Comparisons
400W vs 800W plug-in solar: which size to choose
The size question for plug-in solar usually comes down to a smaller system (around 400W, often one panel) or a larger one (around 800W, often two). Doubling the panels roughly doubles the generation — but whether that's worth it depends on how much you can actually use.This guide compares the two. The same logic covers in-between sizes like 500W. For the underlying sizing, see the wattage guide.
Written and edited by Christopher Panteli
Christopher is the founder and editor of MyPlugInSolar. He oversees the site’s research standards, data tools and editorial process. He is not an electrician or solar installer, and specialist technical claims are sourced from official documentation or reviewed by appropriately qualified professionals.
Output: bigger generates more
On generation alone the comparison is simple: in the same spot and conditions, an 800W system produces roughly double a 400W one, and a 500W system sits in between. Capacity scales output more or less proportionally. What it doesn't tell you is how much of that extra generation you'll actually benefit from. Estimate both for your location with the calculator.
Savings: self-consumption is the catch
The saving comes from using output as it's generated, not from generating it — see solar self-consumption. A 400W system's smaller output is more likely to be fully used by your background demand. A larger 800W system generates more, but if your daytime base load is low, much of the extra can be exported — and exported plug-in solar may currently earn nothing (export). So a bigger system doesn't always mean proportionally bigger savings.
Match size to use
Cost, space and practicality
A larger system costs more and needs room and mounting for a second panel — see solar panel brackets and the mounting hub. Two panels also let you split orientation. Weigh the extra cost against the extra usable output, not just the headline generation; see plug-in solar cost and payback.
| Factor | ~400W (one panel) | ~800W (two panels) |
|---|---|---|
| Generation | Lower | Roughly double |
| Space needed | One panel | Two panels |
| Best for | Modest daytime use | Higher daytime base load |
| Export risk | Lower | Higher if usage is low |
| Mounting | Simpler | More to fix and orient |
Frequently asked questions
- Is an 800W system better than a 400W one?
- It generates roughly twice as much, but it's only better value if you can use the extra output during the day. If your daytime demand is modest, a 400W system may be used more fully, while much of an 800W system's output could be exported for little or no return.
- What about a 500W system?
- A 500W system sits between the two: more output than 400W, less than 800W, with the same rule applying — its value depends on how much you use as it's generated. The choice is really about matching capacity to your daytime use, not maximising generation.
Sources
- 1. PVGIS (Photovoltaic Geographical Information System) — European Commission, Joint Research Centre
Estimate your solar potential
See how much electricity a small system could generate at your postcode, and the indicative bill saving.