Time-of-Use Arbitrage with Batteries: Making the Math Work Under Colorado's New Rates

Battery time-of-use arbitrage is a simple idea with real money behind it: you charge your home battery when electricity is cheap, either from your own solar production midday or from the grid during off-peak hours, and then you discharge it during the expensive peak window so you buy as little high-priced power as possible. As Colorado utilities move toward time-of-use rates and add peak-demand charges, this load shifting strategy has become one of the clearest ways a battery earns its keep. This guide shows the arithmetic of TOU battery savings under the specific rate changes hitting Colorado homes in 2026.

We design and install storage across the Front Range and the Western Slope, so the examples below reflect how these utility rate structures actually behave, not a generic national average.

How battery time-of-use arbitrage works

Under a flat rate, every kilowatt-hour costs the same no matter when you use it, so a battery has little price advantage to capture. Time-of-use pricing breaks the day into windows: an expensive on-peak window, usually in the late afternoon and evening, and cheaper off-peak hours the rest of the day. That price gap is the whole opportunity.

The play has two reliable ways to fill the battery:

• Charge from solar. Your panels produce most of their power around midday, well before the evening peak. Instead of exporting that midday energy for a low credit, you store it and use it yourself when prices are highest.
• Charge off-peak from the grid. On nights when solar did not fully refill the battery, it tops up during the cheapest overnight hours so it is ready for the next peak.

Either way, the battery discharges during the costly peak window to cover your evening cooking, air conditioning, and EV charging from stored cheap energy. The savings on each kilowatt-hour equal the difference between the peak price you avoided and the off-peak or solar cost you paid to store it. Stack that across roughly 300 to 350 evenings a year and the numbers add up.

Why 2026 changed the math

For years, one-to-one net metering made the timing of your usage almost irrelevant: a kilowatt-hour exported at noon offset a kilowatt-hour pulled at 8 PM at the same value. As Colorado utilities shift to time-of-use rates and add peak-demand charges, that simple swap no longer holds, and a battery becomes the tool that restores the value of your solar. We walk through the broader rate shift in our guide to Xcel time-of-use rates and solar, but the headline is that peak-rate avoidance now matters more than it used to.

The numbers under Colorado's new rate structures

The value of TOU battery savings depends entirely on your utility's rate design. Here is how arbitrage plays out across four Colorado structures we work with regularly.

Xcel Energy: the 5 to 9 PM peak

Xcel residential customers are on mandatory time-of-use rates with a peak window from 5 to 9 PM. That four-hour evening block is precisely when most households cook dinner, run laundry, and charge an EV, and it is also when solar production has dropped off for the day. A battery charged from midday solar or off-peak power can carry the home through that 5 to 9 PM stretch, so the grid sees almost none of your highest-priced demand. The wider the gap between Xcel's peak and off-peak prices, the more each shifted kilowatt-hour is worth.

CORE Electric Cooperative: a per-kW demand charge

CORE's three-part residential rate includes a demand charge of $1.50 per kW measured during the 4 to 8 PM on-peak window. This is a different lever from a simple energy-price spread. A demand charge bills you on your single highest interval of power draw during that window, so even one evening where your dryer, oven, and air conditioner run together can set the charge for the whole month. A battery that discharges to cap your draw during 4 to 8 PM holds that peak kW down, which trims the demand charge directly rather than just the per-kilowatt-hour energy cost.

Gunnison County Electric: a new 2026 demand charge

GCEA added a residential peak-demand charge starting January 1, 2026. As with CORE, the strategy shifts from shaving energy cost to shaving peak kilowatts: the battery discharges during the costly window to keep your metered demand low. In territories that pair a demand charge with a battery rebate, the storage case gets stronger from both directions, lower bills and an upfront incentive.

Holy Cross Energy: rate design that rewards storage

Holy Cross has been restructuring its rates toward delivery and demand components, which reduces the value of simply exporting solar and pushes more value toward storing and self-consuming your own power. In that environment, a battery that shifts your usage into the right windows recovers value the new rate structure would otherwise erode.

Working a simple arbitrage example

The core calculation is the same regardless of utility. To estimate annual TOU battery savings, you need four inputs:

1. Usable battery capacity in kilowatt-hours, which is how much energy you can move out of the peak window each evening.
2. The price spread between the peak rate you avoid and the off-peak or solar cost to charge.
3. Any demand-charge savings, if your utility bills on peak kW.
4. The number of evenings per year the battery can fully execute the shift.

For an energy-spread utility like Xcel, the rough annual energy savings equal usable kWh shifted, times the price spread, times the number of effective evenings. For a demand-charge utility like CORE or GCEA, you add the monthly demand-charge reduction times twelve. Real systems rarely hit the theoretical maximum every single day, because some evenings the battery runs low or the peak is small, so a conservative estimate uses a realistic effective-day count rather than 365. For a full breakdown of how to model payback and lifetime value, including battery degradation and replacement, see our solar battery economics deep dive.

What makes an arbitrage battery worth it

Not every home is a strong arbitrage candidate. The cases that pencil out best share a few traits:

• A wide peak-to-off-peak spread or a meaningful per-kW demand charge. The bigger the price difference you are arbitraging, the faster the battery pays back.
• High evening usage. Households that cook, run AC, and charge an EV during the peak window have the most expensive demand to shift.
• Solar to charge from. Filling the battery with midday solar is cheaper than buying off-peak grid power, which widens your effective spread.
• A utility incentive. Several Colorado utilities pair these rate structures with battery rebates or virtual power plant payments that stack on top of the arbitrage savings.

If your evenings are quiet and your utility still offers a narrow price spread, arbitrage alone may not justify a battery, though backup power during outages can still tip the decision. The point of storage is that it stacks several jobs at once: peak-rate avoidance, demand-charge reduction, self-consumption of solar, and backup. We cover how those benefits combine in our home battery storage guide.

Getting an estimate for your home

Because the savings hinge entirely on your specific rate schedule and your evening usage pattern, the only honest way to size the benefit is to look at your actual bills and interval data. The same battery that delivers strong returns on an Xcel time-of-use plan or a CORE demand rate might barely pencil out on a flat-rate co-op, so the rate design is the first thing we check.

ProGreen Solar designs and installs storage across the Front Range and the Western Slope, and we model arbitrage against your real utility rate before recommending any equipment. If you want to know what a battery would save at your address, reach out through our residential solar and storage page and we will run the math against your bills.

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