Getting the voltage off the panels isn’t actually that easy. But I believe you wrote that there would be voltage in the cables at the inverter end regardless of the safety switch position; there shouldn’t be any voltage there if the safety switch is in the 0 position.
In a traditional string inverter, panels are typically in a string of about 5–25 panels, which the inverter’s tracker aims to adjust so that the combination of current and voltage provides the best possible yield. Each panel model has its own characteristic curve for different levels of solar irradiance to achieve optimal power.
If panels of different types or those receiving different amounts of solar radiation are in the same string, the regulation will not function optimally. For panels oriented in the same direction, when a shadow falls on one, it causes the yield of that entire panel string to collapse. Because of this, all panels in the same string should be installed so that the amount of radiation they receive is as identical as possible.
If panels are installed, for example, on both slopes of a gable roof, each side must always be connected to a different tracker. Typically, these residential-scale inverters have 1 or 2 trackers, while some large ones can have more than 10.
The curved installation you described would be feasible if panel-level optimization is used, either with microinverters or by using optimizers.
A panel’s performance regarding radiation coming from “the side” can be thought of like this: from the sun’s perspective, the Earth is two-dimensional, so if a panel pointed directly at the sun receives 1000 W/m², one tilted 45 degrees in the wrong direction would receive 500 W/m². In addition to this, panels also receive diffuse radiation, reflections, etc.
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I re-read my message carefully and it seems I was just writing nonsense. Of course, the separate DC safety switch cuts the voltage between the switch and the inverter.
Nowadays, they are rarely even installed anymore.
That’s exactly how it is in practice. It doesn’t even take a large shadow for the output of the entire array to collapse. The solution is micro-inverters, which allow each panel to function independently of the others.
I have a traditional inverter where panels in two directions are on their own inputs. Additionally, I have two 2-channel micro-inverters for their own 2-panel arrays. From the early spring data, you can clearly see the effects of those shadows – the large arrays clearly tank from even a small shadow on a couple of panels. If one panel in a small array is shaded, the other one still pumps out its best to the inverter.
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Clear and well explained. Thank you.
This opened the path to understanding.
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Some panels have bypass diodes because of shading, so that it doesn’t cause the output of the entire array to collapse, but instead only partially or fully bypasses those panels that are in the shade. Still, I think shading is used as a scare tactic far too much; of course, they have to sell microinverters somehow.
If the array is small or poorly dimensioned, then it will indeed collapse the yield of the entire array.
Naturally, the temperature in the array rises when there is shading, and it is obviously not an optimal situation if part of the array is shaded.
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Yes, and nowadays practically all new panels use half-cut technology. If such panels are installed, for example, on a pitched roof parallel to the roof with the short side facing the eaves/ridge, and in the spring as the snow melts the panels are halfway revealed, the system can already operate at half power. Without half-cut technology, the power drop would be much greater.
A very large part of the annual yield comes from diffused radiation during hours when it is bright outside but there is no direct sunlight. The kWh accumulation from those hours when the plant produces at over 90% capacity is usually a few percent at most.
However, it’s worth using common sense in panel placement; you shouldn’t install a panel directly in the shadow of a chimney, whether there are optimizers or not.
Current low panel prices would likely be poison for the sale of optimizers. Since for the price of optimizers, you can alternatively buy a few more panels and get a better annual yield.
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Today, dividends are raining from the sky again at an average tax-free price of about 17 cents. Almost everything produced is being sold, so probably around 30–35 kWh will go to sales and just a few kWh for consumption. At night, I use purchased electricity as needed. Consumption over the last five days has been 17 kWh, or about 3.4 kWh/day, while the panels seem to have generated 143 kWh. I suppose one has to hope they get those nuclear power plants producing, or soon electricity will be expensive at night too; tonight might have pricey electricity as it looks like the price between 23:00 and 24:00 is over 28 cents/kWh—well, we’ll see that in the afternoon. I can’t help but give a little jab whenever the profitability of solar panels is discussed; at least for me, the last three years have proven to be quite a worthwhile investment.
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And to add to this, these annual maintenance shutdowns for nuclear power plants will continue in the future, which will keep spot prices higher than normal during certain spring months. It remains to be seen when grid companies will come up with a monthly fee or other such costs for small-scale production.
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Here, from May 1st to 6th, the panels have produced 244 kWh, of which 79 kWh was for own use and 165 kWh for sale.
May has been excellent so far, whereas April was weaker than last year.
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What kind of hole in the ground are you living in if your daily consumption is 3.4 kWh/day?!
It’s been well over 20 kWh/day now that the heat pump has had to start heating again.
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during the same period, for my 80s house, weekly consumption was 366.58 kWh = €2.76. No panels in use.
The whole of May was 1,185.78 kWh and €54.94. If this could be replaced with own production, the savings would be minimal.
So, transferring those 1,186 kWh costs about €85, meaning if you produce it yourself, you have to count the TRANSFER FEE as part of the return, because you won’t have to pay it…
Solar panels pay for themselves in just under 10 years, and this spring, the panels have blocked expensive kilowatt-hours from spot-price electricity whenever it happened to be sunny at those moments…
Calculating the returns on panels is easy, and you shouldn’t forget the savings on transfer fees—something that many people, incomprehensibly, do…
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If anyone has it, I would be super interested in hearing about the actual yield of solar panels over, say, a couple of years. Yield in kWh / installed capacity. Preferably from Southern Finland, “south of Jyväskylä”. And of course, the more granular the production data series is, the more accurately the benefit can be evaluated.
In the past, I couldn’t make the investment profitable as a spot-price electricity customer, but perhaps the panels have improved and/or prices have come down.
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Behind that link is the first year for my own system.
Maybe a yield of around 5%-6% is achievable.
Perhaps the systems have become cheaper in 1.5 years?
There is also the threat of energy companies investing in solar power, meaning electricity customers are now charged a 50%+ higher average price than before, and then they invest in panels (and other nice things).
One can, of course, also think of it as investing the sum in question and achieving the return that way.
But as a detached house resident in the Helsinki metropolitan area, it is very important for the property value to show the house’s energy consumption as low as possible. A home buyer can be scared by a large figure, and you can’t get them to pay a better price for the house by saying: buy stocks, generate a return, and pay your electricity bills with that…
I wouldn’t necessarily buy them for a house in a municipality with a declining population.
As a top priority, I would buy (and did buy) 2 x air source heat pumps for winter heating, with the summer cooling option as a bonus. Also, being at the mercy of spot price electricity, Shelly relays for easy control of the hot water heater, and for underfloor heating too, of course.
Excel shows the variation in solar power production. April 2023 was sunny, and the 2024 spring cold snap and a second cold snap cut April’s production in half (1000 vs 500 kWh). In May, just under 15% more has come in than in 2023. Then,
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Thanks for the time series.
When I apply that to my own consumption, I get annual savings of €700, taking into account the selling price (spot), transmission costs, and taxes. In reality, the savings might not be this high because consumption is weighted towards the evenings and nights, and I can’t, for example, drive my car home in the middle of the day to charge it for this purpose. Additionally, there would likely be many situations where I would be producing electricity for sale while the price is negative.
So, let’s assume that by making changes to heating and hot water timers after installing the panels, I would still get an annual benefit of about €600.
I’m still perhaps not excited about a €9,630 investment to get a €600 annual benefit. But it wouldn’t be such a bad “hobby”! It’s under consideration, since the place is in a growing city, after all.
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System prices have definitely come down. Currently, a 10 kWp system can be purchased for around 7,000 euros. Even in the stock market, it’s difficult to get a consistent net return of 8 percent. On the other hand, I don’t believe the share of self-consumption would be so high that the benefit would be quite that large. It’s hard to utilize 50 kWh of production for self-consumption on a summer day, except for a very small portion, unless you have a swimming pool or an electric car with a large battery sitting in the yard.
Is the tax credit for household expenses included in those investment figures? How do you calculate these in general—is the value of saved electricity, for example, “different” than, say, the dividends used for comparison? Money saved in a household is net income, whereas dividends and realized capital gains are gross. I’m considering panels myself, but I haven’t gotten around to looking into it more closely yet.
If the panels face south and there isn’t much shading, a 3kW system will consistently produce 2500kWh per year, so multiply by 0.85 to get an indicative figure (×1000).
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There was the household deduction
It’s true that a proper investment calculator should be used. Payback calculations get complicated if you factor in the cost of capital, taxation, electricity market price risks, etc. That’s why I called this a “hobby”—meaning in a positive sense, like any kind of tinkering or DIY.