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Quick Answer
A typical 2,500 sq ft home needs 2-3 batteries (26-40 kWh) for whole-home backup lasting 12-24 hours. Essential-only backup (fridge, lights, internet, sump pump) needs just 1 battery (13 kWh) lasting 24-48 hours. Cost: $12,000-16,000 for 1 battery, $24,000-40,000 for whole-home.
Use this table for a fast estimate. Battery counts assume ~13 kWh per unit (Tesla Powerwall 3 equivalent). Your actual needs depend on specific appliances and usage patterns.
| Home Size | Essential Only1 day | Whole Home1 day | Whole Home2 days |
|---|---|---|---|
| 1,500 sq ft | 1 13 kWh $12,000 - $16,000 | 2 26 kWh $24,000 - $30,000 | 3 40 kWh $35,000 - $44,000 |
| 2,500 sq ft | 1-2 13-26 kWh $12,000 - $30,000 | 2-3 26-40 kWh $24,000 - $44,000 | 4 52 kWh $46,000 - $58,000 |
| 3,500 sq ft | 2 26 kWh $24,000 - $30,000 | 3-4 40-52 kWh $35,000 - $58,000 | 5 65 kWh $58,000 - $72,000 |
~9 kWh/day | 1 battery = 24-48 hrs
~104 kWh/day total | 2-3 batteries
Prices include installation, electrical work, and permits. All products listed below are available through NuWatt in our service areas.
Capacity
13.5 kWh
Power
11.5 kW continuous
Price
$12,000 - $16,000
Capacity
16 kWh
Power
7 kW continuous
Price
$13,000 - $17,000
Capacity
5 kWh per unit
Power
3.84 kW per unit
Price
$6,000 - $8,000 per unit
Capacity
9-18 kWh (configurable)
Power
9 kW continuous
Price
$14,000 - $22,000
A standalone battery provides finite backup. Solar + battery provides renewable backup that recharges every day, extending outage protection from hours to days or even weeks.
Solar panels recharge your battery during the day, even during a grid outage. A 8 kW solar system can replenish a full 13 kWh battery in 2-3 hours of good sun.
Without solar, a battery dies after 12-48 hours. With solar, you can ride through multi-day nor'easters and ice storms common in the Northeast.
Even without outages, solar + battery lets you store cheap daytime solar and use it during expensive peak hours, maximizing your savings year-round.
In Massachusetts, Connecticut, Rhode Island, and Vermont, utilities pay battery owners to dispatch stored energy during peak demand events. This can offset 40-60% of your battery cost over 10 years.
| Utility | Summer Rate | Winter Rate | Annual Revenue (6kW) |
|---|---|---|---|
| Eversource (MA/CT) | $275/kW | $50/kW | ~$1,950/yr (6kW) |
| National Grid (MA/RI) | $225/kW | $50/kW | ~$1,650/yr (6kW) |
| RI Energy | $225/kW | -- | ~$1,350/yr (6kW) |
| GMP (VT) | Varies | -- | ~$900/yr (6kW) |
Revenue estimates based on 6 kW continuous output battery (e.g., one Tesla Powerwall 3) participating in all eligible dispatch events. Actual revenue varies by dispatch frequency and battery state of charge.
For a typical 2,500 sq ft home, you need 2-3 Tesla Powerwalls (26-40 kWh) for whole-home backup lasting 12-24 hours. A single Powerwall (13.5 kWh) can cover essential loads (fridge, lights, internet, sump pump) for 24-48 hours. The exact number depends on your energy usage, which appliances you want to back up, and how long you want backup to last.
A whole-home battery backup system costs $24,000-$40,000 installed for a typical home, which includes 2-3 battery units, an automatic transfer switch, and installation. A single battery for essential-only backup costs $12,000-$16,000 installed. There is no federal tax credit for standalone batteries in 2026 (Section 25D expired), but batteries paired with solar may qualify through third-party ownership structures.
Yes, this is one of the biggest advantages of solar + battery. During a daytime outage, your solar panels continue generating power that recharges the batteries, extending backup duration indefinitely in good weather. Without solar, batteries provide finite backup (12-48 hours depending on size). This makes solar + battery particularly valuable for multi-day outages like nor'easters.
Essential backup covers only critical loads: refrigerator, lights, internet, medical equipment, sump pump, and phone charging -- typically 5-10 kWh per day. Whole-home backup powers everything including AC/heat pump, electric dryer, stove, EV charger, and hot water -- typically 30-50+ kWh per day. Essential backup costs 50-60% less and lasts 3-5x longer on the same battery capacity.
A single 13 kWh battery powers essential loads for 24-48 hours. For whole-home backup, a single battery lasts only 4-8 hours depending on usage. Two batteries extend whole-home backup to 12-16 hours. Three batteries provide 18-24 hours. With solar panels recharging during the day, multi-day backup is possible even with fewer batteries.
Yes. In Massachusetts, Connecticut, Rhode Island, and Vermont, the ConnectedSolutions program pays you to dispatch your battery during peak grid demand. Eversource pays $275/kW in summer and $50/kW in winter. For a typical 13 kWh battery with 6 kW output, that is roughly $1,650-$1,950 per year. Over 10 years, this can offset 40-60% of the battery cost.
We analyze your actual energy usage, critical loads, and outage history to recommend the right battery size. Free assessment, no obligation.