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Old 07-05-20, 03:48 PM   #1
Piwoslaw
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Default Piwoslaw's 2.7kW PV system

After years of thinking, reading, wanting, etc., we finally made the move!
Polish government created a financial incentive for PV systems, where homeowners can get up to 5000PLN (over 1100EUR) back after installing.

We found a contractor who would do all of the work, installation, and paperwork for us. After measuring our consumption (he was amazed that I have been recording the reading from our electrical meter every day for 12 years, and found it very helpful) and our roof, he decided on 8 panels, 340W each. 4 are facing southeast, 4 facing southwest.
Southwest string:


The inverter communicates with each panel and if 1 panel is shaded it does not lower the output of the others. It is sized so that we can still add another 2 panels (bumping the max output from 2.7 to 3.4kW) in the future, should our consumption grow (for example: mini-split).

I can track the output live through a webpage or phone app, and noticed on a cool but sunny spring day that the system was producing 2.8kW, a bit more than the rated 2.72kW. Now that the days are warm (above 25 deg C), the output maxes out at 2.3kW. On the other hand, the day is so long now, that the panels start producing power as early as 5am, until 8pm.
Based on results from the last 2 weeks, on a good day the system cranks out up to 18kWh, while our house has a daily consumption between 4-6kWh

So what happens when I produce more electricity than I use in a day? According to the tariff (based on the gov't plan), our new 2-way meter separately measures ingoing and outgoing current, so it only sees the difference between production and consumption. For each 1000Wh I produce above what I consume, I can take back 800Wh from the grid within 1 year. If (in a year) I consume more than I produce, I pay for the difference at the normal rate. If vice versa, I lose any excess I didn't use within a year.

To sum up:
- It is most efficient to use power at the moment it is produced, so we have to learn to use the timer on some appliances (washing machine) to turn on in the middle of the day, not in the morning or evening like until now.
- If I cannot use all of that power when it is produced, I can use the grid as a battery with 80% efficiency, and 1 year expiry.

So now I hope to produce as much as possible in the summer, to cover what we use in the short winter days. We'll see how this averages out over the next 12 months.

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