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TESLA’S POWERWALL:
A Game Changer?
Purely by co-incidence, as we were reviewing and writing about the Tesla
Model S, internet whispers started appearing about a secret new product
being worked on by Tesla. Then came the official word: CEO Elon Musk
would be hosting a major press launch on April 30 to reveal the big secret.
By Ross Tester
B
y the time Elon Musk took to
the stage, the whispers had become a roar – Tesla was about
to release battery backup systems for
home and industry. It was a natural
progression from their work on the
lithium-ion battery packs they’d developed for their electric vehicles but the
detail was all that was left to reveal.
As well as the “live” press launch,
it was also beamed to the world as a
webinar, so wherever you were, you
could see the same message. And the
message was pretty “cool”, at least as
far as Tesla were concerned.
For far too long, we’ve been saddled
with lead-acid batteries as the main
storage for, particularly, solar (PV)
power systems. Lithium-ion batteries
were simply too expensive.
Of course, most installations (at least
here in Australia) don’t have any storage; they’ve been grid-based systems
which fed any excess power back into
the electric power distribution grid.
Those who got in early have been
blessed with very high value feed-in
Tesla CEO Elon Musk launching the PowerWall
and PowerPack (for utilities), April 30 2015.
siliconchip.com.au
June 2015 25
One of Tesla’s 10kWh PowerWalls.
Inside is 350-450V of lithium-ion cells
and a DC/DC converter. It’s about
1300mm high, 860mm across, 180mm
deep and weighs 100kg.
rewards – as much as 66c per kWh.
Those heady days have long gone but
even today, you can put a solar power
system in and reduce your electricity
charges.
But Tesla’s system is rather different
to that. It is intended for either standalone (ie, not grid-connected) systems
or hybrid systems, where there is battery backup as well as grid tie-in.
Musk reasoned that everything
about electricity production, usage
and charges were out of step – the
highest usage was in the morning,
after most people had gone to work,
and in the evening/night, after most
people had come home. Either way,
solar generation is minimal in the early
morning and zero in the night, when
you needed it most. You pay top dollar
for power at these times too.
What if the generation and storage
of electricity could be “time shifted”
- generate the power during the day
when the sun was shining and use it
26 Silicon Chip
during the peak periods mentioned
above. All you would need would be
a storage system capable of doing so!
OK, that’s a bit of an over-simplification but you get the idea!
immediately on announcement. (However the latest news [May 10] is that
production through to the middle of
2016 is sold out – over 38,000 reservations had been received in that time)!
Lead-acid battery
disadvantages
What’s in it?
One of the major reasons for not
using lead-acid batteries for storing
electricity is the cost. Deep-cycle storage batteries are not cheap.
Moreover, they need a lot of maintenance; they emit dangerous hydrogen gas when being charged; they
sometimes leak (and their electrolyte,
acid, is nasty stuff); they’re pretty temperamental about amount and depth of
discharge; they don’t like being overcharged . . . and to top it all off, their
life span can be pretty short (3-5 years
is about average, 10 years exceptional;
indeed, most deep cycle batteries only
have a 2 year guarantee).
Finally, when they have reached
the end of their life, disposal is not as
easy. They can’t be used in landfill,
they can’t be destroyed and even many
recycling centres that used to take
plenty of lead-acid car batteries are
becoming a bit reluctant to take them.
Small wonder that most people with
solar panels on their roofs stayed wellenough away from lead-acid batteries.
Lithium-ion battery
advantages
While there are some parameters
that need monitoring, for the most
part lithium-ion batteries don’t suffer
the disadvantages of lead-acids. They
don’t need much maintenance at all,
they’re much happier about charging
and discharging (mainly because each
cell is monitored and if necessary,
equalised with other cells), they have
a long lifespan (10 years would be
minimum, possibly a lot more) and
they don’t contain volatile materials
so can even be disposed of in landfill.
Or, as we reported in the earlier Tesla
S85 story, they are looking at recycling
as much as 90% of each cell in the
future.
Tesla’s PowerWall
Two (related) products were announced on April 30, the PowerWall
and the Tesla PowerPack. The latter is
intended for large-scale applications.
The first will start shipping shortly
(within a couple of months) – in fact,
Tesla Energy started taking orders
The basic PowerWall comes in
10kWh “weekly cycle” and 7kWh,
“daily cycle” models. Each contains
enough lithium-ion cells to achieve a
350-450V supply. The PowerWall is
designed to attach to a wall, inside or
outside. Overall size of a single PowerWall unit is 1300mm high, 860mm
wide and 180mm deep and weight is
100kg.
Note that there is no DC-to-AC inverter built in but it does have a DC-DC
converter, which means it should be
compatible with solar panels (which
generate DC).
Up to nine PowerWalls can be interconnected to satisfy virtually all
domestic demand.
And the cost?
The daily cyle (7kWh) PowerWall
will sell in the US for $3000; the
10kWh weekly cycle for $3500.
Let’s look at the more expensive one:
in Australia, at current exchange rates
and with GST that will probably sell
for around $5000.
For that, you get a ten year guarantee
and minimal maintenance.
Try buying, say, a 350V deep cycle
lead-acid battery pack with anything
like a 10kWh rating. Because you
can only safely cycle down to, say,
40% you’ll need around 16kWh to
be safe. At the moment, you’re looking at between $20,000 and $25,000.
Invariably, that only gets you a 2-3
year guarantee and it also gets you
all the trials and tribulations that go
with large lead-acid battery installations, not the least of which is a total
replacement after perhaps five years.
Of course, prices are dropping . . .
and Tesla’s PowerWall will have a lot
to do with that!
Other power sources
One of the main reasons that Tesla’s
PowerWall is likely to be a gamechanger is that for the first time, it
makes economic time-shifting power
demands.
Solar panels are not the only means
of charging batteries –wind and smallscale hydro are often mentioned.
But the one which is often forgotten
siliconchip.com.au
PEAK
SOLAR
MORNING DEMAND
EVENING DEMAND
The average home uses more electricity in the morning and
evening than during the day when solar energy is highest.
Tesla’s Powerwall is designed to smooth out these curves.
is the power grid itself. During peak
periods, power charges are high. At
“shoulder” times they’re lower and
during off-peak times they can be
quite low.
Why not use cheap off-peak power
to charge the batteries and either use it
instead of expensive peak power. Or if
you can get a reasonable feed-in tariff,
sell it back to the power companies
during peak times?
We can already hear the screams:
“you can’t get enough feed in tariff any
more to make it worthwhile.”
siliconchip.com.au
Thinking big: Tesla also have plans for power generators
and distributors to use very much larger battery banks to
smooth out their own peak and trough cycles.
Oh yeah? Go for a walk with Dr
Google – you might be surprised to
find that there are now companies in
Australia (not the power companies!)
who will buy stored power from you
at much higher prices than the power
companies offer. They on-sell it to
match peak demand and therefore
peak $$$ – and reward you with the
proceeds (less their commission).
If you think we’re talking cents per
kWh, think again. It can be $/kWh!
It is for all these reasons that we
believe Tesla, and their $5000 lithium-
ion battery, will be a game changer.
Whether you’re using it to go
completely off grid (now very much
cheaper than it was), or putting in a hybrid system; whether you are looking
at solar power or simply time-shifting
cheap off-peak power into peak times,
it’s a whole new ball game.
And the best part? The game has
only just begun!
For more information, visit www.teslaenergy.com – or Google “Tesla Powerwall” and “Tesla Powerpack”
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June 2015 27
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