Building sustainability with solar panels at home

As part of the house-building project, we had the option to think about solar panels. I have friends who have opted for a few panels, and some have opted for more. I’ve been indifferent up until now, as previously, we lived in a high-rise and did not have the means to install or benefit from panels.

A bit of background first

Our house, which we started planning in late 2019, is now about finished (in September 2022). In total, it’s about 300 square meters (~3300 sqft) of heated space on three floors, of which one is a full-height basement. As we’re located in Helsinki, the summers – in recent years – have been sunny and warm, while winters have been less cold than we’re used to. Of course, we still get below zero temperatures from ~November to early ~April. Less snow, also.

The traditional and historically used heating option has been direct heating via electricity, district heating, and burning wood. Electricity pricing has also traditionally been semi-affordable – often bouncing between 5 c/kWh to 10 c/kWh ranges.

Our house is what you would call a ‘stone house,’ and the two core components are lightweight concrete and light gravel ingots.

You can see in the picture above, taken before the exterior was completed, the lightweight concrete blocks (in white) and the plastered light gravel ingots on the ground level. The walls are thick and well insulated. Wood is mostly used for support structures only.

We’re required by local law to perform a third-party analysis of the energy efficiency of the completed house. For us, it yielded grade A, the highest you can get. This tells us the structure’s energy efficiency, but not for the people living in it.

With these starting points, I got to work.

Solar panels

I’m not an energy expert or an electrician. I spend all my free time building platforms, systems, and architectures for my customers using cloud computing and other platforms. As such, I didn’t do a deep dive into all possible options when it comes to solar panels.

Our house faces south. This was by design. We wanted to get the morning sun through the living room and kitchen windows (that face south also), and in the evening, we’re getting the last glimpse of the sun through our upstairs bedroom and balcony. And throughout the day, we hope to get as much sunlight as possible.

The roof is the logical and obvious position for solar panel installation. The long side of our roof, facing south, is angled at 11 degrees. The optimal angle for Helsinki would be between 6 degrees (winter time) and 54 degrees (summer time). I didn’t want to build a mechanical solution for this, so we just settled on the current angle of 11 degrees for installation.

Eventually, I chose to go with 36 panels rated at 370 Wp, adding up to a total of 13,32 kWp. They are about 100 € each, plus taxes, shipping, and handling. See them here. As you need an inverter also, it’s a Sungrow SG12RT – rated for 12 kW. I can see it’s being sold online for about 1472 €.

Here is the inverter during initial installation:

It’s installed on the outer wall, on the far back end of the house. That portion of the house is mostly in shadow throughout the day. The cabling from the roof to the inverter was embedded within the plaster of the wall, and it turned out pretty clean. The alternative approach would have been to finish the house and add the inverter and necessary cable rundown. I wanted the final installation to look neat, though.

The rundown cable is of type 5X6, which translates to the physical cable having five sub cables, each six mm2. They have to be shielded when embedded in the plaster; ideally, you’d like to avoid UV light.

The inverter has support for Wi-Fi and Ethernet, which is nice. I didn’t bother running an Ethernet cable from the inverter to my network gear, as it was modern enough to pick up my Wi-Fi signal and hop to my internal wireless network without a glitch. More on this in a bit.

How do the solar panels look, then?

Well, for one, they take up all space on the roof. The lower portion was left empty, as you need space to step on, and there are snow barriers to block snow and ice from falling on people.

That one odd panel on the lower right corner was added because I ordered 36 panels, and my chimney had to be adjusted to a slightly different position at the last minute. My internal OCD is screaming, but at the same time, I like it. Also, I will never see these – the height of the house prevents me from ever seeing the roof unless I use a drone.

What about the other side of the roof? Admittedly, I could add perhaps 16 panels on that side to catch more of the evening sun. I figured it wasn’t worth the trouble or the cost. At least for now.

Getting online

Once all the cabling work is done, it’s time to get this thing online. There are two components here: connecting to the inverter to configure it and getting small-scale production sold back to the grid accounted for.

First the inverter. You can connect directly to the inverter by pressing a button to enable the ad-hoc Wi-Fi network. It’s useful for checking something quickly. Once that’s done, you can then configure – through that ad-hoc network – the bridge to your real Wi-Fi network. Assuming it has coverage for the inverter.

There is a mobile app you can use called iSolarCloud (iOS, Android). It works pretty well. You can use the web interface once you are back on your computer. I use both. Through this app, you provision your virtual solar plant. There are a lot of settings you can tweak and fiddle, but the defaults more or less suffice.

A few crucial settings you do have to get right, such as the electricity settings. The electrician conducting the base deployment for me politely said to “opt for 50 Hz, unless you have a thick wallet” – presumably implying that if I mess this up, I end up paying for the damages throughout the neighborhood.

The app, once everything is working, has a basic view which is super handy:

I’m writing this article at 2 pm in the afternoon, so real-time power is tolerable. It’s a cold and cloudy day. Once you click in, you get the full view.

I don’t have a battery to store any of my energy. I either use it as I get it or sell it back (“feed-in”) to the grid. I do both – I sell any excess energy from the solar panels back to the grid.

The revenue value you see in the picture above is imaginary. I just set the kWh feed-in sell price to 10 c/kWh to make it look nice. The inverter cannot know which bits of energy you’re using directly, which bits of energy you’re selling – and at what price of a given day or hour. It’s spot market prices, so they update hourly, I think. To check spot market prices here in the Nordics, I use Nord Pool.

Once all of this works, it’s smooth sailing. You don’t have to do anything. It’s neat to open the mobile app at random times of the day to say, “look! so much free energy flowing!” but it doesn’t matter.

On a typical (sunny) day in August, I am getting a solid yield of 40 to 55 kWh. My house, which is still new, consumes about 2 kWh/hour. Why? Well, I have a lot of servers, PCs, gadgets, and stuff. For August, I’m looking at an overall consumption of 1200 kWh through the reporting my energy provider shares with me. With solar, I’m getting roughly 800 kWh to 900 kWh of energy from the sun. Optimally, I would then just purchase about 300 kWh of electricity.

In practice, it doesn’t work like this. I’m using energy when I need to – like fixing dinner in the oven for the family at 2 pm when it would make more sense to sell those kilowatts back to the grid.

How is the connectivity, then? I’m thankful for running network gear that is able to let me peek inside the data generated from the inverter!

The inverter doesn’t generate much traffic. Here is the default view as seen from the Unifi dashboard:

Drilling down further, from the past three weeks, the total amount of egress data to iSolarCloud is just 22.6 MB:

MQTT is a lightweight messaging protocol often used for IoT deployments. In essence, it seems my inverter is simply sending data points, every now on then, to a public cloud endpoint.

The challenges

The setup was an unexciting event. The installation company was very professional, but they were also very busy with all the customer requests flooding in. Instead of having all this installed in one go, I had to split the installation into two phases: physical installation of the panels and installation of the inverter. This was because I wanted to hide all the surface cables beneath the plaster.

I had the solar panels installed in March 2022. I got to the plaster phase of the house in July, and then I got the inverter installed in late July. And all systems connected once we got permission from the energy provider in early August. I ‘lost’ a good portion of free energy from June and July, and that’s a bummer. But I’ll rather have a beautiful, even plaster on the house than get a few more euros and a crappy exterior of the house.

In Finland, you can buy your energy from a chosen energy provider. But you also have to buy the transfer of the energy from your local (often monopolized) energy provider. And somewhere in, there was a configuration mismatch between the small energy provider I use and the huge corporation that transfers the energy to me. For a few weeks, I did calls to both companies every few days. The large corporation never has the capacity to pick up the call, so they have a call-back service. Which randomly calls you back at the worst time of the week, usually. During one of these lengthy calls, someone blurted out an issue with EDI messages, which took me back a few decades mentally.

So we danced back and forth on the issue for about two weeks. I could see from the national energy grid reporting that my location was consuming energy, and at times I was not consuming any energy from the grid. Yet, I wasn’t pushing energy back to the grid. Odd, indeed. Finally, either one of the companies – nobody ever admitted anything – changed something, and the reporting – and feed-in to the grid started working just a few days ago.

Here’s a non-helpful bar chart from the national reporting system of my feed-in energy. It’s not helpful, but at least I see that from noon to early afternoon, I’m selling energy back to the grid like it’s going out of fashion.

Once these small hiccups were settled, it’s been smooth sailing. The mobile app is stable and fast, and it just works. I’m surprised how flexible and good it is. The reporting capabilities are very adjustable and perhaps have even too many options to drill down on the raw data. It’s like Excel in a browser without Clippy.

I’ve yet to tinker with the API of the inverter. It would be a fun side project to pull real-time data from the inverter and compare that with the spot market prices to determine which systems to shut down in the house if we’re looking at peak prices. But that’s perhaps a plan for another time.

My feed-in (sold) data to the grid from the past six days looks like this:

I’ve generated (and sold) 89 kWh back to the grid between Monday midnight and Sunday 11:59 pm.

In closing

The first question people ask me, after learning that I have solar panels, is what is the return on this investment? I have no idea. I realize at the same time that for many, the actual ROI is key here. For me, it’s something else: resell value of the house + ease of use + sustainability + cheaper energy. Not just ROI.

The total investment – including the inverter, the panels, all installation, all electrical work, and testing, was 12 590 €. This includes local taxes (VAT 24 %). I think I can deduct some from the yearly taxation for certain services I’ve purchased, but I haven’t looked into that yet.

As energy prices are going through the roof now, I’m not even sure how to calculate the ROI on this. The goal is to become more sustainable while also saving money.

The iSolarCloud has a simple calculator for this:

The numbers look nice after just three weeks. Perhaps relatively small in comparison, but better than nil, anyway. I’m eager to see how the solar panels perform through the cold but sunny winter days. I’ll see if I’ll revisit this topic a year from now with updated statistics.