Inverter
An inverter converts the direct current from the solar panels into the alternating current required by the domestic and public grids. The choice of inverter determines whether the PV system can be fitted with a battery storage unit, how many roof areas can be used separately, and what you will later see in the app. The range comprises around 75 inverters, from 800 W for balcony power plants up to 125 kW for large roofs, from Growatt, Solplanet, SunGrow, Huawei, EcoFlow, Fronius, Trina, APSystems and Deye, as well as kits with storage units and accessories for monitoring and measurement.
Four designs and what they are intended for
The first question is not about power output, but about the design. This depends on whether a storage unit is planned and whether the system is grid-connected.
| Configuration | Power ratings in the range | Battery | Typical application |
|---|---|---|---|
| hybrid inverter | 0.8 to 29.9 kW | Yes | Roof-mounted system with storage, now or later |
| Grid-tied string inverter | 0.8 to 125 kW | No | System without storage |
| micro inverter | 0.8 to 2 kW | No | Balcony power plant, small areas |
| Off-grid inverters | 3.5 and 6 kW | yes | Garden shed, workshop, holiday home without mains connection |
A hybrid inverter manages modules, the battery and the domestic grid in a single unit. It is the ideal choice if a storage system is part of the setup from the outset or is to be added later. A grid-tied inverter combines several modules into strings and feeds power into the grid without a battery; the range extends from the Growatt MIC 800TL-X to the SunGrow SG125CX-P2. A micro inverter is installed directly behind two to four modules and is the standard technology used in balcony power plants. For systems without a grid connection, two off-grid inverters from Growatt are available.
The key figures in the data sheet
The rated power depends on the module power, but not on a one-to-one basis. Each technical data sheet specifies a maximum recommended module power. For the grid-tied units listed here, this is usually 1.4 to 1.5 times the AC power; for hybrid units, depending on the model, it ranges from 1.3 to just under 3 times. A 10-kW unit therefore typically accommodates up to 15 kWp.
The number of MPP trackers – that is, the separately controlled module inputs – ranges from one in the Growatt MIC to twelve in the SunGrow SG125CX-P2. Two trackers are sufficient for a roof with east and west-facing sides. Single-phase units in the range go up to 6 kW, whilst three-phase units start at 3 kW. According to the data sheet, the European efficiency ranges between 96 and 98.5 per cent, depending on the unit.
The protection rating is important for the installation location. Most units are rated to IP65 or IP66 and are mounted on the external wall, whilst micro inverters rated to IP67 are installed beneath the module. Off-grid units are rated to IP20 and must be installed in a dry indoor location. The manufacturer’s warranty is generally ten years. The micro inverters from Growatt and APSystems come with a twelve-year warranty, whilst those from Deye and the hybrid inverters from EcoFlow come with a fifteen-year warranty. Shorter warranties apply to the Huawei, SUN2000-36KTL-M3 and the Growatt MID 25KTL3-XH (five years) and the off-grid units (two years).
Which battery is compatible with which inverter
Batteries and hybrid inverters only work together if the manufacturer approves the combination. According to the manufacturers’ lists, the following applies to the devices in the range:
- Growatt MOD HU (6 to 15 kW): only with the Growatt battery APX
- Growatt MOD XH: with ARK, APX, AXE and ARK LV
- Growatt MIN XH: with ARK and APX
- Solplanet ASW H-T2 and H-T3: only with Solplanet Ai-HB
The Growatt AXE features its battery management system (BMS) integrated into the module. For the ARK, APX and Ai-HB, a separate BMS unit is included with the battery tower. For all other devices, please refer to the storage list in the data sheet; if a storage unit is not listed there, the combination is not approved. If you are purchasing both at the same time, you will find compatible pairs under Storage-inverter sets.
Retrofitting, backup power and monitoring
A grid-tied inverter does not accept a battery. For an existing system, there are nevertheless two options: the Growatt SPA 6000TL3 BH-UP has no module input; it is installed on the AC side alongside the existing inverter and connects a high-voltage storage unit. The data sheet specifies which batteries are approved for this purpose. According to the manufacturer, the EcoFlow PowerOcean DC Fit converter connects a storage unit on the DC side without the need to replace the existing inverter.
Backup power is a separate feature and is specified in the data sheet. It also requires a changeover device in the meter cupboard; for the Fronius, for example, this is the backup power changeover switch available as an accessory. For monitoring, depending on the model, a device requires a Wi-Fi, LAN or mobile data stick from the manufacturer; for feed-in control and storage control, a meter is required at the property connection. Both are available as inverter accessories.
For photovoltaic systems and their essential components, no value added tax is charged where the conditions of Section 12 (3) of the German VAT Act (UStG) are met. You state during the ordering process whether they apply to you.
Frequently asked questions about inverters
Which inverter is suitable for my PV system?
Firstly, the design: a hybrid inverter if you have a storage system, a grid-tied inverter if you don’t, and a micro inverter for a balcony installation. Then the power rating: the module power of your system must be below the maximum recommended module power specified in the data sheet.
How large does the inverter need to be for 10 kWp?
In most cases, a unit with a capacity of 8 to 10 kW is sufficient. According to the data sheets, the 10-kW units from Solplanet and Growatt SPH can handle up to 15 kWp, whilst the 8-kW units from Solplanet, SunGrow and Trina can handle up to 12 kWp.
Can I retrofit a battery later on?
With a hybrid inverter, yes, provided the battery is on the manufacturer’s list. With a grid-tied unit, this is only possible via an additional device such as the Growatt SPA or the EcoFlow PowerOcean DC Fit converter.
What is an MPP tracker?
A device that automatically regulates the operating point of the modules connected to it. With two or more trackers, roof areas with different orientations or levels of shading can be operated separately, without the weaker area holding back the stronger one.
Where is the inverter installed?
Units with IP65 or IP66 may be mounted on an external wall. Units with IP20 must be installed in a dry indoor location. Connection to the domestic mains supply is carried out by a qualified electrician, and the system is registered with the network operator.
How long is the warranty valid for?
Most units come with a ten-year manufacturer’s warranty; micro inverters come with a twelve- or fifteen-year warranty; and the EcoFlow model comes with a fifteen-year warranty. The exact details are specified for each unit.