How do solar panels work?

The physics behind the Photovoltaic (PV) effect:

Photovoltaic (PV) modules, a.k.a. “solar panels,” absorb and convert sunlight into direct current (DC) electricity via a naturally-occurring phenomenon called the photovoltaic effect. The photons in sunlight strike the surface of the solar cell composed of a semi-conductor material, typically silicon, that is coated with a reactive element such as boron or indium known as a doping agent. The photon provides enough energy to dislodge valence electrons in the solar cell. Once freed from their bond, the electrons are attracted toward a pathway created by embedding metallic wires into the solar cell.

The movement of electrons through the metallic wires in the cell creates electrical current. Multiple cells positioned and wired together makes up one solar module, commonly referred to as a “solar panel.” When multiple cells are configured in series “strings” (positive to negative, like batteries in a flashlight), the voltage of the circuit increases. When those strings of cells are then connected in parallel (positive to positive), the amperage or current of the module is increased. One solar module is typically made up of several parallel-connected strings of cells connected in series. Solar modules are then connected together, typically in series but sometimes in parallel, to produce usable voltage and current for the consumer. Since most homes and businesses run on alternating current (AC) electricity, the DC electricity is then passed through an inverter to convert it to usable AC electricity. At that point, the building either uses the electricity or sends it back to the electric grid.

Do my solar panels produce power when the sun is not shining?

The amount of power your solar energy system can generate is dependent on sunlight. As a result, solar panels produce less energy in inclement weather, and no energy at night.

What do I need to do to maintain my solar PV system?

Solar panel systems are made of durable tempered glass and require little maintenance. If made well, solar PV panels can last over 50 years with no maintenance at all. The amount of energy produced by a solar panel does depend on the amount of sunlight reaching the solar cells. It is a good idea to clean any dirt or debris off of the solar panels using just water or a mild, environmentally-friendly soap if needed.

What is off-grid versus on-grid and does a grid-tied system still work when the grid goes down?

A grid-connected solar PV system allows you to use grid power when the sun is not shining and to send power back to the grid when you produce more energy than you use – which, incidentally, results in a greater return on your solar investment. Off-grid solar requires an added component of battery storage and typically requires significantly more upfront investment.

Grid-connected solar systems are required by the National Electric Code to shut down automatically in the event of a utility grid failure in order to ensure the safety of utility line workers and emergency responders. Solar systems ​that have been designed and installed with battery storage provide power when the grid is not available. These systems include an automatic transfer switch that allows the solar system to continue to function without placing line workers or emergency personnel at risk.

An off-grid home uses a bank of batteries to supply power to the house loads via the battery-based inverter and the solar is the primary source of charging for the battery bank. A generator is often incorporated for battery charging when sunlight is not available.

A third type of solar electric system is called battery-based or battery back-up. This is a hybrid between off-grid and on-grid systems. The solar is electrically connected to the utility grid but also has the ability to provide power to the home in the event of grid failure by incorporating a bank of batteries and a special, battery-based, grid inverter.

The cost difference between on-grid and off-grid solar is typically in the tens of thousands of dollars. On-grid, battery-based systems are typically the most costly. For example, if a standard on-grid system costs $20,000. That same system with an off-grid inverter and a bank of batteries might cost closer to $30,000, while the on-grid, battery-based system might be closer to $35,000. However, as with all solar pricing, each system is custom and costs vary considerably, depending on many factors such as equipment manufacturer, contractor, geographical region, utility provider, household loads, solar system performance estimate, sun exposure, and solar panel mounting location.

The benefits to an on-grid system are primarily cost savings. The other systems not only cost more, but on-grid system costs are hedged against money that would have been spent in the purchase of utility power in an unpredictable and inflating utility energy market.

The main benefit to battery-based systems is that you have power available 24/7, regardless of utility power-outages. In this scenario, the battery bank helps to “load shift” the power draw from the utility.

Load-shifting occurs when the power from your solar array goes into a battery bank during peak sunlight hours (10am to 2pm) and then is discharged from the batteries onto the utility grid at peak billing hours in order to take full advantage of high time-of-use rates from your utility thereby leveraging a buy low/sell high scenario.

Another drawback to battery systems is that with added components comes added complexity and added user maintenance. There are new products on the market that attempt to minimize user interface and maintenance, such as the Sonnen Batterie, Tesla Powerwall, SolarEdge StorEdge, and the Enphase battery. All of these products are good options, if the ROI makes sense.

The final drawback to consider is that the load-shifting benefit is only viable for utilities that offer higher time-of-use pricing. Once the time-of-use tariff is no longer used, load-shifting is no longer needed.

Is solar good for the environment?

Yes! Using clean solar energy to power your home and charge your vehicle will significantly reduce emissions of harmful compounds that contribute to climate change, as well as reduce air pollutants like sulfur dioxide and particulate matter, which can cause serious health problems, especially in our youth. Buildings are responsible for 38 percent of all carbon emissions in the U.S.

A typical residential solar system can eliminate three to four tons of carbon emissions each year — the equivalent of planting over 100 trees annually.

Can solar energy help me to save money?

A properly designed solar energy system can save you hundreds of dollars off of your monthly electricity bill and protect you against rising electricity rates in the future. The amount of savings available to you depends on many factors including your own electricity use in the home and your home’s solar exposure. In most cases, solar financing is less costly than utility payments and creates immediate positive cash flow as soon as you make the switch to solar.

The long-term benefits are also attractive with systems typically yielding investment returns between 10-18% and lifetime savings in the hundreds of thousands.

Real-world studies have demonstrated that installing solar on your home can add value to your property and help your home sell faster. Currently, the federal government offers a 30% tax credit off of the amount you spend on your solar purchase.

What are the differences between roof and ground mounted solar systems?

Other than the physical mounting location, the differences are cost and performance. Typically a ground-mount system can produce about 10% – 15% more power than a roof-mounted system due to the ground system operating at lower temperatures as a result of increased air flow. However, the cost of a ground-mount system can easily exceed 15% beyond the cost of a roof-mounted system.

Does solar impact property values?

Studies indicate that homes with solar energy systems sell for more than homes without them. Property value only increases if you own, rather than lease, a solar panel system, and you work with a knowledgeable real estate agent and appraiser.

How do I choose a solar professional?

Make sure that a solar contractor is properly licensed, bonded, and insured. A California State License C-46 or C-10 is required to contract on solar jobs, unless the job includes two other trades such as roofing and gutters. You may request to see a copy of the contractor’s license and then verify the number on the Contractor’s State License Board license lookup tool. The license should be active and in good standing, with all the appropriate insurance and bonds attached. It is also recommended to research peer reviews of the company. Guild Quality is a web-based, consumer protection and customer satisfaction surveyor similar to Yelp but more professional. Organizations like the Better Business Bureau and CalSEIA can also give consumers confidence when choosing a solar professional.

What qualifications should I look for in my solar professional?

Your solar contractor should, at a minimum, hold a valid contractor license in either the C46 or C10 category. Ideally, your solar contractor is also part of the North American Board of Certified Energy Practitioners (NABCEP). This certification is the highest standard in solar certification and is designed to give consumers peace of mind by ensuring that the NABCEP contractor will adhere to industry best practices and all of the correct codes and standards. It is also wise to work with CalSEIA members as they are vetted through an application process and must adhere to industry best practices and a strict code of ethics.

How do I compare solar quotes?

If you have multiple quotes from different solar installers, they may not be “apples to apples,” making comparison difficult. Start by identifying the power output of the system in kilo-Watt-hours (kWh), and note the associated savings and payback (in years and ROI), both long-term and short-term. Not all solar panels (modules) are made the same. Look closely at the quantity and type of panels; your investment will be more secure if your bid includes a quality product. Check the warranties on system performance, product manufacturing, and labor. Check consumer reports on both the product manufacturer and contractor. Verify the type and size of inverters used (string inverter versus micro-inverter versus power optimizer). Note whether or not the solar system includes a monitoring system.

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