Diesel/ Battery Hybrid System
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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 battery charging.

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 automation required.

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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.

Generator loading

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.

Generator start/stop

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.

Battery operation

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. Please contact us for details and current rates.

Reliability Issues

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 on.

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.


Phone Crystal at Planetary Power

For more information email
or phone Crystal on
07 40 962 420
at Planetary Power

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Planetary Power - Renewable Energy Solutions
   P.O Box 198 Herberton 4887 North Queensland- Australia
email: info@planetarypower.com.au   web: www.planetarypower.com.au    phone: 07 40 962 420

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Diesel/ Battery Hybrid System