Utilities on time of use (TOU) rates bill very different prices depending on when you use energy, my SMUD plan is $0.3765/kWh on Peak (5–8 PM weekdays), $0.2139 Mid-Peak, and $0.1550 Off-Peak on the Summer Plan. On these plans, when you use energy matters as much as how much, and every utility shows this breakdown on their own billing site.
The Opower integration (SMUD, PG&E, ConEd, Duke, Exelon utilities, and ~40 others) currently imports total consumption and cost only, so the Energy dashboard can’t show which portion of your usage and money went to each rate period.
It turns out the Opower API already returns the per-period breakdown in the same responses the integration fetches today, the library just doesn’t parse it. I’ve verified this against live SMUD data (per-period kWh and cost sum exactly to the totals, and each period’s cost/kWh reproduces the published rates), and the same response field also covers tiered rates, so both rate structures benefit.
Here’s what it looks like with the parsed data feeding the Energy dashboard, each TOU period as its own grid source with its own cost (this is a real day from my meter):
And a full month 
I made a couple github entries, a library change, submitted as tronikos/opower#208, with the investigation in issue #207. Purely additive, no new API requests.
And a Home Assistant integration change that creates per-period statistics automatically, ready to submit as a follow-up PR once the library change is merged and released.
No config changes would be needed; the integration simply creates additional statistics, for example Peak/Mid-Peak/Off-Peak energy and cost next to the existing totals, and you’d add them in your Energy dashboard settings if you want the breakdown.
If you’re on a TOU or tiered rate with an Opower utility and want this in your Energy dashboard, you could drop a comment here 
Time of Use (Peak/Mid-Peak/Off-Peak) cost breakdown in the Energy dashboard from the Opower API — SMUD, PG&E, and friends · home-assistant · Discussion #4488 · GitHub