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The voltage asymmetry of batteries discharge in the off-grid solar systems Krzysztof Sztymelski Tomasz Kraszewski SURFINT-SREN IV 23-26. November 2015
The voltage asymmetry of batteries discharge in the off-grid solar
systems
Krzysztof Sztymelski
Tomasz Kraszewski
SURFINT-SREN IV
23-26. November 2015
SURFINT-SREN IV 23-26. November 2015
Agenda
• Off-grid solar system
• Battery
• Battery examination
• Conclusion
SURFINT-SREN IV 23-26. November 2015
Off-grid solar system
1. Photovoltaic panels
2. Voltage regulator
3. Battery
4. Inverter
SURFINT-SREN IV 23-26. November 2015
Off-grid DC solar system
SURFINT-SREN IV 23-26. November 2015
Off-grid DC solar system
SURFINT-SREN IV 23-26. November 2015
Off-grid DC solar system
• PV power peak: – Max 500 Wp – 2x 250Wp parallel
– Typical 190-250 Wp – 1 x PV
– Min 90 Wp
• Slope ~60o – better for winter time
• Battery capacity: – Max 4 x 200Ah
– Typical 2 x 110Ah
– Min 1 x 60Ah
• Load – LED head with dimming – Max 56 W
– Typical 28 W
– Min 16 W
SURFINT-SREN IV 23-26. November 2015
Battery
• Pb acid – not used: not tolerate low temperatures, damage at deep discharge
• Pb GEL – can not charge below 0oC, buried 1m below ground
• Pb AGM – can charge below 0oC, can be installed in the lamp
• LiIon, LiPo, LiFe4 – 4 x more expensive than Pb, do not take energy below 0oC, the possibility of an explosion or fire above 50oC, need a BMS (Battery Management System)
SURFINT-SREN IV 23-26. November 2015
Pb Battery
• Charge 14.4 – 14.8 V
Iopt=0.1C – difficult to obtain
„I” depends on PV system
• Discharge 11.5 V – min voltage
Optimal capacity (30% - 2000 cycle; 100% - 500 cycle)
SURFINT-SREN IV 23-26. November 2015
Pb Battery 24V string
• In large system i.e. with wind turbine
SURFINT-SREN IV 23-26. November 2015
Battery discharge - examination
• Min discharge: 23V (2 x 11.5 V)
• Max I: 2.5A
Battery New, the same
type
Few hundred
cycle, the same
type
Unknown
number of
cycle, different
type
Umax 96 mV 1.126 V 2.427 V
SURFINT-SREN IV 23-26. November 2015
Battery discharge - examination
• parallel
0
2
4
6
8
10
12
14
16
2015-09-11 22:40 2015-09-12 03:28 2015-09-12 08:16 2015-09-12 13:04 2015-09-12 17:52 2015-09-12 22:40 2015-09-13 03:28 2015-09-13 08:16
V VA
VB
-2,0%
-1,5%
-1,0%
-0,5%
0,0%
0,5%
1,0%
1,5%
2,0%
2,5%
2015-09-11 22:40 2015-09-12 03:28 2015-09-12 08:16 2015-09-12 13:04 2015-09-12 17:52 2015-09-12 22:40 2015-09-13 03:28 2015-09-13 08:16
%
SURFINT-SREN IV 23-26. November 2015
Battery discharge - examination
• series: – new battery
0
2
4
6
8
10
12
14
2015-09-13 07:462015-09-13 12:342015-09-13 17:222015-09-13 22:102015-09-14 02:582015-09-14 07:462015-09-14 12:342015-09-14 17:22
V VA
VB
-2,0%
0,0%
2,0%
4,0%
6,0%
8,0%
10,0%
12,0%
14,0%
2015-09-13 07:46 2015-09-13 12:34 2015-09-13 17:22 2015-09-13 22:10 2015-09-14 02:58 2015-09-14 07:46 2015-09-14 12:34 2015-09-14 17:22
SURFINT-SREN IV 23-26. November 2015
Battery discharge - examination
• series – bad battery
0
2
4
6
8
10
12
14
2015-09-13 21:10 2015-09-13 23:34 2015-09-14 01:58 2015-09-14 04:22 2015-09-14 06:46 2015-09-14 09:10 2015-09-14 11:34 2015-09-14 13:58 2015-09-14 16:22 2015-09-14 18:46
V VA
VB
-80,0%
-70,0%
-60,0%
-50,0%
-40,0%
-30,0%
-20,0%
-10,0%
0,0%
10,0%
2015-09-13 21:10 2015-09-13 23:34 2015-09-14 01:58 2015-09-14 04:22 2015-09-14 06:46 2015-09-14 09:10 2015-09-14 11:34 2015-09-14 13:58 2015-09-14 16:22 2015-09-14 18:46
SURFINT-SREN IV 23-26. November 2015
Conclusion
• In every cases the voltage asymmetry have been observed. In the system with new batteries voltage asymmetry is very low and voltage balancing of each battery seems to be unnecessary. The costs associated with it will not cover any power gain.
• In the system with the use of the same batteries in a few hundred cycles voltage asymmetry is bigger. The voltage of each battery may be considered passive or active balancing. However, it is an expensive solution and it should be remembered that unlike the batteries of LiION type there is no risk of changes of the polarity of given cells and all over voltage OV and under voltage UV phenomena evoke very little risk of explosion or fire.
• The most interesting was third case. In the first month the asymmetry began to decrease significantly to a level not exceeding that described in second test. Batteries are constantly working, a permanent reduction in capacity and balancing of such disadvantageous case is not justified from the engineering and economical point of view.
SURFINT-SREN IV 23-26. November 2015
Thank you
• Tomasz Kraszewski, PhD Eng
• Krzysztof Sztymelski, PhD Eng
