Home solar power questions

[rover-56]

Have been looking at grid connected rooftop solar for a few weeks now and it looks financially viable.
There are a couple of things I don't quite understand, so I hope someone can enlighten me.

1. Seems that a solar inverter will not supply power to the house when the mains power is interrupted, unless I install a 'hybrid' inverter and batteries. (expensive).
I understand 'anti islanding' but I would have thought a double pole mains isolating switch would make things safe. Backup generators seem to be usable in that situation, why not a solar system?
Can someone explain please?

2. I would like to be able to heat hot water in the afternoons from the solar system by pressing the 'boost' button on my smart meter.
I have had about a 50/50 split of answers from various sources which some say the solar will supply the power and others say the power will still come from the mains supply. Be nice to get a clear answer.
There are add on devices (greencatch) which can apparently divert solar power to the water heater, so why are people telling me solar won't heat water?

Most likely will go ahead with it, but quite hard to get clear info sometimes, and a bit of a learning curve here for me.

Thanks, Terry

[JDNSW]

Have been looking at grid connected rooftop solar for a few weeks now and it looks financially viable.
There are a couple of things I don't quite understand, so I hope someone can enlighten me.

1. Seems that a solar inverter will not supply power to the house when the mains power is interrupted, unless I install a 'hybrid' inverter and batteries. (expensive).
I understand 'anti islanding' but I would have thought a double pole mains isolating switch would make things safe. Backup generators seem to be usable in that situation, why not a solar system?
Can someone explain please?

2. I would like to be able to heat hot water in the afternoons from the solar system by pressing the 'boost' button on my smart meter.
I have had about a 50/50 split of answers from various sources which some say the solar will supply the power and others say the power will still come from the mains supply. Be nice to get a clear answer.
There are add on devices (greencatch) which can apparently divert solar power to the water heater, so why are people telling me solar won't heat water?

Most likely will go ahead with it, but quite hard to get clear info sometimes, and a bit of a learning curve here for me.

Thanks, Terry

1. My understanding is that, apart from the anti islanding issue, inverters depend on the mains waveform to ensure they operate in phase and at the correct voltage relevant to the mains. While it would be possible to design a system that, when mains power shuts down, automatically disconnects, handles changes in local load correctly, shuts down when power demand exceeds available sunlight, and when mains power returns, adjusts phase and voltage and reconnects. Without batteries this becomes a very complex design, and there is the question whether it is worthwhile if the lights go out when the sun sets. Automatic changeover to a generator is much simpler - just switch from one to the other - there will be at least a few seconds gap unless the generator is running all the time, but there is no requirement for the voltage and phase of the generator to match mains.

2. I think that when you press boost, the water will be heated by whatever power is available, depending on how it is wired. And how it is wired probably depends on which provider installed the system and smart meter.

[BradC]

I understand 'anti islanding' but I would have thought a double pole mains isolating switch would make things safe. Backup generators seem to be usable in that situation, why not a solar system?
Can someone explain please?

The issue is while a double pole mains isolator will make things safe for the linesman, you have 3 potential situations.
- Normal. Grid is connected (and up) and solar is making power
- Islanded. Grid is connected (and down) and solar is not allowed to make power
- Stand alone. Grid is disconnected and solar is allowed to make power.

How do you manage 2 & 3 without having the potential to accidentally squirt power back into the grid. With a genny its a simple changeover as you never want the Gen and grid connected together.
The simple solution from a grid perspective is mandate the inverters can't run isolated. That means even if someone does something dumb, there's a significantly reduced risk of splatting a linesman.

As for the HWS. Its just another appliance. It'll use whatever is available from wherever it can get it. If you are consuming more than you are making then the grid makes up the shortfall.

I've heard of some pretty clever widgets that will work with a smart meter and inverter to determine what your surplus is and divert that to another load (like the HWS), so you only consume what you use, but all the ones I've seen in passing have been fairly homebrew and quite complex.

[rover-56]

1. My understanding is that, apart from the anti islanding issue, inverters depend on the mains waveform to ensure they operate in phase and at the correct voltage relevant to the mains. While it would be possible to design a system that, when mains power shuts down, automatically disconnects, handles changes in local load correctly, shuts down when power demand exceeds available sunlight, and when mains power returns, adjusts phase and voltage and reconnects. Without batteries this becomes a very complex design, and there is the question whether it is worthwhile if the lights go out when the sun sets. Automatic changeover to a generator is much simpler - just switch from one to the other - there will be at least a few seconds gap unless the generator is running all the time, but there is no requirement for the voltage and phase of the generator to match mains.

2. I think that when you press boost, the water will be heated by whatever power is available, depending on how it is wired. And how it is wired probably depends on which provider installed the system and smart meter.

Thanks John,
Yes I can see that the need to match phase would be an issue, I suppose the 'hybrid' inverter has the required smarts to do all the switching and matching - hence the price asked.
I suppose the problem with the basic inverter is that someone would need to be home (and remember) to isolate the grid supply to keep the power grid repairers safe. A problem there when no one is home when the power goes out.

Differences in wiring probably would explain the varying answers to the boost power question. I suppose if the HW power is wired to only use mains power that would be an annoying problem.
Cheers,
Terry.

[rover-56]

The issue is while a double pole mains isolator will make things safe for the linesman, you have 3 potential situations.
- Normal. Grid is connected (and up) and solar is making power
- Islanded. Grid is connected (and down) and solar is not allowed to make power
- Stand alone. Grid is disconnected and solar is allowed to make power.

How do you manage 2 & 3 without having the potential to accidentally squirt power back into the grid. With a genny its a simple changeover as you never want the Gen and grid connected together.
The simple solution from a grid perspective is mandate the inverters can't run isolated. That means even if someone does something dumb, there's a significantly reduced risk of splatting a linesman.

As for the HWS. Its just another appliance. It'll use whatever is available from wherever it can get it. If you are consuming more than you are making then the grid makes up the shortfall.

I've heard of some pretty clever widgets that will work with a smart meter and inverter to determine what your surplus is and divert that to another load (like the HWS), so you only consume what you use, but all the ones I've seen in passing have been fairly homebrew and quite complex.

Thanks Brad,
I suppose the whole system is set up to keep linesmen safe from dopey housholders, and I can see a problem with a manual switch over if no one is home.
I am assuming that these 'hybrid' inverters are capable of doing the required switching and phase matching to allow unattended operation. They are quite a bit more pricey compared to the basic grid connected units.
With the hot water boost, as John says, the wiring configuration would affect the power source. Mine might be ok and it might not. I guess we'll see.
Those clever widgets (greencatch is one) look like they work ok, but for $1500 installed I would rather just press the boost button if I can.

I used to work as a fitter at a plastic moulding plant once. They used 5 natural gas fuelled 2000kW ship engines to generate the power needed. A 6th engine was on standby for backup if needed, and the connection phase matching was done manually - a 300mm dia motor coupling was regularly sent through the plant roof.:clap2: They eventually set up an electronic system.

Terry

[Vern]

https://www.google.com/url'sa=t&source=web&rct=j&url=https://www.powerdiverter.com.au/&ved=2ahUKEwi65Nrr0qniAhVM7HMBHUjPCFkQFjAAegQIARAB&usg=AOvVaw0A_uhsDDakTCUyKEKMHZIE

I have installed these in the past, work great.

[Graeme]

My Fronius non-hybrid inverter has a data management option whereby a user-supplied relay with 12V coil and 240V contacts is switched on and off according to the amount of surplus power being exported. I generally set the limits to switch on just below the maximum allowed export of 5kW and off at 1kW as the HWS element is 3.6kW but mid-winter I set the limits to switch on when 4kW export and off when nil export. A lower rated element (eg 2400W) would allow the HWS to switch on more often but I always have the option to switch on the original HWS timer set to off-peak times (overnight here).

My electrician installed the relay in parallel with the HWS timer (which had been set to off-peak but now almost always OFF) and I supplied the 12V supply for the relay coil.

Because my PV system including the inverter is distant to the house, I provided a master/slave wifi system that is switched by the inverter's 12V o/p which in turn switches the relay coil at the house. If the PV system was on the house where the HWS timer is located then its a simple 12V connection from the inverter to the relay.

[Disco4Dave]

Be sure you are better off using solar power for your hot water. We are on the solar-savers plan with AGL which pays a feed-in of 20c/kWh, and charges approx 14c/kWh (inc GST) for off peak. For us, it was better to keep the hot water connected to off peak, and export instead.

[rover-56]

Rooftop solar makes financial sense at the moment long term, the issue of power with the grid down would have been icing on the cake but the cost of a grid connected battery system is not financially attractive - even with the various government rebates intended to make solar look competitive with coal power.
I can see that lineman safety is a very important issue.
As for the HW boost from solar sources we will have to see what happens after installation, maybe I can get some wiring or programming changed.
I heat water in the winter from a kitchen wood stove, so don't pay for power then. using the boost control would avoid the installation of a dedicated solar water heater on the roof in parallel with the stove heat exchanger. All very interesting.

Thank you for the replies everyone.
Terry

[rover-56]

Be sure you are better off using solar power for your hot water. We are on the solar-savers plan with AGL which pays a feed-in of 20c/kWh, and charges approx 14c/kWh (inc GST) for off peak. For us, it was better to keep the hot water connected to off peak, and export instead.

Yes I'll do the sums when I see the real world costings.
I am with Red, and they only pay $0.12 feed in atm.
Terry

[rover-56]

https://www.google.com/url'sa=t&source=web&rct=j&url=https://www.powerdiverter.com.au/&ved=2ahUKEwi65Nrr0qniAhVM7HMBHUjPCFkQFjAAegQIARAB&usg=AOvVaw0A_uhsDDakTCUyKEKMHZIE

I have installed these in the past, work great.

That's a lot cheaper than the $1500 quoted by the solar installer for a Greencatch.
I will keep that link handy.
Thanks Vern

[Graeme]

Be sure you are better off using solar power for your hot water. We are on the solar-savers plan with AGL which pays a feed-in of 20c/kWh, and charges approx 14c/kWh (inc GST) for off peak. For us, it was better to keep the hot water connected to off peak, and export instead.
My FIT is 20c incl GST whereas off-peak is 20.7c incl GST so marginally better to use the solar power but the real benefit is that I still have surplus power to export which can be in excess of 3kW while using 3.6kW.

[fredd63]

I have noticed that linemen now use a big cable to short the wires to earth, via a big earth stake. Must have had a few close calls with wrongly connected solar.

[DiscoMick]

Our youngest son has just signed with Origin for 6.6kw of solar panels and a 20 rebate for $6000 after a $3000 state government subsidy which is predicted to totally eliminate their power bill. Installation is next month after the reno on their house is completed.

[DiscoMick]

You might find useful information at this site:

Renew - Leading in Sustainability (https://renew.org.au/)

[DiscoMick]

Grid-interactive solar - Renew (https://renew.org.au/resources/how-we-can-help/solar-and-batteries/grid-interactive-solar/)

[DiscoMick]

This is the solar company our son is using.

Instyle Solar - Queensland's Leading Solar Supplier (https://instylesolar.com/)

[Arapiles]

Backup generators seem to be usable in that situation, why not a solar system?
Can someone explain please?



You also can't connect a generator to the house when there's a power outage, unless you have a switch to isolate the house from the grid, for exactly the same reasons - you'll electrocute the linesmen.

I want to add batteries to my solar but at the moment the cheaper option would be to get a manual switch fitted and use my new generator to run the house when the power goes off.

[BradC]

I have noticed that linemen now use a big cable to short the wires to earth, via a big earth stake. Must have had a few close calls with wrongly connected solar.

That has been SOP for years. Long before direct feed in solar was even viable. Too many potential sources in a grid without even considering something being back-fed from a house. It was just less obvious in the past as stuff wasn't painted safety yellow.

[DiscoMick]

During the Brisbane floods when the grid was down in some areas there was a problem with flooded houses having live solar panels, I remember.

[rover-56]

You also can't connect a generator to the house when there's a power outage, unless you have a switch to isolate the house from the grid, for exactly the same reasons - you'll electrocute the linesmen.

I want to add batteries to my solar but at the moment the cheaper option would be to get a manual switch fitted and use my new generator to run the house when the power goes off.

Yes, I knew the mains had to be isolated. Same with home solar. I now realise the problem is mains going out with no one home to switch the isolator.
Terry

[DiscoMick]

So the son's new 6.5 kW of solar panels have been turned on two weeks before they move back into their renovated home, meaning there is no current draw and all the power is going back into the grid, earning 20 cents a kW hour.
So far it's earning them about $5 a day. So as long as they use less than $5 a day in electricity they will be in credit.
That experience might help those considering solar.

[BradC]

earning 20 cents a kW hour.

That's the bit that ****s me. The energy provider is required to subsidise these installs to "encourage" people to install solar, and now they are constantly in the red.

I don't have an issue with the government mandating green power subsidies like that (and make no mistake, it's a subsidy), but when they do it and then complain about the power companies no longer being profitable it kinda stinks.

Pay people the going rate for their FIT and remove the "solar rebate" and see how many will "do the right thing".

[Slunnie]

So the son's new 6.5 kW of solar panels have been turned on two weeks before they move back into their renovated home, meaning there is no current draw and all the power is going back into the grid, earning 20 cents a kW hour.
So far it's earning them about $5 a day. So as long as they use less than $5 a day in electricity they will be in credit.
That experience might help those considering solar.

Mick is that with Origin Solar?

[DiscoMick]

Yes, but I believe AGL is also offering 20 cents.
These rebate numbers are a commercial decision by the companies, not a government requirement. I understand AGL decided to raise it's rebates to win customers and Origin had to match it to compete.
As homeowners increase their solar to cut power costs, and wire their houses to run first on their solar and only export the surplus to the grid, energy customers have to offer a worthwhile rebate or lose their customers. It's the free market at work.

[Graeme]

I changed to the 20c FIT but lost most of the 25% reduction on their standard usage rates being only 3%, but overall I calculated that my overall power cost would be less due to the extent of surplus from my 8kW system, even though a maximum of 5kW feed-in. Last I looked Origin had reduced the 20c to 18c for new "plans".

I have no hesitation in looking elsewhere for a lower total cost of power, mostly because prior to investigating the viability of installing solar Origin had kept quiet that they were charging me 33% more for power that I could have been paying because I didn't know to ring them to tell them that I wanted the 25% discount that has no strings attached, which I regard as very disgraceful.

[DiscoMick]

There is a thing called 'demand response' which helps people to cut power bills, but access to it needs to be widened so it is not a monopoly of the energy companies.

Households cut power bills with 'demand response', but big energy retailers want to keep grip on market - ABC News (Australian Broadcasting Corporation) (https://www.abc.net.au/news/2019-06-24/households-cut-power-bills-with-demand-response-but-big-retailer/11232056)

[rover-56]

There is a thing called 'demand response' which helps people to cut power bills, but access to it needs to be widened so it is not a monopoly of the energy companies.

Households cut power bills with 'demand response', but big energy retailers want to keep grip on market - ABC News (Australian Broadcasting Corporation) (https://www.abc.net.au/news/2019-06-24/households-cut-power-bills-with-demand-response-but-big-retailer/11232056)

Handy if you live in a world of mobile phone service and text messaging......

[rover-56]

Well the 5.2kW solar was installed last week.
Making power and feeding into the grid.
Apparently won't get any credit until inspections and paperwork finalised. About 3 weeks.
I have given SPAusnet 50kWh so far.[bighmmm]
I wonder if they will backdate?
Terry

[gavinwibrow]

If anything like my provider NO!

After my 2nd bill on the new system (the first bill only included a week of solar) I was told I was not connected. It then took a total of 6 months free power to them before I started earning credits, and that was under the 40 cents scheme, which runs out for us in 2021.



Well the 5.2kW solar was installed last week.
Making power and feeding into the grid.
Apparently won't get any credit until inspections and paperwork finalised. About 3 weeks.
I have given SPAusnet 50kW so far.[bighmmm]
I wonder if they will backdate?
Terry

[DiscoMick]

Why don't you get it rewired to run your property first while it's making solar, and only feed the excess into the grid?

[rover-56]

Why don't you get it rewired to run your property first while it's making solar, and only feed the excess into the grid?

That's what it's doing. I am running everything I can think of - the excess goes to the grid.

[DiscoMick]

That's good.

[theelms66]

Why don't you get it rewired to run your property first while it's making solar, and only feed the excess into the grid?Isn't that how they all work?

[Vern]

Isn't that how they all work?Yep

[DiscoMick]

It used to be common for all the power generated to be sent straight to the grid, that's how our house in Brisbane is still wired, because we're still getting 40 c/kW hour rebate, but when the rebates were cut it became common to go the other way and power the house first, because the rebate was less than the cost of drawing on grid power.

[Graeme]

So PV output must be wired into the grid side of the supply meter - that's a handy way to make money when feed-in rate is higher than grid rate!

[Vern]

Pv isn't wired in in any special way, the meter they use are called a bi directional meter.

[BradC]

It used to be common for all the power generated to be sent straight to the grid, that's how our house in Brisbane is still wired, because we're still getting 40 c/kW hour rebate, but when the rebates were cut it became common to go the other way and power the house first, because the rebate was less than the cost of drawing on grid power.

You might need to clarify that because what you say isn't, and has never been "common". In fact, without a completely separate import and export metering setup (ie two completely separate meters joined only at the grid side) it's quite impossible.

If you generate more than you are using, then you are exporting and get the subsidized 40c rate for the surplus. If you use more than you generate then you are importing and pay (I dunno what you pay. Here it's 26c) rate for the shortfall.

If it worked the way you said it did, then you'd be getting a credit of 14c for every unit you consumed while you were generating even if it was even (you generate 5kw and consume 5kw). I don't think so Tim.

[Graeme]

Pv isn't wired in in any special way, the meter they use are called a bi directional meter.Certainly my recent installation uses a bi-directional meter.

[DiscoMick]

Our solar on our house here was installed about 6 years ago. It sends the solar to the grid. I can stand there and watch the meter rolling over.

[Graeme]

Do you have 2 meters where both can be ticking over at the same time while sending to the grid and using power?

[DiscoMick]

I believe so, but I'm at work now and can't check.

[rover-56]

The installer fitted what Fronius call a 'smart meter'. The readout is positive watts when drawing from the grid, and negative when feeding into the grid. Interesting to watch while the solar radiation varies.
Terry

[austastar]

Hi,
We have a single meter, it is digital and scrolling through the menu gives the readout on the different tarrifs. We only have two, general tariff in and export tarrif. Hot water tariff is not allowed if the cylinder can be heated by other means.
The bill is crazy, it shows the export as power used but is charged in negative values.
I much preferred the analog meter running backwards.
Cheers

[Graeme]

Our pre-solar meter was electronic that didn't run backwards for the 6 months it took to get the smart meter installed so not nearly as beneficial as a mechanical meter running backwards but at least it didn't keep running forwards during exporting, which we were warned that some do.

[TrakTorNator]

Solar power is amazing, you have some many advantages with them installed. At first, it might cost a fair bit, but it's worth it. the most significant attraction to solar power is that once the capital cost of installation is paid off the energy is free. This means the only real question is whether the payback period on the capital investment is better than the returns you would get from investing the same money in other ways. I can definitely say after I installed my panels from Solar Panels and Solar Panel Kits - SolarHub.energy (https://solarhub.energy) my bills were not as scary as before. Installing a solar power system on your home means you can lock in a price of energy for at least the 25-year life of the solar panels. You know how much energy the solar panels will produce so that once you get an accurate price quote you know exactly how much each kilowatt-hour of energy will cost you over the next 25 years.

[Arapiles]

You might need to clarify that because what you say isn't, and has never been "common". In fact, without a completely separate import and export metering setup (ie two completely separate meters joined only at the grid side) it's quite impossible.

If you generate more than you are using, then you are exporting and get the subsidized 40c rate for the surplus. If you use more than you generate then you are importing and pay (I dunno what you pay. Here it's 26c) rate for the shortfall.

If it worked the way you said it did, then you'd be getting a credit of 14c for every unit you consumed while you were generating even if it was even (you generate 5kw and consume 5kw). I don't think so Tim.

Actually, in some places OS that's exactly what happens - you get paid for what you produce, not what you export. There were proposals for that system to operate in Australia but the governments didn't like it.

[rover-56]

Rooftop solar makes financial sense at the moment long term, the issue of power with the grid down would have been icing on the cake but the cost of a grid connected battery system is not financially attractive - even with the various government rebates intended to make solar look competitive with coal power.
I can see that lineman safety is a very important issue.
As for the HW boost from solar sources we will have to see what happens after installation, maybe I can get some wiring or programming changed.
I heat water in the winter from a kitchen wood stove, so don't pay for power then. using the boost control would avoid the installation of a dedicated solar water heater on the roof in parallel with the stove heat exchanger. All very interesting.

Thank you for the replies everyone.
Terry

5kW solar system now installed. Wow there are a few people with their hands out trying to cash in....
SPAusnet reprogrammed the meter on 16 August to accommodate feed in.
Still waiting for that to take effect. 3 weeks and counting... They are going to charge me $450 for that, supposedly a special visit by a skilled technician.[bighmmm]
Was done by regular meter reader (manually read) on his normal rounds, took 5 minutes.:soapbox:
Red energy immediately increased my peak tariff from 28c/kWh to 43c/kWh.

AND I noticed that when I am generating 3.5kW and feeding 3kW into the grid, the meter code7 (hot water) is incrementing upwards when I switch on boost. So I will be charged for my own power. HW element is 2.8kW.
Ausnet say "oh no sir that is not possible"

Gah!!

Terry

[Slunnie]

Hi,
I much preferred the analog meter running backwards.
Cheers
That'd be great! matching buy rate and FIT. I think just about everybody would agree with you!

[Slunnie]

Signed the contract on Friday. 13kw system going in at the end of the month.

Will be interested to see what the power bills come out at each quarter once the system goes in.

[DiscoMick]

The son's place is now generating twice as much power as it consumes. Will be interesting to see the next bill.

[Graeme]

Signed the contract on Friday. 13kw system going in at the end of the month.

Will be interested to see what the power bills come out at each quarter once the system goes in.Single or 3-phase? My single phase 8kW system gets throttled-back for several hours a day due to the 5kW single phase export limit even at this time of year if the sun is shining.

[Graeme]

The son's place is now generating twice as much power as it consumes. Will be interesting to see the next bill.So far this month our's has exported more than 3 times the imported power but we're only $7 in front.

[Slunnie]

Single or 3-phase? My single phase 8kW system gets throttled-back for several hours a day due to the 5kW single phase export limit even at this time of year if the sun is shining.

Hi Graeme, it's 3 phase. 13kw panels and 10kw inverter. It shouldn't be throttled. I'm hoping to not be paying for electricity once its installed but we will see.

[Graeme]

Do you have 3-phase reverse cycle a/c? No 3-phase here but we went for 8kW as we were considering installing a/c but have since decided to stay with the evaporative cooler for summer and bottled gas for heating.

[Slunnie]

Do you have 3-phase reverse cycle a/c? No 3-phase here but we went for 8kW as we were considering installing a/c but have since decided to stay with the evaporative cooler for summer and bottled gas for heating.

Good question! I think the AC is single phase, it just looks like a standard circuit breaker at least. Interesting with the gas heating! I was looking to change the HWS from heat pump to bottle gas but I think now I will be better off with staying with the heat pump when the current system blows.

[Graeme]

My 8kW of panels which can produce 8.3kW has plenty of surplus capacity to heat the 3.6kW electric HWS on sunny winter days where I set the switch-on feed-in to just below the 5kW export limit to maximise feed-in while heating. Off-peak heating is almost always disabled, only having been used twice over winter after a run of cloudy days.

[DiscoMick]

Do you have 3-phase reverse cycle a/c? No 3-phase here but we went for 8kW as we were considering installing a/c but have since decided to stay with the evaporative cooler for summer and bottled gas for heating.
The son's place is wired up to power the house first from solar all day and export the surplus to the grid, so that means they can run their reverse cycle aircon for free all day and cool the house, and then turn it off at night and the house stays cool for several hours.