Balcony Solar Panels — the Complete Guide and Results

This solar system is my second attempt at using solar power in the city apartment. I did the first experiments three years ago, but later everything was disassembled because of my relocation. Finally, at my new place, I decided to start from scratch using the experience I’ve got before.

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Why solar panels?

I am sure that the question “why” will be the very first in the comments so that I will answer it right now. From the profit perspective, the solar battery on the balcony is mostly unprofitable, alas, the scale of generation is too small It depends on the geographical location, the profit in Spain will be more than in Finland, but anyway, it’s better to place solar panels, if possible, not on the balcony but on the house roof. But from a technical and engineering perspective, even a balcony system is quite interesting in terms of studying new and modern technologies. Plus, we should keep in mind that apartments consume more and more energy nowadays. We have a lot of always-connected devices: routers, smart bulbs, smart plugs, smart cat feeders, smart doorbells and other things. Compensating this consumption with solar energy, in principle, is not bad and environmentally friendly. Well, last but not least, looking at the electricity meter and seeing on the screen “current consumption -50W” is merely nice.

General Information

As we know, there are two main principles of using solar power.

  1. Feed the energy back to the power grid.
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1. Solar Panels

The first important issue is the choice of solar panels. I’ve read the opinion that solar panels have different efficiency, and only the most effective ones should be taken. It is difficult to argue with this. However, the difference is really not so big. According to the Most Efficient Solar Panels 2020 article, the top 10 most efficient panels look like this:

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2. Grid-tie Inverter

The choice of inverters for such small power is not so great. I chose this one:

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Collecting the data

In principle, our system is ready — it’s enough just to connect the solar panels to the inverter, plug it into a standard outlet, and everything will work. However, it is interesting to see, at minimum, how much power is given from the solar panels, and as a maximum, to have more advanced logging of the collected energy.

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from kasa import Discover, SmartPlug, SmartDevice
import datetime, logging, time, asyncio
log_format = "solarlog-%Y-%m.csv"def get_power_from_meter() -> float:
try:
logging.debug("Connecting the smart plug...")
devices = asyncio.run(Discover.discover())
for addr, dev in devices.items():
if dev.is_plug:
asyncio.run(dev.update())
if dev.has_emeter:
logging.debug("Smart Plug found: %s", addr)
emeter_status = asyncio.run(dev.get_emeter_realtime())
power = emeter_status['power']
return float(power)
logging.debug("Smart Plug was not found")
except Exception as e:
logging.error("get_power_from_meter exception: %s", e)
return -1.0
def write_log(power: float):
log_name = datetime.datetime.now().strftime(log_format)
with open(log_name, "a") as logfile:
logfile.write(f'{datetime.datetime.now().isoformat()},{power}\n')
if __name__ == "__main__":
logging.basicConfig(level=logging.DEBUG, format='[%(asctime)-15s] %(message)s')
logging.debug("App started") # Read meter and save to the log
try:
while True:
power = get_power_from_meter()
logging.debug("Power reading: %f W", power)
write_log(power)
time.sleep(60.0)
except KeyboardInterrupt:
pass
logging.debug("App done")
2020-06-25T11:36:27.021849,0.0
2020-06-25T11:37:32.646114,0.593
2020-06-25T11:38:38.207308,0.731
2020-06-25T11:39:43.695290,0.738
2020-06-25T11:40:49.320069,0.785
2020-06-25T11:41:54.805750,0.344
2020-06-25T11:43:00.367353,7.137

Results

First, I live in the Netherlands, not the sunniest country in the world, in other places, results may vary.

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Export to the grid

Finally, I’ll describe the issue of exporting energy to the grid. Everything is simple from a technical point of view but is complicated from the legal point of view. Technically, we are simply adding a new energy source to our household. This energy will be first consumed by the devices inside, and the excess through the electricity meter (and this is important) will be transferred to the city grid. The meter is important here because it will depend on it how the exported energy is calculated.

  • An old disk meter without a reverse blocker will turn the disk in the opposite direction, i.e. meter readings will decrease, which, of course, is beneficial to the owner of the solar panels. But such meters are not in stock now and have become a museum rarity.
  • A digital meter that “does not know” how to calculate the energy export, will consider it “modulo” regardless of direction, i.e. for every kilowatt-hour sent to the city, the owner of the solar panels will pay as for consumed.
  • A modern digital meter that can count both energy export and import will show individual values ​​for all parameters. In total, there are four readings on such a meter: daytime import, nighttime import, daytime export, nighttime export. Solar panels generation at night is obviously zero, but two tariffs are usually provided by a local electricity supplier.
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Conclusion

Getting solar energy is a rather exciting hobby project in terms of learning something new. After all, as we know, the best way to study a new technology is to try it. We can read many other people’s articles, but it’s much better to do stuff yourself. It’s getting much more knowledge of how the system works, how parameters vary, like the influence of the panels tilt, rain or fog, learning how to make wind protection, how to collect statistics, and so on. It is much more exciting and finally gives more experience and understanding of different nuances.

Python and IoT Developer, science and ham radio enthusiast

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