What Are Solar Panel Inverters?Updated June 22, 2022 Solar
Solar panels are the hot new home retrofit on the block, and if you’re looking to save money on energy costs, they make an excellent addition to your home.
Micro Parallel Inverters for Solar Panels
If you’ve ever installed a solar panel on the roof of your house, you may have noticed that all the wires coming from your solar panel have to be routed through a little metal box before they can be routed into your house’s electrical grid. That box is called an inverter, and it is responsible for taking the DC current produced from the photovoltaic effect in your solar panels and converting it into the AC current used by your home.
Choosing the right type of inverter for your solar panels can have a huge effect on installation costs, cabling, and energy savings.
For a long time, solar panel users only had two types of inverters to choose from, micro inverters and string inverters. Now a new type of inverter is on the block, the micro parallel inverter could save homeowners up to 75% on solar installation, cabling, and activation. Let‘s dive into the basics of how inverters work.
Alternating Current vs Direct Current
Before we can dive into what an inverter is, you need to understand the two types of currents: alternating current (AC) and direct current (DC). Solar cells, batteries, and many modern devices work with direct current, or the unidirectional flow of electric charge. Charge flows in only one direction.
In alternating current, the flow of electric charge alternates or periodically changes direction at a given frequency. The movement is often resolved with a sine wave, although other wave forms may be used depending on the application.
The War of Currents
Our story begins in the late 1880s with the War of Currents, a battle between Thomas Edison and George Westinghouse over who gets to power America and the rest of the world. In one corner, we have the incumbent, Thomas Edison the Wizard of Menlo Park, a major supporter of using direct current to power America’s homes.
In the other corner, you had George Westinghouse of Westinghouse Electric, who had acquired many of Nikola Tesla’s patents for alternating current. He had even hired Tesla himself as his consultant. As the inventor of the incandescent light bulb, Edison had already established DC current as the standard for the United States electrical grid. He held all the patents and did not want to lose his royalties.
Edison initiated his infamous smear campaign, which culminated in the famous electrocution of an elephant using AC voltage. The DC power grid required larger cables and made transferring electricity over longer distances costly. With the development of a transformer AC power could be delivered over long distances in smaller wires for a much lower cost. The results were clear and AC current became the norm for delivering power from power plants to homes.
How Inverters Work
Since the photovoltaic process within your solar cells produces direct current, that is charge that flows in only one direction, this presents a bit of a problem when it comes to integrating that flow into your house's power grid, which uses alternating current. That’s where the inverter comes in – taking your unidirectional flow of electric charge and reversing polarity from positive to negative 50 – 60 times a second or 50-60 Hz. This is where the mains frequency rating.
The easiest way to conceptualize how an inverter works is to imagine a simple circuit with a 9 volt battery hooked up to a volt meter. When you line up the positive lead of your volt meter with the positive terminal of the battery and the negative lead of your volt meter with the negative lead of the battery, your meter will read 9 volts on the display.
If you reverse the leads, touching the positive lead to the negative terminal and vice versa, the volt meter will read -9 volts. If your hands were deft enough to switch the wires in this manner 50 times per second, you would effectively be serving as a crude mechanical inverter that takes the DC current of the 9 volt battery and transforms it into AC current at 50 Hz.
Square Waves vs Sine Waves
The simple mechanical inverter in our previous example would produce a square wave. Since the current is switching polarity drastically, it creates a large harmonic distortion or a “dirty” supply. While some devices like light bulbs wouldn’t notice the difference, a square wave can be damaging to many devices.
It is far better to aim for a sine wave, where the polarity changes gradually into a nice smooth curve. Higher quality inverters produce waves that are closer to a true sine wave. Your mains power supply from the power plant is delivered to you as a sine wave, which is why you don’t have to worry about what devices you plug into your wall socket. Actual inverters use inductors and capacitors with pulse width modulation to switch currents more gradually and produce a sine wave.
Picking the Right Inverter for your Utility Grid
As you might imagine, the type of inverter you use to integrate a solar panel array into your house’s electrical grid needs to be able to match the frequency and sine wave of your mains supply. If the crests and troughs of your inverter are out of phase with the mains supply you get destructive interference where the two waves cancel each other out. If the two waves are in phase you get constructive interference which results in a large sine wave.
For solar power to enter your electrical grid, the two waves must be in phase. Therefore, you need an inverter that is capable of sensing the phase of your mains supply and matching it. This phase matching capability is what differentiates grid-tie inverters from regular inverters, and is also why they tend to be more expensive. Now let’s look at the two main types of grid-tie inverters used in the home solar retrofit industry.
String Inverters String inverters treat your entire solar panel array as a single giant solar panel. Some of the benefits of string inverters include a lower initial cost per peak watt price and easier install. Since string inverters accept DC current from multiple panels, wiring tends to be easier on initial install. However, since string inverters treat the entire system as a single large panel, performance problems experienced by one panel are extended to the other panels in the array.
Micro inverters take a more modular approach and must be installed on each solar panel in an array. Since multiple smaller units must be installed in tandem with each solar panel, installation costs tend to be higher. The advantage of using micro inverters is that if one solar panel fails or experiences more shade, it does not affect the rest of the panels in the array.
Micro inverters use maximum power point tracking (MPPT) to monitor the environmental condition of a cell and apply the proper resistance or load to ensure maximum power is obtained from the panel. The modular design also makes it easier to locate points of failure.
Micro Parallel Inverters Technology Research Corporation TRC designed the micro parallel inverter with the goal of combining the ease of installation of string inverters with the ease of maintenance and efficiency of micro inverters. A single micro parallel inverter contains four separate channels that can each be hooked up to a separate solar panel.
Each channel is like a modular micro inverter, capable of using MPPT to maximize power output from the attached solar panel. Unlike the string inverter, the micro parallel inverter is aware of the status of each individual solar panel, and if performance drops from one panel due to shade, performance of the rest of the panels will remain unaffected.
A study conducted by the U.S. Department of Energy revealed that installation labor is the largest expense associated with solar power installations. The costs of installing a solar power system often outweighed the price of the panels, framing, and wiring themselves.
Recognizing this issue, TRC designed the micro parallel inverter with the installation technician in mind. The micro parallel inverter gets its name from its ability to invert four panels in parallel. What this means for the technician is that they can save the time spent installing four separate micro inverters by routing all the cables to a single micro parallel inverter.
Each channel on the micro parallel inverter can be removed for maintenance. The micro parallel inverter takes a plug-n-play approach to installation and can easily be configured for grid tied, emergency backup, or off grid applications. It can be mounted in 4.8 kW clusters in rows of four and may be attached to the panel frame, panel array or directly to the roof. Quick disconnects make routing solar panels to each of the four channels a snap.
Multiple micro parallel inverters can be connected to a single disconnect at the breaker panel. Up to 16 solar panels may be tied to a single disconnect, as opposed to 16 separate disconnects for a conventional micro inverter system. With such a drastic reduction in the number of installations, it is clear how the micro parallel inverter can save someone up to 75% in certain situations.
The micro parallel inverter is a smart system that allows it to control four 300-W solar panels at once via four separate channels. The modular architecture supports individual fault knowledge, power sharing, health status, and other communications.
The system can tell you when an individual panel needs to be cleaned, if an inverter has failed, or if a channel requires a service visit. Even if three out of the four panels fail, the micro parallel inverter will continue using MPPT to invert the maximum power output from the remaining solar panel.
Electricity Monitor and Control (EMC)
The Electricity Monitor and Control (EMC) can provide self-mapping and automated control to the micro parallel inverter. The EMC can be hooked up to the breaker panel and may connect directly to the site’s internet router or a computer via an Ethernet cable.
The EMC uses Power Line Carrier Communication (PLCC) to communicate directly with the individual micro parallel inverters which in turn relay information from the attached solar panels. As a result, a micro parallel inverter system can map the physical locations of its components automatically.
The owner or installation technician can log in to the EMC website and follow the instructions to complete installation, startup, checkout, and commissioning. The web interface also provides some logistical data and can alert the user via email in the event of a failure. TRC’s micro parallel inverters have been ruggedized with an internal thermal failsafe that protects the hardware against heat-related failures via a power output throttling circuit.
When a panel reaches its limit, the circuit can be throttled to prevent generation overages from occurring. Instead of immediately cutting the circuit, throttling allows the panels to operate optimally at higher temperatures with a reduced risk of failure. Finally, the EMC offers remote access to the owner, allowing them to activate or deactivate the system remotely.
The Conext SW 2524 Inverter/Charger, And Why It's A Good Deal
The Conext SW 2524 Inverter/Charger gets good reviews on its versatility. It is also simple to install and very competitively priced. The Conext SW 2524 will charge your battery bank using the grid, a gas-powered generator, or your solar, hydro, or wind energy sources.
The mounting bracket is designed for studs spaced 16 inches apart, and the wiring hooks in on the side, making for easy access and connections. It is compatible with a variety of battery banks, including FLA and Custom batteries, and you can customize your unit using the control panel and a Combox, which will also remotely monitor the system over the web.
This Inverter/Charger is also stackable. A single unit provides an output of 4 kW, and adding a second one allows for up to 8 kW. There are two versions of this device, one for North and some of South America (a 120/240V split phase) and one for Europe, Australia, Africa, and some of South America (230V single phase). It can operate at 50Hz or 60Hz making it useful in unique markets, such as Jamaica's 110V 50Hz and Asia, where electrical standards vary quite a bit, depending on your location.
Before installing a Conext SW inverter/charger, know your power requirements.
Inverter/charger power systems generally involve one DC source, one AC source, one inverter/charger, and a control/monitoring device. Inverter power systems vary depending on the power requirements and where the user is located. An off-the-grid house with an AC generator, a battery, and a Conext SW inverter/charger with a System Control Panel (SCP), is one example.
A house in the city, connected to the power grid, and requiring a backup system to cope with rolling blackouts, is another example. There is also the possibility of capturing and storing renewable energy such as solar, wind, and hydro energy, for future use.
When choosing a location for the inverter/charger, it should not be installed near water or other fluids which could drip or splash on it. It should be protected from the environment, including rain and snow. A normal ambient air temperature between 0 °C and 25 °C (32 °F and 77 °F) should be maintained. It should be close to the battery bank, but not in the same compartment. The length and size of your DC cables will affect performance. (Shorter is better, as direct current, unlike alternating current, loses voltage quickly based on distance.)
The inverter/charger should not be installed in the battery compartment because of the possible presence of explosive hydrogen gas from the batteries. Give the inverter/charger as much space around it as possible. It is strongly recommended other objects and surfaces should be at least 250 mm away from the ventilation openings for the best performance.
CSIRO specializes in perovskite solar cells, which derive their name from the ABX3 crystal structures of the photo absorber materials used in this type of cell. The perovskite structure is any material that maintains the same structure as calcium titanium oxide (CaTiO3). The letters A and B denote two cations of significantly differing sizes, and the X refers to the anion that bonds to the cations. In the case of perovskite solar cells, the X is a halogen such as indium, bromine, or chlorine.
The Conext SW inverter/chargers provide a variety of multiple unit configurations. This gives you (and/or the installer) more options to work with when designing a system to meet your load demands. Multiple inverter/chargers of different power levels can be installed in a system as a standalone, or in parallel. In a multiple unit configuration, only two Conext SW inverter/chargers of the same model can be used.
Two Conext SW 4024 230 units can be configured/stacked because both units have a 24-volt rating and a power rating of up to 3500 watts. With this configuration, the inverter/charger capabilities of a system are doubled. If two Conext SW 4024 230 units are being used, the inverter power rating doubles to 7000 watts, and the charging output current doubles to 180 amps. But, the AC transfer relay rating of 30-amps remains the same. Two inverter/chargers can operate from different battery banks, meaning each unit is connected to its own battery bank.
The battery bank size, or capacity, is just as important as the type of battery. The batteries are a very important part of your system. Consequently, it is recommended you purchase as much battery capacity as possible. A large battery bank will extend running time and ensure your inverter/charger delivers its full rated surge. You should have a minimum battery bank size of 100 amp-hours (Ah) for moderate loads (1000W) and more than 200 Ah for heavy loads.
There are different standards used in rating battery energy storage capacity. Amp-hour capacity is typically used for inverter/chargers, and represents the number of amps a battery can continuously deliver during a specified number of hours. It is expressed by the product of the two, or amps times hours. A battery bank rated at 100 Ah can deliver 5 amps for 20 hours (5 amps × 20 hours = 100 Ah). This same battery bank can also deliver a lower or higher current for more or less time.
All in all, the Context SW 2524 Inverter/Charger is a very good deal at the present. I would like to see it become a little less expensive (dream on), but considering how well it’s designed, it does seem to be worth the money.
Micro Parallel Inverter for Solar Panels
It is clear that the micro parallel inverter effectively offers the best of both worlds, but is it really a new class of inverter?
The micro parallel inverter effectively combines the benefits of string inverters and micro inverters into one assembly. Whether you consider the micro parallel inverter to be four micro inverters on a single panel, a “smart” string inverter with multiple channel functionality, or an entirely new class of inverter, only one thing is for certain.
With enhanced ease of installation, modular design, and powerful logistics and communications capability, the micro parallel inverter is sure to make your solar panel installation technician’s job go a lot quicker.
Solar Inverter Sizing
How to choose the right solar inverter size for your solar power system.
Solar inverters convert the low voltage DC electricity created by your solar panels to the 120 volts AC electricity used by household appliances.
Sizing a solar inverter is an important part of any solar installation, big or small. Since your solar energy system is going to be producing and sending DC electricity to your inverter, you're going to need to have an inverter size that can handle the load and convert it to AC power. This requires knowing how to size an inverter properly.
How To Size an Inverter
To understand how to size an inverter you must first understand how inverters are rated.
How Inverters Are Rated
The first way inverters are rated is in Watts (or Continuous Watts).
1. Continuous watts is the total amount of watts the inverter can support indefinitely. A 2000 watt inverter can power up to 2000 watts continuously. A bigger inverter size could handle more.
For your inverter to be right for your system, its watts rating must be approximately equal to your solar system's watts rating. This is the correct way to size an inverter.
Therefore, if your solar system is rated at 2000 watts, you'll need a solar inverter with about 2000 watts, maybe a little bit more. But not too much more or the efficiency will drop.
If you want to run multiple appliances at the same time and want to make sure your inverter can handle the load, just add up all the Continuous Watt ratings of all the appliances that may be running simultaneously.
Depending on the total continuous watts you get, you can determine if your inverter can handle it. This is also an important part of inverter sizing (how to size an inverter).
So if the total continuous watts of all the appliances that may run at the same time is 3000, it's too much, you'll have to run fewer appliances at the same time.
The second way solar inverters are rated is in Surge Watts.
A surge watt is the amount of power the inverter can support for a very short time, usually momentary. A 2000 watt inverter rated at 4000 surge watts can handle up to 4000 watts momentarily while starting things like motors - which usually require more power than normal to get started.
For your inverter to be right for your system, its surge watts rating must be approximately equal to (or greater than) the potential surge watts of each appliance.
You can find this out by looking at the sticker on the back of all of the appliances you will be using with your solar system and checking the potential surge watts of each appliance. By doing this you can determine the minimum surge wattage you'll need your inverter to be rated for. Usually, you'll need about 1.5 to 2 times as many surge watts as continuous watts for a good measure of surge protection (more, if powering heavy duty equipment).
Therefore, if the highest surge watt rating on any of the appliances you plan to use with your solar system is 4000, you'll need a solar inverter with a little over 4000 surge watts.
Input Voltage - Should I get a 12v 24v or 48v inverter.
The next rating you have to look at when sizing an inverter is the input voltage.
For correct solar system sizing, your solar panels, inverter, and battery bank all need to use the same voltage.
So the input voltage of your inverter will depend on the inverter's power or watt rating. For inverters with a relatively small amount of power like 100 watts, the voltage will be 12V, 24V and 48V. For higher powered inverters, the input voltage will likely be more.
Length of Wire & Solar Inverter Performance
One of the factors that can affect your inverter's performance is the distance between your solar panel array and your battery bank. The longer the wire used here, the lower your inverter's voltage should be to perform optimally, because with long wires voltage drops and current increases.
The higher the voltage and the lower the current, the shorter length of wires you can use. With longer wires, you would need to use thicker wires.
Inverter Stacking (Using Multiple Inverters)
Sometimes people connect more than one inverter together to "stack" up more power. This would typically be done if you have many smaller inverters and want to join them together to form a bigger one.
If your inverter demands increase in time (because you added more solar panels) you can either buy a bigger solar inverter or wire multiple inverters together.
When you install and wire two inverters together, it's called inverter stacking and it can provide either more power or higher voltage.
If two compatible inverters are wired together in series, you can double the output voltage. This inverter stacking technique would be used if you only had two smaller inverters and had to provide 120/240 volts AC.
However, if you were to wire them in parallel, you would double your power (watts). This solar inverter stacking technique would be used if you had two smaller inverters but also had a solar system that was rated at much higher watts (power) than what a single inverter could handle. If you wired two 2000 watt inverters together in parallel, they would be able to handle 4000 watts (4KW) of power.
Inverter Performance With Less Sunlight
By correctly matching your solar panels and battery banks to your inverter's rated capacities, you can improve the performance of grid-connected solar systems.
However, when the sun is not at its brightest and the system isn't producing at close to full capacity, the inverter will be operating at partial load and its efficiency will drop.
Energy loss also occurs when an inverter is too small to operate in conditions of overload. Another important thing to consider is PV inverter sizing.
Solar Inverter Prices
An average quality Modified Sine Wave solar inverter can cost anywhere from $400 - $1000. These low to medium quality range inverters can operate with small to medium sized systems and relatively speaking provide good performance, reliability, and consistency.
Obviously, unlike more expensive inverters (True Sine Wave inverters)there is typically a moderate amount of energy or performance loss, but not if your appliances aren't too high tech and your solar application isn't too demanding.
If you want to get a good quality inverter for a pretty big system, it would probably cost you about $900 to $1500 for a 2000 to 3000 watt Modified Sine Wave solar power inverter.
If you want to be able to run basically anything plus have all the automatic features, you would likely have to pay about an extra $500-$1000 for a True Sine Wave solar power inverter.
These higher quality Sine Wave inverters are computer compatible and computer-controlled which will add automation and true convenience to monitoring and protecting your solar power system. Never forget to factor in convenience and practicality when doing your solar inverter sizing.