WEBVTT

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Hi.

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I'm Bruce Hankins.

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This was one of the PV arrays
I ever worked on.

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PV, that's short for
photovoltaics, solar

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electricity.

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When I was installing this
system in the field behind me,

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a farmer was plowing with
a horse drawn plow.

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Behind him, the power plant,
and then these arrays.

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To me, it was postcard perfect,
the past, the

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present, and the future.

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The past, many folks around here
for reasons of faith have

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disavowed the use of many modern
conveniences, things

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like motorized equipment
and electricity.

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Now how many of you think of
electricity as a convenience?

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More like a necessity.

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Without it, we're
really hurting.

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In fact, our whole way of
civilization depends on us

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keeping that power flowing.

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The present, the system for
generating and delivering that

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electricity to our homes and
our businesses and our

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factories is the most complex
machine ever built.

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This power plant is part of the
larger picture is one of

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150 in Pennsylvania.

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But how many of them happen to
be running at any one time?

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Depends on how much
electricity we

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happen to be using.

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Think about it.

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Every time you flip a switch on
or off, you're changing how

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much electricity they
have to produce.

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And you're not the only one
flipping the switches.

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Millions of us are.

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And if millions of us decide to
do the same thing at about

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the same time like go to the
refridge during the Super Bowl

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commercial break,
the demand --

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that's how much power is being
drawn from the system

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at any moment --

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that demand can change quick.

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And it can change a lot.

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And the utilities, they
think about this.

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And they prepare for it.

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The reason is this:

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If the demand, how much we're
using, is more than the

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supply, those generators
want to slow down.

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If the supply is more than the
demand, those generators want

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to speed up.

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And how fast those generators
are spinning affects what our

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electrical frequency is.

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And we need to have a steady
electrical frequency for our

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electrical equipment that
we use to work properly.

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So any time that they add or
remove a power plant from the

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system to try to balance the
load, they have to do it

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without affecting the voltage
or the frequency.

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Otherwise, our lights flicker,
our motors stall out, and our

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televisions and our computers
become toast.

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So balancing the demand
and the supply --

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and the demand is always
changing --

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and keeping the generators
running steady

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that's no easy task.

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In addition, the wiring network
that connects all

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these power plants to our loads,
commonly known as the

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grid, is reaching its limits.

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Especially on hot summer days
when everybody's air

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conditioner is cranked
all the way up.

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So if we need more power, adding
power plants isn't

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going to help.

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The lines are maxed out.

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And woe to us if one of our
transmission lines goes down.

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The instability caused by the
electricity seeking new paths

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to the loads through the lines
that are left, lines that are

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already maxed out themselves,
starts domino effect.

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How big will shut down be?

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No one knows.

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The situation's been likened
to a giant pile of rice.

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Where you're adding one grain
of rice at a time.

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You never know which grain of
rice it'll be that will start

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an avalanche or how big that
avalanche will be.

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Could just be your neighborhood
that goes out or

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maybe your city or maybe the
whole Northeast coast or maybe

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the one that happened in India
that affected 9% of the

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world's population.

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One solution is to make
the grid bigger.

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That's easier said than done.

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That's like making the
highways bigger.

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No one wants a new highway
through their backyard.

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And everybody wants to know
where the money's

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going to come from.

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That leaves us with
load reduction.

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We have to reduce
our power usage.

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Some methods for doing this
include energy conservation

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and energy efficiency.

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If you drive your car less
that's energy conservation.

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If you switch to a car that gets
better gas mileage that's

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energy efficiency.

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Adoption of energy conservation
and energy

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efficiencies measures have
been mandated by law.

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Not only must we reduce our
consumption in general, but we

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have to reduce our
peak demand.

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We have to relieve the pressure
that's on the grid.

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And now to the future.

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You've probably seen a few of
these here and there lately.

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In the last four years, over
7,000 roof and ground mounted

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PV arrays have been installed
in Pennsylvania alone.

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Most people think of
energy conservation

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when they see these.

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But what they don't realize
is that one of the primary

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benefits of these systems is
demand relief for the grid.

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This solar array is technically
a distributed

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electrical power generating
source.

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Distributed is engineer speak
for "at the load".

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For the rest of us,
it means on site.

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If we make the power where we
use it, we don't have to

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transport it through the grid.

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This photovoltaic array
changes sunlight into

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electricity which is great on
hot August afternoons when the

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air conditioners are
working overtime.

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Our peak output from the PV will
reduce the output needed

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from the utilities.

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But it doesn't make any
power at night.

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And it makes less on cloudy
days than on sunny days.

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The power these systems
make varies

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too much to be reliable.

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So we connect them to
the grid, grid tied.

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If it's at night, the grid
supplies all of our

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electricity.

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If it's cloudy, maybe
half of our power is

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provided by the sun.

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And if the sun shines bright,
all the power we need and

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maybe more we can
get from our PV.

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When we make more than we need,
the power is sent out

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onto the grid for sale
to your neighbors.

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And you receive a credit
on your electric bill.

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These systems are great because
they're all solid

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state with no moving parts
to break and virtually no

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maintenance needed.

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They're self activated, self
controlling, and self

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monitoring.

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You flip the switch, and
they do the rest.

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One important thing, however, if
the utility power goes out,

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they shut down.

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Without the utility power as
support, these systems produce

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power that is too variable
for us to use.

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Safety is the other reason
for the shutdown.

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We don't want to be sending
power out onto a line that a

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lineman thinks is turned off.

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This is a required feature
of grid tied systems.

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And it's called anti-islanding.

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And it happens automatically.

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And yet some people are
surprised when their solar

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shuts down that they don't
have any power.

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Hey, Bruce, the power's
out and my PV system

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isn't making anything.

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It is maddening.

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All this power making
potential.

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And you can't use it.

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I can almost hear somebody say,
well, if you want backup

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power, just add a battery
to the system.

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Come on.

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Nothings that easy.

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For one thing, batteries are
DC, and almost all the

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electrical equipment
we use is AC.

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So you'll need something to
change from the DC power to

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the AC power.

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And you're going to have to know
how much of that power

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you're going to be using and for
how long so that you can

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get enough batteries
to run your loads.

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And you're going to have to keep
those batteries charged.

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The good news is such
battery-based systems exist.

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And they can be added to
existing grid tied PV systems.

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The method for connecting
existing renewable energy grid

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tied powered systems to battery
based energy storage

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systems is called AC coupling.

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AC coupled.

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Coupled, when we're talking
about electrical

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things, means connected.

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And there's two ways to connect
things electrically in

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series or in parallel.

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These batteries are connected
in series.

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This would be a series
alignment.

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These are 1 and 1/2
volts each.

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So connected in series,
we build voltage.

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1 and 1/2, 3, 4 and 1/2.

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This PV array is built on
the same principle.

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This is our photovoltaic cell.

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These are connected in series.

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They make about a half
a volt a piece.

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Half a volt, 1 volt, 1 and 1/2,
2, 72 cells in a module,

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be about 35 volts.

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35 volts a module, the modules
are connected in series.

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35, 70, 350 volts.

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The three parts of our array are
each producing 350 volts.

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But then we connect these
all in parallel.

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So that's 350, 350, and 350.

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Sends 350 down to the house.

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The only thing is these cells
are temperature sensitive.

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So that voltage is
always changing.

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So the voltage going down to
the house could be anywhere

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from 300 to 500 volts.

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So in parallel, 1 and 1/2, 1 and
1/2, 1 and 1/2 connected

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this way outputs
1 and 1/2 volt.

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But we can run three
times as much.

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Or we can run something for
three times as long.

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How about connecting something
like this in parallel?

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This little gas generator
here.

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You never hear somebody say, I
need more power so I'm going

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to hook up two of these little
gas generators together.

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It just doesn't happen.

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They just buy a bigger one.

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It's too complicated to do.

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Now if you were paying
attention, you could say to

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me, Bruce, earlier you were
telling us about the

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utilities' hard task of keeping
our electricity steady

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and strong.

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And you were talking about how
the PV arrays output was so

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variable that you really
couldn't use it unless you had

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the utility to help.

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Now, you're telling us not
only is its output

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intermittent, but that its
voltage changes with the

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temperature.

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And that it's DC.

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It's not even the AC like the
utility power we use.

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If you can't connect two systems
like this that are

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basically the same, how are you
ever going to connect two

00:12:55.680 --> 00:12:58.840
systems like this and like
the utility that

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are so totally different?

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Allow me to introduce you
to the grid tied utility

00:13:04.840 --> 00:13:07.920
interactive inverter.

00:13:07.920 --> 00:13:12.600
The solid state power level
electronics device that's

00:13:12.600 --> 00:13:16.460
changing all the rules of what
we can and cannot connect

00:13:16.460 --> 00:13:18.680
electrically.

00:13:18.680 --> 00:13:22.700
These inverters perform
three major functions.

00:13:22.700 --> 00:13:27.440
One, they maximize the amount
of power that's

00:13:27.440 --> 00:13:29.730
drawn from the array.

00:13:29.730 --> 00:13:33.050
So these inverters are sized
according to the potential

00:13:33.050 --> 00:13:35.610
maximum output of the array.

00:13:35.610 --> 00:13:41.590
8,000 watt array, 10,000
watt inverter.

00:13:41.590 --> 00:13:46.320
Two, they change the highly
variable DC output of the

00:13:46.320 --> 00:13:50.360
array to usable AC electrical.

00:13:50.360 --> 00:13:56.310
Three, they monitor utility,
voltage, and frequency.

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And if everything is stable on
the grid, and the sun is

00:14:00.350 --> 00:14:05.800
shining, they electronically
matched the utilities voltage

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and frequency.

00:14:07.870 --> 00:14:13.720
And click, our distributed power
generation system is now

00:14:13.720 --> 00:14:16.150
parallel connected
to the grid --

00:14:16.150 --> 00:14:18.784
grid tied.

00:14:18.784 --> 00:14:23.660
The inverter will shut down
automatically if utility power

00:14:23.660 --> 00:14:27.670
is lost or if something
isn't just quite

00:14:27.670 --> 00:14:29.185
right with the grid.

00:14:29.185 --> 00:14:34.000
The inverter monitors the
situation for five minutes.

00:14:34.000 --> 00:14:37.700
And if everything is fine,
the inverter will

00:14:37.700 --> 00:14:39.740
reconnect to the grid.

00:14:39.740 --> 00:14:42.110
Some people refer to this
type of inverter as a

00:14:42.110 --> 00:14:44.430
battery-less inverter.

00:14:44.430 --> 00:14:46.700
It doesn't need a battery.

00:14:46.700 --> 00:14:52.100
Its purpose is to allow us to
use the power we make on site

00:14:52.100 --> 00:14:56.080
in place of the utility power.

00:14:56.080 --> 00:14:59.910
Which is good for the utilities
because it relieves

00:14:59.910 --> 00:15:02.200
pressure on the grid.

00:15:02.200 --> 00:15:05.710
It's good for the environment
because we're making our power

00:15:05.710 --> 00:15:08.690
from a clean, renewable
energy source.

00:15:08.690 --> 00:15:11.600
And it's good for the customer
as a hedge against rising

00:15:11.600 --> 00:15:13.570
electrical prices.

00:15:13.570 --> 00:15:16.880
But it's no good when
the power goes out.

00:15:16.880 --> 00:15:21.370
For that, we need a battery
based system.

00:15:21.370 --> 00:15:25.480
This is our battery based
inverter charger system.

00:15:28.000 --> 00:15:31.440
This is our energy storage
system, commonly known as a

00:15:31.440 --> 00:15:33.040
battery bank.

00:15:33.040 --> 00:15:37.710
Individual batteries are
connected in series and

00:15:37.710 --> 00:15:41.800
parallel to build voltage
and capacity.

00:15:41.800 --> 00:15:45.770
The same method that we
used for our PV array.

00:15:45.770 --> 00:15:49.140
Current electrical codes limit
residential battery

00:15:49.140 --> 00:15:52.430
systems to 48 volts.

00:15:52.430 --> 00:15:56.340
This system is what's going to
enable us to have backup power

00:15:56.340 --> 00:15:58.850
when utility power is lost.

00:15:58.850 --> 00:16:04.160
Our battery-less system went out
when the utility went out.

00:16:04.160 --> 00:16:06.850
This one doesn't need
the utility.

00:16:06.850 --> 00:16:08.810
It can stand alone.

00:16:08.810 --> 00:16:13.160
So sometimes these systems are
called standalone systems.

00:16:13.160 --> 00:16:15.900
This is an older style of
electrical meter most of us

00:16:15.900 --> 00:16:17.880
are familiar with.

00:16:17.880 --> 00:16:23.160
This little dial spinning here,
this little disk, how

00:16:23.160 --> 00:16:27.100
many times that spins in a month
that tells us how much

00:16:27.100 --> 00:16:28.660
energy we've used.

00:16:28.660 --> 00:16:32.400
We measure our energy
in kilowatt hours.

00:16:32.400 --> 00:16:34.330
It's got a time element.

00:16:34.330 --> 00:16:38.400
We have to size our battery
bank according to how much

00:16:38.400 --> 00:16:41.050
energy we want to store.

00:16:41.050 --> 00:16:45.770
How fast this dial spins around,
sometimes it barely

00:16:45.770 --> 00:16:49.460
moves other times it's spinning
like a buzz saw,

00:16:49.460 --> 00:16:52.060
represents how much electricity
is actually

00:16:52.060 --> 00:16:54.690
passing through the metering
and the wiring at that

00:16:54.690 --> 00:16:56.190
particular moment.

00:16:56.190 --> 00:16:58.010
That's what we call demand.

00:16:58.010 --> 00:17:01.150
It's an instantaneous
power measurement.

00:17:01.150 --> 00:17:05.609
We talk about it in kilowatts,
no time element.

00:17:05.609 --> 00:17:10.569
If we use larger loads like
stoves, toasters, water

00:17:10.569 --> 00:17:14.460
heaters, our demand goes up.

00:17:14.460 --> 00:17:18.710
If we use a lot of little loads,
light bulbs, computers,

00:17:18.710 --> 00:17:21.819
that pushes our demand up too.

00:17:21.819 --> 00:17:26.040
So we need to know what we're
using and what we're using all

00:17:26.040 --> 00:17:27.569
at the same time so that we can

00:17:27.569 --> 00:17:30.180
calculate our maximum demand.

00:17:30.180 --> 00:17:32.480
Because that's how we're
going to size all of

00:17:32.480 --> 00:17:35.150
our wiring and equipment.

00:17:35.150 --> 00:17:39.420
This is our essential
loads panel.

00:17:39.420 --> 00:17:42.610
This is where we brought the
circuits that control the

00:17:42.610 --> 00:17:45.530
things that you've
just got to have.

00:17:45.530 --> 00:17:49.430
Now the more loads that you
have, the bigger your battery

00:17:49.430 --> 00:17:52.900
bank is going to be and the
bigger that your wiring and

00:17:52.900 --> 00:17:55.250
the bigger that your inverters
are going to have to be.

00:17:55.250 --> 00:17:58.845
So pick wisely the
loads you choose.

00:17:58.845 --> 00:18:03.900
At this place, they
use communication

00:18:03.900 --> 00:18:05.070
and computer equipment.

00:18:05.070 --> 00:18:08.410
So we took those circuits, and
we pulled them out of their

00:18:08.410 --> 00:18:12.050
regular, main electrical panel,
and we moved them into

00:18:12.050 --> 00:18:13.550
this panel.

00:18:13.550 --> 00:18:17.540
Also, we moved the heating
circuit to this panel.

00:18:17.540 --> 00:18:21.090
In the summer they could open
a window, but in the winter,

00:18:21.090 --> 00:18:23.570
we need heat.

00:18:23.570 --> 00:18:27.080
The owners they live
next door.

00:18:27.080 --> 00:18:29.600
So we took a line over to
their house, and we

00:18:29.600 --> 00:18:30.880
gave them some heat.

00:18:30.880 --> 00:18:34.260
We gave them power for their
water pump, power for their

00:18:34.260 --> 00:18:35.510
refrigerator.

00:18:35.510 --> 00:18:39.380
We brought all those circuits
here and attached them to the

00:18:39.380 --> 00:18:42.080
correct breakers to protect
those circuits according to

00:18:42.080 --> 00:18:43.990
the National Electrical Code.

00:18:43.990 --> 00:18:47.540
But now we need to figure
our demand.

00:18:47.540 --> 00:18:53.400
What we did was we took
individual readings on each

00:18:53.400 --> 00:18:57.740
circuit, added them up, and
that gave us our potential

00:18:57.740 --> 00:18:59.400
maximum demand.

00:18:59.400 --> 00:19:04.700
The thing is most of these
circuits won't be running at

00:19:04.700 --> 00:19:06.310
the same time.

00:19:06.310 --> 00:19:09.580
To get a clear picture of what
your actual demand is going to

00:19:09.580 --> 00:19:12.210
be, you could use a
system like this.

00:19:12.210 --> 00:19:15.820
It's a home energy monitoring
system.

00:19:15.820 --> 00:19:22.410
You can take selected circuits,
two, four, six, and

00:19:22.410 --> 00:19:25.690
you can get a record of
how those circuits act

00:19:25.690 --> 00:19:27.530
over, say, a month.

00:19:27.530 --> 00:19:30.980
And you can calculate how much
energy you're going to use,

00:19:30.980 --> 00:19:34.440
and what your demand will
be of those circuits.

00:19:34.440 --> 00:19:39.740
Demand is expressed in
watts or kilowatts.

00:19:39.740 --> 00:19:42.130
Let's say that our
demand is 7,000

00:19:42.130 --> 00:19:45.200
watts, or seven kilowatts.

00:19:45.200 --> 00:19:50.580
Our wiring and components must
be sized to handle that much

00:19:50.580 --> 00:19:57.330
power, both on the AC side
and the DC side.

00:19:57.330 --> 00:20:03.210
One of these inverters is
good for 4,400 watts.

00:20:03.210 --> 00:20:06.130
That's not enough to carry the
7,000 watts we said our

00:20:06.130 --> 00:20:07.560
demand could be.

00:20:07.560 --> 00:20:10.540
So we'll need two of them
connected together and

00:20:10.540 --> 00:20:13.830
parallel which would give
us the capability

00:20:13.830 --> 00:20:16.920
to carry 8,800 watts.

00:20:19.710 --> 00:20:24.450
Battery based systems must be
sized according to the maximum

00:20:24.450 --> 00:20:26.260
demand of the loads.

00:20:26.260 --> 00:20:31.410
We don't use our batteries when
we have utility power.

00:20:31.410 --> 00:20:36.040
So the inverter manufacturers
have built an internal

00:20:36.040 --> 00:20:40.620
transfer switch inside these
that closes when we have

00:20:40.620 --> 00:20:44.740
utility power and sends the
power to our essential loads.

00:20:44.740 --> 00:20:48.980
If we lose our utility power,
the switch opens --

00:20:48.980 --> 00:20:54.890
that provides the isolation of
the system from the utility so

00:20:54.890 --> 00:20:56.950
we have our anti-islanding.

00:20:56.950 --> 00:20:59.510
And we don't kill our linemen.

00:20:59.510 --> 00:21:03.160
I've been calling these
inverters, but when utility

00:21:03.160 --> 00:21:06.190
power is present, they are
actually battery chargers.

00:21:09.080 --> 00:21:12.380
They keep our batteries
in tip top shape

00:21:12.380 --> 00:21:14.660
until they're needed.

00:21:14.660 --> 00:21:17.540
These chargers are
sophisticated.

00:21:17.540 --> 00:21:21.150
Batteries come in many different
voltages and types:

00:21:21.150 --> 00:21:25.750
lead acid, gel, AGM.

00:21:25.750 --> 00:21:28.040
Different types of batteries
have different charge

00:21:28.040 --> 00:21:29.840
parameters.

00:21:29.840 --> 00:21:34.010
The size of your battery bank
and the types of batteries you

00:21:34.010 --> 00:21:41.350
use determine how long, how
fast, and to what voltage you

00:21:41.350 --> 00:21:43.400
can charge your batteries.

00:21:43.400 --> 00:21:46.930
Batteries are also temperature
sensitive.

00:21:46.930 --> 00:21:50.960
Their energy capacity changes
with the temperature.

00:21:50.960 --> 00:21:55.110
So it's an important thing that
the charger can take this

00:21:55.110 --> 00:21:56.880
into account.

00:21:56.880 --> 00:22:02.820
This is a thermal sensing unit
attached to this charger.

00:22:02.820 --> 00:22:07.200
So that it can change the
charging parameters so that we

00:22:07.200 --> 00:22:10.830
don't overcharge or undercharge
our batteries when

00:22:10.830 --> 00:22:12.750
that capacity changes.

00:22:12.750 --> 00:22:18.550
There's a saying, "batteries
don't die, they're murdered."

00:22:18.550 --> 00:22:22.170
So you need to know what you're
doing, or you need to

00:22:22.170 --> 00:22:24.900
get the advice of somebody
who does.

00:22:24.900 --> 00:22:29.090
Now earlier, I mentioned that
we size our battery bank by

00:22:29.090 --> 00:22:31.150
the energy requirements.

00:22:31.150 --> 00:22:34.170
That energy has a time
element to it.

00:22:34.170 --> 00:22:37.140
Now we could ask how long can
I operate this system at

00:22:37.140 --> 00:22:39.060
maximum demand?

00:22:39.060 --> 00:22:42.550
But 99% of the time that
won't be the case.

00:22:42.550 --> 00:22:45.400
We will be using much less.

00:22:45.400 --> 00:22:48.710
That's another reason why a
home energy monitor helps.

00:22:48.710 --> 00:22:51.610
There is another time element
that is involved in sizing a

00:22:51.610 --> 00:22:57.160
battery bank and that is how
long we want to be able to go

00:22:57.160 --> 00:22:59.400
without having to recharge
the batteries.

00:22:59.400 --> 00:23:04.350
This period of time is
known as autonomy.

00:23:04.350 --> 00:23:08.110
For one day of autonomy,
we have to size our

00:23:08.110 --> 00:23:10.810
battery bank this size.

00:23:10.810 --> 00:23:14.610
For two days of autonomy,
we have to size our

00:23:14.610 --> 00:23:16.960
battery bank this size.

00:23:16.960 --> 00:23:21.340
For three days of autonomy,
you get the picture.

00:23:21.340 --> 00:23:24.460
There's a definite connection
between the size of the

00:23:24.460 --> 00:23:28.490
battery bank and how many days
of autonomy you want.

00:23:28.490 --> 00:23:34.780
So the big question is, can we
recharge these batteries

00:23:34.780 --> 00:23:37.350
without utility power?

00:23:37.350 --> 00:23:40.380
The answer with this
system is yes.

00:23:40.380 --> 00:23:45.090
We have a PV array up on the
hill that can produce enough

00:23:45.090 --> 00:23:50.110
electricity to run all of our
essential loads, charge our

00:23:50.110 --> 00:23:54.460
batteries with power to spare.

00:23:54.460 --> 00:23:57.300
But this is Pennsylvania.

00:23:57.300 --> 00:24:02.160
And we've been known to have
days, weeks without sunlight.

00:24:02.160 --> 00:24:07.300
So we can guesstimate how many
days we'll be without sunshine

00:24:07.300 --> 00:24:11.770
and build our battery bank to
that many days of autonomy.

00:24:11.770 --> 00:24:14.870
Or we can do what we did here.

00:24:14.870 --> 00:24:19.410
We added a small propane powered
generator that we can

00:24:19.410 --> 00:24:22.730
use to recharge the
batteries if we go

00:24:22.730 --> 00:24:25.800
over our days of autonomy.

00:24:25.800 --> 00:24:29.430
Generators work well with
battery systems.

00:24:29.430 --> 00:24:33.820
The generator isn't just sitting
here running burning

00:24:33.820 --> 00:24:37.290
fuel waiting for somebody
to use electricity.

00:24:37.290 --> 00:24:42.660
Instead, use the generator to
charge the battery, turn it

00:24:42.660 --> 00:24:46.240
off, draw the power you
need from the battery.

00:24:46.240 --> 00:24:50.030
If your battery needs recharging
again, come turn

00:24:50.030 --> 00:24:52.110
your generator on again.

00:24:52.110 --> 00:24:57.090
The addition of this generator
allows us to keep our battery

00:24:57.090 --> 00:24:59.140
bank smaller.

00:24:59.140 --> 00:25:03.040
Now we have two systems,
the grid tired

00:25:03.040 --> 00:25:05.340
and the battery based.

00:25:05.340 --> 00:25:09.000
We're going to connect them
together in parallel, and the

00:25:09.000 --> 00:25:13.310
resulting new system is called
an AC coupled system.

00:25:13.310 --> 00:25:17.720
Our PV array power is now used
not only to offset our

00:25:17.720 --> 00:25:21.310
electrical utility use but
also to keep our backup

00:25:21.310 --> 00:25:25.540
standalone system powered
and charged.

00:25:25.540 --> 00:25:29.060
There are battery-based systems
that do what AC

00:25:29.060 --> 00:25:30.940
coupled systems do.

00:25:30.940 --> 00:25:34.640
But the PV array voltage has to
be reduced to the battery

00:25:34.640 --> 00:25:40.010
voltage, and the AC coupled
system uses the 240 volt AC

00:25:40.010 --> 00:25:42.460
power to charge the batteries.

00:25:42.460 --> 00:25:47.940
Using the higher DC voltage of
the grid tied array allows us

00:25:47.940 --> 00:25:50.966
to have greater distance between
our system components.

00:25:59.430 --> 00:26:03.030
This AC coupled system will
allow us to look at the system

00:26:03.030 --> 00:26:09.250
parts side by side, the grid
tied and the battery based.

00:26:09.250 --> 00:26:11.650
We'll also discuss how these
two systems are going to

00:26:11.650 --> 00:26:14.440
interact once they've
been coupled.

00:26:14.440 --> 00:26:17.340
The grid tied system was
installed first under the

00:26:17.340 --> 00:26:20.850
state solar rebate program.

00:26:20.850 --> 00:26:23.940
The owners have an all electric
house and a ground

00:26:23.940 --> 00:26:26.380
source heat pump, but they
wanted to reduce

00:26:26.380 --> 00:26:28.170
their carbon footprint.

00:26:28.170 --> 00:26:32.840
Their utility makes 35%
of their electricity

00:26:32.840 --> 00:26:34.520
from burning coal.

00:26:34.520 --> 00:26:38.530
Then came heavy rains
and flooding.

00:26:38.530 --> 00:26:42.000
Power was out for an extended
period of time.

00:26:42.000 --> 00:26:46.110
The sump pumps failed and
the basement flooded.

00:26:46.110 --> 00:26:48.540
Time to get a backup system.

00:26:48.540 --> 00:26:53.020
In keeping with their low
carbon philosophy, they

00:26:53.020 --> 00:26:55.560
decided to skip the generator.

00:26:55.560 --> 00:26:58.390
They wanted to use the PV array
to keep their battery

00:26:58.390 --> 00:27:02.040
backup system powered
and charged.

00:27:02.040 --> 00:27:05.280
That required increasing the
size of their battery bank to

00:27:05.280 --> 00:27:07.240
give them the required
days of autonomy.

00:27:09.900 --> 00:27:17.990
The resulting standalone system
uses renewable energy,

00:27:17.990 --> 00:27:23.500
is sustainable, and will
generate power any time under

00:27:23.500 --> 00:27:26.260
any weather conditions.

00:27:26.260 --> 00:27:30.270
The battery backup system may
have to provide the power for

00:27:30.270 --> 00:27:33.690
the essential loads for an
extended period of time.

00:27:36.210 --> 00:27:39.290
Although not all household loads
will be powered by the

00:27:39.290 --> 00:27:43.660
battery backup system, the
homeowners do have the option

00:27:43.660 --> 00:27:48.340
to add additional convenience
loads such as the electric

00:27:48.340 --> 00:27:51.330
range and the electric water
heater depending on the

00:27:51.330 --> 00:27:53.780
availability of the
power they have.

00:27:53.780 --> 00:27:59.110
When utility power is present,
which is most of the time, the

00:27:59.110 --> 00:28:03.470
current drawn by the loads
passes through the main

00:28:03.470 --> 00:28:08.500
electrical panel to the AC/DC
distribution panel of the

00:28:08.500 --> 00:28:12.210
battery based system and through
the internal transfer

00:28:12.210 --> 00:28:17.170
switches of our three parallel
connected backup inverters.

00:28:17.170 --> 00:28:20.650
While the grid is operating,
these inverters are in

00:28:20.650 --> 00:28:25.760
charging mode, making sure our
batteries are fully charged

00:28:25.760 --> 00:28:28.780
and ready to go when needed.

00:28:28.780 --> 00:28:33.480
If no current is being used by
the loads, and the grid tied

00:28:33.480 --> 00:28:37.790
system is generating AC current,
that current must

00:28:37.790 --> 00:28:41.090
pass through the internal
transfer switches of our

00:28:41.090 --> 00:28:46.420
backup inverters to feed
power to the grid.

00:28:46.420 --> 00:28:49.610
Why three backup inverters?

00:28:49.610 --> 00:28:53.610
That's the size needed to carry
the maximum current from

00:28:53.610 --> 00:28:59.530
our solar array or the maximum
demand to our loads.

00:28:59.530 --> 00:29:03.080
Especially that ground
source heat pump.

00:29:03.080 --> 00:29:04.970
So what happens at the
inverters when we

00:29:04.970 --> 00:29:07.580
lose utility power?

00:29:07.580 --> 00:29:11.980
First, the grid tied inverter
shuts down.

00:29:11.980 --> 00:29:15.480
Then the internal transfer
switches in the backup

00:29:15.480 --> 00:29:17.780
inverters open.

00:29:17.780 --> 00:29:21.630
The open transfer switches
provide the isolation from the

00:29:21.630 --> 00:29:24.560
grid and the nonessential
loads.

00:29:24.560 --> 00:29:28.390
And the essential loads now pull
the power they need from

00:29:28.390 --> 00:29:30.370
the battery bank.

00:29:30.370 --> 00:29:33.560
So how smoothly does
this all happen?

00:29:33.560 --> 00:29:37.530
The battery based system
provides replacement power for

00:29:37.530 --> 00:29:42.090
the essential loads in less
than 16 milliseconds --

00:29:42.090 --> 00:29:45.030
20 times faster than you
can blink your eye.

00:29:45.030 --> 00:29:47.480
That's why telecommunications
and data centers

00:29:47.480 --> 00:29:49.400
love battery backup.

00:29:49.400 --> 00:29:52.010
Nothing shuts down.

00:29:52.010 --> 00:29:54.750
And though the grid is
down, the grid tied

00:29:54.750 --> 00:29:57.140
system still works.

00:29:57.140 --> 00:30:01.670
If the sun is shining, the grid
tied inverters will check

00:30:01.670 --> 00:30:04.930
for proper voltage
and frequency.

00:30:04.930 --> 00:30:07.330
And after five minutes,
if everything is

00:30:07.330 --> 00:30:10.130
good, they'll reconnect.

00:30:10.130 --> 00:30:13.430
The battery based system has
now taken the place of the

00:30:13.430 --> 00:30:18.240
grid, providing the AC voltage
signal that the grid tied

00:30:18.240 --> 00:30:21.030
system needs to operate.

00:30:21.030 --> 00:30:24.790
And here's where we've coupled
our systems together.

00:30:24.790 --> 00:30:27.790
The grid tied system used to
be connected to the main

00:30:27.790 --> 00:30:32.370
service panel with any power
generated going to serve the

00:30:32.370 --> 00:30:37.040
household loads and any extra
electricity being sold out

00:30:37.040 --> 00:30:38.770
onto the grid.

00:30:38.770 --> 00:30:42.960
Now we're isolated
from the grid.

00:30:42.960 --> 00:30:45.990
Our grid tied system and our
battery based systems are

00:30:45.990 --> 00:30:49.820
connected in the essential load
center, both supplying

00:30:49.820 --> 00:30:55.010
power to the loads, and any
extra electricity generated by

00:30:55.010 --> 00:30:58.460
the grid tied system goes
to provide power to

00:30:58.460 --> 00:31:01.190
recharge the batteries.

00:31:01.190 --> 00:31:04.900
If the batteries are fully
charged, and the loans aren't

00:31:04.900 --> 00:31:08.830
demanding any power, we need
to keep our batteries from

00:31:08.830 --> 00:31:11.130
overcharging.

00:31:11.130 --> 00:31:14.250
Different systems' manufacturers
have different

00:31:14.250 --> 00:31:16.480
ways of doing this.

00:31:16.480 --> 00:31:20.610
Some have a communication link
between the two system

00:31:20.610 --> 00:31:26.550
inverters, telling the grid tied
inverter to reduce output

00:31:26.550 --> 00:31:28.710
or stop output.

00:31:28.710 --> 00:31:32.050
Others use what's called
frequency shift.

00:31:32.050 --> 00:31:38.070
Grid tied inverters operate in
very narrow frequency range.

00:31:38.070 --> 00:31:43.390
When the batteries reach a
certain threshold, the battery

00:31:43.390 --> 00:31:47.490
based inverter's voltage output
is moved to a different

00:31:47.490 --> 00:31:49.470
frequency that's out
of the grid tied

00:31:49.470 --> 00:31:51.625
inverter's frequency range.

00:31:51.625 --> 00:31:55.440
That shuts down the grid tied
inverters and prevents our

00:31:55.440 --> 00:31:57.640
batteries from overcharging.

00:31:57.640 --> 00:32:02.080
For extra protection, if the
electronic overcharge

00:32:02.080 --> 00:32:06.220
prevention circuits fail, a
diversion load, such as a

00:32:06.220 --> 00:32:09.860
water heater, can be
added to the system

00:32:09.860 --> 00:32:12.230
to protect the batteries.

00:32:12.230 --> 00:32:15.550
The water heater will use the
excess electricity that would

00:32:15.550 --> 00:32:18.030
have been overcharging
our batteries.

00:32:18.030 --> 00:32:22.410
What's exciting is not only can
we connect these systems

00:32:22.410 --> 00:32:26.960
together and then parallel
connect them to the grid, but

00:32:26.960 --> 00:32:31.950
we can connect AC coupled system
to AC coupled system.

00:32:31.950 --> 00:32:36.430
In fact, entire islands are now
being powered by systems

00:32:36.430 --> 00:32:39.800
based on AC coupling methods
and technologies.

00:32:39.800 --> 00:32:42.560
We could also connect
neighborhoods together in what

00:32:42.560 --> 00:32:44.530
is known as a micro-grid --

00:32:44.530 --> 00:32:47.730
battery based grids
within the grid.

00:32:47.730 --> 00:32:52.440
A communication link, part of
the smart grid, would enable

00:32:52.440 --> 00:32:55.730
the utilities to also
control demand.

00:32:55.730 --> 00:32:57.980
So the future is here.

00:32:57.980 --> 00:33:02.020
AC coupled systems provide
backup power and load

00:33:02.020 --> 00:33:05.690
reduction for the grid, and
enable us to better use our

00:33:05.690 --> 00:33:08.030
renewable energy sources.

00:33:08.030 --> 00:33:09.470
That's a win for everyone.

00:33:09.470 --> 00:33:45.988
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