What is a solar inverter and how does it work?
With the increased interest in renewable energy sources across the globe, the interest in solar systems has also shot up at amazing rates. The ability of the sun to power an entire home is a huge environmental plus (think of all the electricity saved!) and is a great use of a resource that we have many hours of each and every week.
But, when it comes to solar systems, do you actually know what they are made up of and how they work? Solar systems consist of solar panels, (or photovoltaic (PV) panels), a solar inverter (super important) and a rack to keep everything in place. They may also contain a battery, depending on the system and an electric meter, and the amount and type of panels for each system will depend on the energy output needed. Considering how important and beneficial solar systems are, we thought we would put together a little information regarding solar inverters, how they work and what to look for in a good solar inverter, given their importance. If you have any questions after you have read this article, give Fallon Solutions a call at 1300 762 260.
How does a solar inverter work?
A solar inverter works by taking in the variable direct current, or ‘DC’ output, from your solar panels and transforming it into alternating 120V/240V current, or ‘AC’ output. The appliances in your home run on AC, not DC, which is why the solar inverter must change the DC output that is collected by your solar panels.
To be a little more technical, the sun shines down on your solar panels (or photovoltaic (PV) cells), which are made of semiconductor layers of crystalline silicon or gallium arsenide. These layers are a combo of both positive and negative layers, which are connected by a junction. When the sun shines, the semiconductor layers absorb the light and send the energy to the PV cell. This energy runs around and bumps electrons lose, and they move between the positive and negative layers, producing an electric current known as direct current (DC). Once this energy is produced, it is either stored in a battery for later use or sent directly to an inverter (this depends on the type of system you have).
When the energy gets sent to the inverter, it is in DC format but your home requires AC. The inverter grabs the energy and runs it through a transformer, which then spits out an AC output. The inverter, in essence, ‘tricks’ the transformer into thinking that the DC is actually AC, by forcing it to act in a way like AC – the inverter runs the DC through two or more transistors that turn on and off super fast and feed two varying sides of the transformer.
Types of solar inverters
Now you know what a solar inverter is and how it works, it’s time to look at the different types of inverters. There are 5 different kinds of solar inverters, all with varying benefits :
A battery inverter is the best option if you are needing to retrospectively fit a battery into your solar system, or are wanting to keep your battery separate from your solar panels and run through a different inverter. A battery inverter converts your battery power into 230V AC and feeds it into your switchboard (instead of grid power) wherever possible.
A central inverter is huge and is used for systems requiring hundreds of kilowatts (or even sometimes megawatts) of volume. They aren’t for residential use and resemble a large metal cabinet, with each ‘cabinet’ being able to handle around 500kW of power. They are generally used commercially for large-scale installations, or for utility-scale solar farms.
Hybrid inverters, otherwise known as ‘multi-mode inverters’, are pretty uncommon in Australia and allow you to connect batteries to your solar system. It engages with the connected batteries through ‘DC coupling’ (when both the solar and batteries use one inverter and the DC from the solar panels charges the batteries via a DC charger) and its electronics organise the charging and discharging of the battery.
As their name suggests, microinverters are super small (the size of a book!) and the ratio of solar panels to microinverters is 1:1. The benefit of a microinverter, among others, is that they optimise each solar panel individually, which offers more energy (especially in shady conditions).
Last but not least, there are string inverters. String inverters are the most common inverter option for residential use, and there is usually 1 string inverter per solar installation. They are known as ‘string inverters’ due to the fact that a string of solar panels is connected to them.
Solar Power Inverter Configurations
Central Inverter Configuration
Central Inverter Configuration – Several branches of the array are connected together in parallel. The complete output of the array is converted to AC through a single central solar power inverter and then fed to the grid. The single inverter is presented with a DC input voltage and current which may be quite large depending upon the configuration of the array.
This type of inverter configuration gives good efficiency, low cost, average reliability and since the PV panels within the same array are evenly matched, the maximum power point tracking (MPPT) selected by the inverter for the whole array ensures that all the PV panels operate at, or close too, their maximum power output.
Branch Inverter Configuration
Branch Inverter Configuration – Each branch or string has its own inverter attached. Then each single branch can have a different number of PV panels, different panel types, positions, orientations or suffer from full or partial shading. The result is that each inverter produces a different power output relative to its connected array.
Therefore the array cannot be efficiently characterised by one single maximum power point (MPP), as each inverter will operate at a different maximum power point with respect to the others. The main advantage of this type of power inverter configuration is that each solar branch can be at a different location or position and not all together in one single array.
Individual Inverter Configuration
Individual Inverter Configuration – Each photovoltaic solar panel has its own power inverter. This enables the inverter to select the optimum power point for the panel giving very good efficiency but at a higher cost per kWp. components in the array means lower reliability and more maintenance.
An increasing number of solar panel manufacturers are offering individual PV panels with solar power inverters built directly into the PV panel, making each solar panel its own complete AC power source allowing it to be plugged directly into the mains grid.
Grid connected solar power inverters synchronise the electricity they produce with the local grids AC grade electricity, allowing the system to feed the solar made electricity directly into the grid, usually through a second electricity kWh “net” meter.
Most grid connected power inverters are designed to operate without backup batteries, but battery based inverter models also are available. The battery based inverters for use in both a stand alone PV system or a grid connected PV system. As modern day power inverters include an inbuilt battery charger, which is capable of charging a battery bank directly from the grid during cloudy or bad weather.
High quality solar power inverters are available in sizes from a few 100 watts, for powering lights, laptops and games consoles from your car, up to tens of kilowatts, for powering large residential solar system with grid connected inverters being designed to automatically shut down when there is no grid power available for safety reasons.
Solar inverters are available in a wide range of power sizes and voltage ratings to suit just about every combinations of installation but there are basically three kinds of DC to AC solar power inverter: square wave, modified sine wave, and pure sine wave.
Square Wave Solar Power Inverter
The Square Wave Solar Power Inverter is the simplest and the least expensive type of inverter available. It is generally not used commercially due to its low quality of output power and very large harmonics. Square wave inverters equipped with thyristor output stages chop and invert (hence the name Inverter) the DC input positive power to generate a square wave alternating positive to negative AC output signal that is later filtered to approximate a sine wave and eliminate undesired harmonics.
Cheaper square wave inverters may also use push-pull transistor circuits with step-up transformers to produce the required output voltage. Square wave inverters are really only used in small stand alone PV systems that will run simple things like lighting or hand tools with universal motors with no problem – but not much else.
Modified Sine Wave Solar Power Inverter
The Modified Sine Wave Solar Power Inverter also called a quasi-sine wave inverter, is basically a modified square wave inverter which produces a square wave output with low harmonic distortion and a small “OFF” time between the positive and negative half cycles as the inverter switches polarity.
Modified sine wave inverters are suitable for most types of electrical and electronic loads, and are a popular type of inverter on the consumer market today due to their good conversion efficiency, relatively low cost, and can be used in solar installations where waveform shape is not too important.
However, modified sine wave inverters may not allow printers, copiers, light dimmers, rechargeable and variable tools to operate correctly due to the switching action of the inverters output stage. Also some audio amplifiers and radios may produce a low frequency background buzz due to the inverters output switching components.
Solar Inverters 101
Sometimes mistakenly called a converter, solar panel inverters deal less with voltage level and more with current type, switching power from DC to alternating current (AC) — what most home appliances use to function. Without a solar inverter, energy harnessed by solar panels can’t easily be put to use.
There are three types of inverters commonly used in solar power systems:
Microinverters: A microinverter is a small inverter situated close to a solar panel, which converts the DC electricity produced by a single panel. Because they work with single solar panels, microinverters allow your array to continue working even if one panel malfunctions. They are, however, more expensive than other types of solar inverters and require more maintenance.
String Inverters: This is a common inverter type for both home and commercial solar power systems. String inverters are highly efficient, robust, and inexpensive compared to other inverter types, but they do not have panel-level monitoring, and their high voltage may present a potential safety hazard.
Central Inverters: These are designed for larger arrays, and they basically function as a more consolidated version of string inverters. They have a low capital price per watt, are highly efficient, and are relatively easy to install. The downsides of central inverters are their size, potential noise pollution, and the fact that if one part of an array fails, the whole system may do so too.
Do note that some more contemporary solar power inverters — especially microinverters — also function as MPPT converters. These options can help simplify your system and cut costs.
What Should You Buy?
The equipment you need will largely be determined by the solar setup you want to run. Users who plan to rely heavily on a battery bank, for instance, should probably opt for a decent MPPT charge controller, while those who anticipate expanding their array in the near future will likely want to go for microinverters, as it’s easier to add panels with that type of arrangement.
The size of the converter or inverter you need should be based on how many watts your solar array can generate and how many watts your household uses. If you get a converter with an input capacity that’s too small, you won’t be able to maximize your array’s efficiency, and you might risk frying the device. If you get an inverter with an output capacity that’s too small, you won’t be able to power all of your home’s appliances.
Popular Solar Products
Here are a few popular converter and inverter options available for purchase online. Keep in mind that not all devices are compatible with all panel setups, so you should consult your panel manual before making a purchase.
Morningstar TS-45 Charge Controller, 155
This PWM controller can manage arrays up to 4000W, and it is designed to work with both sealed and flooded battery banks.
Pros: Users rate this device highly for reliability.
Cons: It works with PWM technology, which may not be as efficient as some MPPT devices.
Renology Tracer 40 Amp Charge Controller, 189
The Tracer can take in a maximum of 100VDC energy. It also has various safety mechanisms to help prevent battery overcharging and discharging.
Pros: The larger input capacity makes this a good choice for solar users who may want to grow their arrays.
Cons: The one-year warranty is shorter than for some other devices.
OutBack Power VFX3648 Vented Off Grid Inverter 3600W 48VDC, 5000,250
This inverter has a high wattage output, making it a great option for running high-use appliances or electronics. It also has bug-proof screened openings which allow for high output AC power even in the hottest of operating conditions.
Pros: This is a great inverter for off-grid setups.
Cons: Very expensive.
Enphase M215 Microinverter, 128
Manufactured by one of Green Tech Media’s Six Solar Inverter Companies to Watch in 2015, this Enphase microinverter works with 60-cell PV modules and runs with high efficiency.
Pros: As a microinverter, it provides more access to information about individual panel function, making it easy to identify system issues.
Cons: Depending on array size, this may be a more costly option, as each panel will need its own separate device.
Don’t feel rushed when deciding what converter or inverter to buy for your solar system. Take your time, and if you’re not sure whether a given product will be a good fit for your array, reach out to solar installation professionals for guidance on how to arrange your specific setup.
Note: Solar Power Authority does not endorse or guarantee any of the products listed here.
WHAT INVERTER SIZE SHOULD I GET?
Solar panel inverters come in different sizes, depending on how much electricity they can intake and output at a time. Knowing which size is right for you depends entirely on how much electricity you will be using throughout the day and how much storage you plan on having.
Consider what home appliances you own. You need to account for everything in your initial estimation, even something as small and mundane as a digital clock.
Another factor to consider is how often you will be using these devices. Ask yourself what you need from day to day.
- How often do you use the microwave?
- Do you watch TV every day? How long?
- How long do you have your phone or laptop plugged into the charger?
- Will you be running a device all day or just an hour?
- Are you using several appliances at the same time?
- Will you switch between plugging in different devices?
These are the types of questions you must ask yourself.
You must have solar panels and battery storage large enough to handle everything you are considering using each day. That’s why estimating is so essential: it impacts every decision when planning out your solar equipment selection.
That’s also why it’s safer to get a size bigger than you think you need. Being able to use electricity whenever you want or need requires a bit of spontaneity.
You never know when you’ll get more electronics added to your home. So, getting a bigger inverter to start with will save you the trouble of getting a new one later on.
If you’re struggling to figure out calculations, you can use our solar calculator here. You can also reference our blog on solar calculation here. Our blog goes into more detail on how to work out the math and helps the planning process!
WHAT OTHER INVERTER FEATURES SHOULD I CONSIDER?
Every inverter has different strengths and drawbacks. Make sure you consider what aspects are most important to you and your situation.
For example, some inverters are easier to set up than others. If you are doing a lot of the work yourself, easy installation options might suit you best!
If you live in a state with harsher weather conditions, you must consider how durable the inverters are. Look up an inverter’s NEMA rating, or check reviews, to see which can handle constant rain, harsh sunshine, strong winds, or any weather you deal with constantly.
Efficiency comes back to using modified or pure sine wave inverters.
Of course, the more features you have, the more expensive it can end up becoming. Costs can range wildly, but generally, the more you spend, the more features and valuable qualities you’ll have included.
That’s not to say you should throw all your money at the biggest and most powerful inverters. You don’t want one that’s too big or doesn’t have a chance to use the advanced features it may have.
Consider what is crucial for you and your situation, then select an inverter accordingly.
DOES BEING ON OR OFF THE GRID MATTER?
There are a few key differences to be aware of when going on or off the grid, so be wary!
Solar panel inverters on the grid are easier to set up since you don’t need a battery bank. Not to mention, putting the electricity you produce onto the grid will be shaving tons of money off your electricity bill without worrying about battery life and what time of day you use your electronics.
Micro-inverters VS DC Optimizers (Solar Inverter)
However, being on the grid means power outages will affect you since the inverter shuts off for safety reasons. You’ll also not be completely self-reliant since your home will still connect to the grid. That’s not necessarily a bad thing. But, it’s much more tempting to use electricity if you’re not worried about battery storage and whatnot.
Inverters off the grid take a bit more to set up and require more planning. You need to consider your battery bank and how much electricity you can run during the day and night.
Offgrid Solar Inverter Buyer’s Guide for Beginners
However, being completely self-reliant means you don’t have to worry about electricity bills or power outages on the grid in case of emergencies. It’ll be work, but you will have complete control and save a lot of money.
Lately, there have been hybrid setups with both an emergency battery bank and a connection to the grid. However, you will need to recognize this will cost more initially and require more planning. Despite this, finding a middle ground between both can be beneficial for those interested.
WHAT IF I’M STILL NOT CERTAIN?
Many factors go into selecting an inverter for your home. Being overwhelmed is shared with anyone looking to set up their solar panel system. Luckily, we have a lot of experience helping customers pick out whatever equipment they may need, inverters being no exception!
Please check out our website for various product selections, or contact us with any questions you might have. Are you looking to learn more about anything and everything solar? Check out our blogs and learn from the experts about the benefits and experiences of going solar.