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How to size Solar Panels as a beginner
Hi all, I have built my inverter/battery system [3000va (2400W) MPII 48v with 10kwh battery bank (2x 52v)], and am now wanting to move into understanding solar side of things more.
So I have some quick newb solar panel questions.
To begin, how would I size the panels in the array?
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Would I try to match the total 2400w potential load of inverter with the equivalent Wattage from solar panels?
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or; Would I try to match my required battery charge wattage only? Which I current have set at 15a x 54v (810w charge)
Then based on the above, is the calculated size of the array’s wattage based on the advertised wattage (lets say a 600w panel) or efficiency rating of the panel (21.3% of 600w panel = 127.8w in reality)?
Thanks
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When sizing solar panels for your inverter battery system, you’ll want to consider a few factors to make an informed decision.
Here’s a breakdown addressing your questions:
Matching Inverter Load vs. Battery Charge Wattage:
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Inverter Load Matching: Matching the total 2400W potential load of your inverter with equivalent wattage from solar panels is a common approach. This ensures that during peak sunshine hours, your panels can potentially provide enough power to run your loads directly while also charging your batteries.
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Battery Charge Wattage Matching: Alternatively, matching your required battery charge wattage (810W in your case) ensures that the panels are optimized to keep your batteries charged efficiently. This is often considered if the primary function is for battery maintenance rather than running heavy loads directly from solar.
Calculating Array Size – Advertised Wattage vs. Efficiency:
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Advertised Wattage: When planning an array, the size is generally based on the advertised wattage. For instance, if you need 2400W and have 600W panels, you’d consider four panels to meet your needs under optimal conditions.
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Efficiency Rating: The efficiency rating of a panel (e.g., 21.3% for a 600W panel) is already factored into the advertised wattage. The efficiency tells you how well the panel converts sunlight into electricity under ideal conditions. So, a 600W panel with 21.3% efficiency is designed to produce 600W under standard test conditions, not 127.8W. The efficiency helps compare the quality and performance of different panels but isn’t used to calculate the total output.
Additional Considerations:
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Sunlight Hours: Understand your local peak sunlight hours. More sunlight hours mean you might need fewer panels.
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Panel Orientation and Tilt: Maximizing exposure to the sun will help achieve the advertised wattage.
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Future Needs: Consider if your energy needs might increase.
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Regulations and Incentives: Check local regulations and incentives for solar installation.
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Professional Assessment: For the most accurate sizing and to ensure safety, consider a professional assessment.
Ultimately, the choice between matching your inverter’s full capacity or just the battery charging needs depends on your daily energy consumption, budget, and future expansion plans.
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If you’re looking to be completely off-grid or have enough power throughout the day, you might lean towards matching the inverter load.
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If you’re more concerned with maintaining battery health and have limited space or budget, then matching the battery charge wattage could be sufficient.
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The efficiency rating of a solar panel is a measure of how effectively it converts sunlight into electricity.
Here’s how it works and relates to the advertised wattage:
Understanding Efficiency Rating:
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Definition: The efficiency of a solar panel is the percentage of solar energy hitting the panel’s surface that gets converted into usable electricity. For example, if a panel has an efficiency rating of 20%, it means that 20% of the solar energy striking the panel is converted into electrical energy.
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How It’s Measured: Efficiency is determined under Standard Test Conditions (STC) which are 25°C (77°F) and an irradiance of 1000 W/m². This provides a standardized baseline for comparing different panels.
Relation to Advertised Wattage:
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Advertised Wattage Includes Efficiency: The advertised wattage of a solar panel (e.g., 600W) already takes the panel’s efficiency into account. This means a 600W panel is expected to produce 600 watts of power under standard test conditions (STC), which includes its efficiency rating.
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Why Efficiency Matters: While the efficiency doesn’t change the advertised wattage, it does affect the size of the panel. Higher efficiency means more power output per square meter of the panel. So, two panels might both have an advertised output of 300W, but the one with higher efficiency will be smaller. This is particularly important if you have limited space.
Practical Implications:
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Space Considerations: If you have limited space for panels, higher efficiency panels can produce more power in the same amount of space compared to lower efficiency ones.
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Cost vs. Benefit: Higher efficiency panels tend to be more expensive. It’s essential to weigh the cost against the benefits of space savings and potential power generation, especially if you have ample space for installation.
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Real-World Conditions: Remember that the actual efficiency can vary based on conditions like temperature, angle of the sun, and shading. Panels usually produce less than their rated power in real-world conditions.
In summary, when you’re looking at the advertised wattage of a panel, that number is what you can expect the panel to produce under ideal conditions considering its efficiency.
The efficiency rating helps you understand how much space the panels might need and how they might perform compared to others.
However, for planning your solar array, you’ll use the advertised wattage to calculate the total power output you can expect.
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The physical size of the panel generally dictates its advertised wattage.
Given the same advertised efficiency rating (most are around 20-21% efficiency rating), a 600W panel will typically be 50% physically bigger than a 400W panel. As the 600W has more surface area, it allows for more solar cells, which can generate more power, but this doesn’t make it more efficient. Efficiency is a measure of how much of the sunlight hitting the panel is converted into electrical energy
For example, let’s consider two real world solar panels to illustrate the calculations:
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JA Solar 405W panel
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Canadian Solar 600W panel
Both panels have similar efficiency ratings, but different physical sizes and wattage.
JA Solar 405W Panel:
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The panel’s has a 1,134mm (width) * 1,722mm (height) = 1.95m2 area.
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The advertised efficiency is 21.2%.
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The advertised wattage is 405W.
Canadian Solar 600W Panel:
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The panel’s has a 1,303mm(width) * 2,171mm (height) = 2.83m2 area.
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The advertised efficiency is 21%.
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The advertised wattage is 600W.
Efficiency rating
The efficiency rating is based on how much power you get for each square meter of panel at 1000W/m² irradiance (at standard test condition of 23°C)
We can calculate Watts per Square Meter (W/m²) using the formula (Watts ÷ m²):
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JA Solar 405W Panel: 405/1.95 = 207 W/m2
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Canadian Solar 600W Panel: 600/2.83 = 212 W/m2
In other words, if each of these two panels covered exactly 1m2, the JA Solar would produce 207W of power and Canadian Solar would produce 212W of power.
We can then use this (W/m²) to calculate the actual efficiency percentage (just to see that the advertised rating is accurate) by using the formula: Efficiency = ((W/m2 / 1000)*100%):
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JA Solar 405W Panel: (207W/m2 / 1000) * 100% = 20.74%
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Canadian Solar 600W Panel: (212W/m2 / 1000) * 100% = 21.21%
Great, so the advertised efficiency ratings are pretty much accurate to their actual calculated ratings so these two manufacturers are truthful in their specs.
What this tells us, is that they produce almost the same amount of wattage, based on the same area covered. So whether you get the JA Solar 405W Panel or the Canadian Solar 600W Panel is irrelevant if they were to cover the exact same area.
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Yes, correct!
For example, let’s calculate how many of each panel type you can fit into a given roof area and what the total wattage output would be.
Solar Panel Measurements:
JA Solar 405W Panel:
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Width: 1,134mm or 1.134m
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Height: 1,722mm or 1.722m
Canadian Solar 600W Panel:
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Width: 1,303mm or 1.303m
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Height: 2,171mm or 2.171m
Roof Area for Calculation:
Now, let’s assume you have a roof area that is 10m (w) x 3m (h). As the height of smaller JA Solar is more than half of 3m, therefore you can only have one row of panels, regardless of which panel you choose. So let’s see how Many Panels Can fit side by side in this scenario:
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For the JA Solar 405W Panel: 10m / 1.134m ≈ 8.82 (8 panels total)
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For the Canadian Solar 600W Panel: 10m / 1.303m ≈ 7.67 (7 panels total)
Total Wattage Output:
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For the JA Solar 405W Panel: 8 panels * 405W = 3,240w.
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For the Canadian Solar 600W Panel: 7 panels * 600W = 4,200W.
In this case, choosing 7x Canadian Solar 600W Panels will yield a higher power output of 4,200w for the given surface area.
Now, let’s assume another roof area is 10m (w) x 3.5m (h). The roof height of 3.5m can now accommodate two rows of the JA Solar panels but only one of the Canadian Solar. Let’s see which is the more optimal choice in this scenario:
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For the JA Solar 405W Panel: 8 (width) * 2 (height) = 16 panels total.
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For the Canadian Solar 600W Panel: 7 (width) * 1 (height) = 7 panels total.
Total Wattage Output:
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For the JA Solar 405W Panel: 16 panels * 405W = 6,480W.
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For the Canadian Solar 600W Panel: 7 panels * 600W = 4,200W.
In this case, choosing 16x JA Solar 405W Panels will yield a higher power output of 6,480w for the given surface area.
Conclusion:
This example shows that the JA Solar 405W panels would better optimize the roof area for solar power generation, as more of these panels can fit into the same space compared to the larger 600W panels, resulting in a higher total wattage output.
The key here is the physical size of the panels and how they fit on the roof, not just the wattage of an individual panel.
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