Two households with identical total electricity usage can pay very different bills if one is on a flat rate and the other on time-of-use or demand-charge pricing. Understanding which structure you are on, and how your usage pattern interacts with it, changes which home-energy purchases actually save you money.
Time-of-use versus flat rate, directly compared
The time-of-use versus flat rate engine runs your usage pattern against both structures to show which one actually costs less for you specifically, rather than assuming time-of-use is automatically better or worse.
Demand charges are a different mechanism entirely
A demand charge bills your single highest power draw during a period, not your total energy used. The demand charge bill impact engine shows how much of your bill that peak-driven charge represents, which is often invisible until you look for it specifically.
Reducing a demand charge with a battery or load shifting
Since a demand charge is driven by your single highest moment, not your total usage, flattening that peak, through a battery discharging during it or simply avoiding running several large appliances simultaneously, can meaningfully reduce this specific charge. The demand charge reduction value engine quantifies that specific savings.
Shifting load to capture a rate spread
On a time-of-use plan, moving flexible loads, like EV charging or a pool pump, to off-peak hours captures the rate spread directly. The rate plan shift value engine estimates what that shifting is worth given your specific peak and off-peak rates.
EV charging adds a specific demand-charge risk
A Level 2 charger draws enough power to meaningfully raise your peak demand if it runs at the same time as other large loads. The EV demand charge risk engine flags this specifically for EV owners on a demand-charge rate plan, a risk that is easy to miss since it depends on your rate structure, not your vehicle.
Reading your own rate schedule
Your utility's rate schedule document, not the summary bill, is the authoritative source for whether you are on a demand-charge or time-of-use structure and what the specific rates and peak windows are. See the reading a utility bill resource for how to locate that detail.
Frequently asked questions
What is the difference between time-of-use and a demand charge?
Time-of-use prices every kWh differently depending on when you use it. A demand charge is a separate fee based on your single highest power draw (kW, not kWh) during a billing period, regardless of your total usage. A bill can have either, both, or neither.
Can a home battery actually reduce a demand charge?
Yes, by discharging during your highest-draw moments to flatten your peak, which is exactly what the demand charge reduction value engine models. The savings depend on how spiky your usage pattern is and how large your demand rate is.
Is switching to time-of-use always a good idea?
No. If most of your usage happens during peak hours and cannot shift, time-of-use pricing can increase your bill compared to a flat rate. Run your actual usage pattern through the comparison before switching voluntarily.