--- title: "How to plan home battery backup loads before choosing capacity" description: "Plan critical circuits, outage duration, power demand and equipment compatibility before choosing home battery capacity." canonical: "https://betterpowered.com/articles/home-battery-backup-load-planning/" locale: "en-US" contentKind: "article" articleFormat: "how_to" articleFormatLabel: "How-to" topic: "roof-solar-resilience" topicLabel: "Roof, solar & resilience" datePublished: "2026-08-23T14:57:03.297Z" dateModified: "2026-08-23T14:57:03.305Z" author: "BetterPowered Editorial Team" --- # How to plan home battery backup loads before choosing capacity Choose the services and circuits that matter during an outage, then let verified power, energy and compatibility requirements determine battery capacity. ## Start with the outage, not the battery Home battery backup load planning begins with a plain question: what must still work when the grid is unavailable? A battery cannot answer that question for the property owner. The property plan has to name the circuits, the acceptable interruption time and the conditions under which a load can be turned off. Write two outage goals before comparing equipment. The first is the minimum goal, such as keeping refrigeration, a few lights, communications and a selected receptacle circuit available. The second is the stretch goal, which might add a well pump, selected cooling or another large load. Keep the two lists separate. Otherwise, a proposal can quietly size the system around the stretch goal while presenting the price as though every item were essential. The [U.S. Department of Energy's Solar and Resilience Basics](https://www.energy.gov/cmei/systems/solar-and-resilience-basics) explains an important boundary: ordinary residential solar panels alone generally do not keep a home powered during a grid outage. Outage operation requires a properly configured inverter and storage system. Your plan therefore needs to cover both the loads and the equipment that will isolate them safely from the grid. ## Build a circuit-level load inventory Walk the panel with a qualified electrical professional and identify the actual circuits behind each outage need. Do not rely on room names alone. One breaker may feed several rooms, and one desired appliance may share a circuit with loads you did not intend to back up. For every candidate load, record: - the circuit and the equipment it serves; - the rated running power or current from the nameplate or manufacturer documentation; - any starting or surge requirement stated by the manufacturer; - how many hours or cycles it may operate during the planning period; - whether it may be shed manually or automatically; and - why it is on the critical list. Use measured property data when it is available, but keep the source and date with the number. A whole-home monitor, a temporary circuit measurement or equipment documentation can answer different questions. None should be presented as a guaranteed future load. For medical or life-safety equipment, do not infer consumption or acceptable interruption from a generic appliance list; use the device instructions and the responsible care or equipment provider's requirements. The inventory should also expose conflicts. If two large loads are not expected to run together, the design may use controls that prevent simultaneous operation. If simultaneous operation is required, the power system has to be evaluated for that case. Make that operating rule visible in the scope instead of leaving it as an installer assumption. ## Separate power from stored energy Battery proposals often place one capacity number at the center of the page. That is incomplete. The Department of Energy's [Solar Energy and Storage Basics](https://www.energy.gov/cmei/systems/solar-integration-solar-energy-and-storage-basics) treats power and energy as separate characteristics: energy capacity is the total amount stored, while power capacity is the amount that can be released at a given time. In practical terms, power is the simultaneous demand the inverter and battery must carry. Energy accumulates as loads run over time. A system can have enough stored energy for the planned period yet still be unable to start or carry a particular combination of equipment. The reverse can also happen: it may carry a high load briefly but lack the stored energy for the desired outage duration. Ask the proposal to show both calculations. The power worksheet should identify the expected coincident loads and every manufacturer-specified starting condition. The energy worksheet should show each load's assumed operating time, the usable battery energy applied by the designer, the planned backup reserve and the treatment of system losses. If solar recharging is included, request a second case with no assumed solar contribution. Cloud cover, time of day and array conditions belong in a scenario, not in a promise. ## Decide what the battery panel will actually serve The next decision is architectural. The design may place selected circuits in a critical-load panel, use listed load-control equipment, or propose another documented arrangement. The right approach depends on the existing service, panel capacity, equipment ratings, wiring and outage goal. Ask for a one-line diagram that shows the utility service, main panel, backup panel or controlled loads, battery, inverter, transfer or isolation equipment, solar connection if present, and the intended power path during normal and outage operation. The drawing should use the exact proposed model numbers. A sales illustration is not a substitute. Compatibility must be evaluated as a system. UL's [Q&A on stationary energy storage certification](https://www.ul.com/thecodeauthority/knowledgecenter/qa-portable-power-packs) identifies UL 9540 as the appropriate certification standard for a stationary battery energy storage system and cautions that combining separately certified products in the field does not create a certified system. Ask the designer to document the listing for the proposed system and its intended use, then confirm installation location, separation, protection and permitting with the authority having jurisdiction and the manufacturer's current instructions. ## Check solar, controls and recovery behavior If the property already has solar, confirm that the existing inverter and the proposed battery architecture can operate together. The DOE resilience guidance notes that grid-connected solar normally switches off during an outage unless the system has the equipment and configuration needed for islanded operation. The proposal should state whether solar can charge the battery while the grid is down, what happens when the battery reaches its reserve, and how the system restarts after shutdown. Controls need an owner-readable plan. List the loads that will disconnect first, the condition that triggers each action and the steps required to restore them. If a mobile app or internet connection is unavailable, document what can still be seen and controlled locally. If equipment requires manual intervention after a long outage, place that instruction in the closeout package. ## Model the property plan, then choose capacity Runtime is a property-specific result, not a feature printed on the battery cabinet. DOE describes [REopt](https://www.energy.gov/cmei/femp/articles/unlock-expert-energy-analysis-reopt) as a tool that can estimate how long distributed energy systems sustain critical loads during a grid outage using site-specific inputs. A residential proposal does not have to use that tool, but it should meet the same basic standard of transparency: named loads, stated operating profiles, weather or solar assumptions where used, equipment limits and more than one outage scenario. Compare at least the minimum and stretch load plans. It is also useful to test a low-solar case and a case in which a discretionary large load is removed. The point is not to manufacture a precise runtime. It is to see which assumption is driving capacity and whether load control changes the design more than another battery module would. This is why battery capacity follows the property plan. First decide which services matter, which circuits provide them and how those circuits may operate. Then verify simultaneous power, expected energy use, equipment compatibility and installation constraints. Capacity is the output of those decisions. ## Require a commissioning record Before closeout, ask the installer to verify the installed model numbers and configured reserve against the approved design. The owner package should include the permit documents, one-line diagram, equipment manuals, shutdown and restart instructions, load-control settings, warranty information and emergency contacts. Where the installer and local requirements allow, commissioning should include a controlled grid-loss test. Record which circuits remain energized, whether the planned load-shedding rules operate, what the local indicators show and how the system reconnects. This test confirms configuration on that date; it does not prove a future outage duration or guarantee performance under every condition. Battery planning fits into a larger sequence. Review [what to size after efficiency work](/articles/solar-and-battery-after-efficiency-what-to-size/) before using old consumption as a forecast, and use the [electrical panel assessment checklist](/articles/electrical-panel-assessment-before-ev-charger/) to document service and panel constraints. A useful battery proposal should make the property's choices visible enough that another qualified professional can follow the logic. ## Use this answer in a whole-property plan - [Whole-home upgrade planning](https://betterpowered.com/whole-home-upgrade-planning/) - [Energy advisory services](https://betterpowered.com/energy-advisory-services/) - [How BetterPowered uses illustrative scenarios](https://betterpowered.com/methodology/illustrative-upgrade-scenarios/) - [BetterPowered Contractor Standard](https://betterpowered.com/contractor-network/standard/) ## Primary sources - [Solar and Resilience Basics](https://www.energy.gov/cmei/systems/solar-and-resilience-basics) — U.S. Department of Energy - [Solar Integration: Solar Energy and Storage Basics](https://www.energy.gov/cmei/systems/solar-integration-solar-energy-and-storage-basics) — U.S. Department of Energy - [Unlock Expert Energy Analysis with REopt](https://www.energy.gov/cmei/femp/articles/unlock-expert-energy-analysis-reopt) — U.S. Department of Energy - [Q&A: Portable Power Packs](https://www.ul.com/thecodeauthority/knowledgecenter/qa-portable-power-packs) — UL Solutions > This article is educational and preliminary. Project scope, savings, eligibility, permits and tax treatment depend on the property and current program rules.