Solar Power How It Works to Power Your Home

Are you puzzled by the various terms solar power installers use when describing a residential solar power system? Does it make you head spin? Find out how solar power works. Learn the basic terminology so that you can make an informed choice on if residential solar power is the right renewable energy source for your home.

Do solar panels have to be mounted on the roof?

The short answer is no. Why are they mounted on the roof? The roof is typically has the largest free space on the property, typically is free from obstructions such as other buildings or tree limbs and is relatively unused space. Depending on the location solar panels have been mounted on poles or on the ground mounting systems.

In order to get the maximum electrical output from photovoltaic panels they need to be oriented to solar south in the northern hemisphere and solar north in the southern hemisphere. The solar panels need to be facing toward the equator to get maximum sun exposure.

Most solar photovoltaic panels are set at home latitude plus or minus fifteen degrees. Depending on if you want a summer or winter bias to the angle of the solar panels. In higher latitudinal areas it makes more sense to have the photovoltaic panels set on a winter bias, so that during the winter the solar panels still get enough sun light to produce electricity.

Some residential solar power systems have adjustable solar panel mounting systems. This allows the home owner to adjust the photovoltaic panel’s angle throughout the year to get the maximum exposure. On some systems the angle adjustment is controlled by a computer that controls servo motors that are attached to the solar panel mounting system.

How does a photovoltaic cell produce electricity?

A solar panel consists of a collection of photovoltaic cells. Each photovoltaic cell is made up of silicon wafer. During the manufacturing process, an impurity is added to the silicon to make conduct electricity. The sun’s photons strike the solar cell and cause an electron to break free. This action creates a small electrical charge. The metal grid that you see on the surface of the photovoltaic cell captures the electrical charge and channels it to the solar panel’s terminals.

Solar panels produce a form of electricity known as DC or direct current. The voltage produced is considered low voltage in the range of 6 to 24 volts. Photovoltaic panels have a nominal output voltage of 12 volts and an effective operating voltage of 17 or more volts.

A solar panel’s electrical output is affected by several factors. They are angle of the photovoltaic panels to the sun, time of day, time of the year and weather conditions. Solar photovoltaic panels produce the most electricity during the middle of the day when the sun is directly overhead compared to the early morning and late evening when the sun light is striking the solar panel at a shallow angle relative to the panel’s face. Think about it, in the summer in the middle of the day doesn’t the sun feel hot? However, in the evening the sun does not feel as hot. This is because in the evening the sun’s light has to pass through more of the atmosphere which is diffusing the light and energy.

Residential solar power system

A residential solar power system consists of four components are: photovoltaic panels, charging controller, battery pack and an inverter. The photovoltaic panels convert sun light into electricity. The electricity is sent to the charging controller who keeps the battery pack fully charged, but not over charged. The battery pack sends the electricity to the inverter who converts the DC voltage to household AC at 120 volts and 60 hertz.

Photovoltaic panels

Solar panels are rated by their wattage. The higher the solar panel’s wattage the more expensive it will be. Since there are so many different factors that affect the amount of electricity produced by a solar panel many manufactures provide the wattage in terms of peak sun hours. Peak sun hours are the hours when the sun is directly overhead and shining directly on the photovoltaic panel.

Solar panels can be connected in either series to increase the voltage or in parallel to increase amperage.

To connect the panels in series is to connect the positive terminal of panel #1 to the negative terminal on panel #2. Measuring the voltage across the two panels terminals results in sum of each panel’s voltage and constant amperage. For example, connecting two 12V 2.4 amp photovoltaic panels in series results in an output of 24V at 2.4 amps.

To connect the solar panels in parallel is to connect the positive terminal of panel #1 to the positive terminal on panel #2. Connect the negative terminal from panel #1 to the negative terminal on panel #2. Thus when to solar panels are wired in parallel the result is that the voltage stays the same at 12V but the amperage increases to 4.8 amps.

It is possible to combine parallel and series wiring of solar panels to increase both voltage and amperage. Taking four solar panels, divide them into two groups. Wire each group series. Then wire the two groups together in parallel. The end result will be 24V at 4.8 amps.

Charging controller

Charging controller or charge regulator controls the charging of the battery pack. It continually monitors the battery pack’s charge state. If the batteries are low, it will feed electricity from the solar panels to the batteries. It also prevents over charging of the battery pack.

When it is night time or a cloudy day the charging controller prevents the electricity from flowing from the battery pack to the solar panels. If it did not do this, at night the solar power system would run in reverse and drain the batteries.

Don’t allow someone to convince you that a charging controller is not really required. Directly connecting the photovoltaic panels to the battery pack can permanently damage the batteries and possibly cause them to explode.

Battery pack

The battery pack’s purpose is to store electricity generated by the solar panels during the day. The battery pack is also connected to an inverter which in turn is connected to the house’s electrical network. When it cloudy or at night, the electricity stored in the batteries is used to meet the power needs of your home.

The battery pack typically consists of lead acid batteries. Lead acid batteries are relatively inexpensive and readily available. There are many different types, sizes and capacities of batteries available. The most popular types of lead acid batteries are gel cell and AGM deep cycle batteries. This is because they are maintenance free and last a lot longer compared to wet cell lead acid batteries.

The most important thing to remember about the batteries is that they need to be deep cycle. Deep cycle batteries are designed to be discharged to nearly empty and slowly recharged. They can handle this cycle thousands of times before the battery is worn out.

Some residential solar power system owners think that they can replace the deep cycle batteries with automotive batteries. The automotive battery cost significantly less than the deep cycle battery. The problem is that automotive batteries are designed to discharge quickly and then immediately be recharged. The act of starting your car drains a significant amount of power from the battery. Once the engine starts the alternator begins to recharge the battery.

Inverter

An inverter converts the DC electricity stored in the battery pack into household 120V AC. Almost everything in your home is powered by 120V electricity. A few things are powered by 240V such as the air conditioner, electric dryer, electric stove and oven.

There are two main types of inverters sine wave and modified sine wave. The power company provides electricity as a sine wave. The electricity’s charge value goes smoothly from positive 120V to 0V to negative 120V and then back up to 0V and finally up to positive 120V. Then the cycle begins all over again. The time it takes to go through the entire cycle is one second.

Modified sine wave is also known as a square wave. Here the electricity’s charge value goes from positive 120V to negative -120 volts in effectively zero seconds. The advantage of the square wave inverter is that it is more energy efficient than the sine wave inverter.

Most household devices will function on a modified sine wave power. Light bulbs and motors work less efficiently as they would on sine wave electricity. Motors will run warmer that usual compact fluorescent light bulbs will give off a hum.

However, there are some electronic devices that will not work on square wave electricity. It will be necessary to check with the manufacture to determine if the device will work on square wave electricity or not before having your residential solar power system designed and installed.

Another function of the inverter is to stop draining the batteries when the batteries have been discharged to a certain level. Most of the time the inverter will stop draining the battery pack when the battery pack has about 40% of its capacity remaining. Completely discharging a lead acid battery will shorten its lifespan significantly.

Selling extra electricity back to the utility company

It is possible to sell excess electricity back to your utility company at a much lower rate than what you pay for electricity. The electricity company would be purchasing electricity from you at a wholesale price and selling it to your neighbor at the retail price.

Not all electric utilities will purchase power from a residential customer. Contact your electric utility and find out what their policy is. If your electric utility will purchase your unused electricity they will require that some additional equipment be installed on your side.

First they will require that the electricity that you are going to sell back to them matches their sine wave and frequency.

Secondly, the utility company will require that in the event of a power outage on the electric grid supplying your home, that your photovoltaic system will not sending electricity into the line. This is referred to as islanding. It can be very dangerous for the linemen who need to work on the line and think it is dead when your photovoltaic system is actually feeding power into the lines.

Whew, that was a lot of material about photovoltaic panels, batteries, inverters and charging controllers. With this basic understanding of solar power how it works, you are in a better position to understand what solar power installers are talking about when they design a residential solar power system for your house.

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