Grid Tying

[John P. Bengi]

Just to put this into perspective for my own understanding here:
You have spent about
Misc c/w batteries $3500 + PV panels $16,000 = $19,500 on your
system
You average about 14kWh per day (based on a years stats)

In my geographical location at $0.10 per kWh the breakeven time (with no
surprise maintenance) would be

Including 3 battery bank changes @ $1500

($19,500 + 3 x $1500) / ($0.10 x 14 x 365) = 47 years

I doubt many of us would be alive that long.

Before people get all bent out of shape about electric rates going up, don't
forget the cost of batteries will be going up, the grid tie inverter may
only average 8-20 years similar to most electronic gadgets this complex and
service, PV panel breakage and the interest you are not getting on the money
you spent have not been considered yet. On top of all that you may never see
panels this cheap again for the next 25 years so newcomers may not do this
well.

If this is a hobby as a PV pioneer? Great!
If this is a necessity because of reliabilty?...Great
If you have an OCD about saving the earth from the Boogieman?... Great!

If you think you will save money on PV at this time in history...gp back to
school and study grade 4 math.

or

Get a part time job at the corner store. It would be more profitable.

 

[John P. Bengi]

If you run your batteries at a voltage that barely keeps them charged, the
cells will become unequal in charge. This means the weaker ones will assume
less voltage while the stronger ones may assume more voltage drop across
them.

If you run your battery bank at a higher voltage your cells may stay equal
but then your water levels will boil off faster and your will have more wear
and tear on your batteries.

The compromise is "equalization". You "Equalize" them on a planned cyclic
basis or when dictated by measurements by "cooking the crap" out of them for
a limited time only with high voltage. This allows you to run them at a
lower "float" voltage most of the time and yet keep some from getting weaker
than the rest. This is taught as the best method of preserving your battery
life.

 

[[email protected]]

Just to put this into perspective for my own understanding here:
You have spent about
Misc c/w batteries $3500 + PV panels $16,000 = $19,500 on your
system
You average about 14kWh per day (based on a years stats)

In my geographical location at $0.10 per kWh the breakeven time (with no
surprise maintenance) would be

Including 3 battery bank changes @ $1500

($19,500 + 3 x $1500) / ($0.10 x 14 x 365) = 47 years

I doubt many of us would be alive that long.

Well, first of all, I was NOT making any argument that there's a viable
financial reason for installing solar when you've got a grid available.
That was NOT my reason for installing a PV system. PV makes financial
sense only if:

a) you're so far from the grid that capital costs to connect exceed
the capital costs of the PV system;

b) you firmly believe that energy costs will skyrocket in the next
decade or so. In SoCal, the current cost is around 18 cents per kWH,
including distribution charge. At 25 cents per kWH, my system would
break even in 12 years -- not a sure bet. How so? While my system cost
around $30k to install, I got CEC rebates and tax incentives that
reduced my out-of-pocket cost to around $14k.

Although I must say that your assumption that energy costs will remain
at an inflation-adjusted cost of 10 cents per kwH is just a wee bit
optimistic. Are you assuming there'll be a breakthrough in cold fusion
or zero-point energy?


No, my point was to refute an absurd claim that maintaining batteries in
a grid-tie environment would cost me more than the panels.

Before people get all bent out of shape about electric rates going up, don't
forget the cost of batteries will be going up, the grid tie inverter may
only average 8-20 years similar to most electronic gadgets this complex and
service, PV panel breakage and the interest you are not getting on the money
you spent have not been considered yet. On top of all that you may never see
panels this cheap again for the next 25 years so newcomers may not do this
well.

If this is a hobby as a PV pioneer? Great!
If this is a necessity because of reliabilty?...Great
If you have an OCD about saving the earth from the Boogieman?... Great!

If you think you will save money on PV at this time in history...gp back to
school and study grade 4 math.

Straw man argument. Nobody (well, at least, I) was making such a claim.

 

[[email protected]]

What is an equalization cycle, and why is it necessary?

You overcharge the batteries for 90 minutes to 2 hours. The idea is to
de-stratify the electrolyte, and dissolve sulfate deposits. It keeps
the batteries healthy.

It's a standard maintenance protocol for wet cell batteries.

Battery manufacturers recommend that you do it only when there's more
than a specified difference in specific gravity among the various cells
in the batteries. I haven't got a precise specific gravity tester, so I
just do it on a periodic basis.

My SW4048 has a programmable equalization cycle, so it's easy enough to
do. You make sure that no cells have exposed plates (adding a little
distilled water, if so). Run the equalization cycle, and then top off
all the cells and close the caps.

 

[John P. Bengi]

oooops. Sorry. I did get the apples mixed up with the oranges.

My bad

 

[John P. Bengi]

There seems to be a general consensus that PV will save people money and I
was using the presented figures to dispute that claim. The argument wasn't
irectly addressed at you..I guess.

Some of your points I had already stated except the sky-rocketting electric
rates. I think the stick market may be more predictable though...LOL

Where I reside in Canada there is no rebate and none on the horizon. PV is a
ridiculous waste of money for any reson if there is grid power available
(agreed). We also have another faction going on here. WE pay $9-$13 per watt
for panels because they come from the US with quadruple and quintuple
markups on them. At this point I bought all my panels from the US second
hand, seconds, and as discounted as I can find them a few at a time. To buy
them here it will cost me almost double, even though the PV panels shippers
are idiots and I have to wait months for shipping damage claims almost every
time... If I needed them in a hurry I could drive 5 minutes and pick them up
in my car for those prices.***sigh**

I guess the confusion comes in that geographic location is a big factor in
these arguments depending on the origin of the argument...LOL

Have a great one.

 

[[email protected]]

There seems to be a general consensus that PV will save people money and I
was using the presented figures to dispute that claim. The argument wasn't
irectly addressed at you..I guess.

I haven't seen any such consensus, except among the "true believers".

Not even my contractor made more than a half-hearted attempt to dispute
my analysis of the matter.

I installed the system because I'm willing to pay for the independence,
and because it cost me less than an SUV while affording me a lot more
satisfaction.

 

[John P. Bengi]

LOL. Whatever floats your boat.

Manly yes. But I like it too!

 

[Steve Spence]

some battery types require a periodic overcharging to get all the cells
back into the same state of charge. Flooded Lead Acid batteries
specifically require this.

Steve Spence
Dir., Green Trust
http://www.green-trust.org

Contributing Editor
http://www.off-grid.net
http://www.rebelwolf.com/essn.html

 

[Mel]

Brian Graham a écrit :

Jim Baber said,

The biggest problem I have with my solar PV (grid
tied) is when the grid is down, so is my solar.
<<

I can't say I know much about the setup of these systems, but is this normal?? Do all Grid-Tied systems go AWOL without the grid? If so, when Iuse PV it certainly won't be tied.

Hi Brian.

You're question is a common one,and I will try to give a short, general
answer (without kicking up to much dust )

Generalising, there are three different types of PV systems:

1/ Stand Alone - for those that can't have the grid (for economic or
physical reasons). PV produces energy that is kept in batteries until
needed. This can be combined with other energy sources to increase the
energy available or deal with weather conditions that produces little PV
power. (generator, wind power, hydro power etc etc).

Here in France the batteries represent about 1/3 of the system cost, and
a Stand Alone system i considerably more expensive than the other two
options they require a certain amount of maintenance, and require that
the user spend a little time getting to know about the technology for
maintenance.

This choice is generally made on economical reason, although people do
also go Stand Alone for idealogical reasons (independence, self sufficiency)


2/Grid-tied - for those that have the grid and are looking for a way to
generate a relatively "clean" decentralised electricity, OR in certain
countries, those who are looking for a good financial investment (I'm
thinking of Germany and maybe Japan and the French overseas
departments... and probably certain areas of the US).

The costs are lower than for stand alone systems (I think about ?1/3?
for an equivalent annual energy production), the owner has no need to
know anything about anything (runs like a fridge or your tv once
installed) but will have to run the gauntlet of grid-connection
procedures (often long & difficult & sometimes expensive)

This is not a choice made by those looking for autonomy. If the grid
goes down, you have no more electricity. For many people (most in
western Europe & Japan, to my knowledge), this is not a problem as the
grid is extremely stable in their area, and outages rarely last longer
than a couple of hours, and there are rarely more than 2 or 3 per year.


3/ Back up systems - these systems are a combination of stand alone and
grid connected. A small back up battery bank is kept charged, and if the
grid goes down, the PV system will switch to feeding the batteries. The
batteries will in turn feed a few priority circuits (lighting, central
heating circulator, fridge, etc..(defined by the owners priorities &
climate)).

The back up battery bank is sized according to the owners needs and the
grid reliability. If you have very unreliable grid power, you will need
to factor this into the system. In France, this type of system is
confined to the overseas departments that are cyclone prone (keep the
fridge & lights running) and mountainous zones (keep the central heating
circulator & lights running).

This type of system costs more than a grid connected system, but by how
much will depend on what is on the priority circuit & the autonomy desired.



The choice between grid connected and back up system will depend on what
you want from your PV system, and why you are doing it. Most people
buying into grid connected PV in France mainland are doing it for
ecological reasons, and don't want batteries because of the disposal &
recycling problems. They have a stable grid, so are not too worried
about the occasional, short-duration blackout

I hope this answers your question!

Mel

 

[Rob Munach]

Brian Graham a écrit :




Hi Brian.

You're question is a common one,and I will try to give a short, general
answer (without kicking up to much dust )

Generalising, there are three different types of PV systems:

1/ Stand Alone - for those that can't have the grid (for economic or
physical reasons). PV produces energy that is kept in batteries until
needed. This can be combined with other energy sources to increase the
energy available or deal with weather conditions that produces little PV
power. (generator, wind power, hydro power etc etc).

Here in France the batteries represent about 1/3 of the system cost, and
a Stand Alone system i considerably more expensive than the other two
options they require a certain amount of maintenance, and require that
the user spend a little time getting to know about the technology for
maintenance.

This choice is generally made on economical reason, although people do
also go Stand Alone for idealogical reasons (independence, self
sufficiency)


2/Grid-tied - for those that have the grid and are looking for a way to
generate a relatively "clean" decentralised electricity, OR in certain
countries, those who are looking for a good financial investment (I'm
thinking of Germany and maybe Japan and the French overseas
departments... and probably certain areas of the US).

The costs are lower than for stand alone systems (I think about ?1/3?
for an equivalent annual energy production), the owner has no need to
know anything about anything (runs like a fridge or your tv once
installed) but will have to run the gauntlet of grid-connection
procedures (often long & difficult & sometimes expensive)

This is not a choice made by those looking for autonomy. If the grid
goes down, you have no more electricity. For many people (most in
western Europe & Japan, to my knowledge), this is not a problem as the
grid is extremely stable in their area, and outages rarely last longer
than a couple of hours, and there are rarely more than 2 or 3 per year.


3/ Back up systems - these systems are a combination of stand alone and
grid connected. A small back up battery bank is kept charged, and if the
grid goes down, the PV system will switch to feeding the batteries. The
batteries will in turn feed a few priority circuits (lighting, central
heating circulator, fridge, etc..(defined by the owners priorities &
climate)).

The back up battery bank is sized according to the owners needs and the
grid reliability. If you have very unreliable grid power, you will need
to factor this into the system. In France, this type of system is
confined to the overseas departments that are cyclone prone (keep the
fridge & lights running) and mountainous zones (keep the central heating
circulator & lights running).

This type of system costs more than a grid connected system, but by how
much will depend on what is on the priority circuit & the autonomy desired.



The choice between grid connected and back up system will depend on what
you want from your PV system, and why you are doing it. Most people
buying into grid connected PV in France mainland are doing it for
ecological reasons, and don't want batteries because of the disposal &
recycling problems. They have a stable grid, so are not too worried
about the occasional, short-duration blackout

I hope this answers your question!

Mel

It seems like a grid tied system and a backup gas or diesel generator
would be ideal. A friend of mine has a stand-alone tracking PV system.
She has to occasionally use a generator to charge her batteries if the
sun ain't shining for long enough.

 

[J Baber]

It seems like a grid tied system and a backup gas or diesel generator
would be ideal. A friend of mine has a stand-alone tracking PV system.
She has to occasionally use a generator to charge her batteries if the
sun ain't shining for long enough.

Jim Baber agrees;
But there is are major problems with trying to get grid tied
inverters to coexist with generators when the grid is down. Grid tied
inverters usually depend on the grid to serve as their load and as a
synchronization signal to provide the 50 or 60 cycle reference to keep
the inverter in phase with the utility grid.

These inverters require a total load that will accept ALL of their
output. They are designed to output their power at a voltage slightly
greater than the utility grid's voltage so that the grid will accept all
the power not used locally.

On the other hand a generator is designed so that as it's load is
increased more power is produced by the engine (because its throttle is
advanced by it's governor) that maintains the alternator's speed so the
frequency remains the same.

The problem occurs when you connect the two (inverter and
generator). The inverter's slightly higher voltage output will reduce
the power output by the generator until it is not generating power at
all, at which point the inverter will also quit since it no longer has a
synchronization signal from the generator. Then you do not see any
power at all until the generator is restarted.

Then, since these grid tied inverters have a safety delay designed
into them (2 minutes per US Codes), after the delay is satisfied the
inverter will restart and the whole problem recurs again then
again..........

Jim Baber

Email [email protected]

 

[Rob Munach]

Jim Baber agrees;
But there is are major problems with trying to get grid tied
inverters to coexist with generators when the grid is down. Grid tied
inverters usually depend on the grid to serve as their load and as a
synchronization signal to provide the 50 or 60 cycle reference to keep
the inverter in phase with the utility grid.

These inverters require a total load that will accept ALL of their
output. They are designed to output their power at a voltage slightly
greater than the utility grid's voltage so that the grid will accept all
the power not used locally.
On the other hand a generator is designed so that as it's load is
increased more power is produced by the engine (because its throttle is
advanced by it's governor) that maintains the alternator's speed so the
frequency remains the same.
The problem occurs when you connect the two (inverter and
generator). The inverter's slightly higher voltage output will reduce
the power output by the generator until it is not generating power at
all, at which point the inverter will also quit since it no longer has a
synchronization signal from the generator. Then you do not see any
power at all until the generator is restarted.

Then, since these grid tied inverters have a safety delay designed
into them (2 minutes per US Codes), after the delay is satisfied the
inverter will restart and the whole problem recurs again then
again..........

Jim Baber

Email [email protected]

I am sure there must be away around this by disconnecting the inverter
from the grid and feeding the house directly with the generator. Maybe
using a transfer switch.

 

[John P@ Bengi]

LOL. Yeah whatever.

Equalization is all about stirring up the liquid and has very little to do
with equalizing any charge if the batteries are kept at float voltage.

 

[Herb]

Hmmm, seems that the Navy submarine battery manuals that I read while
serving in subs, said that equalizers were all about driving sulfates
back into solution, so that the plates were once again exposed to
electrolyte vice insulated from the electrolyte by a layer of sulfate.

 

[John P Bengi]

You're wasting you time. It was only a troll.

Hmmm, seems that the Navy submarine battery manuals that I read while
serving in subs, said that equalizers were all about driving sulfates
back into solution, so that the plates were once again exposed to
electrolyte vice insulated from the electrolyte by a layer of sulfate.

 

[daestrom]

Hmmm, seems that the Navy submarine battery manuals that I read while
serving in subs, said that equalizers were all about driving sulfates
back into solution, so that the plates were once again exposed to
electrolyte vice insulated from the electrolyte by a layer of sulfate.

Windsun wrote:

From one 'bubblehead' to another, you're right. Of course, submarine
batteries also had air-lift pumps to prevent stratification (remember
cleaning out the little plastic orifice going into the top off each cell???)

But nuc boats used lead-calcium grid type batteries for normal 'float' and
only occasional discharge. While diesel boats used lead-antimony. The
antimony type suffered more self-discharge, but could stand a lot more
cycles before developing problems (as is typical in diesel boat ops).

daestrom
(former EMC(SS) )

 

[Herb]

From one 'bubblehead' to another, you're right. Of course, submarine
batteries also had air-lift pumps to prevent stratification (remember
cleaning out the little plastic orifice going into the top off each
cell???)

Oh no, I was lucky, the worst I ever had to do in the battery well was
a battery charging lineup on a boomer. Didn't have to hop gravities,
or add water, didn't have to clean the carbon dust generators either!
Thank God.
Herb ETC(SS) Ret.