How does a solar concentrator work? Concentrating parabolic solar collector. Hot water supply in the country and at home How to make a parabolic solar concentrator

For a very long time I wanted to make a solar parabolic concentrator. After reading a lot of literature on making a mold for a parabolic mirror, I settled on the simplest option - a satellite dish. The satellite dish has a parabolic shape that collects reflected rays at one point.

I looked after the Kharkov plates "Variant" as a basis. At a reasonable price for me, I could only get a 90-centimeter product. But the goal of my experience is high temperature in focus. To achieve good results, you need a mirror area - the more the better. Therefore, the plate should be 1.5m, and preferably 2m. In the assortment of the Kharkov manufacturer there are these sizes, but they are made of aluminum, and, accordingly, the prices are exorbitant. I had to dive into the Internet in search of a used product. And here in Odessa, the builders dismantling some object, offered me a satellite dish 1.36m x 1.2m in size, made of plastic. A bit short of my wishes, however the price was good and I ordered one plate.

Having received the plate in a couple of days, I found that it was made in the USA, it has powerful stiffeners (I was worried if the case was strong enough and would not lead it after the mirrors were attached), and a strong orientation mechanism with many settings.

I also bought mirrors, 3mm thick. I ordered 2 sq.m. - a little with a margin. Mirrors are sold mostly 4 mm thick, I found a C to cut it easier. I decided to make the size of the mirrors for the concentrator 2 x 2 cm.

After collecting the main components, I started making a stand for the hub. There were several corners, pieces of pipes and profiles. Cut to size, cooked, cleaned and painted. Here's what happened:

So, having made a stand, I start cutting mirrors. The mirrors are 500 x 500 mm. First of all, I cut it in half, and then with a 2 x 2 cm grid. I tried a bunch of glass cutters, but now it is not possible to find at least something sensible in stores. A new glass cutter cuts perfectly 5-10 times, and that's it .... After that, you can immediately throw it away. Perhaps there are some professional ones, but they should not be bought in hardware stores. Therefore, if someone is going to make a concentrator out of mirrors, the question of cutting mirrors is the most difficult one!

The mirrors are cut, the tripod is ready, I'm starting to glue the mirrors! The process is long and tedious. My number of mirrors on the finished concentrator turned out to be 2480 pieces. Clay picked the wrong one. I bought a special glue for mirrors - it holds well, but it is thick. When gluing, squeezing a droplet onto the mirror and then pressing it against the plate wall, there is a possibility of unevenly pressing the mirror (somewhere stronger, somewhere weaker). Because of this, the mirror may not be glued tightly, i.e. will direct its ray of the sun not into focus, but near it. And if the focus is blurred, there is nothing to expect high results. Looking ahead, I will say that my focus turned out to be blurry (from which I conclude that it was necessary to apply a different glue). Although the results of the experiment were pleasing, the focus was about 10 cm in size, and around a still blurry spot of another 3-5 cm. The smaller the focus, the more accurate the focusing of the rays, the correspondingly higher the temperature. It took me almost 3 full days to glue the mirrors. The area of the cut mirrors was about 1.5 square meters. There was a marriage, at first, until he adapted - a lot, later much less. Defective mirrors were probably no more than 5%.

The solar parabolic concentrator is ready.

When measured, the maximum temperature at the focus of the concentrator was at least 616.5 degrees. The sun's rays helped set fire to a wooden plank, melt tin, a lead sinker, and an aluminum beer can. I conducted the experiment on August 25, 2015 in the Kharkiv region, Novaya Vodolaga village.

The plans for the next year (and maybe it will work out in the winter) to adapt the concentrator for practical needs. Possibly for heating water, possibly for generating electricity.

In any case, nature has given us all a powerful source of energy, we just need to learn how to use it. The energy of the sun covers a thousand times all the needs of mankind. And if a person can take at least a small part of this energy, then this will be the greatest achievement of our civilization, thanks to which we will save our planet.

Below is a video in which you will see the process of making a solar concentrator based on a satellite dish, and the experiments that were made with the help of the concentrator.

By the principle of operation, solar concentrators are very different from. Moreover, thermal-type solar power plants are much more efficient than photovoltaic ones due to a number of features.

The task of a solar concentrator is to focus the sun's rays on a container with a coolant, which can be, for example, oil or water, which are good at absorbing solar energy. Concentration methods are different: parabolic cylindrical concentrators, parabolic mirrors, or heliocentric towers.

In some concentrators, the sun's radiation is focused along the focal line, in others - at the focal point, where the receiver is located. When solar radiation is reflected from a larger surface onto a smaller surface (the surface of the receiver), a high temperature is reached, the coolant absorbs heat, moving through the receiver. The system as a whole also contains a storage part and a power transmission system.

The efficiency of the concentrators is greatly reduced during cloudy periods, since only direct solar radiation is focused. It is for this reason that such systems achieve the highest efficiency in regions where the level of insolation is especially high: in deserts, in the equator region. To increase the efficiency of using solar radiation, the concentrators are equipped with special trackers, tracking systems that ensure the most accurate orientation of the concentrators in the direction of the sun.

Since the cost of solar concentrators is high and the tracking systems require periodic maintenance, their use is mainly limited to industrial power generation systems.

Such installations can be used in hybrid systems in conjunction, for example, with hydrocarbon fuel, then the storage system will reduce the cost of electricity produced. This will become possible, since the generation will take place around the clock.

Parabolic Tubular Solar Concentrators are up to 50 meters long, they look like an elongated mirror parabola. Such a concentrator consists of an array of concave mirrors, each of which collects parallel rays of the sun and focuses them at a specific point. Along such a parabola, a pipe with a coolant is located so that all the rays reflected by the mirrors are focused on it. To reduce heat loss, the pipe is surrounded by a glass tube that extends along the focal line of the cylinder.

These concentrators are arranged in rows in a north-south direction, and they are certainly equipped with solar tracking systems. The radiation focused into the line heats the coolant to almost 400 degrees, it passes through the heat exchangers, generating steam, which rotates the turbine of the generator.

For the sake of fairness, it should be noted that a photocell can also be located in the place of the pipe. However, despite the fact that with photocells, the dimensions of the concentrators can be smaller, this is fraught with a decrease in efficiency and the problem of overheating, which requires the development of a high-quality cooling system.

In the California desert in the 80s, 9 power plants on parabolic cylindrical concentrators were built, with a total capacity of 354 MW. Then the same company (Luz International) also erected a SEGS I hybrid plant in Deggett, with a capacity of 13.8 MW, which additionally included natural gas ovens. In general, as of 1990, the company has built hybrid power plants with a total capacity of 80 MW.

The development of solar power generation at parabolic power plants is carried out in Morocco, Mexico, Algeria and other developing countries with funding from the World Bank.

As a result, experts conclude that today parabolic power plants are inferior both in terms of profitability and efficiency to solar power plants of tower and disc type.

- these are, similar to satellite dishes, parabolic mirrors, with which the sun's rays are focused on a receiver located in the focus of each such dish. At the same time, the temperature of the coolant with this heating technology reaches 1000 degrees. The heat transfer fluid is immediately supplied to a generator or engine, which is combined with a receiver. Here, for example, Stirling and Brighton engines are used, which can significantly increase the performance of such systems, since the optical efficiency is high, and the initial costs are low.

The world record for the efficiency of a parabolic dish-type solar plant is 29% efficiency achieved when converting thermal energy into electrical energy, on a dish-type installation combined with a Stirling engine at Rancho Mirage.

Due to the modular design, solar poppet systems are very promising, they allow you to easily achieve the required power levels for both hybrid consumers connected to public electricity networks and for stand-alone ones. An example is the STEP project, which consists of 114 parabolic mirrors with a diameter of 7 meters, located in the state of Georgia.

The system produces medium, low and high pressure steam. Low pressure steam is fed to the air conditioning system of the knitting mill, medium pressure steam is fed to the knitting industry itself, and high pressure steam is fed directly to generate electricity.

Of course, solar disc concentrators combined with a Stirling engine are of interest to owners of large energy companies. Thus, Science Applications International Corporation, in collaboration with three energy companies, is developing a system using a Stirling engine and parabolic mirrors, which will be able to produce 25 kW of electricity.

In tower-type solar power plants with a central receiver, the solar radiation is focused on the receiver, which is located at the top of the tower.... Around the towers are placed in large numbers reflectors-heliostats... Heliostats are equipped with a biaxial sun tracking system, thanks to which they are always turned so that the rays are stationary concentrated on the heat receiver.

The receiver absorbs thermal energy, which then turns the turbine of the generator.

The liquid coolant, circulating in the receiver, transfers steam to the heat accumulator. Usually works are water vapor with a temperature of 550 degrees, air and other gaseous substances with a temperature of up to 1000 degrees, organic liquids with a low boiling point - below 100 degrees, as well as liquid metal - up to 800 degrees.

Depending on the purpose of the station, steam can rotate a turbine to generate electricity, or directly used in some kind of production. The temperature in the receiver ranges from 538 to 1482 degrees.

The Solar One power tower in Southern California, one of the first of its kind, originally produced electricity through a steam-water system, producing 10 MW. Then it underwent modernization, and the improved receiver, now operating on molten salts and the heat storage system, became significantly more efficient.

This has led to a breakthrough in solar concentrator technology for heat storage tower power plants: power in such a power plant can be produced as needed, since the heat storage system can store heat for up to 13 hours.

Molten salt technology makes it possible to store solar heat at 550 degrees, and electricity can now be generated at any time of the day and in any weather. Tower station "Solar Two" with a capacity of 10 MW, became a prototype of industrial power plants of this type. In the future - the construction of industrial plants with a capacity of 30 to 200 MW for large industrial enterprises.

The prospects are enormous, but development is hampered by the need for large areas, and the considerable cost of building industrial-scale tower stations. For example, in order to place a 100 megawatt tower station, 200 hectares are needed, while for a nuclear power plant capable of producing 1000 megawatts of electricity, only 50 hectares are needed. Parabolic-cylindrical stations (modular type) for small capacities, in turn, are more cost-effective than tower ones.

Thus, tower and parabolic cylindrical concentrators are suitable for power plants from 30 MW to 200 MW, which are connected to the grid. Modular disk concentrators are suitable for autonomous power supply of networks that require only a few megawatts. Both tower and plate systems are expensive to manufacture, but they give a very high efficiency.

As you can see, parabolic-cylindrical concentrators occupy an optimal position as the most promising solar concentrator technology for the coming years.

(Canada) has developed a versatile, powerful, efficient and one of the most economical solar parabolic concentrators (CSP - Concentrated Solar Power) with a diameter of 7 meters, for both ordinary homeowners and industrial use. The company specializes in the manufacture of mechanical devices, optics and electronics, which has helped it create a competitive product.

According to the manufacturer's own assessment, the SolarBeam 7M solar concentrator outperforms other types of solar devices: flat solar collectors, vacuum collectors, solar concentrators of the "chute" type.

Exterior view of the solar concentrator Solarbeam

How it works?

The solar concentrator automatics track the movement of the sun in 2 planes and direct the mirror exactly to the sun, allowing the system to collect maximum solar energy from dawn to late dusk. Regardless of the season or location of use, SolarBeam maintains a targeting accuracy of up to 0.1 degrees to the sun.

The rays falling on the solar concentrator are focused at one point.

SolarBeam 7M Calculation and Design

Stress testing

Methods of 3D modeling and software stress testing were used to design the system. Tests are performed using the FEM (Finite Element Analysis) method to calculate stresses and displacements of parts and assemblies under the influence of internal and external loads in order to optimize and verify the design. This rigorous testing suggests that the SolarBeam can operate under extreme wind and climatic conditions. SolarBeam has successfully simulated wind loads up to 160 km / h (44 m / s).

Stress testing of the parabolic reflector frame and strut connection

Photo of the Solarbeam Hub Mount

Solar Concentrator Rack Stress Testing

Production level

Often, the high cost of manufacturing parabolic concentrators prevents their massive use in individual construction. The use of dies and large segments made of reflective material has reduced production costs. Solartron has utilized many of the innovations used in the automotive industry to reduce costs and increase production.

Reliability

The SolarBeam has been tested in the harsh conditions of the north and offers high performance and durability. SolarBeam is designed for all weather conditions, including high and low ambient temperatures, snow load, icing and high winds. The system is designed for 20 or more years of operation with minimal maintenance.

The SolarBeam 7M parabolic mirror can hold up to 475 kg of ice. This is approximately equal to 12.2 mm of ice thickness over the entire area of 38.5 m2.
The installation normally works in snowfalls due to the curved design of the mirror sectors and the ability to automatically perform "auto snow removal".

Performance (comparison with vacuum and flat collectors)

Q / A = F ’(τα) en Kθb (θ) Gb + F’ (τα) en Kθd Gd -c6 u G * - c1 (tm-ta) - c2 (tm-ta) 2 - c5 dtm / dt

The efficiency for non-concentrating solar collectors was calculated using the following formula:

Efficiency = F Collector Efficiency - (Slope * Delta T) / G Solar Radiation

The performance curve for the SolarBeam Hub shows an overall high efficiency over the entire temperature range. Flat solar collectors and evacuated collectors show lower efficiency when higher temperatures are required.

Comparative plots of Solartron and flat / vacuum solar collectors

Solartron efficiency versus temperature difference dT

It is important to note that the above diagram does not include wind heat loss. In addition, the above data indicates maximum efficiency (at noon) and does not reflect efficiency during for. The data is given for one of the best flat and vacuum manifolds available. In addition to being highly efficient, SolarBeamTM produces up to 30% more energy by tracking the sun on two axes. In geographic regions where low temperatures prevail, the efficiency of flat and evacuated collectors is significantly reduced due to the large absorber area. SolarBeamTM has an absorber with an area of only 0.0625 m2 in relation to the collection area of 15.8 m2, thus achieving low heat loss.

Please also note that due to the dual axis tracking system, the SolarBeamTM Hub will always operate at maximum efficiency. The effective collector area of a SolarBeam is always equal to the actual surface area of the mirror. Flat (stationary) collectors lose potential energy according to the equation below:
PL = 1 - COS i
where PL is the loss in energy in%, of the maximum at displacement in degrees)

Control system

SolarBeam control uses "EZ-SunLock" technology. With this technology, the system can be quickly installed and configured anywhere in the world. The tracking system tracks the sun with an accuracy of 0.1 degrees and uses an astronomical algorithm. The system is capable of general dispatching via remote networks.

Abnormal situations in which the "plate" will automatically be parked in a safe position.

If the coolant pressure in the circuit falls below 7 PSI
When the wind speed is more than 75 km / h
In the event of a power outage, the UPS (Uninterruptible Power Supply) moves the dish to a safe position. When power is restored, automatic sun tracking continues.

Monitoring

In any case, and especially for industrial applications, it is very important to know the status of your system to ensure reliability. You must be warned before a problem occurs.

SolarBeam has the ability to monitor through the SolarBeam remote dashboard. This panel is easy to use and provides important SolarBeam status, diagnostics, and energy production information.

Remote configuration and management

SolarBeam can be remotely configured and quickly changed settings. The plate can be controlled remotely using a mobile browser or PC, simplifying or eliminating on-site control systems.

Alerts

In the event of an alarm or a need for service, the device sends an e-mail message to the designated service personnel. All alerts can be customized according to user preferences.

Diagnostics

SolarBeam has remote diagnostic capabilities for system temperatures and pressures, power generation, and more. At a glance, you can see the status of the system.

Reporting and charts

If energy production reports are required, they can be easily obtained for each plate. The report can be in the form of a graph or a table.

Mounting

The SolarBeam 7M was originally designed for large scale CSP installations, making installation as easy as possible. The design allows for quick assembly of major components and does not require optical alignment, which makes installation and system startup inexpensive.

Installation time

A team of 3 can install one SolarBeam 7M from start to finish in 8 hours.

Accommodation requirements

The SolarBeam 7M is 7 meters wide with a 3.5 meter offset. When installing multiple SolarBeam 7Ms, an area of approximately 10 x 20 meters should be allocated per system to maximize solar gain with the least amount of shading.

Assembly

The Parabolic Hub is designed to be assembled on the ground using a mechanical lifting system, allowing for quick and easy installation of trusses, mirror sectors and fixtures.

Areas of use

Generating electricity using ORC (Organic Rankine Cycle) units.

Industrial water desalination plants

Thermal energy for desalination plant can be supplied by SolarBeam

In any industry where a lot of heat energy is required for the technological cycle, such as:

Food (cooking, sterilization, alcohol production, washing)
Chemical industry
Plastic (Heating, exhaust, separation, ...)
Textile (bleaching, washing, pressing, steam treatment)
Petroleum (sublimation, clarification of petroleum products)
And much more

Place of installation

Suitable locations for installation are regions that receive at least 2000 kWh of sunlight per m2 per year (kWh / m2 / year). I consider the following regions of the world to be the most promising manufacturers:

Regions of the former Soviet Union
Southwestern USA
Central and South America
North and South Africa
Australia
Mediterranean countries of Europe
Middle East
Desert Plains of India and Pakistan
Regions of China

Solarbeam-7M Model Specification

Peak power - 31.5 kW (at a power of 1000 W / m2)
The degree of concentration of energy - more than 1200 times (spot 18 cm)
Maximum temperature in focus - 800 ° С
Maximum coolant temperature - 270 ° С
Operational efficiency - 82%
Reflector diameter - 7m
Parabolic mirror area - 38.5 m2
Focal length - 3.8m
Electricity consumption by servomotors - 48W + 48W / 24V
Wind speed during operation - up to 75 km / h (20 m / s)
Wind speed (in safe mode) - up to 160 km / h
Sun tracking in azimuth - 360 °
Vertical Sun Tracking - 0 - 115 °
Support height - 3.5m
Reflector weight - 476 kg
Total weight -1083 kg
Absorber size - 25.4 x 25.4 cm
Absorber area -645 cm2
The volume of the coolant in the absorber - 0.55 liters

Overall dimensions of the reflector

Finally, I took a vacuum manifold for 20 tubes, I will assemble a concentrator from them. 1 tube filled with water (3 liters) was heated from 20 * C to 68.3 * C (boiling water to the touch) in 2 hours 40 minutes. Outside the window on May 26, in the sun 42 * C in the shade 15 * C the time of the experiment from 16.27 to 18.50 the sun sets ...
And in the concentrator the meter showed 19 minutes! up to the same 68 * С. The speed can be increased by increasing the area of the hub, but then the windage increases and the integrity of the structure deteriorates ...
The area of the concentrator is 1.0664 sq. M. (62x172 cm.)
Focal length 16cm.
Buy a 1-well vacuum tube, and remove from it as with 7 in my version, if you count by area. Below is a video of one of the pioneers, which prompted me to my feat.

Faced so far with the problem of poor adhesion of acrylic with glue for mirrors. Easily peeled off from the base ... Also, the glue for mirrors is very soft and the system "walks" needs to strengthen the structure.
said):
On the advice of FarSeer; I positioned the axis horizontally (east-west orientation for winter). Such an arrangement is structurally simpler, the wind loads are less, the withdrawal (overturn) from precipitation is also easier.
Due to the fact that I will place my "scoops" horizontally in the east-west directions, so as not to get stuck on the trackers, I had to think about how to make heat extraction more efficient, since the standard scheme with liquid condensation may not work in theory, so as there is no condensate drain down and, accordingly, the rise of steam up to give off its heat. Made 2 types of heat extraction from the vacuum tube.
Option-1 (on the right, in photo-1) The native tip (thickening where steam is collected) is actively washed by a coolant.
Option-2 (average, in the photo-1), 2 tubes are taken, one 10mm. in diameter, the other 15 mm. in diameter and inserted into one another, by analogy with recuperators, the inner one does not reach the end of a couple of cm. and the outer one is plugged at the end, and from above these tubes are disconnected by a tee, see the photo. Experiments have shown that between the horizontal tube and the one standing under 45 * at temperatures of about 80 * the difference was about 5 * although I was told that in a horizontal position this tube would not work at all!
I'm waiting for the warmer to dig holes under the pillars, because the ground is still frozen and it's not realistic to dig it.
As for the emergency modes, everything is already well thought out, there is a 1.5 kW Smart type batteryless unit with additional batteries.
The second and, in my opinion, the most significant moment for solving emergency situations, closing the mirrors or the concentrator from the sun or turning it away from the focus axis, which will bring the concentrator to the minimum power of a simple vacuum tube in the hottest season, for example, according to the same principle, can be adjusted the total power of the concentrators bringing some out of focus.
As a variant of a concentrator made of scrap material, see the photo.