CN105526737A - Nanofluid heat absorption type photovoltaic-solar heat pump system - Google Patents

Abstract

The invention relates to a nanofluid heat-absorbing photovoltaic-solar heat pump system, which combines a photovoltaic-solar heat pump component and a frontal heat-absorbing nanofluid component. The photovoltaic-solar heat pump component includes a DC compressor, a water-cooled condenser, an air-cooled condenser, a Flow valve, air-cooled evaporator, PV evaporator, front endothermic nanofluid components include PV evaporator, nanofluid storage tank and nanofluid circulation pump. The invention combines the photovoltaic-solar heat pump system with the front endothermic nanofluid PV/T system, the heat pump system solves the cooling problem of the nanofluid, and improves the photoelectric efficiency of the front endothermic nanofluid PV/T system; the nanofluid The optical characteristics can absorb solar energy in sub-bands, which improves the comprehensive utilization rate of solar energy and the performance coefficient of the heat pump system.

Description

Nanofluid heat-absorbing photovoltaic-solar heat pump system

technical field

The invention belongs to the field of solar energy applications, in particular to a nanofluid heat-absorbing photovoltaic-solar heat pump system.

Background technique

The energy issue is the primary issue of social and economic development. In recent years, along with the rapid economic development, my country's demand for energy presents a trend of rapid growth. At present, due to the low efficiency of energy utilization in my country and the excessive use of fossil energy such as coal, my country's energy problems have become more severe and environmental damage has become increasingly serious, which has greatly restricted my country's economic development. Solar energy is an important alternative to traditional energy because of its renewable and environmentally friendly advantages. The current application of solar energy is mainly photothermal conversion and photoelectric conversion.

How to efficiently use solar energy has always been the focus of research. Solar photovoltaic/photothermal comprehensive utilization (PV/T, Photovoltaic/Thermal) has significantly improved compared with a single photoelectric system or photothermal system. Typical solar PV /T The top of the collector is a layer of glass cover, the middle is an air layer, and the bottom is a photovoltaic cell and its substrate layer; behind the photovoltaic cell substrate is welded a copper tube, and the copper tube is a heat exchange medium, usually water .

The conversion process of solar energy is as follows: the solar radiation first reaches the surface of the glass cover, most of the solar radiation will pass through the glass cover, and a small part is reflected and absorbed by the cover and dissipated; the solar radiation passing through the glass cover reaches The middle air layer, in the middle air layer, still most of the solar radiation will pass through the middle air layer to reach the surface of the photovoltaic cell, but also a small part due to scattering, the gap between the photovoltaic cell and the glass cover Multiple reflections, absorption of the air layer and other reasons dissipate; part of the solar radiation reaching the surface of the photovoltaic cell is absorbed by the photovoltaic cell and converted into electrical energy (mainly the visible light part), and the rest is all converted into heat energy (mainly the infrared part) ; The converted electric energy can be directly used, and the converted heat energy will be absorbed by the photovoltaic cell and its substrate except for a small part of it dissipated into the environment, so that the temperature of the photovoltaic cell and the substrate will increase, and then transferred in the form of heat conduction Supplying the copper tube increases the temperature of the copper tube; then the copper tube and the working medium in the tube transfer heat energy to the working medium under the combined effects of heat conduction and convection, and the temperature of the working medium rises. From the above transfer process of solar energy, it can be seen that part of the effectively absorbed solar energy is converted into electrical energy, part of it is converted into heat energy of circulating working fluid, and the rest is dissipated due to thermal resistance.

Ordinary PV/T collectors use the back absorption method. From the above solar energy transfer process, it can be seen that PV/T collectors have their own shortcomings: 1) The improvement of the photothermal efficiency of the system is at the expense of photoelectricity. The existence of the intermediate air layer reduces the heat loss of the system, but at the same time reduces the amount of solar radiation reaching the surface of the photovoltaic cell; 2) The laminated structure of the photovoltaic cell and the substrate is relatively complicated, and the thermal resistance of the intermediate TPT and EVA Larger, solar light and heat absorption is mainly done through black TPT (some studies also use black paint on the surface to reduce the number of TPT layers), and black TPT and black paint have limited absorption rates; 3) Photovoltaic cells And the heat capacity of the substrate is small, and the temperature rise after heat absorption is large, resulting in large heat loss of the system.

Nanofluids disperse nanoscale particles into the base liquid to form a uniform and stable suspension. Nanofluids have relatively special thermal radiation characteristics and enhanced heat transfer properties, making nanofluids have a good application prospect in the field of solar energy. Studies have found that nanofluids such as zinc oxide, silicon dioxide, and aluminum oxide have high transmittance for visible light bands, and high absorption rates for other bands, especially infrared. This characteristic of nanofluids makes positive Endothermic PV/T becomes possible. Nanofluid has a high transmittance in the visible light part (up to about 95%, which is greater than the transmittance of the intermediate air), which can improve the photoelectric efficiency of the system. Based on the absorption rate of black TPT and black paint) can improve the photothermal efficiency of the system. The frontal heat absorption of nanofluids can simplify the structure of PV panels and reduce the thermal resistance of the system; the presence of nanoparticles increases the thermal conductivity of the base fluid and enhances the heat transfer coefficient between nanofluids and PV panels; nanofluids The heat capacity of the solar cell is much larger than that of the photovoltaic cell and its substrate, which can greatly reduce the heat loss of the system. Studies have shown that the comprehensive efficiency of nanofluid frontal heat-absorbing PV/T systems is higher than that of ordinary PV/T systems.

However, the nanofluid heat-absorbing PV/T system also has its own shortcomings in practical applications, because the nanofluid is in direct contact with the photovoltaic cell layer (the TPT of the outer layer can be waterproof and electrically insulated), so the temperature of the nanofluid directly affects The temperature of the photovoltaic cell has the same problem as that of ordinary PV/T, that is, as the cycle continues, the temperature of the nanofluid will gradually increase, and the photoelectric efficiency will be affected. In addition, because it is troublesome to produce a large amount of nanofluids, many scholars use heat exchange to cool the temperature of nanofluids when studying the application characteristics of nanofluids. It reduces the application possibility of positive heat-absorbing nanofluid PV/T, which has become one of the problems to be solved urgently.

Contents of the invention

The object of the present invention is to provide a nanofluid heat-absorbing photovoltaic-solar heat pump system that improves the coefficient of performance of the heat pump while ensuring the photoelectric efficiency of the system in order to overcome the above-mentioned defects in the prior art.

The purpose of the present invention can be achieved through the following technical solutions:

Nanofluid endothermic photovoltaic-solar heat pump system (NE-PV-SAHP, NanofluidsEndothermic-PhotovoltaicSolarAssistedHeatPump), which combines photovoltaic-solar heat pump components and front endothermic nanofluid components,

The photovoltaic-solar heat pump assembly includes a DC compressor, a water-cooled condenser, an air-cooled condenser, a throttle valve, an air-cooled evaporator, and a PV evaporator,

The positive heat-absorbing nanofluid component includes a PV evaporator, a nanofluid storage tank and a nanofluid circulation pump,

The water-cooled condenser is connected in parallel with the air-cooled condenser, and the described air-cooled evaporator is connected in parallel with the PV evaporator;

The nanofluid storage tank is connected to the PV evaporator through a nanofluid circulation pump,

The photovoltaic-solar heat pump assembly and the front heat-absorbing nanofluid assembly share a PV evaporator, and the electric energy output end of the PV evaporator is connected to a DC compressor and a nanofluid circulating pump respectively through a power switch, so that the electric energy of the PV evaporator The output is divided into two parts, and the output power of the electric energy should match the DC compressor and the nanofluid circulating pump respectively.

Preferably, the inlet and outlet ends of the water-cooled condenser, the air-cooled condenser, the air-cooled evaporator, and the PV evaporator are all equipped with electromagnetic valves for controlling opening and closing.

More preferably, the PV evaporator is composed of a glass cover plate arranged in sequence from top to bottom, a nanofluid channel, a photovoltaic cell and a substrate, and an insulating layer. The nanofluid channel is filled with flowable nanofluid. There are freon pipes in the layer.

More preferably, the flow direction of the nanofluid is opposite to that of the Freon in the Freon pipeline. The nanofluid is zinc oxide, silicon dioxide or aluminum oxide nanofluid.

Preferably, the air-cooled evaporator and the PV evaporator are switched for use according to different climatic conditions, and the air-cooled condenser and the water-cooled condenser are switched for use according to different needs of users.

The photovoltaic-solar heat pump system (PV-SAHP, photovoltaicsolar-assistedheatpump) is effectively combined with the front endothermic nanofluid PV/T system. The frontal absorption of solar radiation by nanofluids can simplify the structure of PV/T collectors; at the same time, the segmental absorption of solar radiation by nanofluids can improve the comprehensive utilization efficiency of solar energy in heat pump systems; the evaporation end of heat pump systems can provide nanofluid cooling. The required cooling capacity ensures that the nanofluid always flows through the PV cell at a lower temperature, which is beneficial to the photoelectric conversion of the photovoltaic cell. In addition, using photovoltaic cells to generate electricity to drive DC compressors and nanofluid circulating pumps can achieve good adaptability between the output of the system and the input of solar radiation; the stronger the solar radiation, the greater the output power of PV cells, and the DC compression The faster the speed of the machine and the nano-circulation pump, the stronger the heat exchange of the system, the more the absorption of solar radiation, and vice versa, the two complement each other, only need a reasonable match to fully realize the self-control, without additional control system. As a supplement, the air-cooled evaporator is used when the solar radiation is not strong or when it is rainy, the system can basically realize all-weather operation; the water-cooled condenser and the air-cooled condenser can meet the different needs of users and have multi-functionality.

The difference between the nanofluid heat-absorbing photovoltaic-solar heat pump system (NE-PV-SAHP) and the ordinary photovoltaic-solar heat pump system (PV-SAHP) lies in the difference in the absorption medium for the part of solar radiation converted into heat energy. The heat energy converted from solar radiation consists of two parts, one part comes from the short-wave part, most of the short-wave part is absorbed by the photovoltaic cell, but there is still a small part that is converted into heat energy of the photovoltaic cell due to the inability to excite electrons; the other part is the long-wave part, This part is basically converted into thermal energy of photovoltaic cells. Ordinary photovoltaic-solar heat pump system, the absorption of the short-wave part is the photovoltaic cell, and the absorption of the long-wave part is black TPT (or other media such as black paint). The direct reflection of the absorbed heat is the temperature rise of the photovoltaic cell and its substrate. High, then this part of the heat energy is absorbed by the low-temperature working fluid at the evaporation end of the heat pump through heat conduction; and for the nanofluid heat-absorbing photovoltaic-solar heat pump system, the absorption of short-wave is also photovoltaic cells, and the absorption of long-wave is nanofluid, therefore, The embodiment of the heat absorbed at this time is also composed of two parts: one is the temperature rise of the photovoltaic cell and its substrate, and the other is the temperature rise of the nanofluid, which is also absorbed by the low-temperature working fluid at the evaporation end of the heat pump through heat conduction (here nano Convective heat exchange is required between the fluid and the photovoltaic panel, but due to the forced circulation, even the heat transfer coefficient of ordinary water is at least an order of magnitude higher than the thermal conductivity of common metals, so it can be ignored here). In the nanofluid heat-absorbing photovoltaic-solar heat pump system, since the short-wave part is rarely converted into heat energy, the temperature rise of the photovoltaic cell is small, which is conducive to photoelectric conversion; for the long-wave part, the heat capacity of the nanofluid is much larger than that of ordinary The photovoltaic panels of the PV/T collector, so the temperature rise of the nanofluid is also smaller. In the case of a certain heat transfer coefficient of the working medium at the evaporation end, a low temperature difference means better heat transfer, that is, a higher solar heat utilization rate.

Compared with the prior art, the present invention effectively combines the photovoltaic-solar heat pump system (PV-SAHP) with the front endothermic nanofluid PV/T system, and solves the problem of front endothermic nanofluid PV/T system nanofluid The problem of circulating cooling is solved, and at the same time, the comprehensive utilization rate of solar energy and the performance coefficient of the heat pump system are improved. Compared with the current common front-cooled nanofluidic PV/T system, this system solves the cooling problem of nanofluids and improves the photoelectric efficiency of PV cells; the introduction of heat pumps increases the versatility of the system, which is different from ordinary photovoltaic- Compared with the solar heat pump system, this system can simplify the structure of the PV/T heat collector, and does not need to add additional control parts; at the same time, the unique optical characteristics of nanofluids can absorb the short and long waves of solar radiation with different media, providing The solar heat utilization rate of the heat pump system is improved, and the performance coefficient of the heat pump is improved while ensuring the photoelectric efficiency of the system.

Description of drawings

Fig. 1 is a structural representation of the present invention;

Fig. 2 is a schematic structural diagram of a PV evaporator.

In the figure, 1 is a DC compressor, 2 is an air-cooled condenser, 3 is a water-cooled condenser, 4 is a throttle valve, 5 is an air-cooled evaporator, 6 is a PV evaporator, 7 is a nanofluid storage tank, and 8 is a Nano fluid circulating pump, 9 is glass cover plate, 10 is nano fluid channel, 11 is photovoltaic cell and substrate, 12 is insulation layer, 13 is Freon pipeline, V1～V8 is electromagnetic valve, S1 is power supply switch.

detailed description

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Example

Nanofluid photovoltaic-solar heat pump system (NE-PV-SAHP), its structure is shown in Figure 1, mainly including DC compressor 1, air-cooled condenser 2, water-cooled condenser 3, throttle valve 4, air-cooled evaporator 5. PV evaporator 6, nanofluid storage tank 7, nanofluid circulating pump 8 and other components, control valve, power switch S1, and corresponding connecting parts.

Among them, DC compressor 1, air-cooled condenser 2, water-cooled condenser 3, throttle valve 4, air-cooled evaporator 5PV evaporator 6, etc. constitute a photovoltaic-solar heat pump assembly, PV evaporator 6, nanofluid storage tank 7 , the nanofluid circulation pump 8 and the power supply switch S1 etc. constitute the front endothermic nanofluid assembly. The photovoltaic-solar heat pump component and the front endothermic nanofluid component share the PV evaporator 6 . The water-cooled condenser 3 is connected in parallel with the air-cooled condenser 2, and the air-cooled evaporator 5 is connected in parallel with the PV evaporator 6. The nanofluid storage tank 7 is connected to the PV evaporator 6 through the nanofluid circulation pump 8, and the power output end of the PV evaporator 6 is respectively connected to the DC compressor and the nanofluid circulation pump through the power switch S1, so that the power output of the PV evaporator 6 Divided into two parts, the output power of the electric energy should match the DC compressor 1 and the nanofluid circulation pump 8 respectively.

The inlet and outlet of the air-cooled condenser 2 are respectively equipped with a solenoid valve V2 and a solenoid valve V4; the inlet and outlet of the water-cooled condenser 3 are respectively equipped with a solenoid valve V1 and a solenoid valve V3. The inlet and outlet of the air-cooled evaporator 5 are equipped with solenoid valves V5 and V7 respectively; the inlet and outlet of the PV evaporator are respectively equipped with solenoid valves V6 and solenoid valves V8, so as to facilitate the real-time control of the above components.

The structure of the PV evaporator is shown in Figure 2. It consists of a glass cover plate 9 arranged in sequence from top to bottom, a nanofluid channel 10, a photovoltaic cell and a substrate 11, and an insulating layer 12. The nanofluid channel is filled with flowable nanofluid For example, zinc oxide, silicon dioxide or aluminum oxide nanofluids can be used, and Freon pipes 13 are arranged in the insulation layer 12 . The flow direction of the nanofluid is opposite to that of the freon in the freon pipe.

Following is the working introduction of the present invention:

(1) Heating

At this time, the air-cooled condenser 2 is used at the condensing end, that is, the solenoid valve V2, the solenoid valve V4 are opened, the solenoid valve V1, and the solenoid valve V3 are closed;

When the solar radiation is good, the evaporation end adopts PV evaporator 6, that is, solenoid valve V6, solenoid valve V8 is opened, solenoid valve V5, solenoid valve V7 is closed, power supply switch S1 is on; the circulation loop is DC compressor 1 → Air-cooled condenser 2 → Throttle valve 4 → PV evaporator 6 → DC compressor 1;

When the solar radiation is not good, the evaporator adopts air-cooled evaporator 5, that is, the solenoid valve V5, the solenoid valve V7 is opened, the solenoid valve V6, and the solenoid valve V8 are closed, the power supply switch S1 is not connected, and the circulation circuit is DC Compressor 1→air-cooled condenser 2→throttle valve 4→air-cooled evaporator 5→DC compressor 1;

(2) Preparation of domestic hot water

At this time, the condensing end adopts a water-cooled condenser 3, that is, the solenoid valve V1, the solenoid valve V3 is opened, the solenoid valve V2, and the solenoid valve V4 are closed;

When the solar radiation is good, the evaporation end adopts PV evaporator 6, that is, solenoid valve V6, solenoid valve V8 is opened, solenoid valve V5, solenoid valve V7 is closed, power supply switch S1 is on; the circulation loop is DC compressor 1 →Water-cooled condenser 3→Throttle valve 4→PV evaporator 6→DC compressor 1;

When the solar radiation is not good, the evaporation end adopts air-cooled evaporator 5, that is, the solenoid valve V5, the solenoid valve V7 is opened, the solenoid valve V6, the solenoid valve V8 are closed, the power supply switch S1 is not connected, and the circulation circuit is DC compression Machine 1→water-cooled condenser 3→throttle valve 4→air-cooled evaporator 5→DC compressor 1;

The process that solar radiation is absorbed in the PV evaporator 6 is as follows: solar radiation first irradiates on the glass cover plate 9, and the solar radiation passing through the glass cover plate 9 is refracted in the nanofluid, and the short-wave part is irradiated on the photovoltaic panel through the nanofluid. The surface of the battery generates a large amount of electric energy and a small amount of heat energy, and the long-wave part is absorbed by the nanofluid and converted into heat energy of the nanofluid; the heat energy absorbed by the photovoltaic cell and the heat energy absorbed by the nanofluid are transferred to the Freon pipeline 13 through heat conduction, and the Freon pipeline 13 and the Freon in the tube The convective heat transfer of the working fluid transfers heat to the liquid freon, and the freon liquid working medium undergoes a phase change after absorbing heat and then becomes a freon gas. So far, part of the effectively absorbed solar energy is converted into electrical energy, and part of it is converted into latent heat of phase change of the working fluid.

In addition, the present invention mainly embodies the combination of nanofluid frontal heat absorption and photovoltaic-solar heat pump. After the combination, the two can be mutually beneficial and complementary, and the performance improvement achieved together is mainly reflected in the present invention. Air-cooled condenser and air-cooled evaporator are added to expand the versatility of the system. Therefore, all the small changes on the core of the combination of the nanofluid frontal heat-absorbing PV/T system and the photovoltaic-solar heat pump system (such as changing the heat exchange mode of the evaporator and condenser, adding Bypass, changing the type of compressor or other components, changing the type of nanofluid, etc.) are all within the protection scope of the patent of the present invention.

Claims (9)

1. Nanofluid heat-absorbing photovoltaic-solar heat pump system, characterized in that the system combines photovoltaic-solar heat pump components and frontal heat-absorbing nanofluid components, The photovoltaic-solar heat pump assembly includes a DC compressor, a water-cooled condenser, an air-cooled condenser, a throttle valve, an air-cooled evaporator, and a PV evaporator, The positive heat-absorbing nanofluid component includes a PV evaporator, a nanofluid storage tank and a nanofluid circulation pump, The water-cooled condenser is connected in parallel with the air-cooled condenser, and the described air-cooled evaporator is connected in parallel with the PV evaporator; The nanofluid storage tank is connected with the PV evaporator through the nanofluid circulation pump; the electric energy output end of the PV evaporator is respectively connected with the DC compressor and the nanofluid circulation pump through the power switch. 2. The nanofluid heat-absorbing photovoltaic-solar heat pump system according to claim 1, wherein the photovoltaic-solar heat pump component and the frontal heat-absorbing nanofluid component share a PV evaporator. 3. The nanofluid heat-absorbing photovoltaic-solar heat pump system according to claim 1, characterized in that, the inlet and outlet ends of the water-cooled condenser, the air-cooled condenser, and the air-cooled evaporator are all equipped with control opening and closing the solenoid valve. 4. The nanofluid heat-absorbing photovoltaic-solar heat pump system according to claim 1, characterized in that, the inlet and outlet ends of the PV evaporator are provided with electromagnetic valves for controlling opening and closing. 5. The nanofluid heat-absorbing photovoltaic-solar heat pump system according to claim 1, characterized in that the electric output power of the PV evaporator should be matched with the DC compressor and the nanofluid circulating pump respectively. 6. The nanofluid heat-absorbing photovoltaic-solar heat pump system according to claim 1, characterized in that, the PV evaporator consists of a glass cover plate arranged in sequence from top to bottom, a nanofluid channel, a photovoltaic cell and a substrate , consisting of an insulating layer, the nanofluid channel is filled with flowable nanofluid, and the insulating layer is provided with Freon pipes. 7. The nanofluid heat-absorbing photovoltaic-solar heat pump system according to claim 5, characterized in that the flow direction of the nanofluid is opposite to that of the Freon in the Freon pipeline. 8. The nanofluid heat-absorbing photovoltaic-solar heat pump system according to claim 5, wherein the nanofluid is zinc oxide, silicon dioxide or aluminum oxide nanofluid. 9. The nanofluid heat-absorbing photovoltaic-solar heat pump system according to claim 1, wherein the air-cooled evaporator and the PV evaporator are switched for use according to different climatic conditions, and the air-cooled condenser And the water-cooled condenser can be switched according to the different needs of users.