California is the first of many states in the United States to mandate Power Control Systems certification as well as UL 1741 SA17/SA18 certification for all grid-interconnected inverters. Both criteria are met by OutBack Power’s most popular inverters for this application.
California Rule 21 refers to these regulatory criteria in the most recent amendments to interconnection laws in California (Phases 1, 2, and 3).
What exactly is UL 1741?
The new safety test standard, UL 1741 SA, certifies items that fulfill the stringent requirements needed to enable safe and reliable grid modernisation initiatives. Beginning September 8, 2017, Hawaii and California will require grid support or “smart inverter” functionality.
Although grid support functions are only required in Hawaii and California for the time being, projected modifications to the IEEE 1547 interconnection standard will make them mandatory in most of North America within two to three years.
Is it possible to utilize a grid inverter off-grid?
Yes, you can utilize an off-grid grid-tie inverter. Only a reference power source, such as a diesel generator, and ZED Advance are required. To create electrical power in synchrony with the reference power source, the Gird-ties inverter required a reference power source. However, employing a generator as a power source necessitated the use of a solar inverter control device, which protects the generator from the solar power plant’s surplus power by limiting the solar power plant’s power generation according to the load need.
How big of an inverter do I need for off-grid power?
A solar inverter is a device that converts DC electricity into AC electricity. There are two types of solar systems: grid-connected (grid-tied) and grid-unconnected (grid-unconnected) (off-grid). Grid-connected systems are significantly easier to understand. The inverter’s job is to convert DC to AC power for your home’s use as well as to transmit excess power to the power grid. Because grid-connected solar power systems have less equipment, the inverter doesn’t have to operate with as many components.
However, with an off-grid solar power system, the solar power inverter will require a battery bank to operate. An off-grid solar power inverter works as follows. The DC solar electricity from your solar panels is fed into the batteries. The solar inverter then turns that energy into AC power for your home.
How to choose the best off-grid solar inverter?
There are a few pointers to consider while choosing an off-grid solar inverter for your solar power system.
This is determined by your load requirements and is usually the same as the normal supply voltage/frequency in your country. The output voltage of an off-grid solar inverter should match the load nominal voltage. In Europe and Africa, 240V is used, but in the United States, 120V is used. In Africa and Europe, the inverter should maintain a frequency of 50Hz, while in the United States, it should maintain a frequency of 60Hz.
Power range is important when it comes to solar equipment. You should be certain that the equipment you purchase is capable of meeting your power requirements. Even if you have enough panels to create the required quantity of power, your inverter will not be able to handle the load. As a result, the power range of your inverter is crucial. The following is a list of the several inverter power ranges and their common applications:
While inverters come in a variety of sizes other than those listed above, these are the most common, with 4 kW and 8 kW being the most prevalent.
Once we’ve decided on the solar inverter power capacity and brand/manufacturer, the inverter specs sheet will list the associated DC input voltage range, which we’ll need to match with the batteries voltage.
MPPT is theoretically superior since it can convert high voltage from solar panels to lower voltage, resulting in low losses (high efficiency) when charging batteries, but it is more expensive than PWM. On the other hand, we can confirm that PWM solar charge controllers will operate as well as MPPT charge controllers if they are appropriately sized according to solar panel specifications.
The technical specifications for solar power inverters are as follows:
Efficiency. When your solar power inverter is performing properly, this is a measurement of how much power it transfers to your home from the batteries. Peak efficiency ratings of 94 percent to 96 percent are considered good.
Temperature Variation. Solar power inverters generate a lot of heat. If you want to install your solar-powered system in your garage or somewhere else where it can be exposed to temperature extremes, pay close attention to the temperature range.
Warranty. The warranties for solar power inverters start at one year and commonly last between three and five years, with a few manufacturers giving a 10-year warranty extension option.
Conclusion
Off-grid inverters have advanced to the point that they can coordinate battery maintenance and charging schedules, as well as turn on backup power automatically, making these systems easier to manage, utilize, and worry-free.
Calculating your electricity loads and usage patterns is crucial to selecting the proper inverter for your off-grid setup. This assessment must be done with care and honesty to yourself in order for your entire system to be properly sized and function without failure.
What is the function of an off-grid solar inverter?
Solar PV systems off the grid function on the basic photovoltaic principle, which states that when solar radiation strikes a solar panel, it generates energy in the form of direct current (DC). The generated DC energy is sent into the charge controller, which regulates charge flow and delivers the battery with regulated power.
What does it mean when a solar inverter is anti-islanding?
When the grid becomes islanded, anti-islanding protection is a regularly required safety feature that shuts PV inverters. For UL1741 / IEEE 1547, anti-islanding protection is necessary. For today’s PV system designers, understanding how this protection approach works is critical. Eric Every, Sr. Applications Engineer, YaskawaSolectria Solar, presented a webinar recently in which he discussed a number of scenarios in which anti-islanding protection is required and how our PV inverters assist anti-islanding protection.
An island is described in this context as a situation in which PV is connected to a feeder and something on that feeder, such as a breakdown, causes the substation breaker to open. If the load equals the remaining generation, that feeder can stay electrified. The load will absorb current from the inverters, creating voltage across it, sustaining a situation where, in theory, everything will run forever, posing a safety and reliability problem across the grid. PV inverters could maintain energization across the connection if there is no anti-islanding protection. If this happens, the voltage and frequency may flow away, posing a risk to equipment.
An Area EPS must be de-energized within two seconds of the establishment of an island, according to IEEE 1547 section 4. In other words, if a PV Plant unintentionally energizes a piece of the grid through the interconnection point, the PV Plant interconnection system must detect the island within two seconds of its construction and stop energizing the grid.
We have two options for making sure this happens. The voltage and frequency are monitored using a passive approach. Second, we have an active anti-islanding strategy in which we change the reactive power output to help destabilize the island and speed up the system’s dissolution to extinguish the island.
We supply the voltage and frequency settings of our equipment to enable the passive technique. Every PV inverter that leaves the factory is put through its paces to ensure that these functionalities are working properly. Customers can request a test report for their inverter from us at any time. These settings will normally trip first in the event of an island, before the active anti-islanding excursions. If the loads are not closely matched but might easily exceed their permitted ratings, the inverter’s settings will turn off all of the inverters at the appropriate times.
We apply a technology called Slip Mode Frequency Shift for the active anti-islanding function. This changes the inverter’s reactive power output. The purpose of this protective strategy is to try to modify the frequency of an islanded feeder in order to destabilize it. The anti-islanding function of the inverter is tested using this diagram from the IEEE 1547 testing method.
To properly detect and disintegrate the island, we purposefully force the frequency out of spec and push against the grid. We evaluate the ability to disrupt the island within two seconds by turning off the anti-islanding mechanism, creating an island, turning it back on, and testing the ability to disturb the island within two seconds. In our experiments, we were able to complete the task far more quickly.
If you have a witness test and your utility comes out to make sure your voltage and frequency settings are correct, your transformer is connected properly, and your recloser is programmed properly, they will often disconnect the entire site to ensure all inverters turn off, and then open one phase out of three to ensure the PV inverters turn off.
The inverters seek for an imbalance of output current in open phase detection. We put the scenario to the test at our equipment’s terminals, which is simple to execute and pass. If there is a transformer between the inverters and the point of interconnection, or if there are motors or other equipment in the way, the inverter’s ability to see through the transformer will be hampered. As a result, make sure to follow your equipment’s transformer specifications. The PV inverter will not be able to identify an open phase state adequately if the transformer is not compliant, hence it will continue to function. Negative Sequence Current Protection should also be enabled in your relay. This will detect current imbalances in the line and will trip the recloser or breaker.
The Yaskawa – Solectria Solar Webinars are often packed with questions, and this one was no different. Here are some of the questions Eric answered.
Q: Is it possible to use a VAR-based active anti-islanding approach in conjunction with a dynamic volt VAR control? What effect does riding through have on anti-islanding protection?
A: For some volt VAR control, we can apply anti-islanding. It’s possible using our most recent firmware. We successfully tested volt-VAR and anti-islanding at the same time.
A: We must give Open Phase Detection at the inverter’s terminals. You should have no problems if you follow the transformer specifications.
Q: Within the next year, would Yaskawa – Solectria Solar PV Inverters meet the NEC 2014 code for quick shutdown?
A: Yes, that’s a possibility. Our website has a presentation that may be downloaded and discussed on our YouTube channel.
If a generator is linked to a PV inverter, wouldn’t the voltage and frequency source switch on the inverter if connected to the generator output?
A: That has happened in some cases, and it has been promoted. Some customers are installing PV in conjunction with generators, disconnecting from the grid and activating the transfer switch so they may run on diesel and augment the energy from the diesel generator with solar to save money on fuel. It’s probable that some extra controls will be required to limit the variance of PV output and slow down the operation of the generator sets in order to achieve equilibrium. There is a lot of research that has to be done first. Some simulations of power systems are required. Although some additional protective controls are required to ensure that the system can self-balance, this is an excellent example of a micro-grid.
Q: Are your transformerless string inverters multi-level inverters or small magnetic converters with high frequency?
A:We use three-level inverters in all of our transformerless string inverters (multi-level). They are able to provide adequate isolation to meet UL 1741 criteria because to the three-level IGBTs and contactors included into the device. Having a low-frequency transformer is often less expensive.
What is the total number of UL standards?
UL is a certified standards developer in the United States and Canada, with over a century of experience in the production of over 1,500 standards. UL Standards collaborates with national standards organizations in countries throughout the world to achieve a safer, more sustainable world as part of its worldwide public safety mission.
Are grid-tied inverters permitted in the United Kingdom?
In the United Kingdom, all small grid-tied inverters (up to 4kW) must fulfill the Energy Networks Association G83 standard. This, among other reasons, necessitates the inverter securely shutting down in the event of a power outage.
What is the difference between an inverter that is off-grid and one that is on-grid?
The term “on-grid” refers to a solar power system that is connected to the utility’s power grid, whereas “off-grid” refers to a system that operates independently and is not connected to the utility’s power grid.
What’s the difference between an off-grid inverter and a hybrid inverter?
Off-grid solar systems necessitate the use of specialized off-grid inverters and battery systems capable of storing energy for at least two days. Hybrid grid-connected systems use lower-cost hybrid (battery) inverters and only require a battery that can produce electricity for 5 to 10 hours (overnight) depending on the application.
Is it possible to power a refrigerator with a 1500 watt inverter?
Most inverters have two capacities listed on the manufacturer’s label. ‘The’ “Continuous wattage is the AC power output that the inverter can provide 24 hours a day, seven days a week for as long as the DC input lasts. ‘The’ “The AC power output the inverter can deliver for a split second is known as peak surge watts. Inverters sold at budget retailers and home centers typically give 1,500 watts of continuous AC power and 3,000 watts of surge power. This unit should easily power a regular 16 cu. ft. refrigerator.
