"Buy the dip" is a popular investing strategy, and it's an intuitive one as well.

Buying stocks on the cheap makes sense, but there's a caveat to that approach. It only works when the stock is down for a temporary reason, and it's an otherwise quality business. Not every sell-off is like that, of course, as sometimes stocks fall for a good reason.

With that in mind, let's take a look at the four worst performers in the S&P 500 this year to see if any are worth buying on the dip.

Several stock charts layered over one another.

Image source: Getty Images.

1. SolarEdge Technologies (down 73.3% in 2023)

SolarEdge Technologies (SEDG -4.09%), which is best known for its solar inverters, has taken a dive this year as the company came into 2023 sporting a lofty valuation and big expectations. Instead, rising interest rates hit the solar industry hard, significantly raising the cost of such projects for homeowners.

The company released another round of disappointing results just last week with revenue down 27% year over year to $725.3 million in the third quarter, and adjusted operating income fell 88% from $191 million to $23.1 million.

SolarEdge expects revenue to plunge again in the fourth quarter, forecasting revenue of $300 million-$350 million and a wide loss on the bottom line.

SolarEdge's technology is promising and it has an estimated 40% market share in the solar inverter industry. But based on its third-quarter results and its guidance, a turnaround is going to take time. For now, investors would be better off watching this stock from the sidelines.

2. Enphase Energy (down 69.5% in 2023)

Enphase Energy (ENPH -0.19%) is also a maker of solar inverters, and it has taken a fall this year for similar reasons to SolarEdge -- demand in the solar industry has dried up largely due to elevated interest rates and a slowdown in the housing market.

Enphase reported revenue of $551.1 million in the third quarter, down 13% from the quarter a year ago, but profits were essentially flat at $114 million, a sign it's managing the downturn better than SolarEdge. It shipped nearly 4 million microinverters in the quarter.

The company's revenue forecast is identical to SolarEdge's, calling for revenue of $300 million-$350 million in the fourth quarter. But it expects to report a generally accepted accounting principles (GAAP) profit in the current quarter.

Enphase stock is more expensive than SolarEdge, but it deserves a premium considering the better bottom-line results. While the cautiousness around solar applies to Enphase, the stock does seem to be on more stable ground. If you're choosing between Enphase and SolarEdge, Enphase looks like the better buy right now.

3. Moderna (down 56.8% in 2023)

Moderna (MRNA -2.23%) stock is another pandemic-era winner that has fallen sharply since. In Moderna's case, its revenue stream from the pandemic has mostly dried up, and investors are waiting to see if the biotech has another blockbuster in the works.

In its third quarter, revenue fell 46% year over year to $1.83 billion. It reported a sizeable loss as it's in the process of downsizing its COVID-19 manufacturing footprint.

The company also forecast $4 billion in revenue next year, down from an expected $6 billion in revenue this year, but sees a return to growth in 2025 as it releases its RSV vaccine and other products. It currently has six products in phase 3 trials.

Biotech stocks are always risky, but Moderna has been a pioneer in mRNA treatments and is working on some exciting drugs, including treatments for cancer. The stock is about as cheap as it's been in three years, and getting some exposure to the stock could pay off if it has another blockbuster. Investors will have to be patient given the guidance, but Moderna still has a lot of profit potential.

4. FMC (down 55.6% in 2023)

FMC (FMC -0.87%) is an agricultural company that sells a range of crop protection and plant health products. The stock went from bad to worse this year, falling 56% after it cut guidance several times and issued a disappointing report.

In the third quarter, revenue fell 29% year over year to $982 million, while adjusted earnings per share were down 64% to $0.44, and it also reported a small loss on a GAAP basis.

Management blamed channel destocking behavior (an industry trend that has resulted from higher operational costs and a correction from elevated inventory levels earlier) for the decline in revenue. Still, the company said on-the-ground application rates for its products are steady, a sign that demand is more solid than it looks.

FMC expects another sharp decline in revenue and profits in the fourth quarter. However, the business should stabilize next year, and the stock looks affordably priced. Investors who buy in now could benefit from a recovery next year once its performance normalizes.