Sunrun Inc. (NASDAQ:RUN) shares have had a horrible month, losing 28% after a relatively good period beforehand. Still, a bad month hasn't completely ruined the past year with the stock gaining 38%, which is great even in a bull market.

Although its price has dipped substantially, you could still be forgiven for feeling indifferent about Sunrun's P/S ratio of 1.6x, since the median price-to-sales (or "P/S") ratio for the Electrical industry in the United States is also close to 1.8x. However, investors might be overlooking a clear opportunity or potential setback if there is no rational basis for the P/S.

How Sunrun Has Been Performing

Sunrun hasn't been tracking well recently as its declining revenue compares poorly to other companies, which have seen some growth in their revenues on average. One possibility is that the P/S ratio is moderate because investors think this poor revenue performance will turn around. If not, then existing shareholders may be a little nervous about the viability of the share price.

What Are Revenue Growth Metrics Telling Us About The P/S?

There's an inherent assumption that a company should be matching the industry for P/S ratios like Sunrun's to be considered reasonable.

Taking a look back first, the company's revenue growth last year wasn't something to get excited about as it posted a disappointing decline of 15%. Still, the latest three year period has seen an excellent 63% overall rise in revenue, in spite of its unsatisfying short-term performance. So we can start by confirming that the company has generally done a very good job of growing revenue over that time, even though it had some hiccups along the way.

Shifting to the future, estimates from the analysts covering the company suggest revenue should grow by 14% each year over the next three years. With the industry predicted to deliver 20% growth each year, the company is positioned for a weaker revenue result.

With this in mind, we find it intriguing that Sunrun's P/S is closely matching its industry peers. Apparently many investors in the company are less bearish than analysts indicate and aren't willing to let go of their stock right now. Maintaining these prices will be difficult to achieve as this level of revenue growth is likely to weigh down the shares eventually.

The Bottom Line On Sunrun's P/S

Sunrun's plummeting stock price has brought its P/S back to a similar region as the rest of the industry. We'd say the price-to-sales ratio's power isn't primarily as a valuation instrument but rather to gauge current investor sentiment and future expectations.

When you consider that Sunrun's revenue growth estimates are fairly muted compared to the broader industry, it's easy to see why we consider it unexpected to be trading at its current P/S ratio. When we see companies with a relatively weaker revenue outlook compared to the industry, we suspect the share price is at risk of declining, sending the moderate P/S lower. A positive change is needed in order to justify the current price-to-sales ratio.

Before you take the next step, you should know about the 4 warning signs for Sunrun (1 can't be ignored!) that we have uncovered.

If you're unsure about the strength of Sunrun's business, why not explore our interactive list of stocks with solid business fundamentals for some other companies you may have missed.

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This article by Simply Wall St is general in nature. We provide commentary based on historical data and analyst forecasts only using an unbiased methodology and our articles are not intended to be financial advice. It does not constitute a recommendation to buy or sell any stock, and does not take account of your objectives, or your financial situation. We aim to bring you long-term focused analysis driven by fundamental data. Note that our analysis may not factor in the latest price-sensitive company announcements or qualitative material. Simply Wall St has no position in any stocks mentioned.