Step 1: separate energy (kWh) from power (kW)
Two different numbers are constantly confused. Energy, in kWh, is how long the battery can run your loads — the size of the tank. Power, in kW, is how many loads it can run at once — the size of the tap. A kettle and an oven together need power; keeping the fridge and lights on all night needs energy. A battery can be big in one and small in the other. The home anchor — the TF-5KW-10KWH system — states both: 5 kW of output power and a 10 kWh-class store. Size energy first, then check the power figure covers your simultaneous loads, including motor starting surges.
Step 2: build the load list
Write down what must run during an outage (or what you want solar to cover in the evening), with running watts and hours. A typical essentials list: refrigerator and freezer at roughly 150 W averaged over the day, LED lighting at 100 W for five evening hours, router and devices at 50 W continuously, a television at 120 W for four hours. That list totals around 3 to 4 kWh per night. Add a comfort tier — an hour of electric cooking, water heating, a washing machine cycle — and the evening total rises to 6 to 9 kWh. Whole-home overnight autonomy with air conditioning can exceed 15 kWh. Your list, not your neighbour's, sets the size.
Step 3: correct for usable capacity
Not all nameplate energy is usable. The Torphan storage lines run a 96% depth of discharge, so a 10.5 kWh unit delivers about 10.1 kWh of working energy — a small correction, but one to make, because older lead-acid practice only allowed around half the nameplate to be used. Apply your inverter's efficiency on top if you are being precise; the lithium line's efficiency rate is 98%, so the depth-of-discharge figure is the main adjustment.
Step 4: match to unit sizes
Now the arithmetic meets the catalogue. Essentials-only backup at 3 to 4 kWh maps to one 5.12 kWh Li-W wall unit (100 Ah) — about 4.9 kWh usable at 96% depth of discharge, before inverter losses — with margin. The typical solar self-consumption home at 6 to 10 kWh of evening load maps to the 10.5 kWh unit (206 Ah) or the 14.3 kWh unit (280 Ah). Larger homes, or homes wanting full overnight cover, parallel wall units — up to six in parallel — or step to the Li-S home systems at 14.3 kWh and 28.6 kWh. Note the second benefit of sizing this way: a battery that cycles deeply every day earns its cost back on solar self-consumption, while an oversized battery that idles at shallow cycles never does.
Step 5: leave a growth path, not a guess
Loads change: an EV arrives, a heat pump replaces a boiler, a home office becomes permanent. The range is modular for exactly this reason — wall units parallel up to six inside their own series, and each series keeps its own BMS and inverter settings, which the quote confirms when a second unit is added. Buy for the load list you have, on a platform that accepts the next unit when the list grows.
If you would rather have the arithmetic checked, send your load list (or your daily consumption from a smart meter) through the quote form, with a note on whether the priority is backup, solar self-consumption, or both. The reply sizes against the units above rather than a generic recommendation.
Worked example: a solar home at the range's unit sizes
Take a three-bedroom solar home with a measured daily consumption of 18 kWh, of which about 8 kWh falls after the array stops producing. Backup priority is essentials — refrigeration, lighting, communications — at roughly 3.5 kWh overnight. The self-consumption target (8 kWh) is the larger number, so it sets the size: the 10.5 kWh Li-W unit (206 Ah) delivers about 10.1 kWh usable at 96% depth of discharge, covering the 8 kWh evening with margin and the 3.5 kWh essentials list just under three times over during an outage — 10.1 divided by 3.5 is about 2.9, before inverter losses. A smaller household with 5 kWh of evening load steps past the 5.12 kWh unit — its roughly 4.9 kWh usable falls just short of a 5 kWh list — and lands on the 10.5 kWh unit or two paralleled wall units; a larger one at 13 kWh of evening load on the 14.3 kWh unit or two paralleled mid-size units. Every case follows the same path: measure the evening load, correct for usable capacity, pick the unit that covers it.
Common sizing mistakes
Three errors recur. Sizing to the array instead of the load buys capacity that cycles shallowly and pays back slowly. Forgetting the power rating buys a battery that can store the evening but cannot start the well pump — check kW alongside kWh. And ignoring the growth path buys a closed system that must be replaced when an EV arrives; the modular platforms exist precisely so the second unit is an addition, not a replacement.
Power rating check: the motors decide
Return to the power side once more, because it is where undersized systems disappoint. Motors — well pumps, air-conditioning compressors, power tools — draw a starting surge several times their running watts. The home system class pairs its storage with a 5 kW output rating, which starts typical household motors comfortably; homes with large pumps or multiple air conditioners should state those loads explicitly in the inquiry so the inverter side of the quote is specified for them. Energy sizing gets the attention because it is easy to calculate; power sizing is what determines whether the lights flicker when the pump starts. A complete quote states both numbers, against your load list, in writing.
The one-page version
List the loads, total the evening kWh, correct for usable capacity, check the kW rating against your largest motor, and pick the unit that covers the result — then confirm the growth path. Five steps, one page of arithmetic, and the battery you buy is the battery your house actually needs.