In both Grid connected and stand alone Solar PV system an inverter is used. Please clarify if we can use a same inverter for both grid connected and stand alone operation of solar PV systems?
Hi Maharaja,
in principle yes you can use the same PV inverter. If you are in a stand alone system you should however have some source to operate in grid forming mode, keeping the frequency constant. Usually, in such microgrid scenario you have a diesel generator for that, since the PV obviously generates power only when the sun shines.
yes you can, however you should modify the control system of the inverter in order to be able to switch between grid connected operations and stand-alone operations.
No you can not. For a grid connected inverter, the modulating signal is obtained from the grid only for successful synchronization. In case the grid fails the inverter also stops functioning. However if a DG within the network starts, the inverer starts operating again but the DG capacity must be sufficiently large depending on the local load. However an off-grid inverter generates its own modulating signal which need battery backup.
I'm coming back to answer to Ramaprasad. I agree with you, that's why I mentioned a microgrid with some other source. If Maharaja refers to a system with only some PV modules an inverter and a load then yes, a battery is necessary.
Typically, inverters operate in P/Q mode (regulation of active and reactive power) in grid connected operation. Differently, they have to operate in V/f mode (regulation of the voltage and the frequency at the connection bus) in case of islanding. Of course, you have to optimally size the plant since the generated power in stand alone mode is a part of the available power from PV panels. In case you can use a battery system in P/f mode and connect a PV plant in parallel regulated to maximize the solar production, according to storage operation (State of Charge)
@ Antonios Marinopoulos, I am expecting the answer for the system which is only having solar PV system as a source...
Question:
1) Is it possible to design a PV system without having any support from any other sources like utility grid, battery etc....
2) if possible to design a above PV system, can we use same inverter in stand alone and grid connected mode....
You should explain your application.
If you are supplying AC loads it cannot work like 1). AC loads are designed to be supplied from the grid so even if you are in standalone mode you still need to "emulate" the grid for your loads and I don't see how to do it without external power source. Some voltage source inverter assisted with temporary power source could achieve it, but even then, PV power alone is variable and it will drop out of sync without external support.
If you are only supplying DC loads then why use inverter? You need some DC-DC converter.
I would not recommend this. The inverter used in stand alone operation of a PV energy system should not be used if the system is to grid tied. Should there be a grid outage, the PV energy system would still be supplying the grid creating a possible safety hazard to linesmen and grid customers. A grid tied inverter senses when there is a failure of the grid and shuts down the PV energy system.
Using a grid tied inverter in a stand alone system is possible only if you have a constant supply (e.g. from a diesel generator) that will allow the PV energy system to maintain connection to the load.
Coming back after some days, after clarification from Maharaja,and the very good contributions from people here you can see that in a very general way the answer is yes, BUT you should use some external source in case you have an AC grid to supply not only from operational but I would add also from practical point of view, unless you can afford your power to fluctuate all the time. The control should be changed as well, or at least the correct control mode should be selected. In a pure DC system you can use a simpler DC/DC converter, like Ognjen said: "why use inverter?"
i too have a doubt regarding a stand alone PV system. consider a 1kw solar plant . is it possible to design an inverter for such a system whose functionality would depend entirely on solar panel output which is used as a dc source for the inverter.(with out involving a battery a or grid tie mechanism)
yes it is possible dear Shankar Kondasamy. but you need more PV panels to be connected in series to maintain the dc input voltage at required level as input to the inverter for smooth and desired operation.
yes you can use the same inverter but not the same control logic. The inverter while working in on-line mode has a different control as when used as off-line mode.
@Oswald Lopez why is the LC filter required only in the case of standalone operation?
The question of grid connect inverters ( string, central, and micro ) has been resolved in the commercial application of the invention and US Patents 8742620 B1 , and 8957546 B2. These Patents and the inventions convert grid connects solar derived system into a paralleling AC generators . Battery storage is never required for AC/AC paralleling , and the 20 % AC/DC/ AC loses associated with battery derived systems do not occur. Commercial name for the systems is WESP Technology . Links to the Patents are attached as well as a YOUTUBE link to a 3 year beta set in a field application environment . Six minute video demonstrates Patent claims over all technology involving AC to AC frequency , voltage and current integration of commercially available Utility connected solar inverters with commercially available AC generators to satisfy a mutually connected AC load , disconnected from Utility AC sources . System operation replaces generator current with available solar derived AC current up to the maximum solar output or the maximum required load automatically under all load, generator and solar power variances. The result as Patent claim is the reduction of fossil fuel consumption to no load and in some cases below no load consumptions. The beta site has been personally witnessed by engineers from S_A US and KA_O New E_ergy , and validated for operational claims . New videos demonstrating commercially available microinverters utilizing WESP Technology to be released soon.
https://youtu.be/0BH3rRHJs44
yes, there are bimodal or bidriectional inverters that are designed to both function as standalone and grid-tied inverters
possible since off grid n (i assume) has a fossil fuel generator
Yes, this is posible. But, I recommend to use a real time PV voltage checker and disconnect the inverter from the grid, if the PV couldn’t generate enough voltage. This is to avoid the inverter acts as a load for the grid power system when its output voltage is equal/less than the the grid voltage. Also, you meed zero crossing detector for safe connecting and disconnecting the inverter to the grid.
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