Photovoltaic solar systems

For those homeowners who would like to achieve long-term energy independence solar photovoltaic (PV) systems using solar panels are one of the very best options. Solar energy systems for the home are relatively simple, last for decades and over the long term can save homeowners significant money, particularly in those states or countries that provide incentives for solar energy.  Moreover, solar PV systems create no pollution and give off no hydrocarbons which makes them one of the best energy options from an environmental standpoint.  They are definitely a home energy option you can feel good about.  A key thing to remember with PV systems is that what they are harvesting is light energy, not heat or solar thermal energy.  That means they work as well in colder climates as they do in warmer climates. All that matters is how much light a location gets and in most of the U.S. there is more than sufficient light on average for PV systems to be very effective.  If you want to learn exactly how much light your location has during the year look at our section on solar maps.  These will show you exactly how many hours of sunlight per day your area gets at different times of the year.

Photovoltaic systems (PV systems for short) are any energy generation systems that make use of photovoltaic cells.  A photovoltaic cell is a cell which generates electricity directly from light energy. Photovoltaic cells come in many sizes, but most are 10 cm by 10 cm and generate a little more than half a volt of electricity. PV cells are bundled together in interconnected solar panels to produce higher voltages and increased power. A 12-volt solar panel typically used in home solar energy applications has 30 to 50 PV cells. and can generate anywhere between  80 to 200 volts of electricity.  In a residential application multiple solar panels are strung together into one or more modules.  The number of panels you need is a function of your energy use and the amount of space you have available on your southern facing roof. 

Grid-Tied vs Off-the-Grid Systems

Photovoltaic systems for the home can generally be classified into those that are designed to make use of an existing electric grid (grid-tied system) or those that are designed for rural use where no electric grid is available (off-the-grid system). In a grid-tied system there is no need for a battery system to store the energy that the solar panels generate.  Instead the power grid itself acts in a sense as a giant battery that uses any excess electricity that your solar panels may generate, and which you can draw from on cloudy days when there is insufficient sunlight to fully power your home.

We believe that grid-tied systems offer a number of advantages over off-the-grid PV systems.  Overall they are less expensive than off-the-grid systems because they do not require either batteries or battery charging controllers.  Because they require less equipment they are also much simpler systems to set up and use.  They take less time to install and require very little maintenance. We also think they are far more efficient and environmentally friendly than off-the-grid systems.  With a grid-tied system none of the energy your PV panels generate is wasted.  On sunny days when your panels are producing more electricity than you are using the energy is transferred to the grid where it can immediately be used by others. In an off-the-grid system, once your batteries are fully charged, any excess electricity being generated by your panels has to be dumped to prevent the batteries from being overcharged.  This results in wasted electricity.

However, in some situations, particularly in rural areas which have no grid, there may be no option other than to go with an off-the-grid system.  For a homeowner to pay the utility company to bring power lines into their property can cost upwards of $10,000 per quarter mile.  For many owners of rural properties this makes hooking to the grid economically non-viable. Off-the-grid systems require more care and maintenance but can give a homeowner a strong sense of independence.  They also have the advantage that the homeowner is no longer subject to the risk of a brownout or a loss of power from the grid.

Components of a Grid-Tied System

A typical grid-tied photovoltaic system will have the following components:

Solar Panels - Solar panels are lightweight flat modules consisting of multiple photovoltaic solar cells.  They are most commonly mounted on the roof of the home though they can also be placed in ground mounted systems or on special tracking arrays which follow the movement of the sun.  The number of solar panels you use will depend upon the amount of electricity you want to generate and the physical space available for mounting them. There are several different types of solar panels, each of which has its advantages and disadvantages when it comes to the trade-off between cost and performance.  Currently solar panel prices are running between $4:50 and $5.00 per watt but prices have are coming down thanks to increased production, improved technology and lower labor costs.  For most grid-tied home systems the solar panels will represent about 60% of the total cost.  For more details about the ins and outs of solar panels look at our section on solar panels.

Solar Panel Mounts - In most home solar energy systems the solar panels are mounted to a home's roof using aluminum racks.  These racks are usually mounted on the side of your roof that faces south so it will have the most sun exposure.  Some rack mount systems are fixed while other can be adjusted during the year to adjust for the fact that the sun is higher in the sky during summer and lower in the sky during winter.   There are also pole base mounting systems some of which contain passive or motorized tracking systems for continually aligning the angle of the panels with the movement of the sun during the day. Certain types of solar panels don't require mounting at all but are actually bonded to the roof's surface in the form of roofing tiles or mats.

Inverter - Solar panels create a type of current called Direct Current (DC) but most home electrical systems are designed to run on Alternating Current (AC). The inverter is an electrical component that will convert the DC electricity coming from the solar panels into AC current that your home can use.  In a typical grid-tied system the inverter sits between the solar panels and the home's electrical panel. 

2 Way Electric Meter - In a grid-tied system the electricity generated by your solar panels is tied into your home's electric meter provided by the power company.  For a grid-tied system the meter needs to be a 2 way meter which can run forwards when you use electricity from the grid and backwards when the sun is out and you are generating excess electricity to put into the grid.  Electric companies have begun installing 2-way meters in many homes.  If you do not have one your electric company can install when your solar panels are installed.

Off-the-Grid Photovoltaic Systems

If you are going to go off the grid, either because you live in a rural area where there is not good grid access or simply because you want the independence of not having to rely on it, there are a few additional components you will need:

Battery Bank - A battery bank is any interconnected group of deep cycle batteries.  The batteries that make up the bank are  usually enclosed in some type of well ventilated structure because most battery systems will vent a small amount of hydrogen gas. 

Charge Controller - Battery banks are normally connected to a charge control which is designed to control the flow of energy in and out of the battery bank to optimize and stabilize the flow of electricity. A charge controller is an essential component because batteries can become damaged if they are overcharged.

That is pretty much it.  There are other optional components that can be added to the system but the components just described make up the core of the photovoltaic system.