R & D

Design of Solar Panels for Bicycles

Solar Panels with Suitable Aspect ratio

Width of the solar panel is important for Solar Bicycles.
BEM has put in efforts to develop solar panels with smaller widths so as to suit solar bicycles. In the image alongside we can observe that the solar panel on the bicycle to the right is having a solar panel with a width of 355 mm that was specially designed to suit the width of bicycles. The length of the bicycle handle is typically 500 mm and hence the panel will not obstruct if the handle can pass through a narrow lane. 

Design of Hybrid MPPT  Solar Charge Controller (Patented)

About the BEM® सवित्रे™  Savitré MPPT  Solar Charge Controller

The BEM® सवित्रे™  Savitré - 2 Amps MPPT  Solar Charge Controller consists of MPPT digital controller and photovoltaic drivers and is designed to control high efficiency DC/DC conversion used in photovoltaic based Li-Ion battery charging application. It is a 2 Amps (Max.) Solar True Maximum Power Point Tracking (MPPT) algorithm based charger for 37 Volt (Nominal), 42 Volt (Maximum) Li-ion battery. This charger provides you with the ability to extract the maximum possible power out of your Solar panel of rating 12 Volt, 40W, and feed it into the  rechargeable Li-ion battery. This means that the E-Bicycle battery would get fully charged in the shortest possible time with a smaller sized (lower cost) Solar panel.  Recommended size of solar panel is 12V, 40W that can be easily fitted on the rear carrier of a standard bicycle 

Set-up is easy as well. Simply, plug the solar panel into one (input) side of the solar charge controller and the e-bicycle battery into the other (output) side, then Switch ON the charger and the battery would start charging at the fastest rate! Ensure that the solar panel is facing the sun, avoid shadows, and keep the panel surface clean for best performance.   

75W, Solar MPPT Charge Controller with OLED Display for E-Bicycle’s 36V Li-Ion Battery 

Features :


BEM® सवित्रे™  Savitré MPPT  Solar Charge Controller with RED and GREEN LED Indicators 

₹ 1376.00 ₹ 2500.00   (inc GST)

₹ 1,166.10 (+18% GST extra)


BEM® सवित्रे™  Savitré MPPT  Solar Charge Controller with OLED Display  (in addition to RED and GREEN LED Indicators)

₹ 1926.00 ₹ 2500.00   (inc GST)

₹ 1632.20 (+18% GST extra)

Description

This is a Maximum Power Point Tracking (MPPT) solar charge controller for 10-cell (10S), Li-Ion  batteries having nominal voltage of 36 Volts typically used in electric bicycles. (Similar chargers for other battery voltages such as 48 V for EVs are also available). This MPPT solar charger gives you the ability to extract the maximum possible power out of your solar panel or any other photovoltaic device and feed it into a rechargeable Li-Ion battery. 

The MPPT feature gives you the ability to charge a bicycle battery, say of 5 Ah,  from a smaller sized solar panel, say of 40W, in the shortest time, say 4 to 5 hours. The small panel size makes it practical for you to mount it on your bicycle and convert it to an elegant looking solar bicycle.  

Set-up is easy as well. Simply insert the 2.1 x 5.5 mm (male) plug on the end of the cable originating from the solar charger (36V DC) output, into your battery socket. Make sure that your 40W, 12V solar panel has a similar 2.1 x 5.5 mm male plug that can be inserted into the input (female) socket of the solar charger (12V DC solar). Switch ON the power switch of the solar charger,  and you are good to start charging!

The OLED model additionally has a  bright OLED (Organic Light-Emitting Diode) (monochrome or blue) display of resolution  128 x 64, and size 0.96 inch, brightly and boldly displays the solar input voltage, battery voltage as well as the battery charging current.  The OLED display has high brightness, self-emission, high contrast ratio, slim/ thin outline, wide viewing angle, wide temperature range and low power consumption.

MPPT Operation

The MPPT charge controller has a ARM Cortex microcontroller and sophisticated software to detect the Maximum Power Pm point. The software also has the ability to control and limit the charging current to the load (battery), so that the solar panel operation is controlled to a voltage Vm corresponding to the maximum power point Pm, to deliver maximum power. This gives the ability to charge a battery from a smaller (lower cost) solar panel in the shortest possible time. 

(In sharp contrast, a PWM charge controller, that is more popular due to its lower cost, offers very little control action. It is merely a switch that connects the solar panel to the battery and offers no control over the solar voltage. Hence, a PWM controller is unable to extract the maximum power from the solar panel.) 

DC to DC Boost Controller

The MPPT charge controller is a DC to DC transformer that is designed as a step-up transformer (boost controller).  The step-up transformer is highly efficient - the output power delivered to the battery is only marginally lower than the power extracted from the solar panel. The loss in the transformation process is small, typically less than 8%. 

Figure 4 shows the characteristics of a boost MPPT charge controller where Pbat = Pm while Vbat > Vm . Figures 5 to 7 show the block diagram of the MPPT charge controller at different hierarchical levels.   

The DC to DC step-up (boost) transformer converts 10 - 24 V solar input to 31 - 42 V output to charge the battery. The boost converter is designed with a huge toroidal inductor and two large heatsinks so that it can handle and boost 100W of solar power. 

Protection

Please note there is no reverse polarity protection. Check the polarity of the solar panel before plugging in. 

All other protections, such as over-voltage protection, over-current protection,  are incorporated in the design and are monitored by the sophisticated software residing in the ARM controller.

Operating Modes 

Table 1. LED and OLED States when the Charger is Switched ON

Sr. No. MODE/OLED Display RED LED GREEN LED STATE NOTES

1. NO DISPLAY   OFF OFF NO SOLAR INPUT     All indicators and OLED  in OFF State; Solar Panel disconnected /
Inadequate solar power fed to charger / Inactive state
2. STANDBY OFF-P OFF-P INITIALISATION In transition; for a short period after Switch ON

3. CHARGING ON OFF-P CHARGING Battery in Charge Mode. 

4. FULL OFF-P ON FULLY CHARGED Battery is Fully Charged. 

5. ERROR 1/2 ON ON ERROR/CHARGED Battery disconnected, or BMS activated indicating FULL charge

*Error State means Battery Management System (BMS) may be refusing further Charge though the FULL Battery Voltage has not been reached. 

Note:

BEM® सवित्रे™  Savitré MPPT  Solar Charge Controller with RED and GREEN LED Indicators (comes fitted on the solar bicycle)

BEM® सवित्रे™  Savitré MPPT  Solar Charge Controller with OLED Display (Optional - available at an extra cost of ₹ 550 (inclusive of GST) in lieu of the Basic model with only LED indicators.)

BEM® सवित्रे™  Savitré MPPT  Solar Charge Controller

SOLAR 12V DC to 42V DC, 2A Charger

Input Voltage: 12 - 22 Volts DC,
Input Current: < 2.3 Amps (Max.)
Input Power: < 40 Watts (Max.)

Output Voltage: 42 Volts DC (Max)
Output Current: 1 Amps (Max.)

Indicators:
RED LED GREEN LED STATE
OFF OFF NO SOLAR INPUT
FLASHING FLASHING IN TRANSITION
ON FLASHING CHARGING STATE
FLASHING ON FULL STATE
ON ON ERROR STATE*

*Error State means Battery Management System (BMS) may be refusing further Charge though the FULL Battery Voltage has not been reached. 

Design of Solar Panel over the Pannier Rack (Patented)

ECarComparison