Thread: Grid can go 75% renewable

Originally Posted by Old Farang

...The point here is that the present state of both solar and wind generation does NOT possess these attributes, and will rapidly disconnect to protect the equipment, which has been proven the case in many countries that have big solar, and more particularly wind powered grids.

In WA the grid is already under stress with supply authorities moving to reduce the risk of renewable energy overloading the state's electricity system.

Daytime solar subsidies to be slashed as WA moves to head off grid overload.

...rooftop solar in WA had effectively become the single biggest power plant in the state and threatened to crowd out the baseload generators needed to keep the grid secure.

Energy analyst Matthew Warren, a former head of industry body the Electricity Supply Association of Australia, likened the number of solar panels in WA to a "giant, invisible power station" that could not be controlled.

Originally Posted by PhilipA

My daughter just installed solar panels in Saratoga Central coast NSW.

Apparently her Inverter is turning off feed in as the voltage in the system is getting too high.

So an electrician has recommended getting the supplier to change her phases on the wires outside.

I can see this becoming more and more of a problem.

What happens if the other phase is also going over voltage?
Regards PhilipA

This is a common problem and not something most people understand. I see it all the time when there is a lot of solar in one area. Each inverter needs to push the voltage up to export its power but the over voltage limits for the grid can’t be exceeded so the inverter shuts down. At my place on a sunny morning - not during lockdown but when things are normal - around 11am the voltage is around 255 volts here which allowing for the voltage drop on my line means the mains is pretty much at its limit. the local zone substation can tap the main incoming voltage up and down automatically but on the feeders the tapping is done manually so once set generally won’t be changed unless there’s a substantial change to conditions to warrant it but high voltage during the day and normal to lower voltage at night means a change in taps at a local level isn’t going to happen.

You can’t just have every house with solar trying to export to the grid if there’s nowhere for it to go - the grid isn’t one big thing that will just move power from wherever to somewhere else, but more localised when actual physics gets involved.

One solution is to get a storage system so the panels can charge them during the day, but of course this comes at a fairly high price. Another option is to load shift as much of their power needs to the day - have appliances with timers that can work during the day - washing machines, dishwashers, etc. If they have hot water you can also use that as a power sink and heat up the water when there is nothing else and nowhere for the power to go.

Originally Posted by Graeme

The grid supply has to be within spec when the inverter is off. If not then the transformer tap has to be changed to bring the voltage within spec. Once voltage is within spec the inverter must throttle back to prevent excessive voltage.
I had to have my supply transformer re-tapped and then the parameters in the inverter changed to prevent excessive voltage. In the end I provided to my PV supplier the parameters that were needed as the PV supplier didn't have a clue as to the use and effect of the parameters.

Is your grid supply on your own transformer, such as a rural supply? If your supply is a common line from a street then it may not be possible to change it. If a 3 phase street supply and you are connecting to a single phase house supply from the street it may be possible to connect to a different phase.

The normal street supply should be via a transformer than has automatic tap changing to compensate for load changes. The supply authority tries to keep the voltage within a small set range with varying loads, using automatic tap changing.

But why is the grid input line voltage not able to compensated for by the inverter? I have not had anything to do with the types of inverter used with solar, so just asking. My view is that the inverter is where adjustments should be made, not the grid supply voltage.

Mine is a rural supply with a transformer just for my use. The grid voltage had been set high when the transformer was installed some 15 years ago to allow for voltage drop on the undersize wires on the long run to the house. The inverter is much closer to the transformer so the grid voltage had to be lowered to spec then the inverter's limits adjusted for the voltage drop during export on the short undersize run to the transormer. However the voltage limits for the various stages were grossly incorrect causing the catch-all limit to shut down the inverter before it had a chance to derate. My inverter is Fronius which is very configurable..

Originally Posted by Old Farang

It doesn't really matter what fuel is used in a thermal power station; coal, gas, nuclear, wood chips, cows farts or whatever will burn. In all of them the energy conversion is to produce steam, which in turn is used to drive a bloody great rotating mass configured as an electrical generator.

As a big rotating mass it possesses a lot of inertia, which directly influences stability, resulting in the ability to absorb grid surges and sudden fluctuations. There also seems to be a lot of misunderstanding about grid frequency. EVERY AC generator connected to a power grid, be it a couple of diesel generators in an outback town off the grid, up to multi MW grid power stations, HAS to run at the SAME frequency, as once connected they are all synchronised by by the simple rotating rising and fall of the voltage, know as a sine wave. They will all stay synchronised regardless of their actual load output, even to the point of becoming a motor if their energy input is less than that required to output power into the grid.

The point here is that the present state of both solar and wind generation does NOT possess these attributes, and will rapidly disconnect to protect the equipment, which has been proven the case in many countries that have big solar, and more particularly wind powered grids.

Fully agree that the current tech needs a lot of modification to allow a stable grid. You missed fuel cells. Scaling up at the moment for iron refining and ships and of interest may work with ammonia or hydrogen. Via electrolysis any spare solar can b

Pretty sure the load balancing via storage will be the main key to changes needed to avoid further co2 emissions. I have a share or two in Ballard TCO is the real cost of ownership which has changed a lot already. Cost of there products has gone down over 80% while several thousand sites are using the tech now. Its a lot like the 1-2kw solar system 20 years ago which cost well over 20k in today terms.

The real point might be follow the MONEY


"To date, 18 governments, whose economies account for 70 per cent of globalGDP, have developed detailed strategies for deploying hydrogen energy solutions. "



https://hydrogencouncil.com/wp-conte...ll-Study-1.pdf

Originally Posted by Old Farang

It doesn't really matter what fuel is used in a thermal power station; coal, gas, nuclear, wood chips, cows farts or whatever will burn. In all of them the energy conversion is to produce steam, which in turn is used to drive a bloody great rotating mass configured as an electrical generator.

As a big rotating mass it possesses a lot of inertia, which directly influences stability, resulting in the ability to absorb grid surges and sudden fluctuations. There also seems to be a lot of misunderstanding about grid frequency. EVERY AC generator connected to a power grid, be it a couple of diesel generators in an outback town off the grid, up to multi MW grid power stations, HAS to run at the SAME frequency, as once connected they are all synchronised by by the simple rotating rising and fall of the voltage, know as a sine wave. They will all stay synchronised regardless of their actual load output, even to the point of becoming a motor if their energy input is less than that required to output power into the grid.

The point here is that the present state of both solar and wind generation does NOT possess these attributes, and will rapidly disconnect to protect the equipment, which has been proven the case in many countries that have big solar, and more particularly wind powered grids.

Yep, the rotating magnetic fields keep the units rotating at exactly the same frequency with the rotor locked together, the magnetic fields are incredibly strong. If you have a group of machine together in sync and one starts to run out of fuel, you can just watch the load drop off it as it starves for fuel but still maintaining the groups frequency. Once it starts to motor, the control system will open the breaker and shut the unit down though on reverse power. Interesting to watch. 👍

Once it starts to motor, the control system will open the breaker and shut the unit down though on reverse power. Interesting to watch. 👍

On ships testing the reverse power trips are always first on the **** list of any surveyor. Even in the old DC ships this was always tested. The old type of open face DC breakers could be spectacular! More modern types of protection devices on AC gens are more of a non-event.

On top of that, most of those critical types of installations had "Preferential" tripping circuits that also had to be set up and tested. The idea being to maintain supply to essential loads. (such as the chief engineers air con. )

Modern generator control systems make a lot of this stuff very dull by comparison to the old days. I learned to sync gensets with a syncroscope and adjusting the governors. Manual closing of the breakers so you needed to have your wits about you. Today you close the first breaker to energise the bus, then each machine is a push of a button and it will automatically sync the machine and close the breaker or you can go one further and have the whole system just do it’s own thing based on load and demand.