New technology to save your Diesel
Diesel Battery Hybrid System
Where more than a few kWh/day is required, diesel/battery
hybrids are currently the most reliable and cost
effective source of power. Solar and other
renewable inputs are readily incorporated into
these systems and this is often done.
Technology originally developed to optimise diesel
generator performance in village and community sized
power plants is now available with a price and performance
benefits to suit the individual homestead.
The underlying principal is that the generator
now need run only for typically about six hours a day, with
240 volt power being provided the rest of the time by the
inverter which draws its power from a specially designed
battery bank. Each day the battery is recharged
when the generator runs.
The microprocessor controls in the inverter ensure
that the generator always runs optimally loaded. It runs
for just sufficient hours each day to ensure the battery
is adequately recharged. The total amount of electricity
consumed remains the same - the savings come from
reduced generator maintenance and lower fuel costs
because the diesel is always optimally loaded.
The diesel/battery hybrid power system as it has
become known is made up of a diesel genset, battery bank
and an interactive inverter. The interactive inverter
handles the flow of electricity between genset, battery
and loads. The inverter also contains all the computer controls
for the automatic scheduling of generator operation and
Solar power or a wind turbine can be readily
incorporated if desired. Their inputs will result in
less generator run time giving a reduced dependence
on the diesel fuel supply. The inverter is able to provide
power to supplement that of the genset, meaning that it
is no longer necessary to size the generator to meet peak
loads. It is this feature that characterises the "generator
interactive inverter". The cost of a system will
depend on the load size, battery capacity and degree of
Diesel/Battery Hybrid addittional notes:
Diesel/battery hybrid systems are computer controlled.
The computer forms part of the Trace interactive inverter.
They are capable of very flexible operation depending on
how they are programmed. Some of the operating characteristics
are summarised in this section.
The maximum loading on the generator can be selected. Usually
this is chosen as the optimum load, being 80% of the nominal
rating. The inverter will try to hold the generator load
at this level by balancing the battery charge/discharge
rate and the appliance loading.
The generator can be programmed to automatically
start or stop according to a variety of criteria including
time of day, appliance loadings and battery state of charge.
Typically during periods of low loads all power is provided
by the inverter from the battery. This may be as much as
18 or even 20 hours per day, depending on the application.
The inverter will allow the battery to discharge to 50%
depth of discharge. The choice of battery size is quite
flexible. The larger the battery, the less frequent will
be starting of the generator just for recharging and it
will in general last longer before it needs to be replaced.
Hence in sizing the battery, one needs to consider the trade
offs between cost, life expectancy and generator run frequency
according to the demands of the application.
Training and Support
We usually find that it takes some time for our customers
to become completely familiar with their system. Explaining
the system once to the customer at the time of commissioning
and leaving them with the 60 page manual is not sufficient.
It is sophisticated and unlike anything they have had to
deal with before.
Planetary Power adopts a two stage approach to training
and support. Firstly we encourage the customer as far as
he/she is able to be present and actively participate in
the installation and commissioning, when the operating parameters
are decided on and programmed in. Secondly we provide ongoing
telephone and email support. This is provided for as long
as is necessary. The emphasis is on giving the customer
the confidence and skills to operate and maintain the system
for themselves. We are proud of our record in this area
and have maintained contact with nearly all of our customers
even years after the original installation.
The system should be checked periodically to ensure that
it is operating satisfactorily. Particular things to check
for are that the battery connections are clean and tight
and that the electrolyte level in the batteries are adequate.
A monthly check will be sufficient. The inverter can be
programmed to automatically start the generator and to provide
an equalising charge to the batteries after a period of
inactivity. This is known as the exercise period and is
usually set at between 21 and 30 days. Planetary Power can
provide twice yearly scheduled maintenance for your system.
us for details and current rates.
Operation In our experience, once the system has been initially
adjusted and commissioned the only significant operational
problem has been a failure of the inverter to synchronise
with the diesel generator. In each case this has been due
to the generator output lying outside the acceptable frequency
window [usually 46Hz - 54Hz]. The solution is to mechanically
adjust the generator to bring the frequency back to 50Hz.
This may require the services of a diesel mechanic. A minor
problem occurs if the inverter is turned off completely
as this causes all the operating settings to be lost. They
need to be reprogrammed in when the inverter is turned back
Faulty 240V wiring
It is possible to damage the inverter and to cause an electrical
shock hazard by incorrectly wiring the 240 volt inputs and
outputs. We have encountered one failure from this cause.
We may require a Certificate of Test issued under the Electricity
Act 1994 for any 240 volt wiring or equipment forming part
of the power supply, which has been installed by a licensed
electrical contractor other than one nominated by us, as
a condition of supporting the installation.
The most common cause of failure of installed inverters
is due to surges caused directly or indirectly by lightning
strike. Experience has shown that the inverter is really
the only piece of equipment susceptible this way. Lightning
protection is covered by Australian Standard AS1768. Lightning
protection equipment is offered as standard with our diesel/battery
hybrid systems. It comprises: (a) installation of bonded
earthing (b) installation of Novaris SD1-40DIN lightning
surge diverter on DC side of the inverter Additionally lightning
protection will be required for the AC input and AC output
circuits.The usual method is to install lightning surge
diverters in the adjacent AC distribution board.
Ants and wasps find the warm, sheltered environment of electronic
equipment attractive and this can cause severe problems.
In one case green ants built a nest inside an inverter and
caused several hundred dollars worth of damage. This type
of damage is not covered by warranty.Inverter manufacturers
warrant their products for indoor use only and in the cooler
climates where they live this implies that insects will
not be a problem. In the hot and humid tropics it is difficult
to eliminate insects altogether. Sometimes the only solution
is to cover all the ventilation and other openings with
insect proof screening.
In very humid conditions such as experienced in the wet
tropics region of North Queensland condensation can be an
annoying problem. There are several things that can be done
to eliminate the problem including placing a continuous
small load on the inverter, thereby forcing it to always
stay on. In any case the inverter should always be located
in a dry well ventilated area.