kVA Inverter 8kw Hybrid Solar System
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Company Introduction: Anhui Daheng Energy Technology Co., Ltd (DAH Solar for short) was established in 2009 with capacity 1.5GW per year.
We are a National High-Tech Enterprise, specialized in PV Modules development and manufacturing, PV power station R D, operation and maintenance.
Our products have been approved by international certification like TUV, IEC, CE, INMETRO, FIDE etc. And China domestic certification like CQC, Leader, ISO9001, ISO14001, OHSAS18001, etc.
DAH Solar has already rooted in domestic market, at the same time, we are actively exploring the international markets, and has established the sales network more than 100 countries from all over the world, such as Ukraine, Germany, Poland, Brazil, Mexico, etc.
DAH Solar continuously invests on the R D of the products and has already gained more than 60 patents at present. The Smart PV module and Cloud monitoring platform developed by DAH Solar goes at the forefront of solar industry. We are determined to be world-renowned Smart PV module and system provider.
We have the ability to provide customized design and support various solar systems, such as commercial and home off-grid solar systems, hybrid solar systems, grid-connected solar systems, solar lighting systems, etc. We have professional engineer team for system design, qualified sales team to offer you solution, thoughtful logistic department colleagues help you customers complete and received the orders safely.
DAH Solar provide solar system design services and technical consultation upon different requests. We have sales engineer always at your service 24/7. Looking forward to have chance working with you, trust you will love our quality and service.
Reviews and information on the best Solar panels, inverters and batteries from SMA, Fronius, SunPower, SolaX, Q Cells, Trina, Jinko, Selectronic, Tesla Powerwall, ABB. Plus hybrid inverters, battery sizing, Lithium-ion and lead-acid batteries, off-grid and on-grid power systems.
February 10, 2023 Jason Svarc
This is a guide only. For less technical information see the basic guide to selecting a home grid-tie or off-grid solar battery system. Solar and battery storage systems must be installed by an experienced licensed electrical professional. Solar and Energy storage systems generate and store huge amounts of energy which can result in damage, fire or serious injury if the installation does not meet all relevant regulations, standards guidelines.
Four Basic Steps to Designing Battery storage or off-Grid Solar systems
Before selecting or purchasing any equipment required for a hybrid or stand-alone power system, the installer should understand the basics of sizing energy storage systems. The most important part of the process is developing the load profile or building a load table to estimate the amount of energy required to be generated and stored per day. If you cannot develop a load table, a professional solar installer or system designer should be consulted.
- Estimate the loads. first, determine how much energy is required per day in kWh. For off-grid power systems, a load table should be developed for both summer and winter requirements. The surge loads, power factors, and maximum or peak demand must also be considered when selecting the battery and inverter-charger.
- Determine the battery size required in Ah or Wh. To ensure accuracy, you need to consider the battery type and chemistry, maximum depth of discharge (DoD), round-trip efficiency, days of autonomy, and maximum charge rate.
- Determine the solar array size in kW. A correctly sized solar array is required to charge the battery and supply the loads, taking into account local conditions, including; average solar irradiance throughout the year (peak sun hours), any shading issues, panel orientation, cable losses, and temperature derating (loss factors).
- After steps 1 to 3 have been established, you can select the appropriate size inverter-charger, solar inverter or MPPT Solar Charge Controller to suit the system.
How to select a hybrid or off-grid inverter
Modern hybrid off-grid energy storage systems have many specifications to consider before selecting and sizing an appropriate battery inverter-charger. There are now many different system types available, including grid-interactive inverter-chargers, hybrid inverters, complete systems with integrated battery storage (BESS) and AC-coupled battery systems. Here we help explain some of the key requirements which should be considered.
- Inverter power output. continuous and surge rating (kW)
- Inverter charge rating (A)
- Solar PV array size (kW)
- Pass through power (A)
- Battery compatibility. System voltage and battery type
- Configuration. AC or DC coupled
- Software and energy management
Inverter Power ratings
Below are two main types of hybrid or off-grid inverters, available in various sizes with different continuous and peak power ratings, measured in kW or kVA.
- Off-grid battery inverter-chargers with heavy-duty transformers are more expensive but provide high surge and peak power output and can handle high inductive loads. Many of these inverters-chargers are also grid-interactive, as explained in more detail below.
- Hybrid inverters and AC-coupled battery systems use transformer-less inverters with ‘switching transistors’. These compact lightweight inverters have lower surge and peak power output ratings but are more cost-effective, being cheaper and easier to manufacture.
Continuous Power Output
Most battery inverters (hybrid or Inverter-charger) are available in a wide range of sizes determined by the continuous output power rating measured in kW or kVA
The inverter should be matched (sized) slightly higher than the load or power demand of the appliances it will be powering. Due to temperature de-rating in hot environments, the inverter should be at least 1.2 times larger than the highest continuous summer demand. Depending on the application, this is often the most important specification to be considered when selecting a hybrid inverter, especially when using a hybrid inverter as a backup power source for dedicated or essential loads. Whether the loads are inductive or resistive is also very important and must be taken into account.
Inverter sizing in kW or kVA
Something to be aware of is whether the inverter power output is listed in kW or kVA. Kilowatts is generally the more accurate rating. This can be a little confusing when sizing an inverter for your needs. The general conversion ratio used for kVA to kW is shown below:
kVA x 0.8 = kW
For example, a 5kVA inverter roughly equates to a 4kW inverter power rating. Another example is a 3000VA (3kVA) continuous power output inverter generally only outputs 2400 Watts continuously, so approximately 80% of the ‘apparent’ power rating.
Off-grid inverter sizing
For off-grid installations, the inverter sizing is critical and must be sized to meet the full load (demand) under all conditions. As mentioned, temperature derating is especially important as the inverter output is derated (reduced) at higher ambient temperatures. For example, a 6kW inverter that is rated and 25°C may only output a continuous power of 4.8kW at 40°C. This derating factor must be taken into account, especially in warmer climates.
Surge or Peak Power Output
The surge or peak power rating is very important for off-grid systems but not always critical for a hybrid (grid-tie) system. If you plan on powering high surge appliances such as water pumps, compressors, washing machines and power tools, the inverter must be able to handle the high inductive surge loads.
The amount of time the inverter can maintain the surge power output is also very important, but can be misleading depending on how it is described by the manufacturer. For example, some inverters may specify the surge output of say 8kW, while others may specify 8kW for 60 seconds. When a surge time (in seconds) is not specified, the surge rating may only be sustained for 1 or 2 seconds. Generally, the high-end grid-interactive inverter-chargers have the highest surge ratings for the longest amount of time. The Selectronic SP PRO is known to have one of the highest surge ratings of any battery inverter-charger on the market.
Backup Power. Continuous
As the chart above highlights, many hybrid inverters have reduced or limited backup power when operating in backup or emergency supply mode (EPS). Depending on the battery used, this can be further limited by the battery capacity and output power rating. However, there are several hybrid inverters (Solax, Redback SolarEdge) that do not have reduced power output in backup mode. The dedicated battery inverter-chargers such as the Selectronic SP PRO and Victron Multiplus do not have any such limitations.
Inverter Charge rating
The battery inverter max charge rating, measured in Amps, needs to be considered to ensure the battery bank capacity and inverter are ‘balanced’ correctly. Ie. ensure the inverter-charger has enough charging capacity to enable the battery to reach the absorption charge voltage. If the battery bank is too large and the inverter charge rating is too small the battery with not achieve a full charge cycle. This will result in poor performance, degradation and possible sulfation (if lead-acid batteries are used).
Many modern lithium battery systems can accept a high charge current to capacity ratio and are able to be charged at a higher C rate. If a large or oversized solar array is used and the inverter charge rate is not adequate then the solar generation may be clipped (reduced) and the system will not perform as efficiently.
Solar Array Sizing Guide
Once you have established the average daily energy consumption (kWh), and taken into account the local solar irradiation and losses, the next step is to determine the solar array size in kW. The battery capacity (kWh) should also be considered for off-grid systems when sizing the solar array. This is not straightforward, as there many variables to consider.
A basic guide is to use the minimum peak sun hours (PSH) in your location. The winter PSH value is typically used to ensure the solar array is large enough to fully charge the battery bank during the shortest sunny day. For example, if you had a 16kWh battery, you want to generate at least 18kWh during the shortest day, taking into account losses and other loads. You can use the Photonik solar design tool to determine how many kWh a solar array will produce throughout the year based on the local PSH, orientation and array tilt angle. Due to the relatively low cost of solar panels, oversizing the solar array is a common practice to ensure the battery is charged even during poor or intermittent weather. In off-grid systems, oversizing will help reduce generator runtime.
MPPT String Voltage
Accurately calculating the string voltages is critical when designing a solar array using string solar inverters or MPPT solar charge controllers. Solar systems must operate under a wide variety of weather conditions and climates, and the ambient temperature significantly affects the string voltage, which in turn impacts the system’s performance, safety and reliability. You can use our free String Voltage Calculator to quickly determine the string voltage using the historical temperature data for your location.
Hybrid inverters have integrated MPPTs with string input voltage and current limits that may limit the solar array size, which can be used (usually around 6-8kW single-phase). In comparison, grid-interactive battery inverter-chargers such as the Selectronic SP PRO and Victron Multiplus can work with either solar inverters or MPPT solar charge controllers in both AC or DC-coupled configurations. These systems can accommodate much larger solar arrays, which can be expanded at a later stage if required.
AC-Coupled PV sizing
In AC-coupled systems, the solar inverter size is often limited by the inverter-charger power rating (kW). For example, the Victron Multiplus and Quattro inverter-chargers can only be AC-coupled with an inverter ratio of 1:1, meaning the solar inverter (AC) power rating must be the same as the inverter-charger AC power rating. I.e. a 5kW solar inverter is the largest size which can be AC-coupled with a 5kW Multiplus inverter-charger. Note, more solar can be added using DC-coupling with a Victron system. Learn more about the Victron AC-coupling factor 1 rule. In comparison, the Selectronic SP PRO inverter ratio is 1:2, meaning it can have double the solar inverter AC capacity connected. For example, a 5kW SP PRO can be AC-coupled with 2 x 5kW Fronius solar inverters or one large 8.2kW Fronius inverter.
NOTE: When designing a ‘managed’ AC-coupled off-grid system, the solar inverter will need to be compatible with the inverter charger. For example, Selectronic certified or ‘Scert’ inverters are modified to enable precision battery charge control using direct communication. In comparison, Victron and SMA AC coupled off-grid systems generally use frequency shifting. This is adequate but not as precise and can affect some sensitive electronic appliances.
DC-Coupled PV sizing
Unlike AC-coupled solar, DC-coupling does not have the same size limitations and the solar array can be greatly oversized to allow for poor weather conditions and changes in seasonal solar irradiance. DC-coupling solar using MPPT solar charge controllers is a very efficient and reliable way of adding solar and has many advantages over AC coupling explained in more detail below. See our detailed article, MPPT solar charge controllers explained for more information about selecting and sizing DC-coupled solar charge controllers.
Inverter Pass-Through Power
The pass-through power feature (also referred to as an ‘integrated transfer switch’) enables the inverter to supply additional power from the grid or backup generator under high loads, when the batteries are low or when solar energy is not available. The ability to pass through additional power from the grid (or generator in an off-grid system) can greatly simplify the installation by not requiring the separation of essential and non-essential loads.
Generally, only high-end grid-interactive inverter-chargers can pass through additional power from the grid or auto start and run a connected backup generator. Selectronic, Victron Energy and Schneider electric inverter chargers all feature inbuilt transfer switches with pass-through power capability. SMA Sunny Island systems require an external contactor to be installed when grid-connected.
Compatible Battery Types
Before the release of affordable lithium battery systems, most battery inverters were designed to operate with the widely available lead-acid batteries (Gel, AGM flooded). Lead-acid batteries are larger, and heavier and can emit gases that require ventilation. In contrast, lithium-ion batteries are lighter, compact, more efficient, and safe to store inside a sealed enclosure. Many lithium battery systems, such as those from BYD, Pylontech and LG energy, have integrated battery management units (BMU), requiring an inverter with compatible communications (CANbus network protocol) to operate safely and efficiently.
Several self-managed lithium LFP battery systems do not require BMS communications to the inverter and will function much like a lead-acid battery system; these include Simpliphi PHI, Powerplus Energy, GenZ LFP, and Zenaji LTO battery systems.
For off-grid systems, lead-acid batteries are still a well-proven and reliable technology with a lifespan of up to 15 years when sized and managed correctly. One of the biggest benefits of lead-acid batteries is that, unlike modern lithium batteries, they will not shut down at a low voltage or low SOC. This is important in emergency situations or when a backup generator fails or is not available.
All hybrid and off-grid inverters are designed to use a specific nominal DC battery voltage, the most common being 48V. Since most lithium battery systems are 48V, this is not a problem. However, many small-capacity inverters use 12V or 24V, so these may only be compatible with lead-acid battery banks of the same voltage. Selectronic, SMA and Schneider have a range of high-end 48V hybrid/off-grid inverters, while Victron Energy and Outback Power supply both dedicated 12V, 24V 48V off-grid inverters.
The first Tesla Powerwall was the first battery system to operate at high voltage (HV) and was connected in line with the solar array, which operates at a similar voltage (200-500V). HV systems are now very common, and many hybrid inverters such as the SolarEdge StorEdge, Goodwe EH and Fronius GEN24 Plus all work with high-voltage battery systems.
Note: Unlike the DC-coupled MPPT solar charge controllers or regulators, hybrid inverters cannot work with multiple battery voltages.
Battery Capacity. KWh
Battery capacity is measured in kWh (kilowatt/hours), or Amp-hours (lead-acid) is the total amount of energy a battery system can store. However, depending on the battery type and specifications, not all of the available capacity is usable. Common Lead-acid deep-cycle batteries (AGM Gel) should only be discharged to 20-35% of total capacity on a daily basis, whereas Lithium-ion and new-generation battery technologies can be discharged to 80-90% SOC. Therefore the battery chemistry and capacity need to be carefully selected to cater to the user’s energy requirements.
Hybrid Vs Off-grid. For a typical grid-connected home with peak (evening) energy use of 8-10kWh from 5 pm until midnight, roughly a 12-15 kWh lithium battery would be sufficient. However, for off-grid systems, the battery system will need to store enough energy for several consecutive days of bad weather. With an average (efficient) home using 10-15 kWh over a whole day, this will require a much larger, more expensive 30-60 kWh battery system, depending on the days of autonomy required and the size of the solar array.
Hybrid Example: If peak energy use (from 6-12 pm) was 6kWh, the system would require roughly 14-16kWh lead-acid battery or a 7-8kWh lithium battery system to cover peak energy consumption adequately.
configuration. AC or DC-coupled
As solar battery systems became larger and more advanced, AC-coupled systems evolved as one of the best configurations due to the use of low-cost, easy-to-install string solar inverters. Most modern off-grid AC-coupled systems use advanced bi-directional inverter-chargers coupled with one or more compatible solar inverters. AC-coupled systems are generally more efficient during the day when there is high AC power demand, such as air-conditioning systems, modern kitchen appliances and pool pumps. However, the new generation high voltage DC-coupled battery systems (HV) are becoming more popular with the growing range of advanced HV hybrid inverters on the market.
For more information, see the detailed AC vs DC-coupled system article.
Software and Energy Management
A high level of power management and system monitoring is required to enable hybrid or off-grid power systems to optimise energy use and prolong battery life. The software used to run hybrid and off-grid systems thus require advanced energy management and monitoring capabilities, and this is where the high-end grid-interactive inverters shine. These powerful inverters, such as those from Victron Energy, Selectronic, Schneider and SMA, have the most advanced software packages with built-in control systems, relays and digital inputs and outputs. These systems also incorporate specialised battery monitoring and temperature sensors to prolong battery life and optimise charging with lead-acid or VRLA battery banks.
Third-party system monitoring
For additional monitoring and control, third-party add-on energy monitoring systems like Reposit Power and Solar Analytics can provide more advanced remote monitoring and intelligent control features.
Two popular add-on remote monitoring and energy management systems
Most hybrid systems with built-in battery storage (BESS systems) also utilise advanced energy management systems and sensors however, some of the low cost all-in-one hybrid inverters have limited capabilities which can result in less efficient use of stored energy.
Virtual Power Plants and Distributed Energy Resources
Larger scale micro-grids and virtual power plants, or VPP’s, require unique technology designed to integrate and manage distributed energy resources (DERs). Switchdin has emerged as one of the leaders in this space with the Droplet controllers allowing integration and control of DERs.
Hybrid off-grid inverter comparison charts
See our detailed inverter comparison charts: