Як поєднати інвертори з рішеннями для зберігання енергії в побутових приміщеннях

The inverter is the power conversion and energy management component in most of the Residential Energy Storage Solutions (RESS) available today. It connects solar panels and batteries to household loads, utility power and backup generators, while ensuring usable AC output.

Choosing an inverter based on rated power may provide limited backup, excessive battery current, inadequate starting capability for motors, and poor integration with the PV array. A practical matching process should evaluate the complete energy system.

From SANDISOLAR's manufacturing perspective, properly configured Residential Energy Storage Solutions should balance six factors: household loads, surge demand, battery voltage, storage capacity, solar input, and regional AC requirements.

What Does an Inverter Do in a Residential Storage System?

In Residential Energy Storage Solutions, the inverter has a few roles that are related.

•   DC to AC conversion: The inverter converts the DC electricity from the batteries and the solar panels to AC electricity so that the home appliances and devices can be used.

•   In solar energy systems, inverters equipped with solar MPPT can change the operating condition of solar panels to optimize the maximum possible solar energy collection.

•   Battery charging regulation: the inverter is able to modify the voltage and current to the charging levels required by the battery.

•   Transfer of backup power: The inverter will change the power source in the event of a power supply interruption or an unstable power supply from the grid.

•   Integration of the generator: The inverter can accept charging from a generator and allow the generator to supply power to the household circuits.

•   Communication of the system: The inverter has the appropriate Wi-Fi and communication ports to allow monitoring of the system and charge management of the battery.

Due to the interrelated nature of the above-mentioned functions, an inverter should be selected during the planning stages of the battery and PV system.

Step 1: Define the Household Load Profile

The first step is to identify which appliances must operate during normal use and which loads require backup during a power outage.

Load Category	Typical Examples	Main Matching Concern
Essential loads	Lighting, routers, refrigerators	Continuous operating power
Навантаження на мотор	Pumps, compressors, air conditioners	Startup surge
Heating loads	Kettles, ovens, water heaters	High continuous demand
Sensitive equipment	Computers, televisions, control systems	Output waveform quality
Optional loads	EV chargers, large HVAC systems	Battery and inverter capacity

The inverter's continuous output should support the combined running power of appliances that may operate at the same time.

A reasonable operating margin is also useful because appliance demand can change during daily use.

Step 2: Evaluate Continuous and Surge Output

Continuous output describes the amount of consumption an inverter can handle during the course of regular operations. Surge output, on the other hand, describes the amount of consumption necessary to start equipment that possesses motors or compressors.

•   Continuous output rating: A rating of continuous output should be beyond the expected maximum just-in-time loads that would be continuous.

•   Surge output rating: A rating of surge output should be sufficient to accommodate the short peak starting currents of pumps, refrigerators, and air conditioning units as well as of power tools.

•   Motor load capacity: This provides an application-based description when choosing an inverter for equipment with inductive loads.

•   Possible expansion by parallel support: This allows certain Residential Energy Storage Solutions to expand as the demand within the household grows.

An example would be the SANDISOLAR range of products, which provide 3kW and 4.2 kW for small systems, 6.2 kW and 7 kW for medium residential loads, and 11 kW and 12 kW for large systems. Selecting a size should be based on the actual load demand, rather than the size of the house.

Step 3: Ensure the Inverter and Battery Voltage are Aligned

The inverter and battery need to be in the same range in terms of compatible DC voltages.

Common Residential Battery Platforms

•   24V systems: Smaller backup loads, with a moderate capacity inverter, are generally served with these systems.

•   48V systems: These systems are usually found in medium and large residential systems, and at the same output power this system reduces the DC current.

•   High-voltage systems: This system may be the foundation of a larger modular storage system, but a dedicated high-voltage inverter is needed.

Due to its design, a 6.2kW inverter drawing power from a 48V battery will generally draw less DC current than a similar inverter drawing power from a 24V battery. The result of lower current is less heating, less voltage drop, and the potential to use a smaller gauge wire. However, all electrical work needs to be in accordance with the relevant electrical standards.

Step 4: Modify Battery Size for Preferred Backup Time

Regarding Residential Energy Storage Systems, "inverter power" and "battery power" do not refer to the same thing.

•   Inverter Power (kW): Highest power output of an inverter.

•   Battery Energy (kWh): Maximum energy that can be stored in the battery.

•   Usable depth of discharge: Amount of battery energy that can be used during the normal function of a system.

•   Conversion efficiency: Refers to the energy loss occurring in the inverter, battery, wiring and at the end-use devices.

A large inverter connected to a small battery may operate high-power appliances, but only for a short time. Conversely, a large battery paired with an undersized inverter may provide long backup time but cannot support several high-power loads simultaneously.

Step 5: Match the PV Array to the MPPT Input

The solar array must remain within the inverter's PV input limits.

PV Parameter	Matching Requirement
Maximum PV voltage	Array open-circuit voltage must remain below the inverter limit
MPPT voltage range	Normal operating voltage should stay within the MPPT range
Maximum PV power	Installed panel capacity should align with supported PV input
PV input current	String current must remain within the permitted input value
Number of MPPTs	Multiple MPPTs can manage arrays with different orientations

Selected SANDISOLAR off-grid inverters support PV input voltages of up to 500V or 550V. The SD-PRO 12kW model has two MPPT channels and is capable of handling 18,000W of PV input, whereas the model SD PRO 6.5kW has one MPPT channel and is capable of handling 9,000W of PV input.

In the design of a string, one must consider the rise in voltage with lowering temperatures in addition to the conditions at the place of installation.

Step 6: Select the Relevant AC Standard

The layout of household electrical systems is not uniform across different regions.

•   230V single phase output: Common in the EU and many international residential markets.

•   120/240V split phase output: Common in many North American residences.

•   50Hz or 60Hz: The inverter frequency has to conform to the appliances and the electrical system of the locality.

•   Pure sine wave output: For electronic and electric equipment of a household, including motors, that are sensitive to wave forms.

SANDISOLAR has models focused on the EU market with single-phase output and models focused on the US market with split-phase output, including the SD-4872WP-US and SD-48120WP-US.

Other Features that Can Add Value

The modern residential Energy Storage Solutions can also have;

•   Adjustable charge parameters: to make the inverter charge compatible with the charging of lithium batteries.

•   Short transfer time: To decrease the interruption to critical loads in the home.

•   Battery free operation: Under certain operating conditions, a few selected models can support loads from both PV and AC sources without the connected battery.

•   Generator support: Further charging can be done from a generator in areas with an unreliable grid, due to the adjustable AC input.

•   Monitoring Built in: With Wi-Fi, communication ports, and data available about the system, the status can be checked.

SANDISOLAR's System-Matching Strategy

SANDISOLAR specializes in developing off-grid and hybrid inverter systems that support different loads, PV systems, battery voltages, and regional AC standards.

The following is a summary of its professional experiences:

•   System-level assessment: Understanding relationships among the home systems and the components: inverters, batteries, PV arrays, loads, etc.

•   Multiple power platforms: Models range from small residential backup systems to large power systems.

•   Integration of lithium batteries: Different configurations are available with variable settings and options for interfaces.

•   Multiple energy inputs: Solar, grid, battery, and generator energy inputs are available depending on the conditions of the site.

•   Control and integration of energy management systems: Multiple options for control and integration.

The power rating is not the only important criterion for selecting an inverter for a Residential Energy Storage System. Continuous and peak demands of the household, configuration and type of batteries and solar inputs, and the desired backup time also play important roles in the selection of the inverter.

Поширені питання

Q1. Can an off-grid inverter operate without batteries?

Some models can function with an input from solar and AC without batteries given the right conditions.

Q2. Should the inverter and battery have the same power ratings?

They need to be aligned, however, the two are measured in different units. Battery power is in kWh and inverter power is in kW.

Q3. Can a 24V battery be connected to a 48V inverter?

No. They must be within the same voltage range.

Q4. Why is it important to have a surge power rating?

Surge power rating is important to the starting of a load, such as a pump or refrigerator, that is driven by a motor.

Q5. What is the role of MPPT in Residential Energy Storage Solutions?

The role of MPPT is to enhance the amount of PV energy that can be captured and used by optimizing the operating conditions of solar panels.