Solar Panel Ratings – Everything You Need to Know - ShopSolar.com

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The article discusses solar panel power ratings, explaining that most panels are rated in watts and range from 100W to 400W. It clarifies that this rating represents the panel's expected power production in ideal conditions. The article also covers the calculation of wattage, emphasizing that it's the product of volts and amps produced by the panel. Factors affecting actual power output, such as positioning, sun hours, and efficiency, are highlighted.

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The difference between monocrystalline and polycrystalline solar cells is explained, with monocrystalline cells being more efficient but costlier. Efficiency ratings, ranging from 15% to 20%, indicate the panel's ability to convert sunlight into electricity. It suggests using solar panel kits for convenient installation and discusses factors like seasonal changes and panel positioning affecting solar panel performance. Overall, it provides comprehensive information to help understand and choose solar panels for various needs.

Introduction

Understanding Solar Power Ratings – Everything You Need to Know About Solar Panel Ratings

Most solar panels you will find on the market today are listed according to their power rating in watts. Typically, they will range from 100 watts to right up to 400 watts, but many people are unsure what these numbers actually mean. 

To help you better understand solar panels, we are going to go over everything you need to know about solar power ratings. We will explain the difference between total capacity and actual power output. We will also explain the different types of solar panels you can choose from. From there, we will even recommend some high-quality solar panels you can choose from to start harnessing the power of the sun right away. 

Once you understand how to properly compare solar panels and other pieces of solar technology, you can start building your own solar power system. By embracing solar power, you can decrease the cost of your monthly electricity bills, reduce your dependence on the utility companies, and do your part to protect the environment and improve local air quality.

What is the Wattage Rating?

When you look at solar panels, most modules are rated between 100W and 400W, usually in increments of at least 50W. What this wattage rating represents is that particular solar panel’s expected power production in one hour of ideal conditions, meaning direct and unfiltered sunlight and perfect weather conditions. 

As you would expect, the higher the solar panel is rated in watts, the more powerful it is. These higher efficiency solar panels can produce more DC electricity in the same amount of space as similarly sized solar panel with a lower power rating.

The Cost

In almost every situation, the higher the watt rating, the more expensive the solar panel will be, which explains why the overall wattage of a solar power system is usually a good indicator of how expensive it was to assemble.

That being said, there are some exceptions to this general rule. For example, some solar panels are more expensive than others because they have useful features, such as a folding design for portability, built-in support legs, and waterproof exteriors. You can also find miniature low wattage solar panels that were specifically designed to pair with portable electronic devices while hiking and camping. However, these relatively expensive, travel-friendly solar panels are not what you would be looking for if you were planning to assemble a residential grid-tied or hybrid solar power system. 

How is Wattage Calculated?

In simple terms, wattage is calculated by multiplying the total volts and amps a solar module can produce. The volts, or voltage, represents the force of the electricity that is generated by the solar panels when they are operating at their full potential. The amp rating refers to the flow rate of that electricity. When electrons flow from a high voltage area to a low voltage area, that flow is measure in amps. 

Basically, wattage refers to the energy produced when flowing electrons encounter resistance. This energy is measured in watts and is always equal to volts multiplied by amps, or Volts x Amps = Watts.

In other words, when sunlight hits a solar panel, voltage and current are produced. This current, pushed by voltage, flows through wires in the electrical system and has to work when it encounters resistance, this work is measured in terms of watts. 

Do Solar Panels Always Produce the Watts They're Rated for?

Unfortunately, the wattage rating of a solar panel only refers to the amount of power it can produce while operating in ideal conditions. In reality, the actual power output of a solar panel will depend on a number of factors, including its positioning, the components the solar panel is connected to, the number of peak sun hours it is exposed to, and environmental factors, like shading and cloud coverage. 

Sun Hours

One of the most important factors you will need to analyze to understand how much power your solar panels will actually generate is the number of sun hours they will be exposed to per day.

Sun hours refers to the number of peak sun hours you typically get in your specific geographic location. The average number of peak sun hours varies rather significantly across the country and around the globe.  This means the amount of sunlight and the intensity of that sunlight your solar panels will be exposed to will depend on where you live. 

While the sun might be shining throughout the day and it may seem like you get 12 solid hours of daylight, you likely only receive around four or five peak sun hours. The term ‘peak sun hours’ is actually used to describe hours where the intensity of the sunlight is at its highest, not just hours where it is bright enough to see outside. Typically, a peak sun hour is defined as an hour in the day when the intensity of the sunlight reaches an average of 1,000 watts per square meter. 

Other Factors That Impact Performance

Seasonal changes play a major role, as the Earth’s tilt alters the amount of sunlight an area receives throughout the year. The peak sun hours chart displayed above actually just refers to the average number of peak sun hours each part of the United States receives. In reality, solar panels can provide far more power during the summer and about 25% to 50% less during the winter months. 

The direction and positioning of the solar panels also plays a major role. In general, you will want to face your solar panels in a southward direction that is not shaded at any point throughout the day. 

The overall efficiency of your solar power system will also impact its power rating. This is why it is so important to match your solar panels with an appropriate power inverter, charge controller, and battery bank. Making sure everything works together efficiently will help prevent the unnecessary loss of power through the system itself.

Monocrystalline and Polycrystalline Solar Cells

There are two main types of solar cells used in solar panels – monocrystalline and polycrystalline. The type of solar cells used within a solar panel can also impact the efficiency and power rating of that particular solar panel.

Monocrystalline solar cells use single-crystal silicone. Monocrystalline solar panels are generally considered premium products, as they are more efficient and can be made much thinner. With a single crystal cell, the electrons that generate a flow of electricity have more room to move, which improves the overall efficiency. 

Polycrystalline solar panels usually have lower efficiencies, but they are also less expensive. Instead of using a single crystal of silicon in the solar cells, manufacturers melt numerous silicon crystals together to form a wafered-style cell. With more crystals in each cell, there is less freedom for the electrons to move, which reduces efficiency.

Efficiency Ratings

While power ratings are designed to indicate the power potential of a solar panel, efficiency ratings are another important indicator of the panel’s overall quality. Efficiency ratings continue to improve, but currently, they tend to range between 15% and 20%. 

The more efficient the solar panel is, the more sunlight it can convert into useable electricity. When shopping for solar panels, keep an eye out for the efficiency rating, as the higher the percentage, the better your solar panel will perform and the more often it will be able to produce electricity at a rate close to its power rating. 

Shopping for Solar Panels

When shopping for solar panels, there are quite a few different options. The first step you will want to take is figuring out how much solar electricity you actually need. Our Solar Watt Hour Load Calculator can help you determine how much electricity you actually need to power your electrical devices and appliances, which will help you determine the number and types of solar panels you will need to satisfy those power needs.

By shopping our Complete Solar Panel Collection, you will be able to choose from a wide range of solar panels with a variety of power ratings.

Solar Panel Kits

One of the easiest ways to get started with solar power is to purchase a complete solar panel kit. Not only do these kits contain efficient solar panels, they come with all of the other pieces of solar equipment you need to start accessing clean solar electricity. In one convenient and affordable package, you get solar panels, a charge controller, power inverter, deep cycle solar battery, and all of the solar cables and connectors you need to wire everything together.

Final Words on Solar Panel Ratings

While it is always important to keep an eye on power ratings and efficiency ratings, they are not the only factors that will determine how much power your solar power system can generate. Pay attention to the number of peak sun hours you receive in your area, as well as other factors, like the angle and direction you use to install your solar panels on.

There are many things you can control to make sure your solar panels are working at their highest potential. As always, you if you have any questions about solar panel power ratings, or any general questions about solar power, you can always reach out to us at any time!

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DC cables are lifelines of the Solar Power Plant and interconnect modules to combiner boxes to inverters. These cables constitute only around 1-2% of total solar project cost but have a significant role and impact on the power output with poor design and/ or cable selection leading to material safety and performance issues.

DC cables are certainly different than the AC cables in construction and perform power evacuation with certain differences in their operation. Though significantly cheaper, Normal AC cables must not be used for DC PV power evacuation. Copper is the ideal material for string DC cables due to the metal’s high flexibility, superior current carrying capacity and better thermal performance. The DC cables should be made of flexible copper conductors. DC power does not demonstrate the skin effect like AC power and therefore any small change in the copper per unit length of the conductor leads to significant impact on the power evacuation capability of the cable.

Duty parameters for Solar DC Cables

DC cables have to endure harsh conditions in India as they have to withstand high temperatures, ultra violet (UV) radiation, atmospheric ozone and fire risk for a life expectancy of 25 years.

High temperature

Sustained exposure to high temperature causes thermal ageing of DC cables.

Arrhenius law –thermal ageing rate doubles for every 10˚C increase in temperature.

Operating temperature of DC cables is typically less than 90˚C.

Technical standards specify testing of cables at 120˚C and require the cables to sustain for 20,000 hours, equivalent to 160,000 hours at 90˚C s per Arrhenius law.

UV radiation

UV radiation in sunlight gets absorbed in the conductor leading to cable breakdown. DC cables are coated with polymer coating (polyethylene or polyolefin) mixed with about 2.5% finely dispersed carbon black to reflect UV radiation. Ideally the Red and Black color used for the identification of the Cables should be in strip form and the outer sheath of both the cables should be Black only.

Such cables have been used for over four decades in outdoor use in the communication sector in Europe.

Fire

DC cables are required to be flame retardant. Low smoke, halogen free insulation is preferred for DC cables. Halogen free compounds are filled with inorganic mineral flame retardant additives.

Ozone

Absorption of ozone results in degradation of DC cables. To ensue durability of DC cables over a period of 25 years, EN standards recommend that cables be tested with ozone concentration of 200-250 parts per million at 40˚C for 72 hours.

Water

Cross-linking of polymer coating material enhances the ability of the cable to withstand exposure to rains and waterlogging. Amongst the techniques available, electron-beam crosslinking is the most efficient and most widely used.

Shock related hazard in DC cable

Damaged cable sheath may lead to electric shock as the conductor would be exposed directly to the environment. Lighting circuit cable energized with an exposed end in the roof space may lead to an electric shock.

Due to above harsh operating conditions, the Solar DC cables are different in their operation to evacuate the power and therefore are subjected to changes in the operating parameters based on several operating parameters. It has been experienced in DC cable that issues like significantly lower yield of solar Power or as extreme as fires. Power output loss in DC cables should be 0.5-2%, however based on the design, copper content and manufacturing process deployed actual losses can be significantly higher. However, Lack of Module, SCB, ACB level monitoring makes it difficult to quantify /measure the actual losses in cables.

Manufacturing Process of DC cables Electron Beam Cross Linking

Under this process, the energy from the electrons creates active sites on the polymer chains which subsequently crosslinks and forms a chain making it hard for material to melt and flow.

Physical cross-linking

The cable insulations should be cross linked with high-energy electrons (betarays) in E-Beam irradiation facility. The electrons cede their kinetic energy when slowed down in the polymer. Through the impact of the electrons radicals are built, which with chemical reaction interlink the molecules.

Electron Beam Cross-linked insulating materials

Cross-linking binds together the polymer chains by means of a chemical linking (in the amorphous phase). This leads to a three-dimensional network. The polymer chain can no longer move freely (irrespective of temperature). Above the melting temperature the material can no longer flow but it goes into a rubber-like elastic state.

Electron-beam cross-linking

Advantages of E Beam cross-linked insulation materials

■■ Increased shear and compressive strength

■■ Improved integrity in case of electrical failures (overload, short

circuit)

■■ Improved resistance to chemicals

■■ Infusible, soldering iron resistance

■■ Improved impact strength and crack resistance

■■ Better weather and abrasion thermalresistance

With the electron-beam accelerators the insulation materials can be cross-linked

within a few seconds. The homogenous irradiation and implicit the homogenous

cross-linking are ensured by thererfore especially adapted handling systems.

Other than in the chemical cross-linking in the irradiation cross-linking

no peroxides or hydro-silicones are incorpored into the synthetic mixtures.

Cable used in solar PV plants can be classified as follows:

DC cables

DC cables connect modules to inverters and are further segmented into two types:

String DC cables: These cables are used to interconnect solar modules and to connect modules with string combiner boxes or array combiner boxes. Cables for interconnecting modules come pre-connected with modules, whereas the cables required to interconnect strings and to connect with combiner boxes are procured separately. String DC cables carry current of only around 10 Ampere (A) and a small cross section (2.5 sq. mm to 10 sq. mm) is sufficient for this purpose.

Figure: Different types of cables in a solar PV project

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Failures in DC Cables

There are many reasons why a cable may fail in service, with the failure at its most serious resulting in fire or other serious fault. Some of the main causes of cable failure include:

Ageing – The service life of a cable can be significantly reduced if it has been expected to operate outside of the optimal operating conditions it was designed for. The ageing process usually results in embrittlement, cracking and eventual failure of the insulating and sheathing materials, exposing the conductor and risking a potential short circuit, a likely cause of electrical fire.

Mechanical failure – If the cable is damaged either during installation or in subsequent use, the integrity of the cable will be affected and reduce its service life and suitability.

An example of mechanical failure in the solar DC cable

Shielding losses / EMC problems – Increased electromagnetic interference (EMI) occurs when the shield, which is designed to protect cable, signals from electromagnetic fields, breaks and abrasions due to continuous bending.

Case of burnt cable

Technical standards

Globally there are three recognized standards for use of DC cables – European (EN), Underwriters Laboratory (UL) of USA and TUV of Germany. The fourth standard, IEC, is currently a work in progress document.

UL standards

UL is an independent safety science company based in USA. It published the first edition of DC cable standards in , which was named UL. Subsequently UL has amended the standards from time to time. UL standards are the most stringent for DC cables globally. UL standards require DC cables to be rated at 2,000 V, the highest among all standards. They allow use of halogenated compounds for making the cables flame retardant even at higher voltage.

Example of an accelerated thermal ageing Arrhenius- Diagram

3.2 EN standards

These standards published in and named EN, are relatively less rigorous than UL. The standards require cables to be able to operate at 1,500 V and specify that the DC cables must be low smoke, halogen free and must have cross linked insulation and sheath. Unlike UL standards, EN standards require cable to comply with Class 5 i.e. the cables must be flexible.Thus, aluminium by virtue of being a relatively rigid metal doesn’t qualify, effectively meaning that EN standards mandate use of copper cables only.

3.3 TUV standards

TUV2Pfg/08. is relatively less stringent than the EN standards. A newer version, TUV 2Pfg/05. was published in , which requires cables to be rated at 1,500 V.

This standard requires the cables not only to be halogen free but also pass fire protection test as per the UL standard without any use of halogenated compound.

Test setup for Flame retardance test as per IEC and UL stnadards

3.4 IEC standards

The key difference is that IEC allows usage of class 2 material, i.e. aluminium for fixed installation. This implies that aluminium can be used for main DC cables, but not for string DC cables, as these cables requires flexibility.

IEC : sets out design requirements for photovoltaic (PV) arrays including DC array wiring, electrical protection devices, switching and earthing provisions.

The new standard includes a number of requirements for construction, materials and testing which cover these environmental threats, as well as covering the electrical requirements of operating to 1.5kV and at high current loads.

The IEC standard is similar in many respects to the European standard, it does however, permit non-halogen free materials to be used as well as halogen free, with the same environmental and electrical performance being achieved.

Standards used in India

BIS Standard

MNRE has indicated that, BIS shall soon adopt a standard for testing and certifying Solar DC Cables There are various Indian standards that are referred for testing of cables on various parameters. Indian Standards have also come up with laying parameters of halogen free compound, flame retardant properties of the cable, etc. Some of the popular/important standards are:

IS – – (various Parts)

IS –

Public sector organizations such as National Thermal Power Corporation (NTPC) and Neyveli Lignite set detailed requirements for DC cables for their own projects, typically setting benchmark for the entire sector:

Voltage drop limit

Neyveli Lignite has mandated limiting aggregated voltage drop to 1%. NTPC has mandated limiting maximum voltage drop to 1% in string DC cables and 1.5% in main DC cables. These are very stringent standards as national electric code of USA limits the aggregate voltage drop to 5%9.

String DC cables standards

Neyveli Lignite has mandated compliance with TUV2Pfg/08.. NTPC used to follow TUV2Pfg/08. or EN , but has recently mandated only EN. This shift is primarily for want of higher thickness of insulation and sheath to cope with tougher operating conditions on site.

DC cable design and selection

Voltage drop typically leads to heating up of cables and increase in temperature associated with increased losses, higher voltage drops may lead to fire accidents. Power loss in DC cables is measured in terms of voltage drop from module to inverter. As current in the cables remains the same, voltage drop implies proportionate loss of power.

Limiting voltage drop

Use of larger cross section cables

Resistance of a conductor is inversely proportional to the cross section. Cables with larger conductor cross section cost more but offer lower resistance. For example, a 2.5 sq. mm cable has 60% higher resistance and a 6 sq. mm cable has 50% lower resistance vis-a-vis a 4 sq. mm cable.

Correlation of cable cross section and resistance for string

DC cables

Upsizing the cable from 4 to 6 or 6 to 10 sqmm might not be a wise choice, as for relatively miniscule advantage there is a significantly higher impact capital cost. While higher cross section can bring lower resistance, it may also mean very high unwanted factor of safety and extra cost for more amount of copper.

Cardinal rule is there may be attempts to optimize the capital costs in order to reduce capital risk exposure but nothing can replace a prudent cable design for performance, efficiency and longevity.

Short-term cost considerations might actually bring higher levellized cost of power or in some cases higher maintenance/ replacement costs considering life-time performance and safety aspects and highest possible returns from these investments.

Reducing cable length

Total resistance of a cable is directly proportional to the length of the cable. Reducing length through design optimization is key to limiting the voltage drop. But cable length is subject to plant layout and there are sometimes other site specific limitations also in limiting cable length.

In -12, a typical solar project used around 15 km/MW of string DC cables and 3-4 km/MW of main DC cables. This has now reduced to between 7-11 km/MW of string DC cables and 1.5-2.5 km/MW of main DC cables effectively reducing voltage drop by around 33% in string DC cables and 30-60% in main DC cables.

A common solution for reducing overall DC cable length is the use of ‘Y Connectors’ to combine two strings and create a single output of double rating. This requires cable of larger cross section for carrying the larger capacity but halves the length used resulting in reduction on voltage drop offsetting a part of reduced losses in DC side.

However, increasing the number of crimp points or termination points leads to likely voltage drop. The design with usage of Y connectors should therefore seek an overall reduction in voltage drop. Another solution for reducing cable length is use of string inverters instead of central inverters. String inverters are used in place of combiner boxes and reduce the length of DC cables required. However, they require an increase in the length of LT cables potentially increasing the losses in the AC side.

Further, the total capital cost of project could increase as string inverters are expensive vis-a-vis central inverters.

Increasing operating voltage

Voltage drop in percentage terms can be reduced by increasing the operating voltage.

Average length of string and main DC cables used in a typical solar project in India has come down from 15 km/MW and 3-4 km/MW in to about 8 km/MW and 2 Km/MW respectively. With large scale projects shifting towards V operating voltage for DC systems the cable requirement per MW will be further lowered.

Until , the most prevalent DC operating voltage was V. But 1,500 V systems have become common now reducing losses by 40% in main DC cables.

The US market is already using 1,500 V systems, reducing voltage drop by a further third. The higher cost and poor availability of compatible modules and other BOS components is a challenge in the near future but Indian solar market has already moved to 1,500 V.

As DC cables operate at relatively low voltage levels resulting in high loss of energy, design optimization is crucial. Final design should aim for minimizing the cost of solar power generation without compromising on safety and quality.

Practical issues during plant operation

Actual voltage drop during operations could be significantly different from what has been calculated during design stages. Some of the practical issues in measuring and limiting voltage drop are given below:

Issues with voltage drop measurement

Measurement of actual voltage drop is very difficult. Theoretical voltage drop is calculated using cable specification sheets but actual ambient conditions including temperature, humidity and air quality are often vastly different. Voltage drop at inverter can be caused by lower power generation from modules and/or faulty interconnections. Significant effort is required to isolate and quantify the role of cables in voltage drop.

Use of poor quality copper

Use of high purity virgin copper is preferred for DC cables. However, inferior products are commonly supplied in the market. It is very difficult for developers and EPC players to ascertain purity levels.

Laying cables

It is common industry practice to lay DC cables via underground conduits to protect them from rodents and enhancing regular cleaning activities.

However, high temperature in underground conditions causes derating of cables

If the cables are left exposed in the air, 360˚ air flow around the cable helps in better heat dissipation.

On the other hand, if cables are placed on surface or inside the conduit, air flow is restricted resulting in excessive heating of cables. This reduces the current carrying capacity of the cables.

Maximum current carrying capacity of DC cable

Inference

DC cables represent only 2% of overall capital cost of a solar project but suboptimal selection and/or design can lead to much greater opportunity loss over the years through loss of output, higher operating costs and risk of fire accidents etc.

ESTIMATED LOSSES FOR 1 MW CAPACITY SOLAR POWER SYSTEM

Cable Losses Optimal Units Gain/Loss Monetary Value in INR Gain in INR 2.0% 14,32,690 Decrease in 7,310 units. 35,81,725/-  

(18,275)

1.5% 14,40,000 – 36,00,000/- 1.25% 14,43,654 increase in 3,654 units. 36,09,137/- INR 9,137 1.0% 14,47,309 Increase in 7,309 units. 36,18,274/- INR 18,274 0.75% 14,50,964 Increase in 10,964 units. 36,27,411/- INR 27,411

**Assumed value of 14,40,000 optimal units at a loss of 1.5%.
**Calculation has been done considering 14,40,000 units as reference.

• If the cable losses increase, the numer of units would be Less hence the monetary value will also decrease at the certain rate per unit. Here, the unit rate taken is about 5 INR /unit.
• Due care needs to be given to cable section, specifications and layout bearing in mind project specific factors including site layout, ambient conditions and other equipment selection. Key overall objective should be to minimize leveled cost of power rather than to reduce upfront capital cost of the project. This change in mind-set together with improved technical and operating awareness is critical to successful long-term operating performance and maximizing financial returns from the project. Very importantly, it is clear that DC cable design and performance related issues are still not fully understood. As India marches towards its ambitious goal of 100 GW by and spends billions setting up new solar capacity and the associated infrastructure, both the government and private sector should make more efforts to:

Setting up more technical training and quality testing infrastructure across India.

References:-      1. Bridge to India report on DC cables

2.LEONI Internal Knowledge bank

Indian Solar DC cable Market

India has added solar capacity of 5.5 GW in -17, registering growth of 370% over last 3 years. New capacity addition Y-O-Y can be fairly estimated to be around 9(-/+1) GW in mid term. As the sector growth is heavily dominated by the govt. tenders on reverse auction basis, the whole value chain in under an increasing amount of pricing pressure.

The cut throat competition to keep self in the game, is leading to products designed for price. This also implies inherently inferior quality, safety and performance figures. A sizeable no of poorly performing projects have triggered several quality control measures by MNRE. It is certainly worthwhile to take note of the imminent losses to investors/ end users, as these measures may take time to trickle down to the projects under implementation.

The situation in relatively organized govt. tenders sector (ground mount and rooftop) can be extrapolated to the unorganized sectors like the Rooftop & distributed Solar, Solar home systems & Solar Pumps. While poor operating performance is a certain detrimental for new investors, it coupled with poor safety aspects and lesser longevity it is also expected to drive the end users away.

All of above is sure to bring concerns and doubts for the market and will be an impediment to evolution of the sector into a mature and sustainable market.

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