In a single hour, the sun bathes Earth with enough solar energy to meet the world’s power needs for an entire year. Not only is sunlight the most abundant energy source available, it’s also the cleanest. So how can we turn this endless supply of sunbeams into useful electricity? The answer lies in the photovoltaic (PV) effect – the phenomenon of converting solar energy into electrical current. Solar cell (also known as PV cell) development has come a long way, and with the increasing demand for clean energy, the future is looking bright for this renewable energy source.

The Science Behind Solar

Look closely at a solar panel and you’ll see that it is actually composed of much smaller photovoltaic cells, also known as solar cells. These cells are made up of silicon, the second most abundant element in the Earth’s crust. Aside from many other types of products, silicon is used in almost all electronic devices (think “Silicon Valley”).

POWER GENERATION

Sunlight is composed of packets of energy known as photons. When photons hit the photovoltaic cell, electrons get knocked loose from their electron/hole bonds and a flow of electrons begins.

1 The P-layer, often created with boron, has extra holes (or vacancies for the electrons) making it positively charged.
2 The P/N junction creates an electric field that sweeps any loose electrons near the N-type layer to the P-type layer. The electrons, if given an external path will seek to recombine with the holes and travel back to the N-type side.
3 The N-layer, often created by treating silicon with phosphorous, has extra electrons making it negatively charged.
4 Wires connecting the two layers provide a path for the electrons to flow through a circuit and recombine with the holes. Since moving electrons create a current, there is now a flow of electricity moving through the wire.
5 We can then use this flow of electrons – which is the
current of electricity – to power anything by adding a load to the circuit. The higher the rate of photons striking the cell, knocking electrons loose, the more power it can produce.

The Solar-Powered Home

Solar cells can be assembled into panels, and then into arrays, to meet a wide range of power needs. From the world’s largest solar farm in India, producing 600 megawatts (MW) of power, to the small strips of solar cells used in toys and calculators – solar energy is a flexible technology. Despite its many benefits, solar still faces challenges, including the cost of installation and manufacturing. Nevertheless, residential solar installation is on the rise. The U.S. Department of Energy projects nearly 1 million homes will be utilizing solar energy by 2020. And, if the industry can lower solar costs from today’s levels, that number is projected to be almost 4 million homes by 2020.

Sunlight
Photons from the sun shine on the solar panel. It’s best to make sure your panel is catching as many photons as possible but even on cloudy days, some light still shines through to create electricity.
Solar Panels
Solar cells combine to make panels, panels combine to make arrays. The cells in the array absorb energy from the photons. This energy is enough to knock electrons loose from their electron/hole bonds. Electrons seek to flow through a circuit, allowing them to recombine with holes.
Inverter
The electricity created by a photovoltaic cell is DC (direct current). An inverter converts DC to AC (alternating current) that is used to power household appliances.
Electrical Distribution Panel: This panel provides electricity to all of the homes’ circuits.
AC Loads
All household lights and appliances use AC.
Electric Meter
The meter accounts for power produced and consumed. If the system generates more electricity than the household uses, the meter spins backward and feeds electricity back into the grid. The electricity bill is credited accordingly.

Net Metering: Selling your Extra Energy

Nationwide interest in rooftop solar panels and other on-site power sources continues to grow. When these distributed generation (DG) systems first came to the market years ago, many states approved net metering – a billing system in which solar panels or other renewable energy generators are linked to a public-utility power grid. If the solar panels end up generating more power than what is used, the surplus electricity is transmitted onto the grid. Customers are credited for any excess electricity generated and sold to the local electric company through the grid. The rate at which they are credited varies.

1Solar panels convert energy from the sun into direct current (DC) electricity.
2An inverter changes direct current (DC) into usable alternating current (AC).
3Clean, renewable electricity generated from the solar panels powers household lights and appliances.
4The bi-directional meter measures electricity moving into and out of the home, business or school.
5Excess energy produced is sent to the public-utility grid and sold to the local electric company.

A Kilo-what?

Once solar panels have turned sunlight into electricity, it’s important to understand just how much electricity its being produced and how to translate that into what appears on your utility bill. Here are a few definitions explaining the essentials of electric units:

Kilowatt (kW)

The rate at which power is generated or consumed at a given moment

Kilowatt Hour (kWh)

Measurement of energy used over a specific period of time.

So, your electricity bill combines how quickly the electricity is used (watts) with the amount of time it is used (hours) to calculate how much energy you used over the billing period.

A 25-watt light bulb (pulling in 25 watts of power at any given moment to work) uses 25 kWh of electricity to shine for an hour.

U.S. Household Energy Use

In 2014, the average annual electricity consumption for a U.S. residential utility customer was 10,932 kWh. Source: U.S. Energy Information Administration

  • Space cooling13% 1,421 kWh
  • Lighting11% 1,202 kWh
  • Water heating9% 984 kWh
  • Space heating9% 984 kWh
  • Refrigeration7% 765 kWh
  • Televisions and related equipment7% 765 kWh
  • Clothes dryers4% 437 kWh
  • Furnace fans and boiler circulation pumps3% 328 kWh
  • Computers and related equipment2% 219 kWh
  • Cooking2% 219 kWh
  • Dishwashers2% 219 kWh
  • Freezers2% 219 kWh
  • Clothes washers1% 109 kWh
  • Other Uses*27% 2,951 kWh

*Includes small electric devices, heating elements, and motors not listed above. Does not include electric vehicle charging. Source: EIA, Annual Energy Outlook, 2015

How The Grid Works

Understanding the path of electricity from the power plant to your home

From the moment the coffee machine starts brewing your cup of morning java until you switch off the television at night, you’re using electricity. If you have solar panels, you may be using energy produced right on your roof, but otherwise (or at night) that electricity is probably coming from hundreds of miles away, traveling over mountains, rivers and forests, before it gets to your neighborhood. Here’s a look at how The Grid makes that happen:

1.Electricity is generated at a power plant by burning fossil fuels, nuclear reactions, or harnessing energy from the sun, wind or water.
2.The electricity is then converted at substations to high voltage for long-distance transmission.
3.The more than 450,000 miles of high-voltage power lines in the U.S. then carry the electricity where it is needed.
4.Next, step-down transformers reduce the voltage to for distribution to businesses and homes.
5.Lastly, your local power lines deliver the electricity to your home to charge cell phones, run washing machines and keep air conditioners cooling our homes.

Interested in knowing where all that power is being generated across the United States? The U.S. Energy Information Administration has a powerful map that reveals the energy infrastructure across the country, from coalmines to solar and hydroelectric power plants to oil pipelines.

U.S. Energy Mapping System

Going Off the Grid with Solar

While most people like the idea of flipping a switch and knowing the lights will turn on, that utility-company convenience comes at a price: global warming, energy dependence and upward-trending electricity rates. But what if you could keep the lights on while cutting the proverbial power cord? It’s called “off grid” and it is possible. For most people the initial start-up costs are prohibitive, plus the maintenance is more than they want to manage. But for those hearty souls who want to consider going off grid, here’s an explanation on how it can work with solar panels:

1Sun shines down on your solar panels. In the initial design phase, it’s important to understand what your daily electricity use is and be sure you build a solar array capable of meeting your energy demands. (If you want to read how solar panels create electric current, scroll back to the top of the page.)
2At the combiner box all the solar panel connections are gathered for electric current to move together.
3The charge controller modifies the voltage and current to be appropriate for battery charging – not overcharging or damaging the batteries.
4The inverter converts direct current (DC) power to household (AC) power.
5Electricity goes to home energy use.
6Excess power goes to the battery bank. When the batteries are full, they stop taking new energy. When the solar panels are not creating energy (at night), your electric current will come from the battery bank.

While panel prices and battery pack costs are dropping significantly as technology improves, all that sun power still doesn’t come cheap. Solar panel kits can range anywhere from a few thousand dollars to power a small cottage minimally to $50,000 and up for a system that will keep the lights on and the refrigerator running all night.