In short
- Size the battery on what you use between sunset and sunrise, not on daily solar production.
- Count on the usable energy of each module, which is lower than its nominal figure.
- Past a point, an extra module stays half empty most of the year; your own data shows where that point is.
The module names hint at their nominal energy, roughly 4.4 kWh for the 4K4 and 5.3 kWh for the 5K3. Check the datasheet of your exact version for the usable figure and the recommended depth of discharge.
Start from your nights
A battery earns its keep by covering what the house uses after the sun has gone: dinner, lighting, standby loads, the fridge, perhaps a heat pump. Many homes use somewhere between 4 and 10 kWh in that window. Your electricity bill or meter app can give you a first estimate.
From kWh to modules
Divide your evening and night use by the usable energy of one module, then round up. A home using 7 kWh at night lands on two modules in most cases. Keep a small reserve at the bottom for power cuts if your inverter offers backup.
The inverter sets a ceiling
More modules store more, but the inverter limits how fast that energy comes in and goes out. A battery that is much larger than what the inverter can charge on a winter day will rarely fill. Check the inverter battery current limit before adding modules.
Seasons change the answer
In Italian summers a cluster fills by noon and empties slowly; in winter it may never fill. Sizing for summer nights gives a battery that is fully used most of the year. Sizing for winter gives spare capacity in summer.
Let your data decide the next module
WeCo Monitor reads each module of the cluster and records charge, energy in and out, and the time spent full or empty. After a few weeks you see whether the battery reaches the bottom every night, which argues for one more module, or stays half full, which says you have enough.
Common questions
Can I add a WeCo module to an existing cluster later?
Clusters are designed to grow, but mixing very old and new modules can limit the bank. Check WeCo guidance for your version and firmware first.
Does WeCo Monitor work with high-voltage WeCo batteries?
No. It is for the low-voltage modules such as 4K4 and 5K3.
Does the box change how the cluster charges?
No. It only reads. Charging is controlled by the battery and the inverter.
