We all know solar and wind are intermittent. We all know winter is especially tough, with shorter days and less sunshine and long overcast periods that are also quiet on the wind front. Aussies call them “energy droughts” and Germans call them Dunkelflaute, the “Dark Lulls”. How will we cope?

Dunkelflaute – the “Dark Lull” – when the wind don’t blow and the sun don’t shine.

On this page:

  • If your grid halves in winter – double it!
  • Australian studies
  • Super-power
  • Real world example: Enera – Germany

If your grid halves in winter – double it!

But the good news is even energy hobbyists have studied the weather data themselves and concluded that because wind and solar are now the cheapest forms of electricity ever deployed, overbuilding renewables is now economically possible. Considering that solar PV is now 1/4 the cost of nuclear – you can afford to overbuild the solar a bit before even hitting the LCOE of nuclear. (And remember even baseload nukes require extra nukes in backup in case one drops off line for some unpredicted reason.)

Australian studies

In fact, overbuilding renewables radically reduces the amount of storage required! Renewables engineer David Osmond studied a year of Australian weather data and concluded:

“If we built enough wind and solar to meet approximately 170% of demand over the year (ie, 70% over-generation), then supply and demand could have been matched on every day of the year with the help of existing hydro. It could eliminate all instances of ‘Other’ or long-term storage requirements. For comparison, this study had 18% of over-generation. Ideally a use would be found for all this over-generation, such as producing hydrogen or charging EVs, so long as they are able to reduce to near zero on the most difficult days of the year.”

“Engineering with Rosie” interviews him here

Here’s a Griffith university weather study analysing 42 years of Australian weather data for renewables performance. (Page 25)

“overbuilding” the renewable energy fleet (that is, allowing for some spilled energy over time) is also likely to be an efficient source of energy firming.”

The Blakers team at ANU have modelled that an all renewable Australian grid with just Wind, Water, and Solar is cheap compared to today’s high energy prices! (The Water is Pumped-hydro storage.)

“PV and wind allow Australia to reach 100% renewable electricity rapidly at low cost. Wide dispersion of wind and PV over 10–100 million hectares reduces cost. Off-river pumped hydro energy storage is the cheapest form of mass storage. There are effectively unlimited sites available in Australia. LCOE from a 100% renewable Australian electricity system is US$70/MWh (2017 prices).” http://www.sciencedirect.com/science/article/pii/S0360544217309568

But not only this – they make this comment on overbuilding for future EV’s.

“In the near future it is likely that electric cars will enter the market in large numbers. There are about 18 million registered cars in Australia. If the future fleet of cars is of a similar size but entirely electric, with an average of 50 kWh of useable storage per car, then the usable storage is 900 GWh. This is twice the storage envisaged in our modelling. Unlike PHES, each storage cycle of a battery causes significant degradation, and batteries may therefore be significantly more expensive than PHES even in the longer term. However, timing the charging cycles is also effective in mitigating peaks in demand. This load is flexible and interruptible.”

Think about it. Most cars sit in a driveway or at work 95% of the time. If you massively overbuild the grid you can charge those cars slowly – and cut charging the moment a cloud bank moves through.

Here’s Tony Seba – just click below as I’ve timekeyed it to the spot. He explains the relationship of overbuild to storage and how it reduces the otherwise MASSIVE storage costs. Look at the graph! There’s some semantic irony here. People keep debating whether we can do a 100% renewable grid. Most of the papers I’m quoting would say ‘yes’ to the English meaning of that. They’re asking “Can renewables keep the lights on?”

But really, the technical answer is NO! We don’t even try to. We’re going to build a 170% renewable grid to replace coal and gas electricity – and when we get into replacing oil the multiples get even higher.

Seba even mentions 300% or 400% or even 500% in some climates. And it’s still the cheapest power system in HISTORY!

Now here’s the question. If you’re building 4 to 5 times your national grid’s normal demand just to cope with your worst month in winter, what do you do with these extra wind and solar farms the rest of the year? Just curtail them? Turn them OFF for 96% of the year?


Um, no! As long as your alternative jobs for it can be seasonal and shut down for your worst weeks in winter, there are all sorts of amazing jobs you could do with super-cheap ‘Super-Power’ as Tony Seba calls it. Imagine an industry that can run pretty much 11 months of the year and then pause for a few weeks – take some holidays – while the electricity is pushed back into supporting the grid in winter.

You could desalinate water and store it. You could use Gasifiers to recycle all our household waste into half the building materials for the next house. Indeed – the main reason we are not using gasifiers now is the cost of power! You could make extra hydrogen to store for industry or airlines. There’s just so much that could be done with 3 or 4 times your national grid’s ORDINARY electricity demand.

As long as they can pause for a few weeks in winter or whenever there’s a strong “Dark Lull” – imagine what could get done? This started off as an exercise in adapting to the intermittent, variable nature of Renewable Energy. But now just might help solve many other problems as well.

Real world example: Enera – Germany

The Enera project in northwestern Germany is being tested in a region where local VRE generation is equivalent to 235% of local annual demand. The project aims to avoid short-term distribution network congestion and redispatch costs by piloting a local flexibility services platform for market-based congestion management.