Integrating Solar Battery Storage: A Guide for Home Energy Systems

“The residential PV-plus-storage market is expected to increase twelvefold, from 180 MW in 2018 to 2,181 MW in 2023.”  Wood Mackenzie

We have the technology, tools, and knowledge to address many environmental challenges. All we need to do is put them to use. Solar energy is one such solution. Battery storage is another tool in our belt to optimize our home’s energy, improve our energy strategy, and secure backup power when needed.

To give you an idea of the several scenarios for implementing battery storage for homes, we’re highlighting a handful of them. Whether you’ve already installed solar and want to add a battery, or you want to implement both a solar and battery storage system simultaneously. A solar battery storage system can also be added to a home without a solar system, and you can power the battery from the grid or another source. There are many reasons and various ways to implement home battery storage. 

In this article, you will learn:

• What inverters are, including hybrid string inverters and microinverters
• How inverters work with your battery storage
• How to identify your inverter brand
• Seven scenarios for implementing battery storage 

Do you want to charge your battery from the grid or solar?

The answer to this can have multiple consequences. The Federal Investment Tax Credit of 30% for the battery is not valid if the battery is charged from and connected to the grid. Moreover, if the grid goes down and your battery draws its charge from the grid, you will only have the existing battery life to rely on until the grid is restored. However, by incorporating a gas-powered generator, you could continually recharge your battery to maintain the power supply. You can learn more about what is the best backup source for power, energy storage vs. a generator here. For this to work effectively, you would need a sufficient supply of natural gas, LPG gasoline, or diesel, depending on the generator you select.

Alternatively, suppose you aim to use the battery for energy arbitrage or peak shaving. In that case, you can charge the battery during off-peak times when energy rates are lower and then discharge it during peak usage periods.

On the other hand, if you opt to charge the battery with solar power, you can replenish your battery whenever the sun is shining. During peak usage times, you can utilize both solar and battery power to reduce the amount of energy you need to purchase from the utility during these high-cost periods.

A crash course on inverters for your new battery

When integrating a new battery into your system, it’s essential to note that it will always be paired with an inverter, as inverters are designed to work with batteries. This arrangement is required because most solar battery storage available today charges using Direct Current (DC). However, your home’s power supply – whether it’s derived from the grid, solar energy, a generator, or a battery – utilizes Alternating Current (AC).

An inverter is a device that converts DC electricity to AC electricity. It does this through a process called inversion. Inside the inverter, there’s an oscillator that creates a flipping or alternating current from the direct current supplied by the battery. This alternating current is in sync with the electrical grid’s frequency, which is typically 50 or 60 Hz, depending on your location.

How to identify the type of inverter used in your home solar system

Begin by inspecting their installation documents, i.e., plans, manuals, and contracts that specify the type of equipment. You can also inspect the equipment around your home’s electrical panel. Look for a sizable box, which is likely your solar inverter. Try to locate a manufacturer’s name or model number on this box. Once you’ve noted these details, you can search online to learn more about your specific inverter type. Check your solar monitoring app, which should provide information on whether you have a string inverter or a microinverter. 

What is a string inverter?

A string inverter is designed to convert the direct current (D.C.) power generated by a series, or “string,” of solar panels into alternating current (A.C.) power, which is used by most household appliances and can be fed into the electrical grid.

In a system using a string inverter, multiple solar panels are connected together in a series, creating a “string.” The DC electricity from all the panels in the string is sent to the string inverter, which then converts it into A.C. electricity.

String inverters use optimizers to prevent other panels from being negatively impacted by the underperformance or shading of a single solar panel within the string.

What are microinverters?

Microinverters have the same function as string inverters, converting D.C. electricity produced to A.C. electricity needed to power the home. The difference is that microinverters are connected to each panel, allowing each panel to be monitored more independently.

What is a hybrid inverter?

Hybrid inverters, like those manufactured by Sol-Ark, function similarly to standard string solar inverters for power generation. The unique aspect of hybrid inverters is their incorporated battery connections, which facilitate energy storage for future consumption. Thanks to this energy storage feature, most hybrid systems can serve as a backup power source during a power outage.

What is a rapid shutdown device?

All new rooftop installations in the U.S., including residential and commercial buildings, must have a rapid shutdown system. Rapid shutdown is gaining global adoption as it ensures the safety of firefighters and other professionals working around solar P.V. equipment.

A rapid shutdown device is a critical safety measure for P.V. systems, as mandated by the National Electrical Code (NEC) in the United States. It allows for the de-energization or reduction of voltage from the solar modules on the rooftop, essentially acting as an “on or off” switch. This mechanism is crucial for firefighters or solar installers, allowing them to perform their duties while avoiding potential electrical hazards safely. The rapid shutdown function is achieved using Module Level Power Electronics (MLPE), which controls the output from each solar panel. Microinverters are one type of MLPE. For central inverter systems like Solaredge, the MLPE function is commonly called DC Optimizers.

What are the most common inverter brands?

Two of the most common inverter brands are SolarEdge and Enphase, which are on the Solar Insure Approved Vendor List (AVL) along with Generac and A.P. Systems, all great quality inverters. 

There are several scenarios for adding solar battery storage to your home; these are seven examples of how that can happen

#1 Existing solar system with a string inverter 

Utilize the existing solar, string inverter, and A.C. couple to your new inverter and battery. Extra wiring, electrical equipment, and work would need to be done. This process would require additional wiring, electrical components, and labor. Note that this configuration doesn’t facilitate charging the battery from the solar panels during power outages. It would be necessary to connect a generator to the battery system to ensure power supply during such instances.

#2 Existing solar system and microinverters, A.C. couple to new inverter and battery 

You can use your existing solar panels and microinverters by AC-coupling them with a new inverter and battery setup. This procedure will need extra wiring, electrical components, and labor. However, it’s important to note that this arrangement does not permit the solar panels to charge the battery during power outages. To maintain power supply during these periods, it would be advisable to incorporate a generator into the battery system.

#3 Retrofitting existing solar system with microinverters and implementing a rapid shutdown device – (only necessary for DC-coupled batteries)

In this scenario, you can modify one string of your existing solar panels by removing the microinverters/optimizers and replacing them with a Rapid Shutdown Device. This change allows you to channel energy to the battery directly. Additional wiring, electrical equipment, and labor would be necessary. The remaining solar energy would be dedicated to household use. This is not required for AC-coupled, where you leave the existing microinverters and combine the solar and battery together on their AC outputs. Many hybrid inverters (like Sol-Ark 15k or SolarEdge) can do DC or AC coupled. Notably, this setup enables charging your battery during a power outage, provided there’s sunlight. 

#4 Existing solar system with a string inverter, DC coupled only additions

In this configuration, you would supplement your current solar setup with a string inverter by adding a new string of panels equipped with Rapid Shutdown Devices. These devices would be placed under new panels and send energy directly to the battery. Adopting this plan would require additional wiring, electrical components, and labor. The residual solar energy would be allocated for household use. Importantly, this configuration allows for your battery to be charged during a power outage, as long as there’s adequate sunlight. DC to DC optimizers, which can be incorporated into string inverters, serve to mitigate the effects of shading on a sequence of solar panels, while also functioning as a quick shutdown mechanism. However, these benefits are accompanied by higher expenses. As a result, for clients who experience minimal to zero shading, this option may not be the most cost-effective solution. 

#5 Modify existing solar setup by installing Rapid Shutdown Devices with new inverters and battery

This setup involves altering your current solar system by installing a Rapid Shutdown Device beneath each panel in a chosen string. These devices are then wired directly to your newly incorporated inverter and battery. This approach will require extra wiring, the addition of more electrical equipment, and additional labor. It is only required for DC-coupled-only additions. This configuration enables your battery to be charged during a power outage as long as there’s sufficient sunlight.

#6: Battery-Only setup without solar system 

Gain from off-peak rates by installing a battery even if you don’t have solar. In this scenario, without solar panels, you can still leverage the battery to store energy during times of low utility rates, typically during nights or weekends. You will need to make a choice regarding the primary use of this stored energy – whether it’s for ‘peak shaving’ and ‘energy arbitrage’ to save costs during high-rate periods or to serve as a backup power source during outages.

#7 Upgrading an existing microinverter setup with Enphase IQ Plus Inverters 

In this situation, a string of panels within your current microinverter system is upgraded to Enphase IQ Plus inverters, or if you’re using the Enphase Battery System with all new features, you will need to use Enphase IQ8 Microinverters. You can also pair old Enphase microinverters with any new AC-coupled systems like Tesla or Sol-Ark. Additionally, an AC-coupled battery is installed. This modification will require extra wiring, the addition of further electrical equipment, and additional work. Under this setup, your battery will charge during a power outage, provided there is sufficient sunlight.

What is the simple workaround with AC vs DC coupled battery storage?

AC-coupled systems provide a simple workaround as they can be easily retrofitted to existing PV systems with minimal effort. In this configuration, the PV system charges the batteries through an AC connection.

On the other hand, DC-coupled systems require more extensive rework since they utilize a new inverter that handles both the PV system and the battery. With this setup, the existing PV modules need to be connected to the new inverter instead of the existing inverter(s).

Fortunately, many of the latest hybrid inverters, such as Sol-Ark, SimpliPhi, Fortress, etc., offer the flexibility to choose between AC or DC coupling. This allows users to select the most suitable configuration based on their specific requirements and system compatibility.

Solar Insure’s 20-Year Battery Monitoring and Warranty 

While the upfront cost may be an initial barrier to some considering battery storage, the overall costs have declined by 11%–25% from 2016–2020, according to an NREL report. Home battery storage systems are taking flight, and there are many ways to jump in and leverage the benefits of having stored energy, whatever your current scenario is. Solar Insure offers a 20-Year Battery Monitoring and Warranty, which is the longest on the market and includes parts, labor, and replacement when the battery falls below 30% capacity from years 11-20. The Solar Insure 20-Year Battery Monitoring and Warranty product must be coupled with the Solar Insure 30-Year Monitoring and Warranty product which covers parts and labor on panels, inverters, optimizers, and roof penetrations within 3 inches. Solar Insure has an extensive network of Solar Insure Certified Installers who have been vetted and approved through an exclusive process, which is helpful for homeowners on the battery installation journey. By adding Solar Insure, you can gain peace of mind when investing in solar battery storage. 

Resources

https://www.nrel.gov/docs/fy22osti/82511.pdf