In extreme low temperature event, the charging/discharging rate of the ESS decreases or even stops. To solve this problem, the Huawei LUNA2000 utilizes a built-in heating unit. This document describes the LUNA2000 heating system.
The built-in battery thermal management unit will increase the temperature of battery cell.
- Work Process: Under Max Self-consumption work mode, the built-in battery thermal management unit will only consume the PV energy during the daytime (Shown below).
Figure 1 Battery Thermal Management System Working Principle
P_bat= P_pv – P_load (The system will not stop charging battery even if the BTMS stops.
1. Under Max Self-consumption work mode, the built-in battery thermal management system will attempt to start. If the charging power is insufficient (Require 300W per 5kWh module), the system automatically exits after 0.2s. (Try again after 10 minutes.)
2. Only when the battery is forced to be charged, the BTMS will consume the energy from grid in order to charge the battery, i.e. TOU or SOC Remaining Process
3. The heating unit of each battery module can work independently. The lowest SOC will be charged firstly if the P_bat is not enough.
4. Disabling logic: (Any of the following conditions is met)
① Battery is not at charging status (discharging or standby)
② P_Bat charging power ≤ 300 W x n (n indicates the number of battery packs.)
③ Minimum cell temperature in the PACK ≥ 13°C
Q&A: Will the heating unit cause the battery SOC to drop?
No, the heating unit does not consume power from the cell and does not decrease the SOC. The heating unit is turned on only in the charging state, the energy is either from PV or grid under two different working mode. The heating unit is turned off once it enters into the discharging state.
Q&A: How long it takes to heat up? How much energy is required?
At -25℃, the heating unit temperature rising rate is 0.36°C/min, if ambient temperature is higher, the temperature rising rate can be as high as 0.447°C/min.
Heating time (min) = (13°C - T_cell) / 0.36
For example, if the lowest cell temperature of a PACK is –10°C, the heating time (13 + 10)/0.36 is about 64 minutes, and the heating power consumption is 0.32 kWh.
Note: Because different battery cells will require different quantity of heat, the time of heating process will depends on the actual situation.）
Q&A: What’s the charging power after heating?
With heating unit, battery charging rate is at 0.5C, it takes only 2 hours to charge battery to full state. When compared to other storage system without heating unit, in the winter, battery can hardly be fully charged in the daytime due to low charge rate.