September has historically been the worst month (by a wide margin) for the S&P 500. That strange phenomenon, referred to as the September Effect, hit the index particularly hard this year. The S&P 500 is down more than 5% since the beginning of September. But patient investors have no reason to worry.

History says the S&P 500 will find its way back to bull market territory, and Wall Street sees compelling buying opportunities where certain growth stocks are concerned. For instance, analysts have set a median 12-month price target of $86 per share for Block (SQ 4.78%), which implies a 93% upside from its current price. SolarEdge Technologies (SEDG 0.57%) has a median 12-month price target of $290 per share, which implies a 127% upside from its current price.

To be clear, investors should take these price target estimates for what they are -- estimates. But the general optimism surrounding Block and SolarEdge is reason enough to take a closer look. Here are the details.

1. Block

Block breaks its business into the Square ecosystem for merchants and the Cash App ecosystem for consumers. Square simplifies commerce by bundling hardware, software, and banking services into a cohesive platform that empowers merchants to manage their businesses across physical and digital channels. Doing so eliminates complicated integrations that are commonplace with other merchant service providers because most bundle hardware, software, and services from different vendors.

Cash App takes a similar tack to simplify consumer finance. It unifies the ability to deposit, borrow, send, spend, and invest money on a single platform, and its digital-first nature means it can offer those services while incurring much lower costs than traditional banks. That means Block can afford to serve consumers that traditional financial institutions cannot, and each new Cash App user accelerates the network effect behind the digital wallet. Indeed, Cash App was the most downloaded digital wallet among U.S. consumers in 2022.

Block reported solid financial results in the second quarter, topping expectations on the top and bottom lines. Gross profit jumped 27% year over year to $1.9 billion, and non-GAAP (adjusted) earnings soared 117% to $0.39 per diluted share. Investors can expect similar momentum in the coming years if Block continues taking sensible steps to capitalize on its $190 billion addressable market (as measured in gross profit), comprising $120 billion from Square and $70 billion from Cash App.

Specifically, Block is pushing upmarket and expanding internationally with Square. Mid-market merchants (i.e., those with more than $500,000 in annual sales) accounted for 40% of gross payment volume in the second quarter, up from 35% two years ago. International merchants accounted for 16% of Square gross profit in the second quarter, up from 8% two years ago.

Additionally, Block recently made Cash App Pay available to Stripe and Adyen merchants, and extending its acceptance network makes Cash App incrementally more valuable to consumers. That strategy could accelerate the network effect behind the digital wallet by driving engagement and drawing new users to the platform, which itself would incentivize more merchants to accept Cash App Pay at checkout.

Shares currently trade at 5.9 times gross profit, the cheapest valuation multiple in the last five years. There is no guarantee shareholders will see 93% returns in the next 12 months, but patient investors should still consider buying this growth stock today. Block sits in front of a large market opportunity, and shares look cheap in context.

2. SolarEdge Technologies

SolarEdge provides a broad range of solar products to the residential and commercial markets. The company is the second-largest manufacturer of solar inverters in the world, and its invention of power optimizers -- devices that maximize solar energy production by mitigating losses from panel mismatch -- has been instrumental in building brand authority. But SolarEdge has spun that success into burgeoning business lines in adjacent areas like energy storage solutions, energy management software, and electric vehicle chargers.

SolarEdge looked sharp in the second quarter. Revenue rose 36% year over year to $728 million, and non-GAAP earnings jumped 176% to $2.62 per diluted share. However, management expects higher interest rates and excess inventory to weigh on the business in the near term. Guidance implies single-digit revenue growth in the current quarter, and that gloomy outlook contributed to the sell-off that has dragged the stock 65% below its all-time high.

Fortunately, that unreasonable bearishness creates an opportunity for patient investors. The coming quarters may be rough, but Grand View Research says the solar energy systems market will grow at 16% annually through 2030, and SolarEdge has a great shot at growing even faster, given its strong foothold in the inverter market. Indeed, Morgan Stanley says SolarEdge could grow revenue at 21% annually through the end of the decade. That makes its current valuation of 2.1 times sales look quite cheap, and it's certainly a bargain compared to the three-year average of 7.5 times sales.

Here's the upshot: Working under the conservative assumption that revenue grows at 15% annually over the next five years, SolarEdge shareholders would see annual returns of 10.2% even if the already-cheap valuation multiple fell to 1.6 times sales. In other words, this growth stock is well-positioned to deliver market-beating returns in the coming years, so investors should jump at the current buying opportunity.