Solar energy can conveniently power devices and supply endless energy, i.e. for remotely located sensors. It can also charge a powerbank or your smartphone while on a mountain trip.
In this section, I am discussing components required to harvest energy from sunshine, how to store harvested energy, and how to re-supply it in a usable form.
Three fundamental parts are required for a DIY solar power supply:
Solar Panel
Solar panels convert light into electrical power. The generated power is in direct correlation to the light intensity. Solar panels by themselves cannot be used as reliable power source as current and voltage may vary greatly.
Charger
Chargers are common place and not restricted to solar applications: they take a wide range of input voltage and deliver a fixed output voltage, plus they incorporate security mechanisms to protect batteries from overcharging and under-voltage.
A solar charger is a slightly misleading term that can represent different things:
- Charger module with MPPT functionality: a regular charger with an additional optimization to take advantage of the sweet spot where solar panels provide the highest efficiency. This is achieved by controlling the current that the charger draws from the solar panel.
- Ready-to-use Solar Charger: a solar panel with integrated circuitry to convert the fluctuating voltage from a solar panel to a useful fixed voltage, i.e. 5V for USB charging.
To power simple DIY projects, a regular charger with an appropriate input voltage range is sufficient. Specialized MPPT charger modules can be benefitial but extra cost is often much better invested into a larger solar panel.
- Rechargeable Battery: Since solar panels deliver power only when the sun shines, a rechargeable battery acts like a buffer: it stores solar energy during sunshine and returns the stored energy at other times.
Lithium-based batteries are commonly used in DIY projects because of their energy density, and because most makers are familiar with them. In commercial devices such as solar-powered garden lamps etc., NiMH batteries are used. They are cheaper, more forgiving, less dangerous (no risk of fire and explosion), and most importantly have a higher temperature tolerance.
- DC-DC Converter: Typically, the battery voltage does not match the intended application: it is either too low or too high. DC-DC converters change the voltage to the required level. Boost converter raise the single-cell voltage to 5V for USB Charging. A buck converter lowers the voltage to 3.3V to power a microcontroller.
LiFePo4 batteries are perfect for powering 3.3V microcontrollers: their voltage range matches the voltage range needed. This saves a DC-DC converter, and more importantly, it considerably improves energy efficiency.
Voltage and Current
All starts with voltage and current - and the many ways to measure and monitor both.
This is the foundation on which tools like multimeters, oscilloscopes but also devices like voltage regulators, chargers and battery protection systems (BMS) operate.
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(content created May 01, 2024)