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Guest

Mon Jan 07, 2019 9:45 pm   



Going off the grid (not me not now but...) we are looking at Tesla batteries for energy storage. These would be charged from solar panels.

It is reasonable to assume the panels are not going to charge at the rate of an AC operated 240 volt one, is that alright ? Will they charge properly ?

Of course there is the option of taking them initially to the station and charging them there, but where this is going there are not going to be any charging stations. If a float charge can be maintained it would work. The reserve would certainly be there and it would be a matter of replacing whatever energy is used.

Is this good for the battery though ? I mean from what I read it will take a towmotor to install the batteries so we can't have them failing soon.

Luckily the whole thing is mobile and under its own power. It will be a truck converted to a camper, but it is not going to live at a campground. Plus I doubt that you can pull enough power from a campground to charge one. Of course the proper fittings can be installed and the thing driven to a charging station but we do not want to HAVE TO do that.

I remember some NiCds that would suffer if they are not run down and recharged periodically. Are these batteries like that ?

The other question is if they suffer from self discharge - much. I don't know, there could be more than one in parallel.

We thought about a 300 volt system but that is nixed for now for a few reasons. However that could change depending on what kind of information I glean about this whole matter.

I might have to actually build a charger, if so I would have to figure out what I can and can't do. Constant current is no problem if that's what's needed. But what would be the minimum current ?

If the batteries are low in voltage, the current would only have to be at a slightly higher voltage than the state of charge dictates, but then can I taper off when it nears full charge ?

And if we simply can't muster the "rated" charging current with the solar, what are the consequences ? If some other type of battery would be more suitable that can be worked in.

I will not say cost is no object, but we know this is not going to be cheap.. And we don't plan on really draining that much. There will be A/C but that will run of a generator. Want cooling go get some fuel for that. It is however not a necessity. We need the necessities to remain away from the grid practically indefinitely. For example I am sure a propane stove would be nice because electric sucks, plus is less cost effective. But there would be electric alternatives. Intermittent use of things like a toaster oven, electric skillet, microwave and all that will be in there. We are aware of what kind of power that uses, so propane, as long as it is plentiful or nearby would be the norm.

However we want to avoid an absorption refrigerator and would prefer to run one on 120 volts. There wouldn't be much running off the inverter but what does will want amps. Al the lighting will be low voltage LED, even fans. Just things with a compressor are the problem there.

I have already did some web searching but the specific numbers I want seem to be elusive. For example I could calculate by what the charger pulls at 240 volts in the garage normally and get an idea. But there are specific that will be lacking unless I can get the whole setup and test it. That would be impractical, we are not buying a whole Tesla, just some batteries. Thus the question about self discharge, used batteries might not quite have the capacity as new ones, so two of them might be better. That is of course if they don't kill each other.

Any advice appreciated. (well almost)

Mike
Guest

Tue Jan 08, 2019 12:45 am   



On 1/7/2019 12:28 PM, jurb6006_at_gmail.com wrote:
Quote:
Going off the grid (not me not now but...) we are looking at Tesla batteries for energy storage. These would be charged from solar panels.

It is reasonable to assume the panels are not going to charge at the rate of an AC operated 240 volt one, is that alright ? Will they charge properly ?

Of course there is the option of taking them initially to the station and charging them there, but where this is going there are not going to be any charging stations. If a float charge can be maintained it would work. The reserve would certainly be there and it would be a matter of replacing whatever energy is used.

Is this good for the battery though ? I mean from what I read it will take a towmotor to install the batteries so we can't have them failing soon.

Luckily the whole thing is mobile and under its own power. It will be a truck converted to a camper, but it is not going to live at a campground. Plus I doubt that you can pull enough power from a campground to charge one. Of course the proper fittings can be installed and the thing driven to a charging station but we do not want to HAVE TO do that.

I remember some NiCds that would suffer if they are not run down and recharged periodically. Are these batteries like that ?

The other question is if they suffer from self discharge - much. I don't know, there could be more than one in parallel.

We thought about a 300 volt system but that is nixed for now for a few reasons. However that could change depending on what kind of information I glean about this whole matter.

I might have to actually build a charger, if so I would have to figure out what I can and can't do. Constant current is no problem if that's what's needed. But what would be the minimum current ?

If the batteries are low in voltage, the current would only have to be at a slightly higher voltage than the state of charge dictates, but then can I taper off when it nears full charge ?

And if we simply can't muster the "rated" charging current with the solar, what are the consequences ? If some other type of battery would be more suitable that can be worked in.

I will not say cost is no object, but we know this is not going to be cheap. And we don't plan on really draining that much. There will be A/C but that will run of a generator. Want cooling go get some fuel for that. It is however not a necessity. We need the necessities to remain away from the grid practically indefinitely. For example I am sure a propane stove would be nice because electric sucks, plus is less cost effective. But there would be electric alternatives. Intermittent use of things like a toaster oven, electric skillet, microwave and all that will be in there. We are aware of what kind of power that uses, so propane, as long as it is plentiful or nearby would be the norm.

However we want to avoid an absorption refrigerator and would prefer to run one on 120 volts. There wouldn't be much running off the inverter but what does will want amps. Al the lighting will be low voltage LED, even fans. Just things with a compressor are the problem there.

I have already did some web searching but the specific numbers I want seem to be elusive. For example I could calculate by what the charger pulls at 240 volts in the garage normally and get an idea. But there are specific that will be lacking unless I can get the whole setup and test it. That would be impractical, we are not buying a whole Tesla, just some batteries. Thus the question about self discharge, used batteries might not quite have the capacity as new ones, so two of them might be better. That is of course if they don't kill each other.

Any advice appreciated. (well almost)

You obviously don't have a clue. That's ok, get some professional
system advice.
Surely there's an off-grid newsgroup with actual relevant experience.

DO NOT COBBLE TOGETHER YOUR OWN BATTERY CHARGER.
Batteries are the most expensive part of the system. You want to make
them last as long as possible. Get a charger configured to interface
with your EXACT source and battery configuration.

DO NOT BELIEVE THE POWER CONSUMPTION RATINGS ON THE PRODUCT STICKER.
Do the math with real numbers.
An electric heater with 1200W on the panel can reasonably be expected.
to consume 1200W. Most other things have non-unity power factor and can
have a significant effect on the numbers you need to calculate.
Don't expect to be able to use more than half of your battery capacity.
Solar panels are rated for noon on a summer day with perfect solar tracking.
On a rainy winter day, you don't get much at all.

A system that keeps you up and running thru a week-long blizzard
is gonna cost you WAY more than you think.
Don't try to plan it a piece at a time.
Determine the exact requirements. Get a quote on a professionally
installed system. Start with the most expensive parts and see if
you can whittle it down to full DIY, or whether you can effectively
purchase some of the system parts.

Cobbling together a system that doesn't meet your needs is a big
waste of money.

bitrex
Guest

Tue Jan 08, 2019 2:45 am   



On 01/07/2019 03:28 PM, jurb6006_at_gmail.com wrote:
> Going off the grid (not me not now but...) we are looking at Tesla batteries for energy storage. These would be charged from solar panels.

Some texting bitch wrecked my first Volt about two year ago, if the
insurance company had let me keep the hulk I'd ship you that one to play
with!

You can pick up 48V 45 ampere/hour surplus individual pack modules off
eBay relatively cheap, tho (it takes about eight of these to make a full
pack for the car)

<https://www.ebay.com/itm/2012-Chevy-Volt-Battery-2kWh-pack-Solar-Golf-cart-/223232038949>

Jeff Liebermann
Guest

Tue Jan 08, 2019 7:45 am   



On Mon, 7 Jan 2019 12:28:49 -0800 (PST), jurb6006_at_gmail.com wrote:

>Going off the grid (not me not now but...) we are looking at Tesla batteries for energy storage.

Forget that idea. Assuming you mean the Tesla PowerWall 1, 2, or 3,
these were not designed to power anything. They were designed to
reduce your peak power usage (time of use load shifting) thus saving
you money on your electric utility bill.

>These would be charged from solar panels.

Really? Solar panels power a charge controller. It's the charge
controller that charges your battery. Misdesign the charge controller
and say goodbye to your battery. There are many more ways to kill a
big battery than there are to use it properly, so be prepared to do
some careful shopping, designing, and building. Trial and error is a
really bad way to design a charge controller.

Also, you'll need to deal with various electrical safety standards. I
don't have any idea what is in fashion in the UK, but in the
Trumpland, we have NEC Article 690. This is old, incomplete, but is
the most readable copy I could find online:
<http://www.energy.gov.bb/web/component/docman/doc_download/71-article-690-solar-photovoltaic-pv-systems>
Many of the safety features, such as the rapid shutdown and
disconnect, can be complexicated and expensive.

Unfortunately, my favorite alternative power magazine ceased
publication last month after the deaths of the owners. The online
archive of back issues are planned to be available eventually.
<https://www.homepower.com/about>
<https://www.homepower.com>
Meanwhile, the web site is full of relevant articles and information.
I suggest you dig through the "project profiles" for design examples
worth stealing:
<https://www.homepower.com/solar-electricity/project-profiles>

>Any advice appreciated. (well almost)

You probably won't appreciate this, but unless you have money to burn
on an over-designed monster system, you will find that going off grid
involves some substantial lifestyle changes and careful energy
management and accounting. Most off-grid failures can be attributed
to the owners unwillingness to grind the numbers and make any
necessary changes. I suggest you delay designing your system and
instead spend some time carefully measuring your current power
consumption and calculating your future off-grid power and storage
requirements. Also, consider that the further north you live, the
more difficult it is to build a usable solar power system.


--
Jeff Liebermann jeffl_at_cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

bitrex
Guest

Tue Jan 08, 2019 9:45 am   



On 01/08/2019 01:32 AM, Jeff Liebermann wrote:
Quote:
On Mon, 7 Jan 2019 12:28:49 -0800 (PST), jurb6006_at_gmail.com wrote:

Going off the grid (not me not now but...) we are looking at Tesla batteries for energy storage.

Forget that idea. Assuming you mean the Tesla PowerWall 1, 2, or 3,
these were not designed to power anything. They were designed to
reduce your peak power usage (time of use load shifting) thus saving
you money on your electric utility bill.

These would be charged from solar panels.

Really? Solar panels power a charge controller. It's the charge
controller that charges your battery. Misdesign the charge controller
and say goodbye to your battery. There are many more ways to kill a
big battery than there are to use it properly, so be prepared to do
some careful shopping, designing, and building. Trial and error is a
really bad way to design a charge controller.

Also, you'll need to deal with various electrical safety standards. I
don't have any idea what is in fashion in the UK, but in the
Trumpland, we have NEC Article 690. This is old, incomplete, but is
the most readable copy I could find online:
http://www.energy.gov.bb/web/component/docman/doc_download/71-article-690-solar-photovoltaic-pv-systems
Many of the safety features, such as the rapid shutdown and
disconnect, can be complexicated and expensive.

Unfortunately, my favorite alternative power magazine ceased
publication last month after the deaths of the owners. The online
archive of back issues are planned to be available eventually.
https://www.homepower.com/about
https://www.homepower.com
Meanwhile, the web site is full of relevant articles and information.
I suggest you dig through the "project profiles" for design examples
worth stealing:
https://www.homepower.com/solar-electricity/project-profiles

Any advice appreciated. (well almost)

You probably won't appreciate this, but unless you have money to burn
on an over-designed monster system, you will find that going off grid
involves some substantial lifestyle changes and careful energy
management and accounting. Most off-grid failures can be attributed
to the owners unwillingness to grind the numbers and make any
necessary changes. I suggest you delay designing your system and
instead spend some time carefully measuring your current power
consumption and calculating your future off-grid power and storage
requirements. Also, consider that the further north you live, the
more difficult it is to build a usable solar power system.



e.g. this is the size of the array required to supply the energy needs
of a small organic farm near me (Boston area); a modest single-family
two-story farmhouse, large barn, and a couple other associated
out-buildings on about 20 hectares of farmland/fields.

<https://imgur.com/a/ZDjSB9T>

five 25 square meter panels mounted on sun-tracking mounts, a 5-10kW
array, maybe.

Martin Brown
Guest

Tue Jan 08, 2019 10:45 am   



On 08/01/2019 06:32, Jeff Liebermann wrote:
Quote:
On Mon, 7 Jan 2019 12:28:49 -0800 (PST), jurb6006_at_gmail.com wrote:

Going off the grid (not me not now but...) we are looking at Tesla batteries for energy storage.

Forget that idea. Assuming you mean the Tesla PowerWall 1, 2, or 3,
these were not designed to power anything. They were designed to
reduce your peak power usage (time of use load shifting) thus saving
you money on your electric utility bill.


You have me interested now. I thought in the USA peak power load was
typically in mid afternoon when aircon was at full stretch and by
implication solar panels also at peak output. Surely the purpose of a
Tesla power wall *is* to store any excess solar power to use later in
the evening when the sun has gone down (rather than dumping it into the
hot water immersion heater - as is common in the UK). A quirk of the
feed-in-tariff is that you get paid a premium rate for half of what you
generate no matter what you do with it (insane).

ISTR they come in 12kWhr blocks and are notable for being able to
withstand being installed outside in the cold (UK never below -15C).

What is the peak discharge rate that they can cope with in practice?
Quote:

These would be charged from solar panels.

Really? Solar panels power a charge controller. It's the charge
controller that charges your battery. Misdesign the charge controller
and say goodbye to your battery. There are many more ways to kill a
big battery than there are to use it properly, so be prepared to do
some careful shopping, designing, and building. Trial and error is a
really bad way to design a charge controller.


In the UK you would also have to worry about the battery being destroyed
during the short grey winter days. There has been less than 10 hours of
sunshine since 1/1 and around 8 hours of daylight. The sun doesn't pack
much punch when it barely gets 14 degrees above the horizon.

It is worth pointing out that "professionally" designed active radar
signs in the UK "please go round the (dangerous) bend" routinely destroy
their batteries every winter. And they are a total waste of time - they
work brilliantly in mid-summer but are dead in the water a couple of
hours after sunset in winter and on every frosty winters morning!

A neighbouring villages cricket pavilion has a solar powered off grid
system (because the cost of running mains to it was prohibitive). It
seems to work OK but mainly because they only use it in summer.

Quote:
Also, you'll need to deal with various electrical safety standards. I
don't have any idea what is in fashion in the UK, but in the
Trumpland, we have NEC Article 690. This is old, incomplete, but is
the most readable copy I could find online:
http://www.energy.gov.bb/web/component/docman/doc_download/71-article-690-solar-photovoltaic-pv-systems
Many of the safety features, such as the rapid shutdown and
disconnect, can be complexicated and expensive.


There are plenty of companies offering solar power systems in the UK but
you have to be careful some are scam artists with incredible (and I use
the word advisedly) predictions of customer savings on electricity bills
that somehow never materialise. Likewise for ground source heat pumps.
Quote:

Unfortunately, my favorite alternative power magazine ceased
publication last month after the deaths of the owners. The online
archive of back issues are planned to be available eventually.
https://www.homepower.com/about
https://www.homepower.com
Meanwhile, the web site is full of relevant articles and information.
I suggest you dig through the "project profiles" for design examples
worth stealing:
https://www.homepower.com/solar-electricity/project-profiles

Any advice appreciated. (well almost)

You probably won't appreciate this, but unless you have money to burn
on an over-designed monster system, you will find that going off grid
involves some substantial lifestyle changes and careful energy
management and accounting. Most off-grid failures can be attributed
to the owners unwillingness to grind the numbers and make any
necessary changes. I suggest you delay designing your system and
instead spend some time carefully measuring your current power
consumption and calculating your future off-grid power and storage
requirements. Also, consider that the further north you live, the
more difficult it is to build a usable solar power system.


The only times I looked at setting up an offgrid supply it turned out to
be much cheaper to have a pair of big lead acid SLA's and charge them
off site weekly. It was an order of magnitude cheaper than solar power -
granted solar PV prices have come down a long way since then.

--
Regards,
Martin Brown


Guest

Tue Jan 08, 2019 1:45 pm   



On Monday, 7 January 2019 20:28:53 UTC, jurb...@gmail.com wrote:

Quote:
Going off the grid (not me not now but...) we are looking at Tesla batteries for energy storage. These would be charged from solar panels.

It is reasonable to assume the panels are not going to charge at the rate of an AC operated 240 volt one, is that alright ? Will they charge properly ?

Of course there is the option of taking them initially to the station and charging them there, but where this is going there are not going to be any charging stations. If a float charge can be maintained it would work. The reserve would certainly be there and it would be a matter of replacing whatever energy is used.

Is this good for the battery though ? I mean from what I read it will take a towmotor to install the batteries so we can't have them failing soon.

Luckily the whole thing is mobile and under its own power. It will be a truck converted to a camper, but it is not going to live at a campground. Plus I doubt that you can pull enough power from a campground to charge one. Of course the proper fittings can be installed and the thing driven to a charging station but we do not want to HAVE TO do that.

I remember some NiCds that would suffer if they are not run down and recharged periodically. Are these batteries like that ?

The other question is if they suffer from self discharge - much. I don't know, there could be more than one in parallel.

We thought about a 300 volt system but that is nixed for now for a few reasons. However that could change depending on what kind of information I glean about this whole matter.

I might have to actually build a charger, if so I would have to figure out what I can and can't do. Constant current is no problem if that's what's needed. But what would be the minimum current ?

If the batteries are low in voltage, the current would only have to be at a slightly higher voltage than the state of charge dictates, but then can I taper off when it nears full charge ?

And if we simply can't muster the "rated" charging current with the solar, what are the consequences ? If some other type of battery would be more suitable that can be worked in.

I will not say cost is no object, but we know this is not going to be cheap. And we don't plan on really draining that much. There will be A/C but that will run of a generator. Want cooling go get some fuel for that. It is however not a necessity. We need the necessities to remain away from the grid practically indefinitely. For example I am sure a propane stove would be nice because electric sucks, plus is less cost effective. But there would be electric alternatives. Intermittent use of things like a toaster oven, electric skillet, microwave and all that will be in there. We are aware of what kind of power that uses, so propane, as long as it is plentiful or nearby would be the norm.

However we want to avoid an absorption refrigerator and would prefer to run one on 120 volts. There wouldn't be much running off the inverter but what does will want amps. Al the lighting will be low voltage LED, even fans. Just things with a compressor are the problem there.

I have already did some web searching but the specific numbers I want seem to be elusive. For example I could calculate by what the charger pulls at 240 volts in the garage normally and get an idea. But there are specific that will be lacking unless I can get the whole setup and test it. That would be impractical, we are not buying a whole Tesla, just some batteries. Thus the question about self discharge, used batteries might not quite have the capacity as new ones, so two of them might be better. That is of course if they don't kill each other.

Any advice appreciated. (well almost)


The idea of running all that lot on solar power is simply impractical. The first things people do when designing an off grid solar system is
a) list what they think they could get away with using, as you have
b) calculate what that would cost. Utter expletives.
c) work out how they could run a way more frugal load.
Anything & everything that can avoid using electricity must do so. The rest needs to be superefficient. Then it might be doable.

Secondly, I don't know the cost of Tesla batteries but would be surprised if they were cheaper than lead acids. Homemade lead acids are not impossible..

3rd, PV panels give 2/3 of almost nothing on an overcast winter's day. In the UK we have 100% cloud cover day after day in winter.

A simpler constant current charger? Ha. At a minimum you need MPPT & a proper charging algorithm.

Calculate your daily energy use is the next move.


NT


Guest

Tue Jan 08, 2019 4:45 pm   



On Tue, 8 Jan 2019 08:50:22 +0000, Martin Brown
<'''newspam'''@nezumi.demon.co.uk> wrote:

Quote:
On 08/01/2019 06:32, Jeff Liebermann wrote:
On Mon, 7 Jan 2019 12:28:49 -0800 (PST), jurb6006_at_gmail.com wrote:

Going off the grid (not me not now but...) we are looking at Tesla batteries for energy storage.

Forget that idea. Assuming you mean the Tesla PowerWall 1, 2, or 3,
these were not designed to power anything. They were designed to
reduce your peak power usage (time of use load shifting) thus saving
you money on your electric utility bill.

You have me interested now. I thought in the USA peak power load was
typically in mid afternoon when aircon was at full stretch and by
implication solar panels also at peak output. Surely the purpose of a
Tesla power wall *is* to store any excess solar power to use later in
the evening when the sun has gone down (rather than dumping it into the
hot water immersion heater - as is common in the UK). A quirk of the
feed-in-tariff is that you get paid a premium rate for half of what you
generate no matter what you do with it (insane).

ISTR they come in 12kWhr blocks and are notable for being able to
withstand being installed outside in the cold (UK never below -15C).

What is the peak discharge rate that they can cope with in practice?

These would be charged from solar panels.

Really? Solar panels power a charge controller. It's the charge
controller that charges your battery. Misdesign the charge controller
and say goodbye to your battery. There are many more ways to kill a
big battery than there are to use it properly, so be prepared to do
some careful shopping, designing, and building. Trial and error is a
really bad way to design a charge controller.

In the UK you would also have to worry about the battery being destroyed
during the short grey winter days. There has been less than 10 hours of
sunshine since 1/1 and around 8 hours of daylight. The sun doesn't pack
much punch when it barely gets 14 degrees above the horizon.

It is worth pointing out that "professionally" designed active radar
signs in the UK "please go round the (dangerous) bend" routinely destroy
their batteries every winter. And they are a total waste of time - they
work brilliantly in mid-summer but are dead in the water a couple of
hours after sunset in winter and on every frosty winters morning!


No wonder.

Take a look at
https://en.wikipedia.org/wiki/List_of_cities_by_sunshine_duration
For UK in December, there are about 50 hours sunshine, i.e. less than
2 h/day. Even mounting the panels vertically on the southern wall
doesn't give a lot of energy in December.

Also remember the air mass (AM) losses due to the low sun angle, when
only a half or quarter solar intensity is available. Thus a "100 W"
panel will produce 25-50 W in December even with optimal orientation
and this is available only 2 h/day on average.


Quote:

A neighbouring villages cricket pavilion has a solar powered off grid
system (because the cost of running mains to it was prohibitive). It
seems to work OK but mainly because they only use it in summer.

Also, you'll need to deal with various electrical safety standards. I
don't have any idea what is in fashion in the UK, but in the
Trumpland, we have NEC Article 690. This is old, incomplete, but is
the most readable copy I could find online:
http://www.energy.gov.bb/web/component/docman/doc_download/71-article-690-solar-photovoltaic-pv-systems
Many of the safety features, such as the rapid shutdown and
disconnect, can be complexicated and expensive.

There are plenty of companies offering solar power systems in the UK but
you have to be careful some are scam artists with incredible (and I use
the word advisedly) predictions of customer savings on electricity bills
that somehow never materialise. Likewise for ground source heat pumps.

Unfortunately, my favorite alternative power magazine ceased
publication last month after the deaths of the owners. The online
archive of back issues are planned to be available eventually.
https://www.homepower.com/about
https://www.homepower.com
Meanwhile, the web site is full of relevant articles and information.
I suggest you dig through the "project profiles" for design examples
worth stealing:
https://www.homepower.com/solar-electricity/project-profiles

Any advice appreciated. (well almost)

You probably won't appreciate this, but unless you have money to burn
on an over-designed monster system, you will find that going off grid
involves some substantial lifestyle changes and careful energy
management and accounting. Most off-grid failures can be attributed
to the owners unwillingness to grind the numbers and make any
necessary changes. I suggest you delay designing your system and
instead spend some time carefully measuring your current power
consumption and calculating your future off-grid power and storage
requirements. Also, consider that the further north you live, the
more difficult it is to build a usable solar power system.

The only times I looked at setting up an offgrid supply it turned out to
be much cheaper to have a pair of big lead acid SLA's and charge them
off site weekly. It was an order of magnitude cheaper than solar power -
granted solar PV prices have come down a long way since then.



Guest

Tue Jan 08, 2019 7:45 pm   



Speaking of used batteries. Tesla battery is around $300/kWh. Leaf battery is around $200/kWh. Leaf battery would be better deal, as long as you don't fast charge it too much.

I am wondering if Tesla would sell real model 3 with smaller battery, I.e. 50 kwhr. No way they can sell for $35k otherwise.

Winfield Hill
Guest

Tue Jan 08, 2019 7:45 pm   



bitrex wrote...
Quote:

e.g. this is the size of the array required to supply the energy needs
of a small organic farm near me (Boston area); a modest single-family
two-story farmhouse, large barn, and a couple other associated
out-buildings on about 20 hectares of farmland/fields.

https://imgur.com/a/ZDjSB9T

five 25 square meter panels mounted on sun-tracking mounts, a 5-10kW
array, maybe.


That sounds more like a 15 to 20kW system, or about 2x larger
than mine. My roof annually generates enough power for my
power-hungry house (including electric hot water and 5kW heat
pump to heat house above 40-deg F). Maybe a system 2x larger
could handle a small farm.

BUT, given cloudy dark days and winter, I absolutely depend on
banking my extra summer power into the grid, with net-metering.
I use average 30kWh. If off-grid, I'd want at least 10 days of
backup, or a 300kWh storage system. Smaller ones need not apply.


--
Thanks,
- Win


Guest

Wed Jan 09, 2019 1:45 am   



>"What is the peak discharge rate that they can cope with in practice? "

That's another question. I doubt they like to run into a short circuit.


Guest

Wed Jan 09, 2019 1:45 am   



>"e.g. this is the size of the array required..."

Damn at looks big. You say 10 KW ? Hmmm. good reason for the A/C to be on the generator for sure.


Guest

Wed Jan 09, 2019 1:45 am   



>"You can pick up 48V 45 ampere/hour surplus individual pack modules off
eBay relatively cheap, tho (it takes about eight of these to make a full
pack for the car) "

We are still in the figuring out the need stage. Part of it can be changed, like a DC fridge is alot more expensive and usually too small, but a bigger invertor and a bit more battery ? Might be worth it.

Those individual pack modules, from what ? Tesla or something else ?


Guest

Wed Jan 09, 2019 1:45 am   



>"You obviously don't have a clue."

That is not advice.

Quote:
"That's ok, get some professional
system advice. "


That is advice. Of course that is why I am here. I figured someone might know about these things.

>"DO NOT COBBLE TOGETHER YOUR OWN BATTERY CHARGER. "

I really want to avoid that like the plague. I know there is more to it than a constant current source.

Quote:
"DO NOT BELIEVE THE POWER CONSUMPTION RATINGS ON THE PRODUCT STICKER.
Do the math with real numbers. "


I know about power factor. The problem with real numbers is obtaining them. I tend to figure worst case. So he has this fridge in mind that is rated 3..5 amps running and 6 amps to start. I think it reasonable to assume that the starting current is going want close to the 720 watts, but in run it is not going to be 400 watts. Thing is, worst case scenario just figure the 400 and enjoy whatever headroom.

>"A system that keeps you up and running thru a week-long blizzard is gonna cost you WAY more than you think. "

I am not sure what this guy thinks it is going to cost, but if he is not afraid of buying Tesla batteries I doubt he intends to be penny wise and pound foolish.

Quote:
"Get a quote on a professionally
installed system. "


Might, or maybe from one of the places that sells them. But it seems to me that whatever they put together could be enhanced.

Quote:
"Start with the most expensive parts and see if
you can whittle it down to full DIY..."


Sounds like a plan.

>"Cobbling together a system that doesn't meet your needs is a big waste of money. "

That's why I'm here.


Guest

Wed Jan 09, 2019 1:45 am   



>"Forget that idea. Assuming you mean the Tesla PowerWall 1, 2, or 3, these were not designed to power anything. "

I had to look that up. No, what he was considering is using actual Tesla car batteries.

>"Really? Solar panels power a charge controller."

I understand that. But one of the main questions I guess I didn't phrase right is if a Tesla CAR battery can be charged slowly, because it is not what you can get form the 240 volt line in the garage. No matter what charge rate the controller would set, the input must be greater than the output. (except in that other universe) Would it hurt to charge too slowly ? The only reason to even think about designing a charger it because it may be that the normal charger cannot be run on too low a current, or voltage depending.... Perhaps the usual charger with a bypass to get it to a certain point where it will rune ? Something like that.

This is new to me, but I don't scare easily. My main concern is the life of the batteries, after the power demands are met.

>"...some careful shopping, designing, and building. Trial and error is a really bad way to design a charge controller. "

Which is why I am here. How much does it take to charge these things ? I mean, what do they LIKE ?

If I have to go store boughten so be it. But, well you know. Do those specs exist somewhere on the net or are they a trade secret or something ? If not, maybe a regular charger could be bought and what it does measured. In fact just having that could come in handy. Maybe it barely keeps up, and if run down takes a week to charge. But then there is the option to just drive up to a charging station and boom, there's the power again. Would like to avoid that if possible but to have the option is good.

And of course he wants to be off the grid but on the net, that is a whole new ball of wax, though I know it can be done.

>"...most readable copy I could ..."

I copied all those links and will read them later. (before doing anything of course)

>" I suggest you delay designing your system and
instead spend some time carefully measuring your current power
consumption ..."

Problem is there is no current power consumption to measure. We are discussing all kinds of options for that. For example he probably will want a microwave, if we do that a modern fridge ain't shit. In no way do I pretend want to put pencil to paper without a hell of alot more information. I also know that there are needed numbers even before contemplating a store boughten system. Off the shelf so to speak.

Quote:
"Also, consider that the further north you live, the
more difficult it is to build a usable solar power system. "


He intends to go mostly south. There will be A/C but that will be separate on a generator. In fact a big enough generator might even run an AC operated charger as rated... Hmmm.

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