Market of PV inverter is still Blue Ocean

The Copenhagen Conference started the era of low carbon economy. The concept of low carbon becomes more popular. Solar power is the most promising clean energy due to its cleanness and wide installation range.
Energy from fossil will be depleted and the reserves can not meet long term need for human. Finding a replacement is necessary. Global warming is becoming more serious. Energy saving and clean technology only can cure the symptoms not the causes. The only way is to find a zero emission new energy. Solar energy is the only choice to meet human development.
Technology advancement and scale effect will make cost of solar power decrease. It is estimated that if the sales of PV battery doubles, the cost will decrease 15~20%. In the mean time, the cost of fossil energy keeps increasing, and the cost of solar power is expected to reach peak price of electricity in 2010~2030 and average price of electricity in 2020~2050.
With the increasing investment on PV industry, cost is decreasing and competition is fierce. After financial crisis in 2008, price dropped sharply, and it is stimulating end market.
From second half of 2009, PV industry strongly recovered. In 2011, PV industry will face a turn point of high growth stimulated by both low cost and policy. Decreasing FIT (Feed-in-Tariff) is an inevitable policy adjusting to cost decreasing, implying the speed up of industry development. EPIA expects that PV installation will reach 22.325GW in 2013.
Following development of PV industry, market of PV inverter grew rapidly. The total market is about 4 billion USD. Because PV inverter does not rely on the different technology of battery, its growth is more powerful. European products take a lead in world market. These years, with growing of world market,, European PV inverter companies have started to expand.

PV inverter is heart of a PV system

Inverter functions to convert direct current (DC) into alternating current (AC), which turns out to be a “reverse” rectification process. Photovoltaic (PV) inverter is the core device of photovoltaic system. The performance improvement of inverter plays a crucial role in promoting the efficiency & reliability and service life of the system as well as reducing cost.
The electricity type generated by solar photovoltaic module is nonlinear DC, which must be converted to AC by DC/AC inverter when transmitting to grid. PV inverter is the core component of a PV system.
There are two types of PV system, on-grid system and off-grid. Accordingly, PV inverters also have two types, on-grid and off-grid. The capacity of on-grid inverter usually is the same as that of PV system, while capacity of off-grid inverter is decided by capacity and type of load, normally it is smaller than that of PV system. Referring to statistical record of PV system installation in the world, on-grid system dominates the total installation volume of world PV system, reaching 90% in a subsidy condition. With the development of technology, when cost of PV power reaches the level of waterpower and thermal power, off-grid application will be more popular. On current stage, on-grid inverter is the main product invested by most companies. Technical specifics of on-grid inverter show the level of PV inverters.

what is DC-AC Inverter

A DC-AC inverter is one which links an DC supply to an ac load, that is, it converters an constant voltage to sinusoidal voltage, the amplification and frequency of which are both controlled. But the voltage so obtained is not the same as a pure sinusoidal voltage containing much more harmonics instead.
Figure 1 shows a single-phase bridge DC-AC inverter with a constant voltage source. The principle is that Lv is positive when T1 and T2 are turned on, and becomes negative when T3 and T4 are gated instead. The switching scheme determines the frequency of the output ac current’s waveform,  while control of the voltage can be obtained by introducing zero periods into the waveform realized by phase-advancing the firing of T1 and T4 compared to T2 and T3 by an angle. With the inductance of the load, the current is continuous, so the voltage is somewhat reduced when the energy stored in the inductance is dissipated during the period T1 and T3 are turned on simultaneously. It must be emphasized that an elapse of a few microseconds after turn-off of T1 and T2 before T3 and T4 are turned on should be offered to avoid the risk of re-conduction in the outgoing transistors, giving a short circuit across the DC source via the two transistors. In this period the energy is fed back to the supply which is very common in inverter circuits.
The DC-AC inverter (shown in figure 2) with a constant current source’s operation is similar to one with a constant voltage source. The only difference is that the load current not the voltage is square wave. The frequency and amplitude of the output waveforms can be controlled by changing the switching frequency and introducing zero periods, which is the same as in the constant-voltage source inverters. If the switching device is fast enough just like the IGBT and MOSFET, even the capacitances of C1 and C2 are not necessary.
Low power level inverters are usually single phase type and medium and large power inverters are three-phase type shown in figure 3. It can work just like AC-DC three phase bridge with each thyristor conducing for 120, but more usual operation is that each thytistor conduces over  180. In this matter, the DC source is connected to the load via one device on one side with two in parallel on the other side. From the output waveform shown in figure 4, it can be conclude that the waveform is more similar to the sinusoidal one.
When the DC-AC inverter works in the inversion mode, it can also reverse the power flow to the supply like an AC-DC inverter. The direction of the power flow is determined by the relationship of the voltage and current. In practice, the AC load most likely to generate is an induction motor being accelerated by a mechanical torque to above synchronous speed. The current from such a generator is at a leading power factor.
Another way to obtain the transfer of a constant voltage to an AC voltage is the pulse-width modulation which has been discussed in detail in chapter 4. With a constant DC input, PWM can  provide a sinusoidal or other shape waveform precisely, but the output voltage cannot be too high.

The classification of waveform

According to Output waveform, inverter can be divided into two categories, one is sine wave inverter, and the other is square wave inverter.
1.Sine wave inverter’s output power is the same as or even better than sine wave AC Power which we use every day, because it does not exist grid electromagnetic pollution.
2.The output power of Square wave inverter(Improved called Modified sine wave inverter) is the square wave AC Power which with poor quality, and the positive maximum to the negative maximum value is almost simultaneously generate, which cause severe destabilizing effect on the load and the inverter itself. At the same time, its load capacity is poor, only 40-60% of the rated load, and can not to run inductive load. If carried load is too large, the three harmonic components contained in square wave current will increase capacitive currents which flowing into the loads, and sometimes it will cause severe damage to filter capacitor of the load.
In response to these shortcomings, there has been quasi-sine wave inverter (or modified sine wave, analog sine wave, etc.),
There’s a time interval exists between the positive maximum value of the output waveform to its negative maximum value, which improved the effect for use, but quasi-sinusoidal waveform is still made by broken line, it belongs to a square wave areas, and the continuity is not good. Overall, the sine wave inverter providing high-quality AC power, it can bring any kind of loads, but the technical requirements and costs are high. Quasi-sine wave inverter can meet most of our electricity demands, and also because of its high efficiency, low noise and moderate prices, Quasi-sine wave inverter become the mainstream product on the market. Square wave inverters produced by using simple multivibrator, its technology is in the level of the 1950s, and it will gradually withdraw from the market.
As the difference between Pure sine wave inverter and Modified sine wave inverter, please view the introductions of our Products:

Sine Wave vs. “Modified Sine Wave”

How clean is a “sine wave”? The manufacturer may use the terms “pure” or “true” to imply a low degree of distortion. The facts are included in the inverter’s specifications. Total harmonic distortion (THD) lower than 6 percent should satisfy normal home requirements. Look for less than 3 percent if you have unusually critical electronics, as in a recording studio for example.
Other specs are important too. RMS voltage regulation keeps your lights steady. It should be plus or minus 5 percent or less. Peak voltage (Vp) regulation needs to be plus or minus 10 percent or less.
A “modified sine wave” inverter is less expensive, but it produces a distorted square waveform that resembles the track of a pendulum being slammed back and forth by hammers. In truth, it isn’t a sine wave at all. The misleading term “modified sine wave” was invented by advertising people. Engineers prefer to call it “modified square wave.”
The “modified sine wave” has detrimental effects on many electrical loads. It reduces the energy efficiency of motors and transformers by 10 to 20 percent. The wasted energy causes abnormal heat which reduces the reliability and longevity of motors and transformers and other devices, including some appliances and computers. The choppy waveform confuses some digital timing devices.
About 5 percent of household appliances simply won’t work on modified sine wave power at all. A buzz will be heard from the speakers of nearly every audio device. An annoying buzz will also be emitted by some fluorescent lights, ceiling fans, and transformers. Some microwave ovens buzz or produce less heat. TVs and computers often show rolling lines on the screen. Surge protectors may overheat and should not be used.
Modified sine wave inverters were tolerated in the 1980s, but since then, true sine wave inverters have become more efficient and more affordable. Some people compromise by using a modified wave inverter to run their larger power tools or other occasional heavy loads, and a small sine wave inverter to run their smaller, more frequent, and more sensitive loads. Modified wave inverters in renewable energy systems have started fading into history.

The Cautions for Modified Sine Wave Inverters to run appliances

The Cautions for Modified Sine Wave Inverters to run appliances:
1. Do not plug small appliances into the AC receptacles of inverter to directly charge their nickel-cadmium batteries. Always use the charger provided with that appliance.
2. Do not plug in battery chargers for cordless power tools if the charger carries a warning that dangerous voltages are present at the battery terminals.
3. Not all fluorescent lamps operate properly with a modified sine wave inverter. If the bulb appears to be too bright, or fails to light, do not use the lamp with the inverter.
4. Some fans with synchronous motors may slightly increase in speed (RPM) when powered by a modified sine wave inverter. This is not harmful to the fan or to the inverter.
5. Do not use a modified sine wave inverter to carry the above two types of equipment.
6. The majority of portable appliances do not have this problem. Most portable appliances use separate transformers or chargers that plug into AC receptacles to supply a low-voltage DC or AC output to the appliance. If the label of appliance states that the charger or adapter produces a low-voltage DC or AC output (30 volts or less), there should be no problem powering that charger or adapter.
7. Certain rechargers for small nickel-cadmium batteries can be damaged if plugged into a modified sine wave inverter. In particular, two types of appliances are susceptible to damage:
7.1 Small battery-operated appliances such as flashlights, cordless razors and toothbrushes that can be plugged directly into an AC receptacle to recharge.
7.2 Certain battery chargers for battery packs that are used in some cordless hand-tools. Chargers for these tools have a warning label stating that dangerous voltages are present at the battery terminals.

How Inverter with Charger Works

How Inverter/Charger Works?
AC Utility(as priority by inverter):That is device tools for convert solar energy into alternating current output.
Batteries: They’re work to convert chemical energy into electrical energy for storage, you can use the DC output.
Power inverter with Built in Charger & ATS: it’s a device that able to convert direct current (DC) into alternating current (AC).
1、AC Utility as priority when it is available, the inverter/charger as a by-pass;
2、when AC Utility is available, the built in charger will automatically charge the battery bank;
3、when AC Utility is off, the inverter/charger will transfer the source from the AC Utility to battery bank;
4、Finally, the inverter converts the direct current into alternating current to run Sump Pump, Laptop, Flourescent Lighting, Television etc.