How Photovoltaics Work
While photovoltaics (or solar cells) may be the most commonly cited and recognizable solar technology, they are also the most expensive and at times hardest to utilize for a residential home. However, when it’s a viable option, PV is still a technology that can revolutionize how we use energy in the decades to come.
So far, we’ve discussed other solar systems that basically concentrate solar energy and transfer it to another medium – either water or air. With a photovoltaic cell, things are done electronically. In short, the cell is converting the energy from the sun into electricity using a silicon semiconductor.
It’s the same technology we’ve using for years to power computers, transistors and other electronics, but instead of a man-made power source, we are using the sun directly. When the sun’s light hits the PV cell, some of that light is absorbed by a semiconductor made of silicon (or a similar material). The energy in the semiconductor then breaks loose electrons that can travel as they please inside the device.
Once inside, these electrons are pushed in a particular direction, thus creating a current. Once the current has been generated, you can use contacts located on the PV cell to draw electricity off of it to power your devices.
I’ve just boiled down a very complex subject to about 150 words so you’ll have to bear with me when I say it just works. Entire books, classes and college degrees are based on this subject so if you’re interested in how electricity, silicon or semiconductors work, there are plenty of introductory resources to draw from.
However, the basic idea is that those PV cells can take the sun’s rays and convert them in real time to electricity which we can use to power various devices – from the solar-powered calculator we all thought was amazing in second grade to the space station orbiting the earth with solar panel wings catching as much radiation as possible with each circuit.
Issues with PV Cells
Since the 1950s, photovoltaic cells have been used by various military, government and commercial outfits, and scientists the world over have tried to determine when this technology would become feasible for residential use. When will we all be able to unplug from the grid and start using solar power only?
The problem, unfortunately, isn’t the sun. The sun’s rays produce 1,000 watts of electricity a day for every square meter of the earth they hit. That’s a lot of juice. The problem is the efficiency of the solar cells, which lose quite a bit of power in the transfer, rendering them fairly weak in terms of electricity generation.
Silicon and other conductive materials are also pretty shiny, which means they shoot all sorts of radiation back out, wasting possible energy sources. Up to 2006, the average solar panel only absorbed 15% of the solar radiation that hit it. The goal is 40%.
Of course, new technologies constantly being developed, and some solar panels have been created that can get efficiencies of 41% or higher. But, the cost is high, which makes it tough for a regular guy or gal like you to take full advantage of the technology.
Tapping into the Sun for Your House
With all that in mind, application of solar panels for your home’s electricity use isn’t necessarily that hard. Once you factor out the cost, you simply need to make sure you have the right angle and direction in which to face your panels.
Ideally, solar panels should be angled upwards and should face south in the Northern Hemisphere or north in the Southern Hemisphere, where the sun will spend most of its time throughout the year. If your home’s roof faces slightly east or west, you can still use the panels, but expect some efficiency loss.
Next, you need to determine how much electricity you use and how much electricity your system can produce. Since it’s impossible to know when the sun will shine, you’ll need to use averages provided by the National Weather Service (in the U.S.), or a related agency in your country. These numbers vary but will give you a baseline from which to work.
You will also need to get your average electrical use from your current power provider. It costs roughly $9 per watt of electricity usage to install a solar system. The more watts you use each day, the more solar cells you’ll need to power your home.
The average home runs on between 100 and 300 watts, but beware – 100 watts of electricity is not very much. If you plan on cutting your electricity use to afford a solar cell system, you’ll want to be realistic about how much you can cut.
Another factor many people don’t realize is that most states have systems in place that will allow you to remain attached to the power grid. In particularly drab months with no sunlight, you can draw as much power as you need, and in bright and sunny months or when you’re on vacation, you can sell power back to the electric or gas company for credit, essentially banking it for later use. You’ll need to check with your local government and power provider to find out if it this is an option for your home.