BACKGROUND

In the construction industry, most building sites require temporary power during construction.  Lengthy delays, high costs and the absence of early infrastructure mean that grid power is not always available.  Furthermore, load shedding and other power disruptions are having a significant impact on productivity.

In response, contractors are forced to purchase or rent mobile generators which are diesel-powered.  These generators have several disadvantages:

• They are noisy and impact neighbours and workers
• Diesel is expensive
• Poor quality generators do not always provide clean electricity and can result in premature failure of power tools and other equipment
• Generators idle at high diesel usage even when lightly loaded
• Often sites, require electricity at night for security, lighting, or continued operations. This means running a big generator for low loads.

THE HYBRID GENERATOR

The hybrid generator is a blend of inverter and battery technology with a traditional diesel or petrol generator.  This is essentially a mobile, off-grid system designed to provide high-quality consistent electricity

The hybrid generator uses robust inverter technology, capable of providing the dynamic energy needs of construction equipment.  Lithium Iron Phosphate batteries with a high charge and discharge current provide the primary energy via the inverters to your site.

The system is designed for the batteries to be charged by either:

• Connecting to grid power when available
• Connecting to the generator
• Connecting to a solar array

It is important to note that either, or a combination of these energy sources, can be applied on a site. 

How does this work?

Power usage on a site is almost always inconsistent.    Consider drilling a 50mm core in a concrete wall for a drainage pipe;

• the generator is running, waiting to provide the electricity needed for the coring drill.
• The artisan, measures and prepares to drill
• The artisan drills the first 50mm and removes the coring bit to clean.
• He repeats the process until the hole is complete

This sequence is shown in the graph below.

In this basic example 4.5 units of fuel are used while the generator is in idle mode and 8 are used in when in service.  No matter how efficient your generator, the idle time uses fuel.  This is similar to the fuel your car uses when waiting in traffic.

The hybrid generator provides the electricity needed with negligible wasted energy in-between load times – much like an electric car.

When the battery reaches a pre-set depth of discharge the inverter starts a smaller generator that is designed to run at 75% of rated capacity (its sweet spot) to recharge the batteries.  The generator operates at a consistent load without risk of overload or tripping.  The power delivered to the construction site is limited to the capacity of the inverter NOT the generator.

The Hybrid Generator is programmed to ensure that batteries are fully charged at a set end of working day time, and clean, and cost-effective quite electricity is delivered to all the night-time loads.

MODES OF OPERATION

Inverter Mode: all electricity is supplied from the batteries via the inverter.  Fuel motor is OFF.

Generator Mode: fuel motor is ON and charging the batteries, inverter is providing the electricity to site.

Power Assist Mode: This feature takes the principle of power control to a further dimension. It allows the inverter to supplement the capacity of the alternative source.  When peak power is required for only a limited period, the inverter will make sure that insufficient generator power is immediately compensated for by power from the battery. When the load reduces, the spare power is used to recharge the battery.[3]

REMOTE ACCESS:

The hybrid generator is IOT enabled and is monitored 24/7.  Owners and users can monitor it in real time.  This allows you to:

• Get notifications of low diesel levels
• Remote monitoring of all alarms and operational changes
• Data logging
• Analysis of energy usage and battery levels
• Productivity indicators
• GPS tracking for asset management

ENERGY ADVANTAGES:

• Up to 60% reduction in diesel consumption
• Up to 60% reduction in generator service costs
• Better than 99% availability
• Reduced CO2 emissions
• Can be charged by grid power when available
• Grid power usage is measured and can be accurately billed, if supplied by a friendly neighbour
• Clean Power reduces premature failure of power tools and other loads
• When demand is low the generator is off
• Seamless operation between inverter/batteries & generator ensures uninterrupted power
• Can be installed alongside an existing generator set
• Inverters have a high-Power discharge
• Three Phase Output, 15kVA, 30kVA & 45kVA
• High Surge Power: The surge power rating of the Victron inverters is roughly 2 to 2.5 times the rated continuous power output for a very short period of time. So, a 10kVA inverter can deliver 20kVA surge power on equipment start up.

 OPERATIONAL ADVANTAGES:

• Remote monitoring and control
• Manual override local or remote
• System safety switch
• Mobile
• GPS Monitored

INVERTERS:

Victron Energy has a strong reputation for technical innovation, reliability and build quality and is especially popular in the highly competitive automotive, camping, and boating industries.  Victron's higher-power battery inverter/chargers, along with a range of smart energy management devices, have been designed specifically for off-grid installations for residential homes, factories and other commercial enterprises.   Building sites, are by definition, a rough environment in which power equipment has to operate.  Victron is probably the leading manufacturer of inverters used in the hybrid generator industry around the world.

They are based in the Netherlands and have been manufacturing inverters since 1975.

Shaun Worthmann, Pr. Eng, CEM, CMVP, CRM, Real Time Energy (Pty) Ltd.; Gary Wiltshire, Logo Industries Africa

INTRODUCTION TO THE AUTHORS

Shaun Worthmann is a professional electrical engineer and the author of “My Powerful Home”, a comprehensive guide to energy efficiency and renewable energy solutions. He has designed and built international award-winning energy projects.

Gary Wiltshire is a serial entrepreneur with commercial interests in various countries on the continent. He also teaches entrepreneurship and gorilla financing to post-graduate students and is involved with various development organizations supporting start-ups in Africa.

REFERENCES:

[1] SANS 50010. Measurement and Verification of energy savings. South Africa Bureau of Standards. Edition 1.

[2] https://www.victronenergy.com/.

https://www.victronenergy.com/upload/documents/Output-rating-operating-temperature-and-efficiency.pdf

[3] https://www.victronenergy.com /upload/documents /Datasheet-MultiPlus-inverter-charger--800VA-5kVA-EN-.