Tasks of the PV inverter

The tasks of a PV inverter are as varied as they are demanding:

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1. Low-loss conversion
One of the most important characteristics of an inverter is its conversion efficiency. This value indicates what proportion of the energy &#;inserted&#; as direct current comes back out in the form of alternating current. Modern devices can operated with an efficiency of around 98 percent.

2. Power optimization
The power characteristics curve of a PV module is strongly dependent on the radiation intensity and the temperature of the module &#; in other words, on values that continually change over the course of the day. For this reason, the inverter must find and continually observe the optimal operating point on the power characteristics curve, in order to &#;bring out&#; maximum power from the PV modules in every situation. The optimal operating point is called the "maximum power point" (MPP), and the search for, and tracking of, this MPP is correspondingly called "MPP tracking." MPP tracking is extremely important for the energy output of a PV plant.

3. Monitoring and securing
On the one hand, the inverter monitors the energy yield of the PV plant and signals any problems. On the other, it also monitors the power grid that it is connected to. Thus, in the event of a problem in the power grid, it must immediately disconnect the plant from the grid for reasons of safety or to help support the grid &#; depending on the requirements of the local grid operator.

In addition, in most cases the inverter has a device that can safely interrupt the current from the PV modules. Because PV modules are always live when light is shining on them, they cannot be switched off. If the inverter cable is disconnected during operation, this can lead to dangerous light arcs forming, which do not go out on account of the direct current. If the cutout device is integrated directly in the inverter, installation and wiring efforts are reduced considerably.

4. Communication
Communication interfaces on the inverter allow control and monitoring of all parameters, operational data, and yields. Data can be retrieved and parameters can be set for the inverter via a network connection, industrial fieldbus such as RS485, or wireless via SMA Bluetooth®. In most cases, data is retrieved through a data logger, which collects and prepares the data from several inverters and, if desired, transmits them to a free online data portal (e.g. Sunny Portal from SMA).

5. Temperature management
The temperature in the inverter housing also influences conversion efficiency. If it rises too much, the inverter has to reduce its power. Under some circumstances the available module power cannot be fully used.

On the one hand, the installation location affects the temperature &#; a constantly cool environment is ideal. On the other hand, it directly depends on the inverter operation: even an efficiency of 98 percent means a power loss of two percent &#;in form of heat. If the plant power is 10 kW, the maximum thermal capacity is still 200 W. Therefore, an efficient and reliable cooling system for the enclosure is very important &#; such as SMA&#;s &#;OptiCool&#; cooling concept. The optimum thermal layout of the components allows them to dissipate their heat directly to the environment, while the whole encasing acts as a heat sink at the same time. This allows the inverters to work at maximum rated capacity even at ambient temperatures of up to 50° C.

6. Protection
A weather-proof enclosure, ideally built in line with protective rating IP65, allows the inverter to be installed in any desired place outdoors. The advantage: the nearer to the modules the inverter can be installed, the lower the expenditure for the comparatively expensive DC wiring.

Discover solar inverters from SMA

What is a solar inverter and how does it work?

Step 1) The solar inverter channels DC power through its internal transformer

Step 2) The inverter transformer function is to lower the voltage and switch to AC

Step 3) The DC runs through two or more transistors

Step 4) The transistors are rapidly turned on and off to feed the transformer&#;s two different sides

A comparison: On grid and off grid solar inverters

Solar inverter connection to grids is gaining in popularity. The connection is made while wiring the system during installation. If the customer's solar panels produce more power than they need, it's transferred to the utility meter and then to the grid.

With an on-grid solar inverter, also known as grid-tied, they can either build credit to reduce their bills for when they need the grid &#; called net metering &#; or depending on where customers live, get paid a feed-in-tariff (FIT). The benefit here for customers is not only reducing their electric bills, but in essence, the grid acts as their battery storage. That said, it&#;s also possible to add a battery to this type of system and store energy yourself, but the customer will need a battery-specific inverter to convert the electricity from AC to DC to store and discharge.

An off-grid solar inverter system is connected directly to the residence or commercial site to work with the building&#;s mains. The customer has no access to the grid, so a battery, which isn&#;t cheap, is needed for storing excess energy. That still might not be enough to ensure energy will always be available, so a generator as a back-up is a good idea.

On-grid solar inverter

Off-grid solar inverter

Connected to the grid

Relies solely on the sun &#; ideal for people who live remotely, away from power lines

Can sell excess electricity to utility company or reduce utility bill for power used

Connected to building or home&#;s mains &#; no electrical bills

Cost effective &#; no batteries involved, though batteries can be added

Requires a charge controller to maintain battery at highest state of charge

Special circuitry matches the voltage,&#;frequency and phase&#;of the grid &#;will not operate if it fails to detect the grid, i.e. power outages

Unaffected by power outages

Smart hybrid solar inverter system

There&#;s also a hybrid inverter, which is grid-tied. It&#;s a solar inverter with battery storage. A solar inverter and battery-based inverter come together to make one piece of equipment to ensure an uninterrupted supply of power. With a hybrid solar inverter, users incorporate storage without the need for separate batteries.

The benefit of a hybrid inverter is that back-up power is available, thanks to the built-in battery &#; which is also a reason why these units tend to be expensive.

What are the types of solar inverters?

There are three main types of solar inverters:

Solar power string inverter

Application: commercial and residential

A string inverter functions in a series circuit. The panels are installed in rows. So if there are 12 panels total, they might be installed three across in four rows. This is called a "series string,"&#;or as some people call it, a multi-string solar inverter.

Each string carries the DC power generated by the solar panels to the string inverter. The solar inverter converts the DC to usable AC power. Depending on the size of the installation, multiple string inverters might be required.

As the solar panels are all wired in a series, what happens to one happens to them all. If one panel is shaded, its sun exposure is limited, weakening not only that one panel's output, but all of the panels. Another point: if the customer wants to add additional panels at some point, a new inverter will have to be added.

Power optimizers

To combat this problem, string inverters can be paired with power optimizers. These devices are installed at the module level. Each panel has one. They're also available already integrated into the panels.&#;The advantage of solar power optimizers is that they mitigate the impact of shading. They achieve a high-energy harvest before sending the DC to the inverter.

Solar panel microinverter

Application: commercial and residential

Solar panel microinverters are similar to power optimizers, as these are module-level electronics. One is&#;placed on each panel, though there are some that can handle two or four. Power optimizers don't convert DC to AC, but microinverters do. Conversion takes place at the panels, so if one panel is shaded, it doesn't affect the other panels' performance.

As microinverters are installed at the module level, they can also monitor the performance of each individual panel. In comparison, string inverters can only show how each string is performing, which is one reason why microinverters cost more. Installing solar panels with microinverters is also more time consuming than setting up string inverters, which adds to the cost.

Central inverters

Application: Industrial &#; typically used on solar farms

This solar power inverter installation will require a mounting pad. Central inverters are similar to string inverters. They&#;re larger, mounting on the ground or floor, and able to support far more strings of panels. Instead of the strings connecting directly to an inverter, they connect to a combiner box. The combiner box carries the DC power to the central inverter, which converts to AC.

They can range in power and are rated for either indoor or outdoor use. Architecture varies in structures this large, but the simplest consists of a single DC-AC conversion stage. You&#;ll find that some inverters have a DC-DC boost stage to increase the maximum power point (MPP) voltage range. To boost the AC voltage and provide isolation, sometimes, a low-frequency transformer is provided at the output. The disadvantage to this is that it reduces the efficiency and increases the size, weight and cost of the inverter. To get around this, inverters without transformer inverters with a front-end boost stage can be used.

Understand more about solar equipment in our guide, Types of solar equipment, explained

Inverters in solar panel systems: at a glance

Inverter:

String

Microinverters

Explore more:
Essential Guide to Testing Your Emergency Lights

If you want to learn more, please visit our website Multi String Inverter for Germany.

Central

Summary

-Solar panels are installed in rows, each on a string

-Module-level electronics so one is installed on each pane

-Microinverters are the smallest inverters and slowly gaining popularity and market share

-Similar to string inverters but much larger and can support more strings of panels

-This type of inverter is the largest in terms of capacity

Design

-Suitable for installations without shading issues &#;can be paired with power optimizers to mitigate these effects

-Available in 3 types: on-grid, off-grid and hybrid

-Good for installations with shading issues or with panels on multiple planes facing various directions

-Designed to connect directly to the electric grid. Require fewer component connections, but require a pad and combiner box

Rated power

-Range from 1kW to 100kW

-Usually range from 250W to 1kW

-Can range from 100kW to a few megawatts

Maximum input voltage &#;refers to the maximum DC voltage that the inverter can withstand on its input side; dictates maximum voltage that PV array can have

-1,000V

N/a: manufacturers of microinverters specify the ratings of PV modules that their microinverters are compatible with

-Usually 1,000V, though some are V

Maximum Power Point Tracking (MPPT)

-Typically 2-3 MPP inputs that accommodate 2-3 PV module strings

-Best MPPT capability, as each PV module is connected to its own MPP input

-Least amount of MPP inputs and are the most inefficient in terms of optimizing the power production of PV modules. However, this is usually not a problem since central inverters are usually used where the PV module&#;s tilt and orientation are uniform

Cost

-Less expensive than systems with microinverters

-Efficient, but often cost more than string inverters

-Installation can be cheap and easy as microinverters are often already integrated into the panel

-Inexpensive in terms of per kilowatt cost

Reliability

-Less reliable due to single point of failure

-Highly reliable as no single point of failure

-Often placed in protective environments, though still open to single point of failure

Typically used

-Great for residential and commercial applications

-Can also be a popular alternative to central inverters in small utility installations smaller than 1 MW

-Popular choice for residential and commercial installations

-As technology improves slowly being used for commercial and even utility-scale applications

-Perfect for large installations with consistent production across the array

-Utility-scale systems such as solar farms

What is a solar inverter monitoring system?

Monitoring systems operate through the inverter. As already mentioned, microinverters monitor the performance of each solar panel. Nowadays, most solar inverter manufacturers and distributors offer a monitoring software setup that works on the cloud, and it&#;s an attractive feature for customers. When the solar inverter system converts DC to AC, they&#;re given information about power levels and the amount of power produced. They can access these details on apps and other smart devices. Monitoring systems also provide diagnostic information, which helps manufacturers identify and fix any issues.

Download free CADs and try before you buy

Download free CADs and request free samples, which are available for most of our solutions. It&#;s a great way to ensure you&#;ve chosen exactly what you need. If you&#;re not quite sure which product will work best for inverters for solar panel systems, don&#;t worry. Our experts are always happy to advise you. Whatever your requirements, you can depend on fast despatch.

You can also learn more from our Quick guide: components for your solar PV system.

Request your&#;free samples or download&#;free CADs now.

Questions?

us at or speak to one of our experts for further information on the ideal solution for your application&#;800-847-.

For more information, please visit Solar Panel String Inverter for Germany.