Solar Battery

Solar Battery – Storage of solar power

Solar Battery - Storage of solar power

At present broadly speaking, only two types of batteries are commercially available for solar photovoltaic system (SPV) applications.
They are:
Lead-acid battery & Lithium-ion Battery
In this type there are mainly three varieties:
(a). Flooded type (Flat plate and tubular plate types)
(b). AGM VRLA battery
(c). Gelled VRLA battery
Of these types, the order of cost is Gelled>AGM>Flooded. But most of the engineers opt for gelled Valve Regulated batteries because of their longer cycle lives and tolerance to higher temperature performance.

Since the flooded batteries require regular maintenance, those who can supervise the batteries can go for this type.  Moreover, these batteries emit hydrogen and oxygen gases and sufficient ventilation should be provided in the space where batteries are installed. Regular topping up of the electrolyte with water and keeping the top of the batteries clean and free from dust and acid spray are important.  If spacious rooms for batteries are not available, sealed maintenance free valve regulated batteries should be preferred. 

People who cannot attend to the maintenance work should prefer AGM or Gel batteries float/charge current for the same voltage. The AGM batteries are better suited for high power applications due to their lower internal resistance. Of these two types, the AGM batteries are warmer due to higher recombination efficiency. This is because of the differences in the pore structures of the two types. The field life of the batteries is dependent on various factors and so scientists and engineers engaged in the R & D work on batteries depend on certain procedures laid down in industrial standards like BIS (Indian Standards ), BS (British Standards), IEC (International Electrotechnical Commission), IEEE (Institute of Electrical and Electronics Engineers), etc.

In accelerated life tests carried out with flat plate batteries and tubular batteries, the life was estimated as 21.3 years at 25°C and 27.5 years at 25°C, respectively. These batteries were made by BAE Batterien GmbH, Berlin. [Wieland Rusch].

For accelerated life tests the standard IEC 60 896-21 requires test temperatures of 40°C and 55 or 60°C and the standard IEEE 535 – 1986 requires 62.8°C. A life time test at 62.8°C on the VRLA-types BAE OPzV (VRLA sealed tubular plate batteries), the Flooded (VLA) types BAE OPzS (flooded tubular plate batteries) and BAE OGi (flooded flat plate batteries) were conducted and the results are reported as given below. The batteries were float charged at the standard values: 2.25V for VRLA and 2.23V for flooded ones. During the test the growth of the poles, the increase in float current and the change of the 3 hour capacity was monitored every 50 days.

Table 1
Life expectancy test results as per IEEE 535-1986
[https://www.baebatteriesusa.com/wp-content/uploads/2019/03/Accelerated-Life-time-Tests-Rusch-2005.pdf
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.611.2155&rep=rep1&type=pdf]

Life as per IEEE 535-1986 OPzV (VRLA Tubular Plate Batteries) OPzS (Flooded Tubular Plate Batteries) OGi (Flooded Flat Plate Batteries)
Life at 62.8ºC (Days) 450 550 425
Life at 20ºC (Years) 34.8 42.6 33
Life at 25ºC (Years) 22.5 27.5 21.3

Table 2
Victron energy gives the following data for their products (www.victronenergy.com)
Cycle life of different types of lead-acid battery

DOD (%) Life in number of Cycles - Flat Plate AGM Life in number of Cycles - Flat Plate Gel Life in number of Cycles - Tubular Plate Gel
80 400 500 1500
50 600 750 2500
30 1500 1800 4500
Fig 5. DOD and number of cycles for AGM Gel and Gel long life batteries 1

Figure 1. DOD and number of cycles for AGM, Gel and Gel long life batteries  (www.victronenergy.com)

Table 3
Float life of AGM, Gel and Gel long life batteries (www.victronenergy.com)

Float Life AGM Deep Cycle Batteries Gel Deep Cycle Batteries Gel Long Life Batteries
Life at 20ºC (Years) 7-10 12 20
Life at 30ºC (Years) 4 6 10
Life at 40ºC (Years) 2 3 5

The GS Yuasa supplies special gelled tubular batteries. Certain innovations have prolonged the life of stationary batteries. Yuasa uses nano carbon technology for Tubular plates with glass tubes technology and granular silica gel electrolyte, which avoids PAM deterioration giving longer life (SLC models).

Yuasa SLC Tubular plate with glass tube oxide holder and granular SiO2
Fig 2. Yuasa SLC Tubular plate with glass tube oxide holder and granular SiO2
Yuasa SLC Tubular plate with glass tube oxide holder and granular SiO2
Fig 3(a). Yuasa SLC Tubular plate with glass tube oxide holder and granular SiO2

Li-ion batteries   

In the Li based type there are several chemistries:          

(a). Li –NCM or NMC  (Lithium-Nickel-Manganese-Cobalt) batteries

(b). Li-NCA (Lithium-Nickel-Cobalt-Aluminium)

(c). Li-LMO (Lithium-Nickel-Manganese oxide)

(d). LFP (Lithium-Iron phosphate)

(e).  LTO (Lithium-Titanium oxide)

(f).  LCO  (Lithium-Cobalt oxide)

Of these, the lithium-iron phosphate (LFP) cells are preferred due to cost consideration, safety and moderately longer life. Whenever cobalt is involved, the cost will be higher. Nickel-based batteries are less costly. Compared to AGM batteries the cost of the LFP battery is lesser by 15 to 25 % (https://www.batteryspace.com/LiFePO4/LiFeMnPO4-Batteries.aspx).

Table 4
Comparison of VRLA AGM and Lithium-ion battery

GS Yuasa (Li-ion (LCO) Li-iron Phosphate (LFP) (Battery Street) AGM (Exide India Ltd) AGM (Amararaja) Microtex Energy Pvt Ltd (Aquira)
Battery (4 * 3.7V=) 14.8V /50Ah1 (4 * 3.2=)12.8V/47 Ah20 12V 40Ah5 12V/65 Ah20 12V/52.5 Ah5 12V/65 Ah20 12V/52.5 Ah5 12V/65 Ah20 12V/55.25 Ah5
Mass (Kg) 7.5 6.5 22 20 21.3
Dimensions (mm) 175*194*116 197*131*182 174*350*166 351*167*165 350*166*174
Volume (Litres) 3.94 4.7 10.11 9.67 10.11
Specific energy (Wh/Kg) 98.7 (1h rate) (battery) (113.6 cell) 92.55(20 h rate) 78.77(5h rate) 35.45(20h rate) 26.5(5h rate) 39(20h rate) 31.5(5h rate) 36.6(20h rate) 29.6 (5h rate)
Energy density) (Wh/L) 188 128 77.1 80.66 77.2
Life (Years) 10 6 5-6 4-6 10
Life (Cycles) 5500 2000 1000 (50% DOD) ; 2500(30% DOD) (NXT Model) 1300 (30% DOD) (Quanta) 1450(20% DOD) 500(50% DOD) (Aquira)
Impedance 0.55mΩ (3.7V/50Ah cell) ≤ 50 mΩ 8 (12V battery) 5.1 (12V)
Cost based on cycle life x Wh of SLA 1.5 to 2.0 0.75 to 0.85 1 1 1
Cost /kWh ($) 900 to 1000 500 to 600 100 100 100

1. Microtex Energy https://drive.google.com/file/d/16pjM25En0pyvg6RzpF4N3j1jtwvo7fMb/view
2. Greg Albright et. al., AllCell Tech http://www.batterypoweronline.com/wp-content/uploads/2012/07/Lead-acid-white-paper.pdf
3. https://static1.squarespace.com/static/55d039b5e4b061baebe46d36/t/56284a92e4b0629aedbb0874/14454Mar 201281106401/Fact+sheet_Lead+acid+vs+lithium+ion.pdf
4. https://pushevs.com/2015/11/04/gs-yuasa-improved-cells-lev50-vs-lev50n/
https://www.batterystreet.be/etiketten/160332_BStreet_CataloogEN_2016_LowR_.pdf
5. NXT https://docs.exideindustries.com/pdf/industrial-export-batteries/products/ups-batteries/12v-agm-vrla-catalogue.pdf
6. https://www.amararajabatteries.com/Files/Products/Quanta%20Catalogue.pdf

Table 5. Battery Technology comparison

Flooded Lead Acid VRLA Lead Acid Lithium-ion (LiNCM)
Energy Density (Wh/L) 80 100 250
Specific Energy (Wh/Kg) 30 40 150
Regular Maintenance Yes No No
Initial Cost ($/k Wh) 65 120 600
Cycle Life 1,200 @ 50% 1,000 @ 50% DoD 1,900 @ 80% DoD
Typical state of charge window 50% 50% 80%
Temperature sensitivity Degrades significantly above 25ºC Degrades significantly above 25ºC Degrades significantly above 45ºC
Efficiency 100% @ 20-hr rate, 80% @ 4-hr rate, 60%@1-hr-rate 100% @ 20-hr rate, 80% @ 4-hr rate, 60%@1-hr-rate 100% @ 20-hr rate, 99% @ 4-hr rate, 92%@1-hr-rate
Voltage increments 2V 2V 3.7V

The efficiency with which batteries work in the Solar Photovoltaic system is not 100 %. Some energy is lost in the cycling process. In the case of lead-acid battery, the efficiency is 80 to 85 % and in Li systems the figure is
95 to 98 %. This is equivalent to saying that if the SPV produces 1000 Wh energy, lead-acid cells can store a maximum of 850 Wh while the Li cells can store 950 Wh.

A Yuasa Lithium-ion battery of 3.7 V * 4= 14.8V/50Ah (1 h rate) capacity weighs 7.5 kg. The volume is (17.5*19.4*11.6) 3.94 litres. The Wh capacity is 14.8*50= 740. Specific energy is 740 Wh / 7.5 kg = 98.7 Wh/kg. The energy density is 740/3.94= 187.8 Wh/litre. [https://www.lithiumenergy.jp/en/Products/index.html]
An Exide AGM VRLA battery of 12V/65Ah capacity weighs 13.8 kg and dimensions are 17*17*19.7 cm and the volume is 5.53 litres. The Wh capacity is 12*65=780 Wh. Specific energy is 780 Wh / 13.8 kg =56.5 Wh/kg. The energy density is 780/5.53=141.0 Wh/litre. [https://docs.exideindustries.com/pdf/industrial-export-batteries/products/inverter-batteries/agm-vrla.pdf]
Lithium iron phosphate battery:12V/47 Ah 6.5 kg.197*131*182 mm. 4.7 litres. 109 Wh/kg. 128 Wh/litre.
48V/30 Ah ReLion 3995 USD (https://relionbattery.com/insight) 1339.5 USD (https://relionbattery.com/insight-echnology)

Which solar battery is most suitable for solar energy storage?

Points for consideration in selecting solar battery

Assumptions:
Stand-alone system
Daily usage of power: 30 Watts per day = 30 W*24 h = 720 Wh.
Assume the system voltage as 12 V.
Four sunless days (4 days autonomy)
The current would be
30 W /12 V= 2.5 amperes*24 hours per day * 5 days (4 sunless days included) = 300 Ah at 2.5 A discharge rate.
(Note: But a battery of capacity 200 Ah can deliver 300 Ah (50% extra) if discharged over 120 hours at 2.5 amperes, i.e., 2.5 amperes for 5 days. Now we are not taking it into consideration)

So the selected battery would be 300 Ah @ 10 h rate

Solar Battery Capacity:
Rate of discharge and capacity
LAB: Lead-acid batteries deliver different percentages of energy at different currents; the higher the discharge current, the lower will be the capacity output.
(See the Table below)
LIB: Negligible difference

Table 6. Rate of  discharge and capacity output Lead-acid battery (LAB)

Duration of discharge (hours) Cut-off voltage for 12V battery (V) Per cent capacity available
120 10.8 150
20 10.8 115
10 10.8 100
5 10.8 85
3 10.5 72
1 9.6 50

Therefore, we have to select a suitable battery depending on the capacity and duration for which the backup is required.
We have selected a 300 Ah battery for a backup of 5 days continuous duration at 30 W.

Temperature correction for discharge capacity of solar battery

Lead-acid battery: The approximate correction factor for temperature can be taken as 0.5 % per degree C
Lithium-ion battery: Need not apply
The rated capacity is given at 27ºC in India. But if the operating temperature is far removed from the reference temperature, we have to increase or decrease the Ah capacity accordingly, in the case of LAB. The lower the temperature, the lower will be the capacity.
In our calculations, we take 25 to 30ºC as the temperature and no corrections need be applied.

Solar battery Correction for efficiency loss in transfer from Solar Photovoltaic to battery and to inverter

Correction for efficiency loss in transfer from SPV to the battery and to the inverter
Lead-acid battery: 15 % loss
Lithium-ion battery: 5 % loss
Assuming that a 300 Ah battery has been selected and if the correction factor is applied, the capacity required would be raised to 345 Ah (300*1.15). So this battery would deliver the required current, taking into consideration the above inefficiency.

Solar battery Safe Depth of Discharge (DOD) limit:

Lead-acid battery: :                80 %

Lithium-ion battery:               80 %

This aspect will further increase the capacity required to 345 /0.8 = 431 Ah

Solar battery Overload Factor (emergency reserve capacity)

Lead-acid battery: 5 %
Lithium-ion battery: 5 %
For overload consideration, we have to add 5 to 10 % of the capacity obtained in step (d) above.
So the capacity would be 431*1.05 = 452 Ah.
Say 12V 450 Ah battery would be needed

Solar battery End of Life factor:

The lead-acid battery (or any type of battery) is considered to have reached the end of life if the capacity has reached 80 % mark.
So we have to add another 25 % extra. So the capacity would be 450/0.8 or 450*1.25 = 562 Ah. The nearest capacity battery shall be selected. Two numbers of 200 or 225 Ah batteries in parallel can be opted.

Solar Battery - Charging time

The charging time depends on the previous output. 10 to 15 per cent extra Ah will be sufficient for a full charge. The SPV charging time depends on the solar irradiation and in any tropical climate countries, the sun shines from 6:00 AM to 5:00 PM. The coulombic efficiency (or Ah efficiency) of a lead-acid battery is about 90 % and the energy efficiency (or Wh efficiency) is 75%. On the other hand, the charge efficiency of the Lithium-ion battery is 95 to 99%.

Solar Battery - Ease of Installation

Both types of batteries lead acid battery or lithium ion battery can be installed without any difficulty. The batteries should be shielded from heat waves and high speed winds.

Which Solar Battery costs better in the long run?

The cost consideration will lead you to lead-acid type as given in the beginning. If the lead-acid battery’s cost is taken as 100 % (on per kWh basis), the Lithium-ion battery will cost 500 to 1000 % (5 to 10 times costlier at the prevailing rates, 2020).

Solar Battery Life expectancy

If the lead-acid battery’s life is taken as 100 %, the Li-ion battery (non-LFP) will last longer at least twice as long, while the life of LFP Li-ion battery is not as long as other Li-ion chemistries. However, it must be duly noted that investment in Lithium-ion battery requires additional investments in expensive sophisticated Battery Management Systems.

How many watts solar panels to charge 12V Solar battery?

How many solar watts to charge 12 V battery?

The right answer: The wattage of the SPV panel required depends on the battery capacity.
A solar panel for 12V solar battery (most solar photovoltaic panels are rated 12V) provides a source voltage of 13.6 to 18V. The wattage can be of any value, but, the higher the wattage, the lower the duration, a battery gets recharged. Similarly, the higher the solar radiation intensity, the higher will be the current produced. Most 100 watt 12-volt panels actually have 30 or 32 cells generating about 0.5 V each, all connected in series to produce 16v to 18 volts open circuit. It will reduce to about 15 volts when the load is connected.

How many amperes can a 12V/100W solar panel can produce?

Even though the panel is rated as 12V, it will produce about 18 V and so:
The current in amperes produced = 100 W/18 V = 5.5A.
Now, we know the voltage and the current supplied by the solar photovoltaic panel during sunny hours.
But we cannot connect the solar photovoltaic panel output directly to the battery terminals. Here, the charge controllers come for help. The battery is inserted between the charge controller and the inverter. The solar photovoltaic panel output is connected to the charge controller.
Charge controller help monitors how much energy is stored in the batteries to prevent overcharging. Charge controllers will also protect the battery from over-discharge and overcharge.

 

Depending on the ampere-hour (Ah) capacity of the battery, the duration will vary for a full charge. If one assumes that the solar radiation is available for 7 hours, then the input for the battery would be 7 x 5.5 A = 38.5 Ah;
Whether the solar battery is fully charged or not depends on the previous output from the battery. If the previous output is less than 38.5 Ah, we can safely assume that the battery has been fully charged. Please note that the coulombic efficiency (or Ah efficiency) of a lead-acid battery is about 90 % and the energy efficiency (or Wh efficiency) is 75%.

Hence the actual input would be 38.5 Ah *0.90 = 34.65 Ah. The Watt-hour efficiency would have a lower value, depending on the output voltage of the solar photovoltaic panel.
If more current (amperes) is required for quick charge, more solar photovoltaic panels can be connected in parallel.
The current acceptance of the battery also has to be considered.
Here, the charge controllers come for help
Similarly, for a portable 10 W solar photovoltaic panel (used in a portable lantern with a 12V/7Ah battery), the current produced will be 10 W/ 18V = 0.55 A

How to connect 24V solar panel to 12V solar battery?

As usual, the solar photovoltaic panel is connected to the battery through a charge controller (or an MPPT charge controller, maximum power point tracking charge controller). As long as there is a charge controller, one need not worry about the higher voltage output.  But care should be taken to see that the Imax specified on the back of the panel is not exceeded. Of course, the solar battery will get a controlled fast charge.

Note: An MPPT or maximum power point tracker charge controller is an electronic DC to DC converter that optimizes the match between the solar photovoltaic panels  and the battery bank or utility grid. That is they convert a higher voltage DC output from solar panels and other similar devices such as wind generators,  down to the lower voltage needed to charge batteries

How to connect solar panels to battery?

The solar photovoltaic panel should not be connected to the battery directly unless it is a dedicated one made for that particular battery. A simple charge controller is inserted between the solar photovoltaic panel and the battery for the smooth functioning of the system.

How to calculate solar panel, battery & inverter?

How to calculate solar panel & battery size?

The first step is to know the load requirements for the user.
a. Tube light 40 W
b. Ceiling fan 75 W
c. LED bulbs (3Nos. * 5W) 15 W
d. Laptop 100 W
Calculate the total wattage and also the duration for which the devices are to be used.
Let us assume the total at 230 watts. At any time 50 % usage is taken into account. Duration of usage is taken as 10 hours.
So, the energy requirements by the appliances will be = (230/2) W * 10 h = 1150 Wh per day.

Multiply the total Watt-hours per day requirements by the appliances by 1.3 (the energy lost in the system) 1150*1.3= 1495 Wh, rounded off to 1500 Wh (This is the power that needs to be supplied by the solar photovoltaic panels.)

Solar photovoltaic panel requirements

Assuming the energy (Wh) requirement for 10 hours will be = 1500 Wh. The summer irradiation maybe 8 to 10 hours. In winter and cloudy days, the sunshine duration maybe 5 hours. We take the former value to calculate the panel power requirement
Hence, the power from SPV required is 1500 Wh/ 10 h sunshine = 1500 W.

On average, a single 12V/100W solar photovoltaic panel will produce about 1000 Watt-hours (Wh) of charge (10 hours* 100 W). Hence, the number solar photovoltaic panels needed = 1500 Wh /1000 Wh = 1,50, rounded off to 2 panels of 12V/100 W. We require 200 Watts solar photovoltaic panels, that is, 2 panels in parallel. Or one panel of 360 W can be used.
If we take 5 hours of solar insolation, we may require 1500 Wh/500 Wh = 3 panels in parallel or one solar photovoltaic panel of 360 W can be used.

Note:
This solar photovoltaic output may not be sufficient in winter, as we have taken 10 h solar insolation for calculation. But in the latter calculations, we take 2 sunless days and so the output may not be a problem in winter. We have to take this risk to avoid a cost increase on solar photovoltaic panels.

For a 100 W solar photovoltaic panel, the following parameters apply

Peak power (Pmax) =100 W
Maximum power voltage (VAmp = 18 V
Maximum power current (IMP) = 5.57 A (100 W/17.99 V)
Open circuit voltage (VOC) =21.84 V
Short-circuit current (ISC) = 6.11 A
Module Efficiency (under STC) = 13.67 %
Maximum fuse rating suggested = 15 A

The efficiency of the solar photovoltaic panel counts in determining the area of the solar panels. The lower the efficiency, the higher the area required. The efficiencies of the commercially available panels vary from 8 to 22 %, all depends on the cost of the solar photovoltaic panel.

Solar Battery Sizing

This is the most difficult part of the sizing exercise. But a simple calculation will show that we require a 12V/125Ah battery. How?
1500 Wh / 12 V = 125 Ah (Remember Wh = Ah *V. Ah = Wh/V).
But there are several inefficiencies we have to consider before finalising the battery capacity. They are:
a. Correction for efficiency loss in transfer of energy from solar photovoltaic panel to battery and to inverter (15 to 30 %. Was taken into consideration while calculating the total Wh requirements 1200Wh became 1560 Wh, by taking 30 % loss under section “How to calculate solar panel, battery & inverter?” above.)

b. Safe DOD limit: (80 %. Factor 1.0 becomes 1/0.8= 1.25 ) (Note: Most professionals take the safe Depth of Discharge (DoD) limit as 50 %. It is too low). Moreover, we are planning to have four sunless days. For 50 % DOD end of life, the factor would be 1/0.5= 2.
c. Overload Factor (emergency reserve capacity) (5 %. Factor 1.25 becomes 1.25*1.05 =1.31).

d. End of Life factor: (80%. When the battery attains 80 % of its rated capacity, the life is said to have come to an end. So the factor 1.31 becomes 1.31/0.8 or 1.31*1.25 = ~1.64).

Hence, the capacity of the battery would be almost two times = 125*1.64= ~ 206 Ah at 10 hour rate. The nearest available capacity would be 12V/200Ah at 10 h rate. 

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Note:

  1. We have calculated only for one day, i.e., 10 hours per day.
  2. We have assumed 50 % of the total load of 2
  3. We have not taken into consideration, any sunless (or no-sun) days.
  4. Normally all the professionals take 3 to 5 days autonomy (that is no-sun days);
  5. If we take even 2 days autonomy, the battery capacity would be 200 + (200*2) = 600 Ah.
  6. We can use three numbers of 12V/200 Ah batteries in parallel. Or we can use six numbers of heavy duty 2V cells of 600 Ah capacity in series.

Solar Inverter sizing

The input rating of the inverter should be compatible with the total power watt of appliances. The inverter must have the same nominal voltage as the battery. For stand-alone systems, the inverter must be large enough to handle the total amount of wattage being used. The inverter wattage rating should be about 25% larger than total power of appliances. If spiking appliances like washing machines, air compressors, mixers etc are included in the circuit, the inverter size should be minimum 3 times the capacity of those appliances to take care of the surge current during starting.

In the above calculation, the total wattage is 230 W (i.e., full load). When we include a safety margin of 25% the rating of the inverter would be 230*1.25 = 288 W.

If we do not include spiking appliances like washing machines etc., the 12V/300 W inverter is enough. Otherwise, we have to go for a 1000 W (or 1 kW) inverter.

Solar charge controller sizing

The solar charge controller should match the wattage of PV array and batteries. In our case we are using 12V/300 Watts solar panels. To arrive at the current divide 300 W by 12 V = 25 A and then identify which type of solar charge controller is right for your application. We have to make sure that solar charge controller has enough capacity to handle the current from PV array.
According to standard practice, the sizing of solar charge controller is to take the short circuit current (Isc) of the PV array, and multiply it by 1.3

Solar charge controller rating = Total short circuit current of PV array= (2*6.11 A) x 1.3 = 15.9 A.
Taking into consideration the wattage calculation shown above, the charge controller should be 12V/25 A (without spiking machines kike washing machines etc.)

How to charge battery with solar panel?

How to charge 12 V lead acid batteries with solar panel?

Can you charge a car battery with solar panels?

First point to be noted is that there should be compatibility between the battery and the solar photovoltaic panel. For example, the solar photovoltaic panel should be 12V if you want to charge a 12V battery. All of us know that an solar photovoltaic with a rating of 12 V/100 watts will produce nearly 18 V open circuit voltage (VOC) and 16V maximum power voltage (VAmp) and a maximum power current (IMP) of 5.57 A (100 W/17.99 V)

Once the battery voltage and capacity ratings are known or available, calculations shown in Section above can be followed.
The most important aspect is that the battery should not be connected directly to the solar photovoltaic panel. As discussed earlier, a charge controller and an inverter of suitable ratings should be used.

Or
If the user can monitor the battery terminal voltage (TV) (that is, go on taking the battery terminal voltage readings every now and then), the solar photovoltaic panel can be directly connected to the battery. Once the battery gets fully charged, the charge should be terminated. The criteria for full charge depend on the type of battery. For example, if it is flooded type of lead-acid battery, the on-charge-TV can go up to 16 V or more for a 12V battery. But if it is a valve-regulated type (the so-called sealed type), the voltage at any time should not be allowed to exceed 14.4 for a 12V battery.

How to connect battery to solar panel?

How to hook up solar panels to RV batteries?

The wiring for Recreational vehicles (RV) Solar Photovoltaic panel is the same as other SPV panels. The Solar Photovoltaic panel should not be directly connected to the batteries. The RV will have its own charge controller and other system components as in the roof-top SPV.
Depending on the Solar Photovoltaic output (more importantly, the voltage), the connections of the batteries should be done. If the Solar Photovoltaic output is 12V, then one 12V battery can be connected via suitable charge controller. If you have more 12V batteries as spares, these spare batteries can be connected to the SPV in parallel with the already connected battery. Never connect them in series.

If you have two numbers of 6 V batteries, connect them in series and then to the Solar Photovoltaic panel
If the Solar Photovoltaic panel output voltage is 24 V, you can connect two numbers of 12V batteries in series.

Different types of connection of batteries to SPV panels
Fig 4. Different types of connection of batteries to SPV panels

Is it worth getting solar battery?

Are solar batteries cost effective?

Yes, it is worth getting solar battery.  Solar batteries are designed especially for solar applications and so they have longer life than other types of lead-acid batteries.  They can withstand higher operating temperatures and give longer life for the intended low discharge application.  Moreover, they are valve-regulated type and so the maintenance cost is almost zero. No need to do the periodical water addition in the cells.

If you mean the solar photovoltaic system, then the answer is: Where do you want to use it? Is it a far off place with no grid connectivity? Then it is definitely profitable and cost-effective.
Except for the battery part of it, all other components have life expectancies of over 25 years. The ultimate financial benefit provided by solar energy will far outweigh any price you pay for solar energy.
The payback period for the cost depends mainly on the cost of electricity from DISCOMs.

Payback Period = (Total System Cost – Value of Incentives) ÷ Cost of Electricity ÷ Annual Electricity Usage
For a 1 kW, solar photovoltaic system the benchmark cost is Rs 65,000. Government’s subsidy is Rs 40,000.
You can have your own calculations.

What is the best solar battery charger?

How to keep a solar panel from overcharging a battery?

All chargers are manufactured with good manufacturing practices.  When a charge controller is connected between the SPV panel and the battery, one need not worry about the chargers.

But, a digital maximum power point tracker (MPPT) is a good option instead of a simple charge controller.  An MPPT is an electronic DC to DC converter that optimizes the match between the solar array (PV panels), and the battery bank.  It senses the DC output from the solar panels, changes it to high-frequency AC and steps down to a different DC voltage and current to exactly match power requirements of the batteries. The benefit of having an MPPT is explained below.

Most PV panels are built for an output of 16 to 18 volts, even though the nominal voltage rating of SPV panel is 12 V. But a nominal 12 V battery may have an actual voltage range of 11.5 to 12.5 V (OCV) depending on state of charge (SOC). Under charging conditions, an extra voltage component has to be delivered to the battery. In normal charge controllers, the extra power produced by the SPV panel is dissipated as heat, while an MPPT senses battery requirements and gives a higher power if higher power is produced by the SPV panel. Thus, wastage, undercharge and overcharge are avoided by using an MPPT.

Temperature affects the performance of the SPV panel.  When the temperature rises the efficiency of the SPV panel decreases. (Note: When SPV panel are exposed to a higher temperature, the current produced by the SPV panel will increase, while the voltage will decrease. Since the decrease in voltage is faster than the increase in current, SPV panel’s efficiency is decreased.).  On the contrary, at lower temperatures, the efficiency increases. At temperatures lower than 25°C (which is the temperature of standard test conditions (STC), the efficiency increases. But the efficiency will balance out over the long run.  

How to calculate charging time of battery by solar panel?

How to charge solar batteries?

At the outset, we should know
1. The state of charge (SOC) of the battery
2. Battery capacity &
3. SPV panel’s output characteristics.
SOC indicates the available capacity of the battery. For example, if the battery is 40 % charged, we say the SOC is 40% or 0.4 factor. On the other hand, the depth of discharge (DOD) indicates the capacity already removed from the battery. In the above example of 40 % SOC, the DOD is 60 %.
SOC + DOD = 100 %.
Once we know the SOC, we can say how much energy has to be supplied to the battery to bring it to full charge.

If the output from the SPV panel is 100 W and the duration of charge is 5 hours, then the input into the battery is 100 W*5h = 500 Wh.  For a 12V battery, this means we have given an input of 500 Wh/12V = 42 Ah. Assuming the battery capacity to be 100 Ah, it means we have charged to 42 % SOC, if the battery had been fully discharged.  Had the battery been only 40 % discharged (40 %DOD, 60% SOC), this input is sufficient for a full charge. 

The proper way is to include a charge controller, which will take of the charging of the battery.

What size solar panel for a 7 Ah battery?

An SPV panel of 12V-10 Wp  is good for 7.5Ah VRLA battery. A charge controller of 12V-10A should be included in the circuit. The charge controller will have provisions to select battery disconnect (11.0 ± 0.2 V or as required) and reconnect (12.5 ± 0.2 V or as required) voltage settings.  The VR battery would be charged at 14.5 ± 0.2 V constant voltage mode.

A 10 W panel will give 10Wh (0.6A @ 16.5V) over an hour under standard test conditions (1000W/m2 and 25°C – equivalent to one hour of ‘peak’ sunshine). For around 5hours equivalent sunshine in summer it will give 50 Wh. Thus, an input of 50 Wh/14.4 V =3.47 Ah will be put into the battery.

Will solar panel fully charge a battery?

The solar panel alone should never be used for charging a battery. As described above, a solar photovoltaic panel charge controller should be inserted between the panel and the battery. The charge controller will take care of the completion of charging.

How many solar panels & batteries to power a house?

There is no straight answer to this question because every household has its own unique power requirement. Two homes of the same size can have entirely different energy needs.
So follow the process given below to arrive at the suitable specifications for the Solar Photovoltaic panel, batteries and charge controllers.
Step 1. Calculate daily power needs and energy needs of the home.

Table 7. Daily power needs and energy needs

Appliances Electrical/Electrical appliance Nos. Total W 5 Hours of usage and total Wh need per day
LED Bulbs 10W 10 100 5 Hours; 500 Wh or 0.5 kWh or unit (15 kWh per month)
Ceiling fans 75W 3 225 5 Hours; 1.25 units (15+37.5=52.5 kWh per month)
Tube Lights 40W 4 160 5 Hours; 0.8 kWh (52.5+24=76.5 kWh per month)
Laptop 100W 1 100 10 Hours; 1.0 Unit (76.5+30=106.5 kWh per month)
Refrigerator 300W (200 Litres) 1 300 5 Hours;1.5 Units (106.5+45=152 kWh per month)
Washing Machine 1000W 1 1000 1 Hour; 1 Unit (152+30=182 kWh per month)

1. Total energy needs per day = 182 kWh / 30 days = 6.07 kWh Say, 6000 Wh
2. But at any time the whole of the above 6000 Wh is not used. So have to calculate the average need in Wh. We can take 50 % of 6000 = 3000 Wh.

Step 2.    Calculate daily solar panel energy needs of the home.

  1. 3000 Wh / 5 hours  = 600 W or 0.6 kW panel is needed.
  2. But we have to take into consideration the efficiency of the SPV panel. So divide this value by 0.9. We get 0.6/0.9 = 666 Wh
  3. We can select four panels of 365 W (PMax  = 370 W) (e.g., LG365Q1K-V5). When using two in parallel and two in series, we have 1380 (WRated) to 1480 (W@40C°) at a voltage of 74.4 (VMPP).) to 87.4 V (VOCV). The array’s rated current is 19.94 A

Step 3. Calculate the energy needs of the battery
1. Batteries can be discharged by 80 % only in Solar Photovoltaic applications. So divide this Wh by 0.8; 6300/0.8 =7875Wh
2. Again, for buffer stock (no Sundays – 2 days), we have to multiply this by 1+2 = 3. So the battery Wh required is 7875 Wh*3 = 23625 Wh.
3. For converting this Wh into Ah, we have to divide the Wh by the voltage of the battery to be procured. 23625 Wh /48 V= 492 Ah. Or 23625 /72 = 328 Ah.

    • If we choose 48 V system, then the Microtex Brand 6 OPzV420 Solar tubular gel VRLA battery is the ideal battery (24 numbers of 2V cells of 512 Ah @ C10) uniquely designed for solar applications. If we choose 72 V system, then the 6 OPzV300 type (36 numbers of 2V cells of 350 Ah @ C10) is good.
    • If we want AGM VRLA batteries for 48V system, then the Microtex Brand batteries six numbers of  M 500V battery (8V, 500 Ah @ C10) is the ideal battery especially designed for long life solar applications. If we choose 72 V system, then the Microtex Brand nine numbers of  M 300 V type (8V, 300 Ah @ C10)  is good

These batteries are compact and are stackable in horizontal racks, with low foot-print

Step 4. Calculate specifications for the charge controller
Since we use a battery of 48 V (24 cells) nominal rating, we require 2.4 V*24 = 57.6 V charge controller. With a MidNite Solar’s Classic 150 charge controller, the charging current will be 25.7 A at a charging voltage of 57.6 V (for 48V battery).

If we use a battery of 72 V (36 cells) nominal rating, we require 2.4 V*36 = 86.4 V charge controller. With a MidNite Solar’s Classic 150 charge controller, the charging current will be 25.7 A  for this voltage, the battery charging current will be 25.7 A. A problem with 72 V battery system is that we have to add one more panel in series; so a total of 6 panels (instead of 4) have to be procured.  Hence it is better to go for 48 V battery system.

Regarding the charge-discharge current requirements, since we use an MPPT of 150V/ 86 A, charge-discharge currents will be correctly taken care of by the MPPT.
But the manufacturers require a charging voltage of 2.25 to 2.3 V per cell (Vpc), the charging voltage can be set at the specified voltage levels.

How to use solar power without batteries?

It is not advisable to use the SPV panels directly, unless the voltage of the array and the appliance are compatible, that too the appliance should be of the DC type.
Otherwise, there should always be a PWM charge controller or a sophisticated MPPT.
When there is no battery to store energy, we have to sell the energy produced in excess to the local DISCOM. So it has to be a grid-connected SPV system.

Abengoa, a renewable energy firm based in Spain, has already built several solar plants that store excess energy in molten salt, which can absorb extremely high temperatures without changing state. Abengoa recently secured yet another contract to build a salt-based 110-megawatt solar storage plant in Chile, which should be able to store 17 hours of energy in reserve. [ https://www.popularmechanics.com/science/energy/a9961/3-clever-new-ways-to-store-solar-energy-16407404/]
A recently developed idea is to pump water using electricity from solar panels to heights (for example on the roof) which means they store potential energy which can then be converted into kinetic energy when it’s flown down and hence, electricity when this flowing water is used to rotate turbines. This is like a solar-hydropower combination!

Another way is to direct the energy from your photo-voltaic system to a water electrolyser that generates hydrogen gas from water. This hydrogen gas is stored and can be used at a later time as a battery to generate electricity. This is mainly used for industrial purposes.[ https://www.environmentbuddy.com/energy/how-to-store-solar-energy-without-batteries/]

The solar panels will absorb photons from the sun which will enter into the system where an aluminium alloy is heated and moves from a solid to a liquid state. With this method, it allows the storage of a very dense amount of energy in the material that will be sent as heat to the Stirling Generator. From there, it turns into electricity with zero emissions and at a lower cost. https://www.sciencetimes.com/articles/25054/20200318/breakthrough-concept-for-storing-energy-without-batteries.htm

How to test solar batteries?

The Indian Standards Organisation has formulated IS 16270:2014 for testing Secondary cells and batteries for solar photovoltaic application.  IEC specification number IEC 62133: 2012 is also available. These two specifications are identical.

The following tests are described in details:

  1. Rated capacity
  2. Endurance (Life cycle test)
  3. Charge retention
  4. Cyclic endurance in photovoltaic application (Extreme conditions)
  5. Recover from sulphation
  6. Water loss on float charge
  7. Efficiency tests

Can I charge a battery directly from a solar panel?

It is not advisable to use the SPV panels directly, unless the voltage of the array and the appliance are compatible, that too the appliance should be of the DC type.

How do solar battery banks work?

Like any other battery banks, solar batteries also give energy on demand. Depending on the power requirements and the duration for which this power is required, the capacity of the battery bank and its configuration will be determined.
The power required and the duration will also determine the solar panel capacity.

The solar panels and the battery are connected via a charge controller so that the battery or the appliances are not damaged due to excessive voltage or current. Again the current from the battery will be DC and this DC will be converted to AC as required by a solar inverter. Some of the appliances operating on DC may be connected to the charge controller.
Users not familiar with connecting batteries should consult an expert before connecting batteries among themselves to make a suitable battery bank or the battery to the charge controller or inverter.

Are gel batteries good for solar?

Yes. Gel batteries are valve-regulated type and so maintenance requirement is almost zero. They offer superior performance in float as well as cyclic applications with no let down in dependability or reliability throughout the life expectancy of the cells. The positive spines are made with special corrosion-resistant alloy with high tin content to offer good performance through the entire life of the cells.
They are well suited for all renewable energy storages, UPS, switchgear and control applications, railways Signal & telecommunications (S & T) applications.

These cells are made with tubular plates manufactured using high-pressure die-casting process and so offer pore-free castings enabling 20 years+ lives. They are ready-to-use factory charged cells with no electrolyte stratification. The cumbersome periodical water addition (topping up) is done away with because of the VR construction.

They have specially designed valves with flame retardant materials so that fire hazards are completely eliminated. 

Can I use car battery for solar?

Any type of battery can be used for SPV application. Automotive batteries are meant for high rate discharges and so manufactured with thinner flat plates. Therefore their life in deep cyclic applications will be very poor.
One can use them in solar photovoltaic applications, but should not expect a long life.

Can I use solar battery in normal inverter?

Yes. There should be compatibility between the inverter and the battery in terms of voltage. The inverter should be having a maximum charge voltage of 2.25 to 2.3 V per cell (Vpc) , that is, 13.5 to 13.8 V for a 12V battery. Then no problem will be encountered.

Can I use normal inverter battery for solar panel?

Yes. But the maintenance aspect will pose problems and also incur cost escalations as opposed to solar gel batteries. Topping up regularly, cleaning the terminals and the washers, bolts and nuts and periodical equalizing charges: these are some of the maintenance aspects.

How many batteries required for a 10 kW solar system?

The specifications of batteries for a 10 kW (off-grid) solar system should be decided taking into consideration several parameters like daily kW and kWh requirements, SPV panel capacity, solar insolation, etc.
However, most of the rooftop off-grid systems of 7.5 kW to 10 kW capacity (700 to 1000 square foot rooftop area required) use 120 V systems of 150 Ah batteries along with 16 modules of 320 WP solar panels.
Grid-tie solar photovoltaic system requires no battery storage.

How to charge multiple batteries with one solar panel?

All solar charge controllers will allow only one battery to be charged. Nowadays, there are charge controllers which have the option of having provision for charging two battery banks. The two battery banks are charged separately using the same controller and solar panels. There are two separate battery connection points on the charge controller.
In the absence of the above type of charge controllers, the two batteries can be charged from one solar panel by using two solar charge controllers. Charge controllers have been specifically designed to be used in this configuration. The two solar charge controllers individually monitor and control efficiently to ensure optimum charging current (amperes) and voltage.

How many solar panels does it take to charge a 12 volt battery?

A single solar panel is enough for charging a 12V battery.  The voltage output from an SPV panel is suited to charge a 12V battery and is in the range of  16 to 17.3 V.

The current depends on the number of solar cells connected in parallel fashion.  Each SPV cell can produce approximately 0.55 to 0.6 V (OCV) and a current of 2 A depending on the size of the cell, the solar insolation (given in W/m2) and the climatic conditions.

35 cells in series produce 35 to 40 W at 17.3. The cell is 4-inch diameter. Normally solar module
the panel is installed in an aluminium frame which was oriented to face the equator (south) and tilted by an angle of about 45° S.
A 40 W cell has an area of 91.3 cm 2 and the voltage is 21 V (OCV) and 17.3 V (OCV). It can produce a current of 2.3 A.
Similarly, a 10 W panel will give 10 Wh (0.6A @ 16.5V) over an hour under standard
test conditions (1000 W/m2 and 25C – equivalent to one hour of ‘peak’ sunshine). For around 5 hours equivalent sunshine in summer it will give 50 Wh.

Which battery is best for solar?

Solar gelled electrolyte batteries are the best for cost considerations.
But nowadays, the Li-ion batteries with their better performance are being preferred by the users.
A lead-acid battery of 24 kWh is equal to:
• 2,000 Ah at 12 volts
• 1,000 Ah at 24 volts
• 500 Ah at 48 volts
For the same 24 kWh, Li-ion battery of 13.13 kWh is sufficient
• 1,050 Ah at 12 volts
• 525 Ah at 24 volts
• 262.5 Ah at 48 volts (https://www.wholesalesolar.com/solar-information/battery-bank-sizing)

Lead acid battery Sizing

10 kWh x 2 (for 50% depth of discharge) x 1.25 (80 % charge efficiency factor) =  25.0  kWh

But if we take 80 % DOD calculations for deep cycle lead-acid batteries, the kWh required will be lower.

10 kWh *1.25 (or 10/0.8) (for 80% depth of discharge) multiplied by 1.25 (80 % charge efficiency), the battery required will be 15.6 kWh

Lithium-ion battery Sizing

10 kWh x 1.25 (for 80% depth of discharge) x 1.05 (95 % charge efficiency factor) = 13.16 kWh

Can I connect a 24 V solar panel to a 12V battery?

Yes.  But we have to include a charge controller between the SPV panel and the battery.  Otherwise the battery may get damaged due to overcharge or even may explode, if conditions favourable for accumulation of hydrogen gas above the dangerous limit and production of a spark.

What is the difference between solar battery & normal battery?

Solar batteries are made with tubular plates manufactured using high pressure die-casting process and so offer pore-free castings enabling 20 years+ lives. They are ready-to-use factory charged cells with no electrolyte stratification. The cumbersome periodical water addition (topping up) is done away with because of the VR construction.  They have specially designed valves with flame retardant materials so that fire hazards are completely eliminated.

Solar batteries are made with tubular plates manufactured using high pressure die-casting process and so offer pore-free castings enabling 20 years+ lives. They are ready-to-use factory charged cells with no electrolyte stratification. The cumbersome periodical water addition (topping up) is done away with because of the VR construction.  They have specially designed valves with flame retardant materials so that fire hazards are completely eliminated.

Gel batteries are valve-regulated type and so maintenance requirement is almost zero. They offer superior performance in float as well as cyclic applications with no let down in dependability or reliability throughout the life expectancy of the cells. The positive spines are made with special corrosion resistant alloy with high tin content to offer good performance through the entire life of the cells.

On the contrary, the normal batteries are made with conventional alloys for the grids and the life is also not longer.  But the maintenance aspect will pose problems and also incur cost escalations as opposed to solar gel batteries. Topping up regularly, cleaning the terminals and the washers, bolts and nuts and periodical equalizing charges: these are some of the maintenance aspects.

How to connect solar panel to battery to charge controller:

The charge controller will be connected between the Solar Photovoltaic panel and battery

A simple off-grid solar photovoltaic system
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