What is Voltage?
When two poles of battery are connected, namely positive and negative, they create pressure, which in turn activate electron flow. This pressure is measured in volts. Other terms used are electric potential difference or electromotive force.
Types of Voltages:
Alternating Current (AC) Voltage: This kind of voltage is bidirectional (reversing positive and negative over time). Periodically Alternating Current reverses the direction, hence voltage level also reverses along with the current.
- Alternating Current (AC) Voltage: This kind of voltage is bidirectional (reversing positive and negative over time). Periodically Alternating Current reverses the direction, hence voltage level also reverses along with the current.
Direct Current (DC) Voltage: This unidirectional electric charge (current) only flows in one direction. Direct Current (DC) is produced from solar panels when sunlight is passed through the solar cells. This energy is stored in batteries for later use to illuminate the lights.
Household appliances are powered by alternating current (AC) and with the help of a solar inverter, the direct current produced by solar panels can be converted to alternating current in order to be used by an off-grid electrical network.
Types of Battery and Voltage Used in Solar Lights:
Lead acid batteries: Generally, these types of batteries are made of 6 cells connected in series. Each cell produces voltage of 2 to 2.1 Volts. Hence, voltage of a lead acid battery is 12 Volts.
Lithium iron phosphate battery (LifePO4): Unlike lead acid batteries, these have 3.2 volts per cell. Only 4 cells are required to generate nominal voltage of 12.8 volts.
Lithium Ion (Li-ion): Each cell produces 3.7 Volts.
Advantages and Disadvantages of Battery Voltages:
With the discharge, voltage of lead acid battery tends to drop. However, Li-ion and LifePO4 produce constant output voltage.
Every solar street light requires a battery that can offer reliable performance and reasonable capacity. It is preferable to use maintenance-free batteries with good efficiency and longer lifespan. All the solar-powered lights in the market now have in-built rechargeable batteries. High quality cells and the most advanced technology are being used to produce these batteries.
Lead acid batteries are used in conventional solar street lights which provide around 500 to 1000 cycles and have a lifespan of around 3 to 5 years. Although lead acid batteries are relatively inexpensive and are dependable, they charge at a slower rate, require regular maintenance and are heavier. The solar panels need to generate at least 12 V to charge these batteries, so lead acid batteries may not be very effective during non-sunny days.
Whether installed at a private or public space, solar street lights are expected to operate throughout the year. Direct sunlight certainly gives the best conditions for solar street lights to give their best performance and it is also pivotal to install the lights in a shadow-free area and strategically place the solar panels. However, the batteries continue to charge although at a slower rate during overcast days with the partial sunlight available.
A good quality battery can directly affect the performance of your solar lights and a fully charged solar street light can run up to 15 hours. The energy capacity of lithium batteries helps the solar lights to continue operating even during overcast weather when the conversion rate is lesser and the batteries charge at a slower rate.
Modern solar street lights use lithium-ion or LiFePO4 batteries of 3.7 or 3.2 volt with upper and lower voltage protection. Both these batteries charge faster and therefore, the solar panels do not have to produce a lot of current to keep charging the batteries. With motion sensor and dimming features of solar street lights, the battery charge tends to last longer for the lights to keep working for at least 2 to 3 nights.