Solar charger/regulator options to improve efficiency of solar panel output

1. Low-Cost Solar Charge Controller with
Maximum Power Point Tracking for the
Developing World
Robert Pilawa
OLPC Presentation
April 4th, 2010

2. Outline
• Charge Controller Basics
• Maximum Power Point Tracking
• Cost considerations
• Our prototype

3. Charge Controller Basics
• Protect battery from over-voltage
• Protect battery from under-voltage
• Low-cost
• Used for low-power applications

4. Maximum power point problem
• Typical 12V panel, Vmp=17 V
• Mismatch between panel voltage and battery voltage
• Does not extract maximum available power from panel
• Think of it as gears on a motor

5. Maximum power point tracker
• Smart power electronics adjust panel voltage to extract
maximum power
• Typically more expensive

6. Cost consideration
• MPPT can capture as much as 30% more of the available
power.
• Typically not used for low (<50W) panels
• With 20% increase in power, you should use it if
additional cost is $0.80/Watt higher than simple charge
controller (for $4/Watt panels)
• So a 30W MPPT charger would be considered if it costs
$24 more than a simple charger
• Today's designs cost > $1/Watt

7. Our low-cost solar charger
• Targeting $0.25/Watt
• Uses innovative new digital control
• Low-cost power electronics components
• Robust implementation
• Able to charge lead-acid batteries, cell-phones, and
OLPC X0
• Expected first prototypes for testing early summer of 2010