Home Battery Storage
-- Specs, Backup Math and Site Fit
Home Battery Storage: Specs, Backup Math and Site Fit
A home battery does two jobs — ride through outages and shave the electricity bill — and they need different sizes. The original version of this page promised "3-7 days of essential power" without ever listing the loads, and quoted "98% round-trip efficiency" without saying which side of the inverter it was measured on. Both numbers are defensible once you attach assumptions; neither survives as a bare claim. This page puts the assumptions back, and states plainly when a battery is not worth buying. Scope note: we manufacture the storage hardware; residential installation is performed by licensed electricians in the installer channel, and the electrical work is never a homeowner DIY item.
The backup math, with the assumptions stated
Backup duration is a division problem, not a marketing number. Take a 10 kWh LiFePO4 pack — the middle of the 10–15 kWh range the original page lists — and two honest load lists:
- Essential loads only. A refrigerator at roughly 1–1.5 kWh per day, LED lighting and device charging at roughly 0.5 kWh per day, and a critical medical device per its rating. Call it 2 kWh per day. A 10 kWh pack at 90% usable depth holds roughly 9 kWh, so the arithmetic gives about four days — inside the original's "3-7 days" claim, at the low end.
- Add HVAC. A typical residential heat-pump or central AC draws 2–4 kWh for every hour of runtime. One evening of cooling can consume the same energy the essential loads use in two days. With HVAC in the backup scope, the same 10 kWh pack is measured in hours, not days.
Those are calculated examples from typical appliance draw, not measurements of your house. The design rule we apply: size the battery to the load list you actually wrote down, and put the load list in the quote. "Whole-home backup" on a 10 kWh pack is a contradiction; either the load list shrinks or the pack grows.
Specifications, with the reasoning behind each number
| Parameter | Typical value | What it actually means |
|---|---|---|
| Capacity | 10–15 kWh per unit, modular | Modular units stack; the inverter caps the total |
| Chemistry | LiFePO4 (lithium iron phosphate) | Chosen for thermal stability and cycle life; safe chemistry for occupied buildings |
| Round-trip efficiency | ~98% DC-side; ~85–90% AC-AC | The 98% figure is battery terminals in and out. Your wall-to-wall number includes inverter losses, and it is lower |
| Cycle life | ~4,000–6,000 cycles to 80% capacity (typical LiFePO4) | At what temperature and depth of discharge — ask |
| Service life | 10+ years under warranty terms | Usually a capacity-retention threshold, not a guaranteed calendar life |
| Backup transfer | Automatic switchover on grid outage | Detection and transfer typically in milliseconds; check the spec, not the brochure |
| Operation | Fanless or near-silent, temperature-controlled | Placement still matters — see the site section |
The bill-management job
Bill savings come from three mechanisms, and each has a condition attached:
- Solar self-consumption. Store midday solar instead of exporting it at a low rate, then use it in the evening. This is the strongest residential case, and it requires the solar array to exist first. A battery bolted onto a small array mostly stores grid power at a round-trip loss.
- Time-of-use (TOU) optimization. Charge when power is cheap, discharge when it is expensive. The benefit is the tariff spread minus round-trip losses and a degradation reserve. Flat tariffs with no time structure leave nothing to arbitrage.
- Peak shaving. Residential rate schedules rarely bill demand charges; where they do not, "reduced peak electricity charges" — one of the original page's bullet claims — simply does not apply to your bill.
Our control system handles the mechanics: weather-informed charging, load-priority management, grid-outage detection, real-time energy-flow monitoring in the mobile app, and predictive-maintenance alerts. The mechanics are table stakes. The question that decides the purchase is your tariff.
Where home storage fits — and where it does not
A battery earns its keep where at least one of these holds: frequent or long grid outages, a TOU tariff with a wide spread, or an existing or planned solar array large enough to fill the battery. Where none hold — a stable grid, a flat tariff, no solar — the honest engineering answer is that the battery is an expensive insurance policy you may never collect on. We will tell you that on the phone before we quote it.
The other site conditions are physical: an installation location within the pack's temperature window (an unheated garage in a cold climate is a poor battery room), ventilation and clearance per code, and a critical-loads subpanel so the backup scope is defined by wiring rather than by hope.
The sizing mistakes we see most often
Three patterns account for most of the mis-sized residential systems we are asked to review:
- Inverter oversized relative to the battery. The inverter can surge loads the battery cannot sustain, and the backup scope silently shrinks in winter.
- HVAC left on the backup circuit. One AC unit on the backup panel can halve the runtime of an otherwise well-sized pack. Put it on a manual transfer or leave it off.
- Battery added before the solar. Where the array comes later, the battery spends its first year arbitraging grid power at a loss.
What this page does not cover
This page covers residential grid-tied battery storage in the 10–15 kWh class. It does not cover off-grid cabin systems (different autonomy rules, different sizing), grid-tied solar without storage, or commercial demand-response programs. To size the storage and control side for a specific house, our controller sizing calculator covers the power-electronics envelope; for the utility-scale sibling of this product, see container battery storage. If your project is lighting rather than house loads, the all-in-one solar street light line is the same battery technology engineered for a different duty.