Contents
With ever-increasing electricity prices, you will inevitably begin to think about using natural sources for electricity supply. One of these opportunities is solar panels for a house or a summer residence. If desired, they can even provide for the needs of a large house.
The device of the power supply system from solar panels and how much it costs
Converting the energy of the sun into electricity – this idea for a long time did not let scientists sleep. With the discovery of the properties of semiconductors, this became possible. Silicon crystals are used in solar cells. When sunlight hits them, a directed movement of electrons is formed in them, which is called electric current. When connecting a sufficient number of such crystals, we obtain quite decent currents: one panel with an area of slightly more than a meter (1,3-1,4 m2) with a sufficient level of illumination can produce up to 270 W (voltage 24 V).
Since the illumination varies depending on the weather, time of day, it is not possible to directly connect devices to solar panels. You need a whole system. In addition to solar panels, you need:
- Battery. During daylight hours, under the influence of sunlight, solar panels produce electricity for the house, cottage. It is not always used in full, its surplus accumulates in the battery. The stored energy is expended by inclement weather.
- Controller. Not a mandatory part, but desirable (with sufficient funds). Monitors the battery level to prevent over-discharging or exceeding the maximum charge level. Both of these conditions are detrimental to the battery, so having a controller extends the life of the battery. The controller also ensures the optimal operation of the solar panels.
- DC to AC converter (inverter). Not all devices are designed for direct current. Many operate on AC voltage of 220 volts. The converter makes it possible to obtain a voltage of 220-230 V.
By installing solar panels for your home or summer cottage, you can become completely independent from the official supplier. But for this you need to spend a decent amount:
- A kit that produces 1,5 kW per day costs about $1000. This is enough to meet the needs of a summer house or a part of the electrical equipment in the house.
- A set of solar panels for the production of 4 kW per day costs about $2200.
- For 9 kW per day – $ 6200.
Since solar panels for the home are a modular system, you can buy an installation that will provide part of the needs, gradually increasing its performance.
Types of solar cells
The solar battery itself is a number of photocells that are located in a common housing, protected by a transparent front panel. For domestic use, solar cells are made on the basis of silicon, since it is relatively inexpensive. Elements based on it have a good efficiency (about 20-24%).
On the basis of silicon crystals, single-crystal, polycrystalline and thin-film (flexible) photocells are made. A number of these photocells are electrically connected to each other (in series and/or in parallel) and brought to the terminals located on the housing. This is called a solar battery or panel.
The photocells are installed in a closed housing. The solar panel body is made of anodized aluminium. It is lightweight and does not corrode. The front panel is made of durable glass, which must withstand snow and wind loads. In addition, it must have certain optical properties – have maximum transparency in order to transmit as many rays as possible. Due to the reflection, a significant amount of energy is lost, so the quality requirements of the glass are high and it is also coated with an anti-reflective compound.
Types of photocells for solar panels
Solar panels for the home are made on the basis of three types of silicon cells;
- Monocrystalline. Each solar cell is one silicon crystal. Monocrystalline solar cells have a good efficiency (about 24,7%), but their cost is somewhat higher. You can distinguish, firstly, by a uniform saturated blue color, and secondly, by the rounded edges of the photocell.
Types of silicon photocells for solar panels - Polycrystalline. Several small silicon crystals are combined into one solar cell. They have a heterogeneous structure, which is why they absorb sunlight worse. This is reflected in the efficiency (20,3%). In fact, this means that a solar panel of the same power will occupy about 20% more area.
- Thin film. They are a semiconductor layer deposited on a flexible substrate. Due to their flexibility, they can be mounted on curved surfaces. They have low productivity (about 10,4%), so they occupy large areas (at least 2 times more than polycrystalline ones).
If you have a pitched roof and the facade is turned to the south or east, it makes no sense to think too much about the occupied area. Polycrystalline modules may well suit. With the same amount of energy produced, they cost a little less.
How to choose the right solar panel system for your home
There are common misconceptions that make you spend extra money on purchasing overly expensive equipment. Below are recommendations on how to properly build a solar power system and not spend extra money.
What to buy
Not all components of a solar power plant are vital for operation. Some serve to increase reliability, but without them the system is operational. The first thing to remember is to purchase solar panels at the end of winter, beginning of spring. Firstly, the weather at this time is excellent, there are many sunny days, the snow reflects the sun, increasing the overall illumination. Secondly, discounts are traditionally announced at this time. Further tips are:
- Buy solar panels for your home with an output voltage of 12 V. It is from this voltage that most household and construction equipment, LED lamps, etc. work. Techniques operating from 24 or 48 volts are much less. You can look at the passports or use the search.
- Do not use incandescent lamps for illumination. They consume too much electricity, and they work from 220 V. Replace them with LEDs. For them, a constant current of 12 V is what you need.
A “complete” solar power system looks like this - Do not try to immediately buy a system of high power to cover all possible needs. To get started, buy a couple of modules without a converter / inverter, connect to them the equipment that runs on DC voltage. If you are satisfied with the system, you can later increase the power, buy an inverter and connect equipment that operates from 220-230 V. And keep in mind that the inverter, even when the load is turned off, consumes electricity (conversion losses are about 30%). That is, at night, when everything is turned off, it simply consumes the battery charge. Moreover, it produces a far from ideal sinusoid. In general, everything that can work from direct voltage is powered directly from batteries.
If you use only these tips, and connect only appliances that operate on constant voltage, a solar panel system for your home will cost a much more modest amount than the cheapest kit. But that is not all. You can leave some of the equipment “for later” or even do without it.
What can you do without
The cost of a set of solar panels for 1 kW per day is more than a thousand dollars. Considerable investment. Involuntarily, you will think about whether it is worth it and what will be the payback period. With current tariffs, it will take more than one year to wait until your money is repaid. But costs can be reduced. Not due to quality, but due to a slight decrease in the comfort of using the system and due to a reasonable approach to the selection of its components.
- Do not buy gel or deep cycle batteries. They are not worth their money. Even used car batteries work great with solar panels for the home. They work fine for at least another 5 years.
If the area is not limited, you can buy a solar battery on polycrystalline photovoltaic cells - In principle, you can get by with even less money. You can not put the controller. It costs at least $150 (and $500 at high power), and its entire task is to monitor the state of charge of the batteries. If the budget is limited, buy a car clock that runs on 12V, which also measures voltage, temperature. They cost 2-5$ and practically perform the same function. And to avoid overcharging, buy an extra battery. Or two. The total power of the “extra” capacity should not be lower than 20%. This will avoid overcharging and increase the capacity of the system.
So, if the budget is limited, you can get by with several solar panels and batteries, the capacity of which is 20-25% higher than the maximum charge of solar panels. For condition monitoring, buy a car clock that also measures voltage. This will save you from having to measure the charge on the battery several times a day. Instead, you will need to look at the clock from time to time. That’s all for a start. In the future, you can buy solar panels for the house, increase the number of batteries. If desired, you can buy an inverter.
Determine the size and number of photocells
Good solar panels for 12 volts should have 36 cells, for 24 volts – 72 photocells. This amount is optimal. With fewer photocells, you will never get the declared current. And this is the best option.
You should not buy dual solar panels – 72 and 144 elements, respectively. Firstly, they are very large, which is inconvenient during transportation. Secondly, at abnormally low temperatures, which we periodically experience, they are the first to fail. The fact is that the laminating film during frost greatly decreases in size. On large panels, due to the high tension, it peels off or even breaks. Transparency is lost, productivity falls catastrophically. The panel is being repaired.
The second factor. On large panels, the thickness of the body and glass should be greater. After all, windage and snow loads increase. But this is not always done, as the price increases significantly. If you see a dual panel, and the price for it is lower than for two “regular”, it is better to look for something else.
Once again, the best choice is a 12-volt solar panel for the home, consisting of 36 photovoltaic cells. This is the best option, proven by practice.
Specifications: what to look for
In certified solar panels, the operating current and voltage are always indicated, as well as open circuit voltage and short circuit current. It should be noted that all parameters are usually specified for a temperature of +25°C. On a sunny day on the roof, the battery heats up to temperatures well above this figure. This explains the presence of a higher operating voltage.
Also pay attention to the open circuit voltage. In normal batteries, it is about 22 V. And everything would be fine, but if you work on the equipment without turning off the solar panels, the open-circuit voltage will disable the inverter or other connected equipment that is not designed for such a voltage. Because for any work – switching wires, connecting / disconnecting batteries, etc. etc. – the first thing you have to do – turn off the solar panels (remove the terminals). After going through the circuit, connect them last. This procedure will save you a lot of nerves (and money).
Case and glass
Solar panels for the home have an aluminum case. This metal does not corrode, with sufficient strength it has a small mass. A normal hull must be assembled from a profile that contains at least two stiffening ribs. In addition, the glass must be inserted into a special groove, and not fixed from above. All these are signs of normal quality.
Even when choosing a solar battery, pay attention to the glass. In normal batteries, it is not smooth, but textured. To the touch – rough, if you run your nails, a rustle is heard. In addition, it should have a high-quality coating that minimizes glare. This means that nothing should be reflected in it. If reflections of surrounding objects are visible at least at some angle, it is better to find another panel.
The choice of cable cross-section and subtleties of electrical connection
It is necessary to connect solar panels for the house with a single-core copper cable. The cross section of the cable core depends on the distance between the module and the battery:
- distance less than 10 meters:
- 1,5 mm2 per 100 W solar panel;
- for two batteries – 2,5 mm2;
- three batteries – 4,0 mm2;
- distance more than 10 meters:
- to connect one panel, we take 2,5 mm2;
- two – 4,0 mm2;
- three – 6,0 mm2.
You can take a larger section, but not less (there will be big losses, but we don’t need it). When buying wires, pay attention to the actual cross section, since today the declared dimensions very often do not correspond to the actual ones. To check, you will have to measure the diameter and calculate the cross section (how to do this, you can read here).
When assembling the system, it is possible to carry out the pluses of solar panels using a multi-core cable of a suitable section, and use one thick cable for the minus. Before connecting to the batteries, we pass all the “pluses” through diodes or diode assemblies with a common cathode. This prevents the battery from shorting out (may cause a fire) if the wires between the batteries and the battery are shorted or broken.
Diodes use type SBL2040CT, PBYR040CT. If these are not found, you can remove them from old power supplies for personal computers. There usually stand SBL3040 or similar. It is desirable to pass through diodes. Do not forget that they get very hot, so you need to mount them on a radiator (you can use one).
The system also needs a fuse box. One for each user. We connect the entire load through this block. First, the system is so safer. Secondly, if problems arise, it is easier to determine its source (by a blown fuse).