Semiconductor panels that convert the energy of the sun into electricity are usually installed for one purpose - to ensure the operation of household appliances. These enthusiasts do not stop there and try to adapt solar panels for heating the house. We suggest discussing this idea, consider possible methods of heating using photovoltaic panels. The profitability of alternative power plants and other financial issues does not make sense, it is a separate issue.
How a solar power plant works
We are not going to take your time and talk about how semiconductor modules generate current. But if you want to organize solar heating of a private house, you need to imagine the principle of the photovoltaic station and know all the nuances that affect its power.
The solar power plant (SES) consists of the following elements (shown in the diagram below):
- one or more panels that receive radiation from the sun;
- rechargeable batteries (batteries) that accumulate the generated electricity;
- the controller monitors the charge level, directs the current to the desired circuit;
- the inverter converts the constant voltage of solar panels into alternating current 220 V.
An interesting point. The price of modules is not more than 30% of the cost of a complete set of equipment. The remaining 70% is batteries, an inverter unit and a controller. Accessories are selected for one operating voltage of 12, 24 or 48 volts.
We simplify the algorithm of the system:
- During daylight hours, batteries generate current through the controller.
- The electronic unit estimates the battery charge level, then directs the energy to the desired line - for charging or to consumers (to the inverter).
- The inverter unit converts direct current into alternating current with standard parameters - 220 V / 50 Hz.
There are 2 types of controllers - PWM and MPPT. The difference between the two consists in the method of charging power elements and the magnitude of voltage losses. MPPT blocks are more modern and economical. Different batteries are used: lead-acid, gel, and so on.
If you plan to use several modules, then they are interconnected in 3 ways:
- A parallel connection scheme allows you to increase the current in the circuit. The "negative" contacts of all batteries are connected to one line, the "plus" contacts to the other. The output voltage remains unchanged.
- The use of a serial circuit makes it possible to increase the output voltage. The “minus” terminal of the first panel connects to the “plus” of the second and so on.
- The combined method is used when you need to change both parameters - current strength and voltage. Several modules are connected in series, then a group is connected to a common network in parallel with other similar groups.
How much solar panels do you need to heat a house
It would seem that everything is simple. Approximately 10 kW = 10,000 watts of thermal energy will be used to heat a small country cottage of 100 m². This is 100 panels of 0.1 kW or 34 large modules of 300 watts. You can’t put so many batteries on the roof of the house, but there’s no talk about the apartment.
Reference. The size of 1 photovoltaic cell with a power of 100 W, manufactured by polycrystalline technology, is about 1020 x 700 mm or 0.71 m². A similar 300 W battery will occupy 1.68 m² (170 x 99 cm).
We’ll make a reservation right away, the result obtained is incorrect, since it does not take into account the specifics of operating solar energy systems:
- The photovoltaic module provides maximum power when the rays fall at an angle of 90 ° to the plane of the battery.If you do not make a tracker - a tracking mechanism that rotates the panel after the movement of the sun, we lose about 40% of energy. On the other hand, such a device also consumes electricity.
- The amount of solar radiation per 1 m² - insolation - depends on the region of residence, altitude, and shaded area. These factors directly affect battery performance.
- Over time, the semiconductor coating of the modules degrades, as a result, approximately 1% of the electrical power is lost annually.
- If the photoelectric layer is overheated by the sun, the performance of the panel also decreases.
- A small fraction of the energy is lost in related equipment - inverters, controllers, batteries. This is a banal heating of parts - transformers, microcircuits, and other elements.
- When the work surface is contaminated with dust or covered with snow, additional losses occur.
- Note that for the sun to heat in winter, the generated electricity should be enough to heat the house and charge the batteries overnight.
Conclusion. A universal calculation of the electrical power of batteries suitable for all countries and regions does not exist. But the figure announced above 10 kW must be doubled (at least) to get a decent result in practice. You will need 200 hundred-watt panels covering an area of over 140 m².
There is a reliable way to get accurate insolation data and calculate the performance of solar panels by contacting your local installation company. Or study the insolation map of the area yourself.
We suggest going the other way - to use the experience of owners of solar autonomous power plants, read their reviews on thematic forums. Find there users living in your area if you want to get real numbers for free. Here are some examples:
- Autonomous system of solar power supply, located in the Leningrad region, Russia. 6 panels of 0.22 kW each (a total of 1.32 kW) were installed, and the peak power on a cloudless winter day was 1,157 watts. The topic is discussed at the famous Russian-language forum.
- Anapa, battery performance - 2.2 kW, the number is not indicated. During daylight hours, the power plant generates about 9 kW.
- Moscow, SES power 2.64 kW. Over the whole of June, the installation generated 304 kW of energy.
Note. You will find reviews and other useful data on the operation of the SES at this address.
Please note: we took into account only solar energy for heating, water heating and other household needs were not taken into account. How to calculate the number of batteries in practice, see the video:
Real heating methods
As you understand their foregoing, it is rather difficult (and expensive) to realize full electric heating of a house with solar panels. Not every owner will decide to buy and install panels on an area of 100-150 m² in order to warm up a small house or cottage. So, the scheme of the electric boiler + water system + heating radiators disappears.
But the idea of heating with solar modules can still not be called utopia. We list the options implemented by homeowners in practice:
- panels plus inverter air conditioners with COP coefficient of efficiency 3.5–4;
- connecting batteries directly to electric heaters without an inverter;
- the construction of a full-fledged SES, the sale of electricity to the state, the proceeds go to pay for traditional heating.
Addition. The use of panels as additional energy sources for basic heating does not make sense to discuss - this is an obvious solution.
Let's start with the third option, which is interesting for entrepreneurs. In countries where the state has established the so-called green tariff, the homeowner can receive electricity from renewable sources and give it to the common energy network, making a profit.That is, the homeowner acquires the same 200-300 solar panels, but sells energy at a good price, and does not waste much in vain.
For example, in Ukraine, the green tariff exceeds the usual 3 times (as of June 2019). It is necessary to withstand 1 condition: the minimum capacity of SES is 30 kW. Build a power plant, supply energy to the grid, and you buy three times cheaper.
The remaining 2 options will be considered in more detail.
Air conditioning
The method is based on the efficiency of inverter split systems that deliver four times more heat to the inside of the house than the energy consumed. How to realize such heating:
- First of all, we maximize the heat loss of the building - we insulate the walls, floors and roof, install energy-saving windows. An ideal heat consumption indicator for a home of 100 m² - 6 kW.
- We purchase 2 air conditioners with inverter compressors operating at negative street temperature. The total performance of the units should be equal to the heat loss of the house, in our case - 6 kW. The consumption of such “splits” will not exceed 2 kW.
- We are installing a solar station capable of providing air conditioning around the clock.
- For heating on the coldest days, it is worth installing any traditional source of heat - a boiler, a wood stove.
The video at the end of this section confirms that the described circuit is fully operational. One significant minus: at a negative temperature, the efficiency of air conditioners decreases sharply, you can not do without the help of a boiler. In temperate and northern climates, solar modules alone can not cope.
Note. Most inverter split systems can function in frosts down to -15 ° C. COP efficiency is reduced to 1.5–2 (twice as much heat is generated as electricity is consumed).
Use of local heaters
We are talking about a significant reduction in the cost of the system in the case of using unpretentious consumers - ordinary fan heaters. Due to the lack of an inverter, 12-volt heaters will have to be connected to the solar modules (you can take a car or do it yourself).
How to assemble a solar power generator:
- We install the required number of batteries with an operating voltage of 12 volts.
- We connect them with 2.5 mm² wires according to the diagram below - without an inverter.
- We connect the load - a low-power fan heater of 12 V.
Below in the video, the specialist describes in detail all the nuances of such a connection. The method is suitable for heating individual rooms with fan heaters 1–1.5 kW. It is more difficult to heat the whole house - you need to collect several separate circuits with solar panels, so as not to increase the cross-section of the wires.
Final conclusion
To make full heating of a private house with solar panels is very difficult. The only more or less realistic scenario is the use of split systems, or better, a geothermal heat pump, little dependent on street temperature. The installation consumes little electricity, so it can work from a home SES.
We specifically excluded financial issues from the article, since we were talking about technical issues. But you need to understand that the equipment of solar energy - batteries, batteries, inverters and control units - cost a lot of money. To successfully solve the problem, you need to be a well-earned enthusiast.
A circuit with vacuum manifolds connected to an indirect water heater will be cheaper. But this option has its own difficulties, for example, the accumulation of heat and stagnation of the collector during heat. There is no easy solution to the difficult task of harnessing solar energy.