Daniel Stouffer asked:


You’re most likely not an electrical engineer so you’ll find that the terms for residential electricity more than confusing and nonsensical at times. The following article explains the terms associated with home electricity and defines the general electrical concepts found in residential solar electric systems. The majority of this article defines on the important terms, principles, and technical definitions that will be further explained in relation to home solar power in another article.

The intent of this article is to help you to understand enough about electricity so that you can understand the technology used in solar photovoltaic (PV) systems. You most likely will review a lot of information and learn many new solar energy terms when you begin the process of purchasing or renting a home solar power system.

When you start researching residential solar energy systems, or even taking a close look at your electric bill, you hear a lot about kilowatts and kilowatt hours. You may have used these terms mistakenly as the same thing in the past. The ideas are really very similar. Both terms are just a measure of relative electricity sizes.

However, they are very different measurements, as you will learn through the electricity definitions included here. In order to understand what they mean, you also need to understand a few basic concepts about electricity.

When talking about electricity, you will be using terms like power and energy. The average person often uses these terms interchangeably in daily speech along with current, potential, charge, electrons, and even photons. You might have learned about all of these electricity terms way back in high school. In use as part of your daily life, you may have confused their meaning.

Common Residential Electricity Terms

Here are the most important electricity concepts you need to know when you begin the process of purchasing or renting a solar energy system for your home. It may be surprising to you that the actual meaning of a few of these is not quite what you expected.

Power: The rate at which work is performed or energy is provided. Power is the amount of energy required or expended for a given unit of time. It is measured in watts (W).

Energy: The actual work done by solar panels installed on your home. In other words, energy is power supplied over a period of time. It is typically measured in joules or watt hours (Wh).

Potential: The capacity of an electric field to do work (i.e. to provide energy). This is similar to the height of water behind a dam. It has capacity to do work. The higher the water, the more potential energy that is available. Potential is calculated and measured in volts.

Current: A passage or movement of materials charged with electricity. This is not unlike the speed of water flow in a river. It is measured in amperes (I or in common terms amps).

Resistance: The characteristic of a material, substance, object, or circuit to limit the passage of electricity. Items letting electricity to pass with low resistance are called conductors and materials that resist electricity from flowing are called insulators. Resistance is measured in ohms (R).

Charge: A property of some subatomic particles, i.e. the charge on an electron (subatomic particle is negative). Charge determines how subatomic particles interact. Electrically charged matter is influenced by and produces electromagnetic fields. Having strengths that can be measured, a charge has two states; either negative or positive.

Field: An effect produced by an electric charge that exerts a force on charged objects in its vicinity.

Electron: A negatively charged subatomic particle. The current is caused by the movement of electrons from different energy levels within its atomic structure.

Photon: An elementary particle that is the carrier of electromagnetic radiation of all wavelengths. The photon is different from many other elementary particles, such as the electron, because it has no mass. That means that it travels at the speed of light across the vacuum of space. Trillions and trillions of photons are blasted out from the sun every second.

Upgrading Your Home to Solar Power

To understand solar electric systems and how they work, you first need to understand the basic principles of electricity. This means learning the language used to explain these principles. In our next article which is a ongoing series related to renewable energy, we will dive into understanding the language of residential solar electric systems.

Understanding the most common electricity terms and technical jargon is a crucial initial step related to the process of renting or purchasing a residential solar energy system. You should feel comfortable talking with solar industry experts about your home solar options. In future articles, we will dig deeper into the details and emerging options for home solar power systems.

Daniel Stouffer asked:


thing you might ask – what is solar radiation and how does it related to solar generated electricity? That is a good question and a topic discussed in our next article in our series dedicated to home solar power. This article, on the other hand, explains how kilowatts are calculated based upon the energy output of your solar array. We will also highlight the difference between solar cells connected in parallel versus in series.

The average American home uses about 25 kWh of electricity per day. The following example illustrates how to calculate the power produced by a residential solar energy system. Looking over a solar radiation grid, we can determine that a residence gets five daylight hours of solar radiation in one day which is then averaged out over the entire year.

Solar radiation maps are highlighted on may websites throughout the Internet. You can do a quick search for “solar radiation” to find one. In any area across the entire United States, they detail out the amount of sunshine hitting a given location based upon the time of year and its address.

Calculating the power from a solar energy system

Divide the average kWh per day by the average sun hours per day. For this example, we take 25 kWh divided by 5 hours of sun per day = 5 kW system This 5 kW system will generate 25 kWhs under optimal conditions in direct sunlight for 5 hours, or 25 kWh on an average day with some at peak production and most of the sunlight at less than optimal angles.

Future articles related to solar energy will continue to explain the effects of sun angle, reflection, and refraction on the design, output, and installation of solar panels.

Energy as it Pertains to Solar Modules

Individual solar modules that are measured in watts have a particular voltage (around 40 volts) and a particular amperage (around 5 amps). A solar module with 40 volts and 5 amps is called a 200-watt module, which means that it has the potential to produce 200 watts of electricity when in direct sunlight, away from trees or shading, and clear of snow or debris. Since most electrical components around your house are only rated for 600 volts DC, it is rare to see a solar array with a string larger the 15 solar modules. On the other hand, since inverters need a minimum voltage or pressure to turn them on, you will seldom have a solar array with a string solar modules with a size smaller then 6.

Electrical components, like solar cells, panel modules or batteries, can be connected in either series or parallel. This makes a big difference in the total quantities of energy produced from the solar energy system, as well as the stability of the technology over time. Each solar module or component has a positive and a negative pole. In essence, this is the same way batteries have their negative and positive poles arranged. Take a look at how you but batteries in a flashlight. Same idea here. The manner in which these poles are connected makes a big difference. Connect Solar Panels in Series

When you connect residential solar energy systems in series, you connect the positive (+) pole on one component to the negative (-) pole on the next. When modules are connected in series, the voltages are added. Adding voltage together in this fashion creates a long chain of solar modules all working together, depending upon each other, and creating a flow of current that increases along the length of the system.

These modules in series are called Strings. The average string is 8-12 modules so the voltage would be 320 – 480. Unfortunately, we encounter some negative aspects of of this type of construction.

Connecting Solar Panels in Parallel

When you connect solar panels or components in parallel, you connect the panels so current can travel to your inverter and to your house via multiple paths. Unlike adding solar modules in series which increases the volume of current as it goes, the solar panels connected in parallel has the effective of leaving the current or volume of electricity passing through the system the same.

Solar panels or strings of solar arrays tied together in parallel are called parallel systems. Their amps are combined together but the total voltage remains the same. Adding amps is like increasing the volume, the pressure stays the same but the volume goes up. Inverters can only handle so much volume so you will seldom see more than 1 to 3 strings in parallel; positive ends to positive ends with negative ends to negative ends.

One of the advantages of parallel connection is that electricity continues to flow, even though one of the components (or strings) is damaged. If a system is entirely in series, one damaged component stops the entire system. You may remember the ever-frustrating Christmas lights that were connected in series. Often difficult to trouble shoot, strings of lights connected in series are hard to fix when one bulb blew out. Now, the modern Christmas lights are connected in parallel. You are able to determine this easily. There are usually two different wires coming in and out of each bulb. You can feel this via their less frustrating maintenance and operation.

Options for Residential Solar Energy Systems

In this article, we explained in some detail how solar modules calculate the power they produce as well as how connecting solar arrays in series or parallel can have an large impact on energy output as well as complexity of design. Our next article will cover how sun angle affects solar energy systems and how to quantify the solar power produced from the sun.

New solar energy system rentals allow you to upgrade your home to solar generated electricity with no large system to purchase. You can rent the solar energy equipment needed to generate up to 100 percent of your electricity needs. Exciting aspects related to clean, green solar energy are emerging all around us.

Daniel Stouffer asked:


cle explains the fundamental terms related to sunlight and residential solar energy systems. You will learn about units of measure, forms of solar radiation, spectral distribution, energy distribution, and solar position.

Germany and Japan are often cloudy or foggy but is where most solar panels now sold in the United States are produced. Because of the way solar modules produce power from direct, diffused and reflected light it works great in these conditions. A very high performing solar array can be found on a foggy beach in California.

Measuring Light and How Solar Panels Use It

The following terms related to different aspects of light and their characteristics as they come in contact with different physical formations on Earth. The definitions below will help explain how some residential solar energy systems seemingly in areas with poor sun quality can actually achieve respectable power output.

Irradiance – The rate of solar radiation falling on a given area at a moment in time. Irradiance is measured in units of kW/m2 (read kilowatts per square meter).

Irradiation – The amount of solar energy over time. Irradiation is measured in units of kWh/m2/day and read kilowatt-hours per square meter per day. Different locations through the United States (and the World) have different levels of irradiation. As in previous articles, you can find many maps on the Internet that will show the average annual solar irradiation throughout the United States.

Light Characteristics and Solar Fundamentals

Deflection – The amount of light lost when the solar panels aren’t facing the sun squarely as the sun moves across the sky. This loss of light is called deflection. Even though solar cells are etched on the surface into little pyramids to collect light from all angles, coated with a light diffusing coating, and protected with light diffusing glass, more light is deflected when the sun is not directly in front of the panels.

Spectral distribution – The bulk of the solar light spectrum which reaches the Earth’s surface is ideally suited for conversion by solar (PV) cells into electrical energy.

The Sun’s Position as It Relates to Solar Energy Systems

Two coordinates describe the position of the sun at any given time. The orientation provide the information to home solar installers to figure out and orientate the solar energy system to collect and convert as much sun energy as possible into residential electricity.

Azimuth – Describes the direction from east to west in degrees (°). North is 0 degrees. East is 90 degrees. South is 180 degrees. West is 270 degrees. The layout of this grid is not unlike the face of a compass. The markings are in degrees indicated on the face.

Altitude – Is the measurement in degrees, like on a compass, that the sun is from the horizon. Altitude is measured in degrees as well. Altitude is the point in the sky where it is located right over head often referred to it’s highest point in the sky. Just like a plane has an altitude that it travels at across the sky as it is measured above the horizon. So does the sun.

Irradiation Example for a Solar Energy System

In the coast area of California, residential solar energy systems are sized using an average of 5.5 sun hours per day. More often than not, most people think or comment that their house gets more like 8 to 15 hours of sunlight per day. This is true but sunlight is different than solar sun hours per day.

The sun hour numbers take into account things like fog, rain, night and, most importantly, deflection. The sun hour ratings listed for different places throughout the United States is the amount of solar irradiation available to be converted into electricity by a fixed mounted solar array facing true south at the optimal tilt angle. A solar module produces its full rated power only when in direct sunlight, so when the sun is to the East or the West of the module it is not at full production.

reThinking the Economics of Residential Solar Energy

Doing your part to choose green, solar power can be a bit confusing and complex at times. There are many terms, aspects of the installation, and details about your sun light hours per day that all influence decisions to upgrade your home to solar energy. A very interesting and attractive option currently development in the solar market is the option to rent a residential solar energy system versus having to pay out up to $40,000 for your own solar panels and related equipment.

The economics of residential solar power have changed. Every American homeowner can decide to upgrade to solar energy and avoid large purchase of a solar energy system. New rental programs are now available that give homeowners the chance to adopt residential solar energy without having to make a huge investment.