Solar Info

Individual photovoltaic (PV) cells are connected to panels. These solar panels convert sunlight into direct current (DC) electricity. An Inverter converts direct current (DC) into alternating current (AC) for electricity in the home.

Photovoltaic (PV) cells, or solar cells, take advantage of the photoelectric effect to produce electricity. PV cells are the building blocks of all PV Systems because they are the devices that convert sunlight to electricity. When light shines on a PV cell, it may be reflected, absorbed, or pass right through. But only the absorbed light generates electricity. The energy of the absorbed light is transferred to electrons in the atoms of the PV cell.

One of the most important components of any solar unit is the solar power inverter, which converts the direct current (DC) that photovoltaic solar cells produce into alternating current (AC). Types of inverters to consider:

• Grid tied Inverters – are connected to the electric utility distribution system. The connected solar system allows you to power your home or small business with renewable energy when the sun is shining. Any excess electricity you produce is fed back into the utility distribution system grid. When the solar system is not running electricity from the utility (grid) supplies your needs. Having the utility as your energy back up source eliminates the needs to purchase costly energy storage device, such as batteries.
• String Inverters - All solar modules are connected in series to a DC electric cable, which is then connected to a single remotely mounted inverter box. The inverter box is typically mounted on a wall by the home’s main AC electrical panel. This creates a very centralized system with a limited amount of labor required to install.
• Micro-Inverters - Instead of having one inverter for the entire array, a micro-inverter could be installed on each panel or every few panels. The micro-inverters convert the DC to AC right at the module; then, AC wires run from the module to the home’s main AC electrical panel. Each micro-inverter would be handling lower voltage and therefore may not wear out as quickly. Micro-inverters allow the system to be more efficient and therefore produce more energy.

When designing a solar system, it’s important to consider what type of inverter will be used with the modules you will install.

• Traditional String Inverter Method - When set up in the traditional method, a solar array is only as efficient as the least efficient panel. If you have five (5) 200 watt panels, but one of them is shaded or dirty such that it’s only producing at 50% efficiency, then the entire system will only work at 50% efficiency. That means that instead of producing 1,000 watts, the system would only produce 500 watts. Additionally, inverters are currently sized according to the number and type of solar panels on the roof, and if a home owner wanted to add more panels in the future that may require a different inverter with a larger capacity.
• Traditional String Inverter with Optimizers Method - Adding DC power optimizers to the panels of a traditional string inverter method can solve most of the above string inverter challenges. Power optimizers optimally tune the performance of the solar panel to match the performance of the string inverter to improve overall performance. They are especially useful when the performance of the solar panels will vary widely, such as differences in equipment, shading, being installed facing different directions or widely separated locations.
• Micro- Inverter Method – In a micro-inverter installation, each panel has a micro-inverter on it. If one panel is dirty or shaded only that panel would be affected. So in the scenario with five (5) 200 watt panels, this time with micro-inverters, one panel would be at 50% and therefore producing only 100 watts, but the other four (4) would still be at 100% producing 200 watts for a total of 900 watts. When micro-inverters are being used and the homeowner decides they would like to add more panels, in theory, additional panels with their own micro-inverter could be added to an existing array without needing to replace anything.

Installed costs of solar are coming down, but it is hard to say what your system will cost until you obtain quotes from contractors. Over the years the installed price per watt has reduced down from $10 per watt to typically less than $6 per watt. It is important to talk to at least three contractors to obtain a clear understanding of your installation and the potential costs. This way you can make an educated decision on the purchase of your solar system.

If you’re paying cash or obtaining a loan for your system, be aware there are a number of factors that vary from home to home and installation to installation. These factors affect the initial cost of the solar system. The initial system cost divided by the cost of the energy offset by solar will provide you with an estimated return on your investment.

When you’re leasing your system or entering into a Power Purchase Agreement (PPA) for your system, initial costs aren’t usually a factor. With these purchase arrangements you’ll be evaluating the energy offset costs of the system. See the Purchasing Option section for more information on leases and PPAs.

The initial cost of the solar system may not be the only question to ask. Consider obtaining answers for “What is the cost of the energy (kilowatt hour) produced by the solar system proposed for my home?”, “What is my current cost of energy from the utility?” and “How do they compare?”

Once the system is designed, the contractor will run a program to estimate how much energy the system designed specifically for your home is expected to produce. The same system facing a different orientation on someone else’s home will produce a different amount of energy. Energy, or kilowatt hours (kWh), is what will offset your electric utility bill. Make sure you understand how much energy is produced by the solar system each month and how it will offset your monthly bill. Your Home Energy Analyzer report will show you how much energy you use each month when you enter your account number and run the report.

Due to the angle of the sun and weather conditions, solar systems produce less energy during the winter months than they do during the summer months, so try to understand the monthly generation. Ask your contractor to show you the California Solar Initiative Expected Performance Based Buy Down Calculation (CSI-EPBB) report for the expected performance of your solar project.

Visit the Google Project Sunroof page.

US Department of Energy produces information on science-based energy upgrades helping homeowners reduce their energy bills. Energy Efficiency Homes and Photovoltaic Technology Basics.

Residential 101

An educational website funded by the US Department of Energy dedicated to educating homeowners about solar power options.

National Renewable Energy Lab Solar Photovoltaic Technology Basics

NREL is a national laboratory of the US Department of Energy, operated by the Alliance for Sustainable Energy, LLE.

Solar Power for Your Home

A Consumer’s Guide

• You may have questions about whether your neighbors can block access to your solar panels with shading.
• Additionally, can Covenants, Codes, and Restrictions (CC&Rs) limit your use of solar?
• State laws in California protect homeowner access to the sun for systems, and these laws have been in place for more than 30 years.
• Many homes today are part of planned communities that require a uniform and consistent appearance within the development. The California Solar Rights Act and the Solar Shade Act provide important information for homeowners considering to go solar.

• The Solar Rights Act was created in 1978 (AB 3250, 1978), and it created a legal framework for solar access.
• The law includes protections to allow consumers access to sunlight (and prevent shading of systems) and limits the ability of homeowner associations and local governments from preventing installation of solar energy systems.
• The Solar Rights Act sought to promote and encourage the widespread use of solar energy and to "protect and facilitate adequate access to the sunlight which is necessary to operate solar energy systems.”
• The Solar Rights Act balances the needs of individual solar energy system owners with other property owners by developing solar access rights.
• The Act limits the ability of CC&Rs, typically enforced by homeowner associations (HOA), and local governments to restrict solar installations. These are the best known and important provisions.
• The Act also creates the legal right to a solar easement for a landowner to obtain adequate access to direct sunlight for a solar energy system.

• The Solar Shade Act (AB 2321, 1978) provides limited protection to solar energy system owners from shading caused by trees and shrubs on adjacent properties.
• The law seeks to prevent a property owner from allowing trees or shrubs to shade an existing system installed on a neighboring property, provided the shading trees or shrubs were planted after the solar collecting device was installed.

There are two helpful reports written by the Energy Policy Initiative of the University of San Diego's School of Law about the Solar Rights Act and the Solar Shade Act:

• Solar Rights Act: A Review of the Statutes and Relevant Cases (December 2014, PDF)
• California's Solar Shade Control Act: A Review of the Statutes and Relevant Cases (March 2010, PDF)

Bringing Solar Energy to the Planned Community: A Handbook on Rooftop Solar Systems and Private Land Use Restrictions. You can download this report as an Adobe Acrobat PDF file (62 pages, 1.0 MB).

Most customers have a simple electric meter that is designed to measure the flow of electricity only from RPU to the customer. To receive the full benefit of your solar system, you need a “net meter” that is designed to spin both forwards and backwards accurately. This is important in solar installations because during high producing times of the day the system may generate more than the home needs, sending excess energy back to the utility. There may be circumstances where two meters are used instead of one, producing the same effect. Customers installing solar will be assessed the cost for the meter upgrade and installation if a net meter is not already installed at the location.

When the solar system is operating during the day, it is possible to have times during the day when the solar system produces more energy than the home is using. When this happens the excess energy generated automatically goes through the net electric meter into RPU's distribution grid, running the meter backwards to credit your account. At other times of the day, your electric use may be higher than the solar system is producing, and you must rely on additional power from RPU. This forward and backward spinning of the meter is instantaneous as power needs change and will not affect the quality of the electric power supplied.

RPU’s net energy metering rules and processes are generally in line with net metering throughout California. Once the Interconnection Agreement is approved, a service order to install a net meter on the home is issued. Following the net meter installation, the Utilities Billing department updates your account to reflect the location as being on a Net Energy Metering rate, or "NEM". This is a special billing arrangement that provides value to you if you have an active solar PV system at your home or business. Under NEM, your electric net meter keeps track of the “net difference” between the electricity you consume and the electricity you deliver to RPU within each billing period.

Once the system is installed, monitoring the energy production will be your means of verifying the solar system is operating properly. Ask your solar contractor what monitoring system comes standard with your solar system, what monitoring upgrade options are available and if there are any costs involved.

Monitoring is used to track and optimize energy production and to reduce long term operational and maintenance costs. Solar system monitoring is available in a multitude of ways. A simple way of monitoring, if you have a string inverter, is to look at the LCD screen and record the information you see on the LCD screen. Other providers may supply a display device to be located in your home or in your garage. And still others may provide an on-line portal to view near real-time energy production graphs. Investigate what is being offered with your system and the options you have available.

At a minimum, monthly monitoring is recommended. More often is better. With monthly monitoring, a system problem or lower than expected energy production may be identified, investigated and fixed providing you with the anticipated rate of return on your investment.

At the end of the year, pull out your solar system contract. Note the estimated annual energy production for your installed system and if there is a performance guarantee. Compare the estimated annual energy production to the actual production obtained from the inverter or monitoring device. Is your solar system performing as anticipated? If not, contact your solar contractor and ask them to investigate.

Solar systems are low maintenance requiring occasional cleaning, electrical system checks and inverter preventive maintenance checks. Having your system inspected every year or two is recommended. Ask your solar professional for guidance on maintaining your system.

Dirty solar panels are the most common maintenance issue and can significantly reduce the energy production of the solar system. Dust, leaves, twigs, bird waste and soot on or under the solar panels can have a negative effect on the system. Keeping the array clean will boost energy production.

Shading on any portions of the solar array will reduce energy production. Shading of the system was considered by the contractor when your system was designed, and the energy production estimate included existing shading issues. Over time shading on the system may change – trees grow and other obstacles that create shade may occur. Routinely check for shading and investigate if there is an unexpected drop in energy production.

Loose wiring connections, cracked panels or other physical problems with the system may occasionally occur. System maintenance inspections should be performed to ensure safe and reliable operation.

To participate in the Riverside Public Utilities Solar Program, all equipment must carry a 10 year warranty. A solar module has an estimated life of 20 or more years. The solar inverter typically has a shorter estimated life and often is the system component to fail first. Proper care and maintenance of the inverter will help extend its useful life.

Ask the installing contractor about a maintenance contract – talk about cleaning above and below modules, checking all mechanical and electrical connections and wiring, inspection of air ducts and cooling fans and checking expected energy production to actual.