Batteries: when they earn, when they don't

Buy a battery for a defined job: keeping selected loads running in an outage, or moving electricity to more valuable hours. Those are different decisions. A battery can improve resilience without paying for itself through bill savings.

Start with energy and power, not a module count

The U.S. Department of Energy storage explainer distinguishes energy capacity (kWh) from power capacity (kW). Energy sets how long a load might run; power limits what can run at once. A large energy capacity does not guarantee that an air conditioner or well pump can start. Ask for continuous output, surge capability, usable energy, reserve settings and supported circuits.

For a planning example, 10 kWh of usable energy serving a steady 1 kW load gives 10 hours before additional losses or reserve restrictions. That is arithmetic, not a runtime promise. Refrigerators cycle, starting loads differ, and heating can dominate demand. Have the installer document an appliance-level load assessment and whether the system can recharge from solar while the grid is down.

Value the imports avoided and exports forgone

Storage is not lossless; DOE explains that conversion and retrieval consume some energy. For each delivered kWh, compare the import cost avoided with the value of the electricity used to charge the battery. Use the rates for the actual charging and discharging hours, not just the average rate on a bill.

Hypothetical daily example: delivering 10 kWh at 90% round-trip efficiency requires about 11.11 kWh of charging energy. If avoided imports cost $0.30/kWh and the solar export credit sacrificed is $0.05/kWh, the gross benefit is $3.00 minus about $0.56, or about $2.44. This excludes installed cost, degradation, financing, reserve capacity and days without enough surplus solar. It is not an annual savings forecast.

With equal flat import and export rates, losses alone can make shifting unattractive. Time-of-use spreads, export restrictions or a documented utility battery program can change the answer. An incentive is not confirmed until your eligibility and any enrollment obligations are established. Do not count the same kWh as both an export payment and avoided evening consumption.

Before you sign

• Request separate solar-only and solar-plus-storage cash prices, including backup hardware and electrical work.
• List the essential circuits, desired outage duration and loads intentionally excluded.
• Ask for a written savings model using your tariff, interval usage and realistic charge availability.
• Read the capacity-retention, throughput and labor coverage terms; a warranty is not a guaranteed bill saving.
• Check who controls charging under any utility program and whether you can reserve energy for an outage.

Taxes and the next decision

The IRS Residential Clean Energy Credit page states that the credit is unavailable for property placed in service after December 31, 2025. Do not automatically reduce a new 2026 battery quote by 30%. State or utility programs need separate verification.

Use the battery planner as a rough sizing screen, then obtain a load study and tariff-specific quote. Its shifting values are before storage losses; use the worked example above to understand that limitation. If resilience is the main goal, compare what essential services you gain rather than describing the purchase as a guaranteed investment.

Source review: 2026-09-20. DOE supports the storage and efficiency concepts; IRS supports the federal tax cutoff. Example rates and equipment values are invented teaching inputs, not local tariffs or market prices.