8kW solar system: daily output, cost with battery, and what it actually runs

Let`s talk a bit about the 8kW off-grid solar kits. Many people end up confused, because the industry uses "8kW" for two different things. Here is the plain-numbers version.

Home running on an 8kW off-grid solar kit with 12 x 415W panels and 20kWh of batteries

"8kW" means two different things

8kW of panels. This is how rooftop installers describe grid-tied systems: about 20 panels of 400W. It tells you how much energy you generate.
8kW (8,000W) inverter. This is how off-grid kits are named. It tells you how much you can run at the same time. The panels bundled with these kits are often only 3-5.5kW.

So when you compare quotes or kits, check all three:

Inverter: how much you can run at once
Panels: how much energy you get per day
Battery: how long you can run at night

Daily output of 8kW of panels

Output = panel kW x peak sun hours x ~0.8 (losses from heat, wiring, dust and the inverter)

PNW / Northeast (3.5) - per day: ~22kWh; per month: ~670kWh; per year: ~8,200kWh
Midwest / Mid-Atlantic (4.5) - per day: ~29kWh; per month: ~870kWh; per year: ~10,500kWh
Southeast / Texas (5.5) - per day: ~35kWh; per month: ~1,070kWh; per year: ~12,800kWh
Southwest desert (6.5) - per day: ~42kWh; per month: ~1,260kWh; per year: ~15,200kWh

The average US home uses about 850-900kWh a month, so 8kW of panels covers a typical home in most of the country, on average across the year. In northern states, winter output can be half of summer's.

Output of an 8kW off-grid kit

Off-grid kits pair an 8,000W split-phase inverter with a smaller array. Three real examples at 4 sun hours:

8kW inverter + 8 x 415W - array: 3.3kW; battery: 10.24kWh; daily output: ~10.6kWh; kit price: ~$5,500
8kW inverter + 5.4kW array - array: 5.4kW; battery: 10.24kWh; daily output: ~17kWh; kit price: ~$7,000
8kW inverter + 12 x 415W - array: 5kW; battery: 20.48kWh; daily output: ~16kWh; kit price: ~$8,900

The inverters usually accept much more solar than the kit ships with (up to about 11kW of PV input on the first one). A common path is to buy the kit, live with it for a season, then add panels.

8kW off-grid solar kit: inverter, LiFePO4 batteries, 8 x 415W panels and wiring

What an 8kW system can run

At 8,000W of continuous 120/240V output, it can run nearly everything in a house, just not everything at full power at once.

Refrigerator - running watts: 150-200W; typical daily energy: 1.2-2kWh
Chest freezer - running watts: 80-100W; typical daily energy: 0.8-1kWh
Whole-home LED lighting - running watts: ~200W; typical daily energy: 1-1.5kWh
TV, internet, computers - running watts: ~300W; typical daily energy: ~2kWh
Well pump, 1 HP, 240V - running watts: 1,000W (3x at start); typical daily energy: 1-2kWh
Washing machine - running watts: ~500W; typical daily energy: 0.5kWh/load
Central AC, 3-ton - running watts: 3,000-3,500W; typical daily energy: 15-25kWh (summer)
Electric water heater - running watts: 4,500W; typical daily energy: 10-12kWh
Electric dryer - running watts: 5,000W; typical daily energy: 3-5kWh/load
Level 2 EV charging - running watts: 7,200W; typical daily energy: 10-30kWh

Essentials (fridge, freezer, lights, electronics, well pump, some laundry) come to about 8-12kWh a day. An 8kW kit with 10kWh of storage handles that comfortably.

The big four (central AC, electric water heating, electric drying, EV charging) are what actually size your system. Each one can double your daily use. Either plan for 20kWh or more of storage and a bigger array, or move those loads to propane or a generator.

Diagram of an 8,000W solar system powering household appliances

What an 8kW system costs with a battery

DIY / electrician-installed off-grid kit: about $5,500-$9,000 for the equipment (inverter, 10-20kWh LiFePO4 battery, 3.3-5.4kW of panels, brackets, cables and breakers). On top of that come racking, permits and electrician labour, which vary a lot by location, so get a local quote.

Full-service grid-tied install with a battery: this is quoted per watt of panels, plus the battery. Once labour, design, permits and installer margin are included, it typically costs several times the equipment price. Get 2-3 quotes and compare $/W and $/kWh of storage.

Tax credit note: the 30% federal residential credit (Section 25D) no longer applies to systems placed in service after December 31, 2025. Some state and utility rebates still exist, and dsireusa.org is the easiest place to check.

House with rooftop solar panels on an off-grid system

8kW vs 10kW vs 12kW

8kW: cabins, off-grid homes with propane appliances, whole-home backup for essentials. Roughly up to 500-600kWh a month off-grid.
10kW: when you add a 240V mini-split or well pump and want 20kWh or more of storage.
12kW: bigger homes running central AC, an electric range or EV charging from solar.

Rule of thumb:

Inverter: peak simultaneous load + 20%
Panels: daily kWh / (sun hours x 0.8)
Battery: overnight use + your cloudy-day reserve

Quick FAQ

How many panels are in an 8kW system? About 20 x 400W, or 17-18 x 450-460W.

Can 8kW run a whole house? Yes, for most homes on the grid. Off-grid, it runs the essentials and most 240V appliances as long as you stagger the heavy loads.

How big a battery? 10kWh minimum for overnight essentials. 20kWh or more for off-grid living with 1-2 cloudy days of reserve.

If you want to see what's inside real kits (inverter, panel count, battery size), here are the 8kW solar kits we currently carry.

Questions about sizing are welcome in the comments. We answer these all day.