Additional considerations in choosing a photovoltaic system

Guaranteed Returns

From the perspective of an individual, following recent economic events, one can examine the option of installing a grid-tied photovoltaic (PV) system as an investment that yields a known annual interest rate for 20 years. This is similar to a long-term deposit, which, according to current cost and average energy output data, carries an annual interest rate of 10%-12%, depending on the installation cost and geographical area. Those seeking a solid investment with a green connection and a touch of economic and energy independence will find considerable logic in such an installation. By the way, not everyone is aware that currently, according to safety requirements, if there is a power outage, the solar system cannot be used as a backup.

Long-Term Installation

If there is one characteristic that stands out in installing a photovoltaic system, it is its long-term nature: the contract with the electricity company lasts for 20 years, at a fixed price indexed to inflation. The system is expected to operate without moving parts, noise, or significant maintenance. The aim is to invest a one-time amount and effort to ensure a deterministic future that will generate profits and economic security for the system owner. All these factors lead to the choice of products and technologies that will withstand the test of time and provide stable output with high efficiency.

Quality Matters

A photovoltaic system consists of two main components: solar panels and inverters. However, upon closer inspection, we find that the quality of wiring and connectors also plays a significant role. Imagine the need to climb to the roof of a building or barn after 10 years to find the faulty wire that has brought the system down, disassemble and replace it, and probably the other cables as a preventive measure. In such a long-term view, reliability and quality are what matter, and unfortunately, these not only come with a return but sometimes also a price. In this case, it seems that the famous Polish saying, "You don’t buy cheap," is indeed grounded in reality.

Here are the components of the system, their expected lifespan, and the types of warranties that can be obtained from manufacturers:

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Solar Panels (MODULES)
A solar panel is expected to last up to 25 years, and typically the manufacturer’s warranty covers up to 20 years. The problematic point is environmental damage such as weather (all installations in Europe are equipped with lightning protection) and vandalism. The larger the installation, the harder it is to locate the source of the malfunction and repair it. Sometimes, there may even be a decrease in performance due to dust accumulation.

There are several leading technologies in the PV field, and we will mention a few main characteristics of each:

1. Silicon-Based Solar Cells (Mono/Poly Crystalline)

   • The oldest and most common technology today.
   • High efficiency of power per square meter (up to 19%).
   • Average panel weight of 22 kg.
   • Sensitivity to the angle of sunlight and inability to utilize diffused light.
   • Performance drop of about 15% with panel heating (on a hot day with full radiation).

2. Thin-Film Solar Cells (THIN FILM)

   • Developing technology.
   • Low efficiency of power per square meter (up to 12%).
   • Average panel weight of 23 kg.
   • Low price per watt.
   • Low sensitivity to the angle of sunlight and ability to utilize diffused light.
   • Less sensitivity to heating - performance drop of about 5% with panel heating (on a hot day with full radiation).
   • Overall the same installation price in a larger area, but with an increase in accumulated energy in warm and/or cloudy areas.

3. Flexible Panels Based on Amorphous Silicon/CIGS

   • New technology similar in characteristics to thin-film technology.
   • Flexible panels for easy installation in problematic contour areas.
   • High price.

4. Building Integrated PV (BIPV)

   • Architectural building blocks with the ability to produce solar electricity (such as tiles, windows, and walls).
   • Typically based on THIN FILM technology.
   • Usually, the efficiency will be even lower than that of TF due to location and angle constraints.
   • The installation of BIPV is characterized by irregular uniformity and shading issues, so it is advisable to pair it with an inverter designed for parallel operation.

Solar Inverters (INVERTERS)

In the financial planning of a grid-tied photovoltaic system, the assumption is that an inverter will be replaced after 10 years. In practice, based on the limited variety of high-quality and reliable inverters available in the market, the calculated lifespan of an inverter exceeds 15 years. Manufacturers provide a basic warranty of 5 years and an extended warranty of 10 years (for a fee), and some even express such confidence in their products that they are willing to offer warranty extensions up to 20 years (for an additional fee) under certain conditions.

Internal load distribution and the dispersion of accumulated operating hours are key to extending the lifespan of the inverter.

The inverter is the component most susceptible to faults in the system, as it is the most complex and intricate, and therefore has the highest likelihood of failure. If an inverter fails, the result is an immediate profit loss that can reach up to 500 shekels per day. Here, it is advisable to read the "fine print" and consider the type of warranty and the response times of the inverter manufacturer/installer.

There are two main architectures from which inverters are constructed:

1. High-Frequency Transformer (HF)

   • An inverter using the HF method is based on two conversion stages (DC to DC and DC to AC) and achieves optimal efficiency across all its operating ranges.
   • The HF transformer provides galvanic isolation that prevents many potential safety issues and allows operation with all types of panels.

2. Transformer-Less (TL)

   • An inverter using the TL method does not contain a transformer and is based on a single conversion stage from DC to AC.
   • This architecture allows for peak efficiency but has potential insulation and safety issues that require additional built-in mechanisms in the inverter.
   • Some panels are not suitable for use with TL inverters, such as SUNPOWER, which requires connecting the positive DC pole to ground.

Efficiency vs. Energy

Actual Solar Voltage Inverter Efficiency

Generally, when referring to a photovoltaic system, people tend to look at the efficiency percentages of the inverter. In this context, it is important to pay attention to the weighted efficiency, also known as EU Efficiency, rather than the maximum efficiency, which occurs only at one operating point and does not represent the device's actual performance. The weighted efficiency calculation takes into account the efficiency at various loads of the inverter. Since this calculation is based on conditions in Europe, it does not mean it is entirely suitable for conditions in Israel, but it serves as a comparison tool "apples to apples" between different inverters.

Solar Cell Efficiency

There are several PV technologies that differ in energy efficiency per unit area, sensitivity to heating, and ability to work with diffused light. All these contribute significantly to the total accumulated energy that the system can produce.

Cable Losses

Energy losses in the system directly lead to income losses. Beyond what has been mentioned above, there is significance to energy losses due to the resistance of the cables.
Connecting the panels in series creates a high working voltage that leads to a lower working current, thus minimizing cable losses (the losses stem directly from the current intensity and cable resistance).
Therefore, the guiding principle is to minimize cable lengths, meaning to place the inverters as close as possible to the solar panels. However, reality often imposes other constraints that often contradict this aspiration, so it is necessary to compensate for cable distances by using cables with a larger cross-section. Thus, a wise installation of a solar panel array will be carried out with several types of cables, where the ones with the larger cross-section will be connected to the panels that are farther away from the inverters.

Accumulated Energy

Ultimately, what matters is the amount of energy produced by the inverter, which is measured in the same units as electricity charges – kilowatt-hours. This is where those performance differences between inverters, which are difficult to quantify from just reading data sheets, come into play. The difference often lies in the ability to utilize the beginning and end of the day, during which the load on the inverter is partial and some inverters may not be able to operate at all at these outer limits.

Environmental Conditions and Protections

A photovoltaic system is expected to operate in outdoor installation conditions. The main influencing factors are:

• Temperature
• Dust
• Wind
• Lightning

Temperature and Power
Ambient temperature affects both the performance of the solar panels and the performance of the inverters.
In principle, the higher the ambient temperature, the lower the performance.
Inverters, like any other power system, have a temperature at which the maximum possible power begins to decrease with rising heat. This is due to both temperature-dependent performance degradation and built-in protection in the inverter. This process is called POWER DERATING, and the point at which it begins significantly impacts the actual power that the inverter can provide in a hot environment. In principle, inverters without adequate cooling will begin the DERATING process at a lower ambient temperature, thus not providing the maximum power specified in practice.
Therefore, even though inverters are generally designed for outdoor installation, it is recommended to install them in conditions with minimal heating, such as shaded areas or even inside a building.

Environmental Protection Standards – Sealing
The IP (Ingress Protection) standard measures the degree of protection of electrical equipment against dust and moisture. The higher the value of IP, the more robust and protected the equipment is.
Inverters designed for outdoor use should have at least IP65 protection, which provides full protection against dust and moisture, while less demanding equipment can function with a lower standard of IP54 or even IP55, especially if they are installed in shaded areas.

Dust
Accumulation of dust on solar panels significantly reduces their performance. A light dust layer can reduce power production by 10%-20%, while layers of dirt or bird droppings can lead to losses of up to 40%. Regular cleaning of solar panels is a must, especially in dry and dusty areas, as well as in agricultural areas where dust accumulation is significant.

Lightning
When planning and installing a photovoltaic system, you should consider the possibility of lightning strikes and take precautionary measures. In Israel, it is recommended to ground the solar panel array and install surge protection at the inverter. It is also advisable to equip the inverter with a connection to a grounding point.

Conclusion

Solar panels constitute an investment whose profitability is measured over many years. As part of this significant investment, one must recognize the importance of the components that make up the system, as they directly affect the long-term performance of the installation. As mentioned, sometimes these products are worth their price, so it is advisable to study the market, examine different manufacturers, and always try to get a warranty that guarantees the product’s performance over time.

to schedule a meeting
Call Advis 912 03-9000
Fax number 1533-9000-930