Solar energy is a subject both broad and deep. In this section, you will be introduced to the basics of solar electric and solar hot water systems, as well as some important information about energy efficiency and conservation. Also included is a section discussing the financial considerations of solar energy.  At the bottom of this page are a list of resources that you might find useful in your exploration of solar energy.

Solar Electric

• Solar electric systems convert the energy embodied in sunlight into electricity. Solar electric systems include solar modules (solar panels) that convert the energy in sunlight to direct current (DC) electricity, power conversion equipment called inverters that invert DC electricity to alternating current (AC) electricity as well as safety disconnects and various metering equipment. Some solar electric systems include batteries to provide power to household appliances during power outages or to power off-grid homes. Some systems include backup generators to supplement solar generation to keep the batteries up. There are three main classifications of solar electric systems that can be installed in your home or business: direct grid-tie, grid-tie with battery backup and off-grid.

• Direct Grid-Tie

  Direct grid-tie systems operate in conjunction with the utility grid to achieve optimal efficiency. When the sun is shining and your solar electric system is producing electricity, the first priority is to power your household appliances. If a surplus of electricity is being produced, the solar inverter feeds any excess electricity back to the utility grid, making your utility meter spin backwards. This builds up a credit with your electricity company, reducing your bill, as well as increasing the amount of green energy on the utility grid. If not enough electricity is being produced by your solar electric system to power your household appliances, power is brought in from the utility grid to fill in the gap. All of this happens automatically without any need for intervention from you.
  
  Direct grid-tie systems do not include batteries. This increases system efficiency as well as reducing equipment and installation costs. These systems use battery-less inverters that are not compatible with battery banks. Therefore, direct grid-tie systems cannot provide power to your household appliances during power outages. Direct grid-tie systems can be retrofitted with batteries for backup capability.

• Grid-Tie with Battery Backup

• Grid-tie with battery backup systems offer the flexibility of being connected to the grid with the security of having backup power during a power outage. These systems feed excess electricity back to the grid in the same way that a direct grid-tie system does, as well as providing power to household appliances during power failures.
  
  Grid-tie with battery backup systems use battery based inverters and a battery bank to store electricity for later use. Because batteries are included in the system, a solar charge controller is needed to optimally charge the battery bank and prevent over charging. A backup generator can be included as well for continued power during prolonged power outages. It is usually not practical to power your entire house during a power outage, so a separate electrical panel, called the critical loads panel, powers critical appliances such as a well pump, refrigerator, heating system, lighting and any other appliances which would increase your comfort.

• Off-Grid

  Off-grid solar electric systems can provide power equal to or surpassing quality of grid service to a remote home location, often at a fraction of the cost. Larger battery banks are used in conjunction with optional backup generators to provide power throughout the year. Off-grid systems use battery based inverters as well as solar charge controllers.

• Solar Electric System Components

  • Solar Modules (Solar Panels) are the components that convert the energy embodied in sunlight into electricity. They consist of solar cells wired together and encapsulated in an aluminum frame and a glass top. Solar modules are rated in Watts. If a module is rated at 200 Watts, this module will produce 200 Watts under certain conditions. (Those certain conditions are a loose approximation of real world conditions. Usually the actual output of a solar module is 5-15% less than the manufacturer's rating.) As an example, you could power two 100 W incandescent light bulbs or six 33 W compact fluorescent light bulbs (which would produce three times as much light) off of one 200 W solar module.
    
    Modules are wired together to form an array of solar modules. The physical size of a 1000 W array (five 200 W solar modules) is roughly 75-100 square feet. A typical Vermont home would need a 4500 W array to provide half of its electrical needs, while an energy efficient Vermont home would need a 4500 W array or smaller to provide all of its electrical needs.
    
    Solar arrays can be mounted on the roof of a house or anywhere that gets good sunshine through out the day.  It is imperative that the array be in the shade as little as possible as this will greatly reduce its output.
  • Inverters are the components that convert DC electricity that is produced by the solar modules to AC electricity that can be used by your household appliances and also be fed back to the utility grid. Battery-less inverters simply feed solar electricity into your household appliances and back to the grid if there is an excess. Battery based inverters perform this function as well as use a battery bank to provide back up power during a power outage. Inverters are also rated in Watts. This rating signifies the amount of electricity the inverter can invert (convert from DC to AC) continuously. If an inverter is rated at 3000 Watts that means it can handle a 3000 W solar array for grid-tie systems or power 3000 W worth of household appliances for off-grid or backup power situations.
  • Batteries are the components that store electricity for later use in off-grid or grid-tie with battery backup systems. Batteries are wired together to match the inverter and to provide sufficient storage capacity. This is called a battery bank. Battery banks typically store anywhere from 4-16 Kilowatt Hours or more for use by your household appliances. Most batteries need periodic maintenance totaling several hours per year to keep them in good condition. Maintenance free batteries can also be used, although there is an increase in cost.
  • Solar Charge Controllers are the components that charge the battery bank from a solar array. They use specific charging algorithms to increase battery life and prevent overcharging of the battery bank.

Solar Hot Water

• Solar hot water systems use the energy embodied in sunlight to heat water directly for domestic hot water, space heating or other hot water needs. This is achieved by the use of solar hot water collectors connected to one or more hot water storage tanks by piping. A pump is used to circulate a heat transfer fluid through the collectors, allowing it to heat up, and return the heated fluid back to the storage tank. A heat exchanger at or in the storage tank is used to transfer the heat in the transfer fluid to the water in the storage tank. The cooled heat transfer fluid is then returned to the collectors and the process starts all over again.
  
  Solar hot water systems usually include two tanks, one to store the solar heated water and one to provide backup water heating during cloudy or cold periods. Most often, your existing hot water tank will function as the backup tank. The output of the solar storage tank is piped to the input of the backup tank, so any water entering the backup tank has been preheated by solar energy, giving you a significant energy savings. For homes with low hot water usage, a single tank can function as both the solar storage tank and the backup tank with good results.

• Solar Hot Water System Components

  • Solar Hot Water Collectors are the components that collect the energy embodied in sunlight by heating the water inside of them. They consist of a metal frame with copper piping inside and a glass cover on top. As heat transfer fluid circulates through the collector, it absorbs heat from the sunlight. Hot water collectors can be connected together like solar electric modules to achieve more water heating.  Each collector is generally 4' x 8', but some are larger or smaller.  Unlike solar electric modules, hot water collectors must be placed as close as possible to the solar storage and backup tanks, preferably on the roof of the house.  This allows for shorter pipe runs so that less heat will be lost during transport of the heat transfer fluid.
  • Hot Water Storage Tanks are the components that store hot water for later use. Some, like the hot water tank in your home have a heat source to heat the water for storage. Solar storage tanks do not usually have a heat source because they are storing hot water that has been heated by the solar hot water collectors. Solar storage tanks are usually larger than normal hot water tanks because that allows you to store solar heated hot water for cloudy periods. The more storage you have, the more you are going to be using water that has been heated by the sun instead of by electricity or gas. Some storage tanks have a heat exchanger integral to the tank, while others need an external heat exchanger.
  • Heat Transfer Fluid is the fluid that absorbs heat in the solar hot water collectors and transfers that heat to the water in the solar storage tank by means of a heat exchanger. Heat transfer fluid is most often a mixture of non-toxic propylene glycol (a type of anti-freeze) and water. The addition of the glycol prevents the heat transfer fluid from freezing during the winter.
  • Heat Exchangers are the components that transfer heat from the heat transfer fluid to the water in the solar storage tank.  They are necessary to prevent the mixing of the glycol in the heat transfer fluid and the potable water in your solar storage tank.  Heat exchanger designs vary.  Some common types are tube-in-shell and flat plate heat exchangers.

Energy Efficiency & Conservation

• Energy efficiency and conservation are the easiest and most cost effective ways to reduce your energy cost and pollution related to energy usage. Something as easy as changing the most frequently used light bulbs in your home can reduce your electric bill by up to 25%. Energy efficiency and conservation are also important when utilizing solar energy systems. Time and money spent on efficiency and conservation will drastically reduce the size and cost of a solar energy system needed to achieve the same reduction in household energy costs. Many households can reduce their total energy bills by as much as 50% by implementing or retrofitting their home with energy efficient building products and practices. Simply becoming aware of your energy usage by calculating the cost of certain appliances or installing a household electricity monitor can be a big step to reducing your energy costs. The Resources section below has many good websites for further information about this important topic.

Financial Information

• Money can be one of the biggest stumbling blocks to owning a solar energy system. Fortunately, our state and federal governments have deemed solar energy technology worthy of investment and have made money available to consumers in the form of rebates, tax incentives and loans. 
• State incentives are primarily twofold. First, equipment for renewable energy systems are sales tax exempt.  Second, the Vermont Energy Investment Corporation funds a renewable energy rebate program administered by the Renewable Energy Resource Center. This program provides a rebate for solar electric, solar hot water and small wind systems that are installed by Vermont Solar or Wind Partners. Solar and Wind Partners are companies that have met certain criteria and have been approved by Renewable Energy Vermont to reserve state rebate funds for their customers.  Bright Earth Solar is a Solar Partner and is approved for solar electric and solar hot water systems.  Currently the rebate is $1.75 per watt of installed DC system capacity for solar electric and $1.75 per 100 Btu per day of installed system capacity for individuals and businesses. For example, if you purchased a solar electric system with 1500 Watts of solar modules, you would receive a $2,625 rebate. For more information about the Vermont Solar & Small Wind Incentive program visit the Renewable Energy Resource Center website.
• Federal incentives for renewable energy systems focus on a personal or corporate tax credit. A tax credit is a dollar for dollar reduction in taxes due as opposed to a deduction which reduces the income on which you are taxed. Currently, the personal tax credit is 30% of the system cost or $2,000, whichever is lesser on solar electric and solar hot water systems. The corporate tax credit is 30% of the system cost for solar electric and solar hot water systems. For more information about the federal tax credit or about other incentives visit the Database of State Incentives for Renewables & Efficiency.

Resources

• Renewable Energy Vermont
• Renewable Energy Resource Center
• Efficiency Vermont
• Solar Energy Industries Association
• National Renewable Energy Laboratory
• US Department of Energy Energy Efficiency and Renewable Energy Office
• Database of State Incentives for Renewables & Efficiency
• Clean Power Estimator