There are plenty of things to like about renewable power sources like solar and wind. However, these sources, on a large scale, are relatively new to the U.S. electric grid. That has major implications that utilities may not be ready to deal with. And that risks leaving you without power and, thus, in the dark.

Zig zag
You likely know all about the benefits of solar and wind. The biggest ones being no emissions from burning fossil fuels and minimal costs once they are installed since they are powered by nature. These are huge benefits that can't be, and shouldn't be, dismissed. It makes sense to include such clean-power options in the mix.

However, if you get so caught up in the upside of renewable power you might lose sight of the downside. And there are some pretty notable negatives that have big implications for a U.S. power system that hasn't been designed to handle intermittent power.

That, in fact, is one of the biggest problems. The sun and the wind can't be controlled. There's no way to tell just how much power you'll get on any given day or at any given moment. This fact has utilities more than a little concerned, since their job is basically to ensure your lights stay on no matter what.

Source: U.S. Energy Information Administration

Just how big an issue is this? Earlier in the year, the U.S. Energy Information Administration put out a graph showing the swings in wind power supply in Texas. The chart, shown above, is full of peaks and valleys. The spike up can mean the grid has to absorb four times as much power from wind as it does during the lulls.

And solar is no better -- and perhaps even worse. Sempra Energy's (NYSE:SRE) San Diego Gas & Electric (roughly 40% of the company's earnings last year), has a rooftop solar penetration rate of around 6% that it expects to double over the next two years or so. Tom Bialek, chief engineer at the San Diego utility, however, points out a problem: "Customers are changing how we view the world just because they are making choices."

Why is this such a big deal? Because customers don't need Sempra's consent to make changes, which means that Sempra doesn't know how much new solar to expect. And that's on top of the fact that you can't predict how much the sun will shine on any given day. Utility customers aren't likely to start installing wind farms, so this is an issue unique to solar.

In fact, Hawaiian Electric Industries (NYSE:HE) is dealing with a big solar problem right now, as so much solar has been installed, a good portion of which it didn't know about, that peak production times are putting it at risk of overloading circuits. The island state has 20 times the average rooftop solar penetration as the mainland. Every utility could be heading toward this dilemma.

Source: ReubenGBrewer, via Wikimedia Commons

Old reliable
This is why utilities like controllable power sources like natural gas, coal, and nuclear. There's no question how much power you'll get -- you run the plant at the level you need. But, that's a legacy issue, too, in a world with increasing intermittent, renewable penetration.

Most base-load plants are designed to be run constantly. This not only allows for peak efficiency, but means that they weren't designed to be turned on and off. If Texas sees a huge wind power spike it has to pull back on power somewhere. Increasingly that's likely to come from the power plants it can control. 

Dealing with the complex dance between controllable and intermittent power has been tricky for utilities. Some have simply put up roadblocks to slow the adoption of renewable power, such as Hawaiian Electric, which now requires homeowners to get approval before hooking to the grid. Others, like Edison International (NYSE:EIX), have worked to refocus their businesses around the distribution of power, minimizing the generation aspect. In fact, connecting often remote renewable power sources will require a large amount of new transmission investment and that's actually a big industry opportunity. Overall, however, utilities increasingly have little choice but to upgrade their systems, which is what Sempra's San Diego Gas & Electric has been doing. But upgrading is a costly and time intensive task and Hawaiian Electric's experience shows that time may not be on the industry's side. 

We take reliable electricity for granted in the United States. The impact of not having power, however, has been on display several times in recent years after natural disasters caused widespread blackouts. Moving too quickly down the renewable road without ensuring a system built for a different time can handle it could cause even more damage. This isn't a suggestion that renewable power is bad or that it shouldn't be an increasing part of the U.S. power system. But it is a word of caution that too much of a good thing could leave you sitting in a blackout.