Climate change will effect us all, to mitigate the effects we are all trying decarbonize our lives. Germany is at the vanguard of this fight with their "Energiewende" (Energy Transition) but will it work without an effective storage solution?

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Storage Requirement Analysis

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In 1980, an environmental think tank coined the notion Energiewende.
“growth and prosperity without
petroleum and uranium”

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In this slide show, German PV, wind & demand data for every hour between January 1st
2012 & December 31st
2013 has been recorded and is used to build an image of the grid as
it stands today. PV & Wind power output is then increased by varying factors to build a
realistic picture of a future German grid.
Hydro & Biomass power output is assumed to be constant at 500MW & 6000 MW throughout.
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This is how the grid looks today, the low points you can see in the demand curve are
weekends, and the larger troughs at the end of the two years correspond to Christmas
holidays. At no point in time was demand met by the renewable energy(RE) infrastructure.
In the summer, photo voltaic cells(PV) work well during the daylight hours, but supplies no
power at all after sunset. Similarly wind in the winter tends to blow strongly for a few days at
a time, but then gives little output for days or weeks. For RE to be effective & replace fossil
fuel it needs to be increased dramatically and its variability somehow reduced or
compensated.
MW
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Even with a huge increase in the supply of RE, there will still be gaps between supply and
demand. For Energiewende to succeed without the burning of fossil fuels, it is vital that a
cost effective method is found to store energy for extended periods. This can then be
released, to fill the gaps where no RE is available to meet demand.
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This chart is wind, solar and exports for June 2013. Notice how the exports coincide with
solar output.
On Energiewende books the exports are marked as being derived from coal, but the
evidence is clear. Without a storage solution Germany exports large amounts of the RE
generated into Europe.
Often so much energy is generated that prices are driven negative. In effect, to save the grid
from harm, recipients are paid to take unwanted energy, driving up German costs.

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When demand is not met by RE, power needs to
be obtained from another source. Currently in
Germany this is derived from fossil fuels, either
gas or coal. In energiewende speak, this is known
as “flexible backup”.
The faster this power can be dispatched the more
efficient it is. Gas fired power can react quickly
but needs to be “spinning” when required.
Coal power is very slow to react to demand, but
can compensate for windy periods, as this can be
forecast reliably, a few days ahead of time.
In reality the “flexible backup” is often far too slow, it performs as it was originally
designed, as a reliable baseload.
Any excess RE is simply exported. Even today, energiewende is crying out for storage.

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When RE power is increased the
duration of wind and solar resource
remains constant. Therefore once
demand has been met, the gains from
increasing RE power diminish.
The red areas on this graphic
represent the shortfall in supply
which would need to be filled.
As can be seen the excess energy
increases with RE in a linear way, but
the amount of time that demand is
met by RE does not.

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Currently 72% of German electricity demand is met by conventional sources.
As more wind & PV capacity is added to the system, so the reliance on “flexible
backup” decreases, but this is not linear (28% for 0-1 but only 3% from 7-8)
Multiplying
Factor
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TWh
The diminishing returns can be clearly seen in this chart of contracting lines,
representing the shortfall between demand and supply.
The takeaway here is that we get more bang per buck in the earlier stages of an RE
rollout.
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At factors of 2 and above the peaks in supply start to satisfy demand, anything over
and above the immediate power requirement is available for export or storage.
Using the actual data it can be clearly seen that the increase is relatively linear with
increasing RE infrastructure.
TWh
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June 2nd
2013
Increasing RE output using factors of 1-8, shows the amount of excess energy
generated on a summers day, currently this excess energy is exported into the EU.
This begs the question, how much can the European market soak up? Already it is
common place for prices to be driven negative, whereby German suppliers pay for the
power to be taken off their hands.
German demand on 2nd
June 2013 peaked at 43,000 MW, even using a factor of 3, the
excess was greater than 50,000 MW. Is it realistic that there will be a market for so
much power or is storage an absolute necessity?
MW
Hour

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With a factor of 8, we get spikes of power up to 200GW, meaning the German
grid would have to cope with 270 GW of power. For reasons of economy, a
more realistic scenario would be to cap the power at 200GW and discard
anything over and above this level.
In either case this will require major upgrades to the grid. A potential solution
to this would be to store power locally to the source.
MW
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The efficiency of any storage solution is a major issue, there is plenty of excess power
using a factor of 8, but this is eaten up if a low efficiency storage solution is used.
Power to gas(P2G) is the solution of choice, often voiced by Energiewende proponents,
but it is only 30% efficient. As can be seen in the chart, during the winter months any
stored methane would soon be exhausted.
TWh
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P2G

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Power to Gas (P2G) uses electrolysis to split water into hydrogen and oxygen, then
combines the hydrogen with carbon to produce methane. When power is required
the methane is used to generate electricity.
Typically this process achieves 30% efficiency, meaning for every 1,000MWh in we
can expect 300MWh out.
http://www.edgar-program.com/news/gas-to-power-on-the-go

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With wind & solar increased by a factor of 8 the bulk of storage is used to fulfill small
gaps in supply, therefore a much better solution, would be to utilize a small amount
of more efficient storage, such as pumped hydro (75% efficient) sized at 800 GWh to
cope with short-term supply requirements, and a longer term, inefficient solution
which has a virtually unlimited capacity for storage such as P2G, for the winter
months.
TWh
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800 GWh 75% Efficient PHS
30% Efficient Power to Gas

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At pumped hydroelectric storage(PHS) power stations, water is pumped back into the
reservoir when there is excess power. At night when there is no sun or wind power,
the water can be allowed to flow back down to produce electricity just like a normal
hydroelectric power station.
Unlike fossil fuelled based “flexible backup” such a system does not need to be
“spinning”, it can be turned on very quickly when it is required to meet demand. PHS
typically achieves 75% efficiency.
(High RE output)

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In addition there are plans to use Combined Heat & power(CHP) systems. This makes
the gas used for space heating more efficient, as it can also generate electricity.
Conversely when the system is needed to generate electricity (“flexible backup”) the
heat generated could either be used for space heating or stored locally.
If this gas can be synthesized using P2G, this is all well and good, if not CHP will merely
entrench fossil fuels
Energiewende is also
concerned with the CO2
generated from space
heating. This will take the
form of insulating buildings
and using more efficient
architectural designs. These
designs will take advantage
of the sun’s heat in winter,
and shade buildings in the
summer months.

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Combined Heat & power (CHP)
While there is no doubt that CHP offers much greater efficiency, if the fuel it needs
cannot be efficiently synthesised, this will not be a practicable low CO2 solution. In
effect the synthesised methane fuel would have to be substituted with fossil fuel.
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No conclusions will be drawn from this research that is up to the viewer.
However there are some questions that we should all be asking.
1.How much will it cost to increase the current RE by a factor of 8?
2.How much will it cost to upgrade the grid to cope with 4X or more the current
power rating (Systems LCOE studies indicate that generation costs could more than
double even for only a 2-3x factor)?
3.With such a massive infrastructure and limited lifespan for each component, how
much will it cost to maintain the system?
4.If PHS is chosen as a storage solution will Germany’s topography be able to meet
this requirement (in other words are there sufficient locations)?
5.If batteries are chosen as the storage solution how much will this cost and is this
even possible (All of the batteries in the world can meet world electricity demand
for 10 minutes. Are there enough resources available to manufacture batteries
capable of backing up the German grid?)
6.The current plan is to use Combined Heat and Power(CHP) to cut CO2 emissions
from heating, using gas synthesised using P2G, is this realistic?
7.Could the 30% efficiency of P2G be improved?
8.Can the P2G process cope with the huge spikes in power, or will it need a constant
supply?
9.Assuming P2G can cope with the spikes, it will mean a process working part time,
how does this impact on the costs? 20