system sizing and panel selection-help please
system sizing and panel selection-help please
I am limited to 25 panel of similar size.
the decision is between Lumina1 SS9-72HD 535 panel vs Philadelphia 144-550w panel.
the inverter of interest is the SRNE-HESP thanks to @42OhmsPA guidance.
the specs are below with my newbie calculation (adjusting for low temp of -3C for my location.)
Please comment on:
1/ 72 cells vs 144 cells panel type in general and which panels would you choose .
2/ temperature calculation
3/ string and system sizing
4/ anything helpful.
thank you
Panels comparison
STDLumina I
SS8-72HD -535w bifacialPhiladelphia M144
550W-bifacialMax Power Pmax535 w 550 wVoc49..25Vmp41..19Short-circuit Isc13..69Max power current Imp12..05module eff20.71%21.3% NMOTMax Power Pmax404wVoc46.30Vmp38.80Short-circuit Isc11.05Max power current Imp10.43Open vol temp coef Voc-0.265%/C-0.22Power temp coef PMP-0.334-0.35NOCT+/-2
SRNE inverter model HESPu
Number of MPPT2Max PV inputw/wMax. input current25Amp + 25AmpMax Voc550Vdc + 550 VdcMPPT vol range125-450Vdc/125-450Vdc
Coldest temp in my area is -3C.
Low temp adjusted calculations and string sizing
Lumina I
SS8-72HD -535w bifacialPhiladelphia M144
550W-bifaciallow temperature adjusted56.11 v per panel55.42 v each2 strings of 6 per MPPT
336.6 V – 27.56Amp amp over limit of 25332 V -27.4 Amp
amp over limit of 252 strings of 6 =12 modules in each MPPT12x535w = w12x550w = wtotal system: 24 modules in 4 strings W W I don't think you can go wrong with either panel choice.
Personally I would go with the Philadelphia solar since they are slightly more efficient being 144 cell.
6S2P per MPPT is the best option for 24 panels, you've already figured that out.
I wouldn't have any concerns being slightly over the "max" current input. In ideal conditions you will lose out on a little bit of power but it will be negligible in the grand scheme of things.
My MPPTs are W 22A limit.
Here's what happens you hit the max.
...nothing, the MPPT just stops taking power in.
Your math looks good to me, nice well laid out post too.
I'm sure some others will chime in soon enough. I haven't double-checked the math, but 6s2p could be 6s oriented SE or SSE and the other 6s oriented SW or SSW. Then likely no clipping at all.
It will reduce depth of cycle of battery, charges earlier in the day an keeps charged later.
Looks like from your figures, only standard test conditions might exceed 25A. NMOT does not.
is 25A max operating current, or max allowed short-circuit current? The data sheets I've found are for different model and don't clarify that.
On the other hand, if you have NEM 2.0 reservation with PG&E, then you may want to favor late afternoon production. But maybe not, since although price is 1.5x or 2x as high, production is reduced when not due South.
Panels are cheap. Batteries are more expensive, unless DIY. So I recommend over-paneling.
25 panels fit? So roof mount? I guess you will have 24 panels as 2x 6s2p.
I see the pallet of 31 is same price as 26 individual panels (It is recommended to buy a couple extra in case broken in shipping or installation.)
Not knowing how they differ, it would seem $ less is the way to go. About 3% less STC wattage rating, only 1.5% less CEC PTC rating.
If you do have 2 strings of different orientations, you may be able to parallel another 6 if you can fit them somewhere. Like vertical on a fence?
I haven't double-checked the math, but 6s2p could be 6s oriented SE or SSE and the other 6s oriented SW or SSW. Then likely no clipping at all.@Hedges
It will reduce depth of cycle of battery, charges earlier in the day an keeps charged later.
Looks like from your figures, only standard test conditions might exceed 25A. NMOT does not.
is 25A max operating current, or max allowed short-circuit current? The data sheets I've found are for different model and don't clarify that.
On the other hand, if you have NEM 2.0 reservation with PG&E, then you may want to favor late afternoon production. But maybe not, since although price is 1.5x or 2x as high, production is reduced when not due South.
Panels are cheap. Batteries are more expensive, unless DIY. So I recommend over-paneling.
25 panels fit? So roof mount? I guess you will have 24 panels as 2x 6s2p.
I see the pallet of 31 is same price as 26 individual panels (It is recommended to buy a couple extra in case broken in shipping or installation.)
Not knowing how they differ, it would seem $ less is the way to go. About 3% less STC wattage rating, only 1.5% less CEC PTC rating.
If you do have 2 strings of different orientations, you may be able to parallel another 6 if you can fit them somewhere. Like vertical on a fence?
thank you for pointing out the the lumina is 144 cells.
Thankyou both Hedges and 42OhmsPA for commenting. I agree that 144 cell (or half cut in general) is a good safe choice. I think it's more likely to hedge against a newbie design error, than it is to confuse an MPPT. Depending on when your main power usage is, it may not really matter (IE if you mostly want to chop summer loads back, you're probably massively overproducing anyway so the half cut giving you an extra 30 min of low angle production, and 0.5% efficiency boost, isn't that much $)
I would recommend holding off on buying the inverter until you have the full inverter + battery approvals (from AHJ and POCO) in hand. With potential tariff changes, there's an argument to buy a more expensive, known quantity for California approval, inverter and battery sooner.
I found this datasheet and it says 25A max input but NO max ISC. Typo? The Euro 230V one has different specs. I don't know if there's an official way in NEC to scale from max input current to max ISC. I think it is fine but I worry about warranty and plan check
Solar panels IMO are mostly determined by how they fit your roof. They do have a different risk (IE, turned out to have missing certifications; can be really expensive to return. If the solar panel can be found in the interconnection application web app it's probably not that bad of a risk).
Attachments
This is the one I am following to see that the 12kpv gets listed, before I start my ESS interconnection application. IT covers the inverter and battery combinationI don't see SRNE on there, so it might just not be approved in this manner, or they delegated approval to a different company & it's showing up as a different name
Alternatively I might just do 18kpv, there's some followup work on my house I dream of doing, which that can help with.
Guide to Solar Panel Size and Wattage: Choosing the Right Panel
Does it matter what size solar panel you have installed on your roof? And how do you figure out which panel is right for your home?
For more information, please visit OUSHANG SOLAR.
The good news is, you don’t have to do it on your own. Partnering with a professional, experienced solar company is a major way to give you understanding and peace of mind. The right system, with the right panel size and wattage, will lead to savings and energy independence from your decision to go solar.
Solar Panel Size vs. Solar Panel Wattage
When searching for different solar panel sizes online, you may find panels are differentiated by their wattage, or by the number of cells on a panel, rather than their physical dimensions or arbitrary sizes like small, medium, and large.
A solar panel’s wattage, or power capacity, refers to its energy generation potential, with higher wattage panels able to deliver larger amounts of solar electricity. Solar panel wattage is abbreviated simply with a “W'' and 1,000W is equal to one kilowatt (kW). If you want to go into more math and the metric system, you can learn more about watts, kilowatts, kilowatt-hours.
Common Sizes and Wattages
While there are no standard sizes, most of today’s premium home solar panels come in one of three primary formats, classified by the number of solar cells.
- 60-cell solar panels: 60-cell modules are the smallest residential solar panels, and today’s products have average dimensions of roughly 5.4 feet by 3.25 feet. Great for fitting on complicated roofs with limited installation space, most 60-cell solar panels are rated under 325W in power capacity.
- 72-cell solar panels: With two extra rows of cells, 72-cell solar panels are about 6.4 feet tall on average (while still 3.25 feet wide) and typically rated 400W or higher. 72-cell solar panels are ideal for residential roofs with ample installation area.
- 96-cell solar panels: Rarely used for residential installations, 96-cell solar panels usually measure around 6.4 feet by 4.3 feet. Commercial 96-cell solar panels may be rated 300W to 450W and higher.
High-quality residential solar installations in the US typically utilize solar panels rated between 250W and 430W. While lower-wattage solar panels (below 250W) may work for small, off-grid systems, higher-wattage solar panels are better suited for commercial or utility installations with fewer space restraints than residential rooftops.
Strung together and wired into your home’s electrical system, solar panel wattages are added together to calculate your total solar capacity. So if you install 20 solar panels, each rated at 325W, your total solar panel wattage would be 6,500W or 6.5 kW.
Solar panels with half-cut cells
Half-cut solar cells are part of renewable energy tech innovation in , with several new products now available from solar panel manufacturers. Made up of solar cells that are “cut in half,” panels with this technology are the same size with double the number of cells. These panels increase power potential in the same installation footprints.
Half-cut panels typically contain 120 or 144 half-cut cells. As a new product, solar panels with half-cut cells may not be available in all markets and are usually more expensive than traditional 60 and 72-cell panels.
Total Dimensions for Home Solar Panel Systems
For efficient electricity production and ease of installation, nearly every home solar energy system is installed with the same panel wattage (and model) per panel throughout. Knowing this, calculating the dimensions of a solar panel array is fairly straightforward. Take the sum of the panels’ dimensions as they are arranged and installed on your roof.
To illustrate how much roof space is needed for solar panels, let’s say you decide to install a 9.6kW system to offset your home’s electricity use. This capacity can be created with 24 72-cell 400W solar panels, covering about 21 square feet each. In this scenario, you would need roughly 500 square feet of installation space (21 square feet x 24 panels) to host your system.
Can You Expand Solar Panel Systems After Installation?
It’s usually possible to add solar panels to an existing system. It’s typically more straightforward and better economic sense to build the system you need at the outset.
Contact us to discuss your requirements of 144 Cell Solar Panel. Our experienced sales team can help you identify the options that best suit your needs.
If your circumstances change after installation, maybe you’re getting and charging an EV for the first time, maybe you’re electrifying your home, it’s likely you can expand your system. You’ll need to figure out if your system’s permitting, components, like the inverter, and your roof are compatible with more panels.
Adding solar battery storage
Another potential answer to maximizing your use of your solar electricity is adding solar battery storage.
Batteries store the unused electricity generated by your panels. You can use the power when needed, such as at night or during power outages. Instead of needing to add panels, you may be able to use your electricity more efficiently. Solar batteries can give you greater reliability, independence, safety, and savings.
How to Choose the Right Solar Panel Size
Unless you are planning a DIY solar panel installation, more often than not, you will not have to worry about choosing the right solar panel size for your home. Instead, a professional solar installer can work with you to determine the best solar panel wattage and size for your roof or property, tailored specifically to your unique energy demand, electricity costs, and available installation space.
Palmetto experts are always available to answer your questions about home solar power and ways to save money. To learn more, contact a Palmetto Solar Advisor today or use our solar savings calculator.
Frequently Asked Questions
How many solar panels do I need?
Palmetto will calculate how many solar panels you need based on your power usage, the goals you have for your solar usage, your potential savings, your roof dimensions, and more. We work with each customer to answer every question and design the specific solar system for your home.
Does the size of my solar panels matter?
Yes, the physical dimensions of your panels matter as they relate to the available space on your roof. Solar panel wattage helps you calculate the overall capacity you need for a system which meets your family’s needs.
What if solar panels don’t generate as much electricity as I need?
If your solar panels are connected to the grid and are not giving your home enough electricity, electricity from the utility company will make up the difference. If this is a problem, potential solutions include adding solar battery storage or adding panel capacity to your system.
What happens if I produce more power than I need?
For more information, please visit 144 Cell 535w Solar Panel.