How large Gen Set required for Hybrid PV System?

[kashif5]

To reduce the load on the generator (and therefore the fuel consumption) during the hours where PV is producing.
As long as the PV does not bring the generator into a situation where the prime mover is operating inefficiently, it will be able to reduce overall costs.
It is critical to this kind of design that the load never go lower than the PV output, with maybe even a 50% safety factor. Otherwise, to prevent destructive backfeeding of the generator, the PV will have to be automatically throttled down.

Well described. However one more point to note is that: its not only about backfeeding, its also about efficiency of generator. May be @ 40% load, generator is consuming less fuel but not efficient consumption of fuel. Also it can also cause wet stacking in generator that can destroy generator engine in longer run.

[Bill NC]

Kashif, you might want to talk with one of the tech guys at steadypower.com I think they have done projects similar to this. They have 600 kw generators and 500kw inverters on their website, so they may be able to help with this.

[SunEagle]

To reduce the load on the generator (and therefore the fuel consumption) during the hours where PV is producing.
As long as the PV does not bring the generator into a situation where the prime mover is operating inefficiently, it will be able to reduce overall costs.
It is critical to this kind of design that the load never go lower than the PV output, with maybe even a 50% safety factor. Otherwise, to prevent destructive backfeeding of the generator, the PV will have to be automatically throttled down.

This is the situation they are having in Hawaii. The amount of pv generation is over 50% of the power used in some areas which has caused the Utility to see major fluctuations in their grid power.

I am presuming depending on the type of non renewable power generation (oil, gas, coal, nuclear) and how quickly it can be throttled or respond to changes in the amount of PV generation will determine the "tipping point" or ratio of pv to gen sets kw.

[sobhan06]

Well described. However one more point to note is that: its not only about backfeeding, its also about efficiency of generator. May be @ 40% load, generator is consuming less fuel but not efficient consumption of fuel. Also it can also cause wet stacking in generator that can destroy generator engine in longer run.

Usually in India, we used to take 30%. The PV system which we are going to sync should be of 30% of DG (Gen set). Also, the kinda inverter which your are planning to use should have the capability to act as a fuel controller or throttler which can reduce DG's working accordingly to the available solar PV at any point of time(SMA, REFUSOL is having that type of system). If you use these type of inverters with fuel controllers automatically your total losses from DG will get reduced.