CYCLE PERFORMANCE FRONIUS SOLAR BATTERY
/ Introduction
The Fronius Solar Battery is based on the Sony FORTELIONTM Technology, a high quality Lithium iron phosphate
(LiFePO4) battery cell.
The main advantages of Sony’s FORTELIONTM Technology are
/ No maintenance needed
/ High level of safety
/ Short charging and discharging times
/ High depth of discharge
/ Long service life
/ High cycle life
The cycle performance of the Solar Battery is one of its major advantages. To underline the outstanding
performance it shall be explained in brief what cycle life exactly means:
/ Definitions:
/ SOC: State of charge (related to usable capacity); The SOC is defined as the available capacity
expressed as a percentage of some reference, sometimes its rated capacity but more likely its
current capacity.
100% = battery fully charged; 0% = battery discharged
/ Cycle: One cycle describes one complete charge process (form 0% to 100% SOC) and one complete
discharge process (100% to 0% SOC) at specific conditions (e.g. temperature).
/ Cycle life: The cycle life describes the number of cycles a battery can perform before its capacity falls below
a specific percentage of its initial capacity. Most often this value is stated at a remaining capacity
of 80%. The number of cycles can be found on mostly every battery manufacturer’s datasheets.
/ EOL End of life. In contrast to other battery technologies (Lead Acid batteries), Li-Ion batteries do not
suffer from “sudden-death” failure. Instead they exhibit a gradual decrease in performance over
their service life. So their EOL is defined by a reduction in initial capacity, by typically 20%.It is
important to remember that a Li-ion battery is not “dead” at its EOL, it has simply reached a predefined measure of aging. For the Solar battery EOL is defined as 80% of its initial capacity which
correspond to more than 8000 full charge and discharge cycles at an ambient temperature of
23°C. (see Diagram 1)
/ Cycle life of the Solar battery:
Under optimum conditions the Fronius Solar battery can be cycled over 8000 times, still having 80% of its initial
capacity. In a typical self-consumption system (loading the batteries during daytime and discharging batteries in
the night) it can be expected that the battery is cycled once a day. Assuming 250* full cycles a year a service life
of more than 20 years can be expected (8000/250 = >20). (* depending on location and PV system design)
As stated, those cycle numbers are measured under optimum conditions. The high cycle life of the battery is
depending on several factors. The ambient temperature can be considered as one of the main influences.
Fronius states an ambient temperature range of 5-35°C on the datasheet of the Solar battery, which is seen as
the optimum temperature range for the battery. In order to reach a maximum of cycles and longest service life we
recommend not to go beyond those temperature values.
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As stated above the cycle life of the battery is mostly dependent on the ambient temperature. In more detail this
behavior can be described like shown in the following diagram:
Cycle Performance Solar Battery
100,0
90,0
80,0
70,0
60,0
50,0
40,0
usable capacity in [%]
30,0
20,0
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
23 °C
45 °C
60 °C
number of cycles
Dia
gram 1: Cycle Performance Solar Battery; Values measured by Sony1
As can be seen in Diagram 1 the best cycle life is reached at low ambient temperatures. An increase of the
temperature leads to less cycle life. The temperature values in the diagram (23°C, 45°C, 60°C) are constant
temperatures. This means that in these tests the battery cells were exposed to those temperatures 24 hours a
day, 365 days a year, which will never occur in reality.
If the Solar battery is operated in temperate climate areas, considering a temperature range of 5-35°C at the
installation site, it can be expected that the average temperature is around 25°C or less. Also in that case up to
8000 cycles can be expected.
/ Warranty
The Fronius Solar Battery comes with a warranty of up to 5 years and extended warranties are available
additionally.
/ Summary
The Fronius Solar Battery is a high quality product designed for a maximum service life and high cycle life. The
cycle performance strongly depends on the ambient temperature of the battery and decreases with higher
temperature values.
Operating the Solar Battery at the optimum temperature range of 5-35 C° it can be expected that the battery
can be cycled up to 8000 times before dropping below 80% of its initial usable capacity.
/ Notes and References
[1] Values of Sony FORTELIONTM battery cell used in the Fronius Solar Battery; Values measured by Sony
SOC: 0 to 100%
Charge: 3.6V, 1ItA (2.85A), 100mAcutoff
Discharge: 1ItA (2.85A), 2.0Vcutoff
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