Short answer
A battery choice starts from the use case, not from kWh. First decide whether you need power (kW for peak shaving) or energy (kWh to cover hours), then check usable capacity, C-rate, cycles, warranty, safety and whether control is available over a documented interface.
HUBCORE internal size classes
Mini, Medium and XL are HUBCORE internal planning classes, not an industry standard or a product range. We use them to keep discussion site-specific and comparable. In every class we assess the same list: applications, power vs energy, chemistry, usable capacity, cycle assumptions, warranty, thermal management, C-rate, fire safety, environment, serviceability, communications, lifecycle cost and expansion.
| Class | Energy | Typical use |
|---|---|---|
| Mini | 5–20 kWh | Single-family self-consumption, small peak shaving, backup for selected loads |
| Medium | 20–200 kWh | Apartment building, small commercial or industrial site, charging buffer |
| XL | 200 kWh to multi-MWh | Large site, infrastructure, aggregated flexibility in the future |
HUBCORE implication
A class alone never decides — it only tells us which scale of logic and which level of safety and service requirements apply on site.
Power vs energy
Power (kW) defines how much can be delivered or absorbed at an instant; energy (kWh) defines for how long. Peak shaving and phase balancing need power; price arbitrage and overnight charging need energy. The wrong ratio makes the battery either too slow or needlessly large.
- The C-rate links them: a 100 kWh battery at 0.5 C delivers roughly 50 kW.
- Continuous power and peak power differ — check both, plus the duration.
- Real system power may be limited by the inverter/PCS, not by the cells.
Chemistries and direction of travel
Stationary storage today is dominated by LFP thanks to lifetime and thermal stability. Sodium-ion is a rising direction for low cost and cold tolerance, LTO is a niche for very high cycle counts and fast charging, and solid-state remains largely in development and pilot stage. No chemistry is automatically good or bad for HUBCORE — the site profile and controllability decide.
| Chemistry | Role |
|---|---|
| LFP | Mainstream reference for stationary storage |
| Sodium-ion | Emerging direction, tracked in pilots |
| LTO | Special purpose: very high cycle counts and fast charging |
| Solid-state | Future-facing, not normal stationary procurement today |
We publish no manufacturer cycle counts or lifetime claims here. Those must be requested from the supplier in writing and tied to warranty terms.
Usable capacity, lifetime and warranty
Nominal capacity is not usable capacity. The usable share depends on allowed depth of discharge, temperature, ageing and reserves kept by the control logic. Warranties must be read as numbers: years, cycles, energy throughput (kWh) and the guaranteed remaining capacity at the end of the period.
- Usable kWh, not just nominal capacity
- Warranty: years + cycles + kWh throughput + end-of-term capacity
- Operating temperature range and cold-weather power derating
- Does the warranty hold under our usage profile (cycles per day)?
Thermal safety and fire protection
Safety is a question of the installation, not only the device. Consider placement, ventilation, fire compartmentation, suppression, gas venting, fire-brigade access and how the BMS reports a fault outwards.
Nothing here replaces the requirements of the designer, installer and rescue authority. Compliance must be evidenced per site.
Communications, service and lifecycle cost
For HUBCORE, communications and service matter as much as the cells. We need at minimum local reads and setpoint writes, clear fault reporting, and clarity on who owns firmware and spare parts across the lifetime. Lifecycle cost includes installation, maintenance, losses, software, insurance and end-of-life handling.
- Round-trip efficiency and standby self-consumption
- Documented register/API map, not just a mobile app
- Machine-readable fault reporting, not only an LED
- Decommissioning and recycling agreed in advance
HUBCORE fit filter
- Controllability — Can the device be safely limited, started and stopped through a documented interface?
- Measurability — Do we get trustworthy measurements (power, energy, phases, state, faults) at sufficient resolution?
- Integrability — Is the interface publicly documented (e.g. Modbus, SunSpec, REST, MQTT, OCPP) and versioned?
- Local operation — Do critical control and safety keep working when the vendor cloud or internet is down?
- Security — Is access authenticated, are rights scoped, is traffic encrypted and firmware updatable?
- Serviceability — Is it clear who owns maintenance, spare parts, firmware and fault resolution?
- Scalability — Can the solution grow (more points, kWh, sites) without redesigning the architecture?
HUBCORE's position
HUBCORE prefers storage whose usable capacity, power limits and fault states are machine-readable locally, and whose safety and service responsibilities are contractually clear. Without those we cannot promise dynamic load management.
Not yet verified
- Which chemistries stay most stable in Estonian outdoor conditions?
- How to report battery degradation honestly and understandably to a customer?