Approximate power available at any given site can be
assessed using the formula:
head (feet) x flow (gpm) / 8 -- Watts
e.g., 100 feet x 30 gpm / 8 = 375 Watts
head (m) x flow (l/m) / 10 = Watts
e.g., 30 m x 120 I/m / 10 = 360 Watts
Making Your Own Clean Electricity
Generating electricity using your own small renewable energy system fits the
circumstances and values of some home and small-business owners. Although it takes
time and money to research, buy, and maintain a system, many people enjoy the
independence they gain and the knowledge that their actions are helping the environment.
A renewable energy system can be used to supply some or all of your electricity
needs. Some people, especially those in remote areas, use the electricity from their
systems in place of electricity supplied to them by power providers (i.e. electric utilities).
These are called stand-alone (off-grid) systems.
Others connect their systems to the grid and use them to reduce the amount of
conventional power supplied to them through the grid. A grid-connected system allows
you to sell any excess power you produce back to your power provider.
These are some renewable energy technologies available for use today:
Small solar electric systems
Small wind electric systems
Small hybrid electric systems (solar and wind).
Before you purchase and install a small renewable energy system, you should analyze
your electricity loads to see if one of the small renewable energy systems can meet all or
enough of your electricity needs—is it economically feasible? You will also want to
research your local codes and requirements for installing a system.
If you're designing a new home, you should work with the builder and your contractor
to incorporate your small renewable energy system into your whole-house design—an
approach for building an energy-efficient home.
Small Solar Electric Systems
A small solar electric or photovoltaic (PV) system can be a reliable and pollution-
free producer of electricity for your home or office. And they're becoming more
affordable all the time. Small PV systems also provide a cost-effective power supply in
locations where it is expensive or impossible to send electricity through conventional
Because PV technologies use both direct and scattered sunlight to create
electricity, the solar resource across the United States is ample for small solar electric
systems. However, the amount of power generated by a solar system at a particular site
depends on how much of the sun's energy reaches it. Thus, PV systems, like all solar
technologies, function most efficiently in the southwestern United States, which receives
the greatest amount of solar energy.
You can also use PV technology to provide outdoor lighting.
How Small Solar Electric Systems Work
Solar electric systems, also known as photovoltaic (PV) systems, convert sunlight
into electricity. Solar cells—the basic building blocks of a PV system—consist of
semiconductor materials. When sunlight is absorbed by these materials, the solar energy
knocks electrons loose from their atoms. This phenomenon is called the "photoelectric
effect." These free electrons then travel into a circuit built into the solar cell to form
electrical current. Only sunlight of certain wavelengths will work efficiently to create
electricity. PV systems can still produce electricity on cloudy days, but not as much as on
a sunny day.
The basic PV or solar cell typically produces only a small amount of power. To
produce more power, solar cells (about 40) can be interconnected to form panels or
modules. PV modules range in output from 10 to 300 watts. If more power is needed,
several modules can be installed on a building or at ground-level in a rack to form a PV
array. About 10–20 PV arrays can provide enough power for a household.
PV arrays can be mounted at a fixed angle facing south, or they can be mounted
on a tracking device that follows the sun, allowing them to capture the most sunlight over
the course of a day.
Because of their modularity, PV systems can be designed to meet any electrical
requirement, no matter how large or how small. You also can connect them to an electric
distribution system (grid-connected), or they can stand alone (off-grid).
Considering a Small Solar Electric System
To help evaluate whether a small solar electric system will work for you, you should
consider the following:
Your available solar resource—do you have clear and unobstructed access to
sunlight for most or all of the day, throughout the year?
The system size—do you have a roof or area large enough to accommodate it?
Sizing Your Small Solar Electric System
Accurately sizing the components of your solar electric system, also known as a
photovoltaic (PV) system, helps ensure that your system will produce the amount of
power you want it to produce. This is especially important for stand-alone systems, which
are not connected to the electricity grid. However, because PV is modular, you can
always add to your solar energy collector should you need more power down the road.
First, consider what portion of your current electricity needs you would like your
PV system to meet. For example, suppose that you would like to meet a certain
percentage of your electricity needs with your PV system. You could work with your PV
provider to examine past electric bills and determine the size of the PV system needed to
achieve that goal. You can contact your utility company and request the total electricity
usage, measured in kilowatt-hours (kWh), for your household or business over the past
12 months or consult your electric bills if you save them.
If you reduce your electricity loads, you can generally buy a smaller, less
expensive PV system.
In addition to how much electricity you'd like to generate, the size of your system
also depends on these factors:
The site's solar resource or available sunlight
The system's orientation and tilt
The system's efficiency at converting sunlight to electricity
Other electricity sources, like a utility, a wind turbine, or a fossil fuel generator.
PV systems are classified by their rated power output (the peak power they produce
when exposed to solar radiation of 1000 watts per square meter at a module temperature
of 25°C). Systems rated between 1 and 5 kilowatts are generally sufficient to meet most
of the needs of home and small business owners.
The table below provides an estimate of the roof area needed for several systems.
Your system supplier/installer can make, or help you make, more precise calculations at
your site before you purchase a system.
Roof Area Needed in Square Feet
PV Module Efficiency (%) PV Capacity Rating (Watts)
100 250 500 1,000 2,000 4,000 10,000
4 30 75 150 300 600 1,200 3,000
8 15 38 75 150 300 600 1,500
12 10 25 50 100 200 400 1,000
16 8 20 40 80 160 320 800
For example, to generate 2,000 watts from a 12%-efficient system, you need 200 square
feet of roof area.
Small Solar Electric System Components
A typical small solar electric, or photovoltaic (PV), system consists of these components:
Modules or panels (which consist of solar cells)
Arrays (which consist of modules)
Small Solar Electric Balance-of-System Components
In addition to the solar cells and modules, a small solar electric (or photovoltaic)
system consists of other parts called balance-of-system components.
The balance-of-system equipment required depends which of the following systems is
Grid -Connected Small Solar Electric Systems
A grid-connected small solar electric or photovoltaic (PV) system receives back-
up power from a utility's grid when the PV system is not producing enough power. When
the system produces excess power, the utility is required to purchase the power through a
metering and rate arrangement.
Net metering is the best arrangement. Under this arrangement, the power provider
essentially pays you retail price for the electricity you feed back into the grid. See
Estimating Energy Cost Savings for a Net-Metered Photovoltaic System.
Stand-Alone Small Solar Electric Systems
A stand-alone small solar electric or photovoltaic (PV) system operates "off-
grid"—it isn't connected to a electricity distribution grid operated by a utility.
A stand-alone PV system makes sense if any of the following apply:
You live in a remote location where it's more cost effective than extending a
power line to a grid.
You're considering a hybrid electric system—one that uses both a PV system and
a small wind electric system.
You need minimal amounts of power; e.g., irrigation control equipment and
Anyone can take advantage of outdoor solar lighting—a stand-alone PV application.
Small "Hybrid" Solar and Wind Electric Systems
According to many renewable energy experts, a small "hybrid" electric system
that combines wind and solar (photovoltaic) technologies offers several advantages over
either single system.
In much of the United States, wind speeds are low in the summer when the sun
shines brightest and longest. The wind is strong in the winter when less sunlight is
available. Because the peak operating times for wind and solar systems occur at different
times of the day and year, hybrid systems are more likely to produce power when you
Many hybrid systems are stand-alone systems, which operate "off-grid"—not
connected to an electricity distribution system. For the times when neither the wind nor
the solar system are producing, most hybrid systems provide power through batteries
and/or an engine generator powered by conventional fuels, such as diesel. If the batteries
run low, the engine generator can provide power and recharge the batteries.
Adding an engine generator makes the system more complex, but modern
electronic controllers can operate these systems automatically. An engine generator can
also reduce the size of the other components needed for the system. Keep in mind that the
storage capacity must be large enough to supply electrical needs during non-charging
Battery banks are typically sized to supply the electric load for one to three days.
A typical small solar electric system usually includes the following balance-of-system
Mounting racks and hardware for the panels
Wiring for electrical connections
Power conditioning equipment, such as an inverter
Batteries for electricity storage (optional).
Stand-by gasoline electric generator.
Installing and Maintaining a Small Solar Electric System
Before you purchase and install a small renewable energy system, you should
analyze your electricity loads to see if one of the small renewable energy systems can
meet all or enough of your electricity needs—is it economically feasible? You will also
want to research your local codes and requirements for installing a system.
If you're designing a new home, you should work with the builder and your
contractor to incorporate your small renewable energy system into your whole-house
design—an approach for building an energy-efficient home.
Analyzing Your Electricity Loads
Calculating your electricity needs is the first step in the process of investigating
renewable energy systems for your home or small business. A thorough examination of
your electricity needs helps you determine the following:
The size (and therefore, cost) of the system you'll need
How your energy needs fluctuate throughout the day and over the year
Measures you can take to reduce your electricity use.
Conducting a load analysis involves recording the wattage and average daily use of
all of the electrical devices which are plugged into your central power source, such as
refrigerators, lights, televisions, and power tools. Some loads, like your refrigerator, use
electricity all the time, while others, like power tools, use electricity intermittently. Loads
that use electricity intermittently are often referred to as selectable loads. If you are
willing to use your selectable loads only when you have extra power available, you may
be able to install a smaller renewable energy system.
To determine your total electricity consumption:
Multiply the wattage of each appliance by the number of hours it is used each day
(be sure to take seasonal variations into account). Some appliances do not give the
wattage, so you may have to calculate the wattage by multiplying the amperes
times the volts. Generally, power use data can be found on a sticker, metal plate,
or cord attached to the appliances.
Record the time(s) of day the load runs for all selectable loads.
How to Read Residential Electric Meters
The basic unit of measure of electric power is the watt. One thousand watts are
called a kilowatt. If you use one thousand watts of power in one hour you have used a
kilowatt-hour (kWh). Your electric utility bills you by the kWh.
The standard electric power meter is a clock-like device driven by the electricity
moving through it. As the home draws current from the power lines, a set of small gears
inside the meter move. The number of revolutions is recorded by the dials that you can
see on the face of the meter. The speed of the revolutions depends on the amount of
current drawn; the more power consumed at any one instant, the faster the gears will
When reading an electric meter, read and write down the numbers as shown on
the dials from right to left. When the pointer is directly on a number, look at the dial to
the right. If it has passed zero, use the next higher number. If the dial has not passed zero,
use the lower number. Record the numbers shown by writing down the value of the dial
to your extreme right first and the rest as you come to them. Should the hand of a dial fall
between two numbers, use the smaller of the two numbers.
Note that some newer electric meters use digital displays instead of dials. The
difference between one month's reading and the next is the amount of energy units that
have been used for that billing period.
Small Wind Electric Systems
Small wind electric systems are one of the most cost-effective, home-based
renewable energy systems. These systems are also nonpolluting.
If a small wind electric system is right for you, it can do the following:
Lower your electricity bills by 50–90%
Help you avoid the high costs of having utility power lines extended to a remote
Help uninterruptible power supplies ride through extended utility outages.
Small wind electric systems can also be used for a variety of other applications, including
water pumping on farms and ranches.
How a Small Wind Electric System Works
Wind is created by the unequal heating of the Earth's surface by the sun. Wind
turbines convert the kinetic energy in wind into clean electricity.
When the wind spins the wind turbine's blades, a rotor captures the kinetic energy
of the wind and converts it into rotary motion to drive the generator. The manufacturer
can provide information on the maximum wind speed at which the turbine is designed to
operate safely. Most turbines have automatic overspeed-governing systems to keep the
rotor from spinning out of control in very high winds.
A small wind system can be connected to an electric distribution system (grid-
connected) or it can stand alone (off-grid).
Evaluating a Potential Small Wind Turbine Site
Estimating Your Wind Resource
To help determine the suitability of your site for a small electric wind system, you
need to estimate your site's wind resource. The wind resource can vary significantly over
an area of just a few miles because of local terrain influences on the wind flow. You can
use the following methods for estimating your wind resource.
Consult Wind Resource Maps
As a first step, you can consult a wind resource map, which is used to estimate the
wind resource in your area. The U.S. Department of Energy's Wind Powering America
Program has wind resource maps by state.
Obtain Airport Wind Speed Data
Another way to indirectly quantify the wind resource is to obtain average wind
speed information from a nearby airport. However, local terrain influences and other
factors may cause the wind speed recorded at an airport to be different from your
particular location. Airport wind data are generally measured at heights about 20–33 feet
(6–10 meters) aboveground. Average wind speeds increase with height and may be 15–
25% greater at a typical wind turbine hub-height of 80 feet (24 meters) than those
measured at airport anemometer heights.
Observe Vegetation Flagging
Flagging—the effect of strong winds on area vegetation—can help determine area
wind speeds. Trees, especially conifers or evergreens, can be permanently deformed by
Use a Measurement System
Direct monitoring by a wind resource measurement system at a site provides the
clearest picture of the available resource. Wind measurement systems are available for
costs as low as $600–$1,200.
The measurement equipment must be set high enough to avoid turbulence created
by trees, buildings, and other obstructions. The most useful readings are those taken at
hub-height, the elevation at the top of the tower where the wind turbine is going to be
Obtain Data from a Local Small Wind System
If there is a small wind turbine system in your area, you may be able to obtain
information on the annual output of the system and also wind speed data if available.
Your home or business is located on at least one acre of land in a rural area
Your local zoning codes or covenants allow wind turbines
You can determine how much electricity you need or want to produce
It works for you economically, and you're comfortable with long-term investments
Your average electricity bills are $150 per month or more
Your property is in a remote location that does not have easy access to utility lines.
Small Wind Electric System Components
To capture and convert the wind's kinetic energy into electricity, a home wind energy
system generally comprises the following:
A wind turbine (blades) attached to a rotor, generator/alternator mounted on
a frame, and usually a tail
Small Wind Electric System Towers
Because wind speeds increase with height, a small wind turbine is mounted on a
tower. In general, the higher the tower, the more power the wind system can produce.
The tower also raises the turbine above the air turbulence that can exist close to the
ground because of obstructions such as hills, buildings, and trees.
Relatively small investments in increased tower height can yield very high rates
of return in power production. For instance, to raise a 10-kilowatt generator from a 60-
foot tower height to a 100-foot tower involves a 10% increase in overall system cost, but
it can produce 25% more power.
The estimated annual energy output and turbine size you'll need can help
determine the best tower height.
Types of Towers
Most turbine manufacturers provide wind energy system packages that include
towers. There are two basic types of towers: self-supporting (free-standing) and guyed.
There are also tilt-down versions of guyed towers.
Most home wind power systems use a guyed tower, which are the least expensive. Guyed
towers can consist of these components:
Tubing, depending on the design
Supporting guy wires.
Guyed towers are easier to install than self-supporting towers. However, because
the guy radius must be one-half to three-quarters of the tower height, guyed towers
require enough space to accommodate them.
While tilt-down towers are more expensive, they offer the consumer an easy way
to perform maintenance on smaller light-weight turbines, usually 10 kilowatt or less. Tilt-
down towers can also be lowered to the ground during hazardous weather such as
hurricanes. Aluminum towers are prone to cracking and should be avoided.
Most manufacturers can provide you with a system package that includes all the
parts you need for your particular application. For a residential grid-connected
application, the balance-of-system parts may include the following:
An inverter (power conditioning unit)
Electrical disconnect switch
Foundation for the tower.
Installation or Mounting
A general rule of thumb is to install a small wind turbine on a tower with the
bottom of the rotor blades at least 30 feet (9 meters) above any obstacle that is within 300
feet (90 meters) of the tower.
Mounting small wind turbines on rooftops is not recommended. All wind turbines
vibrate and transmit the vibration to the structure on which they are mounted. This
vibration can lead to noise and structural problems with the building, and mounting on
the rooftop can expose the turbine to excessive turbulence that can shorten its life.
Installing and Maintaining a Small Electric Wind System
With proper installation and maintenance, a small wind electric system should last up to
20 years or longer.
Before installing your system, you first need to do the following:
Find the best site
Size your wind turbine
Decide whether you'll have a grid-connected or stand-alone system
Understand your local zoning, permitting, and neighborhood covenant
The manufacturer/dealer should be able to help you install your small wind electric
system. Many people elect to install the systems themselves. Before attempting to install
your wind turbine, ask yourself the following questions:
Can I pour a proper cement foundation?
Do I have access to a lift or a way of erecting the tower safely?
Do I know the difference between alternating current (AC) and direct current
Do I know enough about electricity to safely wire my turbine?
Do I know how to safely handle and install batteries?
If you answered no to any of the above questions, you should probably choose to
have your system installed by a system integrator or installer.
Although small wind turbines typically are sturdy and reliable machines, they do require
some annual maintenance.
Check and tighten bolts and electrical connections as necessary.
Check machines for corrosion and the guy wires for proper tension.
Check for and replace any worn leading edge tape on the turbine blades, if
Replace the turbine blades and/or bearings after 10 years if needed.
If you do not have the expertise to maintain the system, your installer may provide a
service and maintenance program.
Microhydropower systems usually generate up to 100 kilowatts (kW) of
electricity. Most of the hydropower systems used by homeowners and small business
owners, including farmers and ranchers, would qualify as microhydropower systems. In
fact, a 10-kilowatt microhydropower system generally can provide enough power for a
large home, a small resort, or a hobby farm.
How A Microhydropower System Works
Hydropower systems use the energy in flowing water to produce electricity or mechanical
energy. Although there are several ways to harness the moving water to produce energy,
run-of-the-river systems, which do not require large storage reservoirs, are often used for
For run-of-the-river microhydropower systems, a portion of a river's water is diverted to a
water conveyance—channel, pipeline, or pressurized pipeline (penstock)—that delivers it
to a turbine or waterwheel. The moving water rotates the wheel or turbine, which spins a
shaft. The motion of the shaft can be used for mechanical processes, such as pumping
water, or it can be used to power an alternator or generator to generate electricity.
A microhydropower system can be connected to an electric distribution system (grid-
connected), or it can stand alone (off-grid).
* Evaluating a Potential Microhydropower SiteEvaluating a Potential
To build a microhydropower system, you need access to flowing water on your property.
A sufficient quantity of falling water must be available, which usually, but not always,
means that hilly or mountainous sites are best. Other considerations for a potential
microhydropower site include its power output, economics, permits, and water rights.
To see if a microhydropower system would be feasible, you'll want to determine the
amount of power that you can obtain from the flowing water on your site. This involves
determining these two things:
* Head—the vertical distance the water falls
* Flow—the quantity of water falling.
Once you've calculated the head and flow, then you can use a simple equation to estimate
the power output for a system with 53% efficiency, which is representative of most
Simply multiply net head (the vertical distance available after subtracting losses from
pipe friction) by flow (use U.S. gallons per minute) divided by 10. That will give you the
system's output in watts (W). The equation looks this:
net head [(feet) Å~ flow (gpm)] ÷ 10 = W
To help make a microhydropower system more feasible, it's a good idea to make every
effort to reduce your electricity usage.
If you determine from your estimated power output that a microhydropower system
would be feasible, then you can determine whether it economically makes sense.
Add up all the estimated costs of developing and maintaining the site over the expected
life of your equipment, and divide the amount by the system's capacity in watts. This will
tell you how much the system will cost in dollars per watt. Then you can compare that to
the cost of utility-provided power or other alternative power sources.
Whatever the upfront costs, a hydroelectric system will typically last a long time and, in
many cases, maintenance is not expensive. In addition, sometimes there are a variety of
financial incentives available on the state, utility, and federal level for investments in
renewable energy systems. They include income tax credits, property tax exemptions,
state sales tax exemption, loan programs, and special grant programs, among others.
Permits and Water Rights
When deciding whether to install a microhydropower system on your property, you also
want to know your local permit requirements and water rights.
Whether your system will be grid-connected or stand-alone will affect what requirements
you must follow. If your microhydropower system will have minimal impact on the
environment, and you aren't planning to sell power to a utility, there's a good chance that
the process you must go through to obtain a permit won't be too complex.
Locally, your first point of contact should be the county engineer. Your state energy
office may be able to provide you with advice and assistance as well. In addition, you'll
need to contact the Federal Energy Regulatory Commission and the U.S. Army Corps of
You'll also need to determine how much water you can divert from your stream channel.
Each state controls water rights; you may need a separate water right to produce power,
even if you already have a water right for another use.
For more information, see state and community codes and requirements for small
renewable energy systems.
* Microhydropower System ComponentsMicrohydropower System Components
Run-of-the-river microhydropower systems consist of these basic components:
* Water conveyance—channel, pipeline, or pressurized pipeline (penstock) that
delivers the water
* Turbine, pump, or waterwheel—transforms the energy of flowing water into
* Alternator or generator—transforms the rotational energy into electricity
* Regulator—controls the generator
* Wiring—delivers the electricity.
Head is the vertical distance the water falls. Higher heads require less water to produce a
given amount of power.
Commercially available turbines and generators are usually sold as a
systems require careful matching of a generator with the turbine horsepower and speed.
Many systems also use an inverter to convert the low-voltage direct current (DC)
electricity produced by the system into 120 or 240 volts of alternating current (AC)
electricity. (Alternatively, you can buy household appliances that run on DC electricity.)
Whether a microhydropower system will be grid-connected or stand-alone will determine
many of its balance of system components.
For example, some stand-alone systems use batteries to store the electricity generated by
the system. However, because hydropower resources tend to be more seasonal in nature
than wind or solar resources, batteries may not always be practical for microhydropower
systems. If you do use batteries, they should be located as close to the turbine as possible
because it is difficult to transmit low-voltage power over long distances.
Reduce Your Electricity Use
Finding ways to reduce your electricity use can help lower your electricity costs and
You can also learn how to read residential electric meters.
Power Conditioning Equipment for Stand-Alone Systems
Most electrical appliances and equipment in the United States run on alternating current
(AC) electricity. Virtually all the available renewable energy technologies, with the
exception of some solar electric units, produce direct current (DC) electricity. To run
standard AC appliances, the DC electricity must first be converted to AC electricity using
inverters and related power conditioning equipment.
There are four basic elements to power conditioning:
* Conversion—of constant DC power to oscillating AC power
* Frequency of the AC cycles—should be 60 cycles per second
* Voltage consistency—extent to which the output voltage fluctuates
* Quality of the AC sine curve—whether the shape of the AC wave is jagged or
Simple electric devices, such as hair dryers and light bulbs, can run on fairly low-quality
electricity. A consistent voltage and smooth sine curve are more important for sensitive
electronic equipment, such as computers, that cannot tolerate much power distortion.
Inverters condition electricity so that it matches the requirements of the load. If you plan
to tie your system to the electricity grid, you will need to purchase conditioning
equipment that can match the voltage, phase, frequency, and sine wave profile of the
electricity produced by your system to that flowing through the grid.
A series of requirements for grid-interactive inverters have been developed by
Underwriters Laboratories, a leading safety-testing and certification organization. These
requirements, referred to as UL 1741, apply to power-producing stand-alone and grid-
connected renewable energy systems. Either you or your installer should contact your
power provider to see which models they accept for grid-connection; most simply require
a grid-interactive inverter listed by an organization such as Underwriters Laboratories.
The cost of inverters is affected by several factors, including:
* Quality of the electricity it needs to produce
* Voltage of the incoming current
* AC wattage required by your
* Power required for the starting surge of some equipment
* Additional inverter features such as meters and indicator lights.
When you size your inverter, be sure to plan for any future additional loads you might
have. It is often cheaper to purchase an inverter with a larger input and output rating than
you currently need than to replace it with a larger one later.