Home power generation

[Burnt]

Hi All,

I need a bit of advise regarding supplying the grid with power 240v 50/60hz,
I am setting up a generating unit that will supply around 50 kW/h, the problem is that it is not an automated system & the rpm can vary & therefore the frequency can & will vary also especially overnight when unattended.

The only way i can see around this is to charge up a battery bank--12v batteries & then use 12v DC to 240v AC inverters to get a sine wave of the correct frequency to supply the grid. Is this a stupid idea for the amount of power that will be generated--50 kW/h.

The way i see it is that a 12v 400amp/hour battery is basically 4.8kW so ten of them is 48kW. Will the batteries be capable of this & or is this correct?

Any advise will be appreciated.

 

[Diver300]

You need to talk to your power grid company. There are all sorts of rules about putting power back into the grid.

Get your units right. You won't impress the technical people. Saying 50kW/h is like saying your car does 30 miles per gallon per hour. It is meaningless.

Power is measured in Watts, or kW. Your generator is rated at 50 kW, if I understand you correctly.

Batteries are rated in Amp - hours or Ah. The battery rating of 400 Ah means that it can supply 1 Amp for 400 h, or 2 Amps for 200h etc. It will also have a maximum current rating in amps.

However, you don't need batteries to convert the frequency. Motor speed controllers convert frequency by changing to DC and back to AC but they keep the voltage largely the same. The only reason that a UPS converts down to 12V and back up again it to match the battery voltage, and the UPS has to run without the mains so the battery is needed.

I would suggest that it is a lot easier to regulate the generator speed than to change the frequency. Also with synchronous generators. the speed of the generator ends up locked to the speed of the grid once connected so you may not have to worry too much about that.

 

[Burnt]

I have talked to the power company & they require the correct voltage & frequency of course,Yes your right about the units--Duhh!
The problem is i cannot regulate the generator speed, i am an automotive engineer & have designed a new type of engine that is fueled by Biomass & the Temperature is very difficult to regulate. The result is the rpm can increase or decrease depending on temperature & as a result of this the frequency is variable.
That's why i thought it would be better to charge batteries & use inverters so the frequency would be stable.

The system works great except for the variable rpm situation, it is very difficult to control the burn rate of Biomass.

 

[Diver300]

A generator set consists of a prime mover (engine) and an alternator. I think that a 50 kW alternator will be a synchronous alternator. Once one of those is connected to the grid, it will hold the speed and you can put any amount of power up to the rating into the grid.

As I understand it, the power produced by the engine varies. If there is a conventional load connected, the power variation causes speed variation.

If that is the case, once you connect to the grid, the power variation from the engine will cause power variations but the speed will stay constant. That is because the load is effectively infinite.

 

[Leftyretro]

A generator set consists of a prime mover (engine) and an alternator. I think that a 50 kW alternator will be a synchronous alternator. Once one of those is connected to the grid, it will hold the speed and you can put any amount of power up to the rating into the grid.

As I understand it, the power produced by the engine varies. If there is a conventional load connected, the power variation causes speed variation.

If that is the case, once you connect to the grid, the power variation from the engine will cause power variations but the speed will stay constant. That is because the load is effectively infinite.

This doesn't sound intuitively true me, but I may not understand all you are trying to explain. Taken to an extreme, say the motor is running and the speed is being maintained by the alternator being wired to the grid. If the motor suddenly died do you mean that the grid would keep the alternator turning a constant speed and therefore keep the motor running, just consuming power rather then generating it?

 

[Willbe]

Don't forget batteries will give back about 2/3rds of the energy you put into them.

 

[Hero999]

This doesn't sound intuitively true me, but I may not understand all you are trying to explain. Taken to an extreme, say the motor is running and the speed is being maintained by the alternator being wired to the grid. If the motor suddenly died do you mean that the grid would keep the alternator turning a constant speed and therefore keep the motor running, just consuming power rather then generating it?

Yes, that is what would happen.

In fact you need to start the alternator as a motor with no load, then connect it to the engine via a clutch to get it up and running.

 

[Leftyretro]

Yes, that is what would happen.

In fact you need to start the alternator as a motor with no load, then connect it to the engine via a clutch to get it up and running.

Well that sounds pretty simple and straight forward and eliminates the need for lots of control electronics. I imagine there would still need to be circuit breakers and other basic electrical protection needs in case of sever mechanical or electrical short circuits.

Lefty

 

[j taylor]

i have the same setup

just google grid-tie inverters the one i use is a windy boy 1100 but i have plans to get a bigger one