In mid-October this year it was published. Electricity Market Act (ZTEE) which introduces a number of novelties of which, for the purposes of this text, we find an interesting part related to the Energy Communities. It is about the possibility of associating citizens into formations that would enable them to jointly produce electricity (here we assume the energy produced by photovoltaic power plant technology) and to share the produced energy in the scope of the same substation. The law provokes divergent views regarding its potential to accelerate individual micro-generation of electricity and the mutual sharing (trading) of generated energy surpluses among members of the energy community. In this first part we present the technical background of financing photovoltaic plants.
Introduction
In recent years, since the prices of solar panels have decreased significantly, photovoltaic power plants have become financially self-sustaining projects. The possibility of achieving profitability by investing in photovoltaic power plants justifiably directs the attention of citizens to investment. Also, lately, the term ‘prosumer’, a word composed of the words ‘producer’ and ‘consumer’, has been frequently encountered to denote the entity that consumes (consumer) electricity, but it also generates (producer).
The role of the entity in the consumption of electricity is known, but questions, especially practical ones, of implementation, arise precisely in relation to the process of production and sharing of electricity. Energy communities, the purpose of which is the production and sharing of electricity produced, can be joined by citizens among themselves, but also, with them or independently, other entities such as local, regional self-government units, institutions, utility companies and other entities gathered around a transformer station. Here, the most intriguing is this limited ability to team up on site included in one substation This significantly limits the sense of sharing the electricity produced, especially in the Croatian context of low population density, which causes a relatively large number of substations with a small number of connections. It is stressed that members of the energy community can share the energy produced; but not to sell. Thus, at least, it can be deduced from insufficiently clear formulations from the regulations.
In most EU countries, it is a practice not to look at the transformer station but at the physical distance (1 km, etc.)
COMPILE Project
Energy production from photovoltaic systems
The technological revolution over the past hundred years has brought democratization and proliferation of numerous products or services that until then were available to a very narrow circle of privileged. It is enough just to recall the expansion of the use of personal vehicles, air travel or the availability of computers and mobile devices. There are hundreds more, but now another highly centralised branch of the economy is on the path of mass decentralisation – electricity generation and distribution.
Photovoltaic power plants are not a new technology, but significant changes have occurred in the past ten years with a dramatic fall in the prices of solar panels and control equipment, so that a typical photovoltaic plant for home installations of 10 kW ten years ago was worth over half a million kuna, while today the price of the plant with installation is about seventy thousand kuna, which, making it available to the average household, i.e. the price is comparable, for example, to the installation of central heating or heat pumps.
In addition to PV, major developments are also taking place in the context of energy storage – batteries, where battery installations are no longer large in size and do not require special maintenance. The growing number of electric passenger cars should not be overlooked, which will also have a major impact on the consumption and storage of electricity in their own batteries, which are often very high capacity. In addition to these technical innovations, innovative exploitation models have emerged that seek to look at the life-long cost of the plant, and then open up some other opportunities in the context of ownership and control of the plant itself, i.e. new long-term more sustainable financial models.
Finally, in an increasingly volatile world, it will be particularly important to secure stable and secure energy sources, thus reducing the dependency and impact of externalities, while it is critical that these energy sources are also environmentally friendly, do not increase their carbon footprint and are economically viable in the long term.
However, each new technology brings some kind of risks (technical and financial), and in order to understand the risks it is important to understand its functioning, so for a start let's look at which are the basic components of the photovoltaic plant.
Types of photovoltaic systems
The key task of the PV system is the direct conversion of solar energy into electricity, which enables the operation of a certain number of AC (AC) or DC (DC) loads. The FN system can also have an additional backup system, typically a battery or generator, which allows isolated operation. Photovoltaic systems consist of PV modules, energy converters and control electronics. Simpler systems (for cottages, etc.) power only DC consumers (smaller lamps, radios, etc.), but with the addition of a DC/AC converter, such a system can then produce electricity for all common AC consumers.
Generally, the PV system can be divided into the following groups:
1. Independent (autonomous) – completely independent from the network
2. Grid, connected to the mains:
- Active (interactive) - bi-directional, can take energy from the grid but also send surpluses from FN
- passive – unidirectional, the network serves (only) as a backup source when there is no production in FN
3. Hybrid, essentially self-contained with the addition of renewable energy sources (most often wind farms).
Autonomous systems are by capital value the most significant of photovoltaic systems connected to the distribution network. The difference in capital value arises due to the existence of a battery system, additional control equipment and regulators. In addition, the network converter for grid-connected photovoltaic systems is simpler by function and typically has less power than autonomous ones.
systems.
Of course, higher capital values of such projects will also cause higher operating costs in the lifetime of the photovoltaic power plant.
Independent (autonomous) PV system
Self-contained systems produce all the energy needed by consumers on their own and this creates significant challenges. For example, when electricity is to be supplied at night or in periods with low solar radiation intensity, a battery of appropriate capacity is certainly needed to serve as an electricity reservoir.
A key component of the system is the controller for controlled charging and discharging the battery, and by adding an inverter (=12 V to ~230 V), the system is also capable of powering regular consumers such as washing machines, televisions, refrigerators, computers and smaller household appliances – naturally according to the installed capacity of the PV system and batteries. Typically used in isolated areas, islands or remote mountain settlements, both for private and business applications (e.g. telecommunication base stations, lighthouses, road monitoring systems, etc.). An example of this system is shown in Figure 1. Due to lower losses, it is desirable to have as many DC loads as possible.
Hybrid PV systems
The basic idea of the Hybrid PV system is to increase the availability and reliability of the system by connecting standalone PV plants with other backup sources of electricity, such as wind turbines, small hydropower plants, auxiliary gasoline or diesel power units.
Modern inverters enable the connection of wind turbines and photovoltaic systems without major problems, giving greater safety and availability of electricity supply and enabling smaller battery capacity as an electricity reservoir. For solutions that use gasoline and diesel aggregates, the systems are dimensioned in such a way that the aggregates are used minimally, which saves fuel, reduces the maintenance costs of the aggregates and extends their service life. An example of a hybrid photovoltaic system is shown in Figure 2.
Passive and active network PV system
The complexity of the PV system is determined by the level of automation. In general, we distinguish passive network PV systems that use the power grid only conditionally, in periods when PV modules cannot produce sufficient amounts of electricity, for example at night when the batteries are empty at the same time (Figure 3). Usually all regulation is manual.
Active, interactive network PV systems use the network dynamically, taking energy from the public network in case of greater needs or when energy is cheap, or returning it to the public network in case of surplus electricity produced in PV modules or when it is profitable to sell energy (Figure 4). Typically, such systems are automated and autonomous, and if they are connected to some AI/ML logic, they can run more complex algorithms for electricity trading.
Connection of the system to the network
Photovoltaic systems are connected via the inverter to the distribution network, where they themselves produce direct current in FN panels, which needs to be subsequently converted into an alternating voltage of the network frequency in order to power consumers or work in parallel with the power grid. Public electric power supply is responsible for maintaining the quality of frequency and voltage, whereby in the event of a deviation, the operation of the inverter is automatically switched off or interrupted.
The problem of grid stability is very complex and goes beyond the scope of this article, but it should be noted that there may be bad effects of PV systems connected to the distribution network (if not implemented by standards), such as increasing short-circuit current, undermining the sensitivity of protection in the electricity network, impact on the quality of electricity, availability of the distribution network, and increasing network losses. Impacts depend on the power of the source (FN system), its consumption at the connection point and the characteristics of the plant, and the characteristics of the distribution network to which it is connected. Connecting the PV system to the network also presents new challenges for network operators who now have power flows in two directions, and not only towards the consumer, therefore necessarily meeting all the positive legal standards.
In addition to the issue of physical electricity production, it is also important to properly measure, record surpluses or deficits, and the entire context of energy trading. In the usual way of connecting the PV system to the network, the output current from the PV system is used to supply primarily consumers in the household, and the produced surplus is fed into the network (Figure 5).
Intelligent system management (electricity generation, consumption and trade)
An important element of the establishment of a sustainable PV plant is the management (if possible automated) of the processes of production, consumption and sale of electricity.
The core of the system is a smart electric meter (Prosumer meter) that allows the control of energy flows in a PV plant. Prosumer can be relatively simple with logic based on smaller rules (time switch or some simple rules such as making decisions based on the state of charge of the battery) or aided by a more complex external system (usually in a cloud with AI/ML properties associated with relevant sources of information on real-time energy prices) that will determine the best moment to buy or sell electricity in accordance with demand and price. In addition to Prosumers, smart appliances that can be remotely controlled are also key. This smartness can be built into devices or (for older equipment) smart sockets can be used that also allow for power quality control.
We can therefore identify the following typical scenarios:
Criteria for selecting equipment
Photovoltaic systems are very different from all conventional sources of electricity, mostly by:
- choosing an individual and by no means routine technical solution
- the critical choice of the size of the photovoltaic and conventional systems, on which the cost-effectiveness depends the most;
- very critical selection of equipment that has to do 25g without repair.
- very important to whom to subject the execution of works.
The most important part of any photovoltaic system are photovoltaic modules, which must meet the appropriate technical characteristics. This means that there must be all the necessary technical documentation to prove the tests, the functionality and the annual production under precisely defined conditions.
The criteria for selecting equipment are:
- Known origin of equipment
- technical documentation of equipment
- Atheists and technical guarantees of equipment
- Instructions for management and assembly
- Contract on technical and production guarantees for equipment
- specific price, term and method of payment, duration of the guarantee
- a list of references of the manufacturer or their authorised representative;
Cost-effectiveness, revenue, expenditure, plant costs
The cost-effectiveness of all energy production technologies, including photovoltaic systems, is determined by:
- revenues and savings from the use of the system
- investment costs (investments)
- Operating costs
- service and maintenance costs
- Dismantling costs at the end of the plant’s life
- indirect (preventive and remediation) costs of preserving the surroundings.
The costs of investing in PV equipment can, in principle, be divided into:
- investment costs for photovoltaic modules
- investment costs for inverters
- investment costs for voltage regulators and battery charging
- Battery investment costs
- investment costs in other equipment
- costs of design and consulting services
- equipment installation costs.
Three key items in the total cost of building a photovoltaic system are:
- PV modules with a cost share of 77.3 %,
- exchanger with a cost share of 9.97 %,
- construction with a cost share of 4.15 %.
Questions about the efficiency of the system
What is the temperature coefficient of the solar panel?
Solar panels are most effective at a temperature of 25 degrees C. For each degree C above this value, the efficiency shall fall by a percentage between 0,3% and 0.5% On average. This percentage is known as the plate temperature coefficient.
In PVGIS, the losses of the photovoltaic system due to the elevated temperature with modules installed next to the roof of the house amount to 15,2%, and with modules mounted on the load-bearing structure 10,5% . The reason for this is due to greater ventilation, and thus a smaller decrease in the maximum power of the module. There are still losses due to reflection. 2,4% and losses of inverters and cables from 4%.
How can I increase the output of my solar panel?
PWM or MPPT regulator? Always use the MPPT solar controller - they are up to 30% More effective than PWM The guy. Regular maintenance and cleaning helps maintain the output power of solar panels. Ensure that the array of solar panels is in direct sunlight without shading. Solar spotlights can help increase the output power, but you need to be careful not to overheat the panels, which will reduce the output.
Which solar panels are the best poly or mono?
Monocrystalline solar panels are more efficient than polycrystalline, but they are also more expensive. However, relative costs and efficiency are approaching and there is little difference.
Is it worth installing a Solar Tracking system?
For fixed installations, it is necessary to choose the optimal angle for maximum annual energy or for maximum energy during the period in which we need more electricity production. It is theoretically the best solution with two-axis monitoring of the apparent movement of the Sun. This can increase the energy obtained by 25-40%. But is that exactly true?
A budgetary example for the area of southern Croatia is given in Figure 1., from it it is evident that monitoring the movement of the sun has certain advantages, but this should then be put in the context of economic profitability, both investment and exploitation. Tracking systems are complex, they have many moving elements – motors or switches that, in addition to increasing investment, are later a significant consumer of energy. This increases the possibility of system failures, and such plants are significantly less resistant to wind gusts, which is a significant factor in our conditions.
Below (Figure 2) we present a realistic example created on the basis of real measurements at a plant in Portugal.
The graph shows the use of a photovoltaic system with a monitoring system that has a uniaxial drive actuator that moves the photovoltaic panel to track the direction of sunlight. This actuator consumes electricity as its source, and the electricity consumed comes from solar panels powered by actuators, which causes a reduction in the energy available to consumers.
In conclusion, compared to fixed panel systems, a photovoltaic system with a solar energy monitoring system less effective to use.
You can learn more about this topic from the excellent manual (you can order it for free) Schrack Technik – Photovoltaic manual.
This is the first part of the extended version of the text originally published in the Journal the Center for Public and Non-Profit Sector Development, Tim4Pin No.1 2022
The second part is available at:
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