Hybrid high-concentration photovoltaic system designed for different weather conditions
In this study, we propose a novel high-concentration photovoltaic (HCPV) cell by considering both the light leakage characteristics of the Fresnel-lens-based solar cell modules and the performance issues arising from Cloud shading in practical use. We use our self-constructed systems to conduct field measurements for up to half a year under various environmental conditions. According to the acquired results, it was surprising to know that in the area other than the focusing area, the so-called light leakage region, there always bears illuminance of about 20,000–40,000 lx whether it is a sunny day or a cloudy day with different Cloud conditions. Such an interesting result is caused by the light scattering of the clouds and the inherent leakage characteristic of a Fresnel lens. To prove this important finding, we simulated the illuminance of the Fresnel lens structure used in the measurement with apertures of different sizes to determine the detected area. In the laboratory, the diffuse plates were used to mimic the situation of varying Cloud layer thicknesses. The trend of calculated and measured results fitted well with the field measurements. Also, the experimental and simulation results show that the round angle and draft facet of the Fresnel lens were responsible for light leakage. This finding prompted us to propose a hybrid high-concentration solar module in which more cost-effective polycrystalline silicon solar cells are placed around the high-efficiency wafer of HCPV to capture the dissipated light leakage and convert it into usable electricity.
Introduction
Among the 17 interlinked global sustainable development goals (SDGs) set by the United Nations General Assembly in 2015, affordable and clean energy is an essential indicator of a better, more sustainable future for all. Therefore, for clean and sustainable energy generation, researchers use various natural resources to obtain so-called green energy, including wind energy, geothermal energy, hydroelectricity, tidal power, solar energy, etc. Among these, solar photovoltaics are less limited by terrain or location and are an energy source that can be obtained almost anywhere in the world 1. Therefore, effectively converting the light energy from the sun into electrical energy that can be easily used has always been the ultimate goal of the development of human life. Solar cell panels made from semiconductor materials are recognized as the most economical manufactured solar power generation device. Over the past few decades, this device has become widely exploited to generate electricity from the sun rays. They can be found on the roofs of public buildings and individual homes worldwide. Generally, the materials used in semiconductor-based solar panels are polycrystalline silicon or III–V and II–VI compound semiconductors, while their photo conversion efficiencies are 15% and 45%, respectively 2,3,4. Regarding the product price, the cost of solar panels made with III-V or II-VI compound semiconductors is much higher than that of polysilicon solar panels. However, for efficiency considerations, III-V or II-VI semiconductors are still used for solar panels in solar power plants. They are used in accompanying sun-tracking systems to improve power generation efficiency 5. over, we can configure an optical lens above the compound semiconductor-based solar panel to effectively FOCUS the nearly parallel incident sunlight on a limited area of such high-cost solar cells 6,7. Solar cell modules with this configuration are called high-concentration photovoltaic (HCPV) 8,9. meaning that through the design and use of optical elements, most of the solar energy can be collected on a small-size solar wafer. In this way, not only can high-performance compound semiconductor materials be fully utilized for solar cell power supply, but also the cost can be greatly reduced due to the reduction of materials used.
In the HCPV systems, the direction of sunlight on the lens is closely related to the amount of solar energy that can be collected by the solar cell, so we need to use a time-varying sun-tracking system to obtain the highest conversion efficiency. Therefore, the structure of the focusing lens also requires a particular design. In addition to the proper focusing distance, we aim to increase the number of focusing lenses per unit area and reduce the weight of the lens itself as much as possible. Conventional focusing lenses are generally challenging to design because of the acceptable focal length and the corresponding lens size, making it difficult to achieve these optimal requirements simultaneously, which in turn makes the price of the sun-chasing system higher. An effective way to solve this problem is to use a Fresnel lens 10. Xie and Sierra et al. studied the application of the Fresnel lens in high solar energy concentration 11,12. Chen and Yamada et al. proposed the Fresnel lens design to improve the distribution of illuminance uniformity 13,14. but they didn’t consider the issue of light leakage of the Fresnel lens and power generation efficiency under heavy-Cloud weather conditions. Although the HCPV system combined with the Fresnel lens effectively utilizes the energy of sunlight, as the clouds in the sky change, the Fresnel lens cannot effectively gather the rays from the sun, resulting in a decrease in HCPV power generation efficiency. This paper presents a novel discovery of light leakage in an HCPV, that could maintain a certain level of illuminance under different Cloud conditions, and proposes a hybrid light collection system appropriate to different weather conditions, and the power generation efficiency stays optimal. New technical findings will be demonstrated through field measurement under various Cloud conditions.
The light leakage by the Fresnel lens
A Fresnel lens is a type of composite compact lens, and the structural design is schematically shown in Fig. 1a, allowing the construction of lenses of large aperture and short focal length without the mass and volume of material that would be required by a conventional lens design 15,16,17. Therefore, a Fresnel lens can be made much thinner than a conventional lens. Fresnel lenses are designed to significantly reduce the weight of the lens so that it can meet the requirements of a sun-tracking system. However, unlike conventional lenses, non-smooth and non-continuous lens surfaces distributed in multiple segments may cause inevitable significant light leakage due to manufacturing errors such as the radii of curvature and draft angles of the fabricated Fresnel lenses, as indicated in Fig. 1b. Subtle changes in these structures may make part of the parallel incident sunlight unable to be effectively focused into the energy harvesting range in the solar cell module through the Fresnel lens, resulting in decreased power generation efficiency. We used a Fresnel lens for simulation calculation with Advanced System Analysis Program (ASAP) 18. where the radius of curvature of the round angles (RVRA) and draft angles were around 0.1 mm and 1°, respectively. The width of the Fresnel lens was 129 mm and the thickness is 1.81 mm. The simulation calculation results are presented in Fig. 1c by Monte Carlo ray tracing 19. where the total simulation ray number was 10,000,000. When using the Fresnel lens as the focusing lens of HCPV, although most of the incident beams can be effectively concentrated into the FOCUS area, which may be equivalent to the energy collection area, still part of the light energy is dissipated out of the energy collection region. The size of the focusing area in the simulation was about 1.1 mm × 1.1 mm, the power ratio of FOCUS was 63%, and the light leakage ratio outside the focusing area was 37%.
Another practical problem encountered when using HCPV solar modules is that the sky cannot always be clear and cloudless. So, when a Cloud layer passes through the sunlight and the solar modules, the sun rays are multiply scattered by the water molecules inside the Cloud, causing the change of the traveling direction of the light entering the solar module, which was nearly parallel. The change in the direction of sunlight travel is related to the thickness of the clouds. When the Cloud thickness is thin, most of the sunlight’s forward direction is not affected, so the sunlight can still be concentrated on the solar cell modules. However, when the thickness of the Cloud layer increases to a certain thickness, the sun rays passing through the Cloud layer collide with water molecules randomly, resulting in a random scattering path. Thus the sunlight is no longer collimated when it reaches the Fresnel lens, and therefore cannot be efficiently concentrated on the solar cell with a lens, and results in a decrease of illuminance on the solar cell. In this case, if an III-V semiconductor-based solar cell is used, the HCPV has almost no power conversion efficiency due to its small light-harvesting area.
Characterization of Fresnel lenses in light leakage
To effectively obtain the dissipated light energy which is due to the use of Fresnel lenses and make high-efficiency solar cell modules that can be used in various weather conditions, this research work first calculated and measured the light energy in the light leakage area of Fresnel lenses with different structures under monochromatic light irradiation. Next, we used diffuse plates with varying penetration rates to mimic the outdoor conditions of different Cloud layer thicknesses and measured the lateral light intensity distribution on the solar cell module. Finally, summarizing the results of outdoor field measurements, we propose a hybrid solar high-concentration photovoltaic module, expecting that such a system can combine the advantages of HCPV and polycrystalline-silicon-based solar panels simultaneously and achieve comparable power conversion efficiency under different weather conditions.
As far as the structure of the Fresnel lens is concerned, neither the draft facet nor the RVRA caused by mold manufacturing can make the incident light converge on the same focal area. Therefore, a light leakage area is formed in the HCPV cell module. The draft facet is a side effect of the lens thinning process. The more the draft facet, the thinner the Fresnel lens. Another thing that occurs along with the draft facet is the round angle. The round angle is generated due to the large angle turning in the structure of the Fresnel lens. Similarly, the round angle structure cannot concentrate the sunlight in the central region. In the fabrication process of the Fresnel lens, a draft angle of at least 1° is required during the demolding process. The round angle usually has a radius of curvature of hundreds of microns or more. These factors can make the light concentration situation even worse. We can estimate its influence on light concentration according to the area ratio of the draft facet structure and the round angle in the Fresnel lens structure. The light leakage L caused by the draft facet and the round angle can be expressed
where the AF is the projection area of the Fresnel lens. AG is the overall projection area of the draft facet, and AR is the projection area occupied by the round angle. Therefore, when the Fresnel lens is thinner, the number of segments will increase, so the proportion of light leakage will also increase. To verify the above statement, we used two Fresnel lenses with similar areas for luminous flux measurement, as shown in Fig. 2. In the experiment, a monochromatic laser beam with a central wavelength of 532 nm was exploited to conduct light concentration experiments. As shown in Fig. 2c, the laser light passed through first an objective lens and then a large-aperture lens to form the collimated light beam. We used this collimated beam to mimic the characteristics of outdoor sunlight. The two Fresnel lenses are shown in Fig. 2, respectively, in the light irradiation path. Fresnel lens #1 is a thinner lens with more segments, and Fresnel lens #2 is a thicker lens with fewer segments. In the end, a light detector with a rectangle aperture of 10 mm × 16 mm was located at its focal plane to measure the luminous flux of the focusing spot. The light leakage ratios of the two lenses were measured 43% and 36%, respectively. Since the simulation shown in Fig. 1 was for the thicker Fresnel lens #2, we could compare the measurement result with the simulation shown in Fig. 1. The light leakage of the measurement was 36% when the focusing area was 10 mm × 16 mm. The simulation of the light leakage was 37% when the focusing area was set 1.1 mm × 1.1 mm, which was much smaller than that in the measurement. The difference in the focusing area can be explained as follows. Although the major important optical parameters of the Fresnel lens were set in the simulation, the simulated Fresnel lens was still in an ideal condition. It means that there was no manufacturing error, and the incident light was well-collimated. These two factors were not possible in the experiment. Thus the focusing spot in the experiment could be laterally extended or blurred in comparison with that in an ideal case, such as in the simulation. However, the simulation and the experimental measurement showed that around 36–37% light leakage could be observed outside the focusing area in both the simulation and the experiment. Without a doubt, the leakage mechanism of a Fresnel lens was well proved.
Another HCPV applicability problem results from wavefront disorder caused by clouds when sunlight passes through the earth’s atmosphere. When light waves pass through clouds with considerable thickness, part of the light will collide with water droplets, cause light refraction or reflection, and finally form random light scattering. Therefore, when the light enters a Fresnel lens, it can no longer be regarded as parallel light, while the concentrated beam will not FOCUS on the center point of the HCPV module. To prove this effect, we used the experimental configuration presented in Fig. 2 and placed different diffusers between the collimating and Fresnel lenses. The three diffusers had different one-shot transmittances, defined as the ratio of the penetrating light flux and the incidence flux of a certain diffuser 20. These diffusers allow different penetration ratios of the collimating beam, which could be used to simulate the influence of clouds on sunlight. The experiment results are summarized in Fig. 3. In Fig. 3a, a clear concentrated beam spot could be observed around the center of the detected area, indicating that most of the energy was collected at a limited location. Such a result might be used to mimic the days with a clear sky. From Fig. 3b–d, we could observe from the photos that the background patterns became increasingly blurred. At the same time, the intensity in the central area decreased, and the illuminance of the surrounding area was closer and closer to the intensity in the central area. Fresnel lenses #1(blue) and #2 (red) exhibited similar properties.
The light source used in the laboratory was derived from a green laser diode, and it did not fit the practical condition. To understand the optical effect affected by the Fresnel lens’s structure, we needed to compare the illuminance by the sunlight illumination and by the corresponding simulation. Therefore, we measured the illuminance of the focused sunlight with the Fresnel lens. In the measurements, we chose Fresnel lens #2 for experiments and used a photodetector (Thorlabs PM16-12) that can be utilized at high-power illumination to measure the power of the focal spot point. Since the measurement was done under moving sunlight, and the focusing spot was not an ideal tiny spot, the illuminance related to the aperture size of the photodetector. The result was that precise measurement of the focusing sunlight became difficult. Alternatively, we changed the aperture of the photodetector to collect more data and tried to find the correlation between the illuminance and the aperture size. The measurement results are shown in Fig. 4, where the vertical axis indicates the illuminance ratio at the FOCUS spot and the ground without a focusing lens. There are three simulation curves. The black curve is the calculated focused illuminance ratio for a conventional lens with the same f-number. The blue and pink curves are obtained using Fresnel lenses with RVRA of 0.2 mm and 0.5 mm, respectively. The slight difference among the three curves was caused by the geometrical structures of the Fresnel lens. The situation of the measurement was different. The moving sunlight made the illuminance measurement through a tiny aperture difficult. Therefore, we decided to change the aperture size and shape (including circle and square). The measurement is shown in Fig. 4, where the measurement result shows a similar trend of the ratio as a function of the aperture area. Thus, the Fresnel lens simulation helped predict the optical property of sunlight.
Field measurement and analysis
To understand the concentrating efficiency and light leakage characteristics of the HCPV module under actual weather conditions, we still selected Fresnel lens #2 for all the following field measurement experiments. We set up a 2 × 2 Fresnel lens array on a box with two rotation dimensions. The Fresnel lens array can be manually adjusted to face directly toward the sun at any time. During the measurement, different weather conditions occurred as the thickness of the Cloud layer changed. Therefore, we could observe at the bottom of the box that the brightness of the light leakage area will vary depending on the change in the Cloud thickness. The illuminance of this area was the physical quantity to be measured in this experiment.
During the half-year measurement process, we can roughly divide the weather conditions into three situations according to the thickness of the clouds. The first is a clear sky, that is, there are no clouds when looking at the sky, and the ground illuminance exceeds 100,000 lx. The second is a lightly cloudy sky, that is, the thickness of the Cloud layer is thin, and the sun can still be vaguely seen through the Cloud layer. On light cloudy days, part of the light is still parallel, so the FOCUS point can still be clearly observed. However, the light intensity at the focal point has been greatly reduced compared with the clear sky. The third is a heavy cloudy sky, that is, the Cloud layer is thicker, and the brightness of the whole sky is more uniform. In this kind of weather, it takes work to know the correct position of the sun. That is to say, after the clouds scatter the sunlight, its wavefront is irregularly distributed. At this time, no FOCUS point can be seen at the bottom of the box. After more than six months of measurements, we measured the ground illumination and light leakage under different weather conditions. The measured results and the ratio between the two physical quantities are summarized in Fig. 5. Figure 5a–c shows the values of the ground illuminance (light-blue bars) and the leakage illuminance (dark-blue bars) for clear sky, lightly cloudy, and heavily cloudy days, respectively. The figure’s red curves record the occupation ratios of light intensity in the light leakage area under a clear sky, lightly cloudy, and heavily cloudy days, which were about 40%, 65%, and 80%, respectively. The experimental results show that the percentage of light leakage under the Fresnel lens was higher when the Cloud layer was thicker. The ground illumination value decreased with the increase in Cloud thickness, which means that the energy converged by the Fresnel lens at the FOCUS point was also reduced.
From the above experimental results, it is important and interesting to find that the illuminance values of the light leakage area show no significant changes even at different Cloud thicknesses. This is because the percentage of light leakage is lower when the ground illumination is higher. The ground illuminance value decreases when the Cloud thickness increases, but the light leakage percentage rises. So we find that the illuminance of the leakage area will be close to a constant value regardless of the weather conditions. The light leakage of HCPV is caused by two optical phenomena, including the scattering of sunlight by clouds and the leakage of light caused by the structure of the Fresnel lens. This kind of light leakage should be adequately utilized. The first idea is to change the base plate of the conventional HCPV from a metal heat sink to a transparent medium so that light from outside the center can reach the ground. This distribution of sunlight between 20,000 and 40,000 lx should support the growth of some plants on the ground. Therefore, medium-illuminated agricultural activities can be carried out by switching to transparent baseboards. In addition, from a power generation point of view, we can also use low-cost solar panels to lay in the leakage area for power generation, so we designed a power generation installation that combines the advantages of both HCPV and polycrystalline solar panels.
Hybrid photovoltaic device
A hybrid high-concentration photovoltaic system is designed and proposed by placing a high-efficiency III-V solar panel at the FOCUS point and laying a polycrystalline silicon-based solar panel around it, as schematically shown in Fig. 6a. In the schematic diagram in Fig. 6a, the parallel beam from the sun passes through the Fresnel lens and is focused on the high-efficiency solar panel. The light leakage from the Fresnel lens structure and the scattered light from the sunlight passing through the clouds can be directed to the polycrystalline silicon-based solar panel (PSSP) for power generation. When the sky is clear, the light is concentrated on the high-efficiency solar cell, so the power generation efficiency is high. In a heavy Cloud, the sunlight cannot be concentrated on the high-efficiency solar cell, so a conventional HCPV cannot effectively generate electricity, but this design can still generate electricity by polycrystalline solar panels.
To estimate the power generation efficiency of our proposed hybrid high-concentration photovoltaic system under different weather conditions, we compared the power generation capacity of the conventional, high-concentration photovoltaic (HCPV) and hybrid HCPV power generation systems. First, we assume that the Fresnel lens area is about 163.8 cm 2. while the area of the III–V solar panel is 0.75 cm 2 so the area of the polycrystalline silicon solar panel is 163.05 cm 2. Since the photon conversion efficiencies are 15% and 45% for the PSSP and III-V compound semiconductors, we assume conversion efficiencies of α and 3α for a PSSP and an III-V solar panel, respectively. Based on the above assumption, we will calculate power generation for different solar cells under various Cloud conditions.
The first is the clear sky scenario referred to in the conditions of Fig. 5a. For simplicity, we assume that the ground illumination is 100,000 lx. Therefore, the power generation of a PSSP in a clear sky can be calculated
The measurement shown in Fig. 5a indicates that the light leakage under the Fresnel lens is 40% of the ground illuminance without the Fresnel lens. We assume that the optical flux at the focusing area of the HCPV is the rest power transmitted through the Fresnel lens where there is an additional 10% of Fresnel loss. The power generation of the HCPV (PHCPV) and the hybrid HCPV (Phybrid) can be respectively written
Equations (3) and (4) indicate that the hybrid HCPV could reserve 40% power leakage under the sunlight in a clear sky, and finally reaches around twice the power generation of a PSSP, as shown in the blue bars in Fig. 6b.
For the next, we discuss the case of heavy-Cloud days referred to the conditions of Fig. 5c. Here, we assume that the illuminance on the ground is 20% of that under the clear sky, i.e., 20,000 lx or 0.2PPSSP. Therefore, the power generation of the PSSP is about 0.2 PPSSP. From Fig. 5c, the light leakage of the Fresnel lens is set at 80%, so the power generation in the light leakage area is around 0.16 PPSSP. In such conditions, there is no prominent focusing spot at the tightened III-V solar cell, as shown in Fig. 3d, so the power generation of the HCPV can be calculated around PPSSP/400. It means that the HCPV suffers from the heavy Cloud in the sky and has no function under such a condition. However, the hybrid HCPV can still reserve 80% of the sunlight owing to light leakage, and the total power generation is around 0.16 PPSSP, as shown in the grey bars in Fig. 6b. As a result, the hybrid HCPV acts better than an HCPV in a clear sky and like a PSSP in a heavy-Cloud sky.
The comparison of the power generation ratio of different solar photovoltaic devices is summarized, as shown in Fig. 6b. The calculation results show that a hybrid HCPV generates more electricity than an HCPV in all scenarios by collecting the leakage light of the Fresnel lens, and power generation is close to that of a PSSP on heavy cloudy days when an HCPV losses its function. The proposed hybrid HCPV is a new design that can improve power generation efficiency and adapt to various Cloud conditions.
Conclusion
In this paper, we started with the theoretical and practical studies of a Fresnel lens and analyzed the inherent light leakage characteristic when using a Fresnel lens as a focusing lens. We pointed out that the light leakage is also caused by Cloud scattering, which is an unavoidable factor for an HCPV. Then a series of experiments were done with the corresponding calculations to prove the light leakage mechanism, including from the Fresnel lens and the clouds. The corresponding field measurement with the use of a Fresnel lens to FOCUS the sunlight was done for six months for various Cloud sky conditions.
According to the acquired results, the most valuable finding was that the solar concentrator based on the Fresnel lens has an illuminance of about 20,000–40,000 lx in the light leakage region, whether it is a sunny day or a cloudy day with different Cloud thicknesses. This is an inherent characteristic of HCPV based on the Fresnel lens and the national sunlight characteristics. Such a property could be helpful in solar power factories with agricultural benefits.
This finding prompted us to propose a hybrid high-concentration solar module in which more cost-effective PSSPs are placed around the high-efficiency wafer of HCPV to capture the dissipated light leakage and convert it into usable electricity. Such a system may exhibit extremely high conversion efficiency under different Cloud conditions. Under the assumption that the conversion efficiencies are 15% and 45% of the PSSP and III–V compound semiconductors, respectively, the proposed hybrid system could reach 190% and 126% power generation efficiency compared with PSSP and HCPV systems, respectively, in the clear sky. When there are heavy clouds, the HCPV system has almost no power generation efficiency, while the proposed hybrid system can maintain more than 80% of the power generation efficiency of the PSSP system. Thus the proposed novel solar power system is useful for reaching optimal solar power generation under different cloudy skies.
Data availability
All datasets from this study are available from the corresponding author upon reasonable request.
Acknowledgements
The author would like to thank Breault Research Organization (BRO), Inc. for sponsoring the ASAP software program. In addition, the authors would like to thank the Fudan High School (Taoyuan) for its support of field measurement. The research was sponsored by the National Council of Science and Technology in Taiwan with grant no. MOST 111-2218-E-008-004 –MBK and MOST 111-2221-E-008.028.MY3.
Author information
Authors and Affiliations
- Department of Photonics, College of Electrical and Computer Engineering, National Yang Ming Chiao Tung University, Hsinchu, 30010, Taiwan Chi Sun Tsung Sheng Kao
- Department of Optics and Photonics, National Central University, Jhongli, Taoyuan, 32001, Taiwan Chi-Shou Wu, Yong-Sheng Lin, Shuo-Ting Fang, Yao-Hsuan Chiu Ching-Cherng Sun
- Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu, 30010, Taiwan Ching-Cherng Sun
Compared: Grid-tied, off-grid, and hybrid solar systems
There are three types of solar panel systems: grid-tied (on-grid), off-grid, and hybrid solar systems.
Each type of system has a unique setup that affects what equipment is used, the complexity of installation, and, most crucially, your potential costs and savings.
What would be the best in your situation? Let’s take a closer look at the benefits and downsides of grid-tied, off-grid and hybrid solar systems.
Calculate the price of solar panel installation on your home
Grid-tied solar systems
Grid-tied, on-grid, utility-interactive, grid intertie, and grid backfeeding are all terms used to describe the same concept – a solar system that is connected to the utility power grid.
DC electricity generated by the solar panels is sent to the inverter, which converts the power into AC electricity. This electricity is first used to service the home loads, while all surplus energy is exported to the grid in return for electric bill credits.
Benefits of grid-tied systems
A grid connection will allow you to save more money with solar panels through net metering, lower equipment and installation costs, and better efficiency rates.
Save more money with net metering
Your solar panels will often generate more electricity than what you are capable of consuming. With net metering, homeowners can put this excess electricity onto the utility grid instead of storing it themselves with batteries.
Many utility companies are committed to buying electricity from homeowners at the same rate as they sell it themselves. As a homeowner, you can use these payments from your utility to cancel out your electricity usage charges. by up to 100%.
Net metering plays an important role in how solar power is incentivized. Without it, residential solar systems would be much less feasible from a financial point of view.
Lower upfront costs and ease of installation
Grid-tied solar systems are the only type of solar system that don’t require a battery to function. This makes grid-tied systems cheaper and simpler to install, and also means there is less maintenance required.
You can use the utility grid as a virtual battery
The electric power grid is in many ways also a battery, without the need for maintenance or replacements, and with much better efficiency rates.
According to EIA data, national, annual electricity transmission and distribution losses average about 7% of the electricity that is transmitted in the United States. Lead-acid batteries, which are commonly used with solar panels, are only 80-90% efficient at storing energy, and their performance degrades with time. In other words, more electricity (and more money) goes to waste with conventional battery systems.
Additional perks of being grid-tied include access to backup power from the utility grid, in case your solar system stops generating electricity for one reason or another. At the same time, you help to mitigate the utility company`s peak load. As a result, the efficiency of our electrical system as a whole goes up.
Equipment for grid-tied solar systems
There are a few key differences between the equipment needed for grid-tied, off-grid and hybrid solar systems. Standard grid-tied solar systems rely on the following components:
Grid-tie inverter (GTI)
What is the job of a solar inverter? They regulate the voltage and current received from your solar panels. Direct current (DC) from your solar panels is converted into alternating current (AC), which is the type of current that is utilized by the majority of electrical appliances.
In addition to this, grid-tie inverters, also known as grid-interactive or synchronous inverters, synchronize the phase and frequency of the current to fit the utility grid (nominally 60Hz). The output voltage is also adjusted slightly higher than the grid voltage in order for excess electricity to flow outwards to the grid.
Microinverters
Microinverters go on the back of each solar panel, as opposed to one central inverter that typically takes on the entire solar array.
Microinverters are certainly more expensive, but in many cases yield higher efficiency rates. Microinverters are particularly useful if you have shading issues on your roof.
Power meter
Most homeowners will need to replace their current power meter with one that is compatible with net metering. This device, often called a net meter or a two-way meter, is capable of measuring power going in both directions, from the grid to your house and vice versa.
You should consult with your local utility company and see what net metering options you have. In some places, the utility company issues a power meter for free and pays full price for the electricity you generate; however, this is not always the case.
See how much a grid-tied solar system can save you annually
Off-grid solar systems
An off-grid solar system (off-the-grid, standalone) is the obvious alternative to one that is grid-tied.
For homeowners that have access to the grid, off-grid solar systems are usually out of question. Here’s why. To ensure access to electricity at all times, off-grid solar systems require high-capacity battery storage and a backup generator. On top of this, a battery bank typically needs to be replaced after 10 years. Batteries are complicated, expensive, and decrease overall system efficiency.
Off-grid systems require large amounts of energy storage as there is no option to import power from the electric grid. As such, they are typically designed using lead-acid batteries, which are a much cheaper alternative to newer (and more efficient) lithium-based solar batteries.
Can be installed where there is no access to the utility grid
Off-grid solar systems can be cheaper than extending power lines in certain remote areas.
Consider off-grid if you’re mor e than 100 yards from the grid. The costs of overhead transmission lines range from 174,000 per mile (for rural construction) to 11,000,000 per mile (for urban construction).
Become energy self-sufficient
Living off the grid and being self-sufficient feels good. For some people, this feeling is worth more than saving money.
Energy self-sufficiency is also a form of security. Power failures on the utility grid do not affect off-grid solar systems.
On the flip side, batteries can only store a certain amount of energy, and during cloudy times, being connected to the grid is actually where the security is. You should install a backup generator to be prepared for these kinds of situations.
Equipment for off-grid solar systems
Typical off-grid solar systems require the following extra components:
- Solar charge controller
- Battery bank
- DC disconnect (additional)
- Off-grid inverter
- Backup generator (optional)
Solar charge controller
Solar charge controllers are also known as charge regulators, or just battery regulators. The last term is probably the best to describe what this device actually does: solar battery chargers limit the rate of current being delivered to the battery bank, and protect the batteries from overcharging.
Good charge controllers are crucial for keeping the batteries healthy, which ensures the lifetime of a battery bank is maximized. If you have a battery-based inverter, chances are that the charge controller is integrated.
Battery bank
Without a battery bank (or a generator), it’ll be lights out by sunset. A battery bank is essentially a group of batteries wired together.
DC disconnect switch
AC and DC safety disconnects are required for all solar systems.
For off-grid solar systems, one additional DC disconnect is installed between the battery bank and the off-grid inverter. It is used to switch off the current flowing between these components. This is important for maintenance, troubleshooting and protection against electrical fires.
Off-grid inverter
There’s no need for an inverter if you`re only setting up solar panels for your boat, your RV, or something else that runs on DC current. You will need an inverter to convert DC to AC for all other electrical appliances.
Off-grid inverters do not have to match phase with the utility sine wave as opposed to grid-tie inverters. Electrical current flows from the solar panels through the solar charge controller and the bank battery bank, before it is finally converted into AC by the off-grid inverter.
Backup generator
It takes a lot of money and big batteries to prepare for several consecutive days without the sun shining (or access to the grid). This is where backup generators come in.
In most cases, installing a backup generator that runs on diesel is a better choice than investing in an oversized battery bank that seldom gets to operate at its full potential. Generators can run on propane, petroleum, gasoline, and many other fuel types.
Backup generators typically output AC, which can be sent through the inverter for direct use, or it can be converted into DC for battery storage.
Hybrid solar systems
Hybrid solar systems combine the best of grid-tied and off-grid solar systems. These systems can either be described as off-grid solar with utility backup power, or grid-tied solar with extra battery storage.
If you own a grid-tied solar system and drive a vehicle that runs on electricity, you already kind of have a hybrid setup. The electrical vehicle is really just a battery with wheels.
In a hybrid solar system, energy generated from the solar panels is first used to service the home’s electrical loads (flow #1). After the home’s energy needs have been supplied, solar power is used to charge the solar battery (flow #2). If there is still a surplus of solar energy, it will be exported to the electric grid in return for credits (flow #3). The system pictured above shows an AC-coupled lithium battery, but hybrid systems can also be designed using either lithium or lead-acid-based DC batteries.
Less expensive than off-grid solar systems
Hybrid solar systems are less expensive than off-grid solar systems. You don’t really need a backup generator, and the capacity of your battery bank can be downsized.
If your battery runs out of charge at night, you can simply buy off-peak electricity from the utility company. This will be much cheaper than operating a generator.
Smart solar holds a lot of promise
The introduction of hybrid solar systems has opened up many interesting innovations. New inverters let homeowners take advantage of changes in the utility electricity rates throughout the day.
Solar panels happen to output the most electrical power at noon – not long before the price of electricity peaks. Your home and electrical vehicle can be programmed to consume power during off-peak hours (or from your solar panels).
Consequently, you can temporarily store whatever excess electricity your solar panels generate in your batteries, and put it on the utility grid when you are paid the most for every kWh.
Smart solar holds a lot of promise. The concept will become increasingly important as we transition toward the Smart grid in the coming years.
Equipment for hybrid solar systems
Typical hybrid solar systems are based on the following additional components:
- Charge controller
- Battery bank
- DC disconnect (additional)
- Battery-based grid-tie inverter
- Power meter
Battery-based grid-tie inverter
Hybrid solar systems utilize battery-based grid-tie inverters, which are also known simply as hybrid inverters. These devices can draw electrical power to and from battery banks, as well as synchronize with the utility grid.
Final thoughts on grid-tied solar systems
The bottom line is this: Right now, for the vast majority of homeowners, tapping the utility grid for electricity and energy storage is significantly cheaper and more practical than using battery banks and/or backup generators.
Hybrid Solar Energy Systems
What is a hybrid solar energy system, and might it be the right option for you?
Most homeowners who choose solar elect to install grid-tied photovoltaic arrays. A second option, although less common, involves going off-grid with a battery bank. Although you may not know it, you have a third option to consider, and it combines the best aspects of on- and off-grid solar.
How Does Hybrid Solar Work?
A hybrid solar power system gives you the best of both grid-tied and off-grid worlds.
This type of PV system is connected to the utility grid, just like a standard grid-tied system, so you will always have power at night and on cloudy days.
But a traditional grid-tied PV system will stop working if the power grid goes down. When a blackout occurs, the photovoltaic system is programmed to automatically shut off for safety reasons. This allows utility workers to safely make repairs without power in the lines.
Hybrid systems solve this problem with the addition of a solar battery bank, and in some cases, a backup generator.
Why Should You Consider a Hybrid PV System?
Blackouts are on the rise, and the Intermountain West could be affected at any time. If the grid has a significant problem, you could be in the dark for days — or longer.
Installing a hybrid solar power system is a great way to prepare for any unexpected event. If a severe storm or natural disaster strikes your area, you won’t be left without electricity — unlike most of your neighbors.
Which Type of Hybrid Solar Power System Is Best?
Hybrid systems are not one-size-fits-all. They come in a range of sizes and configurations to meet your specific home energy needs.
Smaller, less expensive systems can keep your home powered up during short blackouts. For power outages that last longer, small hybrid systems will provide enough electricity for a day or two, as long as you limit your consumption to running only the most critical appliances.
If you want to make sure that your entire home has power no matter how long an outage lasts, you’ll need more solar panels and a larger battery bank.
The best type of hybrid system is one that is designed to meet your needs and objectives. Consulting with a professional photovoltaic contractor is the easiest way to determine the ideal size and configuration of your home solar energy system.
The professional team at Intermountain Wind Solar offers free photovoltaic energy consultations to homeowners and businesses throughout Idaho, Utah, Colorado, Wyoming and Nevada. Contact us today to learn more and to determine if a hybrid solar energy system is right for you.
Hybrid wind-solar power system for residential applications
Dutch startup Airturb has developed a 500 W hybrid wind-solar power system featuring a vertical axis wind turbine and a solar base hosting four 30 W solar panels. The system can be used for rooftop or off-grid applications.
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Netherlands-based startup Airturb has developed a 500 W hybrid wind-solar power system that can be used for residential or off-grid applications.
“The system consists of a vertical axis wind turbine with a modified helical Savonius shape and a base with four monocrystalline panels,” CEO Serkan Kilic told pv magazine.”It has a roof load of 131 kg/m2.”
The solar base consists of a structure made of galvanized steel and rubber. It measures 1.14 m x 1.14 m x 20 mm and weighs 35 kg. It can host four solar panels with power outputs of 30 W each. It includes four Eco Line ES30M36 modules from Germany-based Enjoy Solar.
“The base can also host other types of solar panels,” said Kilic.
The small wind turbine measures 1.8 m x 1.14 m x 1.14 m and weighs 70 kg. It has a ballast weight ranging from 70 kg to 100 kg and can operate with a temperature ranging from.25 C to 60 C. Every panel is made with glass fiber reinforced polyester, weighs 1.5 kg, and measures 1.5 m x 0.7 m x 1.5 mm.
The wind power system also includes a 300 W axial flux PMS alternator (PM SA) that converts the mechanical energy into electrical energycharacterized as a three-phase alternating current. The hybrid system features a DualVolt Hybrid Inverter with an output of 500 W.
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“It is engineered, developed, and manufactured by Airturb,” Kilic said.
The device measures 540 mm x 430 mm x 139 mm and weighs 25 kg. It must be placed separately on site, with a maximum distance to the system of 25 meters. Airturb offers the systems in two versions, with or without solar panels.
“Both models are pre – assembled by Airturb and delivered on-site by the installer,” Kilic said. “Currently, only the system including the base and solar panels are available. The system without the base and solar panels is being developed and we will offer it from the third quarter of this year.”
The complete package with the solar base and the DuoVolt wind inverter costs €4,235 (4,626), not including installation costs, according to the company’s website.
“The system is engineered, designed, and developed in The Netherlands, manufactured in Turkey and assembled in The Netherlands,” said Kilic.
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Emiliano Bellini
Emiliano joined pv magazine in March 2017. He has been reporting on solar and renewable energy since 2009.