How to install a solar panel on a roof
Everyone has probably heard about solar power and the benefits it brings. Renewable energy sources have been actively discussed for at least the last 10 years, and after the Green Tariff law was passed in December 2019, this topic has become a trend. And profitable. At least for companies that put solar panels on the roof of the house. But with the benefits for the owner of a solar home power plant (SES), everything is not so clear.
Usually, companies that sell solar panels entice customers with autonomy, environmental friendliness, savings on electricity and even earning money from selling it to the government. That’s not to say they’re deceptive in doing so. But they do not tell the whole truth, as is customary in advertising.
There are cases where installing solar panels on the roof is really a great investment for the future. In all senses, from conserving nature to making money. But situations where installing a home solar power plant doesn’t make the slightest bit of sense are also not uncommon. The trick is to learn how to distinguish the first situation from the second. And to do this, you need to understand the principles of solar panels, their types and the factors that affect the performance of the batteries.
Briefly about the basics: what solar panels are and how they work
Solar panels are modules that consist of several dozen photovoltaic cells connected in series or in parallel. As soon as light falls on the photovoltaic cell, it begins to produce electricity, and the more intense the light, the more electricity can be obtained. In the middle belt in the summer quality solar panels for the house can produce about 150 W/m2 at peak and about 120 W/m2 in normal conditions.
Types of solar panels
The vast majority of solar panels are made of silicon (Si), but there are promising batteries made of cadmium telluride (Cd-Te) and gallium-copper-indium deselenide (CIS or CIGS). Potentially they will significantly reduce the cost of a home solar power plant, but that’s only in the long run. So far only a few companies in the world produce non-silicon photovoltaic cells, and their price per watt is higher, so such solar panels for homes are almost never used in.
Regardless of the material, solar panels come in three varieties:
- Monocrystalline. These solar panels are made from a single crystal of pure silicon. They have the highest efficiency – up to 22% – in bright sunlight, and degradation of the structure is slower than other types of batteries – manufacturers give at least 25 years warranty on monocrystalline elements.
- Polycrystalline. As the name suggests, these panels are made not of one, but of many differently oriented crystals of silicon. This affects the efficiency – usually it does not exceed 18%, and the service life – polycrystalline panels age faster. Nevertheless, in polycrystalline solar panels are most often installed on the roof of a private house, because they are significantly cheaper than monocrystalline ones.
- Thin-film or amorphous. This type of solar panels is the cheapest, because they require the least amount of silicon. The latest generation thin-film solar panels have an efficiency of only 8-12%, but they work better than crystalline cells in diffuse light conditions – in cloudy weather or shade from a nearby tree amorphous solar panels produce 10-15% more electricity than monocrystalline modules.
In addition to “pure” panels, which are based on one type of material, in the last few years hybrid heterostructured (HJT or HIT) solar cells have appeared. They use both crystalline and amorphous silicon, which increases the panels’ efficiency and improves their operation in conditions of diffused light and elevated temperatures.
How to choose solar panels
Most people choose solar panels on the roof of the house about the same principle as a coffee maker or vacuum cleaner. That is, they are guided mainly by the price, advertising and reviews on the Internet. But this approach is fundamentally wrong: no one is waiting for the vacuum cleaner, which will serve at least 25 years, and even all this time working in the street under the scorching rays of the sun. With such a long lifespan, reviews from people who put solar panels on the roof of their house a year or two ago at most just don’t hold any value. Not to mention the fact that this is a non-mass product, which is why reviews of real people are literally drowning in the mass of custom.
Therefore, when choosing a set of solar panels, it is advisable to consider such characteristics:
- Manufacturer. This is a key factor. The manufacturer of the solar panel should be included in the rating of the largest and, preferably, it should have a full production cycle: from the silicon to the batteries themselves. Yes, you will have to overpay for branded panels, but relatively little – 10-15%, while when buying noname panels there is a risk of losing the entire amount. In this case, do not be afraid of Chinese manufacturers, large companies like JA Solar, Suntech or Helios House produce solar panels of high quality. Although, of course, it is better to choose European or North American companies: First Solar, Canadian Solar, Solarworld, Viessmann Group. Excellent performance and solar panels from Japan and South Korea: Hanwha Solar One, Sharp, Kyocera, Sanyo.
- Tolerance. This is the difference between the nameplate capacity and the real capacity of a solar panel. If the real power is less than the nameplate power, then the tolerance is negative, if more, then positive. Tolerance should be zero or positive, because with a negative tolerance you still pay full price, that is, you pay for non-existent watts. With cheap panels, negative tolerance is acceptable, but only if it is no more than 2-3%. This means that with a rated power of 100 kW/m2 the panel should deliver at least 97-98 kW/m2.
- Temperature coefficient. As the temperature increases, the output of the solar panel decreases. The temperature coefficient shows how much the power will drop as the temperature rises, so the lower it is, the better.
- PTC value. So that solar panels from different manufacturers can be compared, they are tested under standard conditions (STC). These conditions are far from realistic, so an independent PTC standard was developed that better reflects the panels’ operating conditions. The closer the PTC/STC ratio is to one, the better the solar panel will perform on the roof of your home.
- Panel efficiency. Here it’s simple: the higher the efficiency, the better the panels convert solar energy into electrical energy. Permissible efficiency is considered to be 15%, but the optimal figure is higher – 18-20%.
- Warranty period. We have already talked about the panel warranty of 25 years. This is the minimum period and the actual industry standard. Therefore, if you want to buy a solar panel for the house, rather than a portable solar module for camping, pay attention to the warranty period and always study the terms carefully.
Now for the price. For most people this is the main parameter of the system, but we recommend looking at it last. Over the long haul of decades, branded and expensive equipment is often more profitable than cheap equipment. Such solar panels age more slowly, produce more power per unit area, and often have positive rather than zero tolerance. All this will compensate for the high initial cost after 5-8 years of operation. Of course, we are talking about justifiably expensive equipment. For example, it is better to buy a solar panel for the roof from monocrystalline cells of a top manufacturer than the same panel made by a small company. If you buy panels that are made with the latest technology or fancy modules in the form of shingles and other roofing materials, then it is difficult to call it a rational purchase.
Also, do not look at the price of the entire battery, but at the cost of 1 watt of energy. This is a more informative indicator, since the capacity of solar panels of the same size, but different manufacturers often differ by tens of percent.
What affects the performance of a solar power plant
The maximum output of a home solar power plant is limited by the capacity of the solar panels. But how much electricity the system will produce in real conditions depends on a number of things that are not always obvious to the buyer.
Quality of equipment
In addition to the solar panel itself, the home SPS includes at least two other devices: a controller and an inverter. And usually they are selected according to the residual principle. Because of this, losses on them can reach 20-25%. That is, you will receive only 75% of the energy generated by solar panels, only because you did not pay enough attention to the choice of inverter and controller. For comparison, the standard loss should not exceed 5%.
A quality inverter is, first of all, a device with high efficiency – from 95%. And this should be a real efficiency, not just numbers on the case. For example, medium and small Chinese manufacturers often overestimate their inverters, but in reality their efficiency may be 85% and even 80%. So it is better to choose controllers and inverters from European, Japanese or American manufacturers. The products of Chinese factories, with the exception of very large manufacturers, should be purchased only if there is an opportunity to check whether the real efficiency corresponds to the nominal one.
In addition, over time, the inverter and controller will need to be replaced. And the higher quality it will be, the later such replacement will be needed. For example, the top devices are replaced after 15-16 years, while cheap inverters often fail before 5 years of service.
The efficiency of conversion of solar energy into electrical energy depends on the angle at which the sun’s rays fall on the panel. In this angle is maximum if the panel is directed strictly to the south. In this case, the home SES will produce the greatest power. Southeast and southwest direction is slightly worse, but it is also a good option – the power will be lower, but insignificantly. To direct the panels to the west, east and, even more so, north is undesirable because of the strong decrease in the performance of the home solar power plant.
If the slopes of the house are directed to the west or east, it is more advantageous to put the panels directly on the ground. This installation of solar panels is a little more expensive because of the foundation and the need for a strong frame, but these costs are recouped by the higher productivity of the panels.
Level of insolation
Not all regions are suitable for the installation of solar panels. In the north of the country, including St. Petersburg, the insolation level is too low for solar panels to have acceptable efficiency. This, again, is due to the angle of incidence of the sun’s rays, only this time not horizontal, but vertical. And the closer to the south, the higher the sun is above the horizon and the more sunny days.
In addition, the angle of the solar panels depends on the geographic coordinates. In the north, they should be placed at a large angle, and as you move south, this angle decreases until it becomes almost zero at the equator.
Regardless of the level of insolation, the output of the solar panels can be increased by placing them on rotating platforms and connecting them to a sun-tracking device. The device rotates the solar panel throughout the day so that it, like a sunflower, is facing the sun at all times. To do this, the panels are mounted on a holder that is parallel to the polar axis. This is the method of mounting that the last line in the table describes. Rotating devices are very effective, but at the same time they are expensive, so solar panels for home are equipped with them rarely.
Have you built a house right in the woods in the shade of tall trees? Congratulations – it’s beautiful and environmentally friendly, but put solar panels on the roof of such a house is unlikely to succeed. Or rather, you can install them, but the efficiency of the panels in the shade is low. The same applies to any other shade, such as from a nearby apartment building or a large cottage neighbor. If there is shade, you must either remove an obstacle, such as a tree, or install the panels not on the roof, but on the sunny part of the homestead.
5 real reasons to put solar panels on your roof
Solar panels are a hot topic. Proponents of this technology attribute many advantages to it, often nonexistent. Opponents, on the contrary, deny even the obvious benefits. The truth, as always, is in the middle. Installing solar panels on the roof of the house in some cases is more than justified for five reasons:
- Autonomy. For homes away from civilization, solar panels are a real godsend. Unlike generators, which can run out of fuel, the sun will always shine. At least for the next five billion years. Therefore, based on solar panels you can build a truly autonomous power supply at home.
- Eco-friendliness. “Greens” actively argue with the environmental friendliness of solar panels, rightly pointing out that the production of some of them consumes more energy than can be obtained over their lifetime. Except that the panels are made thousands of miles away from your home, and the gasoline generator poisons the air on your porch. Therefore, solar panels are clearly more environmentally friendly.
- Protection against power outages. For security and fire alarms, a heating boiler and even a refrigerator, a long power outage causes problems. Solar panels provide uninterrupted power to critical consumers in all conditions, even at low power.
- Power savings. Mounting solar panels on the roof of the house greatly reduces the cost of electricity bills. And the payback period of the panels is only 7-10 years, depending on tariffs and monthly consumption. After that, they begin to bring a net profit.
- Increasing the service life of the roof. Although this is a side effect of installing solar panels, it does not become less significant. When properly installed, solar panels protect a significant portion of the roofing material from precipitation and also reduce the amount of ice on the slopes, as they emit heat during operation.
Of course, these benefits must be weighed against the effectiveness of solar panels in specific conditions, as well as the cost of the system.
Installing solar panels in a private home
Installing solar panels on the roof is a complex task, because you need not just fix the batteries on the roof, but also to properly connect them and assemble them into one system. Therefore, installation should be carried out by specialists. In this case, the preparatory phase of work – the responsibility of the owner of the house.
At the preparatory stage you should assess the condition of the roof. Installing solar panels on the house makes major repairs to the roof very expensive, so you must be sure that the roof will last at least another 25 years. If you have any doubts about this, it is better to re-shingle the roofing.
Make sure that the rafter system will withstand the additional load. On average the panels themselves weigh 15-18 kg/m2, which is usually not critical. But if the roof is sloping, the batteries are sloped with the help of retaining structures. In this case, the snow will accumulate on the slope itself and on the panels, and then the load can become significant. If you have such a case, reinforce the rafter system with shoring and additional stops.
Finally, always check what installation kits the builders will use. Avoid homemade – branded mounting kits are carefully calculated by the manufacturers and, most importantly, tested. Therefore, they can withstand storm winds and heavy snow weight without any problems, which cannot be said about homemade brackets and rails.
For the rest you will have to trust the installation team. At the same time try to monitor the quality of work at each stage. This will help you video, which shows the features of the installation of solar panels on the roofs of different materials:
Solar panels – a progressive “green” technology that allows you to make a home autonomous and independent of the local electricity supplier. In addition, it can help you save money on your electric bill and extend the life of your roof.
When choosing solar panels, you need to consider their manufacturer, tolerance, temperature coefficient, efficiency, PTC and warranty periods. But even the best solar panels will perform poorly if you point them north instead of south, install them in a location where the shade falls, and save money on other elements of the system: the controller and inverter.
Solar panels should be installed by professionals. But control over the quality of work, as well as the preparatory phase is usually the responsibility of the homeowner. It is necessary to check the condition of the roof, to make sure that it can withstand the additional load, and to ensure that the batteries are installed on branded mounting kits.