Attention, electrical experts… How much significance/difference does it make if the solar panels are 5 meters or 25 meters away from the inverter? My neighbor is pondering the inverter’s placement a bit. So, how much resistance is there per meter in the DC cable, or does it have any practical significance at all?
It depends on the wire thickness and the current flowing through the system. Here you can find a guide table for cable thickness with different wire lengths and current: https://www.lumise.fi/storage/product_files/0/Latausyksikk_-5A.pdf?name=0/Latausyksikk_-5A.pdf&srsltid=AfmBOoqkklTQE554kYaHe5OChglRQPNa_pw2Yv_l2LLUy0D1YXsDFqTV
1 Like
We had the panels installed in 2021 approx. 70m away from the inverter. Both the panel seller and installer told us then that the limit was approx. 100m, but of course, the closer the better.
I don’t remember the wire thicknesses, but they don’t differ much from 1.5mm wires. If I recall correctly, they stated that nowadays, since amperage can be increased, the distance can be increased. The system is not large, however, but just over 1kW.
1 Like
Or actually, since the voltage (i.e., volts) has increased in new panels, the same power can be transferred with less loss in the cable, because the amperes are correspondingly smaller. Power = volts * amperes, i.e., voltage * current
5 Likes
The order of magnitude sounds quite reasonable. Even in small power plants for shopping centers, logistics buildings, etc., there are always at least tens of meters of long DC cables.
Usually, a greater reason than power losses for placing inverters as close as possible to the inverter is related to fire/electrical safety and costs (the per-meter price is higher for a bundle of DC cables than for an AC cable).
1 Like
It has been good days for panel owners, if the sun has been visible.
You can read research results on panel tilt and orientation from there.
when the aim is to maximize the entire year’s yield, solar panels should be installed on the roof facing southeast or south. The second best is the east direction due to the sun’s path, and the third best is the southwest direction
panels should be set at a low 28° angle instead of the traditional 43–48° angle
6 Likes
I’m a bit critical of this in the sense that, on an annual basis, more kilowatts probably come from the sky at a low angle, but as a spot market electricity user, the greatest financial benefit can be achieved with an angle of around 80-88 degrees, as electricity is generated when it’s most needed and the compensation price for surplus is high. In summer, that electricity isn’t consumed as much, and the spot market price is cheap anyway. In summer, the inverter also limits production from the panels, as does heat. With a vertical installation, that electricity can be obtained as early as possible in spring and as late as possible in autumn, not to mention that the panels remain snow-free. This, of course, seems to have focused on maximum production volume.
14 Likes
Yes, that’s how it is, it wasn’t studied here, and there are certainly different studies for optimizing spot market electricity.
“The measurement results provide independent information for optimizing the utilization of solar energy in northern regions. The results can also be used, for example, in urban planning and construction design.”
The study seemed to focus more on how to zone, etc., to optimize the potential of future buildings regarding solar panels. Additionally, unique to this was the “carousel” with panels pointing in every cardinal direction, which provides data at Oulu’s latitude.
In my opinion, this is very welcome and important research in the north. Keep up the good work!
The data is available, however, so everyone can study what they wish. It has 90-degree and 40-degree angles.
But throughout the year, roof panels tilted at a 28° angle facing south produced 20 percent more energy than wall panels at a 90° angle. The long summer days also produced peaks in energy production. In May-July, the panels produced almost two-thirds of their entire year’s production.
If one charges electric cars and charging can be done during sunshine, then that should naturally be considered here.
Someone could download the entire dataset and calculate the differences for 40-degree and 90-degree panels, taking into account only the “winter months,” e.g., November-March! Anyone?
5 Likes
I got this far and concluded that further analysis is unnecessary. Summer production is 10-100 times higher compared to winter, so even if in the best winter month the difference in favor of 90-degree panels is 500-fold, it has no significance in the big picture, even if electricity were 10 times more expensive in winter than in summer. The absolute yield is just so small, no matter what you do in November-February. As a side note, based on that data, 90-degree panels produce more when oriented southeast than directly south, whereas the yield of 40-degree panels was best when oriented directly south. The graph compares the best orientations for both angles.
12 Likes
It’s also good to remember the realities here, as it’s very rare to be able to install panels in any direction without issues from shading.
The more vertically the panels are installed, the more shading becomes a problem. In many neighborhoods, it’s probably impossible to find a single detached house where a wall-mounted panel wouldn’t suffer from shadows. For ground installations at 40 degrees, the situation is almost as difficult.
In practice, for detached houses, it’s most sensible to install them parallel to the roof on pitched roofs and on flat roofs, on racks angled at 10-20 degrees.
If there’s a good installation location, in Southern Finland, a 90-degree angle can yield better financial returns than, for example, a 20-degree angle. This depends on the power plant’s sizing, electricity consumption profile, shading, spot price, etc.
2 Likes
A new update has been released for the PVGIS simulation and sizing system, developed as an EU project, which corrects some previous inaccuracies. This is a good tool for anyone planning to acquire a solar power plant. PVGIS allows for simulating yield with different panel quantities and installation methods:
How do the rest of you implement the compound interest principle for your solar power plant’s yield?
Adding individual panels once a year is a bit cumbersome, so I personally choose each year a stock to be bought with the savings from the panels (+dividends from previous years’ stocks), which I also actually buy into my portfolio to hold, and I monitor the annual return from both the panels and the dividends from the stocks bought with their savings.
1 Like
The same observation in practice with a few years of experience. This year’s February production was exceptionally high because there was little snow and I brushed the panels experimentally after a few snowfalls.
My diligence was rewarded, as I managed to increase February’s production to a new record, and February 2025 production will exceed the combined production of February 2023 and 2024!
Doubling the typical 50 kWh to just over 100 kWh simply doesn’t make wonders in an annual production of 6500 - 7000 kWh, so based on this observation, I won’t start adjusting the panel angles. If one wanted to do something, it would be better to buy more panels or an electric car, into which one could put one’s own surplus production during the summer.
4 Likes
There are so many variables in the profitability of solar panels that a simple formula taking everything into account is unlikely to be found easily. The benefit is affected by the installation angle, panel type and inverter, installation cost, installation location, transmission and energy price, electricity contract type (i.e., fixed or do panels enable a spot market contract), use during low prices, meaning can you charge heat into a boiler or an electric car. I don’t have an electric car yet, but it’s under consideration. Currently, 59 cents per kilometer is paid for work-related travel, meaning fuel would be almost free, and that benefit would be almost entirely realized. However, the purchase price of a used electric car is still higher than a fuel-efficient petrol car, so the benefit is likely on a psychological level. For some, panels are a truly economically sensible purchase, for others not; everyone should calculate their own situation. From my own panels, I always sell when the compensation price is sufficient, I push it to the hot water tank when the price is low, perhaps in the future to an electric car battery, but I will still stick with spot market electricity.
3 Likes
You are right, the calculation is not entirely trivial, but all the details you mentioned can indeed be clarified. Many different averages appear in public, and what they have in common is that they are rough generalizations whose validity at one’s own home address is not guaranteed. The reason for significant regional differences is not geometry but weather.
PVGIS, built as an EU project, is a good sizing tool that can simulate the possible installation of a solar power plant on one’s own roof. It can also model the sizing, how many panels and in which direction should be installed. The advantage of PVGIS is that it is not just a calculator of geometric angles but it takes into account the weather observations of each locality over the years.
My own solar power plant has now matched the forecast of the previous PVGIS version with reasonable accuracy for three years, although on the coast, it has slightly exceeded the expected value each year.
I didn’t understand your comment about the possibility of using spot market electricity? Could you elaborate on that?
Today seems to be the best “dividend day” of the year so far regarding solar panels. Yesterday, the panels produced over 30 kWh, and the sky looks almost cloudless right now. For me, these electricity market prices at this time of year are just right, so the compensation price for panel production is also good. It’s a bit like a rollercoaster with both the electricity market and the regular stock market – plenty of speed and dangerous situations.
4 Likes
Yeah, the panels are generating now, unfortunately, we have some thin high clouds.
April was 25% better than last year, as the panels weren’t covered in snow.
Indeed, in March when spring begins, it’s worth clearing snow from the panels if they are not in a very difficult spot. A long-handled shovel from Puuilo and the panels can get to work.
2 Likes
And I just paid the electricity transmission and electricity tax bill for Q1, and it cost 7.54 cents/Kwh. The fee is staggering when the 365-day average spot electricity price is 4.91 cents/kWh.
For all the electricity one uses from the panels’ output, this outrageous fee is not charged. So try to concentrate electricity consumption to the time when the panels are producing!
2 Likes
I brush the panels on the roof of the garage wing, which is lower than the main building, a few times in winter starting from the end of February, when I can reach them from a ladder leaned against the eaves without climbing onto the roof. In the early part of the year, there won’t be any significant power even if the panels are clean.
“Shovel” sounds scary? You’re not scratching the surface with any hard object, are you?
I myself have used a telescopic car wash brush from an auto parts store. A soft brush is at least safe.
For us, the panels’ output is weakened by the affordable transmission price, including taxes, 5.7 c/kWh. This is just one manifestation of the negative correlation between solar power plant output and electricity price. Panels produce best when electricity is most expensive. If electricity is cheap, a resident of an all-electric house can tolerate it.
In addition to conscious use of household appliances, home automation should be programmed to utilize solar hours, if it hasn’t been done already. Shifting water heater and underfloor heating usage to own electricity hours or controlling continuously heated floors to at least avoid the most expensive morning and evening hours lowers the average price of purchased electricity and increases the share of own consumption if the panels have overcapacity.
An electric car has been on the shopping list for a long time, but right now I’m not interested in liquidating a car-sized amount from income-generating investments.
1 Like
Yesterday, I spoke with a salesperson from a company called 1KOMMA5°. They were selling a solar panel + battery + CheckWatt system with quite strong “promises”. We even talked about a 5-6 year payback period for a package costing approximately €14k, consisting of 8kW panels + 10kW inverter + 13kW battery.
CheckWatt is thus a “reserve market aggregator” through which an ordinary consumer, with their batteries, can join Fingrid’s reserve market system. Fingrid pays compensation for the reserve capacity provided by the battery, according to the salesperson’s pitch, even more than what one saves on the electricity bill with the panels themselves (although CheckWatt naturally takes its cut). Fingrid has reportedly estimated that the need for reserve capacity in Finland will grow by over 130 percent in the next five years.
To my ears, it sounds too good to be true. A quick search didn’t reveal any discussion on the topic here yet. Does anyone have experience with CheckWatt or the reserve market through some other means? On Facebook, I found a group with a few negative comments regarding actual earnings. Someone also complained that the system had charged the battery fully at a high price and sold it to the reserve market cheaply.
7 Likes