Most investors seeking out mega-gains prefer individual stocks over exchange-traded funds. By definition, funds dilute potential upside by virtue of being a basket of stocks rather than a single, story-based prospect.

Sticking with individual stocks in search of big gains isn't a necessary risk, however. Plenty of ETFs offer lots of growth opportunity as well. Here's a closer look at three such prospects capable of producing surprisingly strong gains for a retirement nest egg.

1. Vanguard Growth ETF

It remains to be seen if we're easing back into an era when value stocks outperform growth. With the Vanguard Growth ETF (VUG 1.10%), though, that dynamic may not entirely matter.

Don't let the name mislead you. While the Vanguard Growth ETF holds growth companies, it's more narrowly focused than the name suggests. Nearly half of its 250 holdings come from the technology sector: Alphabet, Tesla, Amazon, Microsoft, and Apple are the fund's five biggest holdings. Another one-fourth of the fund's picks are consumer discretionary stocks. While these arenas are some of the market's most volatile sectors, they're also the most rewarding. Since 2012, consumer discretionary tickers have collectively beaten the S&P 500, and tech stocks have nearly tripled the performance of the S&P 500 since 1990. There's no particular reason to think this leadership will shift in the foreseeable future, if ever.

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Data by YCharts.

The kicker: Whatever gains this ETF's holdings achieve are almost entirely passed along to its owners. In typical Vanguard fashion, the Vanguard Growth ETF's expense ratio is a scant 0.04%. That's next to nothing, which is a big deal when you're talking about a multiyear holding that could become a multidecade holding.

2. Invesco Solar ETF

The Invesco Solar ETF (TAN 5.23%) can't make a similar claim. While plenty of other ETFs cost considerably more to manage, this fund's expense ratio of 0.66% will give some investors pause.

This is a case, though, where the opportunity is worth the price of admission.

Just as the name suggests, the Invesco Solar ETF is a means of owning a basket of solar stocks when it's difficult to pick just one or even a few. The fund holds between 40 and 50 solar-related names at any given time, allowing investors to participate in the industry's broad, long-term potential. Its top holdings right now include solar power management technology outfits Enphase Energy and SolarEdge Technologies and solar panel makers like First Solar and Xinyi Solar. It's a compelling prospect, because it offers exposure to several great solar stocks that don't otherwise trade in the United States.

Anyone keeping tabs on TAN likely knows it's been a hot-and-cold performer for a decade now. This short-term inconsistency isn't apt to change anytime soon, either. That's just the nature of the solar power business's stocks, which are highly subject to regulatory and legislative changes.

Take a step back and look at the bigger picture, though. Solar has great long-term growth prospects. For perspective, industry research outfit Wood Mackenzie expects the planet's solar power production capacity to expand from 129 gigawatts right now to 336 gigawatts by 2027. That's a five-year, 160% increase in the globe's current solar power production capacity that took roughly 20 years to build up to its present level. To get there, however, the world has to be leaning heavily on the companies held by this fund.

3. Vanguard International High Dividend Yield ETF

Finally, add the Vanguard International High Dividend Yield ETF (VYMI 0.78%) to your list of funds that can supercharge your retirement savings.

It's not a particularly great first and/or solitary holding. The Vanguard International High Dividend Yield ETF is not only volatile because high-yielding stocks tend to be erratic but also because factors like ever-changing exchange rates can make foreign stocks even more unpredictable than they already are.

If you're prepared for a bit of volatility, though, this fund is worth the swings.

As it stands right now, the fund's current dividend yield stands at an above-average 5.6%. The thing is, that's a payout domestic investors can count on, perhaps more than they can count on with stocks of dividend-paying companies based in the U.S. 

The underlying issue is the pronounced inflation affecting the U.S. relative to other countries. Although the U.S. inflation rate is falling, the most recent overall increase of 7.7% was still high and came in above most other developed countries. This alone can skew a dividend stock's price, because the market is perpetually adjusting valuations to the environment. Further skewing domestic dividend stocks' prices are the rising interest rates meant to curb inflation, or at least investors' expectation of future rate hikes. That's why yields on U.S. stocks have been so volatile since early 2020 -- the market's very much aiming at a moving target.

Most foreign stocks aren't subject to nearly as much underlying volatility right now. While most countries' inflation rates are above their long-term levels at this time, the bulk of the countries most represented within the Vanguard International High Dividend Yield ETF aren't seeing as severe levels of inflation as the U.S. As a result, central banks in these countries aren't moving as abruptly or as aggressively as the Federal Reserve is. It ultimately means these dividend-paying names aren't fighting the headwind of rapidly rising interest rates that generally work against dividend payers.

This won't always be the case, of course. What will always be the case is the Vanguard International High Dividend Yield ETF brings a great deal of high-yielding diversity investors couldn't achieve on their own with a purely domestic portfolio. Just be sure you're reinvesting whatever dividends the ETF is paying into more shares of the fund itself.