How to choose a solar panel
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How is energy generated in solar panels and what factors affect efficiency?
A solar panel is a set of photovoltaic cells, each of which is made of two layers of semiconductor - P-type and N-type. The most popular material is silicon, but phosphorus is also mixed in to improve energy production efficiency. In simple terms, when sunlight hits a surface, electrons are released and move in an orderly manner, which is essentially the definition of electric current.
The process can be schematically represented as follows:
One module can consist of a different number of photovoltaic cells. There are also several ways to process silicon. The maximum efficiency (efficiency) of a solar panel depends on these characteristics, on the basis of which power is calculated for specific projects. But the amount of energy received also depends on secondary conditions related to location and maintenance.
Choosing a solar panel will be much easier if you determine all the factors that affect the efficiency of electricity generation:
- Manufacturing method and number of photovoltaic cells;
- Manufacturing materials;
- Daily solar activity;
- Presence of clouds;
- Direction and angle of inclination of panels;
- External surface contamination level.
It is important to understand that solar panels are only a part of a complete system, and additional equipment will be needed to implement the project:
Since the main volume of annual generation occurs from April to October (70%), there is no point in considering the use of solar energy for electric heating in winter. But when deploying a large-scale “farm” to earn money, this option is also possible. In most cases, home solar power systems cover daily household needs, with the option of storing excess in batteries for backup power on cloudy days.
Advantages of stationary and portable models depending on terrain conditions and purpose
When choosing solar panels, it is important to determine their purpose. Manufacturers offer portable and stationary equipment that is suitable for specific conditions.
Portable solar panels
Designed to meet minimal needs and occasional use. This is a mobile option for a summer house, picnics, car, tourists and extreme sports enthusiasts. The design is most often foldable and fits into the trunk or backpack.
To deploy such a system, it only takes a few minutes; no tools or experience are needed. Most often, panels are equipped with controllers and all the necessary connectors for powering laptops, mobile gadgets, USB lamps, etc.
Advantages of portable solar panels:
- Small size and weight;
- Easy to install and operate;
- Does not require additional costs;
- Availability of USB / DC connectors.
The disadvantage of portable solar panels is the limited output power, which rarely exceeds 300 W. This is not enough to cover the needs of household appliances, power tools and heating systems. The best use case is creating backup LED lighting, recharging smartphones, power banks, flashlights, powering computer equipment, network equipment, and portable speakers.
Stationary panels
Designed for the implementation of complex projects aimed at creating an autonomous energy supply for a private house or apartment, earning money on the “feed-in tariff”. Installation is carried out on the ground or roof using special structures that can have different functionality. Some are fixed, others allow you to manually change the angle of inclination depending on the season. The most advanced are solar trackers that automatically rotate panels following the movement of the sun.
Stationary solar modules are assembled into a single system and are capable of generating sufficient energy to power household appliances and even heating equipment. The output power will depend on the number of panels, and, accordingly, on the size. Such systems can occupy tens of square meters for domestic use and hectares in the case of business projects.
Advantages of stationary solar panels:
- Provide complete autonomous power supply;
- Allows you to earn money from excess generated power.
It is important to understand that installing solar panels is not cheap, and the payback period is about 10 years. This is a long-term project for many years to come. Low-quality panels wear out faster and lose efficiency, generating less electricity. Let's decide what characteristics you need to pay attention to in order to make the right choice.
What type of crystalline coating should I choose to obtain maximum efficiency?
Solar panels can have different silicon crystal structures. Production technology determines the type of panel, its maximum efficiency and other properties.
There are 3 main types of solar panels on the market:
To make it easier to compare the characteristics of each type, we suggest that you familiarize yourself with the table:
| Index | Monocrystalline (Mono-Si) | Polycrystalline (Poly-Si) | Thin film (TFSC) |
|---|---|---|---|
| Efficiency / efficiency | High (up to 22%) |
Average (before 18%) |
Low (about 10%) |
| Durability | High (about 30 years old) |
High (about 25 years old) |
Low (about 10 years) |
| Temperature coefficient | Low | High | Average |
| Price | High | Average | Low |
Obviously, monocrystalline modules are the most advanced, which affects the cost. They are made from a single piece of silicon with various additives to increase efficiency and durability.
Mono-Si panels reveal their full potential when in direct contact with the sun's rays and are optimally suited for southern regions. Low temperature coefficient minimizes losses when heating the surface. Although even with diffused light, the efficiency will be quite large, which makes them the most popular. The panels allow you to get maximum energy (about 1 kW out of every 6 - 8 m²), so they fit well into the limited area of a private household. Visually, they can be identified by the rich black color of the surface.
Polycrystalline modules are made up of multiple silicon crystals, making them effective at handling diffuse or high-angle light (sunset and sunrise). Poly-Si is optimal for regions where there is little solar activity throughout the year and the sky is often overcast. It is worth noting that the difference in efficiency between single crystals and polycrystals is small, but the latter require a large surface area to generate electricity (about 1 kW out of every 8 - 10 m²). Thus, polypanels are well suited for global projects where there are no size restrictions. The modules have a good price/efficiency balance, so the payback is faster. But you need to take into account the high temperature coefficient - when heated from direct sunlight, the efficiency decreases. Surfaces are visually highlighted in blue.
Thin film panels are characterized by increased flexibility and minimal weight. They are easy to stick on the roof of a house or car, fasten them to supports and frames, bend them at different angles and take them with you on the road. Thin wafers of silicon don't produce much power, but output is more consistent regardless of solar angle and heat. The stumbling block is low durability and rapid loss of generation efficiency with each year of operation. The flexible design features also prevent the creation of reliable protection against mechanical damage, which is inherent in mono and poly panels.
How to calculate power for various projects?
The first step is to determine the actual electricity consumption taking into account peak loads. To do this, you need to carry out calculations based on the characteristics of all household appliances. Let's look at the example of a small private house with an area of about 100 m² in the summer.
The main consumers are:
- Refrigerator – 150 W;
- Computer/laptop – 200 W;
- TV – 100 W;
- Dishwasher – 1500 W;
- Washing machine – 1500 W;
- Iron – 1500 W;
- Microwave oven – 600 W;
- Oven – 600 W;
- Air conditioning – 2000 W;
- Indoor and outdoor lighting – 300 W;
- Chargers for gadgets – 15 W.
The total figure will be very large, but it is impossible to even imagine the simultaneous use of all devices. The main consumer in this case is the air conditioner. Considering the area, this can be one powerful device with a central air duct or 3 conventional split systems installed in different parts of the house (kitchen, corridor, bedrooms).
Therefore, it is necessary to determine the maximum that a family can consume during the day:
| Equipment | Power consumption, W/h | Total power, W/h |
|---|---|---|
| Fridge | 150 | 4700 |
| PC | 200 | |
| TV | 100 | |
| Air conditioner | 2000 | |
| Dishwasher, washing machine or iron | 1500 | |
| Microwave or oven | 600 | |
| Indoor or outdoor lighting | 150 |
Thus, providing a total panel power of 4700 W/h, a private home and all its users will be able to fully function without any special restrictions.
Now let's calculate how many panels will be needed to achieve the desired figure, and how much area the home solar power plant will occupy. Let's take as a basis a standard stationary monocrystalline battery with a declared rating of 400 W and dimensions of 1700 x 1000 mm (1.7 m²). It is worth considering that the figures are relevant under ideal conditions in which products are tested at the production stage (STC). Actual generation rates (NOCT) are usually lower and depend on many factors that we identified at the very beginning of the article. Please read the product data sheet carefully. Trusted brands always indicate standard and nominal parameters.
The estimated power of the panel will be 320 W. As a result, we will need 15 such modules (15x320=4800 W/h), and the occupied area will be at least 25.5 m². But that’s not all, since the volume of generated electricity decreases in the morning and evening due to the high angle of the sun’s rays, as well as in cloudy weather. Moreover, part of the energy will be spent on charging the batteries (another about 20%). Therefore, the user then has 2 options:
- Leave the calculated power output unchanged. In sunny weather, production will be maximum and sufficient. In other conditions, you will have to use backup batteries, central power supply, or reduce consumption (for example, turn on 1 air conditioner at the same time or at minimum power).
- Compensate for possible losses (about 40%) by installing additional panels (about 6 pieces), which also increases the occupied area to almost 36 m².
Thus, it is quite possible to place such a solar power plant (solar power plant) on the roof or in the yard. The surplus can be given to the state, making a profit, or spent on site maintenance (lighting, watering) or entertainment (swimming pool, electric grill, attractions).
Manufacturer's warranty on technical components and productivity
Many countries and manufacturers are offering their developments in the field of natural energy generation. But it is impossible to visually determine the quality of production of products. To do this, you need to pay attention to two main indicators:
- General guarantee for the product(integrity of the frame, protective glass, performance).
- Guarantee for maintaining productivity(there are different names - real degradation period, guarantee of compliance with power level, etc.).
A sign of good quality is a general guarantee for a period of 10 - 15 years. The second indicator is more specific and useful. It displays generation efficiency of at least 80% of original values over a period of 25 years. This way, you can be sure that electricity generation will be efficient and cost-effective throughout its entire lifespan.
When purchasing a solar panel, two warranty cards must be issued, and you need to pay attention to the periods specified in them. Otherwise, you run the risk of buying a low-quality product that will break down even before the breakeven point, and you won’t be able to replace it under warranty.
When choosing, it is important to pay attention to the availability of service centers in the country or region. This will make it easier to solve problems related to connecting, maintaining and replacing solar panels.
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