How many grid-tie inverters can a grid support?

Ubbquittious

Is there any theoretical maximum amount of grid tie inverters that can be connected to an electrical grid before things start to go wrong?

If you have an island with 1,000 houses each with their own grid tie inverter what else is needed to keep the system going? Presumably by default none of them will switch on because there is no mains signal but would creating one by connecting a small Honda generator be enough to bring them all to life?

If the inverters start producing too much power as a whole the voltage should rise beyond some cut off point prompting batches of them to disconnect in order to prevent "islanding" so presumably some island-sized dump load is required to stop this from happening or a modified firmware that lets the inverters reduce output rather than cutting out

murphaph

In Germany large installations >30kWp must be fitted with a radio receiver that can cause the installation to suspend feed in if the network operator requires it (almost never happens apparently). Operators of installations smaller than this can optionally pay for this or must limit their feed in to 70% of the nominal max the installation can generate. The 70% can be "hard" so the inverter is permanently limited or "soft" so it's software controlled and will allow more than 70% production if the excess above 70% is being consumed and not fed in. (the actual losses are estimated for a perfect roof in Southern Germany to be around 4% a year because the max theoretical output of the system is only achieved a few days a year when it's very sunny and also has a breeze to cool the panels to better efficiency). If more and more people keep adding small installations they will presumably reduce the 30kWp threshold.

Ubbquittious

Interesting. What type of radio standard are they using? Do they address individual installations and have the system progressively disable more inverters until the excess production goes away or a broadcast signal to disable all the inverters in range?

murphaph

Ah sorry, that was an error. There are some radio receivers available (I believe they just use GSM actually but they are apparently very expensive) but the "standard" way of remotely disconnecting the feed in (or stepping it down) is through a Rundsteuerempfänger which receives it's command signals through the actual electricity network. The same protocol is used to switch night tariff meters between tariffs, so I presume this tech already exists in the Irish grid too. It can only broadcast apparently and it's a one way system from network operator->consumer (generator).

quentingargan

Similar systems also exist in Ireland to curtail wind farms at night if production is exceeding demand. But the first line of defense during the day is that gas fired stations can be turned up and down. There is enough demand during the day that solar may never require curtailment unless there is a huge roll-out.

It is unlikely that domestic systems would disrupt the grid, except locally, where a number of inverters may cause local voltage to rise. If that happens, the overvoltage causes them to trip out. New grid standards in some EU countries require the inverters to scale down rather than trip out to make the transition smoother.

The greatest test was during a recent solar eclipse in the UK when all solar panels were switched off at pretty much the same time. The grid's spinning reserve managed the situation OK.