With so much going on this summer -- action movies! roller coasters! ice cream! -- who has time to sit around babysitting their portfolio? For investors who want to spend more time at the beach and less time buried in a spreadsheet, solid low-risk investments are a must.

Magellan Midstream Partners (NYSE:MMP)Royal Dutch Shell (NYSE:RDS-A)(NYSE:RDS-B), and Darling Ingredients (NYSE:DAR) are three energy industry companies that are safe bets to buy and then forget about all summer long. 

A smiling man watches a girl with a piggy bank and stacks of coins.

Babysitting should be for kids, not for your portfolio. Image source: Getty Images.

A reliable income stream

You may be planning on traveling this summer, which means that you are likely going to fill up you gas tank a few extra times. The U.S. has more than 2.5 million miles of petroleum products pipelines, many of which are operated by master limited partnerships (MLPs) like Magellan Midstream Partners.

Note that MLPs have some extra tax requirements, so they're not for everyone. And even among MLPs, which tend to be steady income generators, Magellan is fairly low risk. It had distribution coverage of a healthy 1.2 times for 2017. In addition, the company has adopted a conservative management style, which has given it a rock-solid balance sheet. Its most recent quarter saw revenues, adjusted EBITDA, and distributable cash flows rise modestly.

While this may sound pretty boring, the partnership has a long track record of outperformance. Over the past five years, the company's unit price -- which is what MLPs call their per-share price -- has appreciated by more than 35%, bucking the industry trend, which has seen many unit prices fall. Lastly, Magellan has raised its distribution practically every quarter since it went public in 2001, and that trend looks set to continue.

Add it all up, and you get a solid, safe place to put your money.

Size matters

When it comes to safety, bigger is often better. A larger company often has resources a smaller company simply doesn't, and these can help it avoid potential pitfalls to its business model. 

Case in point: energy behemoth Royal Dutch Shell. The integrated oil major -- one of the largest companies in the world by revenue -- weathered the oil price slump of 2014-2017 far better than some of its smaller industry peers, thanks to aggressive cost-cutting and the savvy purchase of British gas company BG Group on the cheap.

In the current era of higher oil prices, all that cost-cutting is really paying off, as Shell's share price has appreciated 5.9% so far this year, and the company is raking in cash. And even if oil prices start to trend downward again, that cost-cutting combined with Shell's strong balance sheet -- not to mention its lucrative downstream operations -- should help keep investors' money safe.

Even with its price appreciation, Shell still sports a 5.3% dividend yield, the highest of any integrated major. If safety is what you're after, Shell is a tough investment to beat.

MMP Chart

MMP data by YCharts

Don't think about it

The last investment on the list is one you won't babysit because you may not want to think about it much. Famous investor Peter Lynch said he liked companies that did something boring, and it was even better if they did something a little disgusting. Fat renderer -- and restaurant grease-trap recycler -- Darling Ingredients is probably just what he had in mind.

I'll try to keep this as clinical as I can, in case you've just eaten: Darling refines byproducts from live and dead animals into components of commercially viable products like soap, fertilizer, and gelatin. You may be wondering why I'm calling it an energy company: That's because one of the products it makes is fuel.

That's right. Through Diamond Green Diesel, its joint venture with Valero, Darling can actually produce biodiesel out of animal fats and recycled cooking oil. In that regard, Darling is a company in the right place at the right time. With the recent reinstatement of the blenders' tax credit, making biodiesel just became a lot more lucrative. Meanwhile, rising oil prices could have companies looking for a cheaper alternative to traditional petroleum-based fuels, growing the overall market. 

Darling's fuel segment is its smallest by both revenue and EBITDA; its much larger feed ingredients and food ingredients segments made up 90.4% of the company's revenue and 79.7% of EBITDA in the most recent quarter. But you can see from those figures that the fuel segment is -- at least, currently -- the most profitable part of the business. 

Unlike the other two companies in this article, Darling pays no dividend. That said, it has performed largely in line with the overall oil and gas industry for the last several years. It's a worthy -- if unorthodox -- addition to a diversified oil and gas portfolio.

Let your portfolio do the work

Summer should be a time for relaxation, and investing in any of these three energy companies should allow you to relax and focus on things that matter, as opposed to the ups and downs of the stock market. While these aren't the most exciting investments in the world -- or, in the case of Darling, the most pleasant -- they represent safe and reliable places to put your money.

With these companies as your investments, the only roller coaster rides you should experience this summer are at the amusement park.

John Bromels owns shares of Darling Ingredients. The Motley Fool recommends Darling Ingredients. The Motley Fool has a disclosure policy.