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Introduction

Types of inverters

Inverters are the electronic devices, which convert the direct current voltage from the accumulator into alternate current voltage ~ 220 V. The accumulator(s) is(are) considered to be charged beforehand: by a specialized DC charger, by the inverter charger, or by the automotive alternator.

Inverter – is the heart of any off-grid independent power supply system. That is why you should pay a very special attention to its selection.

The pricing and features of the inverters may vary significantly, despite the rated power capacity will be the same.

There are several scenarios of the inverters use:

  1. For providing the uninterruptible power feeding at AC grid power failure. Such a system usually includes one inverter and a battery bank, that are installed in a cottage, country-house. It can be thecritical industrial installations as well.

  2. Same system, enhanced with using of solar/wind energy in priority before the grid. It can help significantlyreduce your energy bills, but the initial investments are quite weighty.

  3. In full off-grid autonomy.

  4. Under field conditions. For long-time yacht, bus or campervan trips and so on.

The market offers many types of inverters:

- with modified or pure sine wave

- produced with high or low-frequency circuits implemented

- with built-in battery charger or without it

- with different DC voltage: 12 V, 24 V, 48 V

- with many different options and features and without that. Among the low-switching frequency models, two main modifications are distinguished: with ordinary transformer and with high-efficiency toroidal one.

Some inverters may include a stabilizer options, the others may have an embedded solar controller.

Apart of that, you may have heard about grid-tie and hybrid inverters. The top-class models have specialized software which can show diagrams of all events and send the notifications by email or SMS.

More information

Power Quality: Sine Wave vs. "Modified Sine Wave"

For a start, let’s examine the difference between two output AC voltage signals (220 V) of two inverters: modified and pure sine wave.

These rectangles represent so called modified sine or strictly speaking – the meander.
In some office building this AC voltage signal may be distorted a bit under some heavy loads.
In power network (grid) we can see the relatively pure, smooth sine.

Many appliances (such as motors, pumps, refrigerators, microwave ovens) will operate with reduced efficiency from such an AC voltage. There are devices such as gas boilers which cannot operate at all from the modified AC sine wave.

Why do producers offer till now such inverters with modified sine? Because these models are considerable cheaper than ones with pure sine. Moreover, some loads are insensitive to such a feeding voltage waveform.

By the way, you would hardly select the inverter for one defined kind of load. If you're limiting home electricity consumption while having the sun energy abundance or you will worry on one or another appliance because of modified sine in your network in time of grid failure: whether that corresponds the life in the 21st century? Only the clean sine AC voltage will ensure the operation of 100% of devices. The old saying: cleanliness is next to godliness.

Our advice: use the inverters with pure sine voltage.

High switching frequency and low switching frequency inverters

High switching frequency inverters

There are low capacity inverters for low-powered devices, as laptop, small vacuum cleaner, hand drill and so on.

Such devices are known as car power inverters. They are designed with high-frequency circuits inside.

The advantages of these inverters are small weight (1-5kg) and size, and the price, as the consequence.

The DC voltage conversion is proceeding at high frequency (usually 20 000 – 30 000 Hz), therefore small transformers and capacitors can be used in circuits.

As it’s said, “Every medal has its reverse”. The high switching frequency inverters produce more electromagnetic interference (EMI). Very rare they have internal chargers, because the grid has a low frequency voltage, while they have no low-frequency transformer.

High switching frequency inverters become unreliable under heavy loads. Their standard capacity rates family belongs to 100 – 1500 W range.

The shown inverter is a good illustration of the above. To obtain 4.5 kW rated power, its designers have combined 3 inverters in 1, simply connecting their inputs and outputs in parallel.
Such inverters are designed to be interconnected or expanded in a modular fashion, in order to increase their capacity. The most common scheme is to "stack" two inverters.
Most of such inverters can still feed a 300W hand drill and only the highest models can supply a refrigerator.

More information

Let's make a small digression to the explanation why the refrigerator requires a high-power inverter for start, despite it consumes 150W only.

Important! What is the starting power?

There is a “starting power” notion. For some appliances the starting power is equal to the rated one. As for example it may be a heater. At start they consume the rated power indicated on its nameplate.

Some appliances, such as electric tools have a starting power a bit higher than the rated one.

Finally, there are many appliances, which have a started power many times higher than the rated one: refrigerators (10 times more), air-conditioning units, deep-well pumps, induction motors, compressors, microwave ovens and so on.Most pumps draw a very high surge of current during startup. The inverter must have sufficient surge capacity to handle it while running any other loads that may be on. It is important to size an inverter sufficiently, especially to handle the starting surge.

Now we will show, as a visual proof, the operation and surge drawing of a refrigerator, that was measured by a special clamp meter.

Look at this picture. In stable operation mode it consumes 0.1 kW only (i.e. 100 W)
Now we power it off and reconnect to AC power again. This clump meter can remember the peak values. Look: 1.15 kW. So, it exceeds more than 10 times.
Therefore, for the refrigerator start you need the inverter, that can provide (at least in a short-run period) 1.2-1.5 kW, and for deep-well pump – 7 kW in a short-run period!

Now we revert to the topic.

Now the producers offer more powerful high switching frequency inverters on 4 kW rated power capacity.

As for example, this inverter (shown in the picture above), is not positioned as a car inverter and is known in Russiaunder different names: Expert, Stark, Combi, Axpert, PIP. It is designed for electricity backing in a house, despite it is high-frequency, though.

As you can see, the transformer is small. This inverter is not made as a combination of 3 smaller inverters as shown above.

Unfortunately, the efficiency of this device, as for the most of high switching frequency inverters, is low – 85% only.

However, we have to give authors their due. Despite it is the high switching frequency inverter, the built-in charger is relatively powerful.

The low switching frequency inverters.

Let’s consider all pros and contras of the low switching frequency inverters. Running ahead, we mention that in many aspects they are opposite to the high switching frequency ones.

In low switching frequency inverters, the AC conversion from battery is proceeding at low frequencies, certainly. To be exact it is 50Hz. It corresponds to AC grid frequency, which has 50 Hz as well. The relatively big and heavy transformers are used to operate at this frequency. Such a transformer serves as a buffer between inverter circuits and the load, which increase the reliability of the device.

TrippLite 6 kW inverter APSX6048VR inside (side view, the standard transformer is on the right)
MAC Pro Hybrid 4,5 kW inverter inside (top view, toroidal transformer is on the left)

You can easily catch sight of huge transformer, which occupies almost the half of the device body.

The pros of such a solution are obvious: the possibility of powerful reliable systems creation (even on tens thousands of watts) and the presence of speedy and powerful AC-DC charger.

Of course, these inverters have some weaknesses: weight, size, and as the consequence – the price.

In the following picture you may see some low switching frequency and high switching frequency inverters with their power capacity and weigh indicated.

You would hardly lift this inverter up. With its record rated power of 12 kW, it has a record weight – 56 kg.
It’s obvious, that a big weight (usually from 12 to 56 kg, that 5-8 times more per power unit than HSF-inverters have in average) is not because the inverter is stuffed by full of stones.
This is the expensive copper in transformers and the aluminum in heat sinks.
If the HSF inverters were equal to LSF ones by reliability and other characteristics, they would have died out as the mammoths.

Our advice:

  1. If you don’t need a charger and summary consuming power in your system does not exceed 1000 W (it’s very important to consider all the starting currents for all the devices), you may buy a HSFinverter. The most typical example is a car inverter.

  2. If summary power consumption of all the appliances exceeds 3 000 W, including starting power, you’d better buy a LSF inverter. The typical example – an inverter for a house or enterprise.

  3. If the loads are in 1000 – 3000 W range, then the choice depends on customer’s preferences and operating conditions. For example, what will be the most important thing: low price or high reliability, low weight or you’d prefer the low EMI, do you need an embedded charger or not. Depending on all these factors, you make a decision.

LSF inverters with ordinary transformer and with toroidal one.

Let’s look once again at ordinary low-frequency transformer in the 6-kW inverter (on the right) and the other 6-kW inverter with toroidal transformer (on the left).

The toroidal transformer is smaller a little. It’s because it has greater efficiency.

Moreover, such a transformer emits less EMI, because the electromagnetic field is concentrated around this “boublik”. The ordinary transformer radiates the interferences perpendicularly to coils.

Toroidal transformer has smaller idle-time consumed power. It’s called “idle power”. That means how much energy is literally “wasted”.

Let’s make a small comparison matrix for these two inverters.

The inverter TrippLite 6 kW (made in the U.S.A.) with aconventional transformer has an idle power72 W. The inverter MAC SIN (6 kW, made in Russia) has the toroidal transformer and idle power 20 W. The efficiency of the first one is 89%, of the second one – 96%. The TrippLite weights 55 kg, MAC SIN – 41 kg.

The only disadvantage of toroidal transformer – is its big price.

However, the most eminent and expensive world brands use in their inverters only the LF toroidal transformers because of their unbeatable characteristics.

Tor in Xantrex inverter (rated power is 5 kW, idle power 22 W, efficiency 96%, weight 42 kg, price is near 6000 USD).

Our advice: if you can afford it, you’d better buy the inverter with toroidal transformer.

The choice of inverter DC voltage.

What battery voltage is preferable: 12, 24 or 48 volts?

Accumulators are different (by capacity, technology etc.) and come in different voltages. As for example: 2 V, 6 V or 12 V. You can connect them in chain to build a bank: in series or in parallel, increasing the total voltage.

The DC input voltage must conform to that of the electrical system and battery bank. 12 volts is no longer the dominant standard for home energy systems, except for very small, simple systems. 24 and 48 volts are the common standards now. Sometimes you can see 96 V inverters, but they are very rare, because such a high voltage is considered to be dangerous.

12 V is used in a car electrical system, 24 V – on buses, yachts.

It’s clear, that any of DC voltages may be used with an inverter for an uninterruptible power supply for the whole house or its part.

However, a higher voltage system carries less current, which makes system wiring cheaper and easier. A lower voltage does not allow to produce high power. It’s used to be considered that for 12 V we can produce not more than 3 kW, for 24 – not more than 9 kW, for 48 – not more than 18 kW.

High switching frequency inverters are used to be made for 12 V and 3 kW size (for the car use). Meanwhile the high-power low switching frequency inverters are represented by 24 or 48 V models with rated power 3 kW and over (for the house or building use).

Of course, there are exceptions. When, for example, some HSF inverters thanks to their low price are trying to take a home-devices market niche.

For example, this one with a rated power of 4 kW and rated for a battery voltage of 48 V.
Or this low switching frequency inverter with toroidal transformer having 900 W of rated power only, tries to take its niche in HSF inverters segment. Thanks to such qualities as reliability, powerful charger and wide functions range.

Our advice: if You are looking for a car- or camping inverter, or inverter for a house with a very small peak power (say, for a boiler backing, or the average power is not more than 2 kW): we recommend you choose a 12 V inverter.

Stabilizer function and a built-in solar controller

Let’s consider the inverters with built-in stabilizer function.

What is a voltage stabilizer? It is a separate device (usually), that allows to equalize the AC grid voltage in a wide range, with good accuracy, if this voltage is too low or too high. So, the voltage stabilizer is designed for maintaining the stable voltage level to provide a constant supply in spite of any fluctuations or changes in supply in order to protect the home appliances.

As for example, a high-quality stabilizer can increase very low AC voltage – 120V to a normal 220V. Or - on the contrary – to lower AC 270 V to a normal one.

The high-quality step-voltage stabilizers are made on triac-controlled circuits (symistors) and have at least 8 grades. The more steps it has – the “narrower”the stabilized voltage range is.

Let’s look at the inverter built-in stabilizer characteristics. Generally, it has 2 or 3 grades only and uses relays instead of symistors. As a result, it has lesser longevity, narrow input AC voltage range and wide output voltage range. Say, from, 205 to 245 V.

There is one more disadvantage of the inverters with built-in stabilizer. They hardly can be used in autonomous off-grid systems. Even though they have a good charger, they cannot charge batteries from the most conventional fuel generators.

Why? Strangely enough, but becauseof the internal stabilizerthey require a stable voltage from the generator on the input. The generator should have a large power reserve: that means it will be very expensive.

Look at that equilibrist – he keeps his balance with great difficulty.You need a lot of training and agility to stay for a while on two movable supports.

Why this stabilizer (a.k.aAVR – automatic voltage regulation) inside an inverter increases the requirements for the power and quality of the fuel gen?

An ordinary synchronous generator has 220 V on the output at rotation frequency 3000 rpm. The generator must maintain this revolutions frequency to ensure the AC frequency 50 Hz. At this rotational frequency the RMS voltage (e.m.f.) is equal to 220 V. The automatic stability control system of the engine rpm is adjusted to maintain the shaft nominal rotation frequency.

At sharp load power surge, the load on the shaft increases as well, the rpm drops sharply, the AC voltage frequency drops, correspondingly, the output voltage itself decreases too. To compensate such a slump and recover the rpm, the generator needs some time. At sharp load drop we observe the opposite process. The load on the shaft drops while the fuel feed still stays the same for a while. The rpm increases, that causes the AC voltage frequency and value increase as well.

Suppose, we have a hi-speed relay stabilizer in the circuit between the generator and load. As the load and generator voltage change, the stabilizer is the first device which will react to the changed conditions. It will switch a relay to another transformer coil. It means that some loads may consume from the generator higher or lower current in such conditions. That may deviate the generator from the operational mode even more.

In some short period, the generator starts to recover its rpm and operation voltage. What the stabilizer does? It switches the transformer coil again. The current changes its growing/falling direction (by value) again, it causes that generator “miss” its rated rpm and deviates to “another” side.

At heavy load (when it is comparable to a gen’s power), and especially with resistive-inductive load, the situation of auto-oscillation is possible. In some time, it fades out, usually. However, there might be another result: the generator protection system triggering or even its damage. So why many producers forbid using their generators with stabilizer.

Certainly, if you use a generator with a capacity which is many times higher than starting current of your appliances, then it handles them very easy and such a situation never happens. That sort of high-powered generators is very expensive, though.

Now let’s consider the inverters with a solar controller built-in.

Is it right to build a solar controller in the inverter? Let’sconsiderthismatter.

Generally, you need a solar charge controller to connect photovoltaic (solar) panels, or solar batteries to a battery bank, which the inverter is connected to. This solar charge controller either converts the energy from hi-voltage panels to a low-voltage battery (MPPT) or simply control the energy flow while charging (referred to PWM controllers).

There are not many such inverters’ models with an embedded controller. This solution has some pros: the price of such a device is a bit lower, it has less external connections.

Let’s consider some disadvantages of a similar solution. Hi-quality and powerful MPPT solar charge controllers (with 98% efficiency, high input voltage and external loads control) are quite large and cannot be integrated into the inverter case.

That is why all embedded controllers, as the built-in stabilizers, are usually cut a little in their capabilities.

You may compare the dimensions (in the photo) of the inverter with embedded controller (on the left) and two standalone solar charge controllers. Standalone controller is almost half of the inverter.

The difference in features is noticeable as well. See detailed overview here: http://microart.pro/products/

Another disadvantage: in case of controller damage you should send the whole device in for repair, therefore you lose your inverter for a certain time. The same as if your inverter were damaged: you lose your controller.

Generally, the top-rated, hi-quality, brand-named inverters containneither stabilizers, nor controllers. That is why any similar device with such embedded items cannot be considered to be a top-level one.

Our advice: we recommend you such devices only either if you cannot afford the standalone ones, or for backup purposes (not for gridindependent systems).

Grid-tie inverters, compared to hybrid ones

Grid-tie inverter.

A grid-tie inverter combines 2 devices at once: aninverter and a photovoltaic MPPT controller.

It is another approach to energy producing, unlike above-mentioned conventional HSF-inverter with an embedded solar charge controller, which is connected to a battery. The grid-tie inverter is totally different. Its ideology derives from some countries conditions (like EU, USA etc).

The grid-tie 500 W inverter is shown. Nothing extraordinary at first sight except for absence of DC terminals for battery connection.

The grid-tie inverter converts the energy from solar panels (are interconnected to gain a high voltage: 200 – 600 V usually) to alternating current of 220 V directly and send it to grid, being synchronized with it. Because the input and output voltages are high, this inverter needs no transformer, and this has to lead to its price reduction. Actually, they cost twice as much as ordinary inverters.

Besides that, the grid-tie inverter needs no any battery bank! Otherwise you should have had to connect them to a very high voltage (between controller and inverter modules), which is very dangerous. How are they used? If available solar energy is lower or equal than the needed by a house, it will be consumed in the whole volume. If it higher (in excess) than the house can consume, it will “upload” to the grid. It means that homeowner’s electricity meter will count in opposite side, decreasing the readings.

It turns that you use the grid as a huge battery. You may “upload” your energy into this accumulator, reducing the meter readings, and then, in the evening, or even much later: in winter-time you can “retrieve” your energy, sent in summer time.

We want to pay your attention, that in case of grid failure, the grid-tie inverter won’t work, even if you have the sun in abundance.

Its design is made in such manner that the AC grid 220 V for it is the supporting and leading.In addition, to ensure the staff safety: to avoid AC generating while the personnel are in progress of the service.

That’s why with a grid-tie inverter + PV panels you will have no electricity at grid failure. A lot of money has been spent for nothing: you will not have a backup system.

Hybrid inverters.

What is a hybrid inverter? It’s a top of the inverters evolution. It combines DC-AC (battery) ordinary inverter and grid-tie inverter.

The same way as a grid-tie inverter, the hybrid inverter can be synchronized with the grid and pump the available energy either (both) from battery bank, or (and) from solar panels, into the grid. I.e., it can do even more. As for example it can “add some power” to the grid capacity at overloads: it means that “on demand” it can add to the grid power some power from the battery bank or/and the solar charging controller power. The hybrid inverter will stay in operation even at grid failure. If you wish, it can limit power addition into the home power network or to the external grid. That’s a workaround if you have an electricity meter that is adding the energy modulo.

The hybrid superimposes its sine wave on the grid sine wave with a bit higher amplitude and can intercept the whole load or its part.If you set in menu, that the power addition from battery is allowed at voltage 12.7 V and higher (that corresponds to 100% charge level), at lack of sun no power will be adding, and all loads will be feed from the grid. If sun is back again – the power addition will be continued in available or requested volume.

Note, that the battery bank is not being spent and not getting out of order despite the power is adding into the network.

You may allow a little consumption from the battery as well: that will allow you to add some power at sun energy absence (say, in the evening), but will cost some battery resource.

The energy addition into AC home network is much better, than the loads switching from the grid onto DC sources (battery bank or/and PV panels). Not only because of the battery drain which leads to its resource reduction, but because of the switching relay rapid wear (in the ordinary inverter).
As the hybrid inverters have a battery bank, they can operate at 220 V grid failure. One more advantage: only this type of inverters can assure off-grid or backup feeding. In such case three inverters are operating, each one on its phase. They are interconnected by supplementary wires to provide the synchronous operation with phases shift on 120 degrees.
Of course, they can generate all 3 phases from the battery bank, or only one/two of the three.
You cannot manage to assure the powering of the 3-phases motors or pumps without such inverters.
It comes out, that the hybrid inverters are almost the ideal solution for many countries.

Our advice:

For home or office use you’d better buy the hybrid inverters.

As the exception: powerful (megawatts) solar power plants (they are designed to use with grid-tie inverters).

The grid-tie inverters may be actual also for industrial plants, that consume the energy only in daytime and don’t need any backup.

The inverters with wide functionality and without

Why do I need some features?” – somebody may think. – “I do need 220 volts, nothing more, anything else are the wasted money.”

Let’s div it out. To waste or not to waste - it’s up to You, of course. What functions we are talking about?

Let’s consider a list of these features. Some ofthem we will describe with the help of a toroidal transformerbased inverter MAC HYBRID (made in Russia).

  1. Grid or generator maintaining mode: i.e. automatic poweraddition from DC sources (inverters + battery) to AC grid or generator power capacity.

    For example, if you have only 5 kW of allocated power per house, you can set up this value on MAC Hybrid 12.0 kW as the consumption limit. The device will raise its output power itself up to 11kW, using the battery bank, through the battery power supplementing to the AC grid or gen power. For example, if you have the allocated power 5 kW per phase, you may limit power consumption to 5kW using your MAC HYBRID 12.0 kW with batteries. Then, the device will increase this power through its capacity up to 11 kW, adding the required DC power, stored in battery to the one, taken from utility grid.

    This ability may be essential while using a generator. Because the low-powered generator of 2 kW – as an example – can handle high starting currents with the help of a hybrid inverter.

  2. Setting of time zones for battery charging and priority.

    If you have the two-rate electricitymeter, you may enable the battery charging in low tariff period only.

    In addition to that, you have the ability if using two-rate ECO mode. It means you have the priority for the charge in the low tariff period and the priority for battery using in a high tariff zone.

    There is one more feature: the generation priority in daytime for the energy accumulated at night (via charging). However, it’s not profitable, because one discharge battery cycle is more expensive than the low-tariff 1 kWh cost.

    Probably, in the future this feature will be essential, when the battery will become cheaper and tariffs become higher.

  3. Compatibility with any accumulator battery type (lead-acid, GEL, AGM, Alkaline and LFP).

    The good inverter should assure the high-quality, 4-stage charging with temperature correction and all parameters adjustments.

    For working with LFP battery bank, the inverter has a special, auto-disconnectable output to BMS (Battery Management System). The batteries of LiFePo4 (LFP) type are the most advanced and perspective accumulators. They have the record life time – up to 30 years – but cost more expensive than the classical ones. Also, they require the special system of charging control – BMS.

  4. Joint operation with grid-tie inverters (with automated control).

    We have described the grid-tie inverters. But they have one more application.

    An advanced inverter can serve as a reference voltage source for the grid-tie inverter, connected to the inverter output (at grid failure too).

    While having the solar energy surplus, the inverter will forward it to battery bank. However, if you have no load at fully-charged accumulators, you should stop the energy generation from the grid-tie inverter. In accordance with grid-tie inverters specifications, it is achieved by alteration of the reference output AC voltage frequency – from 50 to 52Hz and backward to 50Hz, at low battery. To have it working automatically you should set it up in MAC Hybrid menu through the special options. Please note, that this feature is designed for the future. Because the use of grid-tie inverter instead of the solar controller is the more expensive solution. Besides that, the grid-tie inverter has a less smooth charging and less functions.

  5. The option of a direct connection to a PC for monitoring and programming.

    The high-class inverters should have a free software for the monitoring of the power networks and device(s) remotely. Very useful can be the feature of the SMS or email sending by events or request, and the collecting the statistics for all the parameters.
    There are four different software packages developed (including ones from the independent developers) for the MAC inverter. These packages have slightly differing features and may be installed on different platforms.

  6. The grid voltage limits settings: for slump and surge protection.

    This protection from voltage slumps and surges can be assured by the switching over to a battery bank at the voltage which is out of the range. This “safe” range is adjusted by the user (175 – 250 V by default). You can narrow this range to provide more tough protection for the appliances.

  7. The inverter hardware/firmware upgrade option.

    Some new features can be added simply through the firmware upgrade, even if you already bought the inverter.

    As for example, in recent times, our customers have got the following features for their MAC inverters:

    1. The ability of charging the brand new LFP batteries with BMS.

    2. External relay control, including generator starting.

    3. Joint operation of the inverter and solar controller via I2C bus.

Our advice: the wide functions range allows you to use it at its full potential. You can never have too much from that. You can buy an ordinary inverter for very simple tasks, such as AC powering in your car, or on the road.

Conclusion

Well-known that it’s better to be rich and healthy that poor and sick.

Not always our desires meeting our possibilities. The smart choice allows to find the optimal solution.

For the simple tasks, as for the in-the-car use, for camping, or if you cannot afford it, you can choose HSF inverters models, or the simplified LSF with ordinary transformer with small features set.

These inverters are (the prices are provided for the Russian market):

HSF car inverters with modified sine wave from Mobilen SP (1.5 kW with no charger. 220 USD), and so on.
HSF pure sine wave car inverters from Meanwell TS (1.5 kW – 500 USD) and so on
HSF with embedded solar controller (like MPPT) for the stationary use. They are almost identical, but are known under different brand names: Expert, Stark, Combi, Аxpert, PIP (with embedded solar controller. 1.6 kW for 550 USD, 2.4 kW for 670 USD, 4 kW for 1200 USD)..
LSF with an ordinary transformer and simple features set: PowerStar W7 (6 kW for 1050 USD).
CyperPower CPS PRO (with built-in stabilizer, 2.5 kW for 1180 USD; 5 kW for 2400 USD).
Tripp Lite APSX (with built-in stabilizer, 3 kW for 1300 USD; 6 kW for 2000 USD)

Our advice:

For the serious missions, such as backup power supply of the houses and plants (enterprises), especially for the independent systems with solar panels, you need the top-grade inverters:

- with pure sine wave

- with HSF technology (It's better if it had a toroidal transformer)

- with the ability of the fast charging of any battery type

- with high range of functions set (and with software).

- if you have AC grid (even in the future) and you are going to install some solar panels, you need a hybrid inverter only.

The followed inverters are the hybrid ones with a toroidal transformer.

SMA Sunny Island (5kW for 4500 USD).
OutBack GVFX (3 kVA for 3000 USD)
Xtender XTH (5 kVA for 6000 USD).
Xantrex XW (CONEXT XW) (4.5 kVA for 4500 USD).
MAC HYBRID (1,4 kW for 750 USD; 6 kW for 2000 USD; 12 kW for 3300 USD).
Victron Quattro (in power addition mode it always forwards the energy to the grid, which might be not suitable for some countries; 10 kVA for 5400 USD).
The best inverters.
MAC (Russia) Outback (USA) Xantrex (CANADA) Schneider Electric (FRANCE) Victron Energy (HOLLAND) Studer Xtender (ZWITZERLAND) Rich Electric (TAIWAN) SMA (GERMANY)
INVERTER MODEL PRO Hybrid DOMINATOR FX и VFX XW Conext SW Phoenix / Quattro XTH XTM XTS Combi Super Sunny Island
PICTURE inverter MAC inverter Outback inverter xnatrex inverter Schneider inverter phoenix inverter xtender1 inverter xtender2 inverter xtender3 inverter invertek inverter sunny
Range of the rated power capacity (kW) Rating: 0,8–13,5
Maximal (20 минут): 1.3-20
Rating: 2–13,5
Maximal (20 минут): 3-20
2,0-3,0 3-6 2,5-4 3-15 3-8 1.5-4 0,9-1,4 1,5-6 2-8
Low switching frequency technology / Toroidal transformer + / + + / + + / + + / + + / + + / + + / + + / + + / - + / +
Overload capability, x Pnominal, seconds 2,5 2 2 2 2 3 3 3 2 2,5
Input voltage stabilizing - - - - - - - - - -
The number of battery charging stages 4 5 4 3 4 4 4 4 4 4
Power adding mode - + + + + + + + + + + +
Input AC consumption limiting + + - + + + + + - +
Fuel generator autostart control - - Internal system, 2 control relays Inverter can control an integrated relay with dry contacs, which gives a control signal to generator start by various events Additional module Xanbus is required events -up to 4 relays and two analog
inputs/outputs
Embedded system. 2 control relays Embedded system. 2 control relays Embedded system. 2 control relays Additional device is required +
AC inputs number 1 1 2 1 2 1 1 or 2. Depends on model 1 1 1 1 2
Output sine wave voltage + + + + + + + + + +
DC Voltage (battery) 12/24/48 12/24/48 24/48 24 12/24/48 12/24/48 12/24/48 12/24 12/24/48 24/48
The priority of the renewable energy sources for the load feeding - + + - + + + + + + + +
AC generation from the battery bank into the utility grid - + + - + + + + + + + +
Battery charging from an AC power source (such as grid-tie inverter) connected to the inverter AC output + - - + + + + + + +
Transmitting the energy surplus from an AC source (such as grid-tie inverter) connected to the AC output to the utility grid + - - - + + + + + +
Maximal inverters number in parallel connection for single-phase supply 1 1 10 10 (up to 30kW 220 V, by means of additional device HUB) 3 2 6 3 3 3 5 (additional module CP-PX) 3
Maximal inverters number for three-phase supply - 3 30 9 (uo to 9kW, by means of additional device HUB) 3 - 18 9 9 9 12 (additional module CP-PX) Up to 120 kW 380В, SMA Multicluster Box is required
Sleep mode + + + + + + + + + +
Sleep mode consumption 2-5 2-6 8 <8 4-10 2-4 2-4 2-4 8-18 4
Idle power 9,6-25 20-23 28 40 15-35 10-34 10-34 10-34 12-36 21-25
Average switching time (grid to inverter) 2–4 ms 20 ms 8 ms 16.7 ms n/a 16 ms 16 ms 16 ms 10 ms n/a
Degree of protection (IP) No, ip21 Depends on model, IP66 / IP20 No, ip20 - No, ip21 No, ip20 No, ip20 ip54 No, ip20 ip54
Warranty 2 years 5 ( with installation supervision services [provided by vendor]) - Further WISS[PBV] 5 WISS[PBV] 1 2 5 WISS[PBV] 5 WISS[PBV 5 WISS[PBV 3 WISS[PBV) 5
Embedded micro-PC - - +
An embedder Raspberry 3 micro-PC. Software for many platforms: Linux, Windows, Mac OS
- - - -
External panel Color Control GX
-
Optional external RCM module:
Remote off/on switching (is controlled by dry contacts on terminals 5 and 6, with the bridge between terminals 3 and 4 or constant or alternating voltage up to 60V between terminals 4 and 5)
Optional: Communication device X-Com LAN / GSM
-
External controller (RCP-4) or External programming and monitoring module are available
-
External control module:
- Sunny Remote Control SRC-20. Retrieves data on SD card
- For remote management: Sunny Home Manager. Connects to router
Control panel embedded MATE system controller embedded XW-SCP embedded XW-SCP embedded VE.Bus RCC-2/3 RCC-2/3 RCC-2/3 embedded embedded
Operating temperatures range -25 to +50 -40 to +60 / -25 to +60 -25 to +70 -20 to +60 -40 to +65 -20 to +55 -20 to 55°С -20 to 55°С -20 to 70 –25 °C … +60 °C
efficiency 92-96 90-93 94-95,6 90-92 92-95 91-94 93-96 93 82-89 95.8
Output frequency range 50/60 50/60 50/60 50/60 50/60 50/60 50/60 50/60 50/60 50/60
Built-in MPPT controller - - - - - - - - - -
Battery monitor +
In Raspberry Pi3
+
In Raspberry Pi3
+
In Raspberry Pi3
- - - SoC calculation External device "Battery Status Processor BSP" is required External device "Battery Status Processor BSP" is required - - Full battery monitoring via Sunny Home Manager system
Average price, Sep 2017 MAC SINE PRO 20kW (rating is 13.5kW), 2300 USD, 2300 USD МАП SINE HYBRID 20kW (rating is 13.5kW), 2900 USD МАП SINE DOMINATOR 20kW (rating is 13.5kW), 3500 USD Outback 3kW, 3700 USD Xantrex XW 6kW, 4200 USD Schneider Electric Conext SW 4kW, 2100 USD Victron Energy Phoenix 1.2kW, 800 USD Studer Xtender XTH 8kW, 8500 USD Studer Xtender XTM 4kW,3800 USD Studer Xtender XTS 1.4kW, 1500 USD Combi Super 3kW, 3100 USD SMA Sunny Island 8kW, 5700 USD

Thus, we have surveyed the different inverters designs. We hope your choice after that will become more thought-out.

In brief about the controller choosing.

We would mention the most important choice criteria.

A good solar controller must:

- be made by MPPT technology

- handle the high voltage from the PV panels side (at least 150 V, 200 V and more is better)

- have a display for settings and control

- not use any coolers

- operate with any type of batteries are connected to any voltage

- have a current sensor for the current consumed by the inverter

- have embedded relays for the external loads control

The details of the first test comparison of the top-grade solar charging controllers see on the site:

We wish you a lucky choice!