Hydropower is one of the oldest forms of energy used and is most often produced in hydropower plants (HPPs). In them, the water flow falls on the turbines, turns them and generates electricity during the rotation process. In 2019, about 16% of all electricity consumed in the world was generated using hydropower. In 2020, in Latvia, approximately 44% of the total amount of electricity was generated using hydropower.

There are three types of HPPs:

• with water storage reservoirs,
• river run-offs,
• pumping plants.

HPPs with a water storage reservoir are most often built. Then it is possible to use the stored water at a time when there is a high demand for electricity or when there is a supply disruption from other countries. The water storage reservoir reduces dependence on the hydrological regime of the river, which can change due to different weather conditions. The volume of river water flow is particularly badly affected by extreme heat, significantly reducing the amount of water in it. Most electricity can be generated from HPPs in the spring months, when snow melts and water supplies in rivers increase.

Although HPPs are one of the most advanced renewable energy technologies, it is still possible to increase the amount of electricity generated in them without increasing the size of the water storage reservoir. The efficiency of HPPs can be improved by using more modern turbines, thus increasing the water flow force falling on the turbines, as well as by digitising HPPs.

Latvenergo AS generates most of its electricity from three Daugava HPPs – Pļaviņas, Ķegums and Rīga, the total installed capacity of which was 1,558 MW in 2020.

Solar energy has the highest potential for providing electricity and heat compared to other RES. Solar energy can be used to heat buildings without additional technologies, as well as it can be converted into heat and electricity with special technologies designed for this purpose.

Compared to other RES, the use of solar energy is a relatively contemporary solution for energy generation. Extensive development of solar energy technologies and installation of solar panels in the world only started in around 2005, while in Latvia, it started even later – around 2012. However, solar energy is currently the third most widely used RES in the world. Although the use of solar energy has begun to flourish, only 1% of all electricity generated in the world in 2019 was generated using solar energy technologies.

In Latvia, the use of solar energy is developing more rapidly as a microgeneration solution in households and individual solar plants for companies, which is mainly intended to ensure their own consumption.

Solar energy technologies convert sunlight and solar heat that reach the Earth into energy. Solar panels that capture photovoltaics from sunlight are used to generate electricity. Heat energy can be obtained with solar collectors, which make the solar heat that reaches the Earth usable for home heating or hot water preparation.

All solar technologies work on a similar principle – the basic technology captures solar radiation (heat or light), concentrating it at some point and converting it into heat or electricity. It is especially important to position the technologies correctly so that the sun shines on them for as long as possible. Most often, solar panels and solar collectors are recommended to be placed to the south with a slope of 42˚ to the horizon.

Solar energy technologies are constantly being developed to increase the amount of energy generated or to make the plant more environmentally friendly and easier to recycle. Solar panels and collectors that follow the sun's rays are also developed so that they remain perpendicular to the rays for as long as possible. In this way, following the sun, it is possible to generate up to 30% more electricity than with a statically placed solar panel.

Elektrum Solar is an opportunity to use independently generated electricity by using sunlight.

• If you have a property with a possibility to install solar panels on the roof or ground, you can generate green electricity independently and use it free of charge for at least 25 years from the first day of installation of solar panels.

Similarly to hydropower, wind is one of the oldest sources of energy. Initially, it was used to operate a windmill, but is now one of the leading technologies for the generation of renewable electricity, despite the volatile nature of wind and the challenges of forecasting wind intensity in the long term. In terms of energy generation, the higher the wind velocity, the more energy can be generated. Therefore, it is possible to get the most electricity from wind in the autumn and winter months.

The amount of wind energy in the total amount of electricity generated is highly dependent on the region's willingness to use and develop the wind energy sector. In total, only 5% of the world's electricity is generated from wind. The European Union (EU) has a higher share of wind energy, providing around 16% of total EU electricity production. The EU generates the most wind energy in Germany and Denmark. In Latvia, wind energy provides only 3% of the total amount of electricity generated.

Wind energy is generated by wind turbines or wind generators. Both vertical axis and horizontal axis wind turbines are available on the market. Horizontal axis wind turbines are most often installed in wind farms both onshore and offshore. Wind farms at sea are called offshore wind farms. They have the greatest growth potential, as their installation is not restricted by land use regulations, buffer zones or land ownership. Compared to onshore wind farms, offshore wind farms generate more electricity as it is possible to install higher wind turbines and offshore wind velocity is much higher than onshore.

Every year, more and more new wind farms are opened, both onshore and offshore. In Latvia, all wind power plants (WPPs) have been installed on land, and wind capacity has not been increased since 2017. Most of the WPPs are located on the coast of Kurzeme, which in terms of wind resources, is one of the richest regions in Latvia as well. Equivalent wind velocity is also available elsewhere in the highlands of Latvia, but the total area for useful energy generation is smaller. At the same time, five offshore WPP projects are being developed, however, so far, none of them have been commissioned.

The wind turns the turbine propeller or rotor, which generates electricity as it rotates. The amount of electricity generated by the wind generator can be increased by increasing the height of the rotor of a wind turbine or by improving the aerodynamics of the blades. Improved blade aerodynamics will allow them to start turning at lower wind velocity, making turbines suitable for countries with low wind volumes.

Geothermal energy is the thermal energy contained in the depths of the earth in the form of hot water or water vapour. There are different types of technologies for the conversion of geothermal energy into electricity or heat for heating. These technologies have different levels of readiness.

Geothermal energy is one of the most unexplored forms of renewable energy. Unlike other sources, the potential and benefits of geothermal energy are unknown, and hot water and steam reservoirs are most often located in nature reserves, nature restricted areas, or nature parks, depriving one of the opportunity to obtain energy. Due to these reasons, geothermal energy is not widespread for commercial energy production. The United States, Turkey, Indonesia, and the Philippines use geothermal energy more than others. The biggest advantage of geothermal energy generation over other forms of energy is the relatively low land consumption for the installation of technology.

The most popular technology for the geothermal energy generation in households is the geothermal heat pump. Heat pumps are not only used to heat residential buildings, but also for heating commercial and public buildings. Heat pumps consist of several parts: the pump, the heating system pipes (located in the house), the heat production pipes (located underground), the evaporator, the compressor, the expansion valve, and the heat carrier. The most important part of a heat pump is the pump that provides heat sources from the ground to the house, as well as the circulation of the heat carrier in the heating system. Underground pipes for heat production can be placed in several ways, i.e., vertically, horizontally, and in loops.

It is not necessary to pump hot water or its steam out of the ground to operate the geothermal heat pump. These heat pumps absorb the heat that is in the soil. The principle of operation of heat pumps is similar to refrigerators, i.e., heat is received from the ground and is used to heat the home (in the refrigerator, the heat is removed from the products and discharged in the kitchen through the cooling element at the back of the refrigerator). In summer, the heat pump can cool the building as well.

Electricity is required for the heat pump to operate and ensure the flow of the heat carrier in the heating system. Heat pumps with a higher COP work best. The COP demonstrates the number of units of heat a device generates by consuming one unit of electricity. It should be remembered that as the outside air temperature decreases, so does the efficiency of the heat pump.

It is also important to choose the model of the heat pump that suits your region. The heat pumps for the Scandinavian region are the most suitable for the climate in Latvia as they continue to operate even in very harsh winters and wet weather. To ensure that the purchased heat pump will even work in particularly cold winters, become familiarised with the technical information provided by the manufacturer about the device before purchasing it.

Bioenergy is a form of renewable energy that is obtained from plants, waste, and animal waste products. Bioenergy is one of the most predictable forms of renewable energy, as it can be stored easily enough in various forms – solid, liquid, and gaseous.

Solid biomass is one of the most widely used forms of bioenergy worldwide. Solid biomass is used in both households and manufacturing. In households, the biomass is mainly used only for heat. In manufacturing, the biomass is used for both heat and electricity generation. A particularly active user of biomass is the EU, which is not only the largest producer but also a consumer of wood pellets in the world.

In Latvia, the heat supplied in the district heating system is mostly (approximately 80%) produced from solid biomass, mainly wood chips. At the same time, heat is also produced by burning firewood, wood pellets, briquettes, wood residues, and non-wood biomass. In cogeneration plants, where both heat and electricity are generated at the same time, the biomass consumption is only 11% as it is still more efficient to use fossil resources in these plants.

Bioenergy is also available in gaseous form. The most widely used biogas today is biomethane. It is mainly obtained from agricultural manure by fermentation. The resulting gas is purified from various impurities to obtain almost pure methane. Biogas can also be obtained from other resources: algae, sewage sludge, and biological waste.

The EU is also the world's largest producer of biomethane. Considering the fact that in general, biogas is used in much smaller amounts in the world than solid biomass, in Latvia, it is also used in smaller amounts, moreover, only in cogeneration plants.

As previously mentioned, biomethane can be used to generate heat and electricity. It can be added as an impurity to natural gas, reducing its impact on the environment, as well as in the transport sector, for the operation of gas vehicles.

There is no unequivocal view of bioenergy in the world. The treatment of bioenergy mainly depends on the resource. For bioenergy to be considered environmentally friendly, it shall be generated from raw materials, from which it is not possible to obtain a higher value product, and it shall help to reduce GHG emissions. Currently, biomethane corresponds to a sustainable energy source in EU legislation. Therefore, several EU and Latvian planning documents envisage the development of biomethane generation from manure, thus reducing GHG emissions in the agricultural and energy sectors.

Energy from water can be obtained not only from rivers, but also from the tidal changes and ocean waves. However, these technologies are not used in Latvia. Tidal energy technologies are like hydroelectric power plants (HPPs). Dams with turbines are installed in the defined intertidal zones. As the water recedes from the shore or, conversely, as it approaches, the turbines are turned, and electricity is generated. To avoid the need to build dams, such tidal technologies have been developed that resemble submarine wind generators. Like turbines in dams, they are turned and generate electricity because of the water flow.

Wave energy technologies most often look like large buoys. These buoys vary in appearance and construction depending on where the energy will be generated: on the coastline, on the coast or on the high seas. Any wave energy conversion device moves with the oscillations of the water surface, converting the mechanical energy of the oscillations into electricity.

It would be most advantageous to generate energy from the waves on the shoreline or on the coast, moreover, it is available more than 300 days a year. The use of wave energy is mostly limited by availability, as it is only economically viable to extract on 2% of the world’s total coastline.

Various innovative solutions are necessary to make the integration of RES into the common energy system more flexible. Energy storage options are already widely used. It is possible to accumulate both electricity and heat.

Currently, the largest electricity reserves are stored directly in HPPs reservoirs, as well as in pumped hydroelectric energy storage (PHES). PHES operates in a similar way to HPPs by pumping extra water from the lower tank to the upper one. To better integrate solar and wind energy into the energy systems, pumped storage will not be appropriate. For now, electricity is stored in batteries. Although, they rapidly lose their maximum energy storage capacity and are still being improved.

In addition to batteries and energy storage in water reservoirs, other solutions for energy storage are being sought both for the short term and long term. Energy storage technologies such as compressed air storage, hydrogen production from renewable energy sources and energy storage in various household electrical appliances, including electric cars, are already being explored as potentially useful in the future. These technologies have not yet been put into practice. Energy storage opportunities are important in both commercial energy generation and energy generation for own consumption.

Currently, the most used solution for the use of surplus energy, especially in households, is grid transfer. If there are several households nearby or households and companies that generate their own energy, they can merge into one energy community. The Energy Community is an organised group of people who take steps to move their immediate surroundings towards the generation and use of clean energy on a non-profit basis. There is no limit to the scale of energy generation, it goes from a few solar panels to a wind farm. Energy communities most often unite the inhabitants of a city, municipal quarter, or street.

The main goal of energy communities is to promote the use of renewable energy in the vicinity of a specific place (village, small town, or city), to preserve the environment and to strengthen the economic potential. Energy communities are united by the fact that locally generated energy is primarily used by local people. For example, if solar panels are installed on an apartment building, then the energy generated is first used in communal buildings, and then it is used by the apartment owners of the existing house. If all the electricity generated is still not fully used, it is transferred to other nearby houses or to the grid.

To use the electricity generated more efficiently, it is also important to use smart technologies.

The smart technologies introduced can be as simple as hybrid technologies (using two or more RES technologies together), installation and synchronisation of storage or charging facilities, up to complex systems that control the consumption of all equipment in buildings or estimate the amount of energy generated from RES in accordance with the weather forecasts.

In the context of renewable energy, the latter will be most important, as when forecasting the amount of renewable energy, there is a greater chance of using it to the full, thus, reducing energy losses.