Information as of 5 October 2026 · guide, not legal or subsidy advice
Many photovoltaic systems in Austria feed surplus power into the grid during the day – and in the evening, expensive electricity comes back from the grid. A retrofitted battery storage system increases self-consumption and – with the right hybrid inverter – can also provide emergency power. This guide explains what is technically possible, what subsidies are available in 2026 and how you as a homeowner can arrive at a clean solution through an installer.
When is a retrofit worthwhile?
A retrofit typically makes sense if:
- your PV system is already running and you use a lot of electricity in the evening or morning (heat pump, electric car, home office).
- you want to increase your self-sufficiency and reduce grid consumption.
- you are planning emergency power/blackout preparedness – modules alone are not enough for this.
According to the Involtis FAQ, a storage capacity of around 15 to 25 kWh is often a sensible range for a typical single-family home – depending on consumption and PV size. The exact sizing belongs in your installer's project consultation.
Two technical routes: AC coupling or hybrid inverter
1. AC-coupled retrofit
The existing string inverter stays. A storage-capable hybrid or battery inverter and the storage unit are connected to the house grid. Advantage: often less intervention on the existing DC side. Disadvantage: an additional conversion step and therefore slightly higher losses.
2. Hybrid inverter (DC-side / system replacement)
A hybrid-capable inverter replaces (or supplements) the existing grid-feed unit and controls PV, battery and grid in one device. The Deye hybrid inverters in the Involtis range (e.g. SUN series 6 / 10 / 12 / 15 / 20 kW, 48 V low-voltage) support, according to the manufacturer's datasheet, among other things:
- Connection of 48 V LiFePO4 batteries,
- AC coupling for retrofitting existing systems,
- Parallel operation of several units,
- Emergency power/island mode functions (backup) in combination with storage and professional switching.
Which option fits depends on the age of the existing inverter, the desired emergency power function and the budget. That is decided by the installer on site – not by an online configurator.
Which storage systems are suitable?
For retrofits on hybrid systems, long-life LiFePO4 storage is common. Easyway UNIV systems (Involtis is the Easyway general importer for Austria) include, among others:
- UNIV 7600 wall battery – 7.68 kWh total energy (7.22 kWh usable), wall-mounted, stackable,
- UNIV 16 kWh and variants – for higher daily capacity,
- UNIV FlexiStack – scalable for larger projects.
According to the manufacturer's datasheet: high cycle stability (UNIV series, among others, ≥ 8,000 cycles under the specified conditions), communication via CAN/RS485, compatibility with many common inverters – to be confirmed per project. More on the cell chemistry: LiFePO4 battery storage.
Subsidies: what applies to a storage-only retrofit?
Federal level (EAG)
In 2026, the EAG investment grant subsidises photovoltaics and – only together with it – battery storage. According to oesterreich.gv.at and WKO:
- Storage: €150/kWh,
- only in combination with a newly built or extended PV system,
- a stand-alone subsidy for storage or storage extensions is not possible under the EAG.
So if you only connect storage to an unchanged existing PV system, the EAG storage subsidy generally does not apply. If the PV is extended at the same time and the storage is included in the application, the storage share may be eligible – the EAG-Abwicklungsstelle checks details and calls.
PV subsidy rates 2026 (guidance according to oesterreich.gv.at): category A up to 10 kWp €150/kWp, B >10–20 kWp €140/kWp, C and D with maximum rates of €130 and €120/kWp respectively. The call from 8–22 October 2026 is one of the 2026 dates. In detail: EAG subsidy for photovoltaics and battery storage 2026.
State level
For Styria, the sources reviewed show no simple, permanently open state lump sum specifically for standard storage retrofits. The state programme “Thermal renovation with a renovation concept” (Wohnbau Steiermark) targets thermal renovation measures – not a flat-rate PV/storage subsidy. Municipalities may offer additional grants: always check the current situation with the state or municipality.
Emergency power: storage alone is not enough
A normal PV system switches off during a grid failure for safety reasons. Storage without a backup-capable inverter and without correct grid switching also means: the battery is full – but the house stays dark. Reliable explanations can be found at the Energieinstitut Vorarlberg and VERBUND, among others.
Anyone planning a retrofit with blackout preparedness should consider the hybrid inverter, storage size and switching device from the outset.
The process in practice (checklist)
- Inventory: module output, inverter type, metering point, annual consumption, planned loads (heat pump, wallbox).
- Define the goal: self-consumption only, or emergency power as well?
- Choose the technology: AC retrofit vs. hybrid replacement; storage size; installation location (cool, ventilated, manufacturer specifications/IP rating).
- Grid operator: report the change or obtain approvals – your installer knows the regional steps (in Styria, among others, via the grid operator Energie Steiermark).
- Check subsidies: EAG only for new/extended PV + storage; state/municipal programmes separately.
- Installation & commissioning exclusively by authorised professionals.
For homeowners: how to get Easyway & Deye
- Talk to your electrician or PV installer and describe the direction you want (retrofit, capacity, emergency power).
- Installers obtain Easyway UNIV storage and Deye hybrid inverters via Involtis – with a warehouse in Austria and delivery typically within 2–5 days of ordering (according to Involtis; availability depends on the project).
- You receive the quotation, installation and service from the installer – Involtis supports the partner technically.
For installers and dealers
Do you plan retrofits regularly? As an Involtis partner, you receive matched systems (Deye + Easyway), datasheets, training and personal support from Styria.
Sources
- EAG-Abwicklungsstelle: Investment grant for photovoltaics and storage (in German) – retrieved 12 Oct 2026
- EAG Investment Grants Ordinance Electricity (EAG-IZV), version of 19 Jan 2026 (OeMAG, in German) – retrieved 12 Oct 2026
- oesterreich.gv.at: photovoltaic funding schemes (in German) – retrieved 12 Oct 2026
- WKO: EAG investment grant 2026 for photovoltaics & battery storage (in German) – retrieved 12 Oct 2026
- Wohnbau Steiermark: thermal renovation with a renovation concept (in German) – retrieved 12 Oct 2026
- Energieinstitut Vorarlberg: PV FAQ on backup power and blackout preparedness (in German) – retrieved 12 Oct 2026
- VERBUND: photovoltaics and backup power (in German) – retrieved 12 Oct 2026
- Easyway: UNIV 16 kWh datasheet (cycles, interfaces) – retrieved 12 Oct 2026
- Involtis: FAQ (storage sizing), dealer information (delivery time) – retrieved 12 Oct 2026