FAQ

Photovoltaics is a process by which the direct conversion of light into electricity is described and made.

• Light – sun – sunlight is the most widespread ecological, sustainable and mainly available source of energy which falls on the Earth’s surface every second whether we like it or not, and therefore we rank it among renewable sources.
• Its use is environment-friendly.
• Solar energy is free, it is shining whether we like it or not, no one can limit it, turn it off or stop it.
• The main advantage of solar energy is that we do not have to pay any fuel, i.e. petrol, coal, gas or wood and so it is basically free.
• Sunlight is inexhaustible, which makes photovoltaics the most promising technology.

The conversion of solar energy into electricity takes place in PV panels. There are several designs, especially small ones in garden lamps, medium ones in street lamps, up to large ones, which we can install on the roof of your family house.

Slovakia and Central Europe in its entirety have relatively good conditions for installing PV panels, so the sooner you install them, the sooner you can make use of their unique advantages.

After installing the system, solar panels will produce free electricity for at least the next 40 years. The sun is shining, the panels are installed and you can plug in any electrical appliance at the end of the wires from the inverter and it will work… without the need to pay a monthly invoice to power plants.

You will be independent with your own PV system, which will produce electricity from an inexhaustible solar source free of charge and in an environmentally friendly manner.

You will also contribute to saving our planet for future generations because you start behaving ecologically, you then contribute to cleaner air.

How long will John keep bringing you the wood? Will he still be bringing it in 10 years? The sun will stillbe shining even after you die. Also for your children and you do not have to rely on John.
8 reasons to choose the solar system

• You will get and use inexhaustible and clean energy from the sun.
• It is green, renewable energy that has no negative impact on the environment.
• Solar conditions in Central Europe make it possible to use solar energy efficiently.
• The PV system operation is cost free.
• Service costs are very low.
• The lifetime of high-quality solar cells is 25 to 40 years.
• The return on investment varies from 3 to 8 years depending on your consumption.
• You do not pay for any fuel and get rid of high monthly invoices for electricity.

The vast majority of Slovak households are connected to the classical electricity grid, so photovoltaics usually works in synergy with normal energy from the power plant. Even the biggest tech giants in the world are connected to power plants. However, it is also possible to have an off-grid system in inaccessible places where there is no electricity connection. It follows that the classic photovoltaic systems operated by a regular user in our country are on-grid.

The larger the PV panel, the more power it is able to provide. As we all know, peak performance depends on the time of day and the weather – power units are typically measured at 25 degrees Celsius. Solar panels in our conditions are mostly oriented to the south with an angular inclination of 30 to 60 degrees.

PV system connected to the grid – itis basically about generating electricity using PV panels that are connected to the grid. The on-grid system consists of solar panels, one or more inverters, a power unit modification and a grid connection of the device. Electricity does not accumulate in batteries but is immediately consumed. Any surplus is transferred to the grid.

The on-grid system is designed primarily for installation on the roofs of family houses and apartment buildings, but also small commercial buildings.

The producer can draw a one-time subsidy for the construction of a resource from the OP Quality of Environment (SIEA), it is not entitled to sell electricity to a distribution company.

These photovoltaic sources are the most widespread due to the simplicity of technical implementation and favourable price.

It is the latest way of using electricity from the sun with the highest rate of self-consumption from a production source. Synchronous hybrid sources work as on-grid during the day; they supply electricity to the wiring in the building from batteries in the evening and at night. They supply electricity to the building in limited mode in the event of a power failure. These are the latest resources and the future is theirs. They stabilise the distribution grid and ensure a minimum consumption from the distribution system for a given supply point. The owner, after installing the source, purchases only the difference in electricity from the distribution company.

This system is a combination of the ON-Grid system and the off-Grid system. This system is especially advantageous in the case of subsidies because we give surpluses to the grid for free with subsidies. However, with this system, we store surpluses in batteries from which we take the energy later when the PV system itself is no longer enough to cover the consumption of the house and we do not buy it from the grid.

This system consists of PV panels that create direct current. It is then converted to alternating voltage in the inverter (voltage converter). This inverter can be single- to multi-phase and, depending on the type of system, designed for 230V or 380V. The inverter includes a battery charging function and a controller that stores excess electrical energy in the batteries and replenishes the energy from the batteries to the house grid when the power drops. The advantage compared to the purely OFF-GRID system is that we do not lose electricity even when the capacity of the batteries is used because then we take electricity from the grid.

With this system, the number of batteries does not have to be subject to the consumption of the house but can be adapted to the financial requirements of the owner since the house is not dependent only on the PV system, as is the case with the OFF-GRID system.

Solar energy advantages:

• Reduce your electricity bills: sunlight is free, so your electricity costs will be reduced once you have paid for the initial installation.
• Solar electricity is green. Renewable energy source does not release any harmful emissions of carbon dioxide (CO2) or other pollutants.
• A typical home solar power system could save more than one tonne of CO2 annually – that’s more than 30 tonnes over its lifetime.
• Faster return on investment thanks to government subsidy from the Zelená domácnostiam program.
• Solar panels on the roof can increase your property’s value.
• They can be integrated into any building where they significantly reduce energy consumption;
• They do not produce noise, are not a source of harmful emissions and polluting gases – silicon is a non-toxic material;
• They are safe and highly reliable. the life of the panels is more than 30 years (their performance does not fall below 80% of the initial power after 25 years of operation); opinions on energy return on investment range from 7 to 10 years (only for comparison purposes: the energy return on investment of a nuclear power plant is 10 to 14 years);
• The PV system operation does not require any maintenance;
  the panels are easy to install;
• The photovoltaic panels and photovoltaics as such can be recycled (in addition to silicon, glass and aluminium are also used for their production).

11 reasons to choose us:

1. We install only the best proven and certified technologies;
2. We guarantee quality, fair prices, professional approach, expertise;
3. We will solve everything and take care of everything for you;
4. Every customer is unique to us and we will design a unique system for you;
5. We will handle the paperwork for connecting to the power plants for you;
6. We have completed hundreds of successful and still functioning installations in Slovakia and abroad;
7. All our clients are our friends and we stay in touch with them to this day.
8. We work in Slovakia, in the EU, but also in Africa and Asia.
9. Our employees are regularly trained and tested
10. So far, no one has fallen off the roof and killed themselves 
11. We can arrange financing from 5 banks in Slovakia

Our offer:

• Complete delivery of turnkey PV system
• The largest range of PV systems in Slovakia
• Professional installation of photovoltaics with attention to detail
• Regular inspection of the solar power systems supplied by us
• Photovoltaics with assembly throughout Slovakia with FREE shipping
• Solving all administrative tasks and handling the Zelená domácnostiam II subsidy
• The latest technology at affordable prices
• Premium solar panels and inverters
• Friendly and individual approach
• Warranty and post-warranty service of photovoltaics

Photovoltaics –roof INSTALLATION

The ideal orientation for installing solar panels in Slovakia is the orientation to the south, with an inclination of up to 10° to the west. The ideal inclination (angle of incidence) for solar panels is 30°. Why orientation to the south? It is under these conditions that photovoltaic panels installed in Slovakia are able to make maximum use of energy from the sun.

If your main goal is to reduce electricity bills, we recommend a PV system without a battery. Surplus energy produced not used for household operation will be used stored in a virtual battery or for domestic hot water (DHW) heating. Where this heating takes place through the preheating of DHW in a separate tank connected to the boiler or directly to heating the DHW in your boiler. This category of solar power systems is characterised by its fastest rate of return. These PV systems also support the installation of battery modules in the future.

Would you like to consume all your produced electricity? Operate household appliances even after sunset or have a backup power supply if there is a power failure? Choose from our range of PF systems with battery storage. This photovoltaics stores unused electricity in batteries where it is ready for its future use. In general, our customers enjoy these types of solar power systems the most. If you like to use your produced energy in batteries even in the event of a power failure, we will be happy to add a BACK UP system to the PV system to make your photovoltaics a reliable backup source.

The technologies open up new possibilities for choosing the PV system components, which allowed us to build a product portfolio from the product ranges of several major global companies where, in addition to a several-year warranty on components, we can offer the quality of the PV systems at affordable prices. We regularly monitor our installed power systems and ensure their reliable functionality so that you can use the inexhaustible energy of the sun to the fullest in cooperation with us.

If you want a battery with great power and high capacity, we offer you a popular solar power system with 10kwp and 20kwh battery, which is the right choice for most of our customers. This PV system can also be extended by additional battery modules (30 kWh maximum), by a virtual battery, which can be used after charging the battery capacity, or by storing surplus for heating hot water.

We have many years’ experience in PV system construction, such as:

• Office buildings
• Engineering and industrial sites
• Storage areas – cooling or freezing plants, food warehouses, etc.
• Shopping centres
• Showrooms
• Data centres, mining centres
• Solutions for developers
• But also containers, solar blooms, etc.

The green bonus is a supplement to the market price of electricity that can be obtained by producers of electricity from renewable sources. The producer sells the produced electricity to the end customer or the electricity trader; it has the right to collect green bonuses from the operator of the regional distribution system. The advantage is achieving a higher yield than in the case of the feed-in tariff regime. The disadvantage is a certain degree of uncertainty because the producer has to look for a customer for the electricity produced and is not guaranteed the consumption of 100% of the electricity produced, as in the case of feed-in tariffs.

The power of the panels is given in Wp, which is the so-called peak power. This nominal value indicates how much electricity PV panels produce under standard test conditions – an incident radiation intensity of 1,000W/m² and an ambient temperature of 25°C.

Annual production: PV panels produce 1,200 to 1,300kWh of power a year under our conditions. Therefore, panels with a power of 4kWp annually produce about 4,800 to 5,200kWh.

Daily production during the summer six months (03/04 – 08/09): 5 to 6 times the power on average, i.e. the daily production at 4kWp is 20–25kWh. Naturally, there will be better and worse days.

Slight deviations will also be logical depending on the location, orientation and inclination of the panels (you can try PVGIS 5 for your location), but these are not significant differences, usually in the range of 5–10%.

The average price of electricity in Slovakia for households is around €0.20–0.25/kWh in 2024 on average (according to Eurostat, the average price in the first half of 2021 for households with a consumption of 2,500–10,000kWh was €0.1668/kWh, but it includes fixed monthly fees that cannot be avoided).

A PV system with a capacity of 4kWp generates electricity worth €1,250 (5,000kWh x €0.25/kWh) a year and this would also be the theoretical maximum savings on electricity.

If all photovoltaic production were consumed in the household or if there was net-metering in our country, the costs of photovoltaics would be able to return in 4–5 years (at current electricity prices). The system has a life span of over 30 years. Does that sound like a good investment? The electricity price will (probably) increase in the future, the question is at what pace.

In fact, it is not a matter of course to achieve 100% use of electricity produced by photovoltaics (however, we have implementations where it is over 90%). Therefore, the actual savings will almost always be lower and therefore the rate of return will be slightly longer. In practice, the use of on-grid photovoltaics in a normal household at higher outputs can often be around 30–40%. The reason is that at the time of the highest production of photovoltaics (from 10 AM to 4 PM), household consumption is often rather below average. And photovoltaics produces relatively little in the morning and evening when the consumption is higher. And nothing at night.

However, it does not matter as much today; thanks to the virtual battery, it is quite possible to save on the electricity generated by photovoltaics at a time when your consumption is lower and the electricity ‘runs off’ into the grid. You can (easily) achieve savings of 75–80% of the ‘value’ of electricity produced by photovoltaics with the virtual battery.

In general, it is possible to achieve a return on photovoltaics within 10 years. The exact time will depend on the price of electricity in the future; the more the price of electricity increases, the sooner the photovoltaics ‘pays off’.

And the answer to the question of whether photovoltaics is worth it depends on how one perceives what ‘worth it’ means. Photovoltaics is essentially an investment that consequently brings savings. It ‘is not worth’ investing in this way for some people even with a return of 5 years, others are fine with a return of 15 years and it is ‘worth it’ in their case. By the way, even the concept of ‘rate of return’ can be tricky; no one today knows how energy prices will develop in the future (although you can find as many forecasts as you want) and the rate of return depends on them.

The power of PV panels is given in Wp, which is the (peak) power that the panel generates under standard test conditions (solar radiation with an intensity of 1,000W/m² and an ambient temperature of 25°C). The power of the entire array of PV panels is also given in Wp, more often in kWp.

However, photovoltaic panels achieve their peak power not so often even on nice sunny days and almost not at all in the summer due to the high temperature of the panels and the decrease in power at higher temperatures. There is also no peak power or maximum power, it can be even more under certain conditions (cold and clear weather).

However, since photovoltaics produces much more in the summer than in the winter (roughly 3/4 in the summer six months and 1/4 in the winter six months), there are basically two basic approaches to dimension photovoltaic power.

The PV system should be dimensioned and designed in such a way that the maximum electricity produced is consumed on site. Photovoltaics produces 5–6 times its peak power a day on average during the season (March/April to August/September). Daily production at 4kWp in the summer is approximately 20–25kWh.

In this case, the annual production of photovoltaics, depending on the nature of electricity consumption and possible battery accumulation, would be at the level of 1/2 to 2/3 of the annual consumption. In this way, it is possible to achieve a reasonable level of use of electricity generated by the panels and to minimise unused surpluses.

When dimensioning the capacity of batteries, it is based on the daily average production of photovoltaics. The capacity of batteries should be approximately in the range of 25–40% of the daily production. In the case of photovoltaics with a power of 4kWp, the capacity of batteries optimally in the range of 5–10 kWh again depends on the specific situation and the course of consumption.

These recommendations are indicative, the optimal power depends on what you will use the photovoltaic for or how you can use it. It is also possible to choose higher power in the case of a solution using surpluses for water heating.

It is suitable for higher electricity consumption, above 6,000–7,000kWh a year, which is often due to electric heating (heat pump, electric boiler, direct resistance heating in the floor).

Photovoltaics is dimensioned to produce approximately year-round consumption per year. Naturally, most of it is produced in the summer when it cannot be directly consumed, but today it is possible to use a virtual battery and similar services to ‘transfer’ this production between summer and winter.

Despite the slightly lower savings with the virtual battery (explained below) compared to using the production of photovoltaics directly (and not taking electricity from the grid), it is not that bad today. This is also due to the increase in the price of electricity and a slight reduction in distribution fees.

All (with rare exceptions) family houses have three-phase electricity. So do you need a three-phase PV system connection? First of all, it depends on the inverter whether photovoltaics is connected to one phase or three phases, and thus supply electricity to one phase or all three phases. It has nothing to do with connecting the panels. Basically, the inverter has input(s) – panels – and an output – either single-phase or three-phase.

In short, whether photovoltaics should be single-phase or three-phase depends on its performance, nothing else.

A single-phase inverter is sufficient for photovoltaic power up to about 4kWp. The advantage of a single-phase photovoltaic connection is also the price of the inverter and the entire system. A three-phase connection, although technically possible, would be unnecessarily more expensive.

A three-phase inverter is required for photovoltaic power above approximately 4kWp. This is stipulated by law (connection of photovoltaics to one phase through a 16A fuse, i.e. 16A x 230V = 3.68 kW). Also, the vast majority of inverters with lower power are produced as single-phase and with higher power usually as three-phase, although there is not an exact boundary.

That is, the savings thanks to photovoltaics will be the same for single-phase and three-phase connection of photovoltaics, i.e. the inverter. There is a cumulative measurement of all phases with an electricity meter in our country (fortunately; unlike, e.g. in the Czech Republic). Although the (four quadrant) electricity meter measures the individual phases separately, the current total consumption/supply from/to the grid measured by the meter is the sum of the current measurements at the individual phases. For example, when 2kW in one phase is supplied from the photovoltaics to the grid using a single-phase inverter (since not all of the photovoltaics is consumed directly and some appliances are connected in other phases), 1.5kW in the second phase and 0.5kW in the third phase, the meter then measures ‘zero’ since the sum of all three phases is zero. However, this happens (for clarification) in real time, not, for example, within an hour, a day, a month…

So even if you do not physically use everything you can from photovoltaics in that one phase, it is ‘compensated’ in the meter and from that point of view, there is no difference in electricity savings between single-phase and three-phase photovoltaics.

There is a minor ‘complication’ with single-phase photovoltaics in monitoring consumption and a hybrid inverter with batteries. If a single-phase smart meter (electricity meter) is used for the inverter, the inverter will not ‘know’ about the consumption in the other two phases and you will not see the correct consumption data in the monitoring and, in the case of a hybrid inverter with batteries, the inverter will also not optimally charge and discharge the batteries.

This can be solved in two ways:

Connecting single-phase household appliances (ideally all) to the phase where electricity is supplied by the photovoltaics. However, there is a limitation – the main circuit breaker. Most family houses have 25A, then the peak power consumption from the grid should not be over 6kW (25A x 230V = 5.75kW + a small reserve due to the switching characteristics of the circuit breaker). So that you do not turn on a lot of appliances with a higher power consumption at the same time – e.g. electric hob/oven, washing machine, vacuum cleaner, iron, kettle… However, this does not pose a major problem for practical life in the vast majority of cases.

Use a three-phase smart meter instead of a single-phase one – our own tested know-how that not everyone knows and uses. In this way, the inverter will know exactly the total electricity consumption and you will see it correctly in the monitoring. You will also achieve better use of photovoltaics with an inverter with batteries – that is, if the inverter ‘solves’ only consumption in one phase (i.e. not the whole household), it would charge the batteries even if it did not have to, that is, if a three-phase smart meter could directly cover consumption in other phases. In that case, the batteries would have been charged much earlier and then the overproduction would have gone into the grid ‘purposelessly’, regardless of whether there is consumption in other phases or not.

not with on-grid inverters,
partially with hybrid ones.

All on-grid inverters must disconnect in the event of a power failure and not supply power from the photovoltaics to the home wiring (physically connected to the grid because the wiring is also powered by it). Such a feature is already part of the inverter, it is called ‘anti-islanding’ (and cannot be turned off, bypassed or otherwise ‘tricked’).

Photovoltaics (in a family house) are connected in parallel to the grid – this means that the photovoltaic inverter supplies the same wiring as the grid. Disconnecting the on-grid inverter is necessary for safety reasons – e.g. sometimes the voltage-free state in the grid is intentional (during repairs) and then it is necessary that there is no voltage or electricity from photovoltaics. Another problem is that un-synchronised electricity from the grid and photovoltaics would ‘hit’ each other when the grid is ‘rebooted’ and cause significant trouble, including damage to more sensitive appliances (electronics) in the household.
If you want to have electricity from photovoltaics even in the event of a power failure, a hybrid inverter with batteries is essential.

GOODWE hybrid inverters have a separate back-up output, to which the inverter ‘supplies’ electricity from panels/batteries even in the event of a power failure. However, this inverter output must not be ‘connected’ to other wiring in the house, ‘backed-up’ appliances must be ‘powered’ directly from the inverter. In practice, we solve this by supplying a separate cable from this inverter output to the switchboard and ‘critical’ appliances/circuits/sockets to be supplied from the photovoltaics even in the event of a power failure are connected to this inverter output. Other hybrid inverters also have the option of such power supply in the event of a power failure, but they do so in a more complex way.

The dimensions of today’s photovoltaic panels are different, starting at 1.7m in height and usually around 1m in width. The power of one panel is currently most often 370–410 Wp for monocrystalline panels, but it is no exception to have over 450Wp, even around 600Wp. However, this is not due to higher efficiency, but due to larger panel dimensions. The power on 1 m² of the gross (outline) panel area is currently just over about 200Wp. So, for example, approximately 15m² of panel area is required for 3kWp.

Furthermore, the roof area for placing the panels should be oriented ideally between the south-east and south-west, without shading (even partial during the day) e.g. by chimneys, dormers, surrounding trees, etc. because this negatively affects the production of electricity by the panels to a certain extent.

The placement of the roof panels should be considered based on the spatial options and the final appearance of the roof after installing the panels. There are also panels with larger dimensions on the market today and thus higher performance per panel (it is over 2 metres high); it is also possible to use such panels for more problematic roofs.

The need for a relatively large roof area (which is usually a problem, especially with jagged roofs) for placing the panels can sometimes be a disadvantage in photovoltaics, compared to e.g. the required area of collectors used to heat water, where an area 3 times smaller is enough.

Building permits are not required since the placement of panels on the roof ‘does not significantly change the appearance of the building, does not interfere with the load-bearing structures of the building, does not change the way the building is used compared to the purpose for which the original building was permitted and does not threaten the interests of society’ in the vast majority of cases. None of this (usually) happens when placing PV panels on the house roof.

A building notification is also not necessary. Although this is not clearly stated in the law, the closest are the provisions stating that the building notification is not required for maintenance works, such as (among others) repair and replacement of roofing or flat roof surfaces, maintenance and repair of technical, energy or the building’s technological equipment, as well as replacing its components, if this does not fundamentally change its connection to the public equipment of the territory or worsen the impact of the building on its surroundings or the environment.

However, since many building authorities (more precisely individual officials) interpret the law in their own way, if you want to be sure, we recommend consulting the need to notify such a ‘building modification’ with the building authority (municipal authority).

First of all, as many people still do not realise it – the own and virtual batteries are not exactly equal in terms of savings: both the virtual battery and the electricity rental will ‘save’ you less than your own batteries.

In the case of a virtual battery or electricity rental, the supply of electricity from photovoltaics to the grid and the reverse ‘taking’ are not charged 1:1. That is, the full/total price for the kilowatt hours that you delivered to the virtual battery and ‘used’ them later would be deducted from the invoice.

The price of electricity for households consists of two basic categories of components: electricity as such (the price of ‘power’ electricity) and distribution fees and other tariffs – namely the variable component of the distribution tariff, the tariff for operating the system, for system services, for losses of electricity during distribution and for contribution to the nuclear fund. These distribution fees must be charged to the customer by law for each kWh of electricity supplied, regardless of whether it is from a ‘virtual battery’ or ‘electricity rental’. There are also fixed monthly fees for the supply point in the invoice, but it is not crucial for this case, they cannot be removed.

The ratio of the price of electricity alone to the price of distribution for households in 2022 is approximately 60% of electricity / 40% of distribution, depending on the supplier and the rate. It used to be the other way around until 2021, around 40% electricity : 60% distribution, but the price of electricity has increased and distribution fees have decreased slightly. Thus, the electricity ‘taken back’ from a virtual battery or electricity rental is not ‘free’, but you pay about 40% of the normal price for it. In addition, there are fees for these services, but they are not significant.

Nevertheless, with a virtual battery and electricity rental, you will save quite a lot today, although not as much as with your own battery (losses when charging and discharging batteries are up to 5% – total, within the entire charge-discharge cycle, it is not significant).

A virtual battery is more advantageous in terms of ‘return’ on investment in photovoltaics than your own batteries in 2022.

For this reason, more customers with high consumption, often 10 or more MWh (due to electric heating – either through a heat pump or resistance), install photovoltaics with annual production per year at the level of their total annual consumption and ‘transfer’ their overproduction from summer to winter (for heating) via a virtual battery. This is quite advantageous today.

However, with a virtual battery, there is one more factor to consider and take into account and that is a certain uncertainty. It is a service offered by the electricity supplier that has no obligation to offer it and also does not have to apply the current conditions permanently. However, this does not yet appear to be a serious and fundamental problem.
We will be happy to answer any questions in person or by phone. Or write us a message to which we will reply as soon as possible.
Registered in the Commercial Register of the District Court in Bratislava I, Section: Sro, Insert: 166383/B
Excerpt from theSlovak Republic Commercial Register (orsr.sk) and Finstat