Flip the oven on at seven, start the dishwasher, and the heat pump ramps up. The evening load spikes, and your monitor lights up. In Tucson last February, Carlos watched this pattern, then opened his bill. The fixed network charge had jumped. The payback his installer promised no longer matched reality.

Key Takeaways

  • Fixed network charges dilute savings. When they rise, exports earn less, and payback can stretch.
  • Your inverter (converts battery DC to home AC) sets power limits. Plan dispatch around its kW rating, not panel size.
  • Focus on billing building blocks. Track fixed fees, any demand charge, energy price per kWh, and export credit rules.
  • Time-of-use (TOU) windows reshape value. A small shift in peak hours can swing savings more than panel tilt.
  • A simple rule helps decisions. If the peak/off-peak spread exceeds $0.12/kWh, prioritize shifting into the peak.
  • Round-trip efficiency (energy out vs. energy in) reduces usable energy. Assume about 88% in example calculations.

Start by unpacking your bill. Then translate each line item into daily battery behavior you can control.

How network tariff components change battery economics

Understanding your bill unlocks realistic savings. The fixed network charge is a flat monthly grid fee. You pay it even if you use very little energy.

Next is the volumetric charge. This is the price per kWh you avoid when the battery covers evening consumption.

Some plans add demand charges. These are fees tied to your highest monthly peak draw. A brief spike can set that value for the month.

Export terms also matter. Export credit is the payment per kWh sent to the grid. Value can be full, partial, or very low.

Here is a concrete lens. At a residential retail price of roughly $0.18/kWh, every kWh discharged in the evening avoids that purchase. If your midday export credit is, for example, $0.08/kWh, exporting at noon would earn eight cents. The gap between those values is what shifting can capture.

Battery size limits daily shifting. An 11 kWh unit can only move that much energy per full discharge. To move more, it must cycle again. Most homes cannot sustain two full cycles daily without faster wear.

Fixed charges change the math differently. They do not care how efficiently you shift energy. If the fixed network charge increases by roughly $200 per year, that increase directly offsets annual savings. To neutralize $200 at $0.18/kWh, you would need about 1,110 extra kWh shifted yearly. That is roughly 3 kWh more every day, which is often not feasible.

A day-to-day observation helps. On a breezy Sunday at 1 pm, Carlos saw two hours of light exports. The new $17 monthly fee outweighed that day’s small energy savings. Now the floor set by fixed parts can dominate a handful of high-value cycles.

This variability leads straight to TOU and export choices. Those rules decide when shifted energy is most valuable.

Time-of-use and export options: what to compare

Picking the right plan protects your savings. TOU means prices vary by hour. A larger spread between peak and off-peak boosts battery value.

Start with a side-by-side comparison. Many who tried two TOU plans for a summer month saw clear differences. A later peak window changed battery discharge timing and the bill shape.

Checklist for a quick comparison:

  • Model two TOU options against your last 12 months of usage.
  • Simulate battery dispatch under each plan using your actual bill data.
  • Confirm your meter type; a smart meter (records interval data) is needed for accuracy.
  • Export treatment clarity: are exports netted hourly, daily, or paid a set low rate?
  • Does the plan include critical-peak pricing (rare very high price events)?
  • Watch for any demand charges tied to your monthly peak draw.

Export treatment changes priorities. With full netting, exporting at noon can offset evening usage at the same price. With net-billing or low export prices, self-consumption becomes the better default. Ask your installer to set export limits when midday value is minimal.

A quick numeric anchor helps scale decisions. A 5 kW unit discharging for 2 hours shifts roughly 10 kWh. If the peak/off-peak spread is about $0.10/kWh, that maneuver saves around $1.00. The amount seems small, yet daily repetition compounds. Over a long, hot month with 30 events, that single maneuver saves about $30 before export adjustments.

Field conditions can surprise. During a July heat wave, one plan’s peak window ran 4–9 pm. The battery emptied by 7:30 pm, then the home paid peak prices again. In the week of July 12–18, one household shifted 9.6 kWh across three hot evenings. On July 15, heavy clouds cut solar charge, and only 2.8 kWh discharged during peak. On July 18, the inverter held 4.8 kW for 40 minutes starting at 6:05 pm. Even so, the battery dipped below the desired reserve by 8 pm, pushing the home onto grid power.

If your peak window is long, spread discharge to cover the full span. That often beats blasting full power early and going empty too soon.

Comparing installers and modeling payback under new tariffs

Quotes must reflect your tariff, not a generic profile. Request itemized system specs, including inverter power and usable capacity. Ask for an explicit dispatch model that uses your last year of bills. Warranties, degradation assumptions, and export treatment should appear in writing.

Insist on clear inputs. Usable capacity, not nameplate, should drive savings. Round-trip efficiency must be included, along with realistic cycles per year. Request sensitivity cases for higher fixed charges or lower export credits.

Here is the step-by-step example calculation you can request in writing:

  1. Usable energy per full cycle. Example calculation: capacity × efficiency = 11 kWh × 88% ≈ 9.68 kWh.
  2. Annual shifted energy. Example calculation: 9.68 kWh × 365 ≈ 3,533 kWh per year.
  3. Value of shifting. For example, use a $0.10/kWh spread between off-peak charge and peak discharge. Annual energy savings ≈ 3,533 × $0.10 ≈ $353.
  4. Net savings and payback. Deduct higher fixed charges from energy savings, then divide cost by the remainder. If fixed charges rise by roughly $200/year, net savings ≈ $153. With a battery installed for, for example, $10,500, simple payback is about 69 years.

What should appear on the quote? A clear table listing usable capacity, the efficiency used, assumed cycles per year, the price spread, and a scenario with a higher fixed charge. Red flags include blanket payback claims with no tariff model, missing efficiency or degradation assumptions, and no scenario showing fixed-fee impacts.

A real buying experience highlights this. One homeowner asked two firms to re-run the same winter week with a higher fixed charge added. Results diverged sharply. The optimistic quote assumed near-daily cycling during storms, which overstated savings.

Protective dispatch settings can help while you compare quotes. Cap midday exports if credits are very low. Favor evening self-consumption, and reserve some energy for the final peak hour. Those tweaks preserve value until a better plan becomes available.

Bottom Line

  • Tariff design now shapes payback as much as hardware. Do not rely on a single generic figure; request scenarios that match your bill data.
  • While waiting on a better plan, switch to the most favorable TOU option for your usage. Your installer can also limit low-value exports.
  • Small, steady shifts compound. For example, moving 1.3 kWh/day with an $0.11 spread saves roughly $52/year.
  • Immediate checklist: get a modeled bill impact from each installer, confirm TOU eligibility with your meter, and insist on itemized warranties and assumptions.
  • Homeowners who track bills monthly often spot tariff changes early. A quick call to your installer can re-tune dispatch before savings slip.
  • Document the model inputs now. You can then re-run numbers quickly if the utility changes fixed charges again.