Grid Tied inverters for household use will soon be useless?

[Faringdon]

Hi,

This is what i mean...
https://www.solarquotes.com.au/blog/grid-voltage-rise-solar/

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?

[NiHaoMike]

Just use an autotransformer to cut the voltage a bit.

[nctnico]

Just use an autotransformer to cut the voltage a bit.

But that will increase the grid voltage even more which in the end damages the equipment in your home.

[Berni]

The power networks need to upgrade to keep up with ever rising energy demands, there is no way around it.

We had a too long line to the transformer that was feeling the whole street. It used to be fine, but as demand rose it just did not cut it anymore. We got a solar inverter and it kept complaining and going into safe mode. So i hooked up a DMM to the worst phase and turns out it sometimes dropped down to 180V for a breif moment. They used to compensate for this by choosing a higher transformer tap, but that was too much for the first houses in the line. We sent the chart to the power company, they came over and left there own dataloger for a bit and came to the same conclusion. As a result they decided to run a new line from a transformer, it went mostly trough our land and our relatives so we helped arrange for approval. Ever since the voltage is rock solid and the solar inverter is happy as can be.

As electric cars become more popular this is only going to get worse. They take massive amount of power from the grid and they typically get charged at similar times of the day when people come home from work.

[Monkeh]

The power networks need to upgrade to keep up with ever rising energy demands

'ever rising'?



But yes, the LV side of the grid is going to have to adapt to significantly different demand peaks and the reality of distributed generation.

[Berni]

I meant for residential costumers.

The largest users of power tends to be industry and those will usually get there own high voltage feed and a dedicated transformer right on the property. They are doing fine and can pump boat loads of solar power into the grid without the voltage going anywhere.

The residents on the other hand are fed over long wires from transformer stations dotted about. These have a limited ability in current handling as at some point the wires connecting them produce too much voltage drop. The transformers themselves are also old and got speced according to how much power they thought they will need in the 60s

Its not that the grid can't handle all this solar power. It's this last low voltage local distribution step that is struggling.

[f4eru]

Yep. Old style networks, not designed for strong local generators, but still can handle it to a point.
Takes time to phase out, but will happen.

[NiHaoMike]

But that will increase the grid voltage even more which in the end damages the equipment in your home.

Not if you put the sensitive loads on the autotransformer as well. But aren't modern electronics designed for as much as 265V?

[nctnico]

But that will increase the grid voltage even more which in the end damages the equipment in your home.

Not if you put the sensitive loads on the autotransformer as well. But aren't modern electronics designed for as much as 265V?

And how about the neighbours? 

[Zero999]

I meant for residential costumers.

The largest users of power tends to be industry and those will usually get there own high voltage feed and a dedicated transformer right on the property. They are doing fine and can pump boat loads of solar power into the grid without the voltage going anywhere.

The residents on the other hand are fed over long wires from transformer stations dotted about. These have a limited ability in current handling as at some point the wires connecting them produce too much voltage drop. The transformers themselves are also old and got speced according to how much power they thought they will need in the 60s

Its not that the grid can't handle all this solar power. It's this last low voltage local distribution step that is struggling.

There has been a fall in electricity consumption by residential customers over the last decade, due to more efficient appliances, such as incandescent lamps being replaced with LEDs.

That will reverse as electric cars become more common and the power distribution network will need to be upgraded to cater for it.

[Berni]

Depends on the area-

Here power consumption is going up because people are moving away from burning fuels to heat the house, now getting heatpumps to do the job. More and more people are also getting air conditioning where compared to before barely anyone had it (It does not get all that hot here to make them a must)

Oldschool gas burning cookers are getting replaced by modern induction cookers that also use lots of power, while the gas one used 0 power.

We really did not use electricity for making heat. About the only common use for it was hot water heaters and ovens.

On top of all that it is common to run 230V for up to 2km down the whole street over just one set of wires. It is 3 phase and pretty chunky wires, but at some point the wire resistance still comes into the equation  for the accompanied voltage drop.

Electric cars are not all that popular yet, but places like Norway that does have a lot of electric cars really had issues with the amount of power they suck up. They had enough power in the grid to make it happen since they have heaps of hydro power, but the last mile low voltage distribution was not up to the job, causing voltages to plummet and light bulbs to dim.

[Faringdon]

Thanks, you are all correct, but the thing that is being missed in the press is that GTI_based_solar is going to crash at some point........because when you have loads of people exporting solar to the grid via their GTI's...this tends to raise the grid voltage...and GTIs stop working when mains voltage goes up to 253VAC.

The only way round this is for households to put their solar into a battery...and then this battery feeds their household loads via an inverter which is not grid tied, ie, not connected to the national grid.

Its the only way, surely you agree?

But the GTI industry is currently in denial of this.

[Monkeh]

Its the only way, surely you agree?

No, because we're not your echo chamber.

[NiHaoMike]

And how about the neighbours? 

They're farther away so they'll see lower voltage. Looking at reference designs for universal input power supplies, they're tested up to 265V, some up to 270V.

Since it's the peak voltage that determines the voltage seen by electronics, perhaps the solar inverters, if they detect the voltage going high, could start pushing more power on the lower parts of the sine wave and less on peak? It could be done in a controlled manner such that the harmonics would be of low frequency and unlikely to cause interference. Conversely, electronic loads without PFC would theoretically help the situation by pulling down on the peaks more than the same amount of load with PFC.

[Cerebus]

Looking at reference designs for universal input power supplies, they're tested up to 265V, some up to 270V.

You seem to be making the unwarranted assumption there that everything connected to the mains has an SMPS at the front of it. This is not the case.

[Cerebus]

Its the only way, surely you agree?

No, because we're not your echo chamber.

Ah yes, the "presumptive close" the trick of every desperate salesman out there.

[NiHaoMike]

You seem to be making the unwarranted assumption there that everything connected to the mains has an SMPS at the front of it. This is not the case.

That's true for an ever increasing percentage of loads. Aside from all the high tech devices commonly thought of as electronics, it also includes most LED lights, modern fluorescent lamps, inverter drive motors, and induction heating appliances.

I'm also pretty sure there's a good reason why 265V or 270V is chosen as the upper test voltage for most universal input power supply designs.

[Cerebus]

And excludes motors and resistive heating elements in washers, dryers, ovens, stovetops, kettles, coffee machines, toasters, grills, most refrigeration etc. I think a few kW each for many of those kinds of loads (my kettle alone is 3.5 kW) rather tips things in their favour against the 5-200W each typical of most household appliances that have an SMPS in.

[bdunham7]

I'm also pretty sure there's a good reason why 265V or 270V is chosen as the upper test voltage for most universal input power supply designs.

I believe that the typical utility voltage upper limit in the US would be 252 volts (240 nominal + 5%) and the voltage tolerance for devices would be 264 volts (+10%) and that is for everything not just SMPS designs.  However, grid-tied inverters are typically set to a nominal upper value of 264 volts, so they keep producing even if the utility voltage is exceeding their 5% tolerance limit.  I don't know overvoltage curtailments are much of a problem elsewhere, but it hasn't happened to me yet.

[Zero999]

my kettle alone is 3.5 kW

How does it not trip the 13A plug top fuse? Presumably that must be the surge rating.

Thanks, you are all correct, but the thing that is being missed in the press is that GTI_based_solar is going to crash at some point........because when you have loads of people exporting solar to the grid via their GTI's...this tends to raise the grid voltage...and GTIs stop working when mains voltage goes up to 253VAC.

The only way round this is for households to put their solar into a battery...and then this battery feeds their household loads via an inverter which is not grid tied, ie, not connected to the national grid.

Its the only way, surely you agree?

But the GTI industry is currently in denial of this.

Or you could just turn on a water heater and air-conditioning to bring the voltage down a bit.

[Faringdon]

Or you could just turn on a water heater and air-conditioning to bring the voltage down a bit.

I think this is asking for too much customer participation.

When people buy solar and a GTI, they expect to be able to profit whenever there is sunlight.......they cannot  necessarily do that if they have a GTI connecting their solar to the grid....which everyone does, or most do at the moment.

I also think GTI's cut off when grid voltage becomes >253VAC.(?)

I think IMHO, we all agree that the Solar_GTI is in denial of the situation.

[nctnico]

I think IMHO, we all agree that the Solar_GTI is in denial of the situation.

No. If you would have followed the news a bit then you'd know the problem is well known and newly developed suburbs are typically fitted with a better grid connection. But that still leaves a large number of houses/buildings that have a less than ideal grid connection which may or may not be upgraded at some point. In the end it is a cost versus benefit calculation. Some people likely get the short end of the stick.

[Zero999]

Or you could just turn on a water heater and air-conditioning to bring the voltage down a bit.

I think this is asking for too much customer participation.

With smart devices, the user doesn't have to do anything. They can communicate with the inverter and use up extra energy when necessary.  Even if you don't have smart appliances, it doesn't take a genius to always set the timer on the washing machine, so it runs through the middle of the day, when the solar panels will power it.

[Psi]

With electric cars driving new/cheaper batteries it will make more sense to store your excess solar energy locally, rather than push it into the grid during peak outs and pull from grid during off hours.
Usually you don't get retail rates for that power, so it costs you extra money to pull it back out again later.

If electric cars get cheaper so do power walls.

[Jester]

Hi,

This is what i mean...
https://www.solarquotes.com.au/blog/grid-voltage-rise-solar/

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?

I appreciate that at the small ends of the distribution system these high voltage conditions may limit how much an individual inverter can push back into the grid at a particular time. However looking at the bigger picture obviously the utility has control of the voltage and frequency. From my perspective having all these inverters gives us a better distribution of source power, many baskets instead of a few big ones.

With electricity rates tied to peak hours, I don’t think to many Tesla owners are charging when they come home at 5pm, that would be foolish.