Solar Integration: Inverters and Grid Services Basics
An inverter is one of the most important pieces of equipment in a solar energy system. It’s a device that converts direct current (DC) electricity, which is what a solar panel generates, to alternating current (AC) electricity, which the electrical grid uses. In DC, electricity is maintained at constant voltage in one direction. In AC, electricity flows in both directions in the circuit as the voltage changes from positive to negative. Inverters are just one example of a class of devices called power electronics that regulate the flow of electrical power.
Fundamentally, an inverter accomplishes the DC-to-AC conversion by switching the direction of a DC input back and forth very rapidly. As a result, a DC input becomes an AC output. In addition, filters and other electronics can be used to produce a voltage that varies as a clean, repeating sine wave that can be injected into the power grid. The sine wave is a shape or pattern the voltage makes over time, and it’s the pattern of power that the grid can use without damaging electrical equipment, which is built to operate at certain frequencies and voltages.
The first inverters were created in the 19th century and were mechanical. A spinning motor, for example, would be used to continually change whether the DC source was connected forward or backward. Today we make electrical switches out of transistors, solid-state devices with no moving parts. Transistors are made of semiconductor materials like silicon or gallium arsenide. They control the flow of electricity in response to outside electrical signals.
A 1909 500-kilowatt Westinghouse “rotary converter,” an early type of inverter. Illustration courtesy of Wikimedia.
If you have a household solar system, your inverter probably performs several functions. In addition to converting your solar energy into AC power, it can monitor the system and provide a portal for communication with computer networks. Solar-plus–battery storage systems rely on advanced inverters to operate without any support from the grid in case of outages, if they are designed to do so.
Toward an Inverter-Based Grid
Historically, electrical power has been predominantly generated by burning a fuel and creating steam, which then spins a turbine generator, which creates electricity. The motion of these generators produces AC power as the device rotates, which also sets the frequency, or the number of times the sine wave repeats. Power frequency is an important indicator for monitoring the health of the electrical grid. For instance, if there is too much load—too many devices consuming energy—then energy is removed from the grid faster than it can be supplied. As a result, the turbines will slow down and the AC frequency will decrease. Because the turbines are massive spinning objects, they resist changes in the frequency just as all objects resist changes in their motion, a property known as inertia.
As more solar systems are added to the grid, more inverters are being connected to the grid than ever before. Inverter-based generation can produce energy at any frequency and does not have the same inertial properties as steam-based generation, because there is no turbine involved. As a result, transitioning to an electrical grid with more inverters requires building smarter inverters that can respond to changes in frequency and other disruptions that occur during grid operations, and help stabilize the grid against those disruptions.
Grid Services and Inverters
Grid operators manage electricity supply and demand on the electric system by providing a range of grid services. Grid services are activities grid operators perform to maintain system-wide balance and manage electricity transmission better.
When the grid stops behaving as expected, like when there are deviations in voltage or frequency, Smart inverters can respond in various ways. In general, the standard for small inverters, such as those attached to a household solar system, is to remain on during or “ride through” small disruptions in voltage or frequency, and if the disruption lasts for a long time or is larger than normal, they will disconnect themselves from the grid and shut down. Frequency response is especially important because a drop in frequency is associated with generation being knocked offline unexpectedly. In response to a change in frequency, inverters are configured to change their power output to restore the standard frequency. Inverter-based resources might also respond to signals from an operator to change their power output as other supply and demand on the electrical system fluctuates, a grid service known as automatic generation control. In order to provide grid services, inverters need to have sources of power that they can control. This could be either generation, such as a solar panel that is currently producing electricity, or storage, like a battery system that can be used to provide power that was previously stored.
Another grid service that some advanced inverters can supply is grid-forming. Grid-forming inverters can start up a grid if it goes down—a process known as black start. Traditional “grid-following” inverters require an outside signal from the electrical grid to determine when the switching will occur in order to produce a sine wave that can be injected into the power grid. In these systems, the power from the grid provides a signal that the inverter tries to match. advanced grid-forming inverters can generate the signal themselves. For instance, a network of small solar panels might designate one of its inverters to operate in grid-forming mode while the rest follow its lead, like dance partners, forming a stable grid without any turbine-based generation.
Reactive power is one of the most important grid services inverters can provide. On the grid, voltage— the force that pushes electric charge—is always switching back and forth, and so is the current—the movement of the electric charge. Electrical power is maximized when voltage and current are synchronized. However, there may be times when the voltage and current have delays between their two alternating patterns like when a motor is running. If they are out of sync, some of the power flowing through the circuit cannot be absorbed by connected devices, resulting in a loss of efficiency. total power will be needed to create the same amount of “real” power—the power the loads can absorb. To counteract this, utilities supply reactive power, which brings the voltage and current back in sync and makes the electricity easier to consume. This reactive power is not used itself, but rather makes other power useful. Modern inverters can both provide and absorb reactive power to help grids balance this important resource. In addition, because reactive power is difficult to transport long distances, distributed energy resources like rooftop solar are especially useful sources of reactive power.
A worker checks an inverter at the 2MW CoServ Solar Station in Krugerville, Texas. Photo by Ken Oltmann/CoServ.
Types of Inverters
There are several types of inverters that might be installed as part of a solar system. In a large-scale utility plant or mid-scale community solar project, every solar panel might be attached to a single central inverter. String inverters connect a set of panels—a string—to one inverter. That inverter converts the power produced by the entire string to AC. Although cost-effective, this setup results in reduced power production on the string if any individual panel experiences issues, such as shading. Microinverters are smaller inverters placed on every panel. With a microinverter, shading or damage to one panel will not affect the power that can be drawn from the others, but microinverters can be more expensive. Both types of inverters might be assisted by a system that controls how the solar system interacts with attached battery storage. Solar can charge the battery directly over DC or after a conversion to AC.
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Working Modes of Hybrid Solar Inverter
A hybrid inverter is an upgrade based on a solar inverter. It contains the functionality of a solar inverter that converts DC to AC and also adds built-in solar controllers like MPPT or PWM types. So, to be precise, a hybrid inverter is a solar inverter with a built-in charge controller. It can also be a combination of off-grid and grid-tied inverters in one machine with the same description you would call a hybrid inverter.
Next we will introduce the five working modes of the hybrid solar inverter.
Photovoltaic high power mode
That is to say, the photovoltaic power generation exceeds the power of the home load and the battery energy storage power, and the excess power will be sent back to the grid in reverse. If you don’t want to have reverse power, you can set the inverter to automatically reduce the photovoltaic power in this case, or increase the battery capacity.
Photovoltaic low power mode
When the photovoltaic power is lower than the load power at home, the battery will release part of the power. If the photovoltaic power and battery discharge power are still less than the load power at home, the grid will automatically supplement the power.
No photovoltaic power mode
For example, at night, when there is no sun, all power is provided by the battery. If the battery power is less than the load power in the home, the grid will automatically supplement the lack of power.
UPS mode
Natural disasters or accidents cause power outages. As long as the battery still has power, the inverter will provide emergency backup power, which is very suitable for places where disasters are frequent or power outages are frequent.
User setting mode
For example, in some places, the electricity bill is particularly cheap at a certain time of the night. At this time, you can set the machine to automatically draw electricity from the grid, and use it or sell it to the grid company when the electricity bill is particularly expensive. It can also be used in some places where there are frequent power outages, as long as there is electricity, the battery will be charged immediately, and electricity will be available when the power goes out.
Let’s just say, this is a very good solution for distributed energy and Smart grids, especially in many places where there are too many people to build large power grids. It can allow more people to use green, low-carbon, environmentally friendly, safe and cheap renewable energy, greatly reduce the demand for fossil energy, and let the people in these war-torn energy producing areas live a peaceful life.
Compared: Grid-tied, off-grid, and hybrid solar systems
There are three types of solar panel systems: grid-tied (on-grid), off-grid, and hybrid solar systems.
Each type of system has a unique setup that affects what equipment is used, the complexity of installation, and, most crucially, your potential costs and savings.
What would be the best in your situation? Let’s take a closer look at the benefits and downsides of grid-tied, off-grid and hybrid solar systems.
Calculate the price of solar panel installation on your home
Grid-tied solar systems
Grid-tied, on-grid, utility-interactive, grid intertie, and grid backfeeding are all terms used to describe the same concept – a solar system that is connected to the utility power grid.
DC electricity generated by the solar panels is sent to the inverter, which converts the power into AC electricity. This electricity is first used to service the home loads, while all surplus energy is exported to the grid in return for electric bill credits.
Benefits of grid-tied systems
A grid connection will allow you to save more money with solar panels through net metering, lower equipment and installation costs, and better efficiency rates.
Save more money with net metering
Your solar panels will often generate more electricity than what you are capable of consuming. With net metering, homeowners can put this excess electricity onto the utility grid instead of storing it themselves with batteries.
Many utility companies are committed to buying electricity from homeowners at the same rate as they sell it themselves. As a homeowner, you can use these payments from your utility to cancel out your electricity usage charges. by up to 100%.
Net metering plays an important role in how solar power is incentivized. Without it, residential solar systems would be much less feasible from a financial point of view.
Lower upfront costs and ease of installation
Grid-tied solar systems are the only type of solar system that don’t require a battery to function. This makes grid-tied systems cheaper and simpler to install, and also means there is less maintenance required.
You can use the utility grid as a virtual battery
The electric power grid is in many ways also a battery, without the need for maintenance or replacements, and with much better efficiency rates.
According to EIA data, national, annual electricity transmission and distribution losses average about 7% of the electricity that is transmitted in the United States. Lead-acid batteries, which are commonly used with solar panels, are only 80-90% efficient at storing energy, and their performance degrades with time. In other words, more electricity (and more money) goes to waste with conventional battery systems.
Additional perks of being grid-tied include access to backup power from the utility grid, in case your solar system stops generating electricity for one reason or another. At the same time, you help to mitigate the utility company`s peak load. As a result, the efficiency of our electrical system as a whole goes up.
Equipment for grid-tied solar systems
There are a few key differences between the equipment needed for grid-tied, off-grid and hybrid solar systems. Standard grid-tied solar systems rely on the following components:
Grid-tie inverter (GTI)
What is the job of a solar inverter? They regulate the voltage and current received from your solar panels. Direct current (DC) from your solar panels is converted into alternating current (AC), which is the type of current that is utilized by the majority of electrical appliances.
In addition to this, grid-tie inverters, also known as grid-interactive or synchronous inverters, synchronize the phase and frequency of the current to fit the utility grid (nominally 60Hz). The output voltage is also adjusted slightly higher than the grid voltage in order for excess electricity to flow outwards to the grid.
Microinverters
Microinverters go on the back of each solar panel, as opposed to one central inverter that typically takes on the entire solar array.
Microinverters are certainly more expensive, but in many cases yield higher efficiency rates. Microinverters are particularly useful if you have shading issues on your roof.
Power meter
Most homeowners will need to replace their current power meter with one that is compatible with net metering. This device, often called a net meter or a two-way meter, is capable of measuring power going in both directions, from the grid to your house and vice versa.
You should consult with your local utility company and see what net metering options you have. In some places, the utility company issues a power meter for free and pays full price for the electricity you generate; however, this is not always the case.
See how much a grid-tied solar system can save you annually
Off-grid solar systems
An off-grid solar system (off-the-grid, standalone) is the obvious alternative to one that is grid-tied.
For homeowners that have access to the grid, off-grid solar systems are usually out of question. Here’s why. To ensure access to electricity at all times, off-grid solar systems require high-capacity battery storage and a backup generator. On top of this, a battery bank typically needs to be replaced after 10 years. Batteries are complicated, expensive, and decrease overall system efficiency.
Off-grid systems require large amounts of energy storage as there is no option to import power from the electric grid. As such, they are typically designed using lead-acid batteries, which are a much cheaper alternative to newer (and more efficient) lithium-based solar batteries.
Can be installed where there is no access to the utility grid
Off-grid solar systems can be cheaper than extending power lines in certain remote areas.
Consider off-grid if you’re mor e than 100 yards from the grid. The costs of overhead transmission lines range from 174,000 per mile (for rural construction) to 11,000,000 per mile (for urban construction).
Become energy self-sufficient
Living off the grid and being self-sufficient feels good. For some people, this feeling is worth more than saving money.
Energy self-sufficiency is also a form of security. Power failures on the utility grid do not affect off-grid solar systems.
On the flip side, batteries can only store a certain amount of energy, and during cloudy times, being connected to the grid is actually where the security is. You should install a backup generator to be prepared for these kinds of situations.
Equipment for off-grid solar systems
Typical off-grid solar systems require the following extra components:
- Solar charge controller
- Battery bank
- DC disconnect (additional)
- Off-grid inverter
- Backup generator (optional)
Solar charge controller
Solar charge controllers are also known as charge regulators, or just battery regulators. The last term is probably the best to describe what this device actually does: solar battery chargers limit the rate of current being delivered to the battery bank, and protect the batteries from overcharging.
Good charge controllers are crucial for keeping the batteries healthy, which ensures the lifetime of a battery bank is maximized. If you have a battery-based inverter, chances are that the charge controller is integrated.
Battery bank
Without a battery bank (or a generator), it’ll be lights out by sunset. A battery bank is essentially a group of batteries wired together.
DC disconnect switch
AC and DC safety disconnects are required for all solar systems.
For off-grid solar systems, one additional DC disconnect is installed between the battery bank and the off-grid inverter. It is used to switch off the current flowing between these components. This is important for maintenance, troubleshooting and protection against electrical fires.
Off-grid inverter
There’s no need for an inverter if you`re only setting up solar panels for your boat, your RV, or something else that runs on DC current. You will need an inverter to convert DC to AC for all other electrical appliances.
Off-grid inverters do not have to match phase with the utility sine wave as opposed to grid-tie inverters. Electrical current flows from the solar panels through the solar charge controller and the bank battery bank, before it is finally converted into AC by the off-grid inverter.
Backup generator
It takes a lot of money and big batteries to prepare for several consecutive days without the sun shining (or access to the grid). This is where backup generators come in.
In most cases, installing a backup generator that runs on diesel is a better choice than investing in an oversized battery bank that seldom gets to operate at its full potential. Generators can run on propane, petroleum, gasoline, and many other fuel types.
Backup generators typically output AC, which can be sent through the inverter for direct use, or it can be converted into DC for battery storage.
Hybrid solar systems
Hybrid solar systems combine the best of grid-tied and off-grid solar systems. These systems can either be described as off-grid solar with utility backup power, or grid-tied solar with extra battery storage.
If you own a grid-tied solar system and drive a vehicle that runs on electricity, you already kind of have a hybrid setup. The electrical vehicle is really just a battery with wheels.
In a hybrid solar system, energy generated from the solar panels is first used to service the home’s electrical loads (flow #1). After the home’s energy needs have been supplied, solar power is used to charge the solar battery (flow #2). If there is still a surplus of solar energy, it will be exported to the electric grid in return for credits (flow #3). The system pictured above shows an AC-coupled lithium battery, but hybrid systems can also be designed using either lithium or lead-acid-based DC batteries.
Less expensive than off-grid solar systems
Hybrid solar systems are less expensive than off-grid solar systems. You don’t really need a backup generator, and the capacity of your battery bank can be downsized.
If your battery runs out of charge at night, you can simply buy off-peak electricity from the utility company. This will be much cheaper than operating a generator.
Smart solar holds a lot of promise
The introduction of hybrid solar systems has opened up many interesting innovations. New inverters let homeowners take advantage of changes in the utility electricity rates throughout the day.
Solar panels happen to output the most electrical power at noon – not long before the price of electricity peaks. Your home and electrical vehicle can be programmed to consume power during off-peak hours (or from your solar panels).
Consequently, you can temporarily store whatever excess electricity your solar panels generate in your batteries, and put it on the utility grid when you are paid the most for every kWh.
Smart solar holds a lot of promise. The concept will become increasingly important as we transition toward the Smart grid in the coming years.
Equipment for hybrid solar systems
Typical hybrid solar systems are based on the following additional components:
- Charge controller
- Battery bank
- DC disconnect (additional)
- Battery-based grid-tie inverter
- Power meter
Battery-based grid-tie inverter
Hybrid solar systems utilize battery-based grid-tie inverters, which are also known simply as hybrid inverters. These devices can draw electrical power to and from battery banks, as well as synchronize with the utility grid.
Final thoughts on grid-tied solar systems
The bottom line is this: Right now, for the vast majority of homeowners, tapping the utility grid for electricity and energy storage is significantly cheaper and more practical than using battery banks and/or backup generators.
What is a Hybrid Inverter?
Hybrid inverters are a new piece of solar technology that combines the benefits of a traditional solar inverter with the flexibility of a battery inverter into a single device. A hybrid inverter is an up-and-coming solution for homeowners who want to install a solar power system that has room for future upgrades, including a battery storage system.
With this guide, you will learn everything you need to know about hybrid inverters, including what a hybrid solar inverter does, the options a hybrid grid-tie inverter gives you for home solar, how hybrid inverters compare to other types of inverters, and more.
What is a Hybrid Solar Inverter?
A hybrid solar inverter is the combination of a solar inverter and a battery inverter into a single piece of equipment that can intelligently manage power from your solar panels, solar batteries, and the utility grid at the same time.
A traditional solar grid-tie inverter converts direct current (DC) electricity produced by your photovoltaic (PV) system into the alternating current (AC) electricity that powers your house, which also allows excess electricity generation to be transferred to the utility grid.
A battery inverter handles the process of inverting DC electricity that’s stored in your solar battery storage into AC electricity that can be used by your home.
By combining these functions into a single device, a solar hybrid grid-tie inverter streamlines and improves the operations of the classic solar inverter. Even better, since the amount of solar power that’s available can depend on the weather and seasonality, a hybrid inverter can draw power from the electricity grid to charge your battery storage system if needed.
What are the Functions of a Hybrid Solar Inverter?
The basic purpose of an inverter is the conversion of DC input from your solar panel into AC output that your home can use. The function of hybrid solar inverter use takes this process to the next level, including the following benefits:
DC-to-AC Bi-Directional Power Conversion: Normally solar batteries are charged by either DC electricity received directly from solar panels (DC coupled), or DC electricity that has been converted from AC electricity by a solar inverter (AC coupled). Then to release that power, an inverter needs to convert that stored DC electricity back into AC electricity.
With a hybrid inverter and battery, one device can do both roles. The hybrid grid-tie inverter can convert DC electricity into AC electricity to power your home, but it can also take AC electricity from the grid, and convert it into DC electricity that can be stored in batteries for later use.
Power Regulation: Solar power can fluctuate as sunshine levels increase and decrease, based upon the time of day and weather patterns. A hybrid inverter regulates this power to ensure the whole system operates within the required parameters.
Power Monitoring: Solar hybrid grid-tied inverters can be fitted with solar power monitoring software to measure and monitor your photovoltaics system via the display screen or a connected smartphone app to help identify any faults.
Power Maximization: Hybrid inverters with Maximum Power Point Trackers (MPPT) check your solar power output and correlate it to the battery’s voltage. This enables optimum power output and conversion of DC electricity to the best voltage for the battery’s maximum charge. MPPT guarantees your solar power system works efficiently under every condition, such as varying amounts of solar light, solar panel temperature, and electrical loads.
How Does A Hybrid Inverter Compare To Other Types Of Inverters?
A grid-tied hybrid inverter allows for a seamless merger between your home’s solar power system and the electricity grid. Once your solar array generates enough power for your home, you can use any excess electricity to charge your solar battery system, and then transfer the rest to the grid after your battery storage is fully charged.
What makes the hybrid inverter stand out from the other central inverters available for your home is its bi-directional power transfer abilities. As we discussed earlier, a battery inverter converts between AC and DC power for storage, while a solar grid-tie inverter manages the relationship between the home, the home’s solar power system, and the electricity grid. (There are three primary versions of solar inverters: string inverter, micro-inverter, and power optimizer. To learn more about the pros and cons of each inverter option, check out our Solar Inverter Guide.)
The hybrid inverter does all of this, and can also use AC power from the grid to charge your solar battery storage if the energy from your solar panels is inadequate or being used to power your home.
Pros and Cons of a Hybrid Inverter
There are definitely some benefits provided by a modern hybrid grid-tie inverter, but there are also some drawbacks that you should be aware of. Below are a few of the hybrid inverter pros and cons that you should consider.
Pros of a Hybrid Inverter
Power Resiliency
Having a solar power system does not always guarantee you will have power during a power outage. If your system uses a traditional solar grid-tie inverter, it will still automatically shut off power from your solar panel system during a blackout for safety purposes.
A hybrid inverter paired with a solar battery storage system is a great solution for such a scenario. It ensures you have both off-grid and on-grid capabilities, so you always have access to power, even during a blackout.
Easily Retrofit Battery Storage
A full solar power installation can be a significant investment, especially if you add an energy storage system to the other individual components. A hybrid inverter is designed to integrate storage at any time, allowing you to forgo the costs of installing battery storage from the get-go. You can then more easily add the battery bank later while still enjoying the full benefits of your solar energy now.
Simplified Energy Monitoring
A hybrid inverter simplifies energy monitoring because you can check vital data such as performance and energy production via the inverter’s panel, or through a connected Smart device. If your system has two inverters, you have to monitor them separately.
Cons of a Hybrid Inverter
Not Ideal For Upgrading An Existing System
If you want to upgrade your existing solar power system to include battery storage, choosing a hybrid inverter could complicate the situation, and a battery inverter might be more cost effective. All you really need is an AC-coupled battery with its own battery inverter to expand your system. Since you already have a grid-tied solar inverter, choosing to install a hybrid inverter requires a complete and costly re-work of your entire solar panel system.
Increased Equipment Expenses
The initial installation of a hybrid inverter can be more costly than a traditional solar power inverter. If your area experiences frequent power outages and you want the option of adding battery backup in the future, having a hybrid inverter can be worth the higher cost.
However, if your power grid is reliable and you have access to net metering, a regular grid-tied system might be sufficient, and would likely be less expensive than a hybrid inverter plus battery storage.
Less Future Design Flexibility
Solar battery design changes with advances in technology, and not all hybrid inverters work with every type of battery. If you install a hybrid inverter now with the idea that you might add a solar energy battery later, your future options may be limited by compatibility concerns. For example, some solar panel energy storage systems now come with built-in inverters, eliminating the need for a separate hybrid inverter altogether.
Should You Invest In A Hybrid Solar Inverter?
While a hybrid solar inverter does require a larger initial investment, it can be worth the extra cost if you plan to include solar battery storage with your initial solar installation, or shortly after.
A hybrid inverter aids in the elimination of issues like intermittent sunlight and unreliable utility grids, so it performs exceptionally well compared to other types of solar inverters. Better still, a hybrid inverter helps you to store energy for future consumption more effectively, including backup power to use during power outages or peak hours.
Hybrid inverters also allow for more efficient power generation and management, especially when it comes to your relationship with the wider electricity grid through net metering and time of use rates. Additionally, ultra-modern tech allows you to conveniently monitor and manage your solar power system from anywhere via connected smartphone apps.
Can A Hybrid Grid-Tied Inverter Help Me Go Off-Grid?
Most home solar panel systems remain tied to the greater electricity grid, meaning they’re not truly off-the-grid. If you want to fully disconnect your home from the power grid, you must install enough battery capacity to power your home for days at a time, when your panels don’t generate enough electricity or there’s a grid outage.
If you do want to go completely off the grid, a hybrid inverter can help, because they are designed to complete multiple tasks as a single device, including solar panel operation, battery storage, and drawing electricity from generators and other sources of power.
Key Takeaways
Even with higher initial costs, a hybrid inverter can pay off in the long run by giving you a solar inverter that maximizes the operations of your PV system. A hybrid inverter can help reduce your reliance on the grid, lower your carbon footprint, enjoy advanced monitoring tools, and enhance your power generation.
If you’re ready to learn more about inverter technology and the right solar power system for your home, get started today with a Free Solar Savings Estimate, and then connect with a solar expert at Palmetto who can walk you through the various options that are available to power your home.