If you purchased a GridFree system several years ago, there is a good chance it is still running one of our earlier inverter and solar-controller combinations.
These may include:
- An EPEVER UPower hybrid inverter (UP3kVa / UP5kVa)
-An EPEVER standalone MPPT charge controller with a separate pure sine wave inverter (Epever Tracer MPPT, Epever SHI Series inverter)
- An earlier Growatt hybrid inverter (SPF5000TL / SPF5000ES)
- A bank of lead-acid GEL batteries
These systems have powered baches, cabins, tiny homes and off-grid properties throughout New Zealand for years. But batteries do not last forever.
If you find that your gel batteries are no longer holding a charge, you may need to consider replacement. A good indicator of this is if your system is running out of battery before the morning - even when the day before was very sunny, and power usage was normal.
Why upgrade from GEL to lithium?
A modern LiFePO₄ lithium battery offers several advantages over a traditional GEL battery bank.
More usable energy
Lead-acid batteries are normally operated with a relatively shallow depth of discharge to protect their lifespan. This means a large portion of the advertised capacity is not intended for regular use.
Modern lithium batteries can generally provide much more usable capacity.
For example, the TBB ES100 II battery is designed for up to 90% depth of discharge (80% is recommended for the longest lifespan) as opposed the 50% depth of discharge for the Gel batteries.
In practical terms, a lithium bank may provide more usable energy without taking up as much space as the GEL bank it replaces.
Longer cycle life
GridFree’s current TBB and BSLBATT lithium batteries are rated for approximately 6,000 cycles under their specified operating conditions.
This makes lithium a strong long-term replacement for a GEL bank that may already be reaching the end of its useful life.
Faster and more efficient charging
Lithium batteries can generally accept a higher charging current and recharge more efficiently than lead-acid batteries.
This is particularly useful during winter or generator charging, when you want to put energy back into the batteries as efficiently as possible.
Built-in battery protection
A lithium battery contains a Battery Management System, or BMS, which protects the cells against conditions such as overcharging, over-discharging, excessive current and temperature problems.
With a compatible inverter and communication connection, the BMS can also share real-time battery information with the rest of the system.
Can I replace them with lithium batteries?
The answer is usually yes, but it may not be the case of just disconnecting the old batteries and installing new ones. To determine what you need for a lithium battery upgrade, we will need to check a couple of things about your system:
- Nominal system voltage - 48V is required for our lithium options
- Battery BMS communication compatibility (for the ES100 & BSL options)
- Existing DC cables, fuses and circuit breakers
- Generator charging and automatic-start configuration
Many legacy hybrid inverters / EPEVER standalone charge controllers & inverters were designed primarily around lead-acid batteries. They may not support closed-loop BMS communication or provide the monitoring and control available from a modern lithium-compatible inverter.
That is why many lithium upgrades are also a good opportunity to replace the hybrid inverter.
Newest GridFree Hybrid Inverter options
Why upgrade the inverter at the same time?
Replacing the inverter may increase the initial cost, but it can turn a battery replacement into a genuine system upgrade.
Better communication with the battery
With closed-loop communication, the battery BMS can share information such as:
- State of charge
- Charging and discharging limits
- Battery voltage and current
- Temperature
- Warning and fault information
The inverter can then respond to the battery’s actual condition instead of relying only on voltage estimates. This improves battery protection and gives you a much clearer picture of how the system is performing.
More accurate generator auto-start
Many older systems use battery voltage to decide when the generator should start.
That approach is less effective with lithium because lithium voltage remains relatively stable through much of the discharge cycle. A voltage-based system may struggle to accurately identify the remaining battery capacity - and causes Auto start/stop to fail.
With compatible BMS communication, a modern inverter can use the reported battery state of charge for generator control.
For example, the generator could be configured to start when the battery reaches a selected state of charge and stop again after it has recovered.
This is more useful than waiting for a low-voltage condition and can reduce unnecessary generator operation.
The TBB E4 monitoring system supports local & remote monitoring, lithium battery data and automatic generator start and stop control within a compatible TBB system.
Better local and remote monitoring
A modern system can give you much more visibility than many older installations.
Depending on the selected equipment, monitoring may include:
- Current battery state of charge
- Solar generation
- Household consumption
- Battery charging and discharging
- Generator status and running time
- Warning and fault history
- Remote system settings and diagnostics
Selected TBB systems can be monitored locally through the E4 display and remotely through the NOVA platform. Selected SRNE equipment also supports local displays, Bluetooth, Wi-Fi or app-based monitoring.
This can make troubleshooting much easier, especially when the system is installed in a remote location.
Low-frequency inverter options
For customers running pumps, compressors, freezers, power tools or other demanding loads, a TBB low-frequency hybrid inverter may provide a substantial performance upgrade.
Transformer-based models such as the TBB RiiO Sun II and TBB Matrix II are designed to provide strong surge and overload capability.
This can be particularly valuable in a permanent off-grid home where multiple appliances may operate at the same time.
Not every customer needs a low-frequency inverter. SRNE can provide a more affordable, modern upgrade for lighter or more predictable applications. The correct choice depends on your loads, generator, solar array and plans for future expansion.
Below, Ollie gives you a good explanation of High- vs Low-Frequency Inverter.
Current lithium upgrade options
GridFree can provide upgrade solutions using current SRNE or TBB hybrid inverters with BSLBATT or TBB ES100 II lithium batteries, subject to confirming the exact inverter model, firmware and system configuration.
SRNE hybrid inverter upgrade
A current SRNE hybrid inverter can be a cost-effective option for customers wanting:
- Lithium battery compatibility
- Modern charging controls
- Improved local or remote monitoring
- Integrated solar, battery and generator management
- More solar-input capacity on selected models
- Dual MPPT inputs on selected models
For example, the current SRNE AEP 6kW provides two MPPT trackers, a dedicated generator connection and a 48V battery platform.
TBB hybrid inverter upgrade
A TBB upgrade is well suited to customers wanting:
- Low-frequency, transformer-based inverter technology
- Strong surge performance
- Closed-loop lithium battery communication
- Generator power assist and automatic start control
- NOVA remote monitoring
- Optional E4 local monitoring
- Modular battery and inverter expansion
TBB options are available for smaller systems through to large permanent off-grid homes.
A second MPPT can solve another legacy-system problem
Customers often want to add more solar panels while upgrading their batteries.
The challenge is that the original solar-panel model may no longer be available.
Solar technology develops quickly. Manufacturers regularly change:
- Panel wattage
- Cell technology
- Operating voltage
- Operating current
- Physical dimensions
- Frame design
- Connector and cable arrangements
A panel installed several years ago may have been replaced by a newer, higher-output model with different electrical characteristics.
Example of our new TW Solar 440W N-Type BiFacial panels
Why shouldn’t different panels simply be mixed together?
Panels connected to the same string and MPPT should have closely matched electrical characteristics.
When mismatched panels are connected in series, the current of the string can be limited by the lowest-current panel.
When different strings are connected in parallel to the same tracker, voltage differences can prevent the arrays from operating at their individual optimum points.
Even if the panels appear to work together, the mismatch can reduce generation and make system design more difficult.
Physical differences may also create mounting and layout problems.
How does dual MPPT help?
A hybrid inverter with two independent MPPT trackers can often keep the original array and the new array electrically separate.
For example:
- MPPT 1 can continue operating the existing panels.
- MPPT 2 can operate a new string of current-generation panels.
Each tracker can then find the best operating point for its connected array.
This means the new panels do not necessarily need to match the original panels, as long as each separate string remains within the inverter’s voltage, current and power limits.
Dual MPPT does not automatically make every combination suitable, but it gives the system designer far more flexibility.
Example above: Tui Solar Nest up to 4 lithium batteries and up to 16 solar panels expansion.
What might be reusable?
A lithium upgrade does not always mean replacing the entire solar system.
Depending on the condition and compatibility of the existing equipment, it may be possible to retain:
- Existing solar panels
- Solar-panel mounting
- Selected MPPT charge controllers
- A suitable standalone inverter
- Generator equipment
- AC distribution equipment
- Some existing DC protection and cabling
However, every component must be checked before being reused.
Lithium batteries can deliver very high current, so cable size, battery protection, isolators, busbars and terminations must be appropriate for the new battery and inverter combination.
Old and new batteries should not be combined into the same bank unless the manufacturers have specifically approved that configuration. GEL and lithium batteries must not be directly paralleled together.
What information does GridFree need?
To assess a legacy GridFree system, please send us:
- Photos of the complete system
- A clear photo of every product label
- Existing inverter and MPPT model numbers
- Battery voltage, quantity, capacity and age
- Solar-panel quantity and wattage
- A photo of the solar-panel specification label, if available
- Generator make and model
- A list of any new appliances you want to run
- Details of any future solar or battery expansion
From there, we can determine what can remain, what should be replaced and which upgrade pathway makes the most sense.
This is more than a battery replacement
If your GEL batteries are reaching the end of their life, replacing them with lithium is an opportunity to improve the entire system.
A properly designed upgrade can provide:
- More usable battery capacity
- Longer battery life
- Faster charging
- Better generator control
- Clearer monitoring
- Improved surge handling
- More room for additional solar panels
- Easier future expansion
Most importantly, it brings an older GridFree system onto a modern platform that can continue growing with your property and power requirements.
Important note: don’t automatically replace an old battery bank with more of the same. Use the opportunity to future-proof your off-grid system.
If you're planning to do an upgrade, talk to the team so we can provide you with the right guidance and offer you the best deal! Send your system photos and model details or request an off-grid solar quote, and we can help you plan the correct lithium upgrade.