, one embodiment provides a solar plant type installation with at least one normal direct sunlight (DNI) measuring device as defined above and wherein said first photosensitive sensor is arranged between said first mirror and a first receiver. This first receiver then comprises at least a first conduit in which a coolant is able to circulate, the first receiver being arranged to receive a solar radiation reflected by said first mirror.

The first photosensitive sensor is preferably arranged at a non-zero distance from the first receiver. Through a DNI measurement obtained using such a device, an evaluation of the available solar resource can be obtained. the receiver of the plant, without having to place a sensor in contact with the receiver and thus prevent the sensor from being subjected to stresses due to the strong flows reaching the receiver.

According to one possible implementation, the solar concentrating plant comprises at least a second receiver having at least a second conduit in which a fluid is intended to flow, the second receiver being arranged to receive a solar flux reflected by at least one other mirror and to another photosensitive sensor arranged between said other mirror and said second receiver.

Thus, when the plant comprises several receivers, the measuring device can be configured to allow at least one measurement of DNI per receiver.

With a dense mesh of sensors one can evaluate the distribution of a solar resource on all the surface of a solar field.

To enable the temperature at the output of its receivers to be controlled, the solar concentration plant is typically equipped with a control system configured to control first fluid flow control means in the first duct and second adapted control means. for regulating a flow of fluid in the second conduit independently of the flow of fluid in the first conduit.

Advantageously, the control control system is configured to control said second flow control means so as to modify the flow of fluid in the second conduit following a detection of a variation of DNI established from measurement data from said other photosensitive sensor. It is thus possible to provide a specific DNI measurement for each receiver and to adapt the flow rate of fluid in each receiver independently as a function of this measurement of DNI.

Advantageously, the device for measuring normal direct sunlight (DNI) comprises at least one second photosensitive sensor disposed between a second mirror and a second zone of the first receiver so as to detect a solar radiation reflected by the second mirror and to said second zone of the first receiver. It is thus possible to establish different DNI measurements for evaluating the available solar resource on different elementary zones of the same receiver.

Advantageously, the control-command system is also able to control a displacement of at least one mirror of said plurality of mirrors following a detection of a variation of DNI established from measurement data from said second photosensitive sensor. Thus, rather than modifying the fluid flow rate when a variation of DNI is detected for a basic zone of a receiver, it is possible to modify the rate of focusing of the mirrors on this zone.

This is particularly useful when the elementary zone in question is an end zone of the receiver located towards the coolant outlet.

The measuring device DNI can thus be provided with a plurality of photosensitive sensors distributed at different points of the concentration plant.

Advantageously, the plant may further comprise: a computer processing unit equipped with a cloud cover prediction module using a cloud trajectory evaluation model implemented from at least a first series of DNI measurements from said photosensitive sensors at a given instant and from at least a second series of DNI measurements from said photosensitive sensors at another time, preceding said given instant.

A DNI measuring device integrated into a solar power station can also be used to check the state in which the mirrors of a concentrating solar power station are located and to detect whether a step of cleaning or maintenance of the mirrors is necessary.

Thus, according to one possible implementation, the solar concentrating plant may further comprise: at least one normal direct reference sun measurement means, in particular at least one reference pyrheliometer capable of producing a reference reference measurement. normal direct sunlight of a solar flux to said first photosensitive sensor. This measuring means of DNI then comes in addition to the measuring device DNI defined above. A comparison of measurements between the reference measurement means and the DNI device defined above can make it possible to provide information on the state of the first mirror. The measurements made to determine the state of a mirror are preferably performed on a clear day. Thus, an image acquisition means of the sky above the central can also be provided to detect an absence of cloud above the central.

The comparison of DNI measurements from the reference measurement means and the DNI device defined above can be performed by means of a computer processing unit, for example belonging to the control system of the solar power station.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood on reading the description of exemplary embodiments given, purely by way of indication and in no way limiting, with reference to the appended drawings in which:

FIG. 1 serves to illustrate a normal direct sunlight measuring device according to an embodiment of the present invention;

FIG. 2A serves to illustrate a single-axis solar tracker associated with a mirror as provided in an exemplary embodiment of a DNI measuring device according to the invention;

FIG. 2B serves to illustrate a dual-axis solar tracker as provided in an exemplary embodiment of a DNI measuring device according to the invention;

FIG. 3 serves to illustrate heating sections of a concentrating solar power station capable of integrating a DNI measuring device as implemented according to the invention;

FIG. 4 serves to illustrate a schematic diagram of a solar power station provided with a DNI measuring device according to an embodiment of the present invention;

FIGS. 5A-5B serve to illustrate a schematic diagram of a concentrating solar power station with a DNI measuring system provided with a plurality of photosensitive sensors associated respectively with a plurality of elementary receiver zones (s) provided for to convey a coolant; FIG. 6 serves to illustrate a solar power plant control method implemented using measurements carried out using at least one DNI measuring device;

Identical, similar or equivalent parts of the different figures bear the same numerical references so as to facilitate the passage from one figure to another.

The different parts shown in the figures are not necessarily in a uniform scale, to make the figures more readable.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

Referring now to Figure 1 which schematically illustrates a device for performing a normal direct sunlight (DNI) measurement as implemented according to an embodiment of the present invention.

The device is provided with at least one photosensitive sensor 2 which may be of the type used in a pyrheliometer, for example in the form of a thermopile, in other words a means which converts a thermal gradient into an electrical signal, or a sensor pyroelectric in which a temperature change causes a variation of electrical polarization. Alternatively, a photovoltaic sensor may be used.

The sensor 2, and in particular its sensitive zone 2a, is arranged so as to receive a solar radiation reflected by a mirror 4. The arrangement of the photosensitive sensor 2 with respect to the celestial vault and the mirror 4 is provided. so as to favor a detection of direct solar radiation R. Preferably, the sensitive zone 2a of the sensor is disposed orthogonally to the radiation reflected by the mirror 4 and incident on the photosensitive sensor 2.

In order to limit the detection of diffuse solar radiation R ', a means 3 for limiting the incident light flux on the sensor 2 at a predetermined solid angle, in other words for limiting the acceptor cone of the sensor 2 can be provided. In the example shown, this means 3 comprises a tube 31 called "acceptance". As a variant, it is possible to associate the sensor 2 with a collimator, for example formed using blades. By eliminating the diffuse radiation which can represent of the order of 10% of direct solar radiation on a clear day and a much larger proportion on cloudy days, one gains in accuracy of measurement of the DNI.

In the particular embodiment illustrated in Figure 1, the mirror 4 is a plane mirror also called linear reflector. In the present measuring device DNI, it is not the photosensitive sensor 2 which follows the course of the sun S but the mirror 4, which is rotatable and is displaced according to the position of the sun S so as to follow the race of the sun S. A particular embodiment of the measuring device even provides a sensor 2 photosensitive which remains fixed, only the mirror 4 being movable. The photosensitive sensor 2 and the mirror 4 are arranged on separate supports or elements. An arrangement may be provided in which the mirror support is a ground-mounted part serving as a support for the sensor, the mirror being movable and placed on a separate element of the photosensitive sensor.

The respective sizes of the mirror 4 and the sensor 2 and / or their relative positions relative to each other are provided so that the photosensitive sensor 2 receives radiation emanating from only one portion. from the celestial vault. Compared to a measuring device with a sensor positioned horizontally and in direct view of the sky, the DNI measuring device limits the capture of diffuse radiation.

An DNI measuring device as implemented according to the invention does not require a specific solar tracker associated with the photosensitive sensor 2 but rather uses a solar tracker associated with the mirror 4. Thus the DNI measuring device can be integrated into a solar installation, for example a concentrated solar power station, already provided with mirrors and trackers associated with these mirrors. This has the advantage of allowing to integrate at a lower cost the DNI measuring system to the solar installation.

The solar tracker used is typically equipped with a bearing structure 6 of the mirror 4, also called a frame, and actuator means 8 for moving the mirror 4 and which are for example provided with one or more motors and / or a cylinder system. The solar tracker may be provided to adapt the position of the mirror 4 relative to the sun S typically along a single axis or along two axes.

According to one implementation possibility, a solar tracker of the type described in Dehelean's "A mirror Tracking Mechanism" document, ResearchGate October 2012 can be used.

A particular example of a single-axis solar tracker that can be associated with the mirror 4 is illustrated in FIG. 2A. The orientation of the mirror 4 varies in this example along a single axis Al which is here a transverse axis substantially parallel to the ground, ie a plane [O; x; y] of an orthogonal reference [O; x; y; z ] given in Figure 2A. When a single-axis solar tracker is employed, a beam collimator is preferably used as a means of limiting the acceptance cone of the sensor 3.

In the case where a single-axis solar tracker is used, provision may be made to place the photosensitive sensor 2 on a movable support element. In this case the support element of the sensor 2 is movable independently of the mirror 4. In particular, if the tracker provides a displacement of the mirror 4 according to the height component, the sensor 2 can be moved along the azimuth whereas when the tracker is adapted to perform a movement of the mirror 4 according to the azimuth component, the sensor 2 can be moved according to the height component.

Alternatively, to avoid having a displacement of the photosensitive sensor 2, the dimensions of the reflective zone of the mirror large enough to maximize the duration during which the photosensitive zone 2a is capable of receiving solar radiation. When the DNI measuring device is integrated into a concentrating solar power plant, it is advantageous to have large mirrors whose length can be of the order of several meters or tens of meters, which can make it possible to avoid move a photosensitive sensor 2 having a photosensitive area of dimensions of the order of several centimeters.

Another example of a solar tracker, this time along two axes, is illustrated in FIG. 2B and may be associated with the mirror 4 of the DNI measuring device. The orientation of the mirror 4 is here modifiable according to two degrees of freedom. A displacement can be made along a first axis AΊ which, in this example is substantially parallel to the ground and along another axis A'2 which, in this example, is substantially orthogonal to the ground. The tracker may be provided with two motors (not shown) and can combine an azimuth rotation movement and an elevation rotation movement. When a two-axis solar tracker is employed, it is preferred to use a tube as a means for limiting the acceptor cone of the sensor 3.

The solar tracker is also typically provided with a control unit for the actuator means, the control unit 10 being configurable to use track data relating to sun tracking and to provide at least one control signal to the means. actuators based on these trajectory data.

The control unit 10 may be adapted to perform an so-called "open loop" command for which the trajectory data is used to actuate the mirror 4 without using measurement data to establish the position of the sun. The trajectory data can then be established from the time of day and GPS coordinates of the mirror support 4 and using calculations using astronomical data of the position of the sun.

The control unit 10 may alternatively be adapted to implement a "closed loop" command, that is to say to produce trajectory data based on astronomical data of the position of the sun and on a measurement derived from another sensor 17 which may be for example that of a reference pyrheliometer.

In a measuring device DNI as described above, the measurement signal from the sensor can be processed by computer to improve the measurement accuracy and / or to make a correction taking into account an effect of optical distortion of the mirror , especially if it is not a plane mirror.

In the case of a curved mirror, it is possible to use a software or processing method comprising a "ray-launching" type calculation technique. In the case of a device in which the means 3 for limiting the acceptance cone of the sensor 2 is a blade type collimator, it does not necessarily have an impact of the normal flow on the sensitive area of the sensor 2. In this case, case, a correction of "cosine" effect can be made.

One or more pyrheliometer type reference sensors may also be provided in the device to provide complementary DNI measurement and improve measurement accuracy.

A device as described above can for example be used in a solar installation such as a solar oven or in a weather station.

The device for measuring normal direct sunlight (DNI) is particularly suitable for being integrated in a concentrating solar power station C, in particular Fresnel type, which already has mirrors with their own associated solar trackers.

A solar C concentration plant typically comprises at least one structure called "heating section" and which is provided with at least one receiver, that is to say a structure comprising one or more conduits carried to carry a heat transfer fluid.

In the example of Figure 3, we can see a simplified block diagram of a portion of the solar plant with several heating sections in parallel, the central being thus provided with several receivers 30a, 30b, 30c, 30d connected in input to a fluid supply in the liquid state. Each autonomous heating section may have a length of the order of several hundred meters long.

Each receiver 30a, 30b, 30c, 30d is provided with one or more conduits in which circulates a heat transfer fluid. The mirrors 4.1, 4.2 of the solar power plant are arranged so as to reflect the light rays on the receivers which has the effect of heating the fluid. The coolant is for example a thermal oil, a molten salt, air, water. According to a particular embodiment, the coolant enters at a temperature between 150 ° C and 300 ° C and emerges at a temperature between 400 ° C and 500 ° C. At the input of a receiver 30a, the fluid is generally in liquid form and is then likely to vaporize by circulating in the conduit or conduits and out of a receiver in the form of superheated or saturated steam.

The flow rate in each heating section and therefore each receiver 30a, 30b, 30c, 30d can be adjusted to maintain a set temperature output. Thus, each receiver and its conduit (s) may be associated with flow control means adapted to regulate a flow of fluid in this or these conduits. The flow adjustment can be performed independently of one receiver to another. The flow control means may be provided with control valves, in particular coupled to pressure regulation on a main supply pump.

A Fresnel concentration solar power plant may be associated with thermodynamic conversion means which are for example in the form of at least one steam turbine T at the outlet of the heating section. In order to protect the turbine from uncontrolled temperature variations, it is important to be able to detect solar resource variations for a receiver.

This detection is here ensured by means of DNI measurements established using a device as illustrated in FIG. 4 and in which a photosensitive sensor 2 is placed between a mirror 4.1 of the central unit C and a receiver. 30a. The central C is generally provided with a plurality of mirrors 4.1, 4.2 each mounted mobile on a frame and associated with a solar tracker to move the mirror and allow it to follow the movement of the sun during the day. A photosensitive sensor 2 is preferably provided so as to receive reflected radiation from a single mirror, while the receiver 30a is capable of receiving reflected radiation from a plurality of mirrors. Thus, the photosensitive sensor 2 is arranged at a predetermined non-zero distance from the receiver 30a so that the photosensitive sensor 2 does not receive reflected radiation from another mirror than the one dedicated to it.

The DNI measurement carried out by means of a photosensitive sensor 2 provides information on the solar flux that is irradiated in an area of the receiver 30a.

The DNI measurement detects the appearance of cloud sails or thicker clouds. One can also distinguish between a cloudy veil translated for example by a measured DNI drop and a thicker cloud translated for example by a DNI null or less than a predetermined threshold. DNI measurement can therefore be used to evaluate the true opacity of a cloud over a solar field.

Depending on the measurement of DNI and an estimate of the available solar resource that can be deduced from this measurement, it is possible to act on certain control parameters of the plant so as to limit variations in the outlet temperature of the plant. a heating section. The control parameters on which one can act are typically the focusing rate of the mirrors and the coolant flow in a receiver.

For this, the central unit C is typically equipped with a control system 50 comprising a human-machine interface and one or more processors and / or one or more electronic cards formed of integrated circuits and / or ASICs and and / or logic and programmable circuits (for example of FPGA type, microprocessor, microcontroller). The control system 50 typically uses a software or program for controlling the mirrors, as well as a software or program for controlling the fluid circuit, and in particular flow control means associated with the receivers of the heating sections.

In the exemplary embodiment illustrated, a measurement of DNI is transmitted (arrow Fl) to the digital control system 50 of the solar power plant which, as a function of the measured value is able to modify (arrow F2) the focusing rate of mirrors 4.1, 4.2 to modulate the solar flux reflected on a receiver 30a. The digital control control system 50 of the solar power station is also capable of controlling the flow rate (arrow F3) of heat transfer fluid in the conduit (s) of the receiver 30a.

Thus, in order to limit the impact of a fall or an increase of incident solar resource on at least one receiver 30a, the control system is configured to modify the focusing rate of mirrors on this receiver 30a and / or to modify the flow rate of fluid in the conduit (s) of the receiver 30a. The fluid flow rate or the rate of focus can be adjusted independently for each receiver without modifying that of the other receivers. The control-command 50 is also configured to, in certain critical cases, trigger a shutdown of the installation, which is translated in particular by an arrangement in which the mirrors do not return solar radiation to the receiver 30a.

When a cloud passes over an installation as described above, it is likely to impact several heating sections over time. It is therefore useful to be able to control the solar resource of each receiver.

By performing a spatial discretization of the device for measuring the incident solar resource, we have a better knowledge of the available solar resource. To achieve this discretization, it is expected that each receiver is associated with at least one photosensitive sensor to enable at least one measurement of DNI per receiver. Preferably, several photosensitive sensors are provided per receiver in order to be able to perform DNI measurements on several surface elements of the same receiver.

An example of a solar installation in which a DNI measuring device is provided with several photosensitive sensors 2.1, ..., 2.20 and in particular several photosensitive sensors per heating section is illustrated in FIGS. 5A-5B.

The photosensitive sensors 2.1, ..., 2.20 are configured to perform DNI measurements translating solar energy variations respectively on elementary zones C1, ..., C20 of several receivers 30a, 30b, 30c, 30d, 30e, each sensor 2.1, ..., 2.20 being associated with a zone or elementary surface Ci (with i an integer between 1 and 20) of receiver irradiated by a mirror reflecting an incident solar resource.

The photosensitive sensors 2.1, ..., 2.20 can be distributed over the solar field in order to be able to characterize an incident solar resource with a discretization step, for example of the order of 10 m.

With such a device, it is possible to know the solar energy incident on zones or heating section portions, which makes it possible to achieve a finer adjustment of the control parameters of the target temperature at the output of the receivers.

The control command of the installation can be provided for at different times simultaneously record the measurement of the photosensitive sensors 2.1, ..., 2.20, and to adjust the temperature control parameters at the output of the installation accordingly either by modifying the flow rate in one or more receivers or by triggering a focusing or defocusing of mirrors.

When, as illustrated in FIG. 5A, a cloud N passes over a given area C1 situated near the input of a receiver 30a, the energy actually collected decreases. "Input" means an area located near the arrival of coolant in the receiver 30a. A DNI measurement by means of a photosensitive sensor 2.1 receiving the reflected solar radiation from a mirror (not shown) focused on this zone C1 makes it possible to know the effect of this shading on the zone C1, without having to use any temperature sensor fixed directly on this zone which may be subject to expansion constraints.

If the cloud N stagnates on the given area C1 of the receiver 30a, the value of DNI measured via the sensor 2.1 is brought down. It is then possible to adjust the flow of fluid in the receiver 30a, and in particular to reduce it to maintain the outlet temperature of the heating sections.

In the case illustrated in FIG. 5B, the cloud N appears this time at the output of the solar field above a zone C4 located near the output of the receiver 30a.

In this case, knowledge of a solar resource through DNI measurements at a time t may be insufficient.

On the other hand, by knowing the mapping of the incident resource on the solar field at a time t and at a time t-1, it is possible to predict, by means of cloud trajectory tracking algorithms, the solar resource available at a given moment. t + 1.

An instrumentation with a plurality of photosensitive sensors C1, ..., C20 for performing DNI measurements can therefore make it possible to make an available solar resource prediction for the plant.

With a matrix arrangement of sensors, it can be detected at a first instant t for example that only a photosensitive sensor 2.4 is in the shade while at a second time t + x, according to the first moment, only another photosensitive sensor 2.7 is in the shade and deduce a speed, a direction and a direction of movement of a cloud. This can lead to a prediction of the positioning of the cloud at a third instant at t + x + y following the second instant.

Thus, an analysis of the DNI measurement data history makes it possible to estimate the displacement of cloud disturbances and to anticipate the arrival of cloud disturbances.

FIG. 5B illustrates another problem when for example a cloud N stabilizes several minutes on a zone C4 at the output of a heating section.

To ensure a regulation of the outlet temperature and to compensate the thermal losses on the end of the heating section created by the cloud N, it is then preferred to act on the mirrors by modifying their focus rather than to act on the flow rate. fluid in the receiver 30a. Indeed, if one acts on the flow while the cloud N leaves the zone C4, the temperature reached at the exit is likely to continue to increase.

Furthermore, with a DNI measuring device as described above, it is also possible to distinguish between a simple cloudy cloud detected for example by a DNI drop and a cloud corresponding for example to a zero measured DNI.

To establish a prediction of cloud cover and therefore of available solar resource, a computer processing unit equipped with a prediction module using a cloud trajectory evaluation model established from DNI measurements from the photosensitive sensors and taken at different times can be expected. Such a computer processing unit can be formed from one or more computers or processors and / or be part of, for example, the control system of the solar power plant.

An example of a control method of a plant using DNI measurements of a plurality of photosensitive sensors 2.1, ..., 2.20 as described above is illustrated in Figure 6 by means of a flowchart.

First of all, the acquisition of a DNI measurement noted m_i_DNI (t) at a time t resulting from a photosensitive sensor 2.i given (step E0).

Using this measure, we update a solar energy calculation model available for a receiver that the solar radiation captured by the sensor photosensitive 2.i is irradiated (step Eli). For this purpose, for example, a calculation is made of: m_i_DNI (t) * Si * optical efficiency * thermal efficiency, with Si an elementary zone or an elementary surface element of the receiver that the photosensitive sensor 2.i is caused to irradiate. The optical efficiency is the ratio between the solar power that impacts the receiver with respect to the incident solar power (m_i_DNI (t) * Si). The thermal efficiency is the ratio between the thermal power collected by the fluid and the power that impacts the receiver.

It is deduced from the established energy model whether an adjustment of the coolant flow must be made (step E12).

It is also possible to associate the measurement m_i_DNI (t) carried out by the photosensitive sensor 2.i at time t with a surface element Si of a receiver (step Eli) that the solar radiation captured by the photosensitive sensor 2.i is brought to irradiate.

This measurement m_i_DNI (t) is also associated with an antecedent measurement m_i_DNI (t-dt) previously carried out by the photosensitive sensor 2.i. (step E31), and then these data are used to calculate a cloud cover displacement vector. We then deduce a solar resource estimate seen by the surface element Si at a time t + dt (step E32).

The matrix arrangement of sensors can make it possible to reconstruct cloud contours on the entire solar field. Cloud masses will be identified and followed. The treatment performed can be global and involve all the sensors, or be limited to a limited number of sensors among the set of sensors distributed on the solar field.

This estimate and the measurement associated with a surface element Si are used to update a predictive dynamic model that can be used by the control system of the plant (step E51).

With the aid of this dynamic model, the control-command system is able to act (step E52) on one or more control parameters by triggering, for example, a change in the flow rate of heat-transfer fluid, a focusing or defocusing of mirrors, or even a stop, in order to maintain a temperature setpoint at the outlet of the heating sections or to maintain a close to a setpoint another operating parameter of the plant. For example, it is possible to provide a minimum flow rate of coolant or to be limited to a maximum local temperature that it is desired not to exceed.

A DNI measuring device as described above can also be used to monitor the state and in particular the degree of soiling of the mirrors of a solar installation. In order to check the state of the mirrors, for example of a concentrating solar power station, it is possible, in addition to the DNI measuring device described above, to carry out a complementary measurement of DNI serving as a reference by means of, for example, one or several reference pyrheliometers.

This type of measurement is preferably carried out in clear weather so that the presence of cloud does not disturb the measurement. A day of clear weather, in other words an absence of cloud, can be detected for example by means of an image capture device of the sky such as a very wide angle camera.

When comparing a measurement DNI m_DNI (t) performed using a measuring device DNI as described above for example in connection with Figure 1 and ref_DNI (t) obtained with the aid of reference measuring means, for example of the pyrheliometer type, several situations can occur.

If m_DNI (t) is equal to or substantially equal to ref_DNI (t) then it can be deduced that the reflecting zone of the mirror is clean.

When m_DNI (t) <ref_DNI (t), the reflective zone of the mirror is likely to include soiling, which is reflected in the value of m_DNI (t) measurement or the mirror may have a reflective zone including irreversible degradation . A distinction between a "dirty" state and a "degraded" state of the mirror can be made for example if a recent cleaning operation has been performed recently on the mirror. The comparison of the measurements made by the pivotable mirror DNI measuring device and the reference DNI measurement means can be performed using a computer processing unit, for example belonging to a control system such as mentioned above, and which may be possibly the same as that for performing the cloud cover prediction. 19

The DNI measuring device according to the invention can therefore make it possible to follow the evolution of the mirror reflectivity of a solar installation or a solar power station and be at the origin of the triggering of cleaning or even replacement interventions. mirrors in the case of irreversible degradation, for example due to oxidation of the reflective layer.

In one or the other of the installations described above, it is possible to provide photosensitive sensors that are autonomous in terms of power supply and that themselves produce the energy required to send DNI measurement signals to the flight deck. of the installation. Such measurement signals can also be transmitted for example by radio wave.

A DNI measuring device as described above can be applied to other types of installations than concentrating solar power plants of the Fresnel type. Such a device can be integrated in particular in an installation with non-planar mirrors, and for example of cylindro-parabolic shape, or even a tower plant provided with heliostats. In the case of a tower plant, knowledge of the solar resource established by means of a DNI measuring device can also make it possible to optimize the pointing strategy of the heliostats towards the tower. Using optical models, we can recalculate, according to the solar resource received by each heliostat, the optimal pointing strategy on the receiver.

Claims

Solar plant with at least one normal direct sunlight (DNI) measuring device, the measuring device comprising:

at least one first mirror (4, 4.1, 4.2) for reflecting direct solar radiation and disposed on a first mobile support (6),

at least one first photosensitive sensor (2, 2.1, ..., 2.20) arranged with respect to the first mirror so as to detect a solar radiation reflected by the first mirror,

at least one solar tracker adapted to orient the first mirror so that the first mirror returns the image of the sun in the direction of said photosensitive sensor, the first solar tracker being provided with first actuating means (8) of the first support ( 6) able to move the first mirror (4, 4.1, 4.2),

a first receiver (30a) comprising at least a first conduit (32) in which a heat transfer fluid is able to circulate, the first receiver (30a) being arranged to receive a solar radiation reflected by said first mirror, said first sensor photosensitive material (2.1) being arranged between the first mirror (4.1) and the first receiver (30a),

the normal direct irradiation measuring device (DNI) further comprising at least one second photosensitive sensor, the second photosensitive sensor (2.4, 2.5) being arranged between a second mirror and a second zone of said first receiver (30a) so as to detecting solar radiation reflected by the second mirror (4.1) and to said second zone of the first receiver (30a) or the second photosensitive sensor being arranged between another mirror and a second receiver (30b) so as to detect solar radiation reflected by the other mirror (4.1) and to said second receiver.

Solar power plant according to claim 1, wherein said first photosensitive sensor (2) is fixed or is disposed on another support member movable independently of said first support.

Solar power plant according to claim 2, wherein said first photosensitive sensor (2) is fixed and in which the solar tracker is adapted to move the first mirror along two axes, the normal direct sunlight measuring device further comprising a means (3) such as a tube for limiting at a predetermined solid angle a luminous flux incident on said first photosensitive sensor.

4. Solar power plant according to one of claims 1 to 3, said first photosensitive sensor (2.1) being arranged at a non-zero distance from the first receiver (30a).

5. Solar power station according to one of claims 1 to 4, wherein the second receiver (30b) is provided with at least a second conduit in which a fluid is intended to flow, the control unit further comprising: a control system controller (50) configured to control first fluid flow control means in the first conduit and second control means adapted to regulate a flow of fluid in the second conduit independently of the flow of fluid in the first conduit, the control system. control controller being configured to control said second flow control means so as to modify the flow of fluid in the second conduit subsequent to detection of a variation of DNI established from measurement data from said other photosensitive sensor (2.2) .

6. Solar power plant according to one of claims 1 to 5, wherein a plurality of mirrors are focused on the first receiver (30a), the solar plant being provided with a control system (50) adapted to control a displacement at least one mirror of said plurality of mirrors following detection of a variation of DNI established from measurement data from said second photosensitive sensor (2.2).

Solar power station according to one of claims 1 to 6, wherein the DNI measuring device is provided with a plurality of photosensitive sensors (2.1, ..., 2.20) distributed at different locations of the central, the central further comprising: a computer processing unit having a cloud cover prediction module using a cloud trajectory evaluation model from at least a first set of DNI measurements from said photosensitive sensors (2.1,. .., 2.20) at a given instant and from at least a second series of DNI measurements from said photosensitive sensors at another time, preceding said given instant.

8. Solar power station according to one of claims 1 to 7, further comprising:

a normal reference direct sun measurement means, in particular a reference pyrheliometer, able to produce a reference measurement of normal direct sunlight of a solar flux to said first photosensitive sensor,

means for acquiring an image of the celestial vault above the central unit in order to deduce a state of absence of a cloud from at least one image originating from said image acquisition means,

a computer processing unit equipped with a state detection module of a reflecting surface of the first mirror (2a), when a state of absence of a cloud is detected:

to make a comparison between a reference measurement of normal direct sunlight resulting from the normal reference direct sun measurement means and a measurement resulting from said first photosensitive sensor,

deriving from said comparison a state of said reflecting surface of the first mirror (2a).

9. Use of a normal direct sunlight (DNI) measuring device for evaluating the degree of soiling and / or the state of a reflective surface of at least the first mirror of the solar power plant according to one of the Claims 1 to 8.