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Net Metering & Small Electrical Generators Net Metering & Small Electrical Generators
Net Metering & Small Electrical Generators
Background
The following material provides reference and resource information about small generators. Small
generating systems include fuel cells, solar photovoltaic panels and wind turbine generators.
There are formal rules for connections and sales between small customer-owned generators and
electric utility providers. Under these rules, or tariffs, customers can sell energy to their local utility
provider. They will be charged for the amount of energy they purchase from the utility company
minus the cost of the energy they provide to the utility company. The tariffs clarify that the customer
is responsible for all costs associated with any modification to the generating facility and utility
distribution system that may be required to connect it to the larger utility system.
Pacific Power recognizes that customers may be interested in purchasing and operating small
generating systems. For that reason, we have compiled an overview of small generators for customer use.
The following illustration shows a small electrical generation systems major components and its
connections to Pacific Powers system.
Inverter
DC/AC
Disconnect
Switch
House
PV
Panel
or Other
Renewable
Energy
Generator
Electric
Service
Panel
Utility
System
Net
Meter
Diagram A
What is Net Metering?
Net metering measures the difference between the electricity you buy from your utility and the
electricity you generate to the utility using your own solar or wind or other acceptable renewable
generating equipment. Your meter keeps track of this difference as you generate electricity and take
electricity from the electricity transmission grid. When you generate more than you use, electricity
flows to the utility.
Normally your electric meter spins forward as it measures how many kilowatt-hours of electricity
you buy, and is read by your utility once a month. A Net Meter allows you to use the electricity you generate first, reducing what you would normally buy from your utility. If you generate more
electricity than you use, the excess goes through you electric meter and into the grid. Your meter
shows the net amount, measured as the difference between the electricity you generate to the utility
and the electricity you purchase from your utility.
What are the benefits of Net Metering?
Net Metering is a simple way to get the full value of the electricity you generate. For example, if you
are a residential customer, you may not be home during the day when your system generates
electricity. Net Metering allows you to store this excess electricity on the grid, reducing or offsetting
the electricity you would otherwise have to purchase.
Generator Technology
Many small generating systems are easily available and environmentally sound. The following
paragraphs describe a variety of generators, including general costs, performance, and sizing
recommendations.
When considering the purchase of energy generation equipment, ask the dealer what agencies
have tested, qualified, or otherwise approved a unit. Underwriters Laboratories (UL) organizations
and the Institute of Electrical and Electronic Engineers (IEEE) certify the safety and performance of
renewable products. Every net metered generation project must meet specific safety and engineering
standards to qualify for interconnection to the utility grid.
Wind
The wind turns a propeller connected to a generator in this renewable technology system. A direct
current wind generator will provide its energy to direct current loads. Alternating current for
refrigerators, computers, TV, etc. would have to be provided by an inverter. If the wind turbine
generator produces 60 cycle alternating current, the generator could serve AC loads directly.
Wind energy experts recommend placing an 65 to 120 foot high residential wind turbine on one or
more acres of land, depending upon the height of the turbine. Smaller lots generally are not
acceptable for safety and noise reasons.
The economics of a 5 to 10 kw residential system are sensitive to the average wind speed and the
cost of electricity. As a general rule, an economical system requires an average wind speed of at least
10 MPH at the turbines location.
Solar Photovoltaic Panels
Solar photovoltaic panels (PV) generate direct current electricity. These solar cells consist of positive
and negative layers on a silicon wafer. Sunlight striking the panels is absorbed, freeing electrons in the
silicon crystal. Electrons activated by the sunlight move through the crystal and out to the load or battery. With this type of electric generation, typically 10 to 15 percent of the energy striking the
panels is converted to electricity. Research continues to increase this efficiency.
Cost of a PV system depends largely on the application. Systems containing 100 watts or more
generally cost between $10 and $20 per watt. Smaller systems are more expensive on a per watt basis.
The cost of the panels is usually one-third to one-half of the total system cost. Each watt of panel
typically produces between two and six watt-hours of energy a day depending on the season and
location. Solar panels can generate electricity in cloudy weather, although their output is diminished.
Energy produced on an overcast day might be as little as five to ten percent of the amount generated
on a bright, sunny day.
Fuel Cell
Fuel cells are similar to batteries in that they produce electricity using an electrochemical reaction.
Unlike a battery, which must be recharged, a fuel cell produces electricity continuously when
supplied by a fossil fuelusually natural gas, propane, methane, or bio-mass. These units are available
commercially in 250 kw sizes. Smaller residential units also are being produced and field-tested at this time.
The National Aeronautics and Space Administration (NASA) first used fuel cells to provide
electricity on space missions. Currently 250 kw applications are found in hospitals, computer facilities
and industrial firms.
A fuel cell has two major sections: the reformer and the stack. Hydrogen is stripped from the fossil
fuel in the reformer. In the stack section, electricity is produced from the hydrogen. The type of
reformer determines the type of fossil fuel that can be used.
While the 200 kw fuel cell can use natural gas, propane or bio-mass, optimum electrical
performance is obtained with natural gas. Using propane or bio-mass will reduce the kw output of
the nominally rated 200 kw unit. Others use methane as its energy source. Fuel cell size, equipment
costs and maintenance requirements, as well as fuel quantity needed, are a few of the factors that
determine the best fossil fuel to use in the fuel cell.
This equipment produces clean and quiet energy. This cogenerator is so clean that it enjoys a
blanket exemption from air quality standards in Southern California, which has the strictest air
quality standards in the country. Micro-turbines
Micro-turbines like their larger counterparts, the combustion turbines use jet engine technology to
produce electricity. The simplest combustion turbine consists of three components: a compressor, a
combustion chamber and a turbine.
Air is compressed in the compressor. This high temperature and high pressure air moves to the
combustion chamber where fuel is injected and the mixture is ignited. In the turbine section, this very
hot mixture expands, turning the turbine shaft that is connected to the generator.
This equipment is designed and operated to produce 60-cycle alternating current and can operate
on multiple fuel sources, including natural gas propane and diesel. Micro-turbines can produce
electricity efficiently and cost-effectively, while emitting very low levels of pollutants. The hot exhaust
can be used for space and water heating.
Summary
The following table summarizes the size and cost of various electric generators.
Small Wind
Photovoltaic
Fuel Cell
Micro-Turbines
Commercial
Availability
Size
Installed
Cost ($/kw)
O&M Costs
(cents/kWh)
Fuel Type
Well
Established
0.30 kw-
2 MW
$6,000-
$10,000
Minimal
Solar
600 watts-
40 kw
$1,000-
$1,500
Varies
Wind
Well
Established
$3000
Hydrogen
biogas,
propane &
methane
1 kw-
200 kw
0.3-1.5
Well
Established
Propane,
NG,
distillate oil
& biogas
25 kw-
75 kw
$500-
$1300
0.2-1.0
New
Industry
Other online resources follow:
American Wind Energy Association, www.awea.org
Energy Efficiency and Renewable Energy, www.energy.gov
Fuel Cells, www.fuelcells.org
Solar Energy Industries Association, www.seia.org Renewable energy without the equipment
Pacific Power offers a new renewable resource program called Blue Sky. Our Blue Sky program uses
the clean, renewable power of wind to generate electricity.
Buying one 100-kwh block of Blue Sky each month for a year has the same en