Solar & Wind's Introduction To Remote Power Systems
1. The Cost Of A Remote Power System:
The cost of a remote power system depends primarily on how much
electricity you need. The
amount of electricity you need is called your load. If your remote power system has a
back up generator, the size of your load and the size of your solar and/or
wind system determine how much of the time your generator runs. Asking how much a remote power
system costs is similar to asking how much a car costs. The cost of a remote power system
varies all over the place from a few hundred dollars to $50 - $60,000 and
more. Most remote power systems cost $35,000 to $60,000.
Only: Cheapest initially,
but this option costs the most by far in the long run. One light bulb will require the
generator to be on and to be very inefficient. Generators require frequent
maintenance (oil and filter
change, check water, etc.) and eventually have high repair costs like
a car. Generators are also
very noisy, polluting -- and they eventually die. Solar modules will probably last
50 to 100 years!!!!
System: A generator with
inverter and battery bank. The
next least expensive option, but more expensive in the long run than a
mostly, or all, solar and/or wind system.
mostly with some solar or wind: More expensive initially, but less
expensive in the long run than option's A and B.
solar and/or wind with generator back up: Even more expensive
initially, but less expensive in the long run.
and/or wind only: The most expensive initially, but the least
expensive in the long run.
2. Comparing The Cost Of Line Electricity
With The Cost Of A Remote Power System:
When comparing the cost of
line electricity to the cost of a remote power system, remember to include
not only the cost of bringing in line electricity but also the cost of
monthly electric bills over several years.
When comparing the cost of mostly generator systems with a solar
only system, remember to include the cost of fuel, maintenance and
eventually a new generator. In
contrast to generators, solar electric modules are warranted for 20-25
years, they will probably last at least 40-50 years and possibly far
longer. They require no fuel,
little maintenance, do not pollute our air or result in nuclear waste, and
they make no noise.
3. Reliability And Owning Your Own
Remote power systems,
especially solar only systems, have become so reliable that they very
seldom are down. Often owners
of remote power systems have electricity while electric utility customers
do not. The owner of a remote
power system owns their own electrical power plant. A, for example, 15 year economic
comparison should consider the fact that after 15 years you will not only
save on electric costs, but you will own your own (if solar/wind) very
clean power plant.
4. Get Some Solar Now and Add Later?
can add more modules later as long as the wiring, disconnects, charge
controller, inverter and related system items are sized to accommodate
more modules later.
can be added to later, but the entire bank will only function as well as
the worst battery in the bank. So
adding batteries later is not a good idea.
to buy an inverter that will meet your needs several years from now. Generally speaking it costs a lot
more to add an inverter, or inverter modules, later.
Efficiency Appliances vs Larger Solar and, or Wind Electric System:
thousands of dollars can be saved by spending more money on high
efficiency appliances and less on your inverter, solar modules, wind
generator, batteries, and by reducing the size, wear, and run time on your
generator, if one is used. Load
A. Fill out a load sheet in order to
determine your load size. (Available from RMSI.) It is very common for purchasers of solar electric systems
to go back to their load sheets after finding out the cost of a solar
system large enough to supply the electricity demand on their first load
sheet. Solar electricity is
still initially much more expensive than utility line electricity. However, solar and wind electricity
not only enable us to live remotely, but to generate our own electricity
without polluting the air or creating nuclear wastes.
B. Use a solar or propane hot water heater,
propane or high efficiency electric refrigerator, and a gas range (without
an electric glow plug in the oven) in order to reduce the size of your
loads (all nonbattery clocks, VCR, TV, garage door opener, answer
machine, furnace transformer...). Switched
outlets can be used to eliminate most phantom loads. Furnace thermostats can be changed
to line voltage, or a relay can be used to keep the furnace transformer
from being on all of the time. If
the furnace transformer is on all of the time, this will cause most
inverters to be on all of the time, which uses a lot more electricity in
Consider replacing your blower motor with a high efficiency
blower motor if you have a forced air furnace. For example, GE makes the ECM
Programmable Motor that can improve your blower efficiency by 1/3 or more.
6. Mounting Methods For Solar Electric
ground mount on a pole, ground rack, or on a roof: A roof mount is generally the least
expensive, however it is important that the roof faces generally South.
The entire array will need to be removed and replaced when the roof is
re-roofed so it is recommended to install over relatively new roofing. Stationary top of pole mounting
should include manual adjusting of modules (2 times per year). Modules should be mounted on theft
7. Wire Sizing And Choosing A 12, 24 or
48 Volt System:
more voltage drop in a wire due to the resistance of the wire, the more
power lost. We recommend that
the wires in a solar or wind electric system be sized large enough so that
the voltage drop of the wires is 2% or less, and so that the over all
voltage drop of the entire system is less than 5%.
from a system voltage of 12 volts to 24 volts, or 24 volts to 48 volts,
reduces voltage drop in wires by 50%., and reduces the power loss in wires
by a factor of 4.
recommends using the following to choose a system voltage size:
If your long term system total watts is less than 1500 watts, then use a
12 volt system.
If your long term system total watts is less than 1500 - 3000 watts, then use a 24
If your long term system total watts is less than 3000 + watts, then use a 48 volt
8. Solar vs Wind Economics:
Solar modules are warranted for 20-25 years and will last
far longer, although with some loss in output. Wind turbines need some
maintenance. Most residential
wind turbines are lightweight, and are likely to last 5-10 years before
they will need new bearings. The
heavier built, more expensive wind generators (which are far less common),
are likely to last at least 20 years before needing to be overhauled and
given new life. One older
heavy weight wind generator lasted 60 years.
(See Home Power Magazine, #90, p 64.)
Which is more economical solar electric, or wind electric,
depends on the climate, on the local wind and sun conditions, the amount
of turbulence and the size and quality of the wind generator. In sunny climates such as the
Southwestern US, solar is generally more economical than small scale wind. Further North in say Montana or
Canada, wind is likely to be more economical than solar. Wind is also more likely economical
if the electrical need is large. Generally the larger the wind turbine the
lower the cost per watt.
In considering a wind system it is important to de-rate for
elevation, turbulence, properly analyze wind speed, adjust the wind speed
for the height of the tower, and then calculate the actual electrical
output per year. The rated output at an arbitrary and high wind is not a
good method by which to compare wind turbines. Use
the watts produced per year at the estimated average wind speed of your
site from wind maps and local conditions. Wind systems have the disadvantage
of having more maintenance and repairs than solar; and wind systems are
less modular, making it more difficult to exactly size your system. The labor to install most wind
systems is also likely to be more than for an equivalent solar system.
A hybrid solar/wind system can take advantage of both the
wind and the sun, so that when you are short on one, the other is likely
to be present. Thus a hybrid
system can be sized a little smaller than a non-hybrid system. But a hybrid system may cost more
to purchase and install than either a comparable solar only, or wind only,
system. It may cost less to
purchase a few more batteries to get you through the times when there is
too little sun or wind. But
batteries have to be replaced. Each
situation has to be analyzed in order to determine whether a solar only, a
wind only, or a hybrid system is most economical.
9. Choosing An Inverter: Modified Sign
Wave vs Full Sine Wave:
wave inverters provide electricity that is basically the same as utility
supplied electricity. Sine
wave inverters therefore supply electricity that is compatible with
virtually any appliance or electrical device. Sine wave inverters do cost
more than modified sine wave inverters.
Modified sine wave inverters are becoming less and less popular. The following is a list of the
electrical devices that can have difficulty running on electricity
produced by modified sine wave inverters:
fluorescent lights (Phillips and electronically ballasted lights like the
Osram EL-15 seem to work best.)
radios, especially AM
Macintosh Computers are likely to over heat the power supply (except some
Note: Most computers work just fine on either a good quality modified sine
wave inverter, or a full sine wave inverter.
But occasionally a computer will crash (need to be rebooted) when
the source of electricity is being switched from an AC source (such as
utility or electric generator) to the inverter. A stand alone solar system sized
large enough to operate year round without the need for a back up power
source would, of course, never encounter this problem.
power tool which employs solid state power or speed control. The components of some of these
tools can be destroyed if powered by electricity supplied by a modified
sine wave inverter.
washing machines with electronic timers.
stereo and audio equipment.
new furnaces because they have microprocessors (computer chips) in their
10) X 10
home automation systems.
the Trace SW Inverters, which are a full sine wave inverter in which the
sine wave is made up of very tiny steps, have problems running some
appliances. The appliances
which can have a problem with the electricity produced by full sine wave
Trace SW Inverters are:
new furnaces because of the microprocessor in the furnace control.
Note: In the event that a furnace does not operate properly, on either a
modified sign wave inverter or a full sign wave inverter, the electricity
to the furnace controller can be modified further by installing a power
conditioner (also called a constant voltage transformer) on the line to
the furnace controller only.
10 home automation systems.
advantages of Trace SW Inverters:
Trace SW Inverters include gen start as a standard feature. Without gen start an additional
control will be needed to auto start.
Trace SW Inverters also work with smaller generators than modified
sine wave inverters, have a 60 A transfer relay, and include some
metering. There is also a
remote control option.
of the engineers who used to be with Trace Engineering (now Xantrex) have
started their own company named Outback Power. Their inverters are in many ways
superior to the Trace/Xantrex inverters.
The Outback Power Inverters are, for example, more modular. They can be stacked to create at
least 14 KW. Their inverters
are generally more efficient, handle surge better, and are fairly
economical. Therefore, we
recommend Outback Power Inverters.
10. Charge Controllers:
Charge controllers prevent the batteries from being over-charged and
regulate the way in which the batteries are charged. Wet cell lead acid batteries
accumulate less sulfation and thus last longer if they are charged to 15.3
Volts in a 12 Volt system, 30.6 Volts in a 24 Volt system, and 61.2 volts
in a 48 Volt system. It may
not be economical, however, to charge your batteries to this degree if you
are using a generator for much of your charging. In most situations it is best to
use a charge controller that has a variable set point that can be set high
enough to meet these requirements, or close to them. (See Home Power Magazine,
#89, p 120.)
Some new charge
controllers such as those made by Solar Boost and Outback Power use
maximum power point tracking. This
new technology converts wasted voltage to amperage increasing the output
of a solar array by roughly 10-30% or more depending on the time of year. The greater percentage savings is
in the winter. Winter is when
more electrical output is generally needed.
Most charge controllers also have pulse with modulation that is
also battery friendly.
Low voltage disconnect
(LVD) prevents the batteries from being discharged too far. Generally even a high quality deep
cycle battery, such as an L-16, should generally only be discharged 80%.
Batteries will last a lot longer if they are discharged regularly only 25%
- 50%. All solar electric
systems, except possibly some small one module systems, should have both a
charge controller and a low voltage disconnect. Many charge controllers now have
LVD built into them, but the voltage setting is usually too simple to be
very effective at knowing what the state of charge of the batteries
actually is. Thus the
manufacturer is forced to make the disconnect point far lower than is
often good for the batteries. Most
good inverters have a far more sophisticated and accurate LVD than the LVD
on most charge controllers. Battery
banks lose capacity at low temperatures and over time, so that should be
(very short life), marine (short life), golf cart (5-8 years), deep cycle
L-16s (7-10 years), industrial (10-30 years).
give off a gas and in very rare instances can explode. Therefore, be sure to locate the
batteries separate from the inverter and charge controller. The batteries must also be vented
(unless the battery box is out doors.)
battery bank with a large number of smaller batteries with small cells is
more likely to have problems with a bad cell than is a battery bank with
larger batteries and larger and fewer cells.
from the battery bank must be from opposite most distant terminals or the
end batteries will wear out sooner than the other batteries. It is also important to tape the
inverter to battery cables together where possible.
conditioners have a sweep pulse technology designed to dissolve sulfation
in lead-acid batteries. There is some evidence that the conditioners
really work. More testing is
needed, but many companies are recommending battery conditioners,
especially on larger battery banks.
12. Deep Well Pumps: (We
generally recommend AC deep-well pumps since they last longer than DC
pumps, plus pump installations require special equipment and skills.)
well pumps in the past were a problem for solar systems. Not only do most deep well pumps
use a lot of electricity due to over-sizing and placing them deeper in the
well than is needed, but deep well pumps also have an even larger need for
electricity when they first start. The
latter is called the electrical surge.
Inverters frequently must be oversized in order to be able to
handle the large surge of some pumps.
Most pump installers install 240 Volt AC pumps due to their
efficiency and so that smaller wires can be used. However, solar/wind inverters are
generally 120 volts. When 240
Volts are needed a step up transformer is used, or two inverters are
stacked. The stacking of
inverters can be done more economically now that Outback Power produces
inverters that are modular.
speaking high efficiency deep well solar water pumps run off of DC
electricity and are in some ways more compatible with solar systems. Since solar water pumps consume DC
electricity they don't have to draw electricity through an inverter. Thus less electricity is lost due
to the inefficiency of the inverter. Electricity
is supplied directly to the pump from the batteries. This means that a
smaller inverter can be used, and that if an inverter ever fails, then the
water pump will still run off of the batteries, assuming the batteries are
still being charged even though the inverter is not working, i.e., by the
sun or a separate charger. Solar
pumps generally do cost more than standard AC pumps, but the over all
system may cost less using a solar pump rather than a standard AC pump if the well is real close
and a low volume producer.
deep well pumps can also be used economically, especially if they are 120
volts and 1HP or less (Note: Three
wire AC pumps plus ground require less electrical surge than two wire plus
ground.) Larger, even 240
volt, AC pumps can be used with solar systems, however, a step up
transformer or two inverters will be required, or water can be pumped into
a cistern manually once a week, or so, using a generator. A DC pump can then be used to
pressurize. (Note: Avoid AC deep well pumps that have
no control above ground. When
the control goes bad the pump will have to be pulled.)
13. Things To Consider When Selecting A
Gasoline, Propane or Diesel Driven Electric Generator:
derate 3 ½-4% depending on manufacturer for every 1,000 ft above 500 ft
in altitude. The larger the
generator the less time it will be on.
Size an air-cooled generator so that it does not run for more than
roughly four hours at a time. Liquid
cooled generators can run for days without stopping at partial load, but
they should only be run for a few hours continuously at full load. Size your generator large enough to
simultaneously charge your batteries and run your loads.
B. Quality\longevity: For example, water cooled
generators usually last 2-3 times as long as air cooled, 1800 RPM
generators will last much longer than 3600 RPM generators, and propane
fueled generators will last far longer than gasoline fueled generators.
start and auto choke.
the generator produce full or only half power when it is putting out
120V? Most small
generators and lower quality generators produce only half their power when
putting out 120V. But most
inverters are charged using 120V electricity. When running a 120 V line
only, can the generator be balanced.
must have a large fuel tank (usually propane or diesel) in order
for your generator to operate automatically.
of the electricity produced. Does
the generator produce electricity that is very close to 60 cycles and the
Availability of a repair shop that will repair your
14. An Example Of The Maintenance Required
On One Of The Highest Quality Generators On The Market:
A. A Kohler 12 KW
Generator (gasoline fired) needs to have the oil and oil filter changed,
water checked, etc. every 50-75 hours of run time. If the generator runs six hours per
day on average, that means changing the oil, oil filter, etc. every 1 ½ -
2 weeks. If a generator runs
three hours per day on average, then the maintenance is every 2-3 weeks. (The time between maintenance will
be significantly greater if the generator is run on propane, and if the
oil used is a high quality synthetic oil such as Amsoil.)
B. Major repairs are
likely to be required on this excellent quality Kohler water-cooled
generator every 4,000 -5,000
hours assuming the unit is well maintained, and, of course,
depending on how many hours a day the unit runs. If the generator runs four hours
per day on average, and if the unit is well maintained, then major work would need to be done on the unit
every approximately three years. (This
is not guaranteed. This is just a
rough average based on talking with a Kohler Service Manager.) If this generator is not well
maintained, then it could need major work in less than six months. (If the
fuel used is propane, and if the oil used is a high quality synthetic,
then the life of the generator will be much longer, possibly even twice as
long or more.)
generators are air-cooled and include far less quality than the above
liquid cooled generator. So
most generators will require repair much sooner than the above generator.
only listed equipment and materials (when available) and pull a permit.
you, or your installer has questions, talk to your inspector prior to
purchasing and installing equipment so as to avoid problems later.
primary reason for the electrical code and inspectors is safety. Purchasing and installing a solar
electric system that meets code has the added advantage of making it
easier to get insurance with some insurance companies, and of selling the
three wire circuits from any house using an inverter system.
The first step in sizing a system, whether it is a
solar system or a generator only system, is to fill out a RMSWI load
A Rocky Mountain Remote Power Load Calculation Sheet
should have accompanied this Introduction.
If you need a load sheet contact:
Mountain Solar & Wind, Inc.
3228 N. Nevada Ave.
and we will provide you with one. Once you have filled out the load
sheet, mail, fax, or email it to RMSWI and we will assist you with the
design and pricing of your system.
power generation Systems are made up of interconnected components, each
with a specific function. One of the major strengths of PV systems is
modularity. As your needs grow, individual components can be replaced or
added to provide increased capacity. Although the selected components will
vary depending on the applications, PV systems generally conform to the
schematic shown below. What follows is a brief overview of a typical PV
Array - The
solar array consists of one or more PV modules that convert sunlight into
electric energy. The modules are connected in series and/or parallel to
provide the voltage and current levels to meet your needs. The array is
usually mounted on a metal structure and tilted to face the sun.
Controller - Although
charge controllers can be purchased with many optional features, their
main function is to maintain the batteries at the proper charge level, and
to protect them from overcharging.
Bank - The
battery bank contains one or more deep-cycle batteries, connected in
series and/or parallel depending on the voltage and current capacity
needed. The batteries store the power produced by the solar array and
discharge it when you need it.
Inverter - An
inverter is required when you want to power AC devices. The inverter
converts the DC power from the solar array/batteries, into AC power.
DC Loads - These
are the appliances (such as lights or radios), and the components (such as
water pumps and microwave repeaters), which consume the power generated by
your PV array.
Balance of System - These components provide the interconnections and standard safety
features required for any electrical power system. These include: array
combiner box, properly sized cabling, fuses, switches, circuit breakers