How to Build a Small Solar Power System | LOW←TECH MAGAZINE
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Image: a solar panel with charge controller and lead-acid battery. Photo by Marie Verdeil.
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Readers have told me they like to build small-scale photovoltaic installations like those that power Low-tech Magazine’s website and office. However, they don’t know where to start and what components to buy. This guide brings all the information together: what you need, how to wire everything, what your design choices are, where to put solar panels, how to fix them in place (or not), how to split power and install measuring instruments. It deals with solar energy systems that charge batteries and simpler configurations that provide direct solar power.
Conventional solar PV installations are installed on a rooftop or in a field. They convert the low voltage direct current (DC) power produced by solar panels into high voltage alternate (AC) power for use by main appliances and rely on the power grid during the night and in bad weather. None of this holds for the small-scale systems we build in this manual. They are completely independent of the power grid, run entirely on low voltage power, and are not powering a whole household or city but rather a room, a collection of devices, or a specific device. Small-scale solar is decentralized power production taken to its extremes.
Most of the work in building a small-scale solar system is deciding the size of the components and the building of the supporting structure for the solar panel. Wiring is pretty straightforward unless you want a sophisticated control panel. You only need a limited set of tools: a wire stripper, some screwdrivers (including small ones), and a wood saw are the only essentials. A soldering iron, pliers, and a multimeter are handy, but you can do without them.
Before you start: safety
Before you start: low voltage or high voltage?
Before you start: do you really need a battery?
What you need: the components of a small-scale solar system
How to connect solar panels in series and parallel
How to wire a solar power system with battery storage?
Batteries
Solar charge controllers
Wiring
How to wire a solar power system without battery storage?
DC-DC converters
Wiring
How to size solar panels, batteries, and other components?
Sizing a solar system without batteries
Sizing a solar system with batteries
Sizing other components: charge controllers, DC-DC converters, cables, connectors & fuses
How to build supporting structures?
How to split power and run multiple devices at the same time
How to include measuring instruments?
Battery voltage meter
Watt, volt, and current meters
Control panels and power outlets
How to obtain low voltage appliances?
Before you start: safety
Low-voltage DC power does not carry a risk of electrocution (a fatal electric shock). That is especially so for 12V systems. Depending on the electric conductivity of your body (and other factors), you could go up to 20-50V before an electric shock may kill you. 1
Nevertheless, solar power systems have their risks. The main dangers are electric shock (non-fatal but painful), fire, battery explosion, and component damage. However, if you stick to some simple rules, you will be OK. During seven years of solar power experiments, I have never caused a fire or received an electric shock, although I have fried some components.
Never touch electric components with wet hands.
Never touch the exposed part of a positive and negative wire simultaneously. You will become part of the electric circuit and receive an electric shock. It is perfectly fine to touch just one wire. The same goes for the battery terminals: it’s OK to touch one, but not two at the same time.
Never let a positive wire touch a negative wire. That will cause a short circuit, leading to physical harm, component damage, fire, or a battery explosion. Use different colors for positive and negative wires and stick to them.
Always put a fuse in your solar system.
Make sure your cables are thick enough.
Never connect a solar panel directly to a battery. Use a charge controller in between.
Never put a lead-acid battery in an enclosed container.
Before you start: low voltage or high voltage?
Electric power (expressed in watts) equals current (in ampère) multiplied by voltage (expressed in volts). Consequently, electric power (W) can refer to a low voltage (V) with a high current (A) or a high voltage with a low current. Conventional solar installations for households always use an inverter, which converts the low-voltage DC power from a solar panel into the high-voltage AC power used by main appliances. You can do...