Power Priorities

[Astrella]

What's the priority on your factory using different power sources?

Right now I have solar panels, steam engines and acumulators, but the factory doesn't seem to drain the acumulators at night as I expected would happen.

[daniel34]

The wiki explains this in great detail and has workarounds to switch off the steam engines at night:
Wiki - Electricity/Priority of power production
Wiki - Power production/Dealing with priorities

Short answer: the priority is Solar panel --> Steam engine --> Accumulator
The factory only drains the accumulators when there isn't enough power generated by solar and steam together.

[Gus_Smedstad]

The issue of wanting to go full solar and use steam as a backup to accumulators, rather than accumulators as a backup to steam, is so well known that there are a variety of solutions to disabling steam power production until accumulator power runs low. They all work by creating an isolated section of your power grid that can only draw power from a single accumulator. That accumulator is part of two power networks - the detector system, and the main grid, so it gets charged and discharged with the rest of the accumulators. When the detector system stops operating due to lack of power, you re-engage the steam engines.

Old systems used inserters moving stuff around so that a smart chest would empty when power cut out. The more current approach is to set up an electronic clock with combinators, and check if it's still changing values from tick to tick.

Old systems would generally control inserters feeding fuel to boilers. When the system triggered, you'd add fuel. More current approach is to use small electric pumps to feed water from the boilers to the steam engines, and turn them on when the system triggers. The electric pump response is very fast, fast enough that you need to figure out a way to delay shutting off when power returns, because otherwise it tends to cycle on and off excessively. The electric pump approach also kind of needs a backup power source, because it's possible for a brownout to shut them down, and which then leads to a total blackout without steam power.

[ssilk]

The "Show your creations"-section is full of creative/innovative ideas, to handle this case.