GRID TIED SOLAR ELECTRIC SYSTEMS

We have the equipment that allows a homeowner to "plug into the sun" and the utility grid easily. You can produce clean, reliable solar power for use by your appliances. In the simplest utility intertie system, the only equipment needed is an intertie inverter and solar modules. Energy produced and not used by your home is "stored" on the utility grid. And when energy use exceeds production, the grid supplies the extra needed. In this way, ordinary citizens can produce and supply renewable energy to the utility grid.
Intertie inverters have all the needed protective electronics to synchronize with the utility grid and to automatically disconnect from the grid in event of an outage. Intertie systems utilizing intertie inverters are installed and working safely in every state in the United States. The intertie system/utility connection varies from state to state and is rapidly changing. Some states are encouraging intertie systems and have passed laws to allow for net metering and streamlined the connection of intertie systems. Solar rebates and tax credits are also available depending on the location of the system.
Under a net metering arrangement, homeowners who install solar systems and produce more power than they are using will run their electric meter backwards as they feed extra electricity back to the utility. This means that the utility "pays" the customer the retail rate for the electricity produced.

SYSTEM SIZING INFORMATION

The size or a solar electric system depends on the amount of power that is required (watts), the amount of time used (hours) and the amount of energy from the sun in a particular area (sun-hours per day). The user has control of the first two of these variables, while the third depends on the location.

If your interested in finding out how much a system would produce in your location you can get approximate information by using NREL's PVWATT program. NREL's photovoltaic performance calculator calculates typical performance of solar electric arrays for more than 200 locations in the National Solar Radiation Database.

CONSERVATION

Conservation plays an important role in keeping down the cost of a photovoltaic system. The use of energy efficient appliances and lighting, as well as non-electric alternatives whenever possible, can make solar electricity a cost competitive alternative to gasoline generators and, in some cases, utility power.

SOLAR COOKING, HEATING, & COOLING

Conventional electric cooking, space heating and water heating equipment use a prohibitive amount of electricity. Electric ranges use 1500 watts or more per burner, so bottled propane or natural gas is a popular alternative to electricity for cooking. A microwave oven has about the same power draw, but since food cooks more quickly, the amount of kilowatt hours used may not be large. Propane and wood are better alternatives for space heating. Good passive solar design and proper insulation can reduce the need for winter heating. Evaporative cooling is a more reasonable load than air conditioning and in locations with low humidity, the results are almost as good. Solar water heaters are the most cost effective way to heat water with either gas or electric backup. A properly sized solar water heater can save 50% to 75% of your annual hot water costs.

LIGHTING

Lighting requires the most study since so many options exist in type, size, voltage and placement. The type of lighting that is best for one system may not be right for another. The first decision is whether your lights will be run on low voltage direct current (DC) or conventional 110-volt alternative current (AC). In a small home, an RV, or a boat, low voltage DC lighting is usually the best. DC wiring runs can be kept short allowing the use of fairly small gauge wire. Since an inverter is part of the system, a home will not be dark if the inverter fails and lights are powered directly by the battery. In addition to conventional-size medium-base low voltage bulbs, the user can choose from a large selection of DC florescent lights, which have 3 to 4 times the light output per watt of power used compared with incandescent types. Halogen bulbs are 30% more efficient and actually seem almost twice as bright as similar wattage incandescent because of the spectrum of light they produce. Twelve and 24-volt replacement ballasts are available to convert AC florescent lights to DC. In a very large installation or one with many lights, the use of an inverter to supply AC power for conventional lighting is cost effective. In a large stand-alone system with AC lighting, the user should have a backup inverter or a few low voltage DC lights in case the primary inverter fails. It is a good idea to have a DC powered light in the room where the inverter and batteries are in case there is a problem. AC light dimmers will not function on AC power from inverters unless they have pure sine wave output. Small fluorescent lights may not turn on with some "load demand start" type inverters.

REFRIGERATION

Gas powered absorption refrigerators are good choice in small systems if bottled gas is available. Modern absorption refrigerators consume 5 - 10 gallons of LP gas/month. If an electric refrigerator will be used in a stand-alone system, it should be a high efficiency type. SunFrost refrigerators use 300-400 watt-hours of electricity/day while conventional AC refrigerators use 3000-4000 watt-hours of electricity/day at a 70-degree average air temperature. The higher cost of good quality DC refrigerators is made up many times over by savings in the number of solar modules and batteries required.

MAJOR APPLIANCES

Standard AC electric motors in washing machines, larger shop machinery and tools, "swamp coolers", pumps, etc. (usually 1/4 to 3/4 horsepower) require a large inverter. Often, a 2000-watt or larger inverter will be required. These electric motors are sometimes hard to start on inverter power, they consume relatively large amounts of electricity, and they are very wasteful compared to high efficiency motors, which use 50% to 75% less electricity. A standard washing machine uses between 300 and 500 watt-hours per load. If the appliance is used more that a few hours a week, it is often cheaper to pay more for a high-efficiency appliance (if one exists), rather than make your electrical system larger to support a low-efficiency load. For many belt-driven loads (washers, drill press, etc.) their standard electric motor can often be easily replaced with a high efficiency type. These motors are available in either AC or DC, and come as separate units or as motor-replacement kits. Vacuum cleaners usually consume 600 to 1000 watts, depending on how powerful they are, about twice what a washer uses, but most vacuum cleaners will operate on inverters larger than 1000 watts because they have low surge motors.

SMALL APPLIANCES

Many small appliances such as irons, toasters and hair dryers consume a very large amount of power when they are used but by their nature require very short or infrequent use periods, so if the system inverter and batteries are large enough, they may be usable. Electronic equipment, like stereos, televisions, VCR's and computers have fairly small power draw. Many of these are available in low voltage DC as well as conventional AC versions, and in general, DC models use less power than their AC counterparts.