Tricking Solar inverter

[maker_vu7m2e8e_1663605226]

Hey guys,

Sorry if this is in the wrong place, I know nothing about electronics, so am hoping you good people can help.

I'm hopefully going to be installing a solar and battery system in my house soon, and it's a big system, so I think my DNO will tell me I'm not allowed to export any energy back to the grid.

Now it's easy enough to do that, I can simply put an isolator switch between my meter and consumer unit. However, if my inverter senses the grid is down, it goes into a crappy mode called EPS, which uses dedicated circuits to power essentials, but from what I've read on a forum (not in the manual), will only power this circuit with energy from the battery and not the solar power.

So, I would like to know if it would be possible to trick the inverter into thinking the grid is still running. It detects if the frequency falls below 50hz, and assumes an issue with the grid. So is there something that I could put in line with the inverter that would achieve this?

Cheers guys,

Jay

 

[Alec_t]

Now it's easy enough to do that, I can simply put an isolator switch between my meter and consumer unit.

I doubt it's as easy as that. Interfacing between your solar system and the grid would have to be via a DNO-approved unit, which ensures that your system doesn't drive the grid when the grid is suppoedly unpowered for maintenance. The DNO doesn't want its workers electrocuted! Also, the inverter has to be phase-locked to the grid before you can throw a switch to export energy.
Welcome to maker.pro.

 

[maker_vu7m2e8e_1663605226]

Hi Alex, cheers for your reply, you are of course correct in everything you say, so thank you.

I obviously didn't explain my intention very well.

I intend to not be connected to the grid unless absolutely necessary. I intend to install an isolator between the meter and my consumer unit, and have it off, hopefully permanently.

That's why I want to trick my inverter.

So no worry about hurting any grid workers, in fact quite the opposite.

So anyone got any suggestions?

 

[Bluejets]

I intend to not be connected to the grid unless absolutely necessary.

A grid connected system is exactly what it says.
There is NO inbetween where you can start fiddling with the system willy nilly.
Reasons why NO running of the inverter on a grid when the grid is down has already been covered above.

If you want a system completely isolated from the grid, you need to purchase and have the correct system installed.
Be aware in many countries, simply being isolated from the grid does not imply you can roll your own with mains level wiring either.

 

[kellys_eye]

will only power this circuit with energy from the battery and not the solar power.

?? Your solar panels will have some circuitry to allow it to charge the batteries in the first place. This is usually 'permanently' connected and the batteries will always be charging except when the solar array is disconnected. The inverter will operate as long as it detects there is sufficient charge in the batteries (kept topped up by the solar array of course) but that won't be 'forever' (depending on the load drawn).

You can't power anything 'directly' from the solar panels - without the required regulator the output will be too variable.

 

[maker_vu7m2e8e_1663605226]

?? Your solar panels will have some circuitry to allow it to charge the batteries in the first place. This is usually 'permanently' connected and the batteries will always be charging except when the solar array is disconnected. The inverter will operate as long as it detects there is sufficient charge in the batteries (kept topped up by the solar array of course) but that won't be 'forever' (depending on the load drawn).

You can't power anything 'directly' from the solar panels - without the required regulator the output will be too variable.

So you think that disconnecting from the grid would be fine as the batteries will keep the inverter going?

My issue is that I read somewhere that the inverter will stop using the solar supply if the grid is down, which doesn't make sense to me. It will continue to power the house using the batteries, but as you said, they will run out of power if the solar isn't there to recharge them.

The manual for the inverter is really poor, but I think I've found on a forum that I can actually set the inverter to not send anything back to the grid, in which case all is well.

 

[kellys_eye]

So you think that disconnecting from the grid would be fine as the batteries will keep the inverter going?

I thought you weren't connecting to the grid?

I can actually set the inverter to not send anything back to the grid,

You shouldn't have any connection to the grid AT ALL unless it is properly certified and professionally installed. It's not appropriate to simply 'program' the unit to not feed back to the grid - that is simply not safe enough.

Failing the pro route, you should treat your system as you would a portable generator - it should be connected to the household circuit via an appropriate change-over switch (manual or automatic) or just connect it to a separate circuit feeding specific socket outlets as required, entirely independent from the main house circuit.

Ge this wrong and you will be liable in every legal sense of the word not to mention up on charges of manslaughter.

 

[maker_vu7m2e8e_1663605226]

I don't want to start an argument, but it does my head in when people say " you can't install this yourself, you should get a professional"! I've been in touch with the DNO who say it's absolutely fine for me to install my own system, as long as I fill in the G99, and the MCS agree with this as well, and told me that they only issue guidelines for best practice, there are no legal requirements to follow these.

As for connecting to the grid, I said that I was going to fit a disconnect switch between my consumer unit and the incoming meter, so I could isolate my system from the grid. I was simply responding to your previous message regarding the solar always being connected to the battery.

The inverter I have is G99 compatible and has an anti islanding feature, so it will not feed into the grid if the grid is down. Me limiting the export is a feature that will be in play while the grid is live, and if I find the unit has the ability to restrict feed in to zero, then I won't have any need for the trickery I have asked about in this thread.

I appreciate your replies, and apologise if I am coming across as irresponsible, I am quite the opposite, I have the utmost regard for other people's safety, It seems i may not be explaining myself properly.

Jay

 

[Bluejets]

there are no legal requirements to follow these.

That depends on which country you are in.
Any mains level installation in many countries requires installation be done and inspected by a certified electrician.
Reason being, some sneaky diyers have no idea of the wiring rules and regulations and put peoples lives in danger.

Failing the pro route, you should treat your system as you would a portable generator - it should be connected to the household circuit via an appropriate change-over switch (manual or automatic) or just connect it to a separate circuit feeding specific socket outlets as required, entirely independent from the main house circuit.

You will find with these the same conditions of installation and inspection are required.

Either the solar inverter is a grid connect type or it is not.
There is no in-between for when it suits you.

 

[maker_vu7m2e8e_1663605226]

Ok guys, I can't explain this any better, and I'm obviously not explaining it very well, so I'll leave this here.

Thanks for trying to help.

Jay

 

[Martaine2005]

Here in the UK, we can do our own electrical work EXCEPT new circuits from the consumer unit as that requires a qualified electrician to sign it off.
Also, we can’t touch ‘tails’ from the meter > main fuse to the consumer unit. This also requires a qualified electrician.
So for the UK, we CANNOT install an isolator between the meter and consumer unit (fuse box) as this would require a qualified electrician to do the work and sign it off.
Just for clarity, our (UK) meter and main house fuses are security tagged/locked to ensure the general public doesn’t touch them. Here is an example picture.

 

[maker_vu7m2e8e_1663605226]

Here in the UK, we can do our own electrical work EXCEPT new circuits from the consumer unit as that requires a qualified electrician to sign it off.
Also, we can’t touch ‘tails’ from the meter > main fuse to the consumer unit. This also requires a qualified electrician.
So for the UK, we CANNOT install an isolator between the meter and consumer unit (fuse box) as this would require a qualified electrician to do the work and sign it off.
Just for clarity, our (UK) meter and main house fuses are security tagged/locked to ensure the general public doesn’t touch them. Here is an example picture.

View attachment 56290

Technically the only people allowed to pull the main fuse are the DNO in the UK, although it seems to be accepted practice that sparkies do it.

 

[Bluejets]

Well I at least have attempted to convey the message, if you are not a qualified electrician with the necessary certification, leave the thing alone.
There is good reason for the warning as has already been explained.

 

[maker_vu7m2e8e_1663605226]

The message isn't anything to do with what I asked, but thanks for conveying it.

 

[kellys_eye]

I 'know' where the OP is coming from and appreciate that the rules will be followed as per the OP's country requirements. As a forum we are 'obliged' to ensure that advice given doesn't encourage anyone to break the rules or give rise to potential harm to the OP or others that may be 'connected' with the tasks at hand.

I'm convinced the OP is 'safe' in that regard but I always feel that a direct query and appropriate response is the best way to alleviate any concerns I myself might have - the OP has satisfied me on that account.

Good luck with your project.

 

[Bluejets]

I 'know' where the OP is coming from and appreciate that the rules will be followed as per the OP's country requirements. As a forum we are 'obliged' to ensure that advice given doesn't encourage anyone to break the rules or give rise to potential harm to the OP or others that may be 'connected' with the tasks at hand.

I'm convinced the OP is 'safe' in that regard but I always feel that a direct query and appropriate response is the best way to alleviate any concerns I myself might have - the OP has satisfied me on that account.

Good luck with your project.

Good luck convincing the supply authority that your opinion should over rule any of their requirements.

 

[Sunnysky]

A good grid-tied inverter or GTI may already have the feature you read was not available.

There are several regulators and many protection features in a GTI that are required by each country and province beyond CE , UL etc. with an order of precedence.

Both grid and PV source must sense the battery and load current separately in order to be sure the charger cuts out when the battery is full while the inverter continues to supply the load. It may also bridge power from the inverter and mains with isolation unless certified for the physical and electrical safety to be tied to the grid. When grid-tied is active with a full-bridge (bidirectional) the inverter supply current is power factor corrected, and sinusoidal. When not a GTI or "tied" to a grid, it is just a half-bridge rectifier or charger that generates power to a DC-DC converter. The unit will prefer the PV source if available and matches impedance to maximize the power transfer from the PV when charging the battery and feeding the inverter load. If the PV load is insufficient the grid power is used but it should NOT cut out the PV source simply if the AC grid is down. (I need a link to a reference manual if you know otherwise.)

Otherwise, it must be operated only like a generator to charge the batteries in a UPS inverter of the type which is always running to dedicated loads from the battery while the dual chargers are running to the battery. (grid & solar)

The weakness of inverters is they prefer a steady AC load and motors draw at least 5x the max rated load on startup can cause a brownout or shutdown to the GTI. So this means special soft start servos or circuits are needed unless the dedicated loads are tolerant to the lights dimming when an air conditioner starts.

So to answer your question, all inverters ought to use PV power during a blackout but must not drive the grid during a blackout. If not, customizing this is not a simple option to isolate the GTI from the grid externally unless certified by all the regulatory agencies for safety.

Although logically it is a trivial matter to have glitch, brownout and blackout sensing control a grid source with a zero crossing switch and/or relay. In some regions like here in Toronto, ON, there are stringent requirements for GTI's.