What happens when the sun does not shine and the wind does not blow?

As is the case now, a mix of different forms of generation on the WA grid will ensure supply regardless of weather conditions. During still nights or during periods of heavy cloud cover, biomass and energy storage will be used. Locating wind plant in many different areas will help ensure that windless periods are short and infrequent. Solar PV, being mainly dispersed on rooftops and varied in it's orientation, evens out the impact of localised cloud cover.  Additionally, energy storage is inherent with Concentrated solar thermal (CST) generation and biomass thermal backup can also be incorporated.

During times when wind and solar generation exceed the load on the grid, storage facilities will be charged with any remaining excess generation curtailed.

What about the peak load?

Solar alone will go along way to supplying the peak load. Energy storage and biomass will be able provide the remaining power requirements.  Peak 'lopping' (by delaying or precooling buildings and cold storage), and shifting of non-critical electricity use to other times, will reduce these peak loads.  Other demand management and energy efficiency options will help even further.

What about Baseload?

Baseload is the load on a system that is on all the time, every hour of the year, the minimum generation required on the network. The load on the South West network varies with the time of day, day of the week, season of the year and the weather. This is demonstrated below by comparing the week with the biggest load (3,744MW, week beginning 20th of January) in 2014 with the week of the smallest load (1,438MW, week starting 7th of April).

    Image is from the IMO website, http://www.imowa.com.au/#weekly-numbers-generation.

Baseload generators are designed to be run 24hrs/day every day of the week at a constant output. They are shut down when they need maintenance.

Baseload generation in WA is supplied by large centralised coal fired power stations that cannot be ramped up and down easily due to their size (thick chunks of steel and concrete can suffer cracking from thermal expansion and contraction if changes are too quick). They are also relatively expensive to build but ‘cheap’ to run and so have typically operated most of the time to make them more economic.

Currently, to ensure that the load is always met, on top of baseload generation, mid merit combined cycle gas turbines are used. They can be ramped up or down more easily to follow the load. This type of plant is cheaper to install but more expensive to run.

For the rare spikes in load that come from air conditioning after a run of hot working week days, peaking plant are used. They are usually cheapest to install but most expensive to run.

Baseload generators are not essential for the network if sufficient alternative generation is available.

Integrating continuously variable wind and solar

Into this mix, ever increasing levels of wind and solar can be added. While both produce according to the wind and sunshine available at the time, the larger renewable energy projects can be curtailed if required. They can do this balancing cheaper and quicker than fossil fuelled generators and, on the rare occasions when high winds cross the entire wind fleet late at night, this already occurs.

Increasing penetration of constantly varying wind and solar generation mean more ramping up and down of gas plant but reduce the actual gas consumed.

As solar only occurs during the day, it has little direct impact on baseload but will reduce the amount of gas consumed in the mid merit generators. Solar generators have the effect of reducing the peak load and pushing it further into the evening.

What about carbon capture and storage (CCS) or 'clean coal'?

Wind turbines, photovoltaics (rooftop solar and solar farms), solar thermal and biomass are proven and widely implemented technologies, while even proponents of carbon geo-sequestration admit it is 10 to 15 years away. The extra energy required for CCS and the limited availability of suitable sites are also obstacles.

Aren't renewable energy technologies expensive?

Depends very much on the resources available but here in WA, rooftop solar is already at 'grid parity' (competing with retail prices). Photovoltiacs have dropped 75% in cost over the past four years and are set to continue, albeit at a more gradual pace. The cost of wind generation continues to drop gradually. Costs of CST (with energy storage) are also competing with new fossil-powered stations. 

Unlike sustainable energy, the burning of fossil fuels has additional costs from pollution, including carbon emissions, particulates, NOx, SOx, mercury and radioactive particles. While these costs are real and affect the health of locals and the environment, they are neglected in the economics of fossil fuelled electricity.  This is a serious deficiency in current energy economics.

Note that the cost of generation is half the electricity bill. The cost of transmission, distribution, balancing, spinning reserve, backup and administration cover the other half.

Does switching to renewables mean fewer jobs?

Renewable energy generally employs more people than coal or gas per MWh generated. As of end of 2013, 21,000 people were directly employed in the renewable energy industry in Australia.