If photovoltaic solar panels are made up of individual photovoltaic cells connected together, then the Solar Photovoltaic Array, also known simply as a Solar Array is a system made up of a group of solar panels connected together.
A photovoltaic array is therefore multiple solar panels electrically wired together to form a much larger PV installation (PV system) called an array, and in general the larger the total surface area of the array, the more solar electricity it will produce.
A complete photovoltaic system uses a photovoltaic array as the main source for the generation of the electrical power supply. The amount of solar power produced by a single photovoltaic panel or module is not enough for general use.
Most manufactures produce a standard photovoltaic panel with an output voltage of 12V or 24V. By connecting many single PV panels in series (for a higher voltage requirement) and in parallel (for a higher current requirement) the PV array will produce the desired power output.
A Photovoltaic Solar Array
Photovoltaic cells and panels convert the solar energy into direct-current (DC) electricity. The connection of the solar panels in a single photovoltaic array is same as that of the PV cells in a single panel.
The panels in an array can be electrically connected together in either a series, a parallel, or a mixture of the two, but generally a series connection is chosen to give an increased output voltage. For example, when two solar panels are wired together in series, their voltage is doubled while the current remains the same.
The size of a photovoltaic array can consist of a few individual PV modules or panels connected together in an urban environment and mounted on a rooftop, or may consist of many hundreds of PV panels interconnected together in a field to supply power for a whole town or neighbourhood. The flexibility of the modular photovoltaic array (PV system) allows designers to create solar power systems that can meet a wide variety of electrical needs, no matter how large or small.
It is important to note that photovoltaic panels or modules from different manufacturers should not be mixed together in a single array, even if their power, voltage or current outputs are nominally similar. This is because differences in the solar cell I-V characteristic curves as well as their spectral response are likely to cause additional mismatch losses within the array, thereby reducing its overall efficiency.
The Electrical Characteristics of a Photovoltaic Array
The electrical characteristics of a photovoltaic array are summarised in the relationship between the output current and voltage. The amount and intensity of solar insolation (solar irradiance) controls the amount of output current ( I ), and the operating temperature of the solar cells affects the output voltage ( V ) of the PV array. Photovoltaic panel ( I-V ) curves that summarise the relationship between the current and voltage are given by the manufacturers and are given as:
Solar Array Parameters
- VOC = open-circuit voltage: – This is the maximum voltage that the array provides when the terminals are not connected to any load (an open circuit condition). This value is much higher than Vmax which relates to the operation of the PV array which is fixed by the load. This value depends upon the number of PV panels connected together in series.
- ISC = short-circuit current – The maximum current provided by the PV array when the output connectors are shorted together (a short circuit condition). This value is much higher than Imax which relates to the normal operating circuit current.
- Pmax = maximum power point – This relates to the point where the power supplied by the array that is connected to the load (batteries, inverters) is at its maximum value, where Pmax = Imax x Vmax. The maximum power point of a photovoltaic array is measured in Watts (W) or peak Watts (Wp).
- FF = fill factor – The fill factor is the relationship between the maximum power that the array can actually provide under normal operating conditions and the product of the open-circuit voltage times the short-circuit current, ( Voc x Isc ) This fill factor value gives an idea of the quality of the array and the closer the fill factor is to 1 (unity), the more power the array can provide. Typical values are between 0.7 and 0.8.
- % eff = percent efficiency – The efficiency of a photovoltaic array is the ratio between the maximum electrical power that the array can produce compared to the amount of solar irradiance hitting the array. The efficiency of a typical solar array is normally low at around 10-12%, depending on the type of cells (monocrystalline, polycrystalline, amorphous or thin film) being used.
Photovoltaic I-V characteristics curves provide the information designers need to configure systems that can operate as close as possible to the maximum peak power point. The peak power point is measured as the PV module produces its maximum amount of power when exposed to solar radiation equivalent to 1000 watts per square metre, 1000 W/m 2 or 1kW/m 2. Consider the circuit below.
Photovoltaic Array Connections
This simple photovoltaic array above consists of four photovoltaic modules as shown, producing two parallel branches in which there are two PV panels that are electrically connected together to produce a series circuit. The output voltage from the array will therefore be equal to the series connection of the PV panels, and in our example above, this is calculated as: Vout = 12V 12V = 24 Volts.
The output current will be equal to the sum of the parallel branch currents. If we assume that each PV panel produces 3.75 amperes at full sun, the total current ( IT ) will be equal to: IT = 3.75A 3.75A = 7.5 Amperes. Then the maximum power of the photovoltaic array at full sun can be calculated as: Pout = V x I = 24 x 7.5 = 180W.
The PV array reaches its maximum of 180 watts in full sun because the maximum power output of each PV panel or module is equal to 45 watts (12V x 3.75A). However, due to different levels of solar radiation, temperature effect, electrical losses etc, the real maximum output power is usually a lot less than the calculated 180 watts. Then we can present our photovoltaic array characteristics as being.
Bypass Diodes in Photovoltaic Arrays
Photovoltaic cells and diodes are both semiconductor devices made from a P-type silicon material and a N-type silicon material fused together. Unlike a photovoltaic cell which generates a voltage when exposed to light, PN-junction diodes act like solid state one way electrical valve that only allows electrical current to flow through themselves in one direction only.
The advantage of this is that diodes can be used to block the flow of electric current from other parts of an electrical solar circuit. When used in a photovoltaic solar array, these types of silicon diodes are generally called Blocking Diodes.
In the previous tutorial about photovoltaic panels, we saw that a bypass diode can be used in parallel with either a single or a number of photovoltaic solar cells. The addition of a diode prevents current(s) flowing from a good and well-exposed PV cells, overheating and burning out weak or partially shaded PV cells by providing a current path around the bad cell. Blocking diodes are used differently than bypass diodes.
Bypass diodes are usually connected in “parallel” with a PV cell or panel to shunt the current around it, whereas blocking diodes are connected in “series” with the PV panels to prevent current flowing back into them. Blocking diodes are therefore different then bypass diodes although in most cases the diode is physically the same, but they are installed differently and serve a different purpose. Consider our photovoltaic solar array below.
Diodes in Photovoltaic Arrays
As we said earlier, diodes are devices that allow current to flow in one direction only. The diodes coloured green are the familiar bypass diodes, one in parallel with each PV panel to provide a low resistance path around the panel. However, the two diodes coloured red are referred to as the “blocking diodes”, one in series with each series branch. These blocking diodes ensure that the electrical current only flows OUT of the series array to the external load, controller or batteries.
The reason for this is to prevent the current generated by the other parallel connected PV panels in the same array flowing back through a weaker (shaded) network and also to prevent the fully charged batteries from discharging or draining back through the PV array at night. So when multiple PV panels are connected in parallel, blocking diodes should be used in each parallel connected branch.
Generally speaking, blocking diodes are used in PV arrays when there are two or more parallel branches or there is a possibility that some of the array will become partially shaded during the day as the sun moves across the sky. The size and type of blocking diode used depends upon the type of photovoltaic array. Two types of diodes are available for solar power arrays: the PN-junction silicon diode and the Schottky barrier diode. Both are available with a wide range of current ratings.
The Schottky barrier diode has a much lower forward voltage drop of about 0.4 volts as opposed to the PN diodes 0.7 volt drop for a silicon device. This lower voltage drop allows a savings of one full PV cell in each series branch of the solar array therefore, the array is more efficient since less power is dissipated in the blocking diode. Most manufacturers include blocking diodes within their PV modules simplifying the design.
Build your own Photovoltaic Array
The amount of solar radiation received and the daily energy demand are the two controlling factors in the design of the photovoltaic array and solar power systems. The photovoltaic array must be sized to meet the load demand and account for any system losses while the shading of any part of the solar array will significantly reduce the output of the entire system.
If the solar panels are electrically connected together in series, the current will be the same in each panel and if panels are partially shaded, they cannot produce the same amount of current. Also shaded PV panels will dissipate power and waste as heat rather than generate it and the use of bypass diodes will help prevent such problems by providing an alternative current path.
Blocking diodes are not required in a fully series connected system but should be used to prevent a reverse current flow from the batteries back to the array during the night or when the solar irradiance is low. Other climatic conditions apart from sunlight must be considered in any design.
Since the output voltage of silicon solar cell is a temperature related parameter, the designer must be aware of the prevailing daily temperatures, both extremes (high and low) and seasonal variations. In addition, rain and snowfall must be considered in the design of the mounting structure. Wind loading is especially important in mountain top installations.
In our next tutorial about “Solar Power”, we will look at how we can use semiconductor photovoltaic arrays and solar panels as part of a Stand Alone PV System to generate power for off-grid applications.
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- Standard Test Conditions
- Temperature Coefficient of a PV Cell
- Bypass Diode
- Solar Cell I-V Characteristic
- Photovoltaics Turning Photons into Electrons
- How Many Solar Cells Do I Need
- Photovoltaic Panel
- Photovoltaic Types
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Photovoltaic Modules (aka Solar Panels, Solar Electric Panels, or PV Modules)
PV modules are known as solar panels or solar electric panels. We’ll be using the terms interchangeably throughout this article although “PV module” is the more technically correct terminology.
Solar panels provide electricity from sunlight. They are typically made of silicon crystal slices called cells, glass, a polymer backing, and aluminum framing. Solar panels can vary in type, size, shape, and color. In most cases the “size” of a PV module refers to the panel’s rated output wattage or electricity generating potential. Solar panels also have voltage ratings. Those with of 12 or 24 Volts are generally preferred for off-grid systems with battery banks. Other solar panels come in less common nominal voltages such as 18, 42, and even 60 Volts. These modules are typically used in grid-tied applications to accommodate the working of grid-tied inverters. Solar panels can be used alone or combined into arrays by wiring them in or in to achieve the needed. The price of most large residential or commercial PV modules can range between 5000.20 and 3.40 per rated watt.
Balance of System (BOS)
In PV system terminology, everything besides the PV modules themselves is called “balance of system” or BOS. We’ll go over the main BOS components below, one at a time, in the direction of electricity flow through a typical system.
Solar panel mounting systems include hardware to permanently affix the array to either a roof, a pole, or the ground. These systems are typically made of aluminum and are selected based on the specific model and number of modules in the array as well as the desired physical configuration. Solar panels work best at cooler temperatures, and proper mounting allows for cooling airflow around the modules. For all locations, wind loading is an installation factor, and it is extremely important to design and pour the cement foundation properly for any pole mount. are a pole mount option to increase energy production by moving the array to face it into the sunlight as the sun moves across the sky. A solar array on a tracker will produce more energy than a fixed array. Trackers are often used in water pumping applications. The cost of a tracker can be significant, and due to the possibility of breakdown, they are best recommended to the mechanically inclined. The cost of a mounting system varies based on the number of modules and type of mount. The average cost is between 250 and 450,000 for a fixed array and 5000,000 and up for a solar tracker. Another cost-estimating factor for mounting racks is
A combiner box is an often-overlooked, yet essential part of most solar electric systems. The combiner box is an electrical enclosure which allows multiple of solar panels to be combined in parallel. For example, if you want to wire together two 12 Volt panels for your 12 Volt system, you will wire each panel’s output directly to terminals inside the combiner box. From the combiner box you can then run just one positive and one negative wire (in appropriate conduit) to the next system component, the charge controller. The combiner box will also house series string fuses or circuit breakers. These boxes are usually outdoor-rated, and meant for placement right next to the array or solar panels. Combiner boxes usually cost between 80 and 140 USD.
Every solar electric system with batteries should have a solar charge controller. A charge controller regulates the amount of current the PV modules feed into a battery bank. Their main function is to prevent overcharging of the batteries, but charge controllers also block battery bank current from leaking back into the photovoltaic array at night or on cloudy days, draining the battery bank.
The two main types are PWM (Pulse Width Modulated) and MPPT ( Maximum Power Point Tracking). PWM technology is older and more commonly used on smaller solar arrays. Choose a PWM charge controller that is the same as your solar array and battery bank. The controller must also have enough capacity (in rated Amps) to handle the total current of the solar array safely. MPPT charge controllers can track the maximum power point of a solar array and deliver 10-25% more power than a PWM controller could do for the same array. They do this by converting excess voltage into usable current. Another feature of MPPT charge controllers is their ability to accept higher voltage from the solar array for output to a lower voltage battery bank. Charge controllers typically cost between 50 and 750 depending on size, type and features.
.50 to 450.00 per rated array Watt.
Batteries for Solar Electric Systems
Batteries chemically store electrical energy in renewable energy systems. They come in many voltages, from 2V to 48V. The four types of batteries that are most common to RE systems are:
Flooded lead-acid batteries are the most cost-effective variety. They require maintenance that involves monitoring voltage, adding water, and occasional. Additionally, FLA batteries vent hydrogen under heavy charging so they must be stored in a ventilated enclosure. Because of the maintenance issues of FLAs, some people prefer sealed batteries, which don’t require maintenance. Since they are sealed, they do not require watering, nor do they typically vent any gasses. AGM batteries cost more and are more sensitive to overcharging than FLAs. Gel Cell batteries are similar to AGMs in that they are also sealed and therefore do not require maintenance, but tend to be the most expensive of the three types. The useful life of all battery types is measured in rather than units of time. is directly related to number of charge cycles possible: the deeper you drain batteries each time you use them, the fewer charge cycles you will get from them. Sealed batteries tend not to last as long as flooded batteries. Well-maintained FLAs can last as long as ten years, with sealed batteries lasting closer to five years. Other factors to keep in mind are that some of these batteries weigh over 200 pounds and, depending upon capacity, can cost anywhere from 20 to 1200 each. So, given the maintenance issues, weight and expense, consider your energy storage needs very carefully. Planning for five days of battery storage for your system may not be your best option!
An inverter takes (DC) from batteries and turns it into (AC) which is used to run most common electrical loads.
Off-grid inverters require batteries for storage. Straight grid-tied inverters don’t use batteries and grid-capable inverters can work either with or without batteries depending on system design. There is a wide range of available inverter features suited to differing system needs and situations. Some inverters have integrated AC chargers so that they can use AC power from the grid to charge the batteries during periods of low sun. Inverters with integrated AC chargers can also be used in conjunction with fossil fuel-based generators for battery charging or running very large loads. Off-grid inverters meant for whole-home usage must have appropriate conduit boxes and accessories that enclose all live wiring. Usually, whole-home inverters are rated to produce 2,000 Watts continuous power or more. Off-grid inverters come in two flavors: those producing current and those producing current. Some appliances (compressors or other inductive loads) and many sensitive electronics (cordless battery chargers, computers, stereos, etc.) will not function properly on modified sine wave power. Off-grid inverters can cost anywhere between 100 to 3,000 depending on size and type.
A straight grid-tied inverter connects directly to the utility grid without the use of batteries. With these inverters, when the grid goes down the PV system also goes down to protect service linemen from injury due to unexpected “live” lines during outages. A grid-capable inverter can both connect to the grid and use batteries, which allows for the possibility of back-up power during outages. Grid-connected inverters also generally produce 2,000 Watts or more and cost about 5000,000 to 4,000.
Solar panels won’t produce optimal results if not installed in the right way. A solar panel stand or mounting structure plays a very crucial role when it comes to mounting the solar panels.
Following are the five different types of mounting structures you can choose from
- – Ground mounts: These are made from aluminium racking supported by galvanised steel. They are ideal for open space applications like solar farms. Ground mounted racks are attached to the ground via footings or concrete pillars. No roof penetration is needed, and they have a risk-free installation.
- – Roof-mounted racks: This solar equipment is a stand that is adjustable to fit the rooftops and hold the weight of the solar panels. The installation cost is low too.
- – Floaters: When you install solar panels on water, they are mounted on interconnected plastic rafts that serve as floating platforms on the water’s surface.
- – Tracking system mounted racks: Suitable for solar water pumping and tracking systems, they’re of two types – One-axis and Two-axis. The one-axis mount measures the sun’s motion. The two-axis mount employs PV concentration systems to track the sun’s daily and seasonal path.
- – Top-of-pole mounted racks: They anchor the PV solar panels on poles, and their design prevents particle accumulation on the solar panel.
- – Side-of-pole mounted racks: These are variants of pole mounts with support placed on the side of the pole. They are better options for places with remote solar lighting systems.
Now that you know about the panels and their mounting, the next most important solar energy equipment is the solar inverter.
Your solar panels produce a direct current charge, while you require an alternating current in your house.
The inverter is that solar equipment that converts and regulates the energy produced by solar panels. Precisely, a solar inverter converts direct current into alternating current.
You can select from the major types of inverters for your solar power systems:
- – Central inverters: Less expensive and more commonly used, these are suitable for solar systems with large solar access. This equipment of solar energy is installed indoors.
A central inverter is capable of converting the power produced by all of the solar panels linked together.
- – Micro Inverters: These are popular for household purposes. They are suitable for areas where a part of the solar panel system stays temporarily blocked from sunlight.
They are placed behind every individual solar panel, allowing monitoring and analysing of each module’s energy production levels. They are expensive but grant a higher level of information access.
- – Battery-based inverters: These can be grid-interactive (on-grid) or stand-alone (off-grid). They reduce grid power consumption and provide you with a continuous power supply. They are affordable and easy to maintain.
Energy Meter or Bi-directional Meter
You can record the energy production via solar panels through an energy meter. Discom mandates replacing an energy meter with a bi-directional net meter in the residential solar system.
What is a bi-directional meter?
As the name suggests, this net metre can send electricity units to the grid and import electricity from the grid as well.
Since a net meter records the power generated and the power consumed, you pay the amount for the net units you consume.
Q What role do AC and DC combiner boxes play?
A DC Combiner box is used to isolate all the wires that are carrying the DC current from the solar panels.
An AC Combiner box connects the inverter’s output to the electricity grid and the energy meter. It provides electrical surge protection and AC isolation.
Q How much space is required for solar panels?
A solar energy equipment installation needs space depending on the energy requirements.
For example, if you wish to install a 3 KW rooftop solar system, you must have at least 300 sq feet of shadow-free area as you will have to install about 7 to 10 solar panels.
Q Can air conditioners run on solar panels?
Yes, air conditioners can run on solar electricity generated by solar panels.
How Much Will a Solar Power System Cost?
For the most part, the equipment isn’t going to be the most expensive part of the investment. Instead, it will have to do with the installation phase as you will want a professional that is the real deal and knows what they are doing every step of the way.
This will ensure the solar power system is maximized and works the way you want it to from a production perspective.
For the most part, your investment will be paid off by the time you hit the 6-7 year mark. Since the solar power system can last for more than two decades, you are going to end up saving quite a bit of money in terms of energy bills.
You can also apply for energy credits to save additional money. This includes sending excess energy to the local power grid as a way to earn even more in credits.
Who Should I Use to Install My Solar Power System For My Home?
This is the most crucial part of the process and has to be done the right way. If there are issues with the installation, you will end up losing production power, which will lead to a loss in your investment.
It is better to get professionals to work on your roof to ensure the solar panels are set up the right way. It is also wise to go with local installers as they will know the lay of the land better.
What is the Best Solar Power System For My Home?
Numerous solar power systems are being sold on the open market, and each one promises excellent results. It is going to come down to finding the right source and making sure they are well-reviewed.
With a proper solar power system, you are going to maximize how the photons are turned into usable energy for your home solar panels. It would be best if you took the time to go through relevant reviews and FOCUS on the market’s best option.