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.
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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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How long will you live in your home?
The majority of solar power systems take at least 5 – 6 years to pay themselves off (this depends on factors such as solar system size and home location).
After this period, your home will essentially be generating free electricity from the sun.
Most solar panel manufacturers back their products with a linear performance warranty for 25 to 30 years. You can therefore expect to be earning free electricity for at least 20 to 25 years.
However, according to iProperty Management, the average length of homeownership for U.S. citizens is 8.17 years. “Only 37% of Americans have lived in their homes for 10 years“
Assuming you only own your home for 8 years (as per the statistics), would it really make sense to invest in a DIY solar system?
Well, according to the average pay-off periods, you would recover your initial investment within that time and would have at least 2 years of solar savings.
But perhaps you have already owned your home for 5 years? Make sure then that you don’t plan on moving out within the next couple of years if you really want to reap the solar rewards over the foreseeable future.
In addition to the above info, it is important to note that a solar system may increase your home’s value by 3.74% on the real estate market.
So even if you plan on moving within the next few years, investing in a DIY solar system can still be worth it.
What is the overall cost of a solar system?
The cost of solar has greatly reduced over the last decade.
As you can see from the charts above, solar has been reducing in cost over the years.
The overall cost of a solar system varies from one manufacturer to another, but on average you can expect to pay anything between 5000 – 30,000 (or more).
Because you will be installing your own solar panels you can expect to save a significant amount of money on labor costs which would cost on average about
What type of roof does your home have?
A DIY solar system can be installed on almost any type of roof. However, some roof types require much more effort than others, resulting in extra costs.
For example, it is very hard to install solar panels on a regular wood-shingled rooftop. If you happen to live in a home with this sort of roof, we would highly recommend that you call an experienced, professional roof-top mounting contractor.
.59 per watt.
Therefore, if you were to install a 6kW (6000 watts) solar system, you would save about 3540 on labor costs alone.
It is worth noting that the cost of labor varies from country to country. For example in Germany, labor costs are.36 cheaper per Watt than in the United States.
Sizing the Battery and Charge Controller
Most companies now offer batteries specified in Wh or kWh. For the load profile in our above example, the battery should be able to store a minimum of 2.74 kWh. Add some safety margin to this, and we can use a reliable battery size of 3 kWh.
Selecting a charge controller is similar. Look for a charge controller with a voltage rating that matches the panel and battery voltage (e.g., 12 V). Check the controller specs to ensure its current capacity is higher than the rated current of the solar panels (e.g., use a 20A controller for 11A solar panels).
Choosing the Inverter
Your inverter selection depends on the ratings of your battery and solar panel. Choose an inverter with a power rating slightly higher than your panels. In the above example, we have 750 W panels and can use a 1,000 W inverter.
Next, make sure that the inverter’s PV input voltage matches the voltage of the solar panel (e.g., 36 V), and the battery input voltage matches the voltage rating of your battery (e.g., 12 V).
You can buy an inverter with integrated ports and connect your appliances directly to the inverter, for ease of use.
Installing the System
By this point, you will have all the correctly sized equipment. This brings you to the final step — installation. Installing a solar power system is not complicated. Most modern equipment comes with ready-made ports and connectors so it’s easy to connect the components.
When connecting the components, follow the wiring diagram shown below. This will ensure that the power flows in the correct sequence and direction.
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Cost of Buying vs. Building Your Solar-Powered Generator
The overall cost of a completely DIY solar system or an option like EcoFlow’s solar generators depends on how much power you need and how you plan to use it. You may need to pay for an installation (or take on a much more complicated and dangerous DIY project) if you want rooftop solar panels as a permanent fixture in your home. Installation can impact price too.
Building your own system will likely cost you less on paper — if it works.
Most DIY projects can be scoped up to cost you less than a professional installation or a plug-and-play portable solar power system. However, once you factor in compatibility and quality issues and your own valuable time, the most compelling reason to go the DIY route is love, not money.
The costs of labor, equipment, installation, repairs, and replacement of incompatible parts can make purchasing an EcoFlow solar-powered generator more cost-effective in the long run.
With this option, you get a generator that’s ready to use and portable solar panels that you attach yourself. There is no need for installation as the solar panels are portable. You can buy the components separately and mix and match them. Plus, you can rest assured of compatibility and ease of set-up. It’s as simple as connecting your solar panels and flipping a switch!
Frequently Asked Questions
The short answer is yes, you can, but it requires research and patience. Solar-powered systems require multiple components and technical knowledge that the average DIY builder might not have.Alternatively, you can look for a trusted brand like EcoFlow and customize your own solar power system to your requirements without worrying about compatibility or quality.
The number of solar panels required depends on your battery storage capacity and how much energy you typically consume. Solar panels also come with different rated power wattages. You may want to purchase multiple smaller panels to create your desired solar array or buy one or two larger panels, depending on where you’re planning to install them.
An inverter and a solar battery are essential parts of a solar generator. EcoFlow’s solar generators also include the charge controller and everything else you need just to plug and play, all in one sleek, compact package.
There are numerous pros and cons to attempting a DIY solar power generator build. You can decide to build a solar generator yourself or take the easy route by customizing your setup with a portable power station and solar panels that suit your needs.
Either way, you’re investing in your energy independence and helping to make a positive change for our planet.
Whatever route you decide to take, solar power is a compelling alternative to conventional utility providers and aging infrastructure.
EcoFlow is a portable power and renewable energy solutions company. Since its founding in 2017, EcoFlow has provided peace-of-mind power to customers in over 85 markets through its DELTA and RIVER product lines of portable power stations and eco-friendly accessories.