Photovoltaics

How Solar Panels work to Make Electricity

Solar radiation (sunlight) is made up of small packets of energy called photons. When a photon of sufficient energy strikes a semiconductor photovoltaic cell, it knocks loose an electron from its normal position through a process known as the photoelectric effect (this is the process Albert Einstein won a Nobel Prize for describing in 1905). The loose electron then becomes part of a flow, or Current, of electricity.

The force pressuring this flow, called the Voltage, is a result of the electric field formed between the two types of semiconductors used to make the PV cell. One semiconductor (n-type) has an abundance of negatively-charged electrons and the other semiconductor (p-type) has an abundance of "holes" which are positively charged. Sandwiched together, these two semiconducting materials create an electric field at their juncture due to their electrical imbalance.

To provide a path for the flowing electricity, highly-conductive contacts are fingered throughout the silicon cell in a grid-like pattern to collect as much current as possible and direct it to the terminals on the back side of the PV module. The amount of power a module produces, measured in Watts, varies depending on cell design, module size, temperature, and sun conditions. Many modules can be connected together in a string in series and/or parallel circuits to achieve the desired amount of electricity.

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Electrical Storage

PV systems require the electricity generated in the PV panels to be stored so it can be used later. While the electricity can be used immediately, it is usually desirable to have electricity when the sun isn't shining and the panels aren't making power. We use lights mostly at night, right?

So the electricity is stored in battery banks or sent to the utility company (proxy storage) or both. Systems that use batteries only are called Stand-Alone and systems that connect to a utility company's grid are called Grid-Tied.

Stand-Alone PV Systems

For a long time, this was the only type of PV system built. Many simple or remote systems are still stand-alone by necessity, but most PV systems these days are connected to a utility grid (Grid-Tie).

In a stand-alone system, electricity generated in the PV panels is stored in deep-cycle batteries. Deep-cycle batteries allow more of their stored energy to be depleted (up to 50%) before recharging and still maintain a long usable life. The use of batteries also requires the use of a charge controller which oversees the charge and discharge rates and levels of the batteries.

The great thing about stand-alone systems is that they can be totally independent of utility companies and bring power to remote locations. The difficulty with batteries is that they add cost and maintenance requirements to the system and they can consume a lot of space.

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Grid-Tied Systems

The ability to connect your PV system to the utility grid provides more simplicity and often times is the most practical design. Indeed, it is empowering to know that you are generating and selling energy back to the utility! You will need to enter into an interconnection agreement with your utility and have an inverter to control the power you send them. Ecofly can take care of all of that for you.

In most cases, the utility will not buy from you at the same price that it sells to you, but they will often give rebates and/or incentives to you when you initially have your system built. Ecofly can file your rebate/incentive applications for you to make sure you get all the benefits possible. You will also use less of "their" power and consequently your bill will be lower.

By being connected to the utility you have the ability to send power back to them when your system is generating more than you are using or take power from them when you need more. This is called net-metering and often results in your electrical meter spinning backwards!

Like any PV system, a grid-tied system can be scaled to most any size you need to suit your power demands and budget. For more information on sizing requirements, see our FAQ or System Sizing pages or simply Contact Us.

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Did you Know?

Many utilities offer rebates and incentives to those who generate their own power!

Learn about incentives here.