Your Panels Are Bigger Than Your Inverter. On Purpose.
A 500 watt panel on a 384 watt microinverter looks like a mistake and is the design: the bigger panel pulls about a third more energy through the same microinverter, every day of the year. The ratio between the two is the DC to AC ratio, and the window is 1.2 to 1.4. Below it you leave that energy on the roof. Above it, each extra watt of panel earns less than the one before.
Any panel. Any microinverter. One division.
In the window. The bigger panel pulls far more energy through the same microinverter than a matched one would, nearly every extra watt reaches the meter, and there is room for 25 years of degradation.
- More energy a year
- +31% than a matched panel on this same microinverter
- The next watt of panel
- 90% of its energy reaches the meter
- Clipped in year one
- 0.5% 0% over 25 years, as the panel ages
Yield and clipping from Enphase's IQ8 simulation for New York City, the coolest large city it modelled and the nearest to our climate, facing due south. Real roofs clip less.
One Panel. One Microinverter. One Division.
Every solar panel carries a DC wattage on its label, measured in a laboratory. Every inverter carries an AC wattage, the most it will ever push to your house. Divide the first by the second and you have the DC to AC ratio, sometimes called the inverter loading ratio. With Enphase microinverters it is one panel over one micro. With a string inverter it is the whole roof's DC over one box's AC.
The number every installer in Nova Scotia should be able to tell you, and the window every pairing should land in, is 1.2 to 1.4. Here are ours.
What We Install Today
| Panel | Microinverter | Ratio | Verdict |
|---|---|---|---|
| Longi 500W 500 W | IQ8HC 380 W | 1.32 | In the window |
| Peimar 400W 400 W | IQ8PLUS 290 W | 1.38 | In the window |
| Bauer 530W Topcon 530 W | IQ8HC 380 W | 1.39 | In the window |
Live from our catalogue. Priced on the pricing page, wholesale cost shown beside every tier.
The Nameplate Is A Lab Number. Your Roof Is Not A Lab.
A panel earns its wattage under standard test conditions: a thousand watts of light per square metre, a cell temperature of 25 degrees, light hitting dead square. A roof in July has none of those. Three things follow, and together they are the whole case for a panel bigger than its inverter.
Heat takes the top off
A cell on a sunny roof runs 30 degrees or more above the test bench, and every degree costs about 0.35 percent. A 500 watt panel at 60 degrees is a 440 watt panel. On the best day of the year it still has not reached the label.
Most of the year is not noon
Mornings, evenings, cloud, November: the panel spends most of its hours well below its rating, and every one of those watts goes straight through the microinverter untouched. More glass means more harvest in the hours that make up most of the year.
Panels age. Inverters do not shrink.
Top panels lose about 2 percent in year one and 0.4 percent a year after that, and warranties allow more. A panel sized above the inverter keeps the inverter productive in year 25. A panel matched to it does not.
Follow two panels on the same 384 watt microinverter for 25 years. The 500 watt panel is a 442 watt panel at the end, 425 at the warranty floor, still above the line, still filling the microinverter on a good day. The 400 watt panel drops under the line in year 7 and never comes back: for the next 18 years it cannot reach the inverter's rating even on the test bench, and in real weather it never came close.
That is the problem with a ratio near 1.0. It is not that something breaks. It is that you paid for the expensive half of the system and then arranged for it to idle.
A 1.0 Ratio Is A Microinverter You Paid For And Never Fill.
The microinverter is the expensive component per watt, and it carries the 25 year warranty, the monitoring and the safety. Pair a 384 watt panel with a 384 watt micro and the two only meet on the test bench. On the roof the inverter runs part full on the best day of the year and emptier every year after that.
Enphase's own numbers make the point. In New York City, the same IQ8HC produces 543 kilowatt hours a year under a 385 watt panel and 649 under a 460 watt panel: nineteen percent more energy from the same microinverter, with no measurable clipping, for the price of a larger piece of glass. At 1.35 it is thirty-four percent more, and the clipping is 0.7 percent of year one and rounds to zero over the life of the system.
A 1.0 system is sold as "no clipping" and "nothing wasted". The thing being wasted is the inverter.
0% clipped
+19%, 0% clipped
+34%, 0.7% clipped
One IQ8HC, New York City, due south at 20 degrees. Enphase technical brief TEB-00013-1.0, June 2023.
Above 1.4, You Are Buying Sunshine The Inverter Throws Away.
When a panel makes more than its microinverter can pass, the micro holds the line and the surplus is never generated. That is clipping. Inside the window it is a rounding error. Past it, the curve bends upward fast: 0.7 percent of year one at 1.35, 2.5 percent at 1.5, 6.5 percent at 1.7. Every watt of panel above the window still earns something. It just earns less than the watt before it, and you paid the same for it.
Enphase is right that clipping shrinks as the panel ages, and that a bigger panel always makes a little more energy. Neither changes what the extra watts cost you up front, or the fact that a micro at the top of the curve sits at its ceiling, hot, for hours at a time every summer afternoon. Enphase builds for that. The string inverter makers do not: SolarEdge caps the ratio at 135 to 155 percent depending on the model, Fronius at 150, SMA at the datasheet's maximum DC input, and the warranty is the thing at stake.
The 1.69 Special
A 500 watt panel on a 295 watt IQ8+. It is sold as more watts for less money, and the ratio is 1.69.
Of year one's energy never reaches the meter in a New York climate. The watts on the sticker you paid extra for are the ones being clipped.
The microinverter runs at its ceiling, at full heat, for hours every clear afternoon. A string inverter run like this is out of warranty.
The Sales Script, And What Is True.
"They are clipping your panels. A 500 watt panel on a 384 watt inverter throws away 116 watts."What is true
A 500 watt panel makes 384 watts or more for a handful of hours a year in Nova Scotia, on the coldest clear days. Enphase's own figure for that pairing is 0.1 to 0.4 percent of year one and 0.0 percent over 25 years. The panel is sized for the other eight thousand seven hundred hours.
"Our 500 watt panel on a smaller inverter gives you more watts per dollar."What is true
Sticker watts per dollar, yes. Delivered watts, no. At 1.69 roughly six percent of the first year never reaches the meter, the inverter spends every summer afternoon at its ceiling, and the watts you paid extra for are precisely the ones being discarded. Ask for the ratio. If they cannot tell you, that is the answer.
We Size For Twenty-Five Years, Not For The Sticker.
Every pairing we sell sits between 1.2 and 1.4, and the ratio is printed beside it. Below the window you have bought inverter you will never use. Above it you have bought panel the inverter cannot pass, on hardware that may not be warranted for the job. We have installed more than forty thousand panels on Enphase microinverters this way, and we publish the production of every one of those systems. Check.
DC To AC Ratio, Asked And Answered.
Between 1.2 and 1.4. Take the panel's rated watts and divide by the inverter's peak AC watts; with microinverters that is one panel over one micro. Below 1.2 the inverter is never full. Above 1.4 clipping grows quickly and the extra panel watts earn less and less.
At 1.2 to 1.4 it is too small to find on a bill. Enphase's own simulation for the IQ8HC in New York City puts first-year clipping at 0.0 to 0.4 percent at 1.2 to 1.3 and 0.7 percent at 1.35, and the 25-year total rounds to zero because panels lose output as they age. At 1.5 it is 2.5 percent of year one. At 1.7 it is 6.5 percent.
Because the inverter is the expensive component per watt and a panel almost never reaches its nameplate on a roof. Match the two and you pay for AC capacity that fills for a few hours a year and then, as the panel degrades, never again. The panel is sized above the inverter so the inverter stays productive for 25 years.
More, not less. The ratio is the whole array's DC watts over the inverter's AC watts, the manufacturers cap it in writing (SolarEdge at 135 to 155 percent depending on the model, Fronius at 150, SMA at the datasheet's maximum DC input), and running above the cap puts the warranty at risk. One shaded panel also pulls the whole string down, so the same nominal ratio delivers less.
Between 1.2 and 1.4. Every panel and microinverter pairing we sell is published with its ratio on this page and on our pricing page, and the production of every system we have installed is public, so you can check the result rather than take our word for it.
The Longer Version
The original article: how to calculate the ratio, Enphase's clipping chart, and the string inverter makers' written limits.
Read the article Why is my PV module rating larger than my inverter rating?Price A System Sized For The Roof, Not The Sticker
Every pairing in the calculator sits in the window, with its wholesale cost beside it. No pressure and no salesperson.
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