COLUMN
WEINHOLD’S POWER LINES
Saving It for a Rainy Day
If renewable power sources are to be integrated into the
power matrix, we must find ways to store more of their
energy. Michael Weinhold, Siemens Energy’s Chief Technology Officer, shares his insights on the challenges and
technical solutions in the first of a series of columns he
will be contributing to Living Energy.
I’m convinced that stronger transmission and distribution
grids are essential for solving this problem. In my own
home country of Germany, transmission grid bottlenecks
limit wind power integration, and the distribution networks are already reaching the limits of capability in certain areas due to the huge numbers of PV units connected.
These infrastructures were originally built to be connected
to central power stations, and are not designed for distributed production and feeding of power into the grid from
the “opposite side,” especially far away from loads.
Besides boosting grids, increasing the flexibility of gasfired power stations for backup capabilities, and demandshifting loads, e.g., with electric heat pumps in households, I regard energy storage technology as a key enabler
for integrating more renewables. Research now focuses
on four areas: First, electrochemical storage units such as
Li-ion batteries are gaining market shares as electric cars
become more popular. The Chevrolet Volt has a 16-kWh
Li-ion battery; the BMW MINI E has a 35-kWh pack, which
means three or four electric cars offer enough storage
to power an average German household for one week.
Second, thermal storage systems for heating and cooling
could activate substantial loads for later use during times of
high winds or intensive solar radiation. Third, mechanical
storage means such as pumped hydrostations are already
used today to control energy and arbitrage trading, but offer
limited potential relative to the anticipated wind and PV
ramp-up.
The fourth and, I think, most promising area is that of
chemical storage. Compressed hydrogen stores vast quantities of energy in a very compact volume. While battery,
thermal, and mechanical storage systems can bridge a few
hours of consumption, hydrogen produced from renewable
energy can help to bridge days or weeks of volatility. It is
attractive for its potential synergies with existing gas pipeline infrastructures and as a complement to conventional
power stations, mainly gas-fired plants. Hydrogen may be
stored in existing salt caverns or in pressurized vessels.
Siemens is developing electrolyzer technology to produce
hydrogen, which not only can be burnt for electricity
again, but can also be used in the chemical industry or to
power cars. Hydrogen stands for what I regard as a key
characteristic of this new electricity age: We cannot optimize
one component independently of the overall system.
The only obstacle to widespread storage systems is cost
reduction. I believe the need for storage offers a substantial
business opportunity that will further promote the integration of renewables into the energy system. Innovative
solutions will, in turn, result in changes to the way the
electricity grid is structured and integrated. And smart grids
will be instrumental for making storage into a key component of the future power matrix. At the risk of repeating
myself: It’s all about grids, flexibility, and storage. p
Living Energy · Issue 6/February 2012
Illustrations: Elisabeth Moch, Michael Weinhold
There are few things that bother me more, as an
electrical engineer by training, than when energy is
wasted. But paradoxically, as demand increases and green
power reaches ever-higher ratings, the power output of
wind or PV power plants must be reduced almost daily because grids – built for a different energy age – cannot
take up their energy. At the same time, the intermittency
of wind and solar means that without sufficient storage
capacities, industrialized societies will be wasting more and
more of the valuable renewable energy. So, are renewables
being hurt by their own success? Not if we can devise better
ways of storing their energy!
An integrated power matrix requires strong grids complemented by innovative storage technology.
Living Energy · Issue 6/February 2012
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