Techniques to Maximize Solar Panel Power Output
Two recent articles, Energy Harvesting With Low Power Solar Panels and Solar Battery Charger Maintains High Efficiency at Low Light, discuss how to efficiently harvest energy with low power solar panels. Both of these articles mention a concept known as maximum power, which in the context of solar panels is the ability to extract as much power as possible from the solar panel without collapsing the panel voltage. When discussing solar panels and power, terms such as Maximum Power Point Tracking (MPPT) and Maximum Power Point Control (MPPC) are often used. Let’s look into the definition and meaning of these terms in more detail.
As can be seen in Figure 1, the output current of a solar panel varies nonlinearly with the panel voltage. Under short-circuit conditions the output power is zero since the output voltage is zero. Under open-circuit conditions the output power is zero since the output current is zero. Most solar panel manufacturers will specify the panel voltage at maximum power (VMP). This voltage is typically around 70 – 80% of the panel’s open circuit voltage (VOC).In Figure 1 the maximum power is just under 140W with VMP just under 32V and IMP just under 4.5A.
Ideally, any system using a solar panel would operate that panel at its maximum power output. This is particularly true of a solar powered battery charger, where the goal, presumably, is to capture and store as much solar energy as possible in as little time as possible. Put another way, since we cannot predict the availability or intensity of solar power, we need to harness as much energy as possible while energy is available.
There are many different ways to try to operate a solar panel at its maximum power point. One of the simplest is to connect a battery to the solar panel through a diode. This technique is described here in the article Energy Harvesting With Low Power Solar Panels. It relies on matching the maximum power output voltage of the panel to the relatively narrow voltage range of the battery. When available power levels are very low (approximately less than a few tens of milliwatts), this may be the best approach.
The opposite end of the spectrum is an approach that implements a complete Maximum Power Point Tracking (MPPT) algorithm. There are a variety of MPPT algorithms, but most will have some ability to sweep the entire operating range of the solar panel to find where maximum power is produced. The LT8490 and LTC4015 are examples of integrated circuits that perform this function. The advantage of a full MPPT algorithm is that it can differentiate a local power peak from a global power maximum. In multi-cell solar panels, it is possible to have more than one power peak during partial shading conditions (see Figure 2). Typically, a full MPPT algorithm is required to find the true maximum power operating point. It does so by periodically sweeping the entire output range of the solar panel and remembering the operating conditions where maximum power was achieved. When the sweep is complete, the circuitry forces the panel to return to its maximum power point. In between these periodic sweeps, the MPPT algorithm will continuously dither the operating point to ensure that it operates at the peak.
An intermediate approach is something that Linear Technology calls Maximum Power Point Control (MPPC). This technique takes advantage of the fact that the maximum power voltage (VMP) of a solar panel does not, typically, vary much as the amount of incident light changes (see Solar Battery Charger Maintains High Efficiency in Low Light for more information). Therefore, a simple circuit can force the panel to operate at a fixed voltage and approximate maximum power operation. A voltage divider is used to measure the panel voltage and if the input voltage falls below the programmed level, the load on the panel is reduced until it can maintain the programmed voltage level. Products with this functionality include the LTC3105, LTC3129, LT3652(HV), LTC4000-1, and LTC4020. Note that the LT3652 and LT3652HV datasheet refer to MPPT rather than MPPC, but this is largely because Linear Technology had not come up with the MPPC terminology when the LT3652 product was released.
A final note about MPPC and the LTC3105 – the LTC3105 is a boost converter that can start up at the exceedingly low voltage of 0.25V. This makes the LTC3105 particularly well suited for boosting the output voltage of a “1S” solar panel (i.e. a solar panel whose output voltage is that of a single photovoltaic cell, even if the panel has many photovoltaic cells in parallel). With a 1S solar panel, there will be only one maximum power point – it is not possible to have multiple power peaks. In this scenario, differentiating between multiple maxima is not necessary.
In summary, many different ways of operating a solar panel at its maximum output operating condition exist. The panel can be connected to a battery (through a diode) whose voltage range is close to the maximum power voltage of the panel. A full MPPT algorithm, including periodic global sweeps to find the global maximum and a continuous dither to remain at that maximum (an example is the LT8490), can be used. Other products implement an input voltage regulation technique (MPPC) to operate a solar panel at a fixed operating voltage including the LTC3105, LTC3129, LT3652(HV), LTC4000-1 and the LTC4020. In the coming months, Linear Technology will introduce yet another technique for operating a solar panel at its maximum power point. Stay tuned!
Author
Trevor Barcelo has over 15 years of experience at Linear Technology as an analog IC design engineer, design manager and product line manager. He began his career at Linear Technology’s headquarters in Milpitas, CA by designing the LTC1733 Lithium-ion battery charger. After moving to the company’s Boston Design Center, he continued designing battery chargers and USB power managers including the LTC4053, LTC4066 and LTC4089. He holds five patents related to power management. He currently defines battery charging, power management and wireless power products while managing a team of design engineers developing those products.
Trevor received an M.S. in Electrical Engineering from Stanford University and a B.A. in Physics from Harvard University.
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How Much Electricity Does a Solar Panel Produce?
In one year, the sun sends an immense amount of energy to our planet, around 222,500,000 terawatt hours [1]. This is more energy than we could ever hope to use, and it represents a vast potential for the solar power. However, to harness this energy, we need to convert it into usable electricity.
The efficiency of this conversion is a critical factor that affects the amount of solar energy we are able to harvest for our use.
Solar panels as devices that convert sunlight into electricity by the photovoltaic effect are the tool that should make this potent source of energy available to us. But the most efficient solar panels on the market today have a maximum efficiency of around 22 percent, meaning they can convert up to 22 percent of the energy from the sun that falls on them into usable electricity [2].
The twist is that most solar arrays you see around reach only up to 18 percent efficiency. This means that, even with the best technology available, we are only able to convert a fraction of the sun’s energy into electricity.
Understanding how much electricity does a solar panel produce is essential to predicting the monthly output of a solar system. This information helps when designing and installing solar systems that should provide sufficient electricity to meet a household’s needs.
So even though, solar energy is free and abundant, there is still a lot of space for improvement when it comes to our ability of harnessing it, and efficiency of solar panels is just one of the limiting factors on the way.
How much electricity does a solar panel produce per day?
The energy output of a solar panel varies based on the size of the panel you have, maximum efficiency and output rating in watts.
Solar panels are commonly evaluated according to the amount of direct current power they generate under standard test conditions. This power output is measured in watts and represents the panel’s potential to produce electricity under ideal sunlight and temperature conditions. Ideal conditions mean a temperature of 25 degrees Celsius or 77 degrees Fahrenheit and unobstructed sunlight hitting the whole surface of a solar panel.
The test temperature represents the average temperature during the solar peak hours of the spring and autumn in the continental United States. The problem is that in real life you have rarely the ideal conditions, so the values will differ.
Most residential solar panels have power output ratings ranging from 250 to 400 watts. This rating affects the total cost of a solar system. Premium solar panels with higher wattage produce more energy but also cost more than the lower rated ones, since the price for solar panels is calculated per watt.
The size of solar panels affects the final power output as well. Larger solar panels (with 72 solar cells) produce more energy than the 60-cell ones, assuming they receive the same amount of sunlight.
The 72-cell panels usually carry higher rating of 300 to 400 watts. Higher energy output simply correlates with the number of solar cells. solar cells mean more energy produced. However, in most residential application, the smaller solar panels with 60 cells are used.
And similarly, solar panels with higher efficiency rating convert more of the sunlight their solar cells receive into usable electricity, resulting in higher energy output. Monocrystalline solar panels still represent the most efficient option for homeowners on the market.
How to calculate the average solar panel output?
How much energy does one solar panel produce in a day also depends on environmental factors like the amount of unobstructed sunlight in a day.
An average solar panel with efficiency of 18 percent usually produces around 250 to 300 watts of power under ideal conditions. In reality, the actual output varies depending on the amount of sunlight available.
To estimate the expected energy output of a solar panel, we can use a simple formula that takes into account the wattage of a solar panel and the amount of sunlight it receives. This formula is as follows:
For example, if we have a 250-watt solar panel and it receives 5 hours of sunlight per day, the expected energy output would be:
Energy output = 250 watts x 5 hours = 1,250 watt-hours per day or 1.250 kilowatt-hours
How many hours of sunlight a solar panel receives is a crucial factor in determining its energy output. The intensity of sunlight varies depending on the location, time of day, and season. In such a large country like the United States, this significantly differs from one region to another.
According to the National Renewable Energy Laboratory (NREL) report, the amount of sunlight received per day can range from around 2.5 to 7.5 kilowatt-hours (kWh) per square meter, depending on the location [3]. This means that a solar panel in sunny Arizona will produce on most days more energy than a panel in Seattle.
You can find a good data on the solar potential for your location in the Global Solar Atlas.
What environmental factors affect total energy output of solar panels?
Although each solar panel has slightly different technical characteristics, there are some environmental factors that affect the total electricity output of every panel. It is good to know them if you want to make sure that you are getting the best of your solar system.
#1 Direction
The position of panels on the roof is crucial. In the northern hemisphere, panels should face south, eventually south-west or south-east, to achieve the best outcome. In the southern hemisphere, it is the other way around.
#2 Roof angle and tilt
Since the most affordable method is to mount panels on the roof, the angle depends on the pitch of your roof. Although, to maximize panels’ output, you can get adjustable installation, where you are able to tilt the panel according to the season.
The basic rule to determine the proper angle is to tilt the panel by 15 degrees more vertically from the starting position in winter and by 15 degrees more horizontally in summer. For example, panels in New York City should be tilted at an angle of around 40 degrees to maximize energy output [4].
#3 Geographical location
Your geographical location determines how much sunlight throughout different seasons your solar system gets. Cloudy or overcast days will result in lower energy output compared to clear, sunny days. The same panel will generate more electricity in California than in Seattle, because Seattle gets generally more cloudy days.
A rule of thumb is to avoid shading as much as possible. A commonly used solar panel consists of 60 solar cells. When just 4 solar cells out of these 60 are in shade, the energy production might decrease by 10 percent [4]. Shade on some cells makes other cells work excessively, and thus decreases the lifetime of the solar panel.
#5 Maintenance
Dust blocks sunlight accessing the panel in a similar way like shade. According to the recent study, the efficiency might drop by up to 25 percent due to the dust. To achieve the best performance, a regular cleaning of panels has to make it to the top of your list of household chores.
#6 Temperature
Solar panels convert the energy of light (not heat) into electricity. Panels are tested under “ideal” conditions, which is in terms of temperature 25 degrees Celsius or 77 degrees Fahrenheit. But when temperature increases by one degree Celsius, panels lose efficiency by approximately 0.4 percent [2]. Colder temperatures are more desirable because cold materials conduct electricity better. The only problem in colder climates is reduced number of sunny days.
It might seem like a lot to take into consideration, but the truth is that the above-mentioned factors are just a common sense combined with physics. Therefore, it should not be such a surprise that either one of these factors or their combination can compromise the production capacity of photovoltaic solar panels that need direct exposure to the Sun.
How much power does a solar panel produce for my direct consumption?
An average quality residential solar panel produces between 250 to 270 watts under ideal sunlight and temperature conditions. Such panel consists of 60 solar cells. One solar cell generates 5 watts, with the efficiency between 15 to 20 percent. The size of the panel in this case is around 65 inches in length and 40 inches in width.
But you can have also good quality solar panels generating as much as 400 watts. You should know, though, that panels with higher output are more expensive and are usually installed when free space is a limiting factor.
On the back of each panel is a number stating the maximum power rating. This number expresses the direct current produced under standard test conditions. Since solar panels produce direct current and our houses run off alternating current, the generated power needs to be converted. During the conversion, further energy losses occur. The losses make around 20 percent [7].
This means that from direct current produced by solar panels we get 80 percent of alternating current for our use. So, if you want to calculate how many solar panels are needed to cover your household energy needs, you have to take this number into consideration.
For example, you need 5 kilowatts (kW) of alternating current in total. 5 kilowatts have to be divided by 0.8 (as 80 percent efficiency during conversion). The final number you get is 6.25 kW of direct current, which equals 25 panels of 250 watts (6,250 divided by 250 watts equals 25 panels) or 20 panels with higher rating of 325 watts.
Both systems generate the same amount of power, your choice depends only on the available space and money you want to invest, because the 325-watt panels cost more.
The energy produced by a solar system in a day
The expected energy output of a whole solar system is calculated by summing the energy output of all the panels in the system.
Our example, a 5-kilowatt solar system consisting of 25 panels rated at 250 watts each, would have an expected energy output of:
Energy Output = 250 watts x 5 hours of sunlight x 25 panels = 31,250 watt-hours per day, or 31.250 kWh per day
This is enough energy to power a typical American household for a day, assuming an average energy consumption of around 30 kWh per day [5].
Now that you know how much solar electricity you can expect one solar panel to produce and how much a whole system can produce, you might be wondering about the cost savings that solar panels can bring.
If you are considering getting solar and would like a rough estimate of the cost and savings of installing a solar system, you can use this solar calculator. The calculator will provide you with an upfront cost estimate and an estimate of long-term savings based on your location. Once you have a better idea of the potential savings, you can begin to explore your solar options in more detail and get real solar quotes from local installers.
What is solar panel efficiency and how does it affect your system’s performance?
Solar panels are an amazing technological achievement. They have no moving parts, they are very safe to operate and, if correctly installed, they can provide clean electricity for decades.
For most consumers, a particularly confusing aspect of solar panels is the term efficiency and what it actually means for the success of their solar investment.
Simply put, efficiency is the ratio that measures how much of the incoming sunlight is converted to electrical output by your solar panels. For example, if 100 Watts of sunlight falls on the panels, and 15 Watts of electricity comes out, the efficiency is 15%. Most solar panels in the market have efficiencies in the range of 10-15%.
Why do we lose efficiency when we package solar cells?
Building blocks of a solar array
The building block of any solar panel is a solar cell. The solar cell is a type of semiconductor that generates electrical power when illuminated by sunlight using the photovoltaic (PV) principle. When we package together a whole bunch of solar cells we get a PV module, a fancy industry term that simply means a small solar panel. Joining multiple modules gives us a bigger solar panel. A typical solar installation includes many of these panels strung together in the form of a PV array.
Why is this all important to understand the efficiency of solar panels? Well, because at each step of this packaging and installation process, we lose a bit of efficiency. For example, if you purchase solar panels that are made up of solar cells with 15% efficiency, the panel itself will have a slightly less efficiency (due to the spacing between the solar cells). If these solar panels are installed on your rooftop as a PV array, the resulting efficiency will be even less than the average panel efficiency due to electrical losses, shading and other factors.
What is the most efficient solar panel today?
Since the invention of the photovoltaic principle in the 19th century, the efficiency of solar panels has been increasing dramatically. In the 1950s, researchers at Bell Laboratories produced solar cells with 6% efficiency. In the 1970s and 1980s, researchers experimenting with different types of materials and production techniques gradually increased the level of efficiency. Today, the most efficient solar cells have around 40% efficiency and researchers around the world are working hard to push this level even higher. Unfortunately, most commercially available solar panels are significantly below this record level of efficiency, but there is no doubt that future solar energy systems will be built using higher efficiency solar cells.
Evolution of solar cell efficiencies as of December 2015 (source: NREL). Please click to enlarge.
What is multi-junction technology?
Solar cells are manufactured using different semiconductor materials. Each material can harvest a specific portion of the solar radiation spectrum. By overlaying cells made of different materials, we can increase the total amount of radiation that can be captured. As the sunlight passes through multiple layers of cells, each one optimized to absorb a certain wavelength of light, the overall efficiency can be increased drastically. Today, best performing traditional silicon solar cells have efficiencies around 25% (blue lines in the above chart), while multi-junction cells have surpassed the 40% level (purple lines). This sounds great, but increased efficiency comes at a price: multi-junction cells are much more complex and, as a result, more expensive than traditional solar cells.
Why do solar panels lose efficiency (degrade) over time?
A study performed by NREL revealed that the output of solar panels decreases by 0.5% to 0.8% every year. This is mainly due to the exposure of the panels to the elements, and in very arid climates, intense ultraviolet rays increase the level of degradation. Therefore, over the expected lifetime of a solar panel (20-25 years), it is natural that the efficiency will gradually decrease.
Should I buy the most efficient solar panels on the market?
Increased efficiency means higher output per unit area of solar panels. Thus, if you have two brands of solar panels with the exact same dimensions, the one with the higher efficiency will generate more electricity. Alternatively, the two brands may have the same power rating, but the higher efficiency panel would be smaller, an important consideration for certain solar energy applications.
Although it is tempting to invest in the most efficient solar panels, this may not necessarily be the best investment decision. Some of the more efficient solar panels are billed as premium products with a higher price tag. If you have limited roof space, or you are interested in a specialty application such as solar energy for your boat or your cabin, then a higher efficiency panel may indeed be the best choice. On the other hand, if you have ample roof space, then the reliability of the panels and the price should be the main drivers of your decision.
If you are considering your solar panel options, why not take them for a spin using WhatNextNow Solar GO? Our free tools will help you test drive different solar energy options at your location and give you a much better idea about how much electricity you can generate. And please remember that you are in this for the long-haul. A reliable panel purchased at a good price point can be your best solar investment, even if it’s not the most efficient model on the market.
Which are the factors that affect solar panels’ efficiency?
Solar power systems are considered a key tool in the energy supply for the present and future generations. Several factors have promoted the development of photovoltaics such as environmental concerns, incentives and tax deductions, a more performing and less expensive technology and the need to replace carbon fossil energy systems with renewables to ensure compliance with the objectives set by the Paris COP y limit global warming to 1.5 ° C.
A solar cell or photovoltaic cell is a device that converts the sunlight into usable energy. The amount of sunlight that can be converted into electricity is referred to as solar cell efficiency. There are some factors that should be taken into consideration to guarantee the optimal efficiency of the solar panels.
Temperature
The temperature influences the efficiency of the photovoltaic cell due to the intrinsic characteristic of the semiconductor material. The efficiency of the solar panels increases when the temperature drops and decreases in high temperatures, as the voltage between the cells drops.
Energy Conversion Efficiency
The solar module has a different spectral response depending on the kind of the module. Therefore, the change of the spectral irradiance influences the solar power generation. The energy conversion efficiency is increased by reducing the reflection of the incident light.
Solar Shadings
Solar PV panels are very sensitive to solar shadings. Total or partial shading conditions have a significant impact rate on the capability of delivering energy and may result in lower output and power losses. Cells in a solar panel are usually connected in series to get a higher voltage and therefore an appropriate production of electricity.
But when shading occurs, this structure presents some limitations. In fact, when a single solar cell is shaded, the current of all the units in the string is determined by the unit that produces the least current. When a cell is shaded, the whole series is virtually shaded too. To prevent the loss of energy, the installation usually includes bypass diodes.
Bypass diodes are wired in parallel to the solar cells. When a solar cell is shaded, the bypass diode provides a current path that allows the string of connected solar cells to generate energy at a reduced voltage. Read more.
The Orientation, Inclination, Latitude of the place and Climatic conditions
The installation of the photovoltaic modules must take into account some factors to take full advantage of solar radiation: the orientation, the inclination, the latitude of the place, the climatic conditions. The correct consideration of these variants will help ensure that they produce maximum energy by being exposed to the greatest intensity of solar radiation for the longest period of time. Learn more.
Operation and Monitoring
OM services help with the management of the implementation of certain processes to avoid or mitigate potential hazards and to guarantee the optimal return on investment. Operations mainly consist of the remote monitoring and control of the PV power plant conditions and performance. Monitoring software provides access to all data collected, which can be used for different purposes: defect detection, performance analysis, improvement, predictive maintenance, and security. A good monitoring system will provide information on the production, alarms, and analytical data, in a timely, efficient, and precise manner to detect any anomaly of the PV plant. Continue reading.
Maintenance
Solar panels are very durable, main warranties last for 15-25 years. However, cleaning solar panels is important to maximize the amount of light available to turn into electrical power. Making frequent physical inspections can help solar panels absorbing light effectively.
archelios™ Suite
archelios™ Suite is a comprehensive software solution that offers a unique approach. Thanks to its advanced computational technology, archelios™ Suite adds value to the life-cycle of any PV project: feasibility and profitability study, simulation, calculation of producible energy, complete electrical sizing, operation, and monitoring.
The software is an efficient tool for any type of PV project.
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