F & W Construction Engineering Services (SL) LTD
SOLAR ENERGY
What actually is solar energy?
Solar or solar energy is the energy that is contained in solar radiation and is converted into thermal or electrical energy using appropriate technologies. Solar energy is said to be the greatest source of energy because the sun's rays are seemingly endless. It is therefore one of the inexhaustible, renewable energies. Energy (in the form of electrical or thermal energy) can be obtained from solar radiation in different ways: Most often, the renewable energy of the sun is harnessed by means of so-called solar power plants. Solar thermal and photovoltaic systems are both solar systems. The difference is that solar thermal systems produce thermal energy and photovoltaic systems produce solar electricity
How does solar energy work ?
Solar energy is created inside the sun by nuclear fusion in the form of solar radiation. This reaches the earth as electromagnetic radiation. There the energy is used differently depending on the technology (photovoltaics, solar thermal energy, solar thermal power plants, solar thermal power plants, Photovoltaics refers to the direct conversion of solar energy into electrical energy: A solar cell captures light energy in the form of solar radiation and converts it into electrical energy - somewhat like a small power plant, but which does not require fuel, turbines or generators. The solar cells are connected in a row to form solar modules and consist of so-called semiconductor materials such as silicon, which is found in rock and sand, for example. As soon as light energy is added, silicon can become electrically conductive and thus become a charge carrier. With the incidence of sunlight, electrical energy is produced via the charge carriers, which is captured by metal contacts. The top layer of titanium oxide with a bluish shimmer reduces reflection losses. It ensures that more light can penetrate the solar cell. The light energy is first converted into direct current, but in order to make the electrical energy usable, alternating current is needed. This is generated by the so-called inverter.
How does solar energy work in solar thermal?
Solar thermal uses solar collectors to generate heat from sunlight. The solar collectors consist of a glass pane on top and a dark absorber layer underneath. This type of solar system works like a garden hose lying in the sun. The heat transfer fluid in the solar collectors is heated by the sun and pumped into the solar storage tank. There, the carrier liquid transfers the heat to the water in the storage tank via a heat exchanger and consequently cools down. It is fed back into the collector where the sun can reheat it.
Store Solar Energy
In order to be able to use solar energy at any time of the day or night, you need a solar power storage unit. But why store solar power at all? An electricity storage system is primarily an option for economic reasons, because with a storage system, more electricity can be consumed and independence from the electricity grid and electricity prices can be achieved. The goal is to use as much of the electricity as possible at home, because electricity is also needed on days with little sunlight or at night. If you are not at home all day and accordingly little power is consumed, a so-called charge controller regulates the power to active consumers (e.g. the refrigerator) and directs the remaining power to the storage unit. Any surplus electricity can be fed into the grid and remunerated according to the EEG.
Solar power is stored in battery storage. The most common battery technology is lead-acid batteries, one in the form of lead-acid batteries and one in the form of lead-gel batteries. The difference is that the sulfuric acid contained in the batteries, which reacts with lead electrodes, is encapsulated in gel in the latter. Lead-acid batteries have a service life of around 10 years, but require regular maintenance due to the chemical reaction.
A newer storage technology is lithium-ion batteries, the lifespan of which is still difficult to predict. According to estimates, however, this is 20 years. They are also more efficient than lead-acid batteries and are therefore considered to be the future of power storage technology.
The purchase of a solar system
When purchasing a solar system, the question inevitably arises as to which solar modules you would like to have installed. Which criteria can you consider when making your selection? Below you will find practical distinguishing features for solar modules.
It's not just the performance that counts, for example whether the solar cells have the best efficiency or which photovoltaic modules could be the best. The price and your actual needs are also decisive factors. If, for example, you can expect higher snow loads, then this plays an important role in the selection of the module. In other cases, the module dimensions can be decisive if a certain size promises the best possible occupancy for your roof.
The development of prices and the quality of the modules is breathtaking. Today's solar cells are two to three times more efficient than 40 years ago, when the first photovoltaic systems were built. At the same time, the costs for solar modules have fallen dramatically due to a high degree of automation in production. The overall level of most modules on the market is of good quality. However, there are differences. These lie, for example, in the mechanical resilience to rain, snow and wind, in the performance and in the long-term stability, which in turn is due to the materials used and the manufacturing quality.
How big should myphotovoltaic be?
A crucial question when planning a solar system is the right size. You define what is right based on your priorities: Is your comfort and independence, economic efficiency or climate protection most important to you? A high level of self-consumption of solar power is decisive for economic efficiency in this country. Here you can find out which system size suits your electricity requirements. At a glance:1. Determine your electricity needs based on electricity bills and wishes.2. Get a first feel for the right system size with numbers. 3. Determine the final system size together with our solar experts. This is how you find out which size suits you. First, look at your most recent electricity bills to see how much electricity you have used so far (kWh per year). With this information you can make an initial assessment of the size of your future photovoltaic system: rule of thumb: Minimum system size =1 kWp per 1,000 kWh annual electricity consumption "Kilowatt peak" (kWp) is the electrical output that the solar modules of a photovoltaic system generate under standardized laboratory conditions. The kWp indicator makes photovoltaic systems comparable.
With a system of this size, you can achieve self-consumption at a level that is economically advantageous, even without battery storage. You have now determined the minimum size of your system. Next, you should consider which consumptions could be added in the future. Modern photovoltaic systems are designed for a service life of at least 25 years, so you should also plan with this period. Purchasing an electric car in particular can make it attractive to choose a larger system. But even if you want to heat your house with a heat pump in the future or are thinking of an electrically operated sauna, for example, larger dimensions can make sense.If you have a rough idea of the size of your future photovoltaic system, the right time has come to talk to an expert about your planning. Because it is decisive for the profitability of your solar system. Usual sizes of photovoltaic systems for single-family houses
For 1 kWp of installed power, solar modules are required on an area of approx. 7 m2. Typical solar systems on single-family houses have an output module area of between 8 kWp 56 m2 10 kWp 70 m2 12kWp 84 m2 15kWp 105 m2
Which solar modules are suitable?
Before we go into individual modules, we can roughly narrow down which solar modules are suitable for rooftop systems. Let's start with the most important component: the solar cell, in which electricity is generated from sunlight.
Which cell type is the right one?
Monocrystalline solar cells - state of the art: Nowadays, monocrystalline modules achieve an output of up to 400 Wp. In conversation, they are often referred to in their short form as "Mono". The high-performance, high-quality monocrystalline solar cells have established themselves in the area of rooftop and ground-mounted systems, as the manufacturing costs have been significantly reduced through fully automated manufacturing processes. In most applications, mono modules are currently the right cell type.
Polycrystalline solar cells: The lower output of polycrystalline solar modules is up to 330 Wp nominal output. For price reasons, they were often installed for a while, since the silicon used in polycrystalline form is cheaper than monocrystalline. Nowadays, poly modules are only used – if at all – in large-scale industrial systems.Thin-film modules: In 2010, there was still a suspicion that thin-film modules would prevail. However, thin-film modules only play a role in the field of building-integrated photovoltaics and in large-scale photovoltaic power plants.
With or without module optimizer?
Module optimizers compensate for a major weakness: In a series connection of solar modules, the entire row (string) can only be as strong as its weakest link (solar module). Whenever individual solar modules are shaded, a module optimizer can prevent the shaded module from minimizing the yield of several solar modules. So if a dormer, chimney, tree or satellite dish is shading part of your roof, consider a panel optimizer. These are permanently installed on some solar modules. Module optimizers also enable monitoring, with which you can keep an eye on your solar yields down to the module level. The additional costs per module are around 55 USD. You can use performance optimizers to increase the annual performance of partially shaded module strings, depending on the type of shading. In the case of partially shaded roofs, the use of a so-called string inverter can be considered as an alternative.rated capacity
The power is given in watt peak (Wp). The English 'peak' means summit and is the maximum output that a solar module achieves under standardized laboratory conditions.
The output of solar modules with a standard format (approx. 1 m x 1.7 m) is now in a range between 300 and 400 watts, with the most powerful solar modules being significantly more expensive. Solar cells are subject to technical aging (degradation). In the case of crystalline cells, the degradation results in only minimal performance losses. Manufacturers often guarantee that solar modules will still produce an output of 80 to 85 percent of the nominal output after 20 years of operation.
Efficiency of the solar modules
The efficiency of solar modules is given in percent. It describes what percentage of the solar radiation is converted into electricity by the solar modules. The efficiency is therefore easily comparable, so that it is determined under the same laboratory conditions as the nominal power.
Typical efficiencies of solar modules with monocrystalline solar cells today are between 19 and 22 percent. Since the conditions in practice often differ, the efficiencies in practical use vary accordingly. The record holder is the Chinese manufacturer Jinko-Solar with a monocrystalline solar cell efficiency of 24.9 percent (as of 01/2021).
Compare the quality of solar modules
Photovoltaic modules are generally tested according to internationally recognized standards such as "IEC 61215" for terrestrial photovoltaic modules and "IEC 61730" for their safety certification.
Compare solar panel prices
Solar modules make up about a third of the total cost of a solar system. The relatively large price differences between different solar modules and manufacturers come into play accordingly. The performance differences are also large.
In the table below you will find some examples of different, typical solar modules and A COMPLETE GUIDE TO SOLAR PANELS IN 2022
Photovoltaic price per kWp
So that different system sizes and offers can be compared, it has proven useful to reduce the acquisition costs to a common denominator: Kilowatt installed capacity (kWp).
If no price is given in CHF/kWp in an offer, you can simply divide the total amount (less VAT) by the installed power of the solar modules (kWp).
Photovoltaic prices [USD plus VAT/kWp] with storage
2–10 kWp USD 2332 10–30 kWp USD 1805 30–100 kWp USD 1230
Manufacturer of solar modules
Half of the ten largest photovoltaic manufacturers in the world come from China, such as LONGi, JinkoSolar or Ja Solar. Also among the largest manufacturers are Canadian Solar (Canada), First Solar (USA), Hanwha Q-Cells (South Korea/Germany) and UREC (Taiwan). The solar modules from the American manufacturer LG are also relatively popular.The brand of solar modules does not play a decisive role in their quality and performance, as most production lines are highly automated. The constant quality control of each production step is decisive. Of course, there are also differences in the processed components. The advantage of larger manufacturers is that as many components as possible come from their own hands.
This is how solar storage works
A solar storage tank is usually designed in such a way that the household can be supplied with electricity from the storage tank from the evening until the next morning, when the photovoltaic system is producing electricity again. If the battery runs out prematurely or there is a high peak load in the household, mains power is also used. A control unit in the solar power storage regulates the flow of electricity between the photovoltaic system, the household, the storage and the feed-in into the public power grid. First, the storage controller determines whether the electricity generated can currently be used in the household, for example for the refrigerator. If the power production exceeds the current consumption, the solar power storage is charged. If the storage is full and the photovoltaic system is still producing more electricity than is needed in the household, the excess electricity is fed into the grid. Increase self-consumption with a solar storage tank. Today's electricity prices in combination with the lower feed-back tariff make it attractive to use as much solar power as possible yourself. Self-consumption can be increased with a battery storage system, because electricity that is not currently required can be used at a later point in time.
Energy transition: Battery storage makes a positive contribution to the energy transition through increased self-consumption. Because they relieve the power grid and serve as important short-term storage for the day and night balancing of the photovoltaic generation. Interlocking with e-cars reduces the need for grid expansion.
Economy: In contrast to direct self-consumption, stored electricity is more expensive. The self-consumption of storage electricity does not increase the profitability of a solar system.Independence: The degree of self-sufficiency indicates the so-called degree of self-sufficiency. The higher, the more independent you become from the power station and fluctuating electricity prices. Whether your household can be self-sufficient with a solar battery depends on the planning and design of the photovoltaic system. The type and size of potential storage, your power requirements and the times when you consume this power (consumption profile) must also be taken into account. The greater the desired degree of self-sufficiency, the larger the power storage device must be designed. With a correctly dimensioned power storage unit, 60-80 percent of the annual power requirement is covered with your own solar power. The household becomes largely independent of the power station (autonomous). A particularly large power storage unit is not automatically the most economically viable option. Smaller storage systems, on the other hand, can be more economical and resource-efficient due to high usage cycles.
photovoltaic system
A photovoltaic system is possible on almost every roof. You can find out here whether your roof is one of them.
In principle, a photovoltaic system can be set up anywhere that there is sufficient brightness or light. The direction and pitch of a roof affect how much solar radiation hits a roof surface over the course of the year. It is optimal if the system faces south. All other points of the compass are also suitable, provided the roof pitch matches the alignment. The highest yields are obtained when the plant is inclined by around 30 degrees. Steeper gradients, on the other hand, increase self-consumption, which is decisive for economic efficiency. The yield losses at other inclinations between 0 and 50° are only small. Losses are higher when there is shading from trees, houses or the like.
Your roof is suitable for photovoltaics. Among other things, roof pitch and roof orientation are taken into account.
If your roof is suitable, it is worth arranging an on-site appointment with one of our customer advisors. He then checks the suitability in detail, including whether your roof is statically suitable for a photovoltaic system.
Arrange an on-site appointment now
What role does orientation play?
Solar systems can be installed on all roofs facing east, south or west, as well as on all flat roofs. A deviation to the southwest/southeast reduces the energy yield only slightly. Good yields can even be achieved on west and east-facing roofs. Even north-facing plants will yield some returns.
An east-west orientation is also well suited for photovoltaics
A solar system oriented to the east and west brings about 90 to 95 percent of the yield of a system with a south orientation. It also has the advantage that part of the yield is shifted to the morning and evening hours, i.e. when demand is usually highest. This can lead to higher self-consumption and thus to better economic efficiency of the system.
Flat north roofs are also good to use
While flat north-facing roofs with an inclination of approx. 7 degrees still work, the yield of a north-facing roof with an inclination of 30-40 degrees is only 40 percent and cannot usually be operated economically.
What role does inclination play?
Photovoltaic systems can be installed at different angles. An angle of about 30 degrees is ideal for the yield when facing south and about 15 degrees when facing east-west. Above and below the yield decreases slightly, but even when installed horizontally on a flat roof, the yield is still 90 percent of the maximum for an optimal southern orientation. With a vertical installation on a south facade, you can still count on 70 percent of the maximum yield. In order for solar modules to be able to clean themselves when it rains, an inclination of at least 15 degrees is required.
There are shadows on my roof. What influence does this have on the electricity yield?
Shading can significantly affect the performance of the panel. However, the losses can be minimized by clever arrangement and connection of the modules. If shading is unavoidable, an optimizer can help reduce the impact on yield.
Partially shaded roofs are not an obstacle to the installation of photovoltaics. Surrounding trees do not necessarily have to be felled. However, shortening the branches in the crown of the tree can make sense.
How can photovoltaics be installed on a flat roof?
The solar modules are mounted on flat roofs and are increasingly attached in a combined east-west orientation and at a flat angle (approx. 10 degrees). In this way, the entire roof area can be used and the solar power is distributed more evenly throughout the day. This often increases the self-consumption of the self-generated electricity.
What role do the statics and the condition of the roof play?
If you have a solar system installed on your roof, then your roof should be in good condition. Because it must remain stable and rainproof over the entire service life of the solar system - 25 to 30 years.
In order to check whether your roof is suitable for a solar system, an expert inspection is necessary. With all roofs, the condition of the roof covering must be taken into account - will it stay tight? Is the supporting structure sufficiently dimensioned to bear the additional load? Gable roofs are usually load-bearing. In the case of flat roofs, on the other hand, a static test is always necessary.
The inverter
You need an inverter for your photovoltaic system. You can only use your electricity in the household and feed it into the power grid if it converts the solar direct current into the alternating current that is normally used. If you want to use battery storage, you need an additional inverter for the solar battery.
Finding the right technology is a challenge given the many technical variants: Is it better if the modules are connected individually or in strings? Is a single-phase or a three-phase mains connection better? How big should the inverter be? And what metrics should you look out for?
There are basically three types of inverters in the solar sector: photovoltaic, battery and hybrid inverters. Exactly what you need depends on whether you want to use a solar storage tank and what your situation is: distinguishing feature connection type
- Photovoltaic inverter: For photovoltaic systems without storage.
- Battery inverter: To retrofit a solar storage system to a running photovoltaic system.
- Hybrid inverters: For new solar systems to which you want to connect a solar storage tank immediately or in the future.
- Stand-alone inverters: Inverters for stand-alone systems that are not connected to the utility grid and have a battery.
For each of these cases, there are particularly well-suited manufacturers and products. Experienced installers pay attention to the combinability with other system components and the service quality of the manufacturer when selecting the inverter. It is advantageous if inverters form a self-contained, functioning system together with the photovoltaic system. When purchasing an inverter, it is important to plan ahead. For example, if you want to supply a heat pump or an electric car with your solar power in the future, then a correspondingly expandable and compatible device should be purchased from the start.In addition to converting direct current into alternating current, the devices contain safety devices. Inverters switch off if grid voltage is no longer detected in the power grid in order to prevent uncontrolled feed-in. For this reason, grid-connected photovoltaic systems without battery storage cannot, in principle, take over an emergency power supply. In addition, the inverter throttles the power feed as soon as the AC frequency deviates too much from the standard in order to prevent disruptions to the power grid.
For performance and energy monitoring, many devices have a display on which you can read current operating data such as energy yields, power peaks and error messages. You can also usually view the performance data on the computer or with a smartphone app. You will usually also receive a warning message on your cell phone if the system is not running.
Modern inverters are the control center of the solar system. Using energy management functions, they enable self-consumption to be optimized, which is important for the profitability of the solar system. In this way you can coordinate the interaction between a wall box for the electric car and the actual electricity yield, i.e. how the electric car can be charged with as much solar power as possible. These functions can either be integrated in the inverter or provided via an external energy management device and thus retrofitted.
Narrow down the technology: What kind of inverter do I need? Before you deal with specific inverter products, it is good if you roughly narrow down which type of inverter is suitable.
distinguish photovoltaic inverters Photovoltaic inverters are differentiated based on the type of connection, i.e. how the direct current enters the inverter and the alternating current comes out again: String inverters are usually installed in single-family homes The way solar panels connect to inverters is a key differentiator:. distinguishing feature
Connection of the solar modules
- Module inverters are connected directly to a single solar module.
- One or more strings with solar modules connected in series can be connected to string inverters.
- On central inverters, all strings are combined in a parallel circuit in front of the inverter and connected to the inverter.
Which type of inverter is right for your photovoltaic system depends on the number of solar modules and the output of the photovoltaic system. Photovoltaic systems for single-family homes with an installed capacity of around 10 kWp mostly use string inverters to which several strings can be connected. This makes it possible to have several roof surfaces with different orientations n to be connected separately. String or module inverters can be used for smaller solar systems. Large solar power plants, on the other hand, are often equipped with central inverters. Larger systems require three-phase inverters Another distinguishing feature is the type of connection of the inverter to the home network or the public power grid. Single or three-phase inverters are available for this purpose. «Phases» are current-carrying lines. Single-phase inverters are only used in very small solar systems.
With or without a transformer? In the past, transformers were installed in most inverters. Nowadays almost only transformerless inverters are used. This has increased the efficiency of the inverters. Transformer inverters are only technically necessary for thin-film modules – which are hardly ever installed anyway.
How big should the inverter be?
The “size” of an inverter is colloquially used to mean its output – the inverter can handle this so-called nominal output. In offers and product descriptions, it is given in kilovolt-amperes (kVA) or kilowatts (kW). The inverter power must match the actual power of the solar modules, which is specified in kilowatt peak (kWp). As a very roughly simplified rule of thumb, you need an inverter with a rated output of 1 kVA for each kWp of installed power. In practice, the ratio is not exactly 1:1. Because only in the rarest of cases does a solar system achieve its theoretical peak performance. The actual performance depends on the roof pitch, the orientation of the solar panels and any shading.
Solar companies use special design tools for dimensioning, with which the actual performance of the solar system is determined by simulation. This takes into account the minimum and maximum number of modules per string that must be connected. It is also considered how many strings can be connected in parallel to the device.
The inverter should be installed in a cool place such as the basement. If this is not possible, the inverter should be dimensioned slightly larger so that it does not get too hot. Higher temperatures also reduce the service life of inverters. If these factors are taken into account, the acquisition costs for larger systems can be reduced by selecting the inverter with slightly smaller dimensions than it would have to be at the specific location. So it is more often operated in the upper power range. However, sporadic yields are lost if rare production peaks cannot be processed. The inverter manufacturers also offer dimensioning aids on the Internet. There you can get an idea for yourself in advance and try out different constellations digitally.
Inverter for solar storage
When selecting an inverter for a solar storage system, it must first be clarified whether you want to connect a high-voltage battery or a low-voltage battery. In both cases you need a suitable device for this. If you want to retrofit a solar battery to an existing solar system (AC-coupled system), you need a battery inverter in addition to your photovoltaic inverter. This is connected to the home network and converts the alternating current back into storable direct current. Most often, storage systems are sold that include both the battery and the associated inverter. Both components are often housed in one housing. However, the inverter and the battery are independent of each other, which is why products from different manufacturers can sometimes be combined with each other.
With a new solar system, the battery system can also be connected to the DC circuit of the solar system (DC-coupled system). This can reduce conversion losses. This requires a hybrid inverter that controls the charging of the battery. This is possible with products from the same manufacturer or with inverter and battery combinations expressly approved by the inverter manufacturer. With new systems, it can be more cost-effective if you have your solar storage tank connected directly to the direct current circuit.
Hybrid inverters are also a good choice if your photovoltaic inverter needs to be replaced and you want to retrofit a solar storage system in the process.
How high is the efficiency?
Despite their numerous tasks, the devices themselves require little energy and little energy is lost during energy conversion. The efficiencies that are common today are in the range of 95 to 98 percent. By definition, there are different calculation methods for efficiencies. This i The technically interesting distinction in detail makes it difficult to compare the different efficiencies. The most common is the so-called “European efficiency” – an efficiency that reflects average European weather conditions. However, the maximum efficiency also specified in the product descriptions is not practical, as it is only achieved with theoretical maximum power.
How many MPP trackers are included?
So-called MPP trackers are installed as standard in all inverters. The trackers increase solar yields by determining and maintaining the optimal operating point (“Maximum Power Point” = MPP) of the solar modules. Good string inverters have separate MPP trackers on each string input. There are further quality differences in the shading management of the MPP tracking. In your offer you should pay attention to whether several so-called MPP trackers are included. You can also compare the information on the MPP efficiencies in the data sheets.
How long does the inverter last?
High-quality inverters are designed and developed by the manufacturers for a service life of at least 20 years. However, it is normal that during the lifetime of a photovoltaic system, the inverter has to be replaced at least once.
Installing the devices in a dry, cool environment without the effects of the weather is beneficial for a long service life - for example in the basement of a residential building. With some inverters (e.g. "trafolos") or combinations of certain modules with inverters, special installation specifications must be observed. These are very important so that the performance of the modules is maintained and no permanent damage occurs. For example, a so-called potential-induced degradation (PID) can be prevented by grounding the inverter, which would otherwise lead to serious power losses.
How is the data visualized?
Most inverters have a display. On this you can read various current operating data such as energy yields, power peaks and error messages. With the help of a data logger, this operating data can be stored permanently and read out via computer or the Internet. Many manufacturers offer internet portals that you can use to access your photovoltaic system from anywhere and, for example, use your smartphone to check the yield of your solar power plant while you're on the road. In this way, performance and yield checks can also be automated and you will receive a warning if the system is not running.
Distinctive features:
- With or without a display on the housing?
- Which internet functions exist for yield control?
- Does it have additional functions for controlling consumption devices and connecting to energy management or smart home systems?
- Does the inverter trigger automatic warning messages?
Price comparison of inverters
In a single-family home, the cost of an inverter accounts for roughly 10 percent of the total price of a photovoltaic system. In the following you will find approximate prices and product examples for photovoltaic, battery and hybrid inverters. When comparing the prices of inverters, always pay attention to whether the price in the offer or an online shop has been given with or without VAT. Power [kVA] Price USD Product name
Hybrid inverter from Europe 10 4000-4500 Fronius GEN24 10
Trina Solar TSM-380
Hybrid inverter from Asia 10 3500 Huawei SUN2000-10KTL-M1
String inverter 10 3200-4500 Fronius Symo 10-3-M
Kostal Plenticore 10.0
SMA Tripower 10.0
SolarEdge 10k (incl optimizer)
Micro inverter 0.3 190 enphase IQ7+ 290VA
The data visualization devices that allow you to monitor your solar system remotely are not always included with an inverter.
If you want to purchase battery storage, you will need either a separate battery inverter or a hybrid inverter. You can also buy battery storage systems with an integrated inverter. You can read more about whether this makes sense for you in our article on the top arguments for and against battery storage.
Battery storage must match the battery inverter and cannot be combined at will. Therefore you should compare the total price for storage + battery inverter.
Manufacturers of inverters
The three largest inverter manufacturers in the world are Huawei and Sungrow from China, and SMA from Germany. Also known are Fronius from Austria, Kostal from Germany and Solar-Edge from Israel.
solar storage
In order to be able to use the solar power produced during the day in the evening and at night, you need battery storage. With the help of a storage system, you can use much more self-generated energy at home and require even less electricity from the grid. This will make you less dependent on the power station and rising energy prices.
If you want to buy a storage system, you will find a confusing range of over 400 products. You have to filter out which storage systems are suitable for you and assess whether the devices on offer offer good value for money and meet your quality requirements.
Before choosing a storage system, many technical questions need to be answered: Should the storage be connected to the DC or AC circuit? How big should the memory be? Which components are necessary and do they fit together?
Regardless of whether you want to have a new solar system with storage installed or have battery storage retrofitted: you are not alone when choosing a suitable storage system. The installation companies usually recommend suitable battery systems as part of an offer. Experienced specialist companies can judge the quality of the storage tanks well, since they have often installed and looked after them. With the following information, you can better assess the solar storage systems on offer, question the choice of technology and compare the prices.
Battery storage for photovoltaic systems is a mature and efficient technology: Good systems only lose around 10 percent of their stored solar power when storing. The safety standards for transport, installation and the devices themselves are high. They are able to store electricity for a few hours or days. The self-sufficiency (degree of self-sufficiency) of a household can easily be increased from 30 to 60 percent in a typical single-family house solar system with storage.
Components of a storage system
- Battery cells that are combined with control and safety electronics to form battery modules
- Charging and discharging electronics to charge and discharge energy from storage
- Battery inverters or hybrid inverters
- Measuring and communication electronics for the control and monitoring of the storage and for safe operation. This can also be used, for example, to call up the filling level and the energy flows of the storage tank using a mobile app.
- Connection technology for integration into the electrical installation of the building and for any emergency power supply
Instead of the battery inverter, so-called hybrid inverters are increasingly being used in new solar systems, to which both the solar panels and the battery storage can be connected.
Pre-selection: What kind of storage system is basically suitable?
When selecting a storage system for a photovoltaic system, the most important thing is how the components work together. In many cases, inverters and storage systems must be compatible with each other. Suitable devices are usually named in the data sheets. There are also all-in-one storage systems. E3DC home power plants and Alpha ESS storage systems include battery storage, an energy management system and a hybrid inverter.
Lithium-ion batteries have prevailed
In modern home storage systems, the lithium-ion cell has established itself as the battery type - the technical race is decided. In contrast to the lead batteries used in the past, lithium batteries cause fewer losses and tolerate frequent charging and discharging much better. Their storage capacity can be fully utilized without damaging the battery. As with electric cars, lithium batteries are therefore also more suitable for use as home storage than other types of batteries. The same battery cells are sometimes installed in home storage systems and electric cars.
Due to their high energy density, lithium batteries are not entirely harmless - but only if they are mishandled. It is therefore particularly important that the storage systems are installed and treated professionally and as described by the manufacturer and maintained if necessary. In order to detect any errors early on, you should keep an eye on the performance data of your memory. You can discuss irregularities or error messages with your installation company. Service contracts are not common in the area of single-family houses.
Alternative battery technologies are also available on the market as exotic species, even if they are not very common. These include sodium ion batteries (“salt water batteries”), which are significantly larger and heavier than lithium ion batteries but are considered more environmentally friendly. Occasionally lead is batteries offered. Redox flow batteries have not been able to establish themselves so far, the development of most of them was stopped after the prototype. However, seasonal electricity storage systems (HPS picea) are now available, which can store solar electricity at home as hydrogen and convert it back into electricity.
How big should my storage be?
Batteries for grid-connected photovoltaic systems have one main purpose: they should store enough of the self-generated solar power during the day that this is sufficient to supply the house overnight, thus significantly increasing self-consumption and self-sufficiency.
The solar system must provide a minimum amount of solar power: at least 0.5 kWp of installed power should be available for every 1000 kWh/a of power consumption. Instead of such a small output, it usually makes more sense to choose a solar system with a slightly larger output.
The memory should be large enough (and not larger) so that it can be charged and completely discharged once a day if possible. In this way you achieve a high number of charging and discharging cycles per year, which means that the efficiency and cost-effectiveness of the battery storage system is at its highest.
When it comes to electricity demand, additional consumers such as an electric car or heating units can also be taken into account in the future. Approximately 1 kilowatt hour capacity of the battery storage can be estimated for every 1,000 kilowatt hours of annual electricity consumption.
The E3/DC home power station S10E with two additional solar inverters has a usable storage capacity of 39.5 kilowatt hours. (Photo: E3/DC)
For several years, the trend has been that the batteries on offer are getting bigger and bigger. Nevertheless, it makes little economic sense to dimension a battery so large that the electricity is sufficient for several days. Seasonal storage from summer into winter is definitely not possible with lithium-ion storage. Therefore, a grid connection remains sensible and mandatory.
The flexibility and combinability of the storage systems available on the market also increases. More and more different batteries can be connected to the same battery inverter. And with modular battery systems, the capacity can be expanded afterwards, but this is usually only for a limited time, since batteries of different ages usually cannot be combined well.
Quotation code: Usable storage capacity
The “size” of the storage is given in kilowatt hours (kWh). For example, 8 kWh means that one kilowatt of the stored electricity can be used for 8 hours. Frequently installed sizes are between 5 and 11 kWh.
The memory size is referred to as "storage capacity" or "battery capacity". For this purpose, the specifications of a nominal capacity (also gross capacity) and a usable capacity (net capacity) differ. The usable storage capacity is relevant in practice. Since power storage cannot be completely discharged, the actual usability depends on the depth of discharge of the storage. The nominal capacity, on the other hand, is only a theoretical value.
Do I use an AC or DC system?
There are various ways in which battery storage can be connected to a solar system. The designation DC system expresses the fact that the battery is connected to the direct current ("DC") side of the photovoltaic system, i.e. there where the solar modules are also connected to the inverter. The direct current generated by the solar modules is therefore first stored in the batteries and only converted into alternating current when the battery is discharged, when the battery is discharged and the current is used. Battery storage can be connected on the DC side of the solar array or on the AC side of the home. The AC system, on the other hand, is not directly integrated into the solar system. It has its own (additional) battery inverter and is connected to the alternating current ("AC") side in the house installation. There it takes the solar power already fed in by the photovoltaic inverter and converts it back into direct current in order to charge the batteries. In order to discharge the memory, the direct current from the batteries is converted back into alternating current. At first glance, the DC system seems to work much more efficiently, because no conversion step between direct and alternating current is initially necessary for storage. However, an electrical adjustment of the solar power is also necessary on the direct current side. The electronics required for this also consume energy. In addition, the losses in today's inverters in the AC system with efficiencies of 90 to 98 percent are very low. However, a cost advantage of the DC system can result from the fact that only one inverter is required for photovoltaics and battery, while the AC system requires one still on the market inverter for the solar system and a second one for the battery system. DC systems are therefore ideal for new systems - i.e. when purchasing photovoltaics and battery storage at the same time. However, the inverter of the AC-coupled battery storage, which is independent of the generating plant, also makes the system somewhat more flexible. AC storage is therefore well suited for retrofitting. When dimensioning, the technical properties of the existing photovoltaic system do not have to be taken into account. There are also special cases in which battery storage can be connected. In this way, DC and AC systems can be combined or the battery can be connected to the generator side of the inverter.
High-voltage or low-voltage battery?
There are two different voltage systems for battery storage: high-voltage and low-voltage.
Low Voltage (NV)
Low-voltage systems work with an output voltage of 48 volts. They have been on the market for a long time, have been tried and tested and can be used flexibly thanks to the extensive selection of components in the 48-volt range. Nevertheless, more and more solar operators are opting for high-voltage systems.
high voltage (HV)
High-voltage systems work with significantly higher voltages, which can be several hundred volts. In the system, there are only minimal voltage differences. This avoids conversion losses. Therefore, the effectiveness and efficiency values of high-voltage systems are usually high. They find their way from electric cars to photovoltaics and can be combined particularly well with hybrid inverters. Their market share has increased significantly in recent years.
New system or retrofit? Overview of suitable battery systems
Depending on whether you want to buy a new system with solar storage or retrofit a battery storage, different storage systems are possible for you.
Battery system for new systems Battery system for retrofitting
Mostly DC systems with a hybrid inverter for solar systems and solar storage.
There are also suitable AC systems. AC storage with additional battery inverter, so that the previous inverter of the solar system can continue to be used.
More like a DC high-voltage system More like a low-voltage system
Visualization of the entire system usually in one app (photovoltaics, storage and possibly energy management) Possibly separate app/visualization of the battery storage
Hybrid inverter systems can output more power. Systems with battery inverters can deliver less power.
New devices are smaller because a second inverter can be saved. Additionally required battery inverters make the systems bigger.
Product selection: Compare and select battery storage
After you've narrowed down the most important requirements for which storage system is suitable for you, or if you already have offers, you can make meaningful comparisons. You can find good products by looking at key metrics and test results. We present these to you here on solar-ratgeber.ch. When choosing the right memory, it is generally recommended to involve experienced professionals.
Technical metrics
Independent testing is a helpful source of information when considering purchasing battery storage. Because the comparison of the data sheets of different manufacturers is complex and confusing. In addition, comparability is not always given.
efficiency of storage systems
Battery efficiency is specified in data sheets for battery storage. This indicates what percentage of the energy originally supplied to the storage system can be used again after storage. Values of up to 95 percent can be achieved here. However, the individual consideration of battery efficiencies is only meaningful to a limited extent, because losses occur at other points in the entire storage system.
Quality of solar batteries
Before you make a purchase, you are sure to ask yourself how well the products on offer are made and how long they will last. Unfortunately, there are no current tests that compare the service life and quality of battery systems.
In principle, all manufacturers must comply with international and national standards, for which they commission independent test institutes. The overall quality of solar storage tends to be high.
Comparative, independent tests fail because of their feasibility because the innovation cycles in the photovoltaic industry are so fast. The test results of long-term tests would possibly only be available when a product is already obsolete. Therefore, the experience of specialist companies is very important. Because they know which manufacturers are the most satisfied and can sort and evaluate many small indicators.
Lifetime metric: charge cycles
The charging cycles are a theoretis e indication of the service life of battery storage, which manufacturers state in their data sheets. The laboratory value indicates how often the battery can be fully charged and discharged again under test conditions up to its theoretical end of life (cycle life or aging). The actual service life of battery cells tends to be shorter when used as home storage, since the service life of batteries is limited by chemical aging processes, regardless of their actual use (calendar aging). According to expert estimates, the service life of lithium batteries is 10 to 15 years.
The manufacturer's information on the charging cycles is not always comparable. In the absence of a standard, they are not determined under identical test conditions. Transparent manufacturers state their test parameters in the warranty conditions or in the data sheet. Charging cycles are only comparable if you find identical test conditions there. The end of life (EOL), the charging/discharging speed (so-called C-rate) and an (ambient) temperature (UT) should have been specified.
In addition, the charging cycles are not always related to the same end of life. In principle, the capacity of all battery storage systems decreases over the years. Many manufacturers define the end (“end of life” = EOL) of the battery at a remaining capacity of 80 percent. After that, the battery won't be usable for much longer anyway.
When choosing the right solar storage tank, the technical properties should not be the only decisive factor. It is better to look at the technical performance in relation to the purchase price.
Prices: How much does battery storage cost?
As a very rough estimate, a solar storage system for a typical single-family home costs around USD 10,000. In order to compare the acquisition costs, they should contain the entire battery system, i.e. the battery storage and the battery inverter. With new systems, the acquisition costs can often be reduced with a hybrid inverter, because in this case only one inverter has to be purchased for the solar modules and the battery storage.
Below you will find approximate prices and product examples for different storage systems commonly used in single-family homes. When comparing the prices of battery storage systems, also pay attention to whether the price is given with or without VAT.
Nominal capacity kWh Usable storage capacity [kWh] Acquisition costs USD[net] Product name [inverter + battery storage]
New system 10.24 9.2 11000 Fronius GEN24.10 + BYD HVS 10.24
New system 7.7 7 9000 Fronius GEN24.10 + BYD HVS 7.7
Retrofit storage 13 11.7 17500 Varta Element 12
Retrofit storage 9.8 8.8 15000 Varta Element 9
The prices quoted include the assembly costs, setting up the remote monitoring/visualization and the early disposal fee (VEG), which INNOBAT uses to ensure recycling or transport and environmentally friendly disposal. For new systems, only the surcharge from the standard to the hybrid inverter is included here.
First of all, it is important for economic efficiency that you select a storage tank of a suitable size. You can also compare the price by calculating the cost per kilowatt hour (kWh) stored. Some include other theoretical factors such as the number of cycles. This does not make sense, however, because these are usually not achieved in practice anyway.
Identification number:
Price per kilowatt hour of storage capacity
You can calculate the price per kilowatt hour of storage capacity using the following simplified formula:
Initial cost with installation divided by storage capacity =usd/kwh
Battery storage manufacturer
The world's largest manufacturers of battery cells and battery modules include CATL (China), Samsung SDI (South Korea), LG Chem (South Korea), BYD (China) and Tesla (USA). The battery cells for solar storage and electric car batteries often come from the same factories. In addition, the same battery cells are sometimes installed in the battery systems of different manufacturers.
planning a solar system
You have decided on a solar system, now a good plan is needed. During the planning phase, it is important to find out which system size is right for your electricity needs – today and in the future: if you are thinking of purchasing an electric car, for example, this should be taken into account right away. The planning also answers whether you need an electricity storage device and if so, how large it should be. As a result, you will receive a profitability calculation and you will find out which components you can use to implement your solar system.
At a glance:
- Determine your current electricity needs based on your electricity bills.
- Consider whether the demand for electricity could increase, e.g. due to electric cars, heat pumps, saunas...
- Let us plan your system for you.
Who plans your photovoltaic system?
In the case of smaller solar systems on one or two-family houses, the installation companies usually plan themselves.
There are also pure solar planning offices. However, the services of such planning offices are only required for large apartment buildings, hotels or larger commercial buildings.
How is a solar system planned?
Installation companies and planning offices usually use suitable software products for the planning and dimensioning of a solar system. Good planning software contains many system concepts and can simulate the solar radiation for your building over the course of the year. The design of the inverter and the solar yields are calculated based on this. Any shading from trees, as well as the orientation and inclination of your roof can be taken into account.
installation
Are we your partner? Yes
Spoiled for choice!
Not only the price, but also the quality, reliability and service are decisive in ensuring that your solar system gives you lasting pleasure and good yields.
Installation experience: yes
Market experience: yes
On-site service: yes
solar offer
- Scope of services: The scope of services is precisely defined in our serious offer and each service is described individually. An offer for a rooftop system, for example, has the following components of the solar system: photovoltaic modules, substructure, inverter, communication technology for system monitoring, overvoltage and lightning protection, DC and AC installation, installation material
- Data sheets: Data sheets have been enclosed with all components.
- Final documentation (operating instructions)
In order to make the final price of a solar system look lower, some offers unfortunately omit costs, which you ultimately have to bear. Experience has shown that the following items are often missing:
- Is scaffolding included?
- Is the AC connection provided by the electrician?
- Are separate travel costs charged for the installation?