"Here ERoEI raises its head again, the energy needed to build the
storage at the bottom of the race, remember it has to involve a
massive earth moving project, the loss in the generating turbines
and the losses in the pump motors are all subtracted from the output.
As I said providing backup always means a large reduction in efficiency ie ERoEI."

Yep, and batteries are worse in their robbing effect on EROEI of than hydro storage in the cases it can be applied.

Indeed Luciferase, batteries have a worse loss than generator -> motor losses.
They always have internal losses and the longer you hold the charge
the greater the losses.

However except for restricted areas batteries for a city are just out
of the question. Imagine the size of battery to keep Sydney going on
a cold winter night while mum is cooking dinner, the kids are watching
two TVs and the older brother is on the internet while the air conditioner
is trying to keep them all warm, as Dad is on the 35th floor waiting
for the lift so he can get to the train.
Street lighting has come on and all the traffic lights are working.

This is what people think can be done when all the pollies, greenies
and pixies at the bottom of the garden are talking alternative
energy, and it can all be done even on a still night.
Gawd, some people need a reality check !

Oh, and for the feminists Mum is a school teacher and has been home since 4pm.

Graeme of Malvern,

No, your scenario couldn't happen. Firstly, as has already been pointed out, a lot of solar power is generated on those hot days. Secondly it's reliable peak load electricity we need, not base load. As Keith Lovegrove said: "People made plants that weren't very good at ramping up and down, looked for things to do with then and called the baseload"

You say renewable energy will ALWAYS need near 100% backup. But how near and 100% of what, exactly? Fortunately we don't need backup supply for anywhere near 100% of the electricity we only use 0.1% of the time, as the conditions that cause demand to be so much higher then than the rest of the time occur when there's a large amount of sunshine.

_____________________________________________________________________________________

Shadow,

Of course we need reliable supply. I never said otherwise, but I contend that reliability is the ability to meet demand. Demand can be met by increasing supply or reducing demand. Either way it's usually a response to a rise in electricity prices.

Keeping supply reliable and the network stable is a technical problem that Germany has apparently failed to adequately address. That doesn't mean it can't be adequately addressed.
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warmair,

The viability of solar thermal depends on how cheaply they can borrow money. At 4% it's commercially competitive without subsidy.

There's a lot more than 8 reasons for the decline of the Roman Empire:
https://www.utexas.edu/courses/rome/210reasons.html

URL fixed: http://www.utexas.edu/courses/rome/210reasons.html

Bazz,
I'm baffled as to why you, and so many others, believe the ludicrous claim that there's a minimum viable EROEI figure of 7. It can't be a technical limit, because if EROEI was 4 then you could just install twice as much and get the same net energy. And it can't be an economic limit because it takes no account of the cost of non energy inputs (though some have tried to factor these in, in a way that inevitably relies on false assumptions). Renewable energy, even with battery backup, is likely to get a higher EROEI figure in future, but that's not what determines viability.

It's time to start ignoring EROEI and focus instead on real viability.

We shouldn't let the difficult (but achievable) task of getting 100% of our energy from renewables deter us from the much easier task of getting 50% from renewables.

As for what the requirements would be to get 100% of our energy from renewables, we really don't know yet. We can't yet tell how fast battery technology will advance, or how much metal smelting we'll do or how good we'll be at varying demand to exploit low electricity prices and avoid high electricity prices. We don't know how good we'll be at exploiting geothermal energy or wave energy. We don't know how good we'll be at synthesising fuel, and how much scope there is for varying that process according to supply. We don't know whether by then we'll be trading electricity with Indonesia. We don't even know what our population will be.

Technology advances all the time and so do our expectations. Try looking at what can be done instead of dubious reasons why it can't.

Adrian
We all fall for the hype from time to time The German grid is one of the most reliable in Europe, it is only the anti renewable people that would have you believe otherwise.
I have given this link before but I guess you missed it.

http://www.cleanenergywire.org/sites/default/files/styles/large/public/images/dossier/saidi-international.jpg?itok=ST5hhpIA

Others
5 or so years ago I would have said to achieve 100% renewable electric power was not practical. Things have moved ahead rapidly since then wind power is nearly competitive with coal and prices continue to fall, solar PV prices are falling even faster. In Australia we still have other options that we have not started to utilize such as tidal, geothermal (conventional) and biomass and for the really ambitious how about ocean thermal energy conversion.

http://en.wikipedia.org/wiki/Ocean_thermal_energy_conversion

Power storage is developing rapidly on many fronts from hot salt storage for solar thermal plants to large scale batteries which all have their uses in particular applications. Hydro pump storage using renewables is the cheapest current available storage and is in widespread use elsewhere. Using pumped storage means that hydro could provide a much higher proportion of our power requirements and nor are we limited to the typical large hydro dam as only relative small amounts of water are needed to provide reliable power source.

It is also a complete furphy that renewables require 100% backup they don't any more than any other type of power source. All power stations can and do break down from time to time, but that does not mean we have twice as many power stations as required running all the time.

http://reneweconomy.com.au/2014/pumped-hydro-the-forgotten-storage-solution-47248
http://ecogeneration.com.au/news/ramping_up_hydro_pumped_storage_schemes/075440/

Aidan,

You are entitled to your opinions but the facts are not for dispute.

Fact:
Power cannot be stored on the networks. Stability is only controlled by matching demand to supply on a second by second basis.

Supply on the networks is managed between the networks and generators in as little as 10 minutes time slices based on actual demand where suppliers bid to supply power and networks accept, based on predicted demand and reserve capacity, subject to the above.

Fact:

Most customers have annual contracts, the price of power has a long term effect, but no short term effect.

Fact:

Consumer demand has a very similar shape in each country with mid level demand during the day, a small peak demand early in the morning and large peak demand in the early evening around 7pm.(roughly double the midday demand when solar is useless) and drops to a very low level in the early morning of about 1/2 of midday. This curve changes with weekends, summer and winter and weather.

Fact:

Networks pay for power from the generators, but also to have reserve capacity available (which is a significant portion of the cost). This is sufficient most of the time to cope with variations sudden consumer demand, low supply from renewables, or equipment failure, but when there is a perfect storm, ie renewable power collapses, and peak demand surges, then it takes very little for the network to lose control.

Fact:

Wind power without heavy subsidies is far from competitive with coal in Australia. In countries that have to import it, it comes closer, but still relies on fossil fuel generation to back it up.

Fact:

Thermal solar is still far more expensive even than wind, and is far from commercially viable.

Fact:

Geothermal or "hot rocks" power has been scrapped because of "technical" and commercial problems.

Fact:

Batteries are progressing rapidly, but need to reduce their cost by a factor >1000 before they become viable for the grid.

Fact:

Commercial hydro plants need huge volumes of water dropping significant distances to be viable. Large storage requires large dams.