solar energy. Potential, resource assessment, barriers. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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solar potential

The annual input of solar energy varies from 900-1000 kWh/m2 in the north of the Baltic Sea region to, for example, 1077 kWh/m2 in Central Europe (Bohemia) and up to 1600 kWh/m2 in the Mediterranean and Black Sea regions on a horizontal surface. In the south, on a sloping surface, the annual solar energy input is 20% higher.

Resource rating

The available solar energy varies throughout the day due to the relative motion of the Sun and depending on cloud cover. At noon in clear weather, the irradiance generated by the Sun can reach 1000 W/m2, while in dense cloudy conditions it can drop to 100 W/m2 or even lower, even at noon. The amount of solar energy varies with the angle of the installation and the orientation of its surface, decreasing as you move away from the south direction.

Commercially manufactured photovoltaic cells have a specific power rating, expressed in watts of peak power (Wp). This is an indicator of their maximum power under standard test conditions, when solar radiation is close to its maximum value of 1000 W / m2, and the surface temperature of the photocell is 25°C. In practice, photocells rarely have to work in such conditions. Approximate power (P) of a photovoltaic system is estimated by the formula:

P (kWh/day) = Pp (kW) * I (kWh/m2 per day) * P where:

Pp is the nominal power in kW, equivalent to the efficiency multiplied by the area in m2, I is the solar exposure on the surface, in kWh/m2 per day PR is the system performance factor.

The average daily value of solar irradiance (I) in Europe in kWh/m2 per day (tilt to the south, tilt angle to the horizon 30 degrees) is given in the table.

Typical Performance Factors:

• 0,8 for systems connected to the network;
• 0,5 - 0,7 for hybrid systems;
• 0,2 - 0,3 for autonomous systems used all year round.

In European conditions, the incoming solar energy in most cases exceeds the energy consumption of the building. For example, a typical multi-family residential building in the Czech Republic receives 1077 kWh/m2, while each floor consumes approximately 150 kWh/m2 for heating and another 25-50 kWh/m2 for lighting and cooking, which in in general equals 875 - 1000 kWh/m2 for a five-story building (floors are measured in m2 of horizontal surface). The solar energy supplied during the year is generally sufficient, but the useful resource is limited by solar energy fluctuations and storage capacity. A correct assessment of the share of useful solar heat can be made taking into account different heat loads.

The limitations of embedded systems are usually that solar heating can only cover 60-80% of hot water demand and 25-50% of heating. It depends on the location of the house and on the type of system. In Northern Europe, the limits are respectively 70% and 30% for hot water and space heating.

Analysis and experience with solar central heating systems show that they can cover 5% of consumption without storage, 10% with 12-hour storage, and about 80% with seasonal storage. These data are based on district heating systems in the residential sector, where the average heat loss is 20%. Solar heating systems without heat storage are by far the cheapest solution.

Solar heating can provide about 30% of the needs of industrial enterprises that use heat below 100 ° C, if their heat consumption is stable. Depending on the time of year and temperature, solar energy can provide 100% of the need for drying products.

Solar heating of swimming pools can almost completely cover the heat load of indoor pools and 100% for outdoor pools in summer.

Thus, calculating solar heating potential is mainly a matter of assessing low temperature heat demand.

Barriers

For the most part, solar heating installations are well developed, and if difficulties are encountered in the way of their development, they are caused more by the lack of certain materials or technologies in a given place, than by the absence of technologies as such. Therefore, the main barriers, in addition to economic ones, are:

• lack of information about existing technologies, their optimal solutions and integration into heating systems;
• lack of qualified personnel for production and installation.

Sometimes the obstacle is the lack of solar energy. With regard to active solar heating systems, it is almost always possible to find a place to install a collector from where you can take the energy of sunlight. In the case of passive solar energy, which typically enters through ordinary windows, the proximity to houses or trees can lead to a serious reduction in incoming energy.

Even after the dramatic price reduction, photovoltaic cells currently cost US$5/Wp. Electricity from solar cells today costs 1 - 0,5 dollar / kWh, that is, more expensive than from other renewable sources. In the future, as they become more widely used, the cost of solar cells should decrease. Despite its high cost, photovoltaic energy can be cheaper than other sources in remote regions cut off from the power grid, or where electricity generation by other means (for example, diesel generators) is difficult or unacceptable for environmental reasons (for example, in mountainous areas) .

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