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[SOLVED] Household domestic grid tied inverters will die out?

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cupoftea

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Hi,
As you know, the effect of multiple households exporting solar or wind energy back to the grid via their grid tied inverter inevitably raises the grid voltage. As solar gets more common, we will see normal grid voltages over UK and EU of 254VAC plus.

As such, Grid tied inverters in people’s houses will simply stop working, as they can’t even connect to the grid if the grid voltage is over 253V. There is already a limit of 5Kw for household export to the grid (in EU and UK) , though when solar gets even more popular, this will have to be reduced down to almost nothing.

This is a statement of the obvious, yet trying to find anywhere on the web that says this is impossible. Possibly because solar panel vendors are sensoring such info, who knows (?)

As such, in future, we will see household solar panels with simply DCDC converters putting the solar energy into a battery in the household. From there we will see non grid tied inverters putting 230VAC into a separated mains wiring system in the house (separate from the national grid mains wiring).

Most houses will then simply use this non grid connected 230VAC for powering their household items, eg boiler, EV charger etc etc.

This will impact on things like PFC laws for household items that are connected only to the “household internal grid”.

So do you agree its goodbye to domestic Grid Tied inverters?
 

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As they may only last 5 - 7 years, GTI's that can only export current to live mains will phase themselves out. I think the upper limit for export to the mains is 245Vac, impedances of the mains mean that local GTI's will supply local loads, obviously at times of peak sunshine and low loadings all GTI's will have to throttle back to 245Vac.

Newer GTI's will have smart switches and stand alone operation so that homes can have quite a bit of local storage ( and this could include the EV, or two, that each household has ) - and programmed so that said local storage can be applied only to the household loads ( islanded from the mains ) - as the domestic load increases the mains will be seamlessly re-connected ( easy ).

All this has ben planned for for quite some while and there are IEEE standards around same
 

cupoftea

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as the domestic load increases the mains will be seamlessly re-connected ( easy ).
Thanks, i was just thinking, such a changeover switch woudl maybe be a fairly bulky contactor in most households. Also, its difficult to see how the switchover from grid to "islanding" and vice versa would be seamless...some mains connected devices may reset or go into fault, whatever?
 

SunnySkyguy

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"As solar gets more common, we will see normal grid voltages over UK and EU of 254VAC plus."

What are the assumptions and logic behind this?

GTI's are unity PF current sources that monitor voltage with limits and are unlikely to become the core source of power that regulates grid mean voltage and frequency. If nukes and hydro did no longer become prime sources, then GTI's would require storage capacity with TOD communication from regulators per the contract pricing.
 

cupoftea

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GTI's are unity PF current sources
Thanks, and as you know, the grid itself is not a unity power factor corrected current source.......since if a non PFC'd equipment draws a high reactive power, the mains will simply supply it. So this is interesting.

When GTIs pump energy into the grid, they always raise its voltage by a little bit....a lot doing it will raise it significantly.
 

SunnySkyguy

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Thanks, and as you know, the grid itself is not a unity power factor corrected current source.......since if a non PFC'd equipment draws a high reactive power, the mains will simply supply it. So this is interesting.

When GTIs pump energy into the grid, they always raise its voltage by a little bit....a lot doing it will raise it significantly.
As I said when that time comes, regulators will cut-off major contributors and expect storage be added . During the over voltage situations, a proposed system will be deactivated and the energy storage system will get power from the grid; as a result, the grid voltage will decrease to an acceptable level.
 

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Thanks, i was just thinking, such a changeover switch woudl maybe be a fairly bulky contactor in most households. Also, its difficult to see how the switchover from grid to "islanding" and vice versa would be seamless...some mains connected devices may reset or go into fault, whatever?
I don't know where you get a lot of your assumptions - but 100A single phase or 50A 3 phase contactors are readily available and cheap, an inverter simply has to match phases and the contactor can close without fuss or issue,

solid state SiC switches for AC mains are being designed right now - and further, control of inverters is progressing to the point where - with a CT on the incomer - the inverter can modulate its output to match the exact load current of the house - negating a real need for an isolator - excepting where the mains fails and the house needs to be islanded so it can have its own power.

Perhaps you do not do and industrial design in these areas ?
 

cupoftea

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and further, control of inverters is progressing to the point where - with a CT on the incomer - the inverter can modulate its output to match the exact load current of the house - negating a real need for an isolator
Yes i see your point...the thing is, if shedloads of houses in a neighbourhood are generating loads of energy and exporting it to the grid, then the mains level will obviously go up.....(Sunnyskyguy appears to agree with this, and sugggets that he believes that the authoirities will deal with this issue)

...since everybody is connected to the same mains phase, then houses who then try and export to the grid from their solar will not even be able to connect to the grid because their grid tied inverter wont connect up.......and as such they wont even be able to supply their own house from their own solar panels.....
...as you rightly point out....your household mains is directly connected to your neighbours'......if its level goes up then you're stuffed...your GTI wont connect............unless you island your premises, how, in this situation, can you coax your GTI to connect and only supply your household electrical items....you cant...surely?

1....The "axis point" of this entire argument, is that a Grid tied inverter, when it exports energy back to the grid, will, inevitably, slightly raise the voltage of that grid.......higher than it would have been if everything was just powered by the local power station....if this axis point is wrong, then please advise?

2....The follow-on point from this, is that GTI's will not connect to the grid if the grid voltage is too high.


..put 1 and 2 together, and you get some interesting, and possibly not very nice , outcomes.

(Granted i got my brain in a twist about the contactor current ratings.)
 

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Like battery chargers, GTI's have CC then CV so overvoltage is protected. (OVP by design but would waste surplus energy available)

What you will see in future is more are energy storage farms to be able to store surplus energy where feasible to utilize cheaper surplus power and cutoff more expensive sources.
 

cupoftea

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Thanks,
To focus on the main point...
This is what i mean...

GTI's have got serious problems up ahead !!!

If people want there own solar generation. Then pretty soon, they are going to have to "island" their household mains from the grid, and just use a standard Non grid tied inverter from the panels to supply their household...

This is obvious, do you not agree?
 

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I can't comment on any regional problem, but if homes have solar GTI's with a problem, the regulators have to expect this and have a process to handle it. Solutions exist, and it's a tradeoff between profits and quality of service. Fortunately our quality is excellent with 5% tolerances >99.9 % of the time with very few outages, usually spring thaw time from aging underground XLPE distribution.

I would think the expansion of EV vehicle sales will increase the overnight load to help regulate surplus power.
I think with Tesla's storage facility in AU and some parts of the USA in process, the costs of quality and energy storage will occur, but depends on the quality-cost trade-offs for each regulator. OV also increases distribution stress and maintenance, so they will make decisions and consider the costs of customer bad feedback with their decisions.

Users with old GTI's lacking features may have to upgrade to prevent reverse charging or just equalize to null usage or something else. Changes will occur, but it is impossible to forecast every region action but there will always be a need to balance all future demand and supply in every case while minimizing cost increases and preserving quality.

Your mileage may vary. The best GTI's I've seen are from Huawei who have political-economic issues with USA and CANADA's support.
 

RCinFLA

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What you will see is utility control on PV power push. If power company begins to lose control on system they will remotely command GT inverters in an area to shut down or at least prevent grid power push.
 

cupoftea

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I can't comment on any regional problem, but if homes have solar GTI's with a problem, the regulators have to expect this and have a process to handle it.
Thanks, but the only way to handle this, is for people to stop using GTI's.

There's no need for the power companys to do anything to help the role out of GTI_based_solar...why should they?....they cant be responsible for customers pumping up the mains voltage. The power companys, if they dont like the effect of high mains voltage, then they need to outlaw the use of GTI's...and governments will have to decree that any solar generated in a house must be put into an "islanded" system, and not connected to the mains......this is what i believe will happen, as there is simply no way of dealing with the GTI_based_solar problem......i would ask if readers agree...but i think its obvious isnt it?......please advise if i have slipped up here though?
 

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1....The "axis point" of this entire argument, is that a Grid tied inverter, when it exports energy back to the grid, will, inevitably, slightly raise the voltage of that grid.......higher than it would have been if everything was just powered by the local power station....if this axis point is wrong, then please advise?

2....The follow-on point from this, is that GTI's will not connect to the grid if the grid voltage is too high.


..put 1 and 2 together, and you get some interesting, and possibly not very nice , outcomes.
You seem to be overly focused on absolutes, if the grid goes to 245Vac, it cannot go any higher due to local GTI's as these all have limits, if you want to use your own power then you have to disconnect if the volts are that high, if the volts are closer to 230Vac say then a modern inverter can control its o/p to match the household loads - by matching current profiles ( CT on the DB ) .... QED.
 

KlausST

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Hi,

There is a huge European grid.
Energy will be produced and will be consumed.
There are times when there is "too much" produced and there are times when too much energy is consumed.
A measure for this is the grid frequency. The frequency is common for the whole grid.
The voltage is a local measure. It is different from town to town, even from house to house.

In former (in my region, before the photovoltaic era) the voltage dropped according load.
A simple formula (ignoring cos(phi) ): V_drop = R_grid × I_load.
The more you live in the periphery the higher R_grid...the more voltage drop.
The grid company compensated this peripheral voltage drop with transformers that produce a higher output voltage.
This worked in that time.

But now there are times where (especially in) the peripheral areas produce more enery than consumed.
Thus the mature "static" solution does not work anymore.

The grid company in my area took much effort to reduce R_grid by installing "stiffer" transformers and thicker cables.
Additionally the installed automatic voltage controllers - responsible for larger areas. Not static anymore - they now react on voltage fluctuations.
In my area one can detect the voltage to go higher when the load drops ... but then they compensate it with a step back (if I remember right it is about 3V steps).
Indeed I'd say we have much less electrical problems due to overvoltage, undervoltage and drop outs than before.
I guess a dropout of more than a couple of minutes is averaged less than once per year in my rural area of Germany.
From random measurements I can't remember a voltage outside 230V +/- 10V.

What I want to say: The technique for stabilizing voltage is available and proven.
So sooner or later something similar will be installed all aver the world. Maybe it already is installed.

*****

Still the GTIs generate a higher risk for blackouts.
Thus I guess in future we need more decentral GTIs with batteries and frequency controlled power control.

Example:
When a power station fails, the grid frequency decreases. To avoid a blackout the GTIs now should be able to detect the frequency drop and push some higher power (from the batteries) into the grid ... to stabilize the system and to save some time for the power plants with slower regulation time to compensate the power demand.

Some information on European grid frequency: mainsfrequency.com

Klaus
 
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