Blog entries tagged with "solar"

Today is the winter solstice and over the last few days it has been quite clear that winter has set in in Melbourne with headlines such as “Melbourne shivers through coldest winter day in four years…” so it seems appropriate I give some updates on how my solar, AC and heat pump hot water system are going.

A big question I asked myself was whether I made a mistake in getting my gas disconnected. Previously I would have the central heating on a schedule that I didn’t think about and my entire house would be warm at the times that I was awake. The AC units in my study (during the day while I am working and then in the evening) and bedroom (a bit in the morning for when I wake up and then a bit in the evening before I go to sleep) do a good job if I close the doors to those rooms, which means the other rooms (kitchen, bathroom, lounge) are cold.

It isn’t actually that bad, but it is noticeable when I move from room to room. Thanks to my monitoring I could also track that when I was in my study that the CO₂ would climb to 1500ppm and at times I do feel a bit sluggish. My mitigation so far has been to get up every hour and go get a drink or go to the bathroom, this lets enough fresh air in to drop the CO₂ down to around 600ppm from where it will start to climb again. The alternative is to leave the door open (like I used to do) but then the AC unit is trying to heat my entire house which is not efficient.

With the shorter and cloudier days there has been a noticeable drop in how much my solar panels are generating. At the peak of summer they would generate almost 30kWh over the day, but the best I have seen recently is 17kWh on a day that was sunny all day, but that is the difference between 13 hours of sun high in the sky versus about 8 hours of sun that is lower. Though even on a day that rained all the way through the panels managed to produce around 3kWh which was about a third of my consumption for that day.

I could also notice a pattern of the solar generation being best in the early afternoon, the day would start out cloudy and the clear up for a bit. To better take advantage of this I changed the schedule on my heat pump hot water from 10am to 1pm with the intent to run it both from solar that I am generating and also to be in a warmer part of the day so it should run a bit more efficiently. I don’t have a way to actually measure this, but it seems like the right thing to do. What I can also see is that where it would run for just over an hour when the ambient temperature was above 20°C, but now when the ambient temperature is below 10°C it is running for a bit over two hours.

All of this is just the detail, what really matters is the long term so it won’t be until the start of next year that I can sit down with the data and compare 2023 with gas heating and no solar against 2024 with solar and three heat pumps…

It has been a month since I last mentioned my solar panels and this time the significant thing is that I have received my electricity bill for the first full month since everything has been set up. No partial feed-in tariff and no admin charges.

It is pretty much as I expected with what I get paid for the solar balancing out what I am charged for pulling from the grid, leaving the daily charge:

I can’t compare the reported usage against what Enlighten reports because my Envoy gateway has been a bit broken (but now replaced). After the long power outage earlier in February it failed to report to the cloud, although the Home Assistant integration was able to pull data from it just fine. Even then Home Assistant data isn’t complete as the Envoy would at times drop off the network, but llowing for some missing data the usage values do line up.

So how does this compare against a time before I got the solar installed. That would be October 2023:

It is nice that my monthly bill is now a quarter of what it used to be, although I expect it to rise as we head into the colder months when there is less sun and I will be using electricity for heating. No more gas bill though :)

So far this summer the weather has been pretty mild so it is odd to think that we are now in February and this is the first time that we have had temperatures in the high thirties. Based on my measurements we reached 36.2°C yesterday and 38.4°C today.

So how did my new air conditioners handle the heat?

I am still working out how I want the schedules and automation to work, but so far I have it that a calendar entry for 24#COOL#STUDY means that I will allow the study unit to be running at 24°C in cooling mode. The automation looks at the current outside and indoor temperatures and will not start the AC until they both reach 24°C

On Saturday that condition was met at 2PM and kept my study at a nice comfortable temperature. I also closed the exterior blinds and had the ceiling fan on low. Today that condition was met at 10:30AM and things also remained comfortable, though since there was plenty of sun I also turned on the bedroom AC unit and lowered them both to 22°C to see how that felt.

Speaking of sun… it was a nice clear day and the generation from my solar panels was the stereotypical ideal curve:

Consumption items of note are:

• hot water running for an hour from 9AM
• spikes at 10:30AM when I cooked an early lunch
• increasing usage with the AC at 24°C and then further increase when both running at 22°C
• spikes in early afternoon when I use the washing machine
• a drop at 5PM when I switched back to one AC at 24°C

It is nice that most of this usage is covered by solar generation. The stats for the day so far are:

• 29.6kWh solar generation
• 15.2kWh consumed
• 4.2kWh pulled from the grid
• 18.5kWh fed to the grid

The reconfiguration of my account for solar finally got done a week ago, so now I am getting credit for what I feed back to the grid. For this day at my current rates the consumption balances the feed-in, making the cost just the daily supply charge. However this is just one day and it is the impact over time that is more important.

I also noticed something odd when looking at the generation from the inverters on each of the solar panels:

So ten of the panels are generating as you would expect for a clear sunny day. But what is up with the other two? In the enphase app the panels are laid out over an aerial image of my roof and I could see that the two panels with slightly lower generation are the two that are next to my tv antenna. So the slight shadow that casts is affecting those panels, changing from one to the other as the shadow changes. While I don’t watch free to air tv often, I won’t get rid of the antenna as there are a couple of shows I still automatically record to watch later.

It has now been one month since I had solar panels installed and I am still working out what I want to monitor and how it will change my behaviour.

So what does the monitoring look like?

The cloud based monitoring that the Envoy controller reports to gives a status page, but I find the energy reporting to be more interesting. This is the report for yesterday:

There were clouds a couple of times but otherwise it was sunny, so there is a nice curve to the solar production. On the consumption side you can see there at 10am the hot water was on for an hour, then I was cooking lunch with my air fryer at 11:30am. It was a warm day so in the afternoon I turned on the air conditioning to keep things cool.

With the integration into Home Assistant I can get a similar view of the same data through the energy dashboard, though not as granular as it is in one hour (instead of 15 minute) increments:

This is getting its data from the “energy production/consumption today” values which are in kWh and reset each day. If I want live information I look at the power values which I have converted to W to be in line with what I get directly from the smart meter, from my UPS and from my tamsota devices. The same day but the power reading which is updated every minute looks like:

It starts to get messy but I can also include the power reading data from the smart meter (updated every 8 seconds):

If the smart meter reading is positive then I am consuming from the grid, while if it is negative then I am feeding power back to the grid. Of course I am still waiting for my meter/account to be reconfigured so I get paid for what I export…

It is clear that on a sunny day in summer that my solar generation will easily cover the large loads such as hot water, dishwasher, washing machine and lunchtime cooking. What would the numbers look like on my bill?

Not as much of a saving as I expected, but this is only a single day and I was running both AC units as an experiment while I would ideally just be running the one in my study. Definitely need to wait and see how the numbers fall for a full monthly billing cycle…

As I have been working through the cost of my electricity and the specific costs for hot water and other appliances I have also been reading up on what it would mean to get solar panels. A great starting point is Solar 101: A Guide To Buying Solar Power Systems and I have been getting information from other sites as well.

I am in the process of getting quotes and one thing common issue is that the shape of my roof isn’t the best. I might not be able to fit that many panels on the north facing section, nothing faces east, very little faces west, and then there is a nice big south facing section. I would definitely get 4.4kW of panels facing north and then optionally a second set facing south. Or even have a second set on the flat roof of my detached garage, but first I need to completely redo that old roof.

One aspect that caught my eye is whether or not a particular load can be completely handled by solar generation. Paying 22c/kWh overnight for power and then getting back 6c/kWh for unused solar during the day, means you are still paying out 16c/kWh. That cost would instead be zero if it were able to be moved to be during the day.

I have four large electrical loads, how easily would they fit within 4.4kW?

1. heat-pump hot water

I plan to leave a heat-pump hot water system on the typical schedule of 10am to 4pm, but in practice I expect it will from from 10am for at most two hours, drawing a constant 1kW for that time. In summer this should be trivial for any solar installation, and hopefully be possible in winter, but there are those cold dark and wet days…

2. dishwasher

Based on the usage I have been tracking so far a typical cycle of my dishwasher will consume around 1.1kWh, but spread over an hour and a half with sustained peaks of 2kW (not this is around 8.5A, so under the 10A rating of the cable, plugs, etc) which makes sense as it needs hot water for both the washing and then the rinsing. Again in summer this should be trivial to run when there is ample solar, then in winter the solution might be to run it in the afternoon when the sun is highest and the hot water has finished.

3. washing machine

I was surprised to see that the washing machine also consumed around 1.1kWh like the dishwasher, but as I showed in the previous post the pattern is quite different, with it running for much longer and only heating up the water (also at 2kW) in the early phases. Unlike the dishwasher that uses hot water for rinsing, the washing machine uses cold water for that. These differences aside I would treat this the same as the dishwasher and run it in the afternoon and not at the same time as each other.

4. reverse cycle heating and cooling

This one is still the most unknown to me as I don’t have it and I cannot compare it against my current gas central heating. I do know when the gas heating has been running and I know when I would like to have cooling:

• Summer: Cooling to take the edge of the hot days and to make the really hot days livable
• Autumn and spring: Heating in the early morning (I start working from home at 7AM) and late evening
• Winter: Heating all though the day from early morning until late evening

The power usage for this system is hard to determine. For one model of system that I have been quoted the energy rating label says that for Melbourne it will use 920 kWh per year. How does that translate for my poorly insulated leaky house? This same model is rated at 3.5A when heating. So is that 0.8kW? I don’t yet know enough…

Do I need to know the detail now? Making these changes should mean that my overall grid consumption is lower so my monthly bills will be lower compared to my previous electricity and gas bills.

Something else I have realised is that the idea of running loads completely from solar means that I will be better off staying on a single rate plan instead of switching to a time of use plan. It doesn’t matter if the rate during the day is 22c/kWh or 19c/kWh if solar means neither is paid, but in the evening when there is no solar I would prefer to only pay 22c/kWh instead of 29c/kWh…