which panel to choose, 18V or 36V? | DIY Solar Power Forum

How does one choose a panel?

I have a 400ah lithium battery, 13.3 resting voltage, 14.4 charging.
I was looking at the panels available. I would like 2 panels of 200W each (that's pretty much what fits on the roof).

Most panels come in 18V and 36V version.

I guess it's for PWM controller in 12V or 24V setups.

But, what about MPPT?
I have a Victron 100/30.

Should I get the lower voltage, but higher amperage wired in series, or the higher voltage, and lower amperage wired either in series or parallel?
Would there be an advantage to either?

Thanks! I would always choose the higher voltage panel (all other things being equal). I am running 250w panels (30.3v / 8.37a) in series sets of three to bump the voltage up to ~92-100vdc and then combining three sets (parallel) into a combiner box.

Ultimately you just need to make more voltage than 14.4v, so either style panel will work. With the Victron 100/30 you will be able to run your panels in parallel or series, so get the less expensive option? With MPPT, you don't really care about the "voltage" of the panels, meaning you don't care if it's a 12v or 24v panel.

Instead, you are primarily concerned that the total voltage of your panels when combined in series does not exceed the Maximum PV Input Volts of the solar charge controller. If you are in a location where it gets cold, you need to leave room for the voltage to climb when it gets cold.

Panels in series, the voltage adds up and the amps remain the same. Panels in parallel, the voltage remains the same and the amps add up.

How does one choose a panel?

For me, in order:

1. what the controller will tolerate. Usually not an issue, but some DC-DC chargers have very low input voltages (~23-25v); in that case the 24v would not be acceptable.
2. what fits the allotted space
3. $/watt

Most panels come in 18V and 36V version.

1. nominal 12v / 36cell / Vmp ~18v
2. nominal 20v / 60cell / Vmp ~30v <-- somewhat less common, but they do exist
3. nominal 24v / 72cell / Vmp ~36v

Would there be an advantage to either?

24v is more common in 200w panels than 12v, so I'd expect them to be a bit cheaper by the watt. I suspect 12v 200w is a niche product that exists to meet the needs of people running 12v systems and PWM controllers. Hopefully someone who knows more than me will chime in. I like paralleling all panels so if one panel is shaded, the others still push amps. This sounds like a great idea, until I balanced that agains wire size for a 50’ run with a 36 amp run for 3% loss and the fact that 10 gauge wire is easier to work with because among other reasons, you can use MC4 connectors, which are limited to 30 amps.

With my six panels, I ended up with a 3S2P set up with 100 watt panels. That’s just the way the math worked out for voltage loss on the wires balanced with high amperage. By going with three panels for a total of 48 volts in series, that made the voltage loss less than 3% for the length of the run.

Others are not that concerned about my 3% loss number for my panels, and find it better to add an extra panel or two to compensate.

I then came up with two other arrays with two separate charge controllers. The second was a portable array. The third was 350 watts of flat panels on the roof,

My second array I added to power my RV was four portable panels, 100 watts each, all in parallel. This works fine. I even tilt it into the sun and because the tilt angle allows more early morning production and evening production, these 400 watts of panels throughout the day can produce more power than the 950 watts of panels I now have on my roof. alright.
on a voltage drop only stand point, it would seem that using two 36V panels rated at 5.5A each, wired in series will keep the amps at 5.5, and ramp the voltage to 72V, which my MPPT can handle.
That way I can use awg10 wire, with only a 0.2% loss over my about 4.5m of wire.

I'm usually parked at the beach, and not much shade, so both panels would always be in the sun, but not tilted.

Reasonable thinking? My box is already at the highest legally possible, so, adding a tilt mechanism would make it too tall.
Also, it's almost perpetual summer here. 25C for about 8 months of the year, and above 30C for some 6 months out of them!

We got 38C today....

Here's a capture of the panels I am looking at. These 200W basically all have the same ratings.

Investing in solar power is like spending money on something brilliant. Solar power is a type of energy that's good for the environment. When you get a solar power system, the solar pv modules are the most expensive part, about 60% of the cost. It's also important to know that once you decide to use solar power, you'll be using it for a long time, like 25 years or more. So, picking the right solar panels is a big deal because they need to last a long time and save you money. That's why it's super important to buy good solar panels. We can help you choose the best solar panel that works for what you need.

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Criteria you should use while selecting a solar panel

When selecting solar panels, it's essential to consider key factors for optimal choice. Efficiency, indicating how effectively panels convert sunlight to power, should be balanced with quality from reputable manufacturers offering reliable products. Consider following points before deciding the solar panels:

1. Solar Panel Type
2. Solar Panel Grading
3. Roof Area, Capacity & Solar Panel Size
4. Compatibility With Inverter
5. Solar Panel Features & Performance
6. Durability
7. Certifications & Warranty

Lets discuss these criteria one by one.

1. Solar Panel Type

There are two main kinds of solar panels you can buy: Monocrystalline and Polycrystalline. They're named after the stuff they're made from. Monocrystalline panels are made from pure silicon, while Polycrystalline panels are made from many small pieces of melted silicon.

Monocrystalline solar panels are more efficient than Polycrystalline solar panels of the same size. They're also good at making electricity when it's not very sunny. But they cost a bit more. Some people pick Polycrystalline panels if they have a big roof and want to save money.

Solar panels come in different grades: A, B, C, and D. These grades depend on how good the solar cells are. Nowadays, most panels are at least B grade because solar technology has gotten better. The difference between A and B-grade panels might not be easy to see, but it matters in the long run. We recommend getting A-grade panels. They look nice and work well. They go through tests to make sure they're good quality. Even though solar panel prices are going up, it's better to spend a little more for good quality.

3. Roof Area, Capacity & Solar Panel Size

When you want to get solar panels, think about what you want them to do:

• Make lots of money for you?
• Save you money?
• Not cost too much at first?

Once you know what you want, you can figure out how many panels and what size you need. There are three sizes: small, medium, and big. Bigger panels make more electricity. Look at your past energy bills to know how much electricity you use, and then you can decide how many panels you need. If you have a big roof, you can get big panels to make more electricity. If your roof is small or has shadows, smaller panels might be better. You can also use a special meter to get credit for extra electricity you make and give back to the power company.

4. Compatibility With Battery

When you think about using batteries with solar panels, it's important to consider how much energy the batteries can store. This is especially useful when you can't use electricity from the grid, or if you want to save solar energy for later in case the power goes out.

To make sure the battery can provide power to your devices and make up for energy lost in inverters, you need to choose the right solar panel. Solar panels create energy from the sun, which can be stored in batteries for later use. The solar panel needs to produce enough energy to charge the battery and cover any energy losses.

Batteries have energy storage ratings mentioned in Ampere-hour (Ah), like 150Ah or 200Ah. They also have a certain voltage, which is like their electrical pressure, usually 12 volts. To pick the right solar panel, match it to the battery's rating and voltage. For example, if you have a 12V battery, use a 12V solar panel. If you have a 24V battery setup (which means you have two 12V batteries connected together), then you need a 24V solar panel.

To figure out how many solar panels and how much energy you need, you have to know how much current is required to charge the battery. For a 150Ah battery, you'll need a certain amount of current to charge it properly.

Imagine you have a 100 watts Mono PERC solar Panel which has a Vmpp (maximum power voltage) of 5 amps, you will need to connect 3 of these panels together to get 15 amps of current. This will help you charge a 150 ampere-hour (Ah) battery in 10 hours. On the other hand, if you decide to use a 190 Watt Mono PERC Solar panel, you will only need 2 of these panels to charge the same 150Ah battery in 10 hours.

5. Compatibility With Inverter

Solar panels generate direct current (DC), while your household appliances require alternating current (AC) to function. Consequently, it is not feasible to directly link solar panels to your home appliances. To bridge this gap, an inverter is necessary to convert the DC generated by the solar panels into the AC that your household devices use.

Just as with batteries, it's important for the solar panel's specifications to match the inverter's capacity. Inverters come in various capacities, such as 12V, 24V, 48V, and so on. This means a 12V solar panel should be paired with a 12V inverter, while a 24V solar panel should be matched with a 24V inverter. Additionally, a series connection is essential to ensure a consistent voltage across the battery, inverter, and solar panel.

12V solar panel – 12V inverter – 12V battery

For more 36 cell solar panelinformation, please contact us. We will provide professional answers.

24V solar panel – 24V inverter – 12V x 2 battery

For 48 Volt Inverter:

Either connect two 24V solar panels in series or connect four 12V solar panels in series, along with four 12V batteries connected in series.

24V x 2 solar panel – 48V inverter – 12V x 4 battery

6. Solar Panel Features & Performance

The electricity output of a given solar panel is determined by various factors, including its power rating, power tolerance, efficiency, and temperature coefficient. These factors collectively determine the panel's potential power generation.

Power Tolerance: Solar panels are assigned a "tolerance" rating, indicating whether the panel will perform below, meet, or exceed its stated "nameplate" rating. This rating is indicated as a percentage range (-%/+%) on the panel's specifications sheet and physical label.

For instance, an ordinary solar panel might claim a guaranteed output of 375 watts, but in reality, it might only produce 370 watts under standard test conditions (STC). This panel could have a tolerance of -3%/+3%, meaning it could produce 3% less than the stated wattage due to production issues, but it also has the potential to generate 3% more than the specified wattage under optimal conditions.

An A-Grade solar panel, such as the Bluebird 400W Mono PERC solar panel, boasts a tolerance of 0%/+3%. This implies that the panel only exhibits positive power tolerance, ensuring it will consistently generate more power than its rated wattage. This tolerance, or efficiency rating, should be a key consideration.

7. Durability

• Must be constructed with A-grade solar cells.
• The robust silver anodized Aluminum frame enhances the panels' durability.
• Essential resistance to PID, salt mist, and ammonia corrosion.
• Anti-reflective (AR) coated tempered photovoltaic (PV) grade glass minimizes light reflection.
• Since solar panels are exposed to outdoor conditions, the solar panel junction box must possess an IP68 rating, ensuring resistance to water and dust ingress.

8. Certifications & Warranty

It's also important to ensure that the solar panels you install are designed to endure the specific conditions of your region. Seek out panels that meet the IEC standard, which is established by the International Electro-technical Commission (IEC) to assess reliability. The IEC involves an accelerated outdoor stress test to verify the panels' durability. In India, solar panels certified by BIS, such as Bluebird Solar, are recognized as a symbol of trust.

Solar product warranties operate similarly to the warranties you receive when purchasing consumer electronics like iPads, televisions, or computers. However, while most electronic products typically offer around one year of coverage, and possibly up to three years with extended protection, PV (photovoltaic) product warranties function differently. Solar technology, lacking moving parts, ranks as one of the most robust energy generation technologies globally. Furthermore, each component undergoes rigorous testing prior to being introduced to the market.

A solar panel is covered by two warranties:

(1) Performance Warranty: Under standard conditions, solar panel output will naturally degrade, though it should not deteriorate by more than 10-20% over 25 years. Typically, performance drops by approximately one-half to one percent annually.

Typically, a solar panel's performance warranty guarantees 90% production for 10 years and 80% for 25 years. When panel performance falls below these thresholds, the performance warranty takes effect, allowing for the repair or replacement of underperforming panels. The company may assess your solar panel either at their testing facility or through a third-party testing facility. After confirming that the panel's underperformance is due to internal defects, they will honour the warranty.

(2) Product Warranty: The manufacturing or product warranty safeguards your product against manufacturing defects.

This includes any deterioration in the product's appearance (such as mechanical wear, rust, hot spots, snail trails, and other aesthetic flaws).

• Damage to the frame or glass.
• Loose junction boxes or faulty connectors.
• Malfunctioning cells or damaged cell connections.
• Flawed back sheet.

When Can the Company Deny Your Warranty?

• If solar panels are repaired without the company's authorization or tampered with in any way.
• If solar panels are exposed to unusually high salt or chemical exposure.
• If solar panels undergo improper installation, application, alteration, unauthorized servicing, or improper system design that results in constant shading on the products.
• If damage to solar panels is caused by power failure or surges, flooding, fire, direct or indirect lightning strikes, or other natural events.
• If damage is the result of accidental breakage, vandalism, explosions, acts of war, or other events beyond the manufacturer's control.
• If solar panels are moved from their original installation location.
• If PV panels are exposed to voltage exceeding the maximum system voltage at the lowest temperature of the location or power surges.
• If the serial number on the solar panel is modified, removed, or becomes unreadable.

What Does the Company Provide Under Warranty Eligibility?

• Replacement of the solar panel. - Replacement of non-functional solar modules with new ones of equivalent labelled power wattage as the Warranted Wattage of the replaced Products (Warranted Wattage refers to the contracted power wattage of the Products minus permissible accumulated degradation).
• Refund of the amount - Refund of the depreciated purchase price paid by the customer for the module as compensation.

Conclusion

The article examined the crucial aspects to take into account prior to selecting the most fitting solar panels for your needs.

Key considerations include:

• Your objectives
• Type of solar panels
• Grading of solar panels
• Rooftop space availability and solar panel dimensions
• Suitability with battery and inverter systems
• Features and overall performance
• Certifications and warranties

If you are considering acquiring solar panels, we are available to help you procure the ideal PV Module that matches your specifications. Please reach out to us for additional details.

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