Battery Storage System Info

Use power from the sun at night too

In recent years the demand for residential battery storage systems has risen considerably. Consumer desire for lower electricity bills and independence have driven up demand and technological innovations have sunk the prices to affordable levels. For private PV system owners it is now cheaper to consume solar electricity themselves than to feed it into the grid and receive feed-in revenue for it. Feed-in tariffs are being phased out globally and affecting all markets, this demand for storage solutions is truly international.

Battery storage 6.6kWh in home

Battery storage system – where is the benefit?

Photovoltaic systems without a storage system produce solar electricity that must be used immediately. This is rarely effective, since solar electricity is mainly generated during the day, while the electricity requirement of most households is low during this period. However, electricity demand increases significantly in the evening. With a storage system the solar electricity that wasn’t required during the day can be used when you really need it. Without having to change your habits, you:

  • permanently reduce your electricity bills
  • personally contribute to the energy revolution
  • optimize your own consumption
  • declare your independence from large energy suppliers

Lead or lithium-ion batteries – a fundamental decision

Battery storage systems for residential use are equipped either with lead-acid, lead-gel, or lithium-ion batteries. Lead-acid batteries were used mostly in the past, amongst other things, as car batteries. Given their considerable advantages, lithium-ion batteries are becoming increasingly accepted over lead-acid batteries. They have come to be regarded as the standard in photovoltaics in recent years. Lifetime: The expected lifetime of lithium-ion batteries is around 15 years, whereas the maximum for lead batteries lies between 5 and 10 years.

Lead batteries must be housed in a ventilated room since they emit gases. This is not necessary with lithium-ion batteries. Depth of discharge: Lithium-ion batteries discharge up to 100% of stored power. Lead-aced batteries, however, can normally only be discharged up to 50%, since deeper discharge reduces their overall lifespan. System efficiency: The system efficiency of lithium-ion batteries can exceed 90%, where only approx. 70% is possible with lead batteries. Photovoltaic systems with lead batteries therefore have to be larger, leading to unnecessary extra costs. Our tip: Choose a photovoltaic storage system with lithium-ion batteries.

Finding the right photovoltaic storage system – what you should consider!

After the fundamental decision between lithiom-ion and lead batteries has been made, further criteria can help you decide which storage system to buy:

Storage capacity

The size or capacity of the storage system should be appropriate to meet residential consumption demand. In principle the storage system should be large enough to supply a household with solar electricity from the evening until the next morning. A size of 4 to 6 kWh is normally sufficient for an average four-person home which consumes around 4,500 kilowatt-hours (kWh) annually. If the device is too small or too big, this results in unnecessary extra costs. If the storage system is too small, not enough energy can be stored to cover the needs. The purchase of additional mains electricity becomes necessary. If the storage system is too large on the other hand, the solar electricity that is not required is permanently stored, reducing the battery’s usage life and not saving you any money.

Depth of discharge

Depth of discharge means what percent of the stored energy can actually be withdrawn from the device. In order to avoid damage, the majority of battery systems for electrical energy need a residual charge. The market norm is a depth of discharge of between 50% for lead batteries and up to 100% for lithium-ion batteries such as the SOLARWATT MyReserve system. According to the Bundesverband Solarwirtschaft e. V. (German Federal Association of the Solar Industry), a battery storage system should never be discharged below its specified depth of discharge, because this shortens the life of the battery.

Individual electricity requirements

For the choice of the right storage system size we recommend you determine your household’s electricity requirement as accurately as possible. To do this you can look at your annual electricity consumption for the last five years, or obtain an estimate from an expert. The rule of thumb for an average four-person household is: Average annual demand (approx. 4,500 kWh) can be met by a photovoltaic system with am output of 4 to 6 kilowatt peak (kWp). A storage system should have a usable storage capacity of at least 4 to 6 kWh’s. The MyReserve battery system has a capacity expandable from 2.4 kWh’s to 60kWh’s with a total efficiency of 96.7% and the package can generate enough electricity to suit almost any household.

Efficiency of the system

Conversion losses occur during the storage process; i.e. part of the energy is converted into heat. The total efficiency indicates what percentage of the energy stored in the system can then actually be used. Fluctuations between 70 and 95% are the market norm. Our tip: Choose a storage system with a total efficiency of over 90%. Please note that battery efficiency and total efficiency are different specifications. Total efficiency depends not just on the battery, but on the complete storage system. Due to conversion losses, total efficiency is usually lower than the battery’s own efficiency and is not disclosed by most vendors. MyReserve is connected behind the inverter. This means that the conversion from DC to AC is omitted and only very small conversion losses occur. The current is only converted when it is fed into the household network. MyReserve stores the current from the solar system directly and thus achieves a world record holding battery efficiency of 99.2% and a total system efficiency of 96.7%. This excellent efficiency is also helped by the system components, which are matched perfectly with one another.


The expected lifetime of storage systems varies between 5 and 15 years, depending on the model and manufacturer. The lifetime of the MyReserve is around 15 years. SOLARWATT also guarantees an output of at least 80% of the battery module’s capacity for 10 years. Our tip: Choose a photovoltaic storage system with a 10-year guarantee.

How battery storage systems work

The purpose of storage systems is clear: They make solar electricity available when you need it – usually in the evening and at night. The principle behind this is as follows: The electricity generated in a photovoltaic system is initially used for self-consumption. This means that active electricity consumers such as chest freezers or other household appliances are immediately supplied with solar electricity. However, if more electricity is available than needed the excess electricity flows into the battery, thereby charging it. The unused electricity only flows into the grid when the battery is full. When electricity is then required at night, the stored solar power is available. If the electricity requirement during the day is higher than the quantity of solar electricity produced by the photovoltaic system, then the stored electricity is also available – regardless of whether the storage system is fully or only partly charged. Further electricity is only procured from the grid when the battery is fully discharged. In this way it is possible to cover a large part of your electricity needs with the power generated by a photovoltaic system.

How can I integrate a battery into my existing PV system?

Most available battery systems on the market cannot be simply integrated into an existing PV system without further ado. Technical changes such as inverter replacement or additional work are usually necessary. The heavy weight and, in some cases, gigantic dimensions of many electricity storage systems limit where they can be safely installed and this can necessitate a great deal of work. Usually several installers are kept busy for at least one day. The MyReserve, conversely, was designed for a simple Plug&Play installation. Its light weight and compact dimensions make a one-man assembly possible. The storage system is installed with connection behind the inverter and stores the direct current directly from the PV modules. Conversion to alternating current takes place only when electricity is fed into the house’s mains electricity network. This avoids conversion loss and enables a total efficiency of 96.7% for charging and discharging. Additionally, this storage system is compatible with all common photovoltaic inverters and can therefore be easily retrofitted. Our tip: Stay on the safe side and only have your photovoltaic storage system installed by a certified specialist.

Is a photovoltaic storage system worthwhile for me?

The investment in a storage system is always worthwhile when purchasing a new photovoltaic system including panels. It enables you to use a large part of your solar electricity yourself, thus considerably reducing the amount of electricity you purchase from an energy supplier. Retrofitting a storage system is worthwhile in every market where the price of electricity is higher than feed-in revenue – where feeding electricity into the national grid no longer makes economic sense. System operators who receive extra remuneration for privately consumed solar electricity should also expand their solar system by a battery storage system. Our tip: Please take into account future developments when choosing a storage system. If it is already foreseeable that the legal boundary conditions will change in the near future or that your solar system will yield a lower profit for some other reason, then you should retrofit a PV storage system.

Costs for a PV storage system – what you should expect

There are presently more than 40 different manufacturers on the Australian storage system market. The pricing depends, amongst other things, on the capacity of the storage systems, whether lithium-ion or lead batteries are used and what components are installed. There is also variation across Australian states in electricity prices, and between installers. On account of large fluctuations in price, we advise you examine the technical data or characteristics of storage systems and determine what is most important to you.

Use valuable solar electricity yourself

With a storage system you can use the solar electricity from your system when you really need it and permanently lower your electricity bill. Sophisticated technology, a long service life, and newly sunken prices make PV storage systems a worthwhile investment – for both new and existing solar systems. We’ll be glad to help you with any questions about topics discussed above or about our MyReserve storage system.


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