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Advanced Electronics Impacting Solar Inverters and Its Market

The Evolving Inverter

Solar inverters have come a long way in the history of solar power generation. It won’t be wrong to say that they have remained one of the most advancing technologies in every decade of renewable energy advancement than anything else. Inverters convert simple DC electricity to AC that changes polarity (positive, negative) at least hundred times every second. AC voltage can be utilized in real world compared to battery power that is DC in nature or solar power for that matter, which is also almost similar. They are an important part of any electricity storage system that uses batteries to provide emergency power backup at home, hospitals, workplaces or places where grid supply does not reach.

Inverters make electricity generated by non-conventional sources useful and grid-worthy, which is natively highly irregular and inconsistent in nature. In wind and solar power generation specifically, inverters not only do this basic conversion but carry out one or more important tasks without which the system may cease to work.
For this very reason they get their own name –
Solar Inverters. Solar Inverters have been, and still are, put through a myriad of tasks and not just simple DC to AC conversion. It was back in 1839 that the photoelectric effect was discovered, a notion that light can produce electricity came into being. Almost 80 years later did we figure out a way to grow silicon crystals that can actually make it happen; and after 36 years to that in 1954, Bell Labs came out with the first commercial photovoltaic cell (solar cell) for space activities. At around the same time, inverters left their bulky form of gas filled tubes and moved to a compact setup, after the introduction of thyristors.

With the advent of transistor and more advanced semiconductor technology developed to work at high voltages, there was an increase in the efficiency and output quality of inverters, while their size decreased. But in many countries, people still use a basic charge controller setup. A typical home setup looked something like one shown in the image.

Inverters make electricity generated by non-conventional sources useful and grid-worthy, which is natively highly irregular and inconsistent in nature. 

MPPT

Maximum Power Point Tracking

Maximum Power Point Tracking or MPPT is technique commonly deployed in Solar PV systems and is one of the most important tasks handled by a solar inverter or related equipment. The output of a panel setup can vary heavily due to the various reasons – panel difference, shading or temperature fluctuations being the few basic problems. Moreover, the load characteristics also affect the amount of power transferred from the system. MPPT is all about making the panel immune to these variations by varying the operating voltage or current of the panel after sampling the output voltage or power – individually or of the whole array.

CENTRAL INVERTER

Charge controller is most popular choice for rooftop solar that can do MPPT for the whole array. Coupled with an inverter and a battery bank, it forms the most commonly used solar setup which gives the flexibility to use generated electricity anytime.

But involving batteries means adding another medium which incurs loses. Current panels extract about 16-20% (max) of the energy they get from the Sun. Over its lifetime, a battery provides 65-70% of this power to the inverter (average for commonly used lead-acid batteries). Until some great innovations happen in the battery domain or present Li-ion technology trickles down to lower cost bracket, a string inverter off-grid setup remains restricted in nature.

Hence, one of the most important tasks an Inverter can do is connect your solar power system directly to the grid. In cities utilities have this provision, grid-tie inverters are one of the most cost-effective ways to get return on your investment with minimal hassle. The battery is ruled out.

Some countries strictly require antiislanding feature on the grid-tie inverter and it is illegal to install one without it.

But if whole of the generated electricity is sent to grid, there would be no backup for self-use during power outages. Some models nowadays provide an optional diversion to local load directly from the system when it is generating.

A costlier alternative is to use a Dual-inverter that, after charging a set of batteries, can sell excess energy to grid. Commercial establishments using PV rooftop for backup lighting makes a perfect use case. Net metering makes it all the more lucrative in places where cost of electricity is very high.

Until some great innovations happen in the battery domain or present Li-ion technology trickles down to lower cost bracket, a string inverter off-grid setup remains restricted in nature.

Choosing The Right Inverter 

When we talk about going solar, solar panels get the entire buzz! But there are other backers like batteries, inverters, and various kinds of wires, bolts, and racks, if not paid equal attention, can quell your dream of energy independence.

First thing before going for a solar power plant is the knowledge about your requirement. If you are installing solar panel on your rooftop, don’t think about running Electric motors, Refrigerators, Air conditioners. For normal domestic usage consider using light loads like Fan, TV, Music Systems etc. If you still want a complete off-grid solution for multiple applications, you can always go for high capacity plants (2 KW to 5 KW).

Here’s a quick brush up on some standard electrical terms

• Watts: Watts is just a measure of how much power a device requires or can supply when turned on. If any device uses 100 watts, that is simply the voltage times the amps. A watt is defined as one Joule per second. It is worth noting that there is nothing like “watts per hour”, or “watts per day”

• Kilowatt hour: A watt-hour (or kilowatt hour, kWh) implies how many watts times how many hours that is used for. For example if a bulb uses 100 watts, and it is on for 9 hours, that is 900 watt-hours. If oven uses 1500 watts, and runs for 10 minutes, that is 1/6th of an hour x 1500, or 250 WH. A kWh is a “kilowatt hour” or 1000 watts for one hour (or 1 watt for 1000 hours).

• Amps: An amp is a measure of electrical current at the moment. It determines what wire size you need, especially on the DC (low voltage) side of an inverter. If your wire is too small for the amps, you can get hot wires and can also result in voltage drop. Amp is equal to the charge of 6.24 x 1018 electrons passing a point in a circuit in 1 second.

• Amp-Hours: Amps x time = AH (Amp-hours), it is the main measure of battery capacity

• Efficiency: The ratio of output power to the input power is termed as efficiency. It is difficult to achieve 100 percent efficiency, because some power is lost in the form of heat. The efficiency of solar inverter depends on load. The specifications of the inverter contain an efficiency graph. It is the graph of efficiency versus load.

• Internal protection: The solar inverter components must be protected from overload, lightning surges, etc. It must contain sensing circuits to sense the problems and automatically shut down. If the supply voltage is less, it must shut off. Otherwise the battery will over discharge and even get damaged. There are 3 major types of solar inverters based on the output it produces: – sine wave, modified sine wave and square wave;

• Sine wave: Majority of equipment available in the market work on sine wave. Local utility and generator produces sine wave. Sine wave guarantees that the equipment will work to its full specifications. Some appliances, such as motors and microwave ovens will only produce full output with sine wave power. Sine wave inverters are always more expensive – by 2 to 3 times as much.

• Modified sine wave: Modified sine wave inverter actually produces a waveform more like a square wave. However, the efficiency or power will be reduced with some device, and they might use more power due to its low efficiency. But they are cheaper than sine wave inverters.

• Square wave: These are the cheapest of the inverters. A square wave inverter will run simple things like tools with universal motors without a problem. But they are rarely in use. Majority of the AC appliances can operate in modified sine wave.

ROLE OF ELECTRONICS

Due to their higher output efficiency, plug-and-play nature, better output quality and extended configurations for remote monitoring they have seen many takers for rooftop installations in developed countries, despite its high cost. 

 

Mounted behind the panels, micro-inverters are the latest talk of the solar power industry. That is the point where electronics enter at a big scale and make everything smaller. It was a refined technology that had seen reluctant adoption due to their high per-watt cost and heating issues. Ironically, though newer models have changed that. OptiMOS and CoolMOS from Infineon, for example, use low and high voltage MOSFETs respectively for low maintenance, panel integrated packages that are small, efficient and offer precise control. A recent study published in IEEE also shows MICs using a DC-link capacitor can prove beneficial in MW-level solar farm installations. Module Integrated Converters or MICs can be modified by employing a two-stage conversion process that can reduce their
per-watt cost. In first step, a LLC resonant DC-DC conversion circuit produces DC-link voltage. Followed by MPPT algorithms developed for LLC resonant topologies, generated DC is then converted to 3-phase AC using three inverter circuits. This Two-Stage Three-Phase Grid-Connected Module Integrated Converter deploys a simple soft-switching scheme that not only guarantees better output voltage regulation and zero MOSFET loses, irrespective of the voltage and frequency needed, but also reduces the harmonic spectrum of any electromagnetic interference (EMI) and allows operation at much higher frequencies that can be used in particular industrial applications.

The increased use electronics and modified electrical components in place of bulky magnetic switching components have made the inverter not only lighter, but more robust as well and free from electromagnetic complications. Using digital solutions to control these components will make the Inverter technology advance at a rapid pace. Both Gallium Nitride and Silicon Carbide have a high critical field compared to Silicon which allows these devices to operate at higher voltages and lower leakage currents. While Gallium Nitride (GaN) has the highest electron mobility and hence can work at the highest frequency out of the three, Silicon Carbide (SiC) devices have better thermal conductivity and hence can operate at higher power densities than Si and GaN. Both GaN and SiC can operate at higher power densities, temperatures, voltages and frequencies that make them sensational solution for use in Inverter solutions.
Moreover, GaN has low Rds_on, low gate charge, low drain-source capacitance Cds and an extremely low Qrr. So the GaN based switches are smaller in size and much cheaper to produce than the current MOSFET and IGBT devices. Due to their drawbacks like the need very fast switching and bunch of other problems they haven’t seen commercialization. But companies are finding solutions to it in the digital and algorithm based techniques. The recent example is the inverter design that bagged first prize at the Google Little Box challenge. The Red Electricals Devil Team from CE+T, Belgium created an inverter prototype with digital control built out of a fast microcontroller-based arrangement. Successfully using Soft Switching over the entire operation range by digitally controlling all GaN transistors, the team was able to reach high power density and high efficiency without breaching thermal or switching barriers.

Two half bridges (HB) generate the neutral voltage, two further half bridges generate the line voltage and the last is used as an active filter.

While stressing the need to GaN package and robustness of GaN control, the winning team revealed various challenges it faced in the designing of the sandwich structure and the heat sink. They used micro-spring contacts, a 0.012 inch thick PCB, Silicone foam to ease GaN contact pressure, and forced air cooling techniques to shrink a 2KVA inverter to size of a portable hard disk. You can read the submission at www.littleboxchallenge.com/pdf/ finalists/56568-Tech.pdf Be it the GaN transistors operating in ZVS topology, or SiC-4H (silicon carbide) based switching, or even algorithms applied to reduce magnetic and electrical components this shows electronic components are ousting aluminum and copper parts and it will be the main driver of cost and performance of the future breed of products.

They used micro-spring contacts, a 0.012 inch thick PCB, Silicone foam to ease GaN contact pressure, and forced air cooling techniques to shrink a 2KVA inverter to size of a portable hard disk.

There are basically four types of inverters used with solar panels

• Standalone Inverters allow for off-grid use or backup power. They are large boxes and use mechanical rotors to switch the direct current to alternating. These inverters integrate battery to store and supply power during an outage and are completely centralized.

• Grid-Connected inverters link your solar panels into the grid at your power meter, it allows you to sell excess power back to the utility company. These inverters do not integrate battery and are often cheaper than standalone inverters.

• Dual-Inverter are hybrid of standalone and grid-connected inverters which allow you to sell excess power back to the utility company as well as supply power during an outage and are completely centralized. Dual- inverters are quite expensive.

• Micro Inverters are new type of inverters that connect to individual solar panels and convert the DC to AC power before it enters your home. These inverters allow each panel to operate self-sufficiently, so that if one goes down, the others can produce power. Microinverters require extra time to install.

SMART INVERTERS

A smart inverter or intelligent hybrid inverter perfectly match the un-defined and highly varied real-life usage needs. You might need to store electricity or you may not; you need to sell it, but keep it for self-use as often, while you expand your setup.

They can work on-grid, off-grid, hybrid style or in backup mode and hence, it won’t be wrong to say, that they are the future of inverters used in commercial and home setups.

Some features of the smart inverters –

Stores energy only when necessary

• A smart inverter can be timed to store energy only when necessary, thus minimizing battery losses

• Sell total energy

• Charge batteries and sell to grid simultaneously

• Only keep solar power for backup, sell the rest

Monitoring and control – With the increase in power generation from renewable energy, the dependency on it will only increase. There arises then, a need for superior monitoring and control methods. With a user interface and integrated Ethernet/Wi-Fi, smart inverters are easy to setup and monitor all stats remotely or on a smart mobile device.

Reactive power control – To keep a healthy balance between the active and reactive power for highest transmission and utilization efficiency, voltage regulators or capacitor banks are generally used. But Smart Inverters are built-in with the capability to correct the voltage by using its self-generated reactive power. This not only improves cost implementation of the system but the quality of power supplied.

Temporary faults – In large scale installations, it is necessary to keep the system up and running with minimal down-time. A connected inverter can faster and more accurately report problems in the system.

Electronic components are ousting aluminum and copper parts and it will be the main driver of cost and performance of the future breed of products.

Can a home inverter be used as a solar inverter?

If we compare a basic solar inverter with a home inverter, the difference is not much. Both are inverters and do the same job of converting DC current from batteries to AC that is supplied to homes. The difference of solar inverter and inverters that we normally use at our home is that the solar inverter consists of solar charge controller and associated switching circuits. Solar inverters have built-in MPPT circuitry that optimizes the output of the system. Solar inverters also have dedicated terminals for connecting battery and solar panels of correct rating. In many countries, inverters connecting to grid also need to have anti-islanding property as a mandatory requirement. Upon detection of islanding, a condition when a local electric power system, like a solar setup, continues to power a location while the utility goes out of power, the anti-islanding functionality will cut-off the setup from the grid automatically (within 2 seconds as per IEEE standards). You can also convert your normal inverter into solar inverter by connecting charge controller along with an automatic transfer switch. If the solar panel gives sufficient supply to charge the battery, then the automatic transfer switch will be directed to the battery and does not take power from main supply.

RATINGS OF INVERTERS

Inverters are rated in watts – all the way from 50 watts up to 50,000 watts. Generally in household or other PV systems not more than 11,000 watts are used. Before you go solar, it’s very important to know what will be the maximum power surge, and its duration.

• Kilowatt peak – To find out KW rating while selecting an inverter, peak power from solar panel is taken into account, which is calculated by assuming 1KW/ square meter of solar radiation falling on the panel.

• Surge: Inverter’s surge capacity indicates how it handles short-term overload before “tripping”. Surge capacity is essential to start up some large loads, especially motors that need 2-3 times their running power to get going. The Surge capacity can vary considerably between inverters. Generally, a 3 to 15 second surge rating is enough to cover 99% of all appliances.

• Rules: The inverters with the lowest surge ratings are the high speed electronic switching type and are typically from 25% to 50% on maximum overload. Surge ratings on these can range up to 300% for short periods. While high frequency switching allows a much smaller and lighter unit, due to the much smaller transformers used it also reduces the surge or peak capacity. Summing up, now when you have decided about the kind of inverter you need, it’s time to look into the capacity. It’s important to choose inverter with slightly more capacity than your required peak power.

The best way to calculate this is to add up the power usage of your largest appliances—refrigerator, tube light, television, music system and air conditioning unit / heater. Though it is rare that you are going to run all the device at a time, even if you plan to run all, make sure your inverter will be able to handle the load.

Many devices require an additional burst of power when first switched on, so look for inverters labeled “surge compliant”. It’s also best to choose an inverter with a slightly higher max output than your estimated energy needs. Finally, contemplate how much power your panels can produce to determine what input capacity you need. If you’ve installed a 10kW system, you should go for an inverter that can handle that input as that is what the system can supposedly produce during peak hours.

THE COLOSSAL INVERTER MARKET

India is on the ramp of ousting other countries from their solar expansion program. It’s not an individual opinion but official reports reiterating that  the target of 20,000 Mw of solar power proposed to be installed in the country has been reset by the NDA government to achieve five times more at one lakh Mw of solar power by 2022.  The target, which looked overambitious, now seems to be within the reach with several States already witnessing silent revolution on rooftop solar power generation with the launch of net metering in the country.  According to the given date 31.10.2015, cumulative capacity of about 38 GW of grid-interactive renewable energy capacity has been installed in the country. 

Solar Inverter – A Market Backdrop 

The logged growth from the solar sector shall not take us on serendipity as the growing sporadic power distribution gave ways to the easy alternative (solar power) market to take the responsibility. Given the umbrella of solar power processes making everyday headlines is because of their given reliability, efficiency and cost. During this transition, Solar Inverters has generated immense capabilities to back the photovoltaic market. Not only growing market like Asia and Latin America have established their individual market for Solar Inverters equally have stride to grow the efficiency challenges in the solar processes.

Talking about the heart of solar panel system, the inverter is what pumps the solar function to the given delivery. Unlike many module suppliers, inverter manufacturers have been very cautious in their expectations of future demand and have maintained capacity and inventory levels at relatively healthy levels. As a result, PV inverter prices have been far more stable than those of PV modules, and the outlook for inverter revenues looks very different.

According to reports, the market has ballooned at a CAGR of more than 60% from FY’2011-FY’2015. In terms of installed capacity, the sector registered a growth of 53.7% during the review period FY’2011-FY’2015. Incredible growth of awareness and collective government dialogues on solar energy’s benefits has been an evident factor behind the incredible growth of this industry. Intense competition and convincing advertisement and promotional strategies adopted by players have enabled the increased adoption of solar inverters across the rural and semi-urban areas.

Big Names Ruling the PV Inverter Market

Huawei and SMA were the leading global vendors of solar photovoltaic inverters in 2015, according to preliminary findings from GTM Research’s report-

“The Global PV Inverter and MLPE Landscape.”

SMA settled at the top ranking list in the inverter-shipment rankings for the first time, despite increasing its global shipments by 44 percent. The rapid rise of Huawei to its position as a global market leader can be attributed to its strong growth in the Chinese market.

Overall, the market is becoming increasingly consolidated. The top 10 inverter vendors accounted for 75 percent of global shipments in 2015, up from 69 percent in 2014 and the highest since 2010. The market is more balanced when viewed by revenue, with the top 10 vendors accounting for 64 percent of the overall market and including residential and commercial inverter players SolarEdge, Enphase, Omron, and Tabuchi.

We asked TMEIC about their current offerings in the inverter domain, this is what Syed had to say:

Lowest levelized cost of energy (LCOE) and reliability have been the bedrock of TMEIC’s design philosophy. TMEIC’s unique experience in PV inverters go back to the dawn of solar farm era in 1985, when we first introduced MW sized inverter which was installed in Carrizo Plain, CA for MW-scale solar project. With over 25 years of research and development, customers can take advantage of TMEIC’s full potential of advanced technology and make the best of an investment in solar power generation plants. With the highest knowledge of energy conversion and power electronics along with years of experience in PV inverter development and manufacturing, there is no doubt that TMEIC is capable of providing maximum profitability and industry’s best solution for PV inverter needs. Having the best Inverter in the industry, we can lower the LCOE and significantly lower PM (Preventive Maintenance) and O&M (Operations and Maintenance) for life of the plant. TMEIC’s current Market offerings are 750-KW, 1-MW. 2.5-MW at 1000Vdc and 1500Vdc.

China clinching the Global Revenue

A growing acceptance of Chinese inverters has earmarked that 63% of PV inverter buyers now believe Chinese inverters offer “Quality-driven” inverters in a competitive price tag. Though, analyst asserts that there remains a concern among inverter buyers that Chinese firms offer inadequate technical support and after-sales service.

Meanwhile, Inverter revenues will increase by 2 percent in 2016 to reach $7 billion. Unit shipments will increase, but the average selling price of inverters will drop significantly to offset this growth. Chinese suppliers are becoming more
competitive in the global PV inverter industry. “In 2015, while Germany’s SMA Solar Technology defended its leading position by revenue, two Chinese suppliers, namely, Huawei and Sungrow, have taken first and second places globally by shipments, on account of the booming Chinese market,” said Frank Xie, senior analyst for PV inverter and balance of system.

The inverter breakdown by type is also changing considerably. IHS forecasts three-phase, low-power inverters (lessthan 99 kilowatts) will account for onethird of the global inverter shipments by 2019, benefiting from the rapid growth of commercial installations in major PV markets, such as China and the U.S. Three-phase, high-power inverters, which include both standard central inverters and turn-key solutions, will continue to lead the market with an annual usage growth of 1,500 volts, as more markets adopt them – and as they demonstrate proven success – beginning this year. With perennial technological advancements and integrated technologies the Indian solar inverter market is reported to be on track. With most of the major players dominating the market, new players are also expected to foray into this segment. In the coming days, the major tussle will be delivering on words and creating long-term market space. Though the Indian market is still nascent curating huge potential for future, the providers will have to look into the market-sense and rationalize their offerings for the future of this industry. Being a new sector into Indian environment, there are skeptics regarding grid architectures, climate volatilities which confine the consistency of an inverter. Therefore robust design, optimum performance, and last-mile commissioninChina clinching the Global Revenue g will define their patrons. The Total Installed Capacity of Solar Inverters inclined at a CAGR of 53.7% during FY’2011-FY’2015 whereas the market for Solar Inverters in India is projected to incline at a CAGR of 76.9%. Lastly, promotional activities, government support, and media awareness will also compliment the growth for this sector in India.