Knowledge Base

Did you buy a classic balcony power plant without a battery a year or two ago? If so, you are one of the hundreds of thousands of pioneers of the decentralized energy transition in Germany. But you're probably also feeling a certain amount of frustration by now: on sunny days, your mini solar system produces tons of electricity while you're at work. This valuable, clean electricity then flows unused and without any compensation into the public grid. The bitter reality for existing customers without a battery is: Around 60 to 70 percent of the hard-earned solar power is given away. At the same time, prices for solar storage have fallen drastically in the last year. Many owners are therefore asking themselves: Do I have to completely replace my existing, faithfully functioning system to finally be able to use my own electricity at night? The clear answer is: No! You can easily, safely and cost-effectively upgrade your existing balcony power plant with a modern storage unit. In this comprehensive guide, you will learn exactly how this works, what legal aspects you need to consider and how you can achieve the perfect plug-and-play upgrade with our new SunEnergy XT-500. How does retrofitting a storage unit to a balcony power plant work? The technical functionality of a storage retrofit is surprisingly simple. You don't have to dispose of your existing micro-inverter or buy new solar modules. The secret lies in the so-called DC-side interconnection (Direct Current). In a balcony power plant without a storage unit, the cables of the solar modules flow directly into the inverter, which converts the direct current from the panels into household alternating current (AC). If you retrofit a storage unit, it acts as an intelligent intermediary exactly in between: The solar modules are disconnected from the inverter and instead connected to the input of the storage unit. The output of the storage unit is connected to the input of your existing inverter via MC4 cables. The inverter remains connected to your Schuko or Wieland socket in your home network as usual. The intelligent energy flow in everyday life: During the day in sunshine: The storage unit only transmits as much electricity to the inverter as your household currently consumes (the so-called base load, e.g. 150 watts). All surplus solar power flows directly into the battery cells. In the evening and at night: As soon as the sun sets and the modules no longer supply electricity, the storage unit switches to discharge. It feeds the stored energy controllably into your home network via the inverter to power televisions, refrigerators and standby devices. The new generation of retrofitting: SunEnergy XT-500 from DRBO Greenenergy If you are looking for an uncomplicated, highly efficient and future-proof solution to upgrade your existing system, DRBO Greenenergy offers a groundbreaking solution with the brand new XT500. The SunEnergy XT-500: The new generation was specially developed for the needs of existing customers who don't want complicated wiring or incompatible software systems. What makes the XT-500 so special for retrofitting? Universal compatibility: No matter whether you own an inverter from Deye, Hoymiles, Growatt or APsystems – thanks to standardized MC4 connectors, the XT-500 can be seamlessly connected upstream of almost any commercially available micro-inverter. Intelligent app control & real-time adjustment: Via the intuitive smartphone app, you can precisely adjust the feed-in power in watt steps to your actual base load. This prevents valuable battery capacity from being fed unused into the grid at night. Real plug-and-play installation: You don't need an electrician or special tools. Installation takes less than 15 minutes even for technical laypersons. Robust LiFePO4 technology: The XT-500 uses state-of-the-art lithium iron phosphate cells. These are considered to be extremely durable (over 6,000 charging cycles), intrinsically safe against overheating and offer excellent performance over many years. Thanks to the smart design of the XT-500, the efficiency of your balcony power plant is maximized and the self-consumption rate is increased from a meager 30% to up to 80% or more in no time at all. Step-by-step guide: How to connect your retrofit storage unit The installation of a retrofit storage unit such as the SunEnergy XT-500 requires no prior craft knowledge. Simply follow these instructions in a structured manner: Preparation: Safety first! Important: Before starting any work, unplug your inverter's power plug (Schuko or Wieland plug) from the socket. Ideally, carry out the installation in the late afternoon or on a cloudy day to avoid high voltage at the MC4 connectors of the solar modules. 1. Disconnect solar modules from the inverter:Duration: 3 min.Release the MC4 plug connections between your solar modules and the micro-inverter. If necessary, use an MC4 release tool to open the safety clips without damage. 2. Position the storage unit:Duration: 2 min.Place the storage unit in a shaded, well-ventilated area. Since modern storage units like the XT-500 are weatherproof (IP65), they can easily stand on the balcony. However, avoid direct, prolonged sunlight to prevent the battery from overheating in summer. 3. Connect solar modules to the storage unit:Duration: 4 min.Plug the MC4 cables of your solar modules into the designated PV inputs (input channels) of the storage unit. Make sure the plugs click into place audibly. 4. Connect storage unit to the inverter:Duration: 3 min.Connect the DC outputs of the storage unit to the inputs of your existing micro-inverter using the supplied MC4 connection cables. 5. Restore mains connection & set up app:Duration: 5 min.Plug the inverter's power plug back into your household socket. Switch on the system, download the manufacturer's app to your smartphone and set the desired feed-in power (e.g. 150 watts for the nocturnal base load). What does retrofitting cost and when does it pay for itself? The key economic question for every German user is: Is it financially worthwhile? Thanks to the extremely low purchase prices for LiFePO4 systems, the amortization threshold is now lower than ever before. Let's look at a realistic example for a typical household in Germany. Starting situation: Existing balcony power plant: 2 PV modules (approx. 850 Wp total output) on an 800W inverter. Annual yield: approx. 800 kWh of solar power. Current household electricity price: 35 cents / kWh. Economic efficiency calculation: Parameter Without storage (existing) With XT-500 retrofit (approx. 1-1.6 kWh) Additional investment costs 0 € approx. 550 € – 750 € Self-consumption rate approx. 30 % (240 kWh) approx. 75 % (600 kWh) Grid electricity saved per year 240 kWh 600 kWh Annual electricity cost savings 240 kWh × 0.35 € = 84 € 600 kWh × 0.35 € = 210 € Additional annual savings - 126 € Amortization period for the retrofit - approx. 4.5 to 5.5 years Since high-quality LiFePO4 batteries are designed for well over 15 years of operation, the retrofitted storage unit generates a pure return year after year after the amortization phase. You become independent of future electricity price increases and finally use almost 100% of your self-generated electricity. Legal requirements: What applies to retrofitting in 2026? The Solar Package I has massively cleared the legal jungle for balcony power plants in Germany. Nevertheless, you must observe a few simple rules when retrofitting a storage unit: No electrician required: As long as your inverter is limited to a maximum feed-in power of 800 watts, you can connect the entire system, including the storage unit, as a ready-to-plug-in system completely independently. Registration requirement in the Market Master Data Register (MaStR): If you have already registered your existing balcony power plant, you must re-register the newly added battery. Simply log in to the Federal Network Agency's web portal with your access data, select your system and add the storage unit, stating its capacity (in kWh) and manufacturer. This takes less than 5 minutes and is completely free of charge. No registration with the grid operator required: Since May 2024, you no longer have to laboriously register your balcony power plant with the local grid operator. Registration in the Market Master Data Register is sufficient. The Federal Network Agency automatically informs the grid operator. Frequently asked questions (FAQ) 1. Can I really retrofit ANY inverter with the XT-500? Yes, basically. The SunEnergy XT-500 uses universal MC4 connectors, which comply with the worldwide industry standard for PV components. It is simply connected between the solar modules and the DC input of the inverter. It works harmoniously with all common micro-inverters (e.g. from Hoymiles, Deye, APsystems or TSUN). 2. Do I need my landlord's permission to retrofit? For simply installing a storage unit on your balcony or terrace, you do not need separate permission. Thanks to Solar Package I, tenants also have a legal right to operate a balcony power plant. The landlord may only prohibit installation for valid, objective reasons (such as extreme monument protection or proven fire hazard). 3. Is a storage unit also worthwhile if my balcony faces east or west? Especially then it can be worthwhile! With east-west systems, solar production is distributed more naturally over the day (morning sun in the east, evening sun in the west). The midday peak is flatter. Nevertheless, there is often unused surplus here too - especially in the morning when no one is at home. An optimally sized storage unit captures this electricity perfectly. 4. What happens when the storage unit is full? As soon as the battery reaches its maximum capacity (100%), the system switches to "bypass". All solar power generated by the panels thereafter is fed directly to the inverter and consumed in the household grid or - if no consumer is active there - fed into the public grid. So nothing is lost and there is no danger to the system. 5. How weather-resistant is a retrofit storage unit like the XT-500? The XT-500 is certified according to protection class IP65. This means it is absolutely dust-tight and protected against water jets from any angle. It can therefore be left on an uncovered balcony or in the garden all year round without any problems. In extreme frost in deep winter, however, it is advisable to store the battery in the house or cellar to preserve the maximum service life of the LiFePO4 cells. 6. Does the storage unit have an emergency power function in the event of a power failure? Pure plug-and-play retrofit storage units for balcony power plants do not offer classic island capability or emergency power supply in the standard configuration. Since grid-connected micro-inverters switch off immediately in the event of a power failure in the public grid for safety reasons (NA protection), the system does not supply electricity via the socket at this moment. However, some modern systems offer separate USB or DC outputs directly on the battery, where you can charge small devices in an emergency. 7. Can I expand the storage capacity later? Yes, that's a big advantage of modern systems. Many storage solutions are modular. If you notice that your electricity consumption is increasing or you want to add more solar modules, with systems like the XT-500 you can usually simply stack and connect additional expansion batteries via plug-and-play, without having to buy a completely new system. 8. How do I ensure that the storage unit does not feed in too much electricity at night? You can easily control this via the associated smartphone app. There you set a fixed limit for the output power (e.g. a constant 150 watts between 10:00 p.m. and 06:00 a.m.). If you want to be even more precise, you can integrate smart sockets or a compatible smart meter (like a Shelly) into your home network. This measures the exact consumption every second and tells the storage unit in real time how many watts it needs to release (zero export).

The energy transition is no longer just taking place on the roofs of large industrial halls. Thanks to the Solar Package I and simplified registration procedures in the market master data register, balcony power plants have become a popular product in Germany. But while classic plug-in solar systems without batteries are already available for a few hundred euros, a new product class is entering the market: balcony power plants with storage. Given falling prices for lithium iron phosphate batteries (LiFePO4), more and more tenants and homeowners are asking themselves: Is the additional investment in a storage unit even worth it? When does the system become financially viable, and what hurdles are there? In this guide, we analyze the raw numbers, provide you with a transparent calculation example, and show how long the payback period really is in practice. What does a storage unit do for a balcony power plant? A classic balcony power plant without storage has a fundamental problem: it generates most of its electricity precisely when the sun is at its highest – usually at lunchtime, when residents are at work and the household's base load (standby devices such as refrigerators, routers, and smart home hubs) is only 100 to 200 watts. Without storage, the surplus electricity is fed unused and without compensation into the public grid. In other words, valuable energy is wasted. A battery storage system captures this surplus. As soon as the solar cells supply more energy than the household appliances are currently consuming, the electricity flows into the battery. In the evening and at night – when cooking, watching TV, and lighting are done – the storage unit releases the energy again. The result: Your self-consumption increases drastically. Without storage: approx. 30 % to 40 % self-consumption rate With storage: approx. 70 % to 85 % self-consumption rate How much does a balcony power plant with storage currently cost? Prices for storage solutions in the plug-in solar system sector have fallen sharply in the last year. Nevertheless, the battery still represents the largest cost block. A typical setup in 2026 is composed as follows: Component Without storage With storage (approx. 1.6 kWh) Solar price (2 modules à 430+ Wp) approx. 180 € – 250 € approx. 180 € – 250 € Inverter (800W incl. cable) approx. 100 € – 150 € approx. 100 € – 150 € Mounting & accessories approx. 50 € – 100 € approx. 50 € – 100 € Battery storage (LiFePO4) - approx. 500 € – 750 € Smart control (Shelly / Smart Plugs) - approx. 30 € – 60 € Total costs (incl. 0% VAT) approx. 350 € – 500 € approx. 850 € – 1,300 € Note on VAT: Since 2023, a VAT rate of 0% applies in Germany to the essential components of PV systems (including balcony power plants and their storage units), provided the system is installed near a residence. Calculation example: When does a system with storage pay for itself? To honestly answer the question "When will I get my money back?", let's consider two realistic scenarios in a typical German three-person household with an annual consumption of 3,500 kWh. Common parameters: System output: 2 solar modules with a total of 880 Wp, south-facing, 35° tilt. Annual yield: approx. 850 kWh electricity generation. Electricity price (purchase from grid): 35 cents per kWh. Scenario A: Balcony power plant WITHOUT storage Acquisition costs: 400 € Self-consumption rate: 35 % (corresponds to 297.5 kWh of directly self-consumed electricity). Annual savings: 297.5 kWh × 0.35 € = 104.13 € Payback period: 400 € / 104.13 € ≈ 3.8 years Scenario B: Balcony power plant WITH storage (1.6 kWh capacity) Thanks to intelligent control (e.g., via a dynamic smart meter like the Shelly 3EM, which precisely adjusts the inverter's output to the household's consumption), the self-consumption rate can be increased to 75 %. Acquisition costs: 1,000 € Self-consumption rate: 75 % (corresponds to 637.5 kWh of self-consumed electricity). Annual savings: 637.5 kWh × 0.35 € = 223.13 € Payback period: 1,000 € / 223.13 € ≈ 4.5 years Comparison of profitability over 15 years (lifespan) Since modern LiFePO4 batteries are designed for over 6,000 charging cycles, they easily last 15 to 20 years without significant capacity loss. Key figure Without storage With storage (1.6 kWh) Investment 400 € 1,000 € Savings per year 104.13 € 223.13 € Savings after 15 years 1,561.95 € 3,346.95 € Net profit (after deducting investment) 1,161.95 € 2,346.95 € Conclusion of the calculation: Although the balcony power plant without storage reaches its break-even point somewhat faster (after just under 4 years compared to around 4.5 years with storage), the system with storage generates significantly more return over its entire lifespan and protects you much better against future electricity price increases. Which factors influence the payback period? The values mentioned above are solid benchmarks, but in reality, individual factors play a crucial role: Your personal load profile (usage behavior): If you work from home during the day anyway and run the washing machine and dishwasher at noon, you will have a high self-consumption rate even without storage. If you only come home after 6 p.m., however, you will benefit extremely from a storage unit. The dimensioning of the storage unit: A storage unit that is too large (e.g., 3 kWh for only two solar panels) will never be fully charged in winter and during transitional periods and will not be economically viable. The ratio of module peak power to storage capacity should ideally be 1:1.5 to 1:2 (e.g., 800 Wp solar output to 1.2 to 1.6 kWh storage). The control technology: Simple time-controlled storage units that rigidly feed in 150 watts in the evening waste potential. Systems with real-time measurement at the electricity meter (zero export) precisely adjust the storage output to current consumption and significantly shorten the payback period. Who benefits from the purchase and who should refrain? A storage unit is particularly worthwhile for you if: Your electricity consumption is mainly in the morning and evening hours. You have to pay an above-average electricity price (over 32 cents/kWh). You strive for maximum self-sufficiency and want to minimize your ecological footprint. The structural conditions (e.g., unshaded south-facing balcony) guarantee maximum solar yield. You should (for now) forgo a storage unit if: Your balcony is in partial shade or faces north (too low yields to fully charge the storage unit). You can already consume all the generated solar power directly during the day. The budget is severely limited – a simple balcony power plant offers the best value for money to get started. Frequently Asked Questions (FAQ) 1. How long does a battery storage unit for a balcony power plant last? Modern balcony power plant storage units almost exclusively rely on lithium iron phosphate technology (LiFePO4). These batteries are characterized by extreme longevity and safety. Most manufacturers guarantee between 4,000 and 6,000 charging cycles before the capacity drops to 80 %. With daily use, this corresponds to a theoretical lifespan of 15 to 20 years. 2. Am I allowed to connect a balcony power plant with storage myself? Yes. According to the German Solar Package I, plug-in solar systems with an inverter output of up to 800 watts (previously 600 watts) and a total module output of up to 2,000 Wp can be easily connected yourself via a Schuko plug or a Wieland socket. The integration of common storage systems (e.g., from Anker, EcoFlow, or Zendure) also takes place via simple plug-and-play. 3. What happens to the storage unit in winter? In winter (November to February), solar radiation in Germany is often not sufficient to fully charge the storage unit. Many systems then switch to a winter protection mode to prevent deep discharge of the battery. It is advisable to place the storage unit indoors (e.g., in the basement) at extreme sub-zero temperatures, as frost can impair the charging performance and lifespan of batteries. 4. Do I need a special electricity meter for a storage unit? No, you do not need a special meter specifically for the storage unit. However, due to legal simplifications, it is already mandatory for your grid operator to install a modern, bidirectional meter (smart meter or digital meter with backstop) when you register a balcony power plant, if one is not already present. Old, analog Ferraris meters that run backward are no longer permitted for continuous operation and will be promptly replaced by the grid operator. 5. Can I retrofit an existing balcony power plant with a storage unit? Yes, in most cases this is easily possible. There are now universal retrofit storage units (such as the Zendure SolarFlow or EcoFlow PowerStream) that are simply connected between the existing solar modules and the existing micro-inverter. You do not need to buy new panels or inverters for this. 6. Is a balcony power plant storage unit frost-proof outdoors? Most modern storage units have protection class IP65 (dust and jet water protected) and are designed for outdoor use. However, lithium batteries do not like to be charged at temperatures below 0 °C. High-quality storage units therefore have an integrated heating foil that brings the battery to temperature before charging in winter. If this is not the case, the storage unit should be operated indoors or in the basement in winter. 7. What does "zero export" mean for a balcony power plant with storage? Zero export means that no self-generated electricity flows unused into the public grid. Intelligent storage systems measure current consumption via a smart meter at the house connection. If the house currently only needs 80 watts, the control system reduces the storage unit's output to exactly 80 watts. The rest remains in the battery for later hours. 8. Are there government subsidies for balcony power plants with storage? This varies greatly by region. While the federal government has reduced VAT to 0%, many cities, municipalities, and districts in Germany offer their own funding programs. Balcony power plants are often subsidized with a flat rate of 50 to 200 euros, and in some cases, there are even extra bonuses for purchasing a storage unit. It's worth checking your local municipality's website before making a purchase.

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