400W vs 800W vs 1,200W Plug-in Solar: Which Size Do You Need?

The NEC 80% Rule: Your Hard Limit

Before you pick a size, understand this: US electrical code (NEC) limits continuous power on a standard 120V, 15A circuit to 80% of the circuit's capacity.

15A × 120V × 80% = 1,440W continuous

This is your ceiling. You can technically plug a 1,500W inverter into a standard outlet, but you shouldn't run it continuously at full power.

In practice, most plug-in systems are sized 400W to 1,200W to safely stay under this limit.

This isn't a ceiling you'll hit under normal conditions (most days, you'll be well below 1,440W), but it's important to know.

What 400W Actually Powers

A 400W system generates roughly 480 kWh per year (in average US sun).

What does that cover?

Daily output (good sun day): 1.5–2 kWh Daily output (cloudy day): 0.5 kWh Monthly average: 40 kWh

For context, the average US home uses about 900 kWh/month. A 400W system covers about 4–5% of household usage.

What 400W powers:

• A full day of lights (LED bulbs) for a home = maybe 0.3 kWh
• A laptop and peripherals running 12 hours = 0.2 kWh
• A refrigerator running 24 hours = 0.5–0.7 kWh
• Several fans or a small AC running daytime = 0.5–1.5 kWh
• EV charging (slow, 120V) = 1.5–2 kWh/overnight

Put together: A 400W system covers many daytime loads—cooking, charging, fans, lights—while the fridge runs on grid power. You're offsetting daytime usage, not replacing nighttime grid draws.

Who needs 400W:

• Apartment dwellers with limited space
• Renters testing the concept
• People with low daytime electricity usage
• Budget-first buyers starting small

Who shouldn't use 400W:

• Anyone wanting to offset 20%+ of household usage
• People with high air conditioning demands
• Those wanting meaningful savings (you'll see $50–100/year in cheap-power states)

What 800W Actually Powers

An 800W system generates roughly 960 kWh per year in average US sun.

This is the sweet spot for most homes.

Daily output (good sun day): 3–4 kWh Daily output (cloudy day): 1 kWh Monthly average: 80 kWh

For the average home using 900 kWh/month, 800W covers about 9% of monthly usage.

But the value is in timing. That 80 kWh is generated during peak solar hours (10 AM–3 PM typically), when you're using electricity for air conditioning, cooking, charging, laundry, and other daytime loads.

What 800W powers (simultaneously):

• Air conditioning running at full: 3–4 kW (but not all day)
• Oven running: 3–4 kW (but only during cooking)
• Washing machine: 0.5–1 kW
• Refrigerator + lights + computer + TV simultaneously: 1–2 kW
• EV charging (120V slow): 1.5 kW

In practice, you won't run all of these simultaneously. But if you're home during the day:

• Morning: coffee maker, shower (2–3 kW at peak)
• Midday: laundry, air conditioning (3–5 kW at peak)
• Afternoon: cooking, fans, computer (2–4 kW at peak)

Your daytime peak usage is probably 3–4 kW on average. An 800W system generates 0.8 kW. You're covering 20–25% of peak demand, offset by the grid supplying the rest.

Who needs 800W:

• Homeowners with moderate daytime electricity use
• People in expensive-electricity states wanting real savings ($200–400/year)
• Anyone with decent outdoor space (patio, balcony, or roof)
• Budget-conscious but wanting more than a starter system

Who shouldn't use 800W:

• Apartment dwellers without yard or patio
• People with very limited sun (Pacific Northwest)
• Those wanting to approach energy independence (you'd need 3–5 kW)

What 1,200W Actually Powers

A 1,200W system generates roughly 1,440 kWh per year in average US sun.

Daily output (good sun day): 4.5–6 kWh Daily output (cloudy day): 1.5 kWh Monthly average: 120 kWh

For a 900 kWh/month home, 1,200W covers about 13% of monthly usage.

What 1,200W powers:

• High daytime air conditioning (4–5 kW) for a few hours
• Multiple appliances running simultaneously (microwave, oven, AC, laundry)
• Significant EV charging (though 120V limits you to 1.5 kW, so faster charging would need 240V)

1,200W is approaching the practical limit for 120V circuits. It's the "max out" system size.

Who needs 1,200W:

• Homeowners with excellent outdoor space
• People in high-sun states (California, Arizona, Texas)
• Those wanting maximum savings from a plug-in system
• Anyone planning to max out their 120V outlet capacity

Who shouldn't use 1,200W:

• Apartment dwellers
• People with limited space
• Those in cloudy regions (output drops significantly)
• Renters (too much hardware to move)

Apartment vs. House: Space Considerations

Apartment with balcony:

• Max space: ~100 sq ft typically
• 400W fits easily (two 200W panels)
• 800W is possible but tight (four 200W panels, or two 400W panels)
• 1,200W is unrealistic unless you have a rooftop access

House with patio (200–400 sq ft available):

• 400W: comfortable
• 800W: comfortable
• 1,200W: comfortable, possibly a bit tight

House with yard (unlimited space practically):

• Any size works
• 1,200W is totally feasible
• Ground-mounted systems can angle for optimal sun

Panel footprint matters. A 200W panel is roughly 3 ft × 5 ft. A 400W panel is roughly 4 ft × 6.5 ft.

Cost Per Watt: Bigger Is Slightly Cheaper

System cost is roughly linear with size:

400W system: $600–900 total ($1.50–2.25/watt) 800W system: $1,200–1,800 total ($1.50–2.25/watt) 1,200W system: $1,800–2,400 total (~$1.50–2.00/watt)

Bigger systems have lower per-watt costs (economies of scale). But the difference is only 5–10%. You're not saving huge money by going bigger.

The real question is: can you use the extra power?

How to Choose Your Size

Step 1: Check your space

• Apartment with balcony? → 400W max
• House with patio? → 800W reasonable
• House with yard? → 1,200W possible

Step 2: Check your electricity rate

• Cheap power (<$0.12/kWh)? → 800W. More savings justify the cost.
• Expensive power (>$0.20/kWh)? → Start at 800W; upgrade later if space allows.
• Very expensive (>$0.25/kWh)? → 1,200W if space permits. The faster payback justifies it.

Step 3: Check your daytime electricity use

• Away from home 8–5? → 400–600W. You won't be home to use extra power.
• Work from home or retired? → 800–1,200W. You'll self-consume more power.
• High air conditioning demand? → 800–1,200W. AC runs during peak solar, maximizing capture.

Step 4: Consider modularity

• Uncertain about solar? → Buy 400W (Craftstrom is modular; add later).
• Confident and have space? → Buy 800W upfront.
• Maxing out your outlet? → 1,200W.

The Modular Advantage (Craftstrom)

Craftstrom's modularity is worth highlighting because it changes the calculus.

Don't know if solar is for you? Buy one 200W panel for $320. Test it for a month.

If you like it, add another for $320 (total 400W now).

If you love it, keep adding.

This eliminates the risk of picking the "wrong" size upfront.

Other brands (Bright Saver, EcoFlow) sell fixed kits. You pick a size; you're committed.

If modularity appeals to you, Craftstrom is the obvious choice.

Real-World Example Sizing Decisions

Renter, NYC apartment, limited balcony:

• Space: 2×4 ft (tiny)
• Available: 400W system
• Cost: $680 (Craftstrom)
• Annual savings: $110–150
• Payback: 5–6 years post-ITC
• Decision: Yes, good starter. Can take it when moving.

Homeowner, Phoenix house, good patio (200 sq ft):

• Space: 800W reasonable, 1,200W possible
• Sun: Excellent (6+ peak hours/day)
• Electricity: $0.14/kWh (moderate cost)
• Annual daytime usage: 3–4 kW typically
• Decision: 800W. Covers peak demand well, good payback. Leave room for future expansion.

Homeowner, California, good yard, air conditioning heavy:

• Space: 1,200W fine
• Sun: Excellent (5.5+ peak hours/day)
• Electricity: $0.26/kWh (expensive)
• Annual daytime usage: 4–5 kW (AC heavy)
• Decision: 1,200W. High rates + good sun + high daytime use = fast payback. Go big.

Upgrades Later

One reality: you can always add more panels later.

A 400W Craftstrom system today can become 800W next year. No big deal.

If you're uncertain, smaller upfront with upgrade capacity later is a valid strategy.

With Bright Saver or EcoFlow, upgrades are possible but less seamless (different systems may not be pin-compatible).

The Honest Truth About Sizing

Most people pick 800W. It's the sweet spot.

• Bigger than 400W (meaningful savings)
• Smaller than 1,200W (fits most spaces, reasonable cost)
• Requires decent sun and moderate daytime use

If you've read this far and are uncertain, guess 800W. You'll likely be happy.

If you're in an apartment, 400W. If you have a yard and high daytime use, 1,200W.

Ready to dive deeper? See how much each size saves in your state or compare product options by size.