How Is Solar Energy Used in Homes?

Humans are becoming increasingly adept at tapping into the 380 trillion terajoules of energy put out every second by the great thermonuclear reactor in the sky, using this virtually limitless energy supply to power our homes and lifestyles.

We can sometimes use the sun’s energy directly, like when we design homes to take advantage of passive solar heat. But when we want to use it for technology, we need ways to convert the sun’s raw output into mechanical, thermal or electrical energy.

Solar panels offer one way to do this. At present, they can convert 22% to 25% of sunlight into electricity. The low efficiency means you need a lot of panels for moderate power output.

I live in an off-grid home powered by solar panels, and we don’t have room for many of them. To keep the size of our array within practical limits, we need to limit our electricity usage.

We heat our water and home, run our refrigerator and cook with propane. That isn’t sustainable, however, especially given California’s intention to move away from gas in the near future. We’ve looked into or tried solar technologies for most of these purposes  — except, perhaps, the refrigerator. Who knows what the future will bring?

PV Panels

Solar panels are more properly called photovoltaic (PV) panels. When exposed to sunlight, they generate direct current (DC) to power 12V appliances or to charge a battery.

Appliances that run on 12V power are fine for camping. But we’ve found you have many more options if you convert to 120-volt alternating current (AC), and for that you need an inverter. Ours is outdated and produces a coarse signal that some appliances can’t use.

Contemporary inverters produce more reliable AC signals. They’re often built into the panels or battery storage units. That makes it easy to tie the system to the electrical service panel. And if you’re on the grid, you can sell the energy you produce back to the power company.

Solar Shingles

Solar shingles are interconnected mini PV panels that cover the whole roof or the sunniest portion. They function like full-size PV panels. But because they’re also a roof covering, the must be flexible, durable and water-resistant.

Each shingle is about the size of a standard shingle and produces between 13 and 63 watts of power, depending on the brand. If there are enough of them on the roof and they get enough sun, they can be a standalone power source. But in most cases, they supplement grid power or charge a storage battery.

We can’t use them, unfortunately, because a huge oak tree shades our whole roof.

Solar Lighting

Tiny PV panels, combined with rechargeable batteries and efficient LEDs, make it possible to have light at night.

The quality of outdoor solar lighting has improved dramatically over the last few years. Now solar landscape, path and string lights can keep burning well into the night and, in some cases, even until dawn. Best of all, they’re cheap, so you can have super-bright, long-lasting outdoor light for a minimal cash outlay.

Solar Water Heaters

About 20% of home energy usage goes to heating water, so a solar water heater can make a big dent in your energy bill. Most solar water heaters consist of a black panel that sits on the roof or on the ground, exposing water to the sun’s radiation.

An active water heating system employs a small pump to circulate water or a heat transfer fluid (for freezing climates) through coils in the panel. Hot water can go directly into a storage tank in the building or on the roof.

When you use a heat transfer fluid, it circulates through a set of coils installed in the water storage tank. The coils transfer heat to the water.

A passive water heating system has no pump and relies on natural convection to circulate water. The solar heater may be a black panel with coils, but it can also be as simple as a water tank covered with a transparent material that lets the sun’s radiation through. This type is a little less expensive and a lot less efficient.

Solar Ovens

Today’s solar ovens are more sophisticated than the one invented by Swiss scientist Horace-Benedict de Saussure in 1767. One of the most popular and easiest to use consists of foldable metal panels that reflect the sun’s energy and focus it on a cooking box. This makes it easy to DIY.

Solar ovens are a godsend to people all around the world with limited access to electricity. But like all things solar, they’re heavily dependent on the weather and don’t work at night. We’ve found when you cook with a solar oven, you must adjust your cooking timetable to coincide with the sun’s movements. That usually means adjusting your meal schedules as well.

Solar Fans

If you want your house to be dry and comfortable and your roof to last, you need good attic ventilation. In some cases, that means circulating air with a fan.

We’ve found running a solar attic fan in the summer really cools the rest of the house. You can also use one to circulate air in the house itself — a kind of solar air conditioner, minus the refrigerant.

A solar fan draws its power from a roof-mounted PV panel, so it costs nothing to operate. But if you want it to run on cloudy days, you’ll need a battery. That’s an extra expense, but not a major one. Here’s everything you need to know about solar-powered attic fans.