Does Australian renewable energy save the earth – or just cost it?

Some Australian states and territories have announced ambitious targets for reliance on renewable energy rather than fossil fuel sources. The current ACT government has announced the Territory will become 100% reliant on renewable energy by 2020.

This requires inter-state shuffling of east coast energy sources. South Australia uses cheap brown coal back-up via the Heywood interconnector from Victoria when the wind doesn't blow. It exports excess wind power to Victoria when it does. The ACT's target assumes renewable energy will be imported from other states.

These are parochial dreams. If intended to deal with a global warming problem, they should be Australia-wide. Even then, we are 1.4% of global emissions and falling. Current inter-state fiddling of east coast supply is a zero-sum game: 'green-wash' window-dressing. The bigger plan, supposedly, is that other states will follow suit.

OK, let's continue dreaming. Assume the ACT's 100% renewables target applies nationally. No fossil fuels need apply. Assume first that the target is met by 100% reliance on solar panels plus energy storage. Let's concentrate first on base-load power, defined as the constant minimum needed 24/7. (We can modify all this later.)

Some power supply basics

Power supply can be measured in power (kilowatts - kW), multiplied by hours supplied (kWh). Suppose our base-load requirement is 100kW, every hour, 24/7.

There's a difference between rated generation capacity and power dispatched. The first measures maximum generation possible, the second, what is delivered.

There's also a difference between generators that can supply power continuously and those that can only do so intermittently. Fossil-fuel base-load generators are examples of the former. Solar (including solar thermal), wind and hydro (including 'pumped hydro') are examples of the latter (cycles range from daily to much longer).

This difference is critical. Fossil-fuel base-load plant can generate the base-load required all the time if it has a capacity rating equal to that requirement (in our example 100kW). Intermittent renewable base-load plant can only do so if its generation/storage capacity is some multiple of the (100kW x 24) daily requirement.

A very simplified solar power example

In practice, this stuff is much more complex than what I'm about to describe. But I'm just trying to illustrate the capacity/cost multiple problem in the ACT 'nirvana' world of 100% renewables. Suppose we assume no cloudy days, no fogs, and the same light intensity every day of the year. This is a 'best case' solar power generation scenario. Let's consider an 'equinox' day (where days and nights are each 12 hours). How will solar panels plus storage fare as a base-load power supplier?

The diagram below approximates the solar panel generation pattern. In our example, 'maximum PV power generation' is 100kW.