Grid-tie inverters: What is this sorcery?

Context first:: I’m not an electrician, and I have almost no idea how electricity works. Undeterred by this, I’ve been looking at putting some solar panels up on my roof, which is a big south-facing tiepi and gets direct sun all day long.

I had been thinking that running house appliances off my toy PV setup would be a nightmare, but then I found a product making a startling claim:

It says “台電的電表是機械電錶,原理是電流產生磁力推動轉盤,如果兩條火線的電流不同,分別產生的磁力共同去推動轉盤,如果一正一負,兩邊的磁力會互相抵消”, which I think roughly means that the Taipower meter wheel is pushed by magnetic force from the current running through it, and that plugging this inverter in (to some sensible breaker circuit) will push current the other way through the meter, cancelling out some of what the rest of the house is using (and perhaps even contributing power back to the grid).

This sounds a little too good to be true, but it does seem to be, and is maybe even pretty standard.

So, some questions:

  • Can this possibly work?
  • Is it legal?
  • What would happen if my meter reading went down over a month?
  • Am I going to make the whole neighbourhood explode?
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Yes, of course it works. But unless there’s some arrangement with Taipower, you’re giving them power for free. Taipower seem to have been consistently against the very concept.

That’s selling to the network, not a novel idea. It’s the whole selling point for all distributed power generation technologies, including solar.
But I have no idea if there is adequate legal groundwork in Taiwan.

I don’t mind giving them power for free, if I’m generating more than I need – it would still mean less coal being burned. But I don’t expect I will be, generally.

I’m just kind of amazed that it’s this simple.

Yeah, it’s mostly the politicians and the power companies who prefer to pretend that it isn’t.

There are some complications - depending on exactly how the nation’s grid is put together - but they’re fairly minor ones. Basically, Taipower would rather take subsidies from the government than move into the 21st century.

The funny part is that Taiwan was promoting (and possibly subsidizing) a whole new PV-panel industry about 10 years ago. About a dozen manufacturers sprung up, and as far as I know they’re now all defunct. They had no market. It never seemed to occur to anyone that they had a viable market right here … or if it it did occur to them, the necessary horse-trading never reached the desired result.

Laws have changed now so you can look into it more.

Yea considering Taipower sells power so cheap (when 6.4nt per kwh is like what people in most developed country pays for being an average user, while with Taipower it’s the absolute max), I don’t know if Taiwanese are that keen on trying to sell power back to Taipower.

Though it’s a good idea if it helps balance the load during the summer months.

I think the law was changed that you can sell directly to some customers ?
Taipower interestingly also contracts private power stations run by Taipower staffers.
There is no way corruption is involved. NO WAY. :grinning:

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I’ve seen various mentions of schemes to let consumers choose where their power comes from, and such, but I haven’t found details. This is generally interesting: https://www.emcsg.com/f1671,123955/3_-_Dr_Chuan-Neng_Lin_Bureau_of_Energy_Taiwan.pdf

I was particularly entertained by Taiwan’s plan for installing renewable capacity, which is “let other people do it while Taipower keeps adding coal and gas”:

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('IPP" in the above is Independent Power Producer).

Where are you getting the solar panels? What’s the output going to be? What does that converter you found need for an input? (I can’t read Chinese). How many of those panels will you need to parallel and/or series up to get any significant power production that is compatible with the converter you found? You going to store any of that power? If not, then you won’t be running much of anything except at peak sunlight.

I’m gonna take a hunch and say that the device you found will need fairly high voltage to run. In which case, if you don’t know anything about electricity, then you could kill yourself. Nobody wants to see that happen.

Take care dude.

Yeah. I’m doing a lot of reading. This guy has 110V inverters that will happily run off 24V or 48V DC, and 220V inverters from 48V DC up, which all seems reasonable. So you wire up a PV array at (say) 48V and feed it through an MPPT charge controller into whatever battery bank you like, and then from there into the inverter.

That part all makes sense to me. It’s just the part where it intersects with the grid power in the house that I’m a bit vague on.

Incidentally, one ridiculous problem I have is that my house used to be two houses, and it has two separate Taipower connections (for which I get separate bills), and two breaker boxes each wired to totally random parts of the house. The good news is that most of the expensive stuff, including the ACs and the roof where I run power tools, is off just one of those. The bad news is that it’s the one that’s less convenient to connect things straight into the breaker box, which is why I’m trying to figure out what happens if I just plug the inverter into whatever socket I can reasonably get at off that breaker.

Just try not to start a fire. Sounds like you’re going down that path IMO.

@ckw_64 is right. If you don’t have any knowledge or experience of electrical work, don’t attempt this. There are rules and regulations that you have to comply with to connect to the grid. In the worst case - if you start a fire - you risk jail time or a very large fine.

Solar panels and 12V batteries might look harmless, but you can easily blow your fingers off by dropping a screwdriver in the wrong place or electrocute yourself by fiddling with the high-voltage side. You may not even feel a medium-voltage DC shock (say, 60-100V), but it can cause you damage all the same. There’s a lot of latent energy in a battery and a lot of power flowing in even a modest solar installation.

Get a professional to specify the parts and install them. Apart from anything else, he’ll be able to calculate the best possible system configuration for your application, and find reputable suppliers for your batteries.

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I’d certainly feel more comfortable having a professional involved, even if just to consult. But I’ve never met an electrician here who could even be trusted to change a lightswitch. Do they exist? References welcome.

Failing that, I’m just going to start small, read a lot, and be careful.

And there comes the battery, storing power for use when the sun doesn’t shine!

Technically I don’t think you will be giving Taipower energy for free, as they use the old analog meters still, it is likely the meter will run backwards when power is being fed back into the grid.

Since they use analog meters they probably can’t easily detect this unless they actually see the meter going backwards.

I know that you can get into trouble in other countries that use the “smart meters” as they can detect when energy is being pushed back into the grid and alert the power company.

Allegedly they’re introducing those here, too, although I’ll believe it when I see it. But in other countries I don’t think you generally get in trouble, the meter just doesn’t run backward.

ah, good point. There are still a lot of those around. And yes, they should run backwards (although not necessarily - it depends on their construction details). I have no idea whether Taipower would get upset about this, but they’d probably never notice if your solar output is less than your overall energy consumption.

As noted, the newer ones can detect reverse power flow.

@Brendon: you’re right, you don’t want your local shui dian doing this. He’ll probably blow himself up. I’m afraid I can’t recommend anyone, but possibly the supplier who’s selling you this stuff will have some ideas?

How much power do you think you’re going to generate? How much do you want to generate?