alt Hacker NewsCan anybody explain how these plug-in solar panels work? I am suprised that it's possible to just plug them in to your wall socket.
For instance, isn't it complicated to have their output be in perfect sync with the frequency that comes in via the electricity net? Because to me it seems that if they won't, you will have lower benefits or even a net minus after plugging it in.
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I guess if you can solve phase alignment then another big problem is grid capability?
If everyone plugged one in, could the transmission network reliably deliver the power generated where it's needed? I thought that was a serious long term challenge for utilities wrt solar.
Not a specialist, just from what I heard: There are two things that make it work. First they are not really "independent" like the title says. They sync with the grid frequency. If the grid is down they shut off for safety. The other reason it works is that the grid power inside the home is just what you get as incoming power 〜230V. For example, I think in the US you get 240V or so delivered to your house, but 120V from the plug.
Typically, you have "dumb" panels connected to a mppt-controller/charger/inverter box which is connected to batteries and and electrical plug. This controller tunes voltage/current that is taken from the panels, optionally manages the attached battery and measures and feeds into the grid connection.
Some systems are capable of running in isolation from grid (providing 230V AC on their own), but this is less common and often unnecessary.
My understanding is that plug-in solar inverters do sense what is coming from the grid and phase-sync to it with a PLL, and also adjust voltage accordingly.
> isn't it complicated to have their output be in perfect sync with the frequency
Not especially, given that the inverter has a microprocessor in it. All it has to do is measure the phase of the existing grid.
I don't have references for how it's actually done, but one obvious approach is simply to wait at each zero-crossing for a new half-cycle to cross a voltage threshold before turning on the output. This also implements the requirement to drop out if the grid goes away. It is probably also possible to measure during the "off" side of inverter output PWM, in the same way that variable frequency motor drivers work.