We’ve all been there – that sound of silence after the cups hit the deck and the dairy is plunged into darkness.

The power is off.

A quick look across the paddocks shows the lights have gone off at your house and at the neighbour’s dairy too.

So it’s not something wrong with your dairy, and it’s not the pole fuse that’s blown.

How long the power is going to be out is always the big question. Whether it’s because of high winds and a branch falling on the lines, a car accident taking out a power pole or flooding – losing power in the dairy is something you don’t want to happen.

Cows need to be milked, milk needs to be cooled and, in a rotary, cows need to get off the platform.

Your first call should always be to your electricity company to find out how long the power is going to be out for. This should be one of your numbers stored on your phone along with the electrician, vet and all the other emergency numbers.

If it’s going to be half an hour or less, drink your coffee which hopefully you’ve got waiting for you in a thermos. If it’s longer than that you’ve got some tough decisions to make. And having a generator on farm, or one you know you can get your hands on quickly nearby, makes life a lot easier.

If you hope to hire one, pray that it’s not a region-wide outage because they will be in short supply.

But hiring a generator is not a quick-fix solution. It needs to be the right size and you’ll need your electrician to wire it in safely.

And the electrician needs to match the phase rotation of the generator to the phase rotation of the dairy or your rotary platform will go the wrong way round, your water pumps will not pump properly and could burn out and the backing gate will go backwards instead of forward.

If the power goes out often on your farm, or there is the potential for storms to take out the electricity lines for days, then investing in an on-farm generator could be a lifesaver for the future.

And if you have a rotary, there is only one way to get the cows out of the dairy and that is with electricity to drive the platform motors.

If you still have a rotary which works on hydraulics, you can hook it up to your tractor hydraulics, but there are few dairies like this left.

Generators can be powered by petrol, diesel or through the PTO shaft on your tractor, which is then powered by petrol or diesel.

It all comes down to the grunt you need, or in other words, the size and type of your dairy.

Hooking up older and smaller herringbone dairies, those which don’t have centrifugal milk pumps, directly to your tractor PTO works fine but newer dairies, and rotaries, need the extra power a generator can provide.

Generators that run off a PTO are cheaper to buy as they don’t need a motor – the motor is your tractor.

And they’re usually guaranteed to start – all you have to do is turn on your tractor. An engine-driven generator, if not well maintained and started regularly, can be frustrating.

Turn on your tractor and set the tractor revolutions at 51 hertz per the PTO generator frequency meter.

Set the hertz at 51 rather than 50 so that if something else is turned on in the dairy it’s less likely to cause the generator problems.

The size of a generator is determined by its kVA. A kVA is 1000 volt-amps which is what you get when you multiply the voltage (the force that moves electrons around a circuit) by the amps (electrical current or electron flow).

Kilovolt-amps measure what’s known as the “apparent power” of a generator which is different to kilowatts (kW) which measure the “true power”. An easy formula is to multiply the KVA by 0.72 to get the approximate kilowatts.

The tractor running the generator needs to be about 1.5 times the generator capacity so a 50kVA generator needs a 75hp tractor and should be enough to milk 250 cows through an older herringbone.

However, most electricians and generator suppliers recommend tractor horsepower should be double the kilowatt output of the generator to manage the various mechanical losses in the single-phase system and to have the tractor operating economically.

But this is a discussion to have with your electrician because in modern dairies there are not only cows to milk and a rotary platform to go round, there are drafting systems, milk meters, lights, yard scrapers, milk cooling and hot water cylinders heating water for the wash.

And don’t forget your electric fences and the pumps that feed your water troughs and effluent system.

Some of these can be turned off, so less grunt is needed. If the power is out due to flooding or snow and the tanker is not going to make it up the road for days, there is probably not a lot of need to cool your milk.

And you might get away with a cold wash, instead of the routine hot wash, or heat the water after the cows are milked.

If using your tractor’s PTO, make sure all belts, pulleys and the PTO have guards before use to keep everything safe. If it’s raining, keep it under cover because water and electricity don’t mix.

In most modern dairies, a generator powered by a tractor will not cut it and you need to have the real thing. At least the price for them has come down dramatically in recent years.

Your dairy should have a change-over switch, installed by your electrician, for an alternative power supply. This keeps everything safe for when the power comes back on unannounced.

Think about fumes and noise. Position generators away from work areas as much as possible and have a wall at least between them and where you’re milking.

Practise regularly operating the dairy using the alternative power supply so everyone is familiar with the switch-over procedures. It will also check the equipment is working as it should.

Make sure you keep the maintenance up on your generator. The oil needs to be changed as per the instructions and generators should be kept in a dust-free environment as much as possible. A yearly service is a good idea.

As well, make sure you have enough fuel for your generator onfarm at all times to last a possible power outage.

And while you’re thinking about all of this, don’t let your coffee get cold.