Green Building Library
Green Power

Some Basics on Renewable Electrical Energy Technologies

Photovoltaics

  • $.10-.30/KWh, $6-12/Watt installed cost, $1000-50,000 per homesite. Add capacity by adding panels and inverter sections.
  • Requires fairly strong sunlight to produce power, but is fine for most of Pacific NW. A backup system is required for long cloudy periods and winter low light conditions.
  • Power production from a few watts to megawatts; enough to run a country. Power proportional to panel area, and intensity and duration of sunlight.
  • 30+ years life, no maintenance required on panels or inverters. Off-grid system batteries are high maintenance, and easy to damage.
  • Direct Current (DC) source, 12 Volt RV appliances compatible, requires inverter for use with conventional appliances and tools.
  • Regulatory issues: electrical codes, utility standards, building codes, architectural CC&Rs.
    Installation options:
    a. ground mounted racks (small 2-8 panel or SMUD parking lot cover sizes)
    b. roof or façade mounted
    c. building-integrated (BIPV) using metal roofing, amorphous glass spandrels, and
    laser-etched amorphous glass panels used as vision glass in windows and skylights.
  • Available in colors and custom shapes for architectural effects. Laser etching in patterns!

Wind: Homesite turbines

  • $.06-.30/KWh, $8-10/Watt installed cost, $1000-15,000 per wind machine.
  • Requires average wind speeds above 10-12 mph, or higher intermittent windspeeds. A backup system is required for long windless periods.
  • Power production from 200 watts to 1.5 megawatts; enough to run a country. Power proportional to rotor diameter, and windspeed to the third power.
  • 20+ years life, maintenance varies. Tilt-up towers avoid climbing! Off-grid system batteries are high maintenance, and easy to damage.
  • DC or AC source, may require inverter or phase synchronization power conditioning equipment.
  • Regulatory issues: electrical codes, building codes, utility standards, architectural CC&Rs, and tower restrictions. Noise may be an issue in residential areas.
  • Installation requires a tower, which needs to be at least 30 feet taller than any thing within at least 300 feet horizontal distance. Not usually mounted on buildings or atop cliffs.

Micro Hydro

  • The most economical RE source; water falls 24 hours a day. $.03-.07/KWh, $3-10/Watt installed cost, or $2000-11,000 per turbine.
  • Requires running water, usually with 20+ feet drop, 10 gpm minimum flow (see hydro power chart), or river/creek with sufficient flow speed (fast walk). Backup system only needed for high demand loads.
  • Power production from 20 watts to several kilowatts, or enough for a neighborhood. Power proportional to water head and volume.
  • 20+ years life, maintenance yearly, or more often for trash rack in high debris water.
  • DC or AC source, may require inverter or phase synchronization equipment.
  • Regulatory issues: electrical codes, utility standards, water agency, wildlife and streambed use.
  • Installation requires a small hydro-generator, a drive-pipe, and inlet and outlet basins. Inlet basins require a trash rack to protect fish and remove debris that can clog nozzles. System may need freeze protection in very cold weather.

Fuel Cells

Fuel cells are not quite ready for the residential market. They operate on pure hydrogen and will be available in 200W to multi-KW sizes. They produce potable 140 degree F. water in operation. $.08-.25/KWh, A low voltage DC source.

Balance of System (BOS) Components

Every RE system requires what are called BOS components to connect the generation source to your home electric system and the grid safely, and to condition the RE power so it can be used with standard electric appliances and equipment. BOS equipment includes various fuses and disconnects, junction boxes, maximum power point trackers, inverters, transformers, and possibly battery banks, battery charging controllers, and engine generators. Different RE system setups will require specific types of equipment. Your RE system suppliers, local electrical inspector, and local electric utility (if you have a grid-connected system) all have to agree on the equipment used and how it is installed. In general, all RE equipment should be UL listed, and all installations should meet National Electrical Code (NEC) standards. Grid intertied systems must also meet IEEE equipment standards.

Net Metering and Grid Connected Systems

Many states, including Oregon, have net metering laws that require electric utilities to allow RE systems meeting electrical codes and IEEE standards to be connected to the electrical transmission grid. The utility then has to pay you retail value for any power your RE system puts onto the grid for others to use. Some electric utilities are turning to RE systems as a source of distributed generation, which allows them to economically add load capacity to their system without building huge and expensive central generation plants and without expensive transmission infrastructure improvements.

Copyright Alan Van Zuuk