Short answer
In our calculator, the step from 400 to 800 W pays more than the step from 800 to 1,200 W. With a south-facing railing kit in 10 cities, a 400 W kit saves 74%–79% of what an 800 W kit does. Going from 800 to 1,200 W adds $5–$12 a year (9%–11% more), because most of the extra power goes to the grid while your home doesn't need it, and our model pays nothing for that. A bigger kit is worth more if your home uses more power in the daytime or your utility credits what you send back.
What each size saves, city by city
A 400, 800 or 1,200 W kit on a south-facing railing, in one big city per state with a plug-in solar law, run through our calculator. Each city uses its utility's rate, or the state average where we couldn't look one up. The home has a steady 150 W always-on load, and power sent to the grid earns nothing.
| City | Rate | 400 W | 800 W | 1,200 W | 1,200 W adds |
|---|---|---|---|---|---|
| Hartford, CT | 29.2¢ | $8782% used | $11655% used | $12841% used | +$12 |
| Newark, NJ | 27.1¢ | $8183% used | $10856% used | $12042% used | +$12 |
| Los Angeles, CA | 24.5¢ | $8283% used | $10654% used | $11640% used | +$10 |
| Portland, ME | 25.6¢ | $7878% used | $10252% used | $11339% used | +$11 |
| Burlington, VT | 23.9¢ | $7280% used | $9454% used | $10440% used | +$10 |
| Manchester, NH | 22.5¢ | $7079% used | $9153% used | $10139% used | +$10 |
| Denver, CO | 16.1¢ | $5778% used | $7250% used | $7937% used | +$7 |
| Richmond, VA | 16.2¢ | $4884% used | $6558% used | $7343% used | +$8 |
| Baltimore, MD | 13.4¢ | $4182% used | $5555% used | $6041% used | +$5 |
| Salt Lake City, UT | 12.3¢ | $4182% used | $5354% used | $5840% used | +$5 |
"Used" is the share of what the kit makes that your home uses. "1,200 W adds" is the 1,200 W column minus the 800 W column. Each city name opens its result page, where you can switch the kit size.
Why a bigger kit adds less
A kit saves you money only for the power your home uses as it's made. At midday a small kit's output mostly goes into the fridge, router and other things that are always on. A bigger kit makes more at the same hours, and more of it goes to the grid. In these cities your home uses 78%–84% of a 400 W kit's output, 50%–58% of an 800 W kit's and 37%–43% of a 1,200 W kit's.
In Denver, for example, the 1,200 W kit makes 1,320 kWh a year, 2.9 times the 400 W kit's 450 kWh. Its savings, $79 against $57, are only 1.4 times as much.
Your home's daytime use decides how big is worth it
The more your home uses while the sun is up, the more of a bigger kit's output it can use. Here is Denver with three always-on loads: a quiet apartment, our default, and a home with more running all day.
| Always-on load | 400 W | 800 W | 1,200 W | 1,200 W adds |
|---|---|---|---|---|
| 100 W | $45 | $53 | $56 | +$3 |
| 150 W | $57 | $72 | $79 | +$7 |
| 300 W | $73 | $113 | $133 | +$20 |
Not sure what your home's always-on load is? Upload your utility's meter file on a result page and the calculator uses your own hourly use.
What the state laws say about size
Of the ten signed state laws, nine set a size cap of 1,200 W and Colorado's sets 1,920 W. Each law measures its cap in its own words. Here is each one's wording, from our state table.
| State | Cap | How the law measures it | Status |
|---|---|---|---|
| California | 1,200 W | maximum aggregated AC output per dwelling | Signed, not in force yet, from Jan 1, 2027 |
| Colorado | 1,920 W | output to the grid; one system per address; ≤391 W exempt from contractor and wiring-alteration rules | Legal |
| Connecticut | 1,200 W | maximum power output; one device per meter; 120 V outlet | Legal |
| Maine | 1,200 W | combined inverter output (AC) per service address; above 420 W: installed by a licensed electrician on a dedicated circuit with a single outlet | Legal |
| Maryland | 1,200 W | maximum power output back to the building's electric system; one system per electric meter; residential use only; ≤391 W exempt from listing rules that would require wiring alterations (§ 7–321(f)) | Legal |
| New Hampshire | 1,200 W | AC inverter output; one system per metered customer | Signed, not in force yet, from Jan 1, 2027 |
| New Jersey | 1,200 W | maximum power output; combined per service address or dwelling unit; ≤400 W exempt from wiring-alteration rules | Signed, not in force yet, from Mar 1, 2027 |
| Utah | 1,200 W | maximum power output of the device; standard 120 V outlet | Legal |
| Vermont | 1,200 W | combined inverter capacity per electric meter | Legal |
| Virginia | 1,200 W | maximum power output per customer (per unit in multi-family); ≤391 W exempt from wiring-alteration listing rules | Signed, not in force yet, from Jan 1, 2027 |
Rules that change at a lower wattage
Some laws set a second line below the cap. In the laws' own terms:
- Colorado: ≤391 W exempt from contractor and wiring-alteration rules.
- Maine: above 420 W: installed by a licensed electrician on a dedicated circuit with a single outlet.
- Maryland: ≤391 W exempt from listing rules that would require wiring alterations (§ 7–321(f)).
- New Jersey: ≤400 W exempt from wiring-alteration rules.
- Virginia: ≤391 W exempt from wiring-alteration listing rules.
Each state's page links to the law itself. All states.
What these numbers leave out
- Kit prices. We don't list any. Divide the price difference between two sizes by the extra savings a year above to see how long the bigger kit takes to earn it back.
- Credit for power you send back. We count it as worth nothing. If your utility credits it, a bigger kit is worth more than shown. You can set an export rate on a result page.
- A battery. A battery stores the midday surplus for the evening, which helps a bigger kit most. What a battery adds.
- Your space. A 1,200 W kit needs room for its panels and a railing or frame that can hold them. Shade on part of the panels cuts output too.
Try each size at your address
Your direction, tilt, rate and kit size, hour by hour.
Kit size: questions
What size balcony solar kit should I get?
In our runs, 800 W was the middle ground: a 400 W kit saved 74%–79% as much, and a 1,200 W kit only 9%–11% more, across 10 cities with a 150 W always-on load. The right size depends on how much power your home uses while the sun is up, your space and your state's cap. Try each size on your own result page.
Is a 1,200 W kit worth it over 800 W?
In our calculator it adds $5–$12 a year with a 150 W always-on load. In Denver, with a 300 W load it adds $20; with 100 W, $3. Compare that with the price difference between the two kits.
Why doesn't doubling the panels double the savings?
Power only saves you money when your home uses it. With no battery and nothing paid for exports, our model counts what the kit sends to the grid as worth nothing. Your home uses 78%–84% of a 400 W kit's output in these cities, but 37%–43% of a 1,200 W kit's.
How big can a plug-in solar kit be?
Of the ten signed state laws, nine set a size cap of 1,200 W and Colorado's sets 1,920 W. Each law measures its cap in its own words. Your state's page shows its law and how it measures the cap.
Is a 400 W kit worth it?
Per watt, it saves the most: in our runs, each watt of a 400 W kit saved 2.0 to 2.2 times what each watt of a 1,200 W kit did. In total it saves less: 74%–79% of an 800 W kit. Some state laws also set rules that change at a lower wattage; the guide lists them.
How we calculated this
Every savings figure is our calculator's own result, run Oct 15, 2026 through the same steps as a result page: NLR PVWatts v8 hourly output for the city and kit size, the default inverter limit (800 W for the 400 W kit, 800 W for the 800 W kit, 1,200 W for the 1,200 W kit), a flat 150 W always-on load, the utility's rate (or the EIA state average), and no credit for power sent to the grid. It's an estimate. Our full method.
The size caps come from our state table, read in each statute (last checked Oct 14, 2026). General information, not legal or financial advice.