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Comment by euroderf | Hacker News Reader

I very much want one of these in Finland, but our provider KSOY said no no no.

Posing the question, is there a valid technical reason or is it just institutional conservatism and inertia ?

Operating electrical power grids requires a very careful balance between production and consumption. Long term trends are regulated on the consumption side through pricing, short term jitter is regulated on the production side through switching power plants on and off.

Traditionally, a power grid only had medium and large power plants, and they are not only connected to the power grid but also a control network. Adding many small power generators poses a problem in how you communicate and coordinate with them.

"Connecting Solar to the Grid is Harder Than You Think" https://www.youtube.com/watch?v=7G4ipM2qjfw

Although 800w per household shouldn't make a difference for the grid.

800w for your house won't make a difference. Multiply by millions of households and that is real power that will make a difference.

800w is the maximum being produced, and not all of it will be fed into the grid. And it is unlikely that millions of households have all installed powerplants which are all oriented in the same direction and not shaded.

Germany is 84 million people. If 1% have solar and they currently average to 400 watts (half capacity from their 800 watts because of positional and shading issues) that is 33 Gigawatts. That much power if not managed will cause problems for any grid.

No, if 1% of them produce 400w that is actually only 320 Megawatts.

You could think the other way around: what prevent every citizen from a region to switch ON or OFF a 7kW load at the same time (such as an EV)

These things just plug into a power outlet. Requirement for Austria is a Smart Powermeter, because the old, analog ones would run in reverse if the solar panels produced more then you are currently using. They may not exceed 800W and are required to turn off if no power grid is detected, e.g. during a power outage. Apart from that, just institutional conservatism and inertia as far as I know.

Have your cake and eat it ? https://solarbringer.de/solar-inselanlage-mit-netzunterstuet...

Yes, this is exactly my configuration! 3.5kw panels, 9kwh battery. Saves at least 1/2 of the daily power usage.

Because they are potentially deadly in certain failure states. Normally system you expect system to be dead when main switch is turned off. But in this case something might be feeding in power. Same goes for over current protection. You really do not want power when you expect there to be none. Even if you should always check.

This is not really an issue. The inverters used in these cases rely on an existing power supply for synchronization with the electrical grid. If there is no power on the socket, the inverter has no means to generate a sine wave on its own and does not provide power on its cable.

This is true (as far as I know) for ALL inverters, apart from "off grid" solutions, so workers can turn off power on a street level. If that wasn't the case, there would be no way for technical staff to make sure that lines going to multiple homes (with solar) are powered off.

I can how it would not switch on if line power is gone. But what if it is on already, there are not many loads on, and the mains go down? Does it switch off? How does it know?

It watches the incoming AC waveform and matches that. If there is no waveform it has nothing to match and so it shuts off.

How do you watch the incoming waveform if you drive your own waveform on the same line? I guess you could look periodically.

Balcony solar requires the 50Hz of the energy grid. If you turn off the main power they will stop feeding into the system.

So if enough of your neighbors have these panels then the grid never gets turned off.

Technically probably yes, provided you had millions of neighbors, the sun never sets and all big users like kettles and heat pumps kindly switch off as well. If either of those conditions stops being true, then either the frequency or the voltage will drop too much and the panels turn themselves off. In practice these balcony panels are not sufficient in the slightest to power a house, let alone an entire apartment building, and they will turn off almost instantly.

READ THE OTHER REPLIES FIRST. I'm going to assume you did as they are right about what this can't happen.

When you backfeed like that your neighbors will draw on your power - but they will attempt to draw more than you can provide and so your circuit breakers will trip. The only way backfeeding could be an issue is if you have a very large generator and the area islanded is only a couple neighbors such that the total power use is less than the theoretical max of your house.

That said, linemen are trained to either treat all wires as live or short them to ground. They can never be sure they are not in that rare exception case and mistakes can be deadly.

In any given moment the power grid must be 1:1 for production and consumption, and lots of smaller renewables pose a problem for big operators because they need to forecast and balance.

I got the feeling that people were just not telling their electricity provider that they were doing this.

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