Quick answer
Inverter Efficiency is the percentage of the DC power entering a solar inverter that leaves it as usable AC power; the rest becomes heat.
Data sheets print two versions. Peak efficiency is the best single test point. CEC weighted efficiency averages tests at six power levels and three voltages, weighted toward how inverters actually run, and is the fairer number for comparing models.
Quick facts
The key facts about inverter efficiency, with sources:
- Formula
- AC output power ÷ (DC input power + any AC input power) 1
- CEC test points
- 6 power levels × 3 DC voltages = 18 measurements 1
- Heaviest weight
- 75% of rated output, weighted 0.53 1
- Typical grid-tied range
- Above 95% under most operating conditions 1
- Microinverter example
- Enphase IQ8PLUS: 97.7% peak, 97% CEC 6
- String inverter example
- SolarEdge SE7600H-US: 99.2% max, 99% CEC at 240 V 7
- Who lists it
- California Energy Commission, after lab testing 2
Key takeaways
- Inverter efficiency is how much DC comes out as AC. The rest is lost as heat.
- Compare the CEC weighted figure, not the peak figure.
- Home inverters print about 97% to 99% CEC weighted.
- Count every step in the chain, such as optimizers, before comparing systems.
- On a shaded or complex roof, layout matters more than one point of efficiency.
What the efficiency number means
An inverter cannot turn every watt of DC into AC. Its switches and filters lose a little energy as heat. Efficiency is the share that makes it through.
Sandia National Laboratories defines it as usable AC output divided by DC input plus any AC input. It notes that typical grid-tied inverters exceed 95% under most conditions 1.
The number is not fixed. Sandia says efficiency changes with AC output power, DC voltage and sometimes inverter temperature 1. That is why one figure on a data sheet can mislead.
Sources: [1]
How the CEC weighted figure is calculated
| Test point (% of rated AC output) | Weight | Why it is weighted this way |
|---|---|---|
| 10% | 0.04 | Early morning, late afternoon, heavy cloud |
| 20% | 0.05 | Low light |
| 30% | 0.12 | Partly cloudy hours |
| 50% | 0.21 | Typical mid-morning and afternoon |
| 75% | 0.53 | Where a well-sized inverter spends its best hours |
| 100% | 0.05 | Full output: brief on most rooftops |
Why the weighted number beats the peak number
Peak efficiency reports only the single best point. The CEC method tests each of six power levels at the lowest, normal and highest DC voltage. That makes 18 readings. It then weights them toward the levels where a solar inverter does most of its work 1.
To be listed by the California Energy Commission, a maker sends weighted-efficiency data from at least five test units. Each is tested at the three voltages and all power levels.
A lab whose OSHA scope covers UL 1741 must produce the data. The maker also reports night tare loss in watts, which is the power the inverter uses at night 2.
Sandia notes any inverter used in a CEC-approved PV system must be tested by an independent lab to this protocol, and the CEC lists results for thousands of inverters 1.
Types of efficiency figure, with published examples
| Product | Type | Peak / max | CEC weighted |
|---|---|---|---|
| Enphase IQ8-60-2-US | Microinverter (per panel) | 97.7% | 97% 6 |
| Enphase IQ8M-72-2-US | Microinverter | 97.8% | 97.5% 6 |
| SolarEdge SE7600H-US | String inverter (with optimizers) | 99.2% | 99% @ 240 V, 98.5% @ 208 V 7 |
| SolarEdge S440 power optimizer | DC-DC optimizer | 99.5% | 98.6% weighted 8 |
| Tesla Powerwall 3 | Hybrid inverter | — | 97.5% solar-to-home 9 |
| Victron SmartSolar MPPT 100/30 | Off-grid charge controller | Above 98% (maximum) | Not CEC tested 10 |
Example: what two points of efficiency are worth
An example with round inputs. Suppose an array delivers 10,000 kWh of DC to the inverter in a year. The only thing that changes is the CEC weighted efficiency.
| System | Math | AC delivered |
|---|---|---|
| Microinverters at 97% CEC | 10,000 × 0.97 | 9,700 kWh |
| String inverter at 99% CEC alone | 10,000 × 0.99 | 9,900 kWh |
| String inverter at 99% behind optimizers at 98.6% | 10,000 × 0.986 × 0.99 | about 9,761 kWh |
Count every conversion in the chain before comparing. Here the optimizer system beats the microinverter system by about 61 kWh a year on efficiency alone, well under 1%. On a shaded roof, panel-level tracking decides far more than this gap. Multiplying two weighted figures is a rough guide, because the test conditions differ.
Where efficiency shows up
- On the inverter data sheet, in the output or efficiency block. Use the CEC row, not “maximum.”
- In production estimates. Design software applies the inverter’s efficiency curve. A proposal that does not name the inverter cannot be checked.
- In the gap between panel DC and meter AC. Losses from wiring, heat and clipping add to inverter loss. See why a system underproduces.
- In night use. The SolarEdge HD-Wave sheet lists under 2.5 W at night 7.
Why a high, well-tested figure helps
What it gives you
- More of the panels’ energy reaches your home.
- Less heat inside the box, which is easier on parts.
- A fair, lab-tested way to compare brands.
- A clear input for production estimates.
What it does not tell you
- How well the system handles shade.
- How the inverter copes with heat on your wall.
- How long it lasts or how good the warranty is.
- Losses from wiring, dirt and clipping.
Limits of the efficiency number
The CEC figure is measured in a lab, not on your roof. Heat changes things. Sandia notes efficiency can shift with temperature 1. The SolarEdge sheet promises full power only up to at least 50 °C 7. The Powerwall 3 sheet says output may be de-rated above 40 °C 9.
The number also covers only one step. A system with optimizers has two steps. A battery adds more. Always ask which path a figure describes.
Does higher efficiency cost more?
We do not print prices. Efficiency is rarely the main cost driver. Inverter type, AC size and panel count matter more. A one-point gain is worth about 1% more energy a year, as the example shows. Judge that against the price gap in your quotes. Our cost per watt guide shows how to compare.
Lifespan matters more than a point of efficiency. The DOE expects inverters to be replaced at least once in a 25-year array life 5. A longer warranty can be worth more than a tiny gain in efficiency.
Sources: [5]
How to check efficiency on your quote
You can do this yourself with the model numbers. No tools or electrical work needed.
- Find the inverter model number on the proposal.
- Download its data sheet from the maker’s website.
- Find the “CEC weighted efficiency” row. Note the figure for your grid voltage, usually 240 V.
- If there are optimizers, note their weighted efficiency too.
- Ask the installer which efficiency the production estimate used.
- Check that the model appears on the CEC Solar Equipment Lists, which update three times a month 3.
Keeping efficiency up over time
Heat is the main thing you can affect. Keep the area around the inverter clear so air can flow. Do not cover vents or stack items against it.
Watch for a slow drift. If your yearly output falls more than panel aging would explain, ask for a check. Our solar repair page covers what a technician tests.
Signs efficiency has dropped, and when to call
Call your installer or a licensed electrician if you see these. Do not open the inverter.
- Output flat-tops below the inverter’s rating on hot afternoons.
- The inverter is hot to the touch or its fan runs loud.
- Monthly kWh falls well below the same month last year.
- Error codes about temperature or derating.
Who sets the test and the listings
The common yardstick for home inverters is the CEC protocol. The California Energy Commission’s instructions were revised on 26 August 2025. They require UL 1741 certification from a recognised lab, and weighted-efficiency data from at least five test units 2.
The CEC list also shows grid-support features. For Supplement SB, the maker must show compliance with IEEE 1547-2018 and IEEE 1547.1-2020 2. IEEE 1547-2018 was published on 6 April 2018 4. The CEC advises checking with your utility which smart-inverter features it requires 3.
Inverter efficiency vs related efficiency terms
| Term | What it measures | Typical place you see it |
|---|---|---|
| Inverter efficiency (CEC) | Share of DC turned into AC, weighted | Inverter data sheet |
| Peak inverter efficiency | Best single test point | Inverter data sheet |
| Panel efficiency | Share of sunlight turned into DC | Panel data sheet; see panel efficiency |
| Round-trip efficiency | Energy out of a battery vs energy in | Battery data sheet |
| MPPT efficiency | How close tracking stays to the true best point | Some charge controller sheets |
Misconceptions
- Myth The highest peak figure wins.
- Reality Peak is one test point. The CEC weighted figure covers 18.
- Myth 99% vs 97% means 2% more money.
- Reality It means about 2% more AC from the same DC, before shade, heat and clipping. Real gaps on a roof can be larger or smaller.
- Myth Microinverters are less efficient, so they make less energy.
- Reality They lose a little in conversion but can gain far more on shaded or mixed roofs.
Efficiency and state rules in SC, GA and VA
In these states, the utility and code checks we found focus on listings, not on an efficiency score. Georgia Power asks for spec sheets showing UL1741SB and IEEE1547-2018 11.
Virginia requires systems to meet NEC, IEEE and testing-lab standards such as UL 12.
In South Carolina, utility size caps such as Dominion Energy’s 20 kW AC limit are set on AC output, which is what the inverter delivers after its losses 13.
When efficiency should sway your choice
Give efficiency real weight when:
- Two quotes use the same layout, such as two string inverters, and differ only in brand.
- Your roof is sunny and unshaded, so layout matters less.
- You compare chains with the same number of steps.
- Otherwise, weigh shade handling, warranty and service first.
Related guides
Questions about inverter efficiency
What is a good inverter efficiency?
Current home inverters print CEC weighted figures from about 97% to 99%. Enphase IQ8 microinverters list 97% to 97.5%. SolarEdge HD-Wave string inverters list 99%. Within that band, roof layout and shade usually matter more than a point of efficiency.
What does CEC efficiency mean?
It is the weighted efficiency measured under the California Energy Commission’s test. The test takes 18 readings across six power levels and three DC voltages. The 75% power level carries the most weight, at 0.53. It is the fairest single number for comparing inverters.
Does inverter efficiency drop with heat?
Yes, it can. Sandia notes efficiency can change with inverter temperature. Inverters may also cut output when hot, which is called derating. The SolarEdge HD-Wave sheet promises full power up to at least 50 °C. Mount the inverter where the installer’s manual says, out of strong sun if possible.
Is inverter efficiency the same as solar panel efficiency?
No. Panel efficiency is the share of sunlight a panel turns into DC. Inverter efficiency is the share of that DC turned into AC. A 22% panel and a 97% inverter measure different steps. Both matter, but they are not compared to each other.
Why does my inverter show less AC than the panels’ DC?
Conversion loss explains a few percent at today’s efficiencies. A bigger gap points to clipping, heat derating, or a fault worth raising with your installer. Compare the two numbers on a mild, clear day for the fairest check.
What is peak efficiency on a data sheet?
It is the best single reading in the test, at ideal power and voltage. The SolarEdge SE7600H-US lists 99.2% maximum and 99% CEC weighted. Peak is always equal to or higher than the weighted figure, so it flatters every inverter.
Do microinverters have lower efficiency?
Per unit, yes, a little. Enphase IQ8 units print 97% to 97.5% CEC. Some string inverters print 99%. But on shaded roofs, microinverters often harvest more energy overall, because each panel is tracked on its own.
How much energy does an inverter use at night?
Very little. The CEC asks makers to report night tare loss in watts. The SolarEdge HD-Wave sheet lists under 2.5 W at night. That is small next to what a home system makes in a day.
Does inverter efficiency get worse with age?
Makers do not print an aging figure for efficiency. What you can watch is total output in your app. A drop much bigger than normal panel aging is worth a call to your installer.
Sources
- Sandia National Laboratories, PV Performance Modeling Collaborative: CEC Inverter Test Protocol, retrieved .
- California Energy Commission, Inverter Listing Request Instructions (rev. 26 Aug 2025), retrieved .
- California Energy Commission, Solar Equipment Lists, retrieved .
- IEEE Standards Association, IEEE 1547-2018, retrieved .
- US Department of Energy, Solar Photovoltaic System Design Basics, retrieved .
- Enphase Energy, IQ8 Series Microinverters data sheet (DSH-00378-5.0-EN-2026-07-13), retrieved .
- SolarEdge, Single Phase Inverter with HD-Wave Technology for North America data sheet (12/2020/V01, distributor-hosted copy), retrieved .
- SolarEdge, Power Optimizer S440 / S500 / S500B data sheet (DS-000091-ENG, 8 Nov 2022, government-hosted copy), retrieved .
- Tesla, Powerwall 3 Datasheet (2024), retrieved .
- Victron Energy, SmartSolar Charge Controllers MPPT 100/30 & 100/50 data sheet, retrieved .
- Georgia Power, Behind-the-Meter Interconnection Summary for Residential Customers (rev. 15 Aug 2025), retrieved .
- Code of Virginia §56-594 (net energy metering), retrieved .
- Dominion Energy South Carolina, Residential Solar Choice rider (Rider to Rate 5), retrieved .
Expert review
Written by the HyreSolar Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Definition, test method and weights from Sandia’s description of the CEC protocol and the CEC listing instructions (rev. Aug 2025); product figures copied from named data sheet revisions. The example multiplies those figures with stated round inputs.
Suggest a correction. We fix errors and say what changed.