More and more homeowners are producing their own solar power. To make this investment pay off faster, they should increase self-consumption and use more cheap solar power than expensive power from the grid. One effective way to increase self-consumption and reduce energy costs is to install battery storage for the solar system.
Your photovoltaic system produces the most electricity when the sun is at its highest. That happens at noon. But you probably need the most electricity in the morning and evening. That's why owners of photovoltaic systems consume on average only 30 percent of the electricity they produce themselves and feed 70 percent into the grid. In return, they receive a feed-in tariff from their grid operator. Because solar power is cheaper than purchased electricity, it is worthwhile to increase your own consumption and use more solar power. You can increase your own consumption, for example, with an electric boiler, an e-charging station for electric vehicles, a heat pump , or a battery storage unit or electricity storage system for your solar power.
According to the Energy Act, each power plant is allowed to set its own feed-in tariff. Therefore, the tariffs are very different. On vese.ch/pvtarif (available in Germand and French), you will find an up-to-date overview of all grid operators in Switzerland and can search by municipality, zip code or electricity utility.
With a battery storage system, owners of a photovoltaic system double their own consumption from 30 to about 60 percent. This makes you less dependent on your grid operator and energy price fluctuations, allows you to use your photovoltaic system more efficiently and reduces your electricity costs.
Optimally, you consume up to 90 percent of your self-produced solar power. 100 percent is impossible because photovoltaic systems produce too little electricity from November to January.
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The battery storage works similar to a car battery. While driving, the alternator generates more energy than the car needs, for example for the lighting or air conditioning. The excess energy is stored in a battery and is available for the next start. An electricity storage system, also called a battery storage system, works in a similar way: It stores electricity that you neither consume yourself nor feed into the power grid. This stored electricity can be used in the evening or at night, or when there is not enough sunshine. You can store electricity for days. But not (yet) for weeks or months. Right now, researchers are working on hydrogen storage systems that split solar electricity into oxygen and hydrogen through electrolysis. The hydrogen is stored in gas cylinders or accumulators and converted into electricity and heat in a fuel cell in the winter. However, the system is not yet fully developed and marketable.
Lead-acid batteries have a limited number of charge cycles, usually about 3,000. In comparison, lithium-ion batteries can go through more than twice as many charge cycles, about 7,000 cycles. In addition, lead-acid batteries are less efficient and cannot be discharged as deeply. This is why a lead-acid battery can be used less efficiently with the same storage capacity. On the other hand, electricity storage systems with lead batteries cost significantly less than those with lithium-ion batteries.
Lithium-ion batteries have a higher efficiency of up to 95 percent compared to a maximum of 86 percent for lead-acid batteries. In addition, lithium-ion batteries can be discharged deeper, almost up to 100 percent, while lead-acid batteries can only be discharged up to 80 percent. Despite the higher initial cost, power storage systems with lithium-ion batteries are the most popular because of their higher performance.
Lithium-ion batteries are characterized by their durability, performance and low weight. That is why they have long been used in smartphones, tablets and electric vehicles. That's why it's no big surprise that the currently most popular power storage device, the Tesla Powerwall 2, is manufactured by an electric vehicle manufacturer. Such storage solutions with lithium-ion batteries can be easily mounted on a wall indoors or outdoors, usually in the basement or garage, and connected to the photovoltaic system on the roof of the house.
Lithium-ion batteries are most commonly used because they are lighter and last longer. Lead batteries are now only recommended in exceptional cases.
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Photovoltaic systems produce direct current (DC), which must be converted to alternating current (AC) for self-consumption or for feeding into the power grid. With AC coupled storage, the battery storage has its own inverter, with DC coupled storage it uses the inverter of the photovoltaic system. What speaks for one or the other variant?
The battery storage is correctly dimensioned if you can cover your electricity consumption from evening to morning with its energy. Calculate with 1 kilowatt hour of storage capacity for 1,000 kilowatt hours of electricity consumption per year. That makes 5 kilowatt hours of storage capacity for an average single-family home with 4,500 kilowatt hours of electricity consumption. For smaller photovoltaic systems, the storage capacity of the battery in kilowatt-hours should not be much larger than the output of the photovoltaic system in kilowatt-peak. Too much battery capacity has disadvantages: The state of charge always fluctuates between half-full and full, which is why the battery ages quickly. A properly dimensioned battery storage optimizes self-consumption, too large a storage only brings little.
Most modern battery storage systems offer an option as an emergency or backup power supply in the event of temporary power outages. You can choose between a simple emergency power socket on the storage unit or a sophisticated emergency power system that automatically switches to backup power in the event of a power failure and supplies your household with energy. How long depends on consumption and battery capacity.
With an intelligent charging management system as a supplement to the photovoltaic system with battery storage, you can increase your self-consumption to around 75 percent, and even up to 90 percent under perfect conditions. Based on your previous energy consumption and weather forecasts, the charging management system controls how much electricity is consumed during the sunny midday hours and how much electricity is stored. In addition, the intelligent charging management system significantly extends the service life of the storage unit because the battery is charged and discharged in a way that is gentle on the battery.
Electricity storage units with direct current are cheaper than electricity storage units with alternating current. The price depends on several factors. Mainly on the storage capacity, but also on the number of charging cycles, the depth of discharge and the power loss. Expect to pay 3,200 to 9,000 Swiss francs for a DC battery storage system or 6,000 to 15,000 Swiss francs for an AC battery storage system. Add to that the cost of installation of 1,000 to 2,500 Swiss francs. Details can be found in the table "Cost examples for battery storage systems" at the end of this article.
Subsidies are currently only available in two cantons: Schaffhausen and Thurgau support battery storage with a one-time subsidy of 2,500 Swiss francs towards the investment costs.
That depends on the general conditions. The higher the electricity price and the lower the feed-in tariff, the more likely it is that higher self-consumption and thus battery storage will pay off. Especially if the prices for solar panels and storage as well as the feed-in tariffs will decrease in the next few years, as experts predict. From an ecological point of view, high self-consumption is already worthwhile: solar electricity is 100 percent renewable, while electricity from the power grid is on average 46 percent renewable. With every kilowatt of electricity that you have to draw less from the grid, you minimize your CO2 emissions, conserve scarce resources and reduce your energy costs.
All prices are indicative only (as of 2023) so you can estimate the cost. If you want an exact offer, ask our certified solar installers from your region.
