Discussions and Suggestions on Configuring a Power System.
First lets determine your power and living requirements;
Determine which appliance you want to keep operational during a power outage.
Personally I would want to keep the lights, refrigerator, telephone accessories, heater
fans (using gas, propane or oil fired heaters), television, stereo, computer, garage door
opener, microwave, hair dryers, and electric blankets operational. Also any medical
equipment and/or water pumps. I would make a list of all the appliances and their load
ratings in either watts or amps and make note of voltage (keep everything consistent).
This list would provide an idea of how large of a generator or inverter I would require. I
would make some assumptions that not all the lights will be turned on at the same time in
order to reduce my generator size. I would assume that all appliances, which are
automatically cycled, could come on at the same time, example refrigerator, heater fans,
and water pump.
The all-electric homes pose special consideration due to the very heavy power demands
from the all electric: water heater, oven/range, space heaters or HVAC, and clothes dryer.
And it is typical that all these devices could operate at the same time.
Next I would make a list of appliances of lower priority, here is where I could wait
for available power in order to use them, examples include the shop saw, air-conditioner,
electric spa heater, vacuum cleaner, and etc.
Some things to consider for managing the all electric home:
Use a heat exchanger on the exhaust of the generator (AC or DC) and recycle this energy
for heating the hot water. You can easily get 5 kW/hr (17,000 BTUs) of waste heat from the
exhaust in generating 6 kW/hr of electricity. If you recycle the heat from the
engines radiator you will be able to capture another 17,000 BTUs (total of 34,000
BTUs of heat). The reclaimed heat may be sufficient to heat both the home and hot water.
If there is sufficient interest Polar can provide heat exchanger kits for the AC
If the electrical load on the AC generator drops so will the amount of heat from the
exhaust and radiator, therefore a small electric heater may still be required to load the
The DC generator can be fitted with a heat pump, the heat pump while providing heat or
air conditioning loads the engine providing more available heat from the exhaust and
A heat exchanger can be fitted to the clothes dryer so this appliance can also operate
off the waste heat from the generator.
The electric oven and range could be converted to propane if gas service is not
available. It can operate from the same propane tank that fuels the generator set. In my
opinion gas does cook better than electricity. Many people are planning to use wood stoves
(make sure they are legal in your area).
Using electricity to produce heat has never been as efficient as using fuel (natural
gas, propane, or fuel oil).
Installation considerations (more on this subject to follow at a later date):
Fuels must not be located inside the home, basement, or garage.
A sound attenuated enclosure adds considerable cost to the generator set. Operating the
generator in the garage or basement increases the risk of fire or carbon monoxide
poisoning in the event of a fuel or exhaust leak. The exhaust must be directed so the wind
does not blow the gases into your or your neighbors home.
The minimum noise specification for an enclosed generator set (AC or DC) should be 65
to 68 dBA at 7 meters. Above 70 dBA the generator is unpleasant and stressful to you and
With either the inverter system or AC generator a transfer switch is required to
disconnect the house from the utility grid. If you do not disconnect, your small power
source will then be connected to all the other homes (overload!) or if the powers comes
back on your AC generator can be damaged (some inverters are protected). More on this
You must investigate the building and local community codes for the permitting process
and regulations. Generally the smaller generators have less restrictions.
Operational considerations using an AC generator:
To effectively keep your space heater and/or refrigerator operational throughout out
the night or day the (AC) generator will have to operate continuously. The increased run
time creates significant engine maintenance. Most homeowners are unable to provide this
level of mechanical maintenance and therefore the generator become less reliable and prone
to quit when its needed.
Operating a generator with a small electrical load is not fuel-efficient. With AC
generators it will not be practical to start and stop the engine every time an appliance
needs to cycle on. This is better suited for an inverter.
Engine and Alternator life
The more hours the generator runs the shorter its life span and more it costs to
generate the electricity.
Most all engines used for these small (less than 20 kW) generators have a design life
of about 1,000 to 2,000 hours burning gasoline. You can overhaul the engine a few times to
extend the life to between 3,000 to 5,000 hours. Propane and natural gas fuels greatly
extend engine life providing that the conversion is done right and the engine is de-rated
to allow for the higher combustion temperatures of propane and natural gas. In my opinion,
there is little data on the operational life of smaller engines using gas as a fuel.
Diesel engines will have a longer design life typically in the 5,000-hour range and with
over-hauls lasts around 15,000 hours.
Some manufactures such as Lister Petter have converted diesel engines over to spark
ignited gas engines. These engines are very heavy duty and offer life spans in the
40,000-hour range. These engines are expensive to purchase but the cost of operation is
Most AC alternators have an average life span of 3,000 to 5,000 hours before requiring
a re-build. The most common failure problems occur in the rotor. The centrifugal forces
and vibration tend to pull apart the wires and other components located in the rotor.
A well designed DC generator using a solid rotor designs should last a very long time
(20,000 to 40,000 hours). The limiting factors are abrasive particles in the air blown
against the stator windings eventually wearing down the insulation, high temperature
ambient causing the insulation to degrade, or a catastrophic engine failure causing the
rotor to be slammed against the stator.
If my home were serviced with propane I would use a propane-fueled generator with
gasoline as a backup fuel. My house does have natural gas service so this would be my
primary fuel and I would probably use propane as a secondary fuel (I use propane for my
barbecue). In California, if there was an earthquake the natural gas lines are
automatically shut off, also a fire, flood, or landslide can shut off gas service. Still
another concern is if the Y2K event did shut down power and if a large number of
individuals used natural gas, then the existing pipe lines may not be able handle the
increased demand. A second fuel source is recommended. The second source would be either
propane or gasoline. Propane would be cleaner burning and reduces engine maintenance, but
during an electrical shortage there may shortages in propane service. I guess the solution
would be having the capability of burning all three fuels. Burning multiple fuels adds to
the cost of the generator.
Polar can provide engines to burn: natural gas, propane, diesel, kerosene, alcohol,
fuel oil, but not all at the same time or in all combinations.
Energy efficiency in a very important factor in system selection not only to reduce
operational cost but also to reduce the amount of fuel stored on site and the number of
AC verses DC Generator System
The lowest cost technology to purchase is the AC generator readily available from
Honda, Onan, Kohler, Generac, etc. Presently it costs more money to manufacture a DC
generator than an AC (due to the cost of magnets) and adding a battery and inverter
further increases the cost. However, if the generator is to see significant use then the
DC generator system may offer an overall cost advantage.
The concern over using an AC generator is being able to maintain proper engine speed.
If the engine develops a simple mechanical (carburetor) or electro-mechanical (spark plug,
governor) problem the engine speed will change and cause the electrical power (frequency
and voltage) to become unsuitable causing damage to certain appliances. The majority of
small generators are used for temporary applications and typically power lights, power
tools, and other devices that can tolerate a wide swing in voltage and frequency. The
concern is the unattended operation (i.e. at night) of the refrigerators, fan motors, and
any electronics left on such as computers, televisions, and stereos, etc. If there is a
problem, its important to shut down the generator as soon as possible. The are
automatic devices which monitor the generator voltage and frequency and will disconnect
the generator set via the transfer switch should a problem arise. These protection
features are important, but the end result is that if the problem arises you are without
power until the mechanic gets there.
The DC generator system consists of: Battery, inverter, transfer switch, and DC
generator. Some inverters have the transfer switches built in. The battery stores the
energy then supplies it to the inverter to convert from DC power to AC power. The DC
generator charges the battery to replenish the energy. The system has the following
An inverter can silently deliver power day or night. Storing (DC) energy in a
battery, then having the inverter power the AC appliances as they are required or cycle on
solves the problem of having to run and AC generator 24 hours a day. It makes no sense to
run a generator overnight so that the heater fan and controls can operate, refrigerator
can cycle, and your VCR can record a late night movie (the light electrical load wastes
fuel and increases engine maintenance). A good inverter/battery is more reliable than any
engine and can provide AC power in an instant.
A battery can store the electrical energy produced by a DC generator directly. If the
engine develops a problem causing a change in its speed there is no effect on the battery,
nor the inverter and appliances. Speed regulation in a DC generator is not very important
and this reduces your maintenance and repair.
Whether you chose the AC generator or DC generator and inverter based system the Y2K
event will be expensive to prepare for. However, if the generator could generate power at
a cost lower than the utility company, and/or if the utility company provided incentives
for customers to generate their own power during peak demand periods then the installation
of a power system is more economically justified.
A micro cogeneration unit can consist of:
Engine converts fuel to mechanical energy.
Alternator, converts mechanical energy into DC electricity.
Heat exchanger, to recover heat from the engines exhaust.
Heat exchanger, to recover heat from the engines radiator.
Belt-driven refrigeration compressor, to provide air-conditioning and heating (heat
Heat pump heat exchangers, to provide space heating and air conditioning.
Auxiliary heat exchangers, for hot water, heating swimming pools and spas, etc.
Polar has build (and is under test) micro-cogeneration units which consists of: a
generator which produces DC power and makes use of the engines waste heat for
heating and hot water. Coupled directly to the engine is a heat pump to provide
air-conditioning and/or additional heat for hot water and space heating. With an engine
driven heat pump one Btu of fuel can generate a total of 1.3 to 2 Btus of heat
depending on climate.
Using the AC generator to power a heat pump or air conditioner:
It is not energy efficient to use an AC generator to power an electric air-conditioner.
Consider the overall system:
The fuel is converted into mechanical energy via the engine at a 70 to 80% loss in
energy (20 to 30% efficiency).
The mechanical energy is converted into electrical energy at a 20 to 40% loss (contrary
to advertising most AC generator efficiencies are 80 to 60%).
The electrical energy is now reconverted to mechanical energy using the refrigeration
compressor motor at a loss of 30 to 40% (the sealed PSC motors are only 60 to 75%
efficient and the three phase motors are 70 to 80% efficient).
If we eliminated the generator and motors energy losses we could save
considerable fuel and be able to use smaller engines.
Here is the math:
With a direct drive air-conditioner using a 25% efficient engine:
- 75% of the fuel energy becomes heat and 25% is converted to mechanical energy for direct
- To produce 12,000 BTU of air conditioning for one hour will consume 0.473 lbs. of
With the most efficient AC generator, engine, and electric air-conditioner:
- 75% of the fuel energy becomes heat and 25% is converted to mechanical energy.
- Of the 25% mechanical energy only 20% gets converted into electricity using an 80%
- With 20% of the electrical energy only 16% gets converted back to mechanical energy
using an efficient 80% compressor motor (three phase).
- To produce 12,000 BTU of air conditioning for one hour will consume 0.738 lbs. of
propane, this is 1.56 time more fuel than the direct drive system. Over a week in the
summer this amounts to a very considerable fuel difference.
The efficiencies of a DC generator/inverter system verses an AC generator are:
The conversion of DC power into AC represents an extra power conversion step. However
the efficiency of a good inverter (90 to 94%) and DC generator (80 to 85%) should equal
the efficiency of a good AC generator (70 to 80%). Some may argue that there are more
efficient AC generators available but the DC generator still comes out ahead in that the
speed can change to match the load saving fuel. Most AC generators can not take advantage
of variable speed to improve fuel efficiency. Others can argue that there are variable
speed AC generators available, but most of these products are DC generators with an
inverter built in.
The efficiency loss in a DC generator and inverter system is in the battery
charge/discharge cycle. A battery is only 80% to 40% efficient depending on the age of the
battery and charge cycle method. I have heard arguments from engineers claiming that
batteries are 90 to 100% efficient and their reasoning is that you can put in 100 amp
hours in charge and get out 100 amp hours to operate a load (discharge). The problem with
this argument is that you have to charge the battery at a higher voltage than it
discharges at. For example a 12-volt battery charges for one hour at 14.4 volts and
discharges at 12.2 volts, we multiply the difference of 2.2 volts times the 100 amps to
find a loss of 220 watt hr. In addition, we all know that as a battery ages it takes more
energy (volts X amps X time) to recharge the battery.
To maximize system efficiency we need to minimize the depth of the charge/discharge
cycle of the battery. Let the generator cycle on to power the long run and heavy power
loads and let the generator stay off when powering the short duration loads such a 5
minute microwave operation or light electrical loads such as a small stereo set.
What type of battery to use:
My first choice is to use the same type of battery that is used in electric forklift
trucks. These batteries are proven to last a long time under daily cycling. Just ask one
of the operators at one of the warehouse stores. These batteries were designed to cycle
once a day or every other day. Not cycling these batteries actually shortens their life.
There is an attraction to use the sealed lead acid batteries because they do not
require the maintenance of having to add water. I do not recommend these batteries because
of their expense and they are prone to failure in warm climates. These batteries are
better suited for use as standby batteries in UPS operations inside air-conditioned
Installation of batteries is very critical due to the possibility of leaking acid and
that during the charge cycles the battery releases hydrogen and oxygen gases. This is true
for all chargeable batteries including starved electrolyte and valve regulated (sealed
type) batteries. I recommend a separate and well-ventilated enclosure next to the
generator. The important factors for enclosure design is to: restrict access to children
(lockable), have a plastic bottom for a containment of spills, keep the solar radiation
from building up heat inside, allow the batteries to cool during charging, and provide
convenient access for adding water to the cells. Polar does manufacture battery boxes.
Eventually I see the use of the new high performance batteries presently being
developed for electric car applications replacing the forklift type batteries. I also
foresee these DC generator systems being use to recharge the electric car batteries and at
the same time cogenerating heating and air conditioning.
Solar and Wind Power:
Solar photovoltaic (PV) arrays produce DC power; wind generators can produce AC or DC
power. The DC generator with inverter and battery provides a system that allows simple
integration of wind, solar, and hydroelectric technologies.
For the past 20 years the photovoltaic industry (and Department of Energy) has been
predicting (or promising) low cost photovoltaic product. 20 years ago the cost was about
$15.00 per peak watt (ppw) with the stated goal of $.75 ppw. Current costs are in the
$5.00 to $6.00 ppw, retail. I foresee the cost dropping to around the $3.00 ppw in the
next 2 to 4 years and I doubt that the cost will ever come close to $.75 ppw.
Wind generators are only practical for farms and homes on large open areas. They
produce noise, requires open space, and their high towers are often unsightly.
If my house were not connected to the utility grid, I would install a 500 to 1,000 pw
PV array in addition to a DC generator. The DC generator would provide the bulk charge to
the batteries early in the morning. The PV array would provide the finishing charge in the
afternoon. The arrangement will save fuel and engine maintenance. The PV array also to
keeps the batteries charged when on vacation so the generator would not have to run. As
the cost of PV became cheaper, I would add additional PV modules to the house and become
less dependent on fuel.
What about fuel cells and other technologies?
Fuel cells is a technology which produces DC power by combining two or more chemicals
together through a catalyst. Hydrogen and oxygen are the two most promising (and popular)
chemicals. What keeps the technology from being commercialized now is the process of
generating the hydrogen from the hydrocarbon fuels such as natural gas and propane. Due to
the complexity of the fuel conversion process there will be a minimum practical size for
economic commercialization. This minimum size maybe 10, 20 or 100 kW. If hydrogen could be
delivered to the users then the on site fuel conversion process would unnecessary. The
fuel cell would then be very simple in construction and without minimum size
restriction. Hydrogen is the cleanest burning of all fuel but there are many individuals
who fear hydrogen as a fuel and oppose its application. There are technologies available
to store and transport hydrogen but the other fear is product liability. With out present
legal system it even would be impossible to introduce gasoline as a new fuel.
Personally I feel that fuel cell technology is 10 to 15 years off into the future. The
important point to note is that the fuel cell produces DC power, so an investment into a
DC generator system would mean that if fuel cells for the home are commercialized then
only the DC generator get replaced after it wears out. The inverters, batteries, and even
the heating system remains in place. The fuel cell will also produces waste heat that can
be used for heating.
Turbo alternators are practical in sizes of 20 kW and larger. The problem with turbines
under 20 kW is poor efficiency due to inability to improve upon the turbine blade
clearances as the unit is reduced in size. Turbines are not very practical using low
pressure natural gas, the cost of equipment to compress the gas so the it can be injected
into combustion chamber is expensive and can consume up to 10% of the electrical power.
The equipment required compressing the natural gas off set any advantage of size, noise,
reliability, and efficiency that a turbine might have to offer. It takes much less energy
and equipment to pressurize and inject a liquid that gas, therefore liquid propane,
alcohol, and diesel are good turbine fuels.
Turbines are better at producing DC power than AC. To produce AC requires a high-speed
gearbox that adds to cost, maintenance and lowers efficiency.
So far turbines are too expensive to own and operate.
Sterling engines are too expensive and complex to maintain.
Other than the technologies discussed herein I see not other near term technologies as
Where does Polar Power stand?
Polar has 20 years experience (since 1979) in designing and building DC generators,
inverters, and renewable energy systems.
We have manufactured micro-cogeneration (air-conditioning, heating, and electrical
power generation) systems in small quantities over the past 4 years. We have almost no
data on their financial impact. Once the systems get installed we have had no means to
collect data. Personally, I have no interest in calculated projections because of all the
use variables and other factors such as the regional variations in fuel quality and cost
verses the local utility costs. The use factors are considerable from region to region.
For example, I live near the ocean in Southern California, I have very little need for
heat and air-conditioning, and this is in high contrast to the needs of homes in the local
desert for heating and air conditioning, or the mountains for heating only.
There has been strong interest from the utility companies on these products. Polar will
be providing a micro-cogeneration system in the next few weeks to a utility company for
testing and financial analysis. It will be in a desert environment and I can keep you
posed as the information is received. Additional utility companies have contacted us for
product to test and evaluate.
Before purchasing a system I would contact the renewable energy department of my local
utility company. If there is no energy department try the sales office. My intention would
be to get financial and technical assistance. Be prepared for the run around. The goal is
to find out if the utility company will:
- Purchase the equipment for you then lease it to you over a 5 to 15 year period.
- Give you cash back incentives or discounts on your utility bill.
- Buy and install the equipment for you and use your home as study site.
- Discount your utility bill for generating your own power during their peak demand.
If you are able to reach an individual with intelligence and interest, their first
concern will be the effect our your equipment on their power grid. Utilities are generally
not interested in buying back electrical energy because they fear the quality of power and
the effect your equipment (or maintenance of the equipment) would have on the grid if
something should go wrong. The utility appears more supportive if you tell them you have
no interest in being connected to the grid while your are generating your own power (at
least for now).
The next organization I would contact is the state governments energy office,
renewable energy office and discusses your project and any response you might have
received from the utility company.
I would also try to gain help and support from friends and neighbors. After all I would
not want to be the only one on the block with electrical power.
I am sure that most people you contact at the utility company and State Energy office
will tell you that there will be no problem with power availability during the Y2K event
and they may be right. No utility companies or state agency will want to participate in a
program based on their potential failure to handle the Y2K event. Your point of focus
should be on backing up your utility power for any natural event (i.e. storm, earthquake,
etc.) and cogeneration of your own energy needs using clean burning gas.
What does Utility Deregulation have to do with the subject above?
Many individuals believe that quality of power service will degrade with deregulation.
Many in the utility industry are concerned about competition within their
"captive" markets from groups that can generate their own power at a rate lower
than what they can purchase. The utilities position could be to join in and help finance,
install, and maintain the equipment for the users and user groups.