STEP 5 - Energy Generation and Offsetting
This section looks at the last piece of the puzzle...
Integrating Photovoltaics (PV) and what you need to know to achieve a Net Zero operational energy outcome.
The section then goes beyond to look at calculating and offsetting embodied carbon, for a True Net Zero carbon home.
AND SO, we come to the Last Step of the recipe.
The final puzzle piece that makes it all work.
The final piece of technology that makes the all-electric Net Zero operational energy outcome achievable.
And have a little look at what is left of the pie...
And what have we given up?
Just pollution & high energy bills...
Now that energy needs are minimised, to achieve Operational Net Zero it's just a matter of putting on a large enough photovoltaic (PV) panel system, so that over the year you produce as much power as you use.
This doesn’t mean that you are always self-sufficient.
Indeed, you use the electricity grid like a battery. On sunny days when you make more energy than you use, your ‘green’ electrons go into the grid to get used by your neighbours. Then at night, or on cloudy days, when panels aren’t producing much, you draw from the grid the ‘brown’ power you need. But over the year, you offset to the grid as much as you draw in. That is, you achieve a Net Zero carbon balance.
And how much PV do you need for Operational Net Zero?
Well, as one point of reference, for our Positive Footprints clients, in the Melbourne climate, for standard 200m2 homes, we find most of our clients start breaking even from 4-7kW of panel, depending on family size, and lifestyle.
This of course is only a rule of thumb for the Melbourne climate.
But now we can do better than rules of thumb!
Now we can actually calculate PV size for Net Zero...
... with the new NatHERS Whole of Home tools coming soon to an energy assessor near you!
WHILE SEVEN STAR HAS GOT A LOT OF TALK, IT’S THE WHOLE OF HOME RATING THAT IS THE REAL GAME CHANGER!
NatHERS is currently accrediting the 4 current house energy rating software tools (Accurate, BERS, FirstRate & HERO), for their Whole of Home roll-out to assessors in October. This is historic for the residential building industry in Australia, because for the first time we will have a government backed tool that can be used to create a Net Zero Home outcome. And this fact has gone right under the radar, in the debate over the merits of 7 stars.
It is in fact Whole-of-Home - the inclusion of appliances & solar - that is really the main event!
Let's look at it...
As we know, the average Australian home is responsible for ~6 tonnes of CO2 production every year from its energy use.
Achieving 6 stars saves a bit over a tonne, compared to the 'average' home (which includes existing), and moving to 7 stars will save in the order of another ½ tonne or so of CO2 depending on climate.
We should do it. Such homes are likely to be more comfortable & resilient.
But, it’s Appliance Selection (STEP 4) & then solar PV inclusion that will REMOVE THE REST of that 6 tonnes, & achieve the Net Zero annual energy outcome.
And now we have a tool that can help designers, builders, & homeowners work out the appliance mix & PV size required to achieve that illusive unicorn – the Net Zero Home!
Ok, so how do you take advantage of this?
From October onwards when you get an energy rating done, don’t just accept a Pass.
Ask your assessor this magic question: “What appliance mix & PV size would I need for a Net Zero Outcome?”
They can then trial options in the new tool.
You will likely find the difference between a Pass, & Net Zero will, in most cases, be efficient hot water & a small PV system, or a couple of kilowatts of extra PV capacity on a system you needed to put onto pass anyway!
The point is, we now have a software tool to guide us.
So, when it comes out make sure you take advantage!
When the Industry realises this, there will soon be a tsunami of Net Zero Homes in Australia!
And what will they save?
Most of that $2000+ annual energy bill that the average dual fuel home uses every year. (See the Carbon Footprint of our Homes)
And for the planet?
~6 Tonnes CO2 saved, every year, for the life of the house.
Make sure you ride the wave…
NOTE: It is always a good idea to size up 1kW extra above whatever is predicted by models, to allow for real-world variations…
Sizing PV for Operational Net Zero (Current)
Operational Net Zero is a great achievement, and as we saw in the Carbon Footprint of our Homes, saves around 300 tonnes of CO2 over a 50yr lifespan of a home - if nothing changes.
Unfortunately, we still haven't addressed the 200T+ of carbon embodied in the materials from which the house is made.
As discussed, this is a harder nut to crack.
But crack it we will...or at least have a good go, later in this section. (See, Offsetting Remaining Embodied Carbon for True Zero Outcomes, here.)
But first there's some things we need to cover for successful PV installation and to achieve operational Net Zero Nirvana.
Let's look at what you need to know when considering a photovoltaic system...
Achieving True Zero (Current)
The PV industry is well established in the Australian market. In fact we have the greatest penetration of roof top solar in the world! There are however still plenty of pitfalls for the unwary.
The following section gives you all you need to navigate supply and installation for a PV system that efficiently turns that lovely sunlight landing on the roof, into free power for clients and homeowners.
WHAT’S THE BEST ANGLE FOR PHOTOVOLTAIC POWER ON YOUR BUILDS? AND IF YOU CAN’T FACE NORTH SHOULD YOU BOTHER?
You probably know in Australia that North is the best direction.
And as a Rule of Thumb, THIS IS TRUE.
(Actually, there can often be some benefit going slightly east to bias morning collection when panels are cooler & panel efficiencies are a little higher. And sometimes climatic tendencies for morning or afternoon cloud build-up can vary this rule a bit too.)
However, if you can’t do direct north, DON'T SWEAT IT.
Look at the graph. There’s a big 90% efficiency band. Indeed, if you go due west or due east you only lose 15% efficiency!
And in fact, putting on some east &/or west panels can extend the hours of usable power each day, often meaning earlier system payback!
SO THAT’S DIRECTION SORTED, IF YOU CAN'T GET TRUE NORTH JUST PUT ON A BIT EXTRA TO MAKE UP, BUT WHAT ABOUT TILT?
The Rule of Thumb here is that for grid connected systems the ideal tilt is your site’s latitude MINUS 10 degrees.
It's MINUS 10 Degrees, because in summer days are long with the sun higher in the sky, so if you flatten off the panels you take advantage of the long hours of intense sunlight, which in turn maximises yearly production. Eg. For Canberra at 35 deg latitude, panels installed at ~25 deg maximise energy creation.
If, however, you are not connected to the grid, but are on stand-alone power, the Rule of Thumb is the latitude of the site PLUS 10 deg.
This maximises winter gain when the days are short & rays are at a lower angle.
These are of course Rules of Thumb only.
If you want to be precise, tools like NREL Solar Calculator will gain you a few more watt hours.
But again, if you are a bit off, DON'T SWEAT IT.
Look at the graph. You get 90% efficiency with panels tilted as high as 60 deg & as low as 5 degrees. Indeed, you only lose 15% efficiency if you go flat!
Note: Flat is not recommended however due to dust build-up. Allow at least 10 deg to allow them to self-clean in the rain.
So, THE POINT IS, angle is not a limiting factor.
But how much space do you need to allow if you want to be Net Zero?
Read on below to find out...
Angles and the effect on production (Current)
HOW MUCH SPACE SHOULD YOU ALLOW ON YOUR ROOF FOR SOLAR PV IF YOU WANT TO GO NET ZERO?
As we noted above, from October 2023 NatHERS Whole-of-Home software will start to be available for assessors, so you can find out the required PV size by asking your Thermal Assessor this question:
"With my house design & fixed appliance set, what size PV do I need to reach Net Zero?"
When you get the answer, it would then be prudent to add 1kW to cover unforeseens (it is only a simulation after all).
And there you have it. Net Zero!
You may also want to consider putting on another 2kW to cover electric car charging. (2kW should supply enough power to cover ~40-50km of daily travel. More on this below.)
Together this leads to system sizes of 8-10kW.
Note: To make best use of this size system, & maximise charging speed, & go all-electric, you will likely need to install 3 phase.
So, now you know the system size you require, but how much space will you need to allow for all this?
With today’s panel efficiency, allow 4.1-4.8m2 per kilowatt of panel on sloped roofs.
See the graphic. Also allow for walking access around panel arrays where you can.
And that’s it.
So, for those who do get involved in design, just keep the roof in mind.
(And if you want to know which direction to face them, see previous heading.)
The future is all electric.
Your house can be a Power Hub…
…IF YOU GET YOUR ROOF SPACE RIGHT.
Roof Space requirements (Current)
YOU HAVE HAD A HOUSE RATING AND WORKED OUT WHAT SIZE PV SYSTEM YOU NEED FOR A NET ZERO OUTCOME, & ADDED A COUPLE OF kW FOR CAR CHARGING. BUT HOW DO YOU KNOW WHAT PANELS TO CHOOSE?
Well, there’s an easy way.
You don’t need to be an expert or read through performance data.
Simply follow this chart from Finn Peacock at solarquotes.com.au
If you listen to the Sustainable Builders Yak Podcast you would have heard Brian & Simon interview Finn, who is a wealth of knowledge in the area. Finn's Youtube is also a great resource on all things solar & highly recommended.
I have used this list as a guide when getting quotes over the years & tried many of the brands on it with success. They are all common brands on the market, & well supported.
So, the first tip when assessing PV quotes would be to check the panels quoted for are on the list. (Note, if a quoted a panel off this list, it doesn’t mean it is no good, just that Fin hasn’t looked at it, so do your own homework.)
The second point to look for on a quote is panel Product Warranty.
This not the 25-year 80% output PERFORMANCE WARRANTY all panels are required to have to be eligible for government rebate.
This is the PRODUCT WARRANTY which is usually 5 - 10 years.
For System Product Warranty, always push for 10 years+.
Some more expensive panels these days are going higher, with Sunpower Maxeon the current highest, giving a 40-year product warranty!
Panel lifespan is really important, when we consider there is a lot of embodied carbon in PV systems, & one of the best ways to limit life cycle carbon is to minimise replacement.
Plus, it’s a hassle pulling down old systems…
The final consideration is price & quality of the install company.
Do your homework, & check reviews.
And check the installer is a Clean Energy Council Accredited Installer.
And that’s it for panels!
Continue below and we will look at the other main system component - Inverters…
(Note: There was no sponsorship of this post [though Solarquotes did sponsor Builders Yak]. This author has just found Fin & the information he puts out through Solarquotes really helpful over the years. Thanks Fin!)
Panel Selection (Current)
SO YOU HAVE CHOSEN YOUR PANELS, WELLDONE (See previous topic). BUT THEY ONLY PRODUCE DC POWER AND YOUR HOUSE USES AC. YOU NEED A CONVERTER…AND ITS CALLED AN INVERTER! BUT WHICH ONE SHOULD YOU CHOOSE?
Inverters come in 2 main flavours:
1) String Inverters (looking like a square box with a little display), and,
2) Micro Inverters (little inverters the size of your hand that sit on the back of each panel).
Sting inverters are the cheaper and more common. And a string is the name given to a group of panels facing the same direction & tilt, that are grouped together in series. If you have a roof with multiple faces and plan to install several of these groups, then you will have to check how many strings the inverter you get quoted can handle.
The other thing to consider with strings is that if one panel fails, or gets shaded, it effects the output of the whole string.
Enter the micro inverter...
Because there is a small 'micro' inverter on the back of each panel, only those panels in shade will have reduced power, and the other panels out of shade will keep performing. So, if you have intermittent shade on your roof, consider micros. Unfortunately, they cost more, so get a quote each way, and advice from the provider on expected power output, then judge.
What about 3-phase?
If you have 3 phase power, and most new all-electric homes will be required to because of the electrical rules, consider a 3-phase inverter. This spreads the power export over 3 wires, and triples export potential to 15kW of export (5kW per phase) in network limited areas.
Ok, but WHAT'S A GOOD BRAND I hear you ask?
Here, like with panels, I check Fin’s list at SolarQuotes. If it’s on the list, it has good support in Australia and a decent reputation. If it’s not on the list, it might still be good but do your homework.
Since inverters are the part of a PV system most likely to fail, consider leaning toward the quality end.
But whatever you choose, look for a 10-year+ warranty!
And make sure you KEEP YOUR INVERTER OUT OF THE SUN if you want that free power for years to come. Unless made for the outdoors, heat and weather will reduce lifespans considerably.
Shade & Inverter selection (Current)
WHAT ABOUT BATTERIES? DO WE NEED BATTERIES FOR NET ZERO OUTCOMES?
In a word, no.
In fact, due to the carbon intensity in our grids, if you do make extra power with your PV system and send those ‘green’ electrons out into the grid for neighbours to use, you are reducing the need for fossil fuels to provide that power & saving the associated CO2.
Unfortunately however, with some feed-in tariffs as low as 5c/kWh, you no longer get paid very much for this service to humanity.
So, is it better financially to add batteries & use the power yourself?
As of 2023, probably not quite yet for most users.
BUT, for those off grid,
or those wanting to support promising technology, batteries should be considered.
And for those wanting resilience in an uncertain future, and power in a blackout, batteries combined with PV are the way to go.
And nothing says STICKING IT TO THE MAN, like installing a battery system!
So, what should you consider if thinking about batteries?
There is a lot…
…from AC or DC coupling, to capacity & power requirements, loads & panel sizing, and battery choice.
You will therefore need to talk to a professional to find a system best for you.
Just remember to ask for a 10-year product replacement warranty, & check that the batteries in the quoted system will be able to charge from PV when the grid goes down.
Lastly, batteries hold a lot of power and HAVE BEEN KNOW TO BURN DOWN HOUSES!
Therefore, proper installation is VITAL.
Batteries need to be installed in a well-ventilated, clean environment, & follow the rules of AS/NZS5139:2019.
And if installed in a garage will need bollards if located where an errant car could hit them!
So, if you want batteries in your new home, make sure your designer knows, and DESIGNS FOR THEM.
Because if your house design doesn’t have the proper space, with proper materials and offsets, you won’t be allowed to install them!
And your dreams of sticking it to the man will remain just that…
And Note: If the future your car may be the battery for the house. (See below.)
Including batteries (pros & cons and what you need to know) (Current)
RESILIENCE IS A BUZZWORD IN HOUSING FOLLOWING A YEAR OF NATURAL DISASTERS. HERE’S AN IDEA YOU CAN START IMPLEMENTING TODAY TO MAKE HOMES MUCH SAFER FOR CLIENTS IN AN UNCERTAIN FUTURE. INSTALL A ’RESILIENCE CIRCUIT’.
A Resilience Circuit is one that keeps operating when mains power goes down, to supply vital services to the home.
It requires 3 things:
1. A home battery/inverter setup that does not go off when the grid goes down, but still provides power to the house.
2. Isolation from the grid, so the house is not inadvertently sending power to the street when servicemen are trying to fix the lines (ouch!)
3. One circuit that powers items needed in an emergency (see pic), so you can turn off everything else & maximise battery life.
Client not having a battery?
Vehicle-to-House connection has already started trials in SA & within 10 years most homes will have electric cars, which when connected to the house will represent a very large battery (2 – 3 times a standard Powerwall), that will keep such a circuit running for days.
These are some of the things you would want on a Resilience Circuit:
LIGHTING – so owners can see at night
FANS – low energy cooling. More people die in power outages in heat waves than cold snaps. Fans give ~3 deg cooling effect as they blow over the skin. This can often be the difference between bearable & unbearable discomfort.
FRIDGE – to keep food fresh. Fridges are the biggest energy user on the Resilience Circuit - all the more reason to purchase an efficient one! (See STEP 4, High Star Appliances)
SELECTED POWERPOINTS – Eg. kitchen for a cup of coffee, or a microwave.
COMMUNICATIONS – powerpoint for the wifi modem, mobile phone charging, & computer to access local emergency reports.
Remember, if you are in an area that floods, make sure the whole resilience circuit is at least 1m above floor level!
And even if a new home is not getting solar or a battery, it’s a lot easier putting in a Resilience Circuit when building, than for owners to retrofit it later when they do get a system.
But, why put on such a circuit?
Why not just battery power the whole home?
Because if you don’t have a resilience circuit & the power goes down, you are very likely not to know, & whole-house-demand will quickly drain batteries flat,
& you will be in blackout,
like everyone else…
The Resilience Circuit (Current)
HOW WOULD YOU KNOW IF PART OF YOUR SOLAR ARRAY WENT DOWN?
Most owners just put them on the roof and get on with life.
If the panel efficiency went down or some panels stopped how would you know? Even if you checked your bills, a higher bill could be because of differences in weather affecting output. Or were you watching Netflix more than usual?
Most of us are too busy to work out PV contribution, and so we pay the bill, and get on with life.
I recently bought a nifty product from a company called Solar Analytics. It clips on to the house circuits in the meter box and through a phone app allows owners to see when you are making power and what you are using it on. It's best feature however is that when you set up the app, you enter your system details and location. The app then looks at the sun data at your location each day, checks your solar output, and if it is producing below what it should be, it sends you an email to let you know there’s an issue.
I got such an email when I put it on! We found that the roof safety switch on one of the panels strings had broken, and 6 panels were down! I had no idea. I don’t know how long it wasn’t producing for.
I bet this is happening all over Australia! I suspect there are millions of kilowatt hours of green power being lost! That’s a lot of extra CO2 being produced that doesn’t need to be, and energy savings owners aren't getting.
The solution: choose an inverter that has such a warning system on board. (Some do).
Or pay the few hundred bucks for an electrician to put on a system like Solar Analytics!
(And no, this wasn’t a paid add – just a useful product worth knowing about…)
The value of Energy Monitoring (Current)
VEHICLE TO HOUSE / VEHICLE TO GRID ISCOMING! TIME TO GET READY!
The future seems to be all electric. And cars are no exception. And in the homes we create today, there will be electric cars in the garages within the next decade.
And guess what? Electric cars have big battery banks.
Enter what is dubbed V2H ('vehicle to home') or V2G ('vehicle to grid') technology.
This is a technology protocol that will enable us in the near future to run our homes off our cars at night, or during a blackout, or during peak periods when power is more expensive.
And instead of the standard 14kWh home battery (eg. Powerwall), car batteries start from 30kWh for the smallest cars, up to 100kWh for bigger cars with a longer range.
Those battery sizes can keep an efficient net zero home, going a long time… and could be a big tick for home resilience in a blackout.
So, we should be putting in provision now, for future car charging!
And what does that mean?
To provision for future electric car charging, install a 32A cable, from just behind the switchboard to the spot in the garage where a future car charger would likely be placed. And make sure there are 2 free slots in the switchboard, to give room for a future circuit.
The 32A cable should be enough to allow for fast charging speeds.
3 phase power will give access to the fastest speeds, and is probably what you will need to put in anyway, if going all electric in the home.
Lastly if you put an extra 2 kW of PV on the roof, (beyond the 4-7kW or so you need for an efficient Net Zero house. See above), that should be enough to offset the charging of an electric car that is driven ~50km per day (the average Aussie daily commute for suburban dwellers).
Your house can fuel your car. And your car can power your house.
Match made in heaven!
Set up for it on your next build...
DID YOU KNOW, NOW MORE THAN EVERY YOUR HOUSE CAN BE THOUGHT OF AS A BATTERY?
If the house is designed well with passive solar principles, it will have the capacity to absorb heat in winter and hold it once the sun goes down, and stay cooler in summer. This ability is enhanced by the use of a bit of mass, be it in the slab, or reverse brick veneer walls.
But that is just the start. That is just passive performance.
If you add solar panels and have an all-electric home, a new world of active performance opens up.
Solar panels change everything!
Now you will almost certainly be making more power than you can use on general appliances during the day, so what do you do with the rest?
You can put it into your house!
Firstly, put it into your hot water. Many heat-pump hot water systems will have timers you can set to turn on during the day when you make your power.
Leftover power can go into efficient A/c heating in winter and cooling in summer. Turn them off when the sun goes down. With good insulation and a bit of mass, the house will hold the temperature through the night.
You have a Big PV system?
No problem – get an electric vehicle or e-bike and charge during the day. Your house can power your transport!
Passive is the foundation, but Active is here.
With a bit of mass, and an all-electric setup your house can be a battery.
Your House as a Battery (Current)
Legitimate, transparent offsetting will be very important to all industries, to mop up any of the remaining carbon after efficiency gains have been maximised. We are currently carrying out research in this area and hope to bring you some practical guidelines soon...
Sorry, this section is still under Construction. Please check back later...
Proceed below to SBA Tool, Webinar Link, and Internet Links
Want all the useful links referenced in the Roadmap to Carbon Zero Homes in one document? Click the pic below!
Whole of Home - Integrating efficient technologies to reach Net Zero
The Net Zero Homes builders' course is a partnership between Design Matters National and the SA Gov, and was created by the author of this website (Jeremy Spencer - Positive Footprints), so covers much the same ground.
If you like listening rather than reading, this course will be for you. The good news is that all 5 modules are completely FREE until end of 2023, and are highly recommended.
Click the link below to go to the site.
Though we suggest watching the videos in order, Module 4 Part 3, deals with the topics discussed in this step most closely.
To work out PV sizes for Net Zero Energy find a Thermal Performance Assessor who is Whole of Home Accredited.
Find an Approved Solar Retailer
To compare costs of various panel/inverter/battery options here's a useful website to try
To get a lot of practical solar information in easy to watch videos
Current Rebates in your State