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If I want to supplement a particular source of AC/mains power with
other sources, what options are available?
The obvious is to convert both to DC and use that to power
an inverter.-a But, this seems like it would be terribly inefficient
(esp at higher power levels).
If I want to supplement a particular source of AC/mains power with
other sources, what options are available?
The obvious is to convert both to DC and use that to power
an inverter.-a But, this seems like it would be terribly inefficient
(esp at higher power levels).
On 26-Aug-25 2:29 pm, Don Y wrote:
If I want to supplement a particular source of AC/mains power with
other sources, what options are available?
The obvious is to convert both to DC and use that to power
an inverter.-a But, this seems like it would be terribly inefficient
(esp at higher power levels).
Combining AC supplies requires the ability to synchronise, which few sources of
AC outside industrial or grid scale are likely to have, though domestic grid-tie inverters would, of course.
There is also the issue of adjusting demand across the supplies, according to
their abilities to supply, costs, etc.
I think you need to say more about your application.
On 8/26/2025 12:03 AM, Sylvia Else wrote:
On 26-Aug-25 2:29 pm, Don Y wrote:
If I want to supplement a particular source of AC/mains power with
other sources, what options are available?
The obvious is to convert both to DC and use that to power
an inverter.-a But, this seems like it would be terribly inefficient
(esp at higher power levels).
Combining AC supplies requires the ability to synchronise, which few sources
of AC outside industrial or grid scale are likely to have, though domestic >> grid-tie inverters would, of course.
Hence the idea of converting each to DC and then driving an inverter
from the combined supplies.
I've also been looking into electromechanical solutions -- mixing
the power mechanically -- but there seems to be an upper limit of about
95% on such a solution (and it would likely be physically large).
On 26/08/2025 4:29 pm, Don Y wrote:
If I want to supplement a particular source of AC/mains power with
other sources, what options are available?
The obvious is to convert both to DC and use that to power
an inverter.-a But, this seems like it would be terribly inefficient
(esp at higher power levels).
On the contrary inverters are remarkably efficient - around 95% or
better - and big ones can do even better. Getting rid of waste heat is a pain, so perfectionism isn't the main motivation.
Electric cars are crawling with inverters, so there's huge market for
some classes of inverters.
On 8/26/2025 12:46 AM, Don Y wrote:
On 8/26/2025 12:03 AM, Sylvia Else wrote:
On 26-Aug-25 2:29 pm, Don Y wrote:
If I want to supplement a particular source of AC/mains power with
other sources, what options are available?
The obvious is to convert both to DC and use that to power
an inverter.-a But, this seems like it would be terribly inefficient
(esp at higher power levels).
Combining AC supplies requires the ability to synchronise, which few
sources of AC outside industrial or grid scale are likely to have,
though domestic grid-tie inverters would, of course.
Hence the idea of converting each to DC and then driving an inverter
from the combined supplies.
I've also been looking into electromechanical solutions -- mixing
the power mechanically -- but there seems to be an upper limit of about
95% on such a solution (and it would likely be physically large).
I'm looking at total output powers in the 5-25KW range.
On 8/26/25 3:48 AM, Don Y wrote:
On 8/26/2025 12:46 AM, Don Y wrote:
On 8/26/2025 12:03 AM, Sylvia Else wrote:
On 26-Aug-25 2:29 pm, Don Y wrote:
If I want to supplement a particular source of AC/mains power with
other sources, what options are available?
The obvious is to convert both to DC and use that to power
an inverter.-a But, this seems like it would be terribly inefficient >>>>> (esp at higher power levels).
Combining AC supplies requires the ability to synchronise, which few
sources of AC outside industrial or grid scale are likely to have, though >>>> domestic grid-tie inverters would, of course.
Hence the idea of converting each to DC and then driving an inverter
from the combined supplies.
I've also been looking into electromechanical solutions -- mixing
the power mechanically -- but there seems to be an upper limit of about
95% on such a solution (and it would likely be physically large).
I'm looking at total output powers in the 5-25KW range.
Many of the off-grid hybrid solar inverters are designed to be paralleled up to
six or twelve units.-a First example that comes to mind in your range is the EG4
Electronics 6000XP.-a It's one box with line power and solar MPPT inputs, a battery charger for 48V batteries, and a 6000 W inverter.-a See all the specs at
https://eg4electronics.com/categories/inverters/eg4-6000xp-all-in-one-off-grid-inverter/
-aThey also have the 12000XP for double the power.-a They can both do 120/240 VAC split phase,
as well.
There are other brands which appear to be the same as the 6000XP, with all the guts
for everyone made in China, of course.-a That would be a plug and play solution for
you, and their website would show you the range that's available.
A decent YouTube channel that has done lots of testing and comparisons of different brands, along with how-to videos to assemble systems of various sizes, is https://www.youtube.com/@WillProwse-a He's not a EE but he knows the solar market.
On 8/26/2025 9:53 AM, Carl wrote:
On 8/26/25 3:48 AM, Don Y wrote:
On 8/26/2025 12:46 AM, Don Y wrote:
On 8/26/2025 12:03 AM, Sylvia Else wrote:
On 26-Aug-25 2:29 pm, Don Y wrote:
If I want to supplement a particular source of AC/mains power with >>>>>> other sources, what options are available?
The obvious is to convert both to DC and use that to power
an inverter.-a But, this seems like it would be terribly inefficient >>>>>> (esp at higher power levels).
Combining AC supplies requires the ability to synchronise, which
few sources of AC outside industrial or grid scale are likely to
have, though domestic grid-tie inverters would, of course.
Hence the idea of converting each to DC and then driving an inverter
from the combined supplies.
I've also been looking into electromechanical solutions -- mixing
the power mechanically -- but there seems to be an upper limit of about >>>> 95% on such a solution (and it would likely be physically large).
I'm looking at total output powers in the 5-25KW range.
Many of the off-grid hybrid solar inverters are designed to be
paralleled up to six or twelve units.-a First example that comes to
mind in your range is the EG4 Electronics 6000XP.-a It's one box with
line power and solar MPPT inputs, a battery charger for 48V batteries,
and a 6000 W inverter.-a See all the specs at https://
eg4electronics.com/categories/inverters/eg4-6000xp-all-in-one-off-
grid-inverter/
-aThey also have the 12000XP for double the power.-a They can both do
120/240 VAC split phase,
as well.
But, will this pass 6000W of "line power" through to the output, in the absence of the battery?
I.e., imagine a wind turbine, solar PV (400VDC), solar Stirling, battery
bank and AC mains (and other similar) going into a "box" (group of your devices) and AC mains coming out the other end, regardless of the relative contributions of the turbine, PV, Stirling, battery and mains?
IME, such solar devices have a "nominal" charging current for the
batteries and can't provide the full inverter-rated current to
the load via that path (if the batteries are absent or if
you don't want to drain them of their charge).
Or, they expect the solar to be grid tied.
There are other brands which appear to be the same as the 6000XP, with
all the guts
for everyone made in China, of course.-a That would be a plug and play
solution for
you, and their website would show you the range that's available.
It will have to be able to support the (e.g.) 6000W load at the inverter output even in the absence of batteries (does that clarify the
functionality
I desire?).-a I.e., run sources THROUGH such boxes and use their ability to be paralleled to effectively tie those sources together AT the output.
I have a similar situation, here, where I use "DC" output from individual panels paralleled to power my load and the battery bank -- skipping the inverter stage (why convert to AC and then immediately back to DC??)
A decent YouTube channel that has done lots of testing and comparisons of
different brands, along with how-to videos to assemble systems of various
sizes, is https://www.youtube.com/@WillProwse-a He's not a EE but he
knows the solar market.
Thanks!
On 8/26/25 5:02 PM, Don Y wrote:
But, will this pass 6000W of "line power" through to the output, in the
absence of the battery?
Yes, they have a "Generator" input and can use that to both charge a battery and pass up to 6000W through to the inverter output, along with a line voltage
battery charger input that can be connected to the grid but this does not pass
through directly to the output.
This is an off-grid system, not a grid-tie
system, so the output cannot be connected to the grid.
-a Look in the manual
starting on page 22 for the input options.-a You may need to connect a small battery, or not - I've absorbed a lot of discussion on these units but have never wired one up myself.-a I knew what you say you wanted, and I'm pretty sure
these will do that, but I can't give you the fine details and nuances.
If I want to supplement a particular source of AC/mains power with
other sources, what options are available?
The obvious is to convert both to DC and use that to power
an inverter. But, this seems like it would be terribly inefficient
(esp at higher power levels).
Don Y <blockedofcourse@foo.invalid> wrote:
If I want to supplement a particular source of AC/mains power with
other sources, what options are available?
The obvious is to convert both to DC and use that to power
an inverter. But, this seems like it would be terribly inefficient
(esp at higher power levels).
If you want to use mains there may be serious legal obstacles:
utilities are quite picky about devices that (at least potentially)
can inject power to the grid.
With AC sources obvious condition is that they must be in sync.
In small signal approximation each source has some voltage and
some impedance. Voltages and impedances decide how power divides
between devices. Using autotransformers you can adjust voltages
to get more desirable power distribution. More modern solution
could use inverter(s) effectively changing both voltage and
impedance.
If you have control of devices you can tell them to adjust their
voltage to get desired power distribution.
Considering your later examples, solar power naturally comes as DC.
Batteries too. Wind turbines have speed of rotation depending on
wind, so probably you need to convert to DC first (and then back to
desired frequency). Classic engine-generator modules probably
run engine at specific RPM to get desired frequency. Classic ones
allowed independent requlation of voltage. I suspect that now some
units use permanent magnets which probably do not allow requlation,
so you would need autotransformer or inverter to adjust voltage.
If you combine sources as AC you need to look at stability of
regulation, which probably means that you need to know characteristics
of your sources.
On 8/26/2025 3:46 PM, Carl wrote:
On 8/26/25 5:02 PM, Don Y wrote:
But, will this pass 6000W of "line power" through to the output, in the
absence of the battery?
Yes, they have a "Generator" input and can use that to both charge a battery
and pass up to 6000W through to the inverter output, along with a line
voltage battery charger input that can be connected to the grid but this does
not pass through directly to the output.
OK, so the "line" input wouldn't be used if the intent was to power
the load FROM the line.-a You would, instead, have one box that connected
the mains to the generator input (so it could power the load THROUGH the box).-a Another box with a genset connected to the generator input to
add it's power to the "supply".-a Another...
A PV array could be attached to any of these and "mixed in".
This is an off-grid system, not a grid-tie system, so the output cannot be >> connected to the grid.
That's exactly the issue.-a Not to rely on the grid for storage *or* supply (though being able to USE it)
-a Look in the manual starting on page 22 for the input options.-a You may need
to connect a small battery, or not - I've absorbed a lot of discussion on >> these units but have never wired one up myself.-a I knew what you say you >> wanted, and I'm pretty sure these will do that, but I can't give you the fine
details and nuances.
Thanks!-a I've bookmarked the page and will download their documentation, later.
On 8/28/2025 10:36 AM, Waldek Hebisch wrote:
Don Y <blockedofcourse@foo.invalid> wrote:
If I want to supplement a particular source of AC/mains power with
other sources, what options are available?
The obvious is to convert both to DC and use that to power
an inverter. But, this seems like it would be terribly inefficient
(esp at higher power levels).
If you want to use mains there may be serious legal obstacles:
utilities are quite picky about devices that (at least potentially)
can inject power to the grid.
Yes, hence an approach that just looks like a LOAD to the grid.
With AC sources obvious condition is that they must be in sync.
In small signal approximation each source has some voltage and
some impedance. Voltages and impedances decide how power divides
between devices. Using autotransformers you can adjust voltages
to get more desirable power distribution. More modern solution
could use inverter(s) effectively changing both voltage and
impedance.
As I mentioned, above. But, at levels of tens of KW, even small inefficiencies are costly. E.g., 98% efficient at 25KW means
throwing 500W off. If efficiency varies with load (likely),
then typical operating point considerations can dominate the design.
If you have control of devices you can tell them to adjust their
voltage to get desired power distribution.
Considering your later examples, solar power naturally comes as DC.
Batteries too. Wind turbines have speed of rotation depending on
wind, so probably you need to convert to DC first (and then back to
desired frequency). Classic engine-generator modules probably
run engine at specific RPM to get desired frequency. Classic ones
allowed independent requlation of voltage. I suspect that now some
units use permanent magnets which probably do not allow requlation,
so you would need autotransformer or inverter to adjust voltage.
If you combine sources as AC you need to look at stability of
regulation, which probably means that you need to know characteristics
of your sources.
I was hoping for a cleverer nonelectronic solution. E.g., combining
power mechanically. But, if you assume motors are ~95% efficient,
you're already at a deficit to pure electronic solutions.
On 8/28/2025 10:36 AM, Waldek Hebisch wrote:
Don Y <blockedofcourse@foo.invalid> wrote:
If I want to supplement a particular source of AC/mains power with
other sources, what options are available?
The obvious is to convert both to DC and use that to power
an inverter. But, this seems like it would be terribly inefficient
(esp at higher power levels).
If you want to use mains there may be serious legal obstacles:
utilities are quite picky about devices that (at least potentially)
can inject power to the grid.
Yes, hence an approach that just looks like a LOAD to the grid.
With AC sources obvious condition is that they must be in sync.
In small signal approximation each source has some voltage and
some impedance. Voltages and impedances decide how power divides
between devices. Using autotransformers you can adjust voltages
to get more desirable power distribution. More modern solution
could use inverter(s) effectively changing both voltage and
impedance.
As I mentioned, above. But, at levels of tens of KW, even small inefficiencies are costly. E.g., 98% efficient at 25KW means
throwing 500W off. If efficiency varies with load (likely),
then typical operating point considerations can dominate the design.
If you have control of devices you can tell them to adjust their
voltage to get desired power distribution.
Considering your later examples, solar power naturally comes as DC.
Batteries too. Wind turbines have speed of rotation depending on
wind, so probably you need to convert to DC first (and then back to
desired frequency). Classic engine-generator modules probably
run engine at specific RPM to get desired frequency. Classic ones
allowed independent requlation of voltage. I suspect that now some
units use permanent magnets which probably do not allow requlation,
so you would need autotransformer or inverter to adjust voltage.
If you combine sources as AC you need to look at stability of
regulation, which probably means that you need to know characteristics
of your sources.
I was hoping for a cleverer nonelectronic solution. E.g., combining
power mechanically. But, if you assume motors are ~95% efficient,
you're already at a deficit to pure electronic solutions.
If you want to use mains there may be serious legal obstacles:
utilities are quite picky about devices that (at least potentially)
can inject power to the grid.
Yes, hence an approach that just looks like a LOAD to the grid.
It does not matter how your device looks to the grid. What matters
is how it look to utility lawyers ("there is galvanic connection
between power source and the grid, illegal"). I suspect that
in practice you are limited to commericial devices which have
appropiate approvals. And your choice as a buyer will be
limited by what utilities approve.
With AC sources obvious condition is that they must be in sync.
In small signal approximation each source has some voltage and
some impedance. Voltages and impedances decide how power divides
between devices. Using autotransformers you can adjust voltages
to get more desirable power distribution. More modern solution
could use inverter(s) effectively changing both voltage and
impedance.
As I mentioned, above. But, at levels of tens of KW, even small
inefficiencies are costly. E.g., 98% efficient at 25KW means
throwing 500W off. If efficiency varies with load (likely),
then typical operating point considerations can dominate the design.
No, you did not understand. I mean inverter in series with power
source (think of elecronic version of auttransformer), so inverter
just needs to compensate for difference in voltages. Say, your source
gives 110 V, but you need 120 V so that it "wins" with other source.
In such case inverter needs to deliver 10 V (at source current), so
its power is less than 10% of source power. Of course, this assumes reasonably well matched voltages.
Also, at high power it is resonable to build inverter with
sections and activate number of sections matching load, so for
rather large variation on load you can get close to maximal
efficiency.
BTW: do you consider efficiency of wires?
If you have control of devices you can tell them to adjust their
voltage to get desired power distribution.
Considering your later examples, solar power naturally comes as DC.
Batteries too. Wind turbines have speed of rotation depending on
wind, so probably you need to convert to DC first (and then back to
desired frequency). Classic engine-generator modules probably
run engine at specific RPM to get desired frequency. Classic ones
allowed independent requlation of voltage. I suspect that now some
units use permanent magnets which probably do not allow requlation,
so you would need autotransformer or inverter to adjust voltage.
If you combine sources as AC you need to look at stability of
regulation, which probably means that you need to know characteristics
of your sources.
I was hoping for a cleverer nonelectronic solution. E.g., combining
power mechanically. But, if you assume motors are ~95% efficient,
you're already at a deficit to pure electronic solutions.
95% efficient motor is rather ambitious.
And you still have problem
of combining sources: power will combine depending on characteristics
of sources, so you need regulation to get desired characteristics.
Your problem is miniature version of problem that utilities need to
solve. And classic solution is to essentially regulate sources.
That is have requlators on generators and multitap transformers.
If you can regulate sources, then you have clever solution. If
your sources do not allow regulation, then you need to provide it
externally (say via autotransformers or inverters). Some of your
sources will need inverters anyway, so you can use them to provide regulation. Or you can use simple solution of convertiong
everthing to DC and having big inverter whith multiple DC
inputs and single AC output.
If I want to supplement a particular source of AC/mains power with
other sources, what options are available?
The obvious is to convert both to DC and use that to power
an inverter.-a But, this seems like it would be terribly inefficient
(esp at higher power levels).
On 8/25/25 11:29 PM, Don Y wrote:
If I want to supplement a particular source of AC/mains power with
other sources, what options are available?
The obvious is to convert both to DC and use that to power
an inverter.-a But, this seems like it would be terribly inefficient
(esp at higher power levels).
The Tesla Energy Gateway does the combining in the AC domain.
Power from the grid, battery inverter and solar inverter together with the house load all connect to the same bus.
There are a small number of operation modes:
In the most common configuration (called Time Based Control) at night the grid
supplies all the power to the load. As solar power becomes available during the
day the solar inverter syncs to the grid and supplants power taken from the grid. If there is excess solar available it then supplies the excess to the grid.
If the battery requires charging; excess solar power is directed to the battery. Excess power can also be directed to charge an electric vehicle.
Another selectable mode referred to as Self-consumption the system will avoid
use of grid power at all and instead use battery power. I normally use this mode during the day but do not have enough guaranteed solar to use it year round.-a The battery inverters sync to the grid to be able to blend the power in
this mode.
None if these controls requires any relays or contactors - it performed by varying the power of the battery inverter to either source or sink.
If the grid fails is is galvanically isolated from the system and the battery
inverter becomes the reference for the solar inverters. The battery can either
supply power if solar is unable to supply the house load or sink power if they
need charging.
If the battery is fully charged there is then nowhere to dissipate the incoming
solar power so the frequency of the battery inverter is raised to signal the solar inverters to curtail production.
The Tesla system does not provide for generator power to be merged into the load. To do so would require that it synchronizes the grid or battery inverter
and there are very few (or maybe no) generators that can do that. Similarly wind turbines would need the same capability.
As a matter if interest most large wind turbines to go through a DC to AC conversion to provide flexibility in rotation speed. The couple of percent loss
in efficiency is considered worth that.
Another mode that some energy management systems can provide is a "non-export"
capability that allows solar power to be added together to grid power but never
to the extent that power flows back to the grid. This can then then be used with Public utilities that don't allow export.