We changed from Contact to Z Electricity in June 2024. Similar pricing - still
3 hours free, from 3am to 6am, as well as half price electricity 9pm to 7am.
But the main change is we've moved from a quite low but safely predictable
8c/kWh solar export price - to the rollercoaster of the wholesale spot price.
That means we earn whatever the spot price is at the time and it changes every 30 minutes. Spring solar export rates
approached 0c/kWh but in summer it's been up around 20, 30 even 40c/kWh. We
were often getting more for exporting solar power than we paid for importing
grid power. February's bill was negative $95!
How is our Payback? How have things changed in the last 3 years?
4½ years more and the panels are paid off
There's been ups and downs, but the payoff has stayed fairly consistent at 8
years.
Is this modelling is breaking down because of inflation? Power prices are
going up, a larger power price will make it look like the panels are saving us
less when they're actually saving us more, right? But turns out that's not
happening after all. I looked at how our prices have changed over the years
and because we've managed to juggle plans to our advantage we're actually
paying roughly the same for power as we were in 2022.
In terms of how our panels are doing, we aren't seeing any degradation in the
solar panels either which is great. Certainly nothing visible that we can
discern from variations in weather. We'd expect this given that they have a 25
year warranty so any noticeable degradation after 3 years would be quite a
worry.
Annual variation
We've had the panels long enough now to see how they perform in winter vs
summer.
2024 seems like a 'typical' year - 773kWh in January compared to just 200kWh
in June. 75% less! That 25% of midsummer generation is still enough to keep
our daytime power free-ish, when the heat pumps aren't warming up the place.
We get a bit of power trickling in even on cloudy and rainy days. This is a
good reason to over-spec your system though - how much power do you want to
bring in, even in mid winter?
We bought an EV!
This will change things! In March we bought an MG ZS EV. It's got 320km of
range and recharges from empty to full in about 24h on a trickle charger,
and from 20% to 80% in 30 min on a fast charger.
For instance, when Angela drove it back from Christchurch to Wellington, it
needed one fast charge in Kaikoura. There are now plenty of fast chargers in
NZ and it's charged up before you know it - 30 min is not quite enough time
for a coffee and a muffin.
24h on a trickle charger sounds like a long time, but it really isn't
- because we don't commute in our car, it stays parked and plugged in in the
garage and that basically means it's fully charged whenever you get into it.
In fact because apparently it's slightly better for the car to not leave it
sitting with a 100% charged battery, the issue is more managing it to
not charge up fully and also to use the free power or the cheap power
to charge it. None of which is actually necessary but it keeps me
entertained. I'm turning into my Dad, who insisted on pushing our car around
on the driveway because it was better for it than cold starting it.
Did we buy a battery yet?
Well, no. But my neighbour just told me about how prices are still
trending down down down:
The lowest automotive prices are down to US $53 per kWh for a cell, and
about US$75 in a vehicle battery pack. Might be an oversupply as EV
sales are down in some markets
They are the later LFP chemistry which is far less fire prone
So A$1000 per kWh for Tesla Powerwalls is extreme, and other storage
batteries for solar also look way overpriced.
I'm still hopeful to see 10kWh batteries available for much cheaper soon -
which is all we need to capture a day's solar to use in the evening, and
cheap/free overnight electricity to use in the morning. $1000 NZD, not
$10,000 NZD would be a good price, and I'd be more than happy with second
life batteries out of a parted-out EV. There is a
bewildering array of batteries available now, this market is finally heating up like it should do. But 50kWh of
home battery storage is still a lot pricier than our MG with a
50kWh battery - and it doesn't come with a free car. That seems ludicrous.
I did some reading and seems like it's mainly because it's a niche market
still. Folks ran through the inverter and installation costs (should only
be a few thousand, certainly not up to the cost of a whole car!),
interspersed with other folks with the expertise to build their own
system, and had, for $1-2000 and showing their aliexpress receipts.
We've just spent a week with Tim and Michelle in Townsville which was
great fun - a battery is a no-brainer up there. Lots and lots of sunshine,
zero and even negative solar export rates because everyone's doing it, and
AC that runs all day and all night. The Aussie government is talking about
subsidising batteries (as an alternative to building more power plants!)
and like solar, anything the Aussies do creates a more mature market that
we Kiwis can tap into.
Anyway, we are getting more than enough return selling our solar back to
the grid right now. We now have backup power with the V2L cable that came
with our MG - in other words, we can run our fridge and phone chargers off
the car for a few days. So there is no point in spending any money on a
battery. I will keep watching with interest.
Heating days
My work colleague, with a ducted heatpump system, has discovered
'heating days' as a metric of electricity usage - especially if a
big portion of your usage goes on heating.
This graph shows kWh usage of his heat pumps (the stacked bars) over the
last 2 years, and the line is the “heating degree days” (HDD), which is
the cumulative number of hours where Wellington was <16C.
The 'Heating Degree Days' line is, as you can see, a good predictor of
actual heating energy usage. July 2024 bucks the trend as he went on
holiday to Aus for 2 weeks 😊.
'Heating Degree Days' is also a good way of visualising whether efficiency
gains have worked - has adding insulation or more efficient heating had an
effect on your power bills when you adjust for Heating Degree Days?
https://Degreedays.net is his source, using NZWN as the weather station. Also lots of
links to articles on that site to learn more.
So we've had our solar panels for just over a year now. How has it gone? Any
regrets? Would we do it again?
The graphs still look good
The black line is our average pre-solar power bills for the six years to 2021;
the red lines are our post-solar power bills for 2022 and 2023. Solar was
fitted in mid-February 2022.
Our very best month was November when our power bill was... $1.92. Pre-solar
it would have been over $230.
We've saved over $2,000 this year in power bills. That sounds like a lot,
but break-even (including interest on the debt, too) is still out in
2029. That's only 8 years out of a 25 year warranty lifespan, and even 25 years later the panels should be only minimally degraded (say 10% or so).
Hot water timer - Sinotimer was the quality you'd expect for $26 ...
Much of the savings is still in making the most of Contact's free electricity
from 9pm to midnight, and having the hot water cylinder come on only at this time.
It keeps piping hot on that schedule no problem at all.
A typical partly cloudy day. Timers come on during the solar
generation time The Hot water cylinder kicks in at 9:05pm when
power is free
It was all good until November when it failed. And it failed off. So no hot
water for us.
Damian the sparky came and unwired it, and we were back to switching the HWC
on manually at 9pm when Alexa told us to, and off again when we blearily got
up.
It's fantastic, and pays itself off in a couple of months. It works via
Bluetooth off a phone app which makes setup nice and easy and I have far more
confidence in getting more than just a few months out of it. You can put it onto the internet to control your HWC remotely with a 'Wiser Zwave Hub' but that's $500, so only worth it if you go all-in on home automation and put similar IoT controls on all your plugs and lights.
The only issue was installation. The timer unit is physically quite large
(deep) in ways that the hot water cylinder's external mounting box is not.
After trying various ways to make it fit I settled on stacking two mounting
boxes on top of each other. It actually worked tidily and well, with long
screws thoroughly securing both boxes to the wall.
Anticlimactic looking for the effort that went into it
Looking for emergency power during a power cut
Oct 2023: According to everybody, if you want emergency power during a power cut you must have a battery hooked into your system. Without a battery, the solar power automatically cuts when the grid power goes down. This is because without a battery sink, the solar panels will liven the grid and make working on it highly dangerous.
However - my sister in law has just had solar installed by eSolar with a great workaround. Her system has a 'magic plug socket' that comes directly out of the inverter and bypasses the meter.
During a power cut, she can plug essential items such as her freezer and phone charger into that plug socket, and it will provide 240V and as many amps as the panels are generating. Neat!
Looking for simple static batteries
It would still be nice to have some battery storage. We usually generate far more than we can use during the day (for 8c /kWh credit) and then use power in morning and evening that we pay 30c /kWh for. It wouldn't take much storage - say 6-8 kWh - to cover off those few hours of usage and use hardly any grid electricity - apart from that free power at night that I'm so obsessed with!
Aug 2023: there seems to be more options now. mysolarquotes have a pretty good writeup and some initial options there. The usual solar-provider suspects all seem to have smaller cheaper batteries available. I might have to revisit this, even if it's so I can write another blog post!
I am on the fence about the ROI still. An EV with vehicle-to-home capability would be ideal, because you're buying a car that happens to be a battery too, but the large outlay would probably take decades to pay off at the meagre returns you'd earn. Even with the 73% margin we pay on export vs import power, the grid is probably a better value "battery" than what we could buy.
What could change this in the future is storage batteries made from old EVs. Either modern crashed ones where the battery will effectively last forever - or old Leaf batteries that are too degraded to use in a car anymore. This degradation isn't a problem for home storage - you just get more of them! - and home use has a much lower draw and recharge rate than a car so the batteries will have a quiet retirement and should last okay.
EVs Enhanced in Christchurch operates a great "cascade" where they fit their own new batteries and high capacity used batteries to Leaf owners who want the best range they can get, then take those batteries and sell them cheap to Leaf owners with almost unuseable batteries; then what happens to the oldest batteries? They are looking for other companies to reuse them and manufacture static storage batteries.
They pointed me at https://www.b3batteries.co.nz/ who they are talking to - they have a 'coming soon' website but let's see what happens there. I'm pretty keen for the right price.
We've had solar for long enough now that we can see the trends. How is it going? Is it everything we hoped and dreamed of?
The good news is - we're saving a LOT of money on our power bill.
The bad news is - we spent a LOT of money on our solar and its payback is pretty slow.
Good news
Look! The black line is our average power spend (in $/day) over the last 6 years. The red line is our spend in 2022. The solar went in in mid February.
In April we had a $40 bill instead of the usual $210 bill. That's pretty awesome.
Bad news
Adding extra Sparky work and the various timers, it's going to take us 8 years to pay off the work from that savings. That's probably about when we will be selling the house, letting the next owner cream all the profit of our hard work.
That's just extrapolating that $170 per month savings out to the future, since we've only had one power bill with everything set up right. Who knows what will happen over winter - we need a year of data to do this properly. But then, power prices may go up, our usage may change ... it'll all be approximate at best.
It's also not like the good news graph is that robust either. Over the last 6 years we've added roof insulation, underfloor membrane barriers and some double glazing. We bought a beer fridge and changed our washer/dryer. Toby went through his teenage years and then left home. We've moved electricity providers and plans a couple of times. Oh, and there was that thing that happened that changed our habits a lot over the last two years!
But I figured that's the best I have to work with, no need to overthink it. (Um, maybe I've already overthought it.)
It's the dashboard too!
You can see the spikes where we boiled the kettle or microwaved breakfast. And just how much usage we can shift to 9pm.
Solar or not, I reckon having direct visibility of exactly what power we're using in real time makes a huge difference. Everybody needs it! You can't budget what you can't measure.
I'm astonished how much you can save running your high use appliances - dishwasher, washing machine, dryer - overnight on cheap power instead of say after dinner when it's convenient to just turn it on without thinking. And it's no change to the usual thing we'd do (for dishes and clothes) of turn it on, go to bed, empty it in the morning. On the other hand, modern lights use next to no power, there's no point turning them off like in the old days with 100W lightbulbs.
You just don't know these things unless you can see what exactly what happens when you turn things on and off.
Solar Web Dashboard - translating tariff jargon
This Fronius Solar Web Dashboard also lets us estimate our costs and savings, if we enter our import and export tariffs. The tariff names are really confusing though. Luckily I found a forum where someone had kindly translated the German English to New Zealand English:
Feed-in tariff (without Fronius smart meter) This is the yield of solar generation, (this is needed only if you do not have Fronius Smart Meter)
Reference tariff (with Fronius smart meter) This is the cost of electricity you pay to the utility in kwh, ( this is needed if you have Fronius Smart Meter)
Feed-in tariff (with Fronius smart meter) This is the how much utility pays to for solar going back to the grid, (this is needed if you have Fronius Smart Meter)
Offset [kWh] The offset Kwh allow you to add in missing kwh hours that the logger has not picked up, eg. you have inverter installed for couple of months and then you start recording the kwh. This allow you add in the total missing kwh here.
Offset Earning The offset earning allow you to add in missing yield that the logger has not picked up, eg. you have inverter installed for couple of months and then you start recording the yield. This allow you add in the total missing yield here.
It's the Electricity plan too!
The big red bars are FREE FREE FREE
Contact Energy's three free hours of electricity is amazing.
Between the solar during the day, and shifting all possible usage to the free power evenings, we don't have to pay for very much power at all.
So little in fact that we've been able to move to a 'low use' plan with a base charge of 30c per day instead of $1.70 per day. Break-even is about $160 per month. We'll see how winter goes.
In a year or so we'll see if there are spot price plans that give us better export rates and maybe really cheap overnight power instead of 3 free hours. Maybe it'll be worth it.
It's the timers too!
I've also installed (or started using) all sorts of timers to restrict anything that doesn't have to run on demand, to when power is cheap.
Hot water (3000W) - Sinotimer - 9pm to 2am
This is the big one and I've written far too much about it already. But if you don't have a timer on your electric hot water cylinder, you're spending hundreds of dollars a quarter that you don't need to.
Beer fridge (some W) - $10 Mitre 10 plug timer - 9pm to 12am, 10am to 4pm
Both Consumer NZ and my mate Gareth from EECA say that beer fridges are one of the biggest power vampires in your house. But (apart from Christmas when it's probably got turkey and ham in it) it's only got beer in it and doesn't have to run 24 hours a day.
This simple little box sits inside your plug box and turns your towel rail on for just 4 hours in 12. It's intended to get your towels warm and fluffy in the morning and evening. But I've set it to use cheap power instead. So our towels are cold and clammy, but they're dry at least.
Bathroom heated floor (some W) - Warmup W3115 timer - 9pm to 12am, 10am to 4pm
This thermostat/timer (that came with our underfloor heating system) was a nightmare to program, I had to study the instructions in detail and write down the algorithm to program in. If it wasn't a one-off job I'd replace this thing for sure. It's pretty old and there'll be much better ones around now.
It's also heating the floor when it's cheap, not when our delicate feet are walking over it. Oh well.
So, is it all worth it?
We went into this for largely non financial reasons, and that's lucky. Solar is going to save us money, but not for a while and if we sell our house this decade, not at all unless we recoup our investment in the sale price.
But we're using far less power, far less dirty peak power, and we understand our usage much better. That's what we wanted and that's what we got.
As part of the solar install, I had to learn far too much about how hot water
systems work - what options you have and how to get the most value out of each
option. You probably don't want to know about hot water systems, but I want to
tell you, and it's my (well, Angela's) blog so you can't stop me.
But read this before you click away!
You should read on for the next paragraph or so though, especially if you have
an old (20+ year) electric hot water cylinder (HWC). It will suddenly fail one
day, and you'll have to make a quick 4-figure-sum decision about what to
replace it with. You need to do your homework now so you are ready to make an
informed decision when it happens.
Get a HWC timer, right now
Hot water used to cost me 30% of my power bill. I added a $200 timer and now
it's 0% (and nothing to do with the solar panels on the roof).
There is no need to run your HWC 24/7, and there are plenty of deals that give
you cheap or even free power in off-peak times. It's an absolute no-brainer to
fit a timer and heat your hot water when it's cheapest.
Pick one out (see links below) and get it fitted next time you need a sparky
to visit.
I've also set up my beer fridge, towel rails and underfloor heating to only
run when power is cheap or free.
A typical day with the HWC running 9pm to 7am. 2 hours or so is all
it takes to heat the day's water. The HWC spikes well beyond what
the solar panels generally give us.
Wrap your old HWC, right now
It's worth mentioning that you can wrap your elderly HWC with more insulation,
and save money that way. Simple and effective. Just do it. Mitre 10 and
Bunnings sell kits.
Get a heatpump HWC
This would definitely be my pick for a replacement hot water system.
All the faff in the rest of this blog post is for trying to optimise the
massive power drain a regular cylinder consumes. Heat pump cylinders use the
magic of heatpumps to do their job on 20-30% of the power of a regular
cylinder. So you just don't need to worry about the kWh and the $ anymore.
Oct 2023: My work colleague Richard has just bought this one - Sanden - Rheem . It has two benefits: the heat pump heating system can be retrofitted to an existing cylinder, and it uses CO2 as its refrigerant. That second one means it's hydrocarbon free, and it runs a lot more efficiently and at a lower outside temperature.
If a heatpump HWC is too expensive for you, think about spending just a little
extra on a stainless steel HWC with a smart mixer valve. (For example,
https://greenglo.co.nz/greenglo-range/
or the standard brands like Rheem). These will work with other heat sources
like wetbacks, because they aren't fussy how hot you get the water. They also
give you the option with solar to over-heat the water when you can, so you can
use them like a battery.
Gas infinity systems are great - but be wary
A gas 'infinite hot water' system, with high pressure gas bottles or
reticulated gas, works really well and avoids that whole electricity bill. But
I'd personally steer away from these since in NZ the govt has a plan to phase
these out in the next 10 years. The gas industry is pretending that hydrogen
will replace natural gas but this is basically vapourware (see what I did
there?) - it won't work, and if it does work you'll need a new appliance
anyway. (Rosie, and Paul Martin,
explain why at length in this video.)
If you must, I'd say bottles will be more long lasting than reticulated gas,
and you want an appliance that can run on different sorts of gas with just a
jet change.
Consider an electric infinity system!
Edit Jan 2023 My workmate is looking at ripping out his gas cylinder
and replacing it with an instantaneous electric system. Something like
what Stiebel-Eltron offer. He's thinking about two of these units, one in each end of the
house. Watch this space!
Technology Connections has gone into how hot water cylinders work and how to
maximise their efficiency in lots of detail. It's a great watch if you like
nerds explaining simple things in extreme detail, just like I do.
So why do I care so much about hot water?
With solar on our roof now, I was expecting to use the hot water cylinder as
our battery. Use a timer and heat the water really hot when the sun is
shining, use it up when it's dark. Easy.
No, not that easy. Three main reasons:
Our HWC is ceramic-coated inside, not stainless steel or copper, which means
it can't hold really hot water. And our mixer valve is simple and dumb, it
cannot adjust how much cold water it mixes in to keep the water temperature
constant at the tap. The whole system is designed to just maintain a steady
60°C in the cylinder, and deliver 50°C to the tap. So it's not an option to
get it to say 90°C when the sun is shining, and store a good lot of hot water
for when it's dark.
Our HWC is either off (0W) or on (3000W). 3000W is far more than our panels
will generate except in the middle of a very sunny day. No option to throttle
the cylinder down to "low" or something, other than replace its elements
completely - a very permanent solution! This means that if the HWC runs during
the day, it's mainly using grid power in spite of the solar panels on the
roof.
Why can't our hot water cylinder do what our $70 heater does? A 24h
timer and a Low/Med/High power setting as well as a thermostat.
But our HWC does have two elements, like most newish cylinders. Surely that
means I can run just one element and drive the HWC at half speed or
something during the day? No. That's not how it works at all.
One element is halfway up the cylinder and the second one is at the
bottom. Only one element will be on at any time. - they are
"non-simultaneous". The idea is that when you run low on hot water, the
top half heats first (giving you hotter water faster since the hotter
water will "float" on top of the cooler water). Then when the top half is
hot, the cylinder switches to heating the bottom half and the rest of the
water. Normally the two elements work like this, handing over from one to
the other, but you can rewire the bottom element to only run off-peak on
your timer. Basically you keep just half the water hot during peak times
and get the whole cylinder hot only at off-peak rates. (This seems to be a
bit of a waste of time to me).
Legionnaires!
Let's get the Legionnaires disease elephant in the room out of the way. If
you run your cylinder luke warm, under 60°C, then you run the risk of
Legionnaires disease getting into the system and putting you in hospital
or worse. But, as long as you get it up to temperature at least once a
week you are fine (source:
EECA via Radio New Zealand).
So it's safe to use a timer to get the cylinder to 60°C each day on cheap
power, then let it slowly cool while power is expensive. Turning the
thermostat down to keep the cylinder permanently cooler to use less power,
is NOT SAFE.
Hot Water Timers - options and links
Updated March 2023
OK this is the long story about hot water timers. Unfortunately, fitting a
HWC timer fell off the manifest for our solar install so I had to
investigate options myself. I found it pretty hard to find out this
information. It's sparsely documented, the sparkies aren't really up with
the play and their suppliers don't really care. You've got to find it out
for yourself and figure out how to source things too.
If a hot water cylinder plugged into a regular 3 pin socket, you could go
to Mitre 10 and buy a $10 timer plug and you'd be done. But because it
uses more like 16A instead of 10A, it's not that simple.
I started out with the sensible path and rang a few electrical
wholesalers/suppliers. They must be able to help, surely? No. They were
either a bit baffled about why I would want such a thing, or confidently
asserted that they were nearly impossible to get. I had to go
elsewhere.
Here is the list of timer units I found, and the pros and cons. It will go
out of date fast, but the principles will stay relevant.
PDL Iconic kit from Eurotech $200
This was my initial second choice (and Angela's first choice!), but
after I "saved" money with the $26 Sinotimer below, and it failed after
just a few months - I went with this one.
Eurotech - https://www.kiwisparks.co.nz - have taken some Schneider/PDL off the shelf components and
bundled them to give you everything you need to put a Bluetooth or
Z-Wave
driven timer into the wall 'socket' that your HWC is wired into. Less
invasive than a switchboard install (assuming you even have the right
switchboard!) and you can change the settings from your phone.
You can find all these components on the PDL website - this is the bluetooth/ZWave device and here are all their timer options - but it's very confusing and hard to follow there. Their website
seemed to be aimed at electrical suppliers who know exactly what they want
to order already. Eurotech have made this and a lot of other home
automation jobs much easier by putting together the things you need and
making them easy to buy.
The installation was a little tricky because the timer is about 55mm deep
and an external mounting box is only 34mm deep. After trying various ways
to make it fit I settled on stacking two mounting boxes on top of each
other. It actually worked tidily and well, with long screws thoroughly
securing both boxes to the wall.
Anticlimactic looking for the effort that went into it
Sinotimer digital timer $26
I bought this in April, because I thought it was cheap and it did the job.
But, it lasted six months before it failed. I don't recommend! The cost of
getting the Sparky to wire it in is far more than the money I saved by
going cheap.
It's a Chinese unit that they also white-label for anyone who wants to put
their "home brand" on it. That's why you'll find any number of timers like
this that all look suspiciously similar. It goes into your switchboard, so
it's definitely something a sparky must fit, and you need to have a modern
switchboard with breakers, not one of those old black panels with fuses
mounted on it.
There are more expensive (and hopefully more durable!) versions of that
electronic switchboard mounted timer you could consider instead, such as
this Italian brand.
This is a mechanical version of those electronic switchboard timers. I
like this one. It's simple and mechanical so it'll arguably outlast
anything electronic or Bluetooth/wifi, and it's 'Made In Germany' so you'd
expect it to be good quality. It's probably the one to pick if you think
paying a sparky to fit a $26 Chinese electronic timer is a false
economy.
My sparky pointed out, though, that any mechanical timer will be noisy so
if your switchboard is close to a bedroom it might not be a great
choice.
It also goes into your modern switchboard.
Lightforce Solar
sell this, it's what they'll give you if you buy a solar panel install
from them. It's also available on TradeMe from sellers like MyTools with listings like
this one.
Honeywell ST9100C timer $585
This is what I would have got from
Harrisons Solar
if it had made the quote. It's beautiful, fully featured and has more
options than you can shake a stick at. But I think it's just too
expensive. It also doesn't connect with home automation systems.
These look ideal if you want a smart timer that talks to your home
automation system. I just didn't know enough about them to take the gamble
that they would work, or even be legal, in a NZ house.
https://sparkydirect.com.au had
a much better range of electrical goods, in a much friendlier form, than
most websites I was browsing. Australia seems a safe bet too since they
share our electrical standards. I did consider this timer unit which does look quite familiar (remember what I said about
SinoTimer white-labelling their stuff?).
A regular timer + a relay
In hindsight perhaps I should have investigated this.
Get a more regular timer, one designed for lights or something, and hook
it up with a relay that has the oomf to control the HWC. This avoids
having to mess with the switchboard and gives you more options for your
timer.
Other options for efficient hot water heating
There are a few other options, that weren't useful for my circumstances. They might be worth looking at if
you have something like a spa pool or a stainless HWC, or you are off-grid
and every joule counts.
Though I wish I'd known about that Fronius Ohmpilot back when I was sorting out my timer.
Hot water Power Diverters
This is the 'holy grail' that I naively assumed would be
straightforward to set up for a solar installation. Talk to the smart
meter/inverter which has a standards based API to tell you how much
excess power is coming off the roof, and funnel the right amount of
amps to the hot water cylinder to maximise its use. Add in some
periods where grid power is cheap and the unit can just suck down all
the amps the grid will give it, too. Done! Optimum use of your solar
power and your grid sources.
The truth is, these units are quite expensive ($1000 or so), and
really need to be paired with a stainless steel cylinder so they can
over-heat the water when the sun is shining. The ROI just wasn't
there. That's serious money you could just put into a heatpump hot
water cylinder instead and not use the power in the first place.
Here's a great article that explains the differences and the pros and
cons.
Mar 2024: my sis-in-law Iona has a Fronius Ohmpilot that was put in as part of her solar install. It looks perfect! A power diverter that talks directly to her Fronius Inverter and just works. I want one.
Solar hot water
Why take sunlight, turn it into DC electricity, put it through an
inverter to make it AC, run it in wires to a hot water element and
heat the element to make hot water - when you could just heat the
water directly by shining sunlight on it? Quite a few years ago
my sister followed that logic and got a solar hot water system
installed.
Unfortunately the system didn't really work. For efficiency it uses a
glycol heat exchanger. It seems to be very problematic - the glycol
leaks away, the pump fails, it seems to need regular expensive
maintenance. She also needed to replace her cylinder with a stainless
steel one to let it over-heat the water.
I have a friend with this system too, she had a better experience but
it still requires a bit of maintenance. The pipe joints have a habit
of leaking because the water temperature inside them varies so much
and they're constantly expanding and contracting.
One advantage is that you have two energy sources - so if your HWC
elements fail then you still have lukewarm hot water to get you
through the fix. Though a power cut still means no hot water since the
pump to the roof doesn't work anymore, and a HWC leak is still
catastrophic too.
These systems have fallen out of favour, since for your money you'd be
better off installing a heatpump hot water cylinder for similar
efficiency gains.
Ripple Control
For completeness, I better mention "Ripple control". This is where the
lines company (not your power company) can switch off your cylinder
remotely in peak usage times to smooth out peaks and troughs. It was
common in the 1970s and 80s, it's still a thing today but I don't know
anyone who still has it. EECA have written a report that talks about Ripple control in terms of the greater good but
don't offer any reasons why as a consumer I would want to have it (or
for that matter why the lines companies would even bother either). The
conclusion seems to be, it's a Good Thing but it will be gone in 5-10
years anyway as smarter management systems come online.
Do you have any advice for me?
If you've got this far you must be quite interested in electrical
efficiency! What did I get wrong? What did I miss? Do you have any advice
for me? Do you know anyone or any company that gives good straightforward
advice and has a range of products that can help?
Please tell me in the comments.
My experiences are also based entirely around living in my particular suburban house in
New Zealand. Different countries have different energy options with
different costs and carbon footprints. Hot water systems are also quite
conservative and one country's common system will be unheard of and
difficult to get in another. If you are rural and/or off-grid, you'll have
completely different needs too. Even for me, if electricity prices or solar
buyback prices change, the equation will change. If I ever add a battery or
buy an EV with vehicle-to-load or vehicle-to-grid capability, everything will change again.
It's an exciting time!
As Angela's said, we now have solar panels on our roof. So how's it going after three weeks or so?
Our motivation for solar was primarily to generate watts of power that didn't need to come from Indonesian coal, shipped across the Tasman to the Huntly power station. Secondary was to save money even if it took a long payback.
We didn't do all the research we should have to fully understand all the nuances of what we were about to do - instead we put ourselves in the hands of Harrisons Solar who had a good reputation both from the internet and word of mouth. We don't regret it, they were extremely helpful, professional, and did a really good job.
We (well, our bank) spent $13k all up on a 12 panel, 4.7kW system. This is for a smallish 3br house with a 250L electric hot water system, nice north facing sun on an appropriately sloping roof, and 2 of us living here (though we wanted to spec the panels for the next owners too). We turned down the $18k Tesla battery.
We also changed power suppliers to Contact Energy who currently offer free electricity between 9pm and 12am - this works really nicely so we only really draw lots of power at dawn and dusk, the rest is mostly either free or helped along by solar. We've changed our behaviour to eg only run the washing machine and dishwasher at 9pm, or in the middle of the day if we need to. I'm going to put timers on the towel rails and suchlike.
Half our panels (the western ones)
So how's it gone then? This is what we've found.
There seems to be a lot to consider in the install. You don't just throw panels on the roof and hope for the best. They're interlinked in a way that means they only give you the power of the least performing panel in the bank; you need an even number of panels in a bank; and so on. There are a bewildering selection of inverters at very different price, functionality and quality points too. A DIY job would take a lot of research and discussion with experts, and the right sparky to work with you, although there are also a lot of websites that do much of this work for you. We ended up with a bank of six north-facing panels, and a 2nd bank of six west-facing panels as the best solution.
It's kinda obvious, but if your roof is dodgy you need to replace or fix your roof before you do the solar work. You don't want to put panels up then need to take them down again to sort your roof. We replaced our roof a few years back, from the original iron the house was built with.
Solar generates steady power, but you use power in short intensive peaks. That means that without a battery, it's hard to ensure that you're using the power you make - you're either spilling to the grid or sucking from the grid for most of the time. And you pay a lot more for power you use, than they pay you for power you export.
In the following pictures,
Yellow = solar power we use ourselves
Grey = excess solar power we export to the grid
Blue line = our actual consumption, when it spikes into the white area that's grid power we're using.
This is the best case - a sunny summer's day.
A more typical day with cloudy periods.
Our inverter is battery ready. I'm expecting batteries to come down in price a lot over the next few years, with increased demand, maturing tech and a heap of second life EV batteries hitting the market. Or we'll have a mobile battery with four wheels and a steering wheel in our garage in the next few years. Even a relatively small one to smooth out the peaks and troughs would be nice. Another thing is that when you sell your house you can take the battery with you no worries. Even if your next house didn't have solar you can charge it at night and use it during the day.
I was expecting to use the hot water cylinder as our battery. But, because its thermostat is either off (0W) or on (3000W) it peaks beyond what the panels can generally provide. After more research than I really wanted to do, I settled on a $26 timer fitted to the switchboard, that switches on the hot water cylinder just for three hours during the Contact Energy 'free power' evening. That's enough to provide hot water all day. I've since written a ridiculously detailed blog post about it.
I'm looking forward to my next electricity bill! I don't really know how our reduced grid usage, free night power and the (not much) money we get exporting power to the grid will all work out. I'm going to do a spreadsheet to see how our payback goes, including paying mortgage interest on the principal. I suspect not all that well. But, Indonesian coal.
