The importance of "base load" power generation

Base load is defined as “the minimum amount of electric power delivered or required over a given period of time at a steady rate”.

The graph below shows electricity being generated throughout a 24-day period at a typical power station. The maximum is 200 megawatts. The minimum, 120 megawatts (shown by the red line), is the “base load”. 

In this graph, the base load is 120 megawatts, in the early hours of the morning. Demand does not fall below this base load at any time during the 24 hours.

Geothermal power is at its best in meeting the base load -- the amount below the red line -- 24 hours a day, 365 days a year.

It’s important to distinguish between base load and peak load (which is the amount that varies above the red line).

Base load power plants operate continuously, stopping only for maintenance or unexpected outages. They can be powered by hydro, diesel, geothermal, nuclear, coal or natural gas. Only hydro and diesel are used at present in Fiji. Nuclear, coal and natural gas are too expensive to use here -- but geothermal is not.

Base load electricity cannot be generated reliably by solar or wind power. These forms of power generation are more suited to helping to meet the “peak load” -- 80 megawatts in the example above. If they are not available when needed (because the sun stops shining at night and the wind can stop blowing at any time), their place must be taken by base load plant such as hydro or diesel-powered generators.

The power output from geothermal is not as easily varied as from hydro or diesel plants, so geothermal’s role is essentially to handle base load. This is especially important for reliably supplying the large amounts of electricity that will be needed for Fiji’s industrial development, such as 24-hours-per-day mining and minerals refining, in addition to existing industries and commerce.

Base load electricity has to be supplied at a constant output -- all day and night, every single day, 365 days a year -- without being varied up or down.

Geothermal is unique among renewable technologies: it can meet high demand for base load electricity, very reliably.

Geothermal power is so reliable that it has provided the majority of base load power for Iceland’s spectacular development during the past 30 years, as shown by the pale blue segment in the graph below. It provides power to 60 million people around the world -- a figure that is growing rapidly as the world moves to reduce its reliance on diesel fuel.

Source: ‘Energy statistics in Iceland, 2006’, National Energy Authority,

Click for more information about renewable energy technologies in Fiji and their limitations.

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