Whole home battery backup: how it works in Maryland

A whole home battery backup separates your house from the grid when the power fails and runs your circuits from stored energy. Output in kilowatts sets what can run at once. Stored energy in kilowatt-hours sets how long. Maryland’s storage rebate is 30 percent of project cost, capped at $5,000 for a home, while program funds last.^1,2,3

What happens to a whole home battery when the grid goes down?

Ordinary grid-tied solar shuts off in an outage so it can’t energize lines while crews repair them. A backup system is built differently. It senses the outage, opens a switch between your home and the grid, and feeds your circuits through its own inverter, which turns the battery’s direct current into the alternating current your appliances use.^1,4,2

The sequence runs like this:

1. In normal service, the battery charges under its approved settings. Solar can feed it where the equipment supports that.¹
2. When the grid drops, an automatic transfer switch disconnects the backed-up circuits from the grid. The battery and inverter supply those circuits within their limits.²
3. If the outage lasts, compatible solar can recharge the battery. When utility service returns, the system reconnects.⁴

A battery bought only to shift energy use doesn’t give you backup by itself. The inverter and controls have to be built to run without the grid.^1,4 Our guide on what solar panels do in a power outage covers the solar-only case.

One detail worth getting in writing: how the switchover feels. Ask whether the transfer is seamless before you count on a desktop computer riding through it.

Whole home or essential circuits: which one do you need?

Whole-home backup tries to keep every circuit available. Essential-loads backup covers a chosen group. Either way, the battery has to deliver enough power for whatever runs together and enough energy for however long you want it to run. Many homes get a separate critical-loads subpanel because the system wasn’t sized to carry the whole house.²

Picture a household that cares about the refrigerator, internet and a sump pump. Start the design with those three. Then price a second option that adds cooling, and compare the circuit lists and equipment each version needs. The example assigns no wattage or runtime. It only shows the order of decisions.

Soleil Energy’s battery storage page says the team picks the backed-up circuits with you and that whole-home backup is possible but costs more than backing up essentials.⁵ Whatever the label on a quote, ask to see the circuit list. “Whole home” alone doesn’t tell you what stays on.

Can a home battery run your heating and air conditioning?

Small cooling loads, yes. Large central systems depend on the numbers. Motors draw far more power for the first moment than while running. The Pacific Northwest National Laboratory (PNNL) says a refrigerator motor often needs 100 to 300 percent more power to start than to run, and that small generators or battery banks can serve only smaller start-up loads.⁶

PNNL and the Florida Solar Energy Center publish a rough guide to what different backup sizes can carry:⁶

Now compare that with a real product sheet. One example home battery lists these figures on its May 2025 data sheet. Other products differ, so treat it as a guide to what to look for on any sheet:⁷

LRA stands for locked-rotor amps, the surge a compressor motor draws as it starts. The match to check is simple: the air conditioner’s starting current must fit under the battery’s start rating, and its running load must fit under the continuous rating. A 5.0 kWh battery also holds the energy for one kilowatt of load for about five hours at best, before conversion losses.⁸

Heating follows the same logic. PNNL notes that a heat pump cools like an air conditioner and also heats, so one backed-up unit can cover both seasons.⁶ For larger ducted systems or electric-resistance heat, the equipment’s own nameplate and the battery’s start rating decide the answer, and the electrician should run that comparison before you sign. Leave the panel covers and equipment closed while you gather model numbers from labels and paperwork.

Battery runtime and battery lifespan are different questions

Outage runtime depends on how full the battery is when the lights go out, what you run, and whether the sun can recharge it. Lifespan is about years and cycles. A lifespan number can’t tell you how many hours you’ll get on a particular night.^1,2

PNNL says backup duration varies greatly with system size and type.² The National Renewable Energy Laboratory (now the National Laboratory of the Rockies, NLR) adds the hard case: if a solar-plus-battery system drains at night or on a cloudy day, no energy is available until sunlight returns.¹ So ask for an outage scenario that assumes a starting charge, your chosen loads, and no solar recharge.

Restart behavior matters in a long outage. After a battery is fully depleted, PNNL says some AC-coupled batteries need a signal from the grid before charging again, while most DC-coupled batteries can restart from solar alone.² That’s a spec-sheet question for any system you’re considering.

For lifespan, the useful facts come from the manufacturer’s warranty. The example sheet above lists a limited warranty of more than 60 percent capacity, up to 15 years or 6,000 cycles, whichever comes first, with restrictions.⁷ NLR’s cost model assumes a 15-year life and about one cycle a day, with augmentation costs built in to keep rated capacity. That is a modeling assumption, not a warranty and not a prediction for your battery.⁹ Our guide on adding a battery to existing solar covers retrofit compatibility.

Which permits and utility approvals does a battery need?

A battery project involves an electrical design, county permit review and utility review, and each is a separate track. Your installer should say in writing who handles each one, including the final inspection and the approvals you’ll need for the state rebate.^10,11,12

Your bill tells you which utility serves you, and its rules apply. Pepco serves most of Montgomery and Prince George’s counties, so a battery project there goes through Pepco’s process instead; see our Pepco interconnection guide.¹³ Before handover, have the installer demonstrate backup operation, and collect the approved circuit list, operating instructions, inspection record and any utility authorization.

If you already net meter

Adding a battery can touch your net-metering status. Under Maryland’s Utility RELIEF (Reducing Energy Load Inflation for Everyday Families) Act (Chapter 353 of 2026), a customer-generator under a net-metering contract or tariff on July 1, 2027 remains eligible until the earlier of several events. The text lists a modification that increases net power flow by adding more photovoltaic modules than the system was first placed in service with, or that increases alternating-current output capacity; a new interconnection agreement; and repowering.¹⁴ The text does not mention batteries, so ask the utility in writing whether your battery design touches any of those events before you build.

What does Maryland’s storage rebate pay?

Maryland’s Residential and Commercial Energy Storage (RCES) program pays 30 percent of total project cost for a home battery, up to $5,000.³ The state statute caps a grant at the lesser of that dollar limit or 30 percent of total installed cost.^3,15 Business and nonprofit properties get the same percentage with a $150,000 limit.³

Total project cost includes purchase, installation and interconnection, and the final payment can be lower than the reserved amount but not higher.³ Some things don’t qualify: a system that isn’t grid connected, costs specific to a paired solar system (unless reasonably necessary for the storage), portable power stations and removable batteries, a system installed by someone without the required certifications and licenses, and a system that already received money from another MEA storage incentive.³

The order of operations is the part people trip over:³

1. Apply for the upfront reservation in MEA’s online portal. MEA says it must approve the reservation before the battery goes in and that a system installed first is ineligible.
2. Install the system. The reservation expires 180 calendar days after MEA’s approval notice, and MEA may extend it for circumstances outside your control or good cause shown, though not past May 1, 2028. An extension request is due at least 30 days before the reservation expires, and filing one doesn’t mean MEA will grant it.
3. Get the utility’s permission to operate. MEA says the utility document must be dated after the reservation date.
4. Submit the payment request with photos and documents.

Applications are due by 3 p.m. Eastern on May 31, 2027, and the portal may close sooner if the budgeted funds are fully requested.³ MEA expects up to $4 million for the year and says the total may be more or less.¹⁶ A funding table on its program page, last updated October 19, 2026, showed a $4,000,000 budget with 20.90 percent requested and 4.15 percent reserved.¹⁶

A contractor proposal isn’t a reservation. Our guide on the Maryland battery rebate walks through the steps, and the home battery versus generator guide compares backup options.

Questions to put in every proposal

Compare the outage design before you compare battery reviews. Reviews of one product can’t tell you whether a proposed installation matches your household, because circuits, loads and utility steps differ from house to house. A solid proposal answers these in writing:

• Which circuits stay on, and which appliances can run together?
• Which starting loads were checked, including pumps and cooling?
• What usable energy and starting charge does the outage estimate assume?
• What happens when the battery empties before sunlight returns?
• Which panel work, transfer equipment and load controls are included?
• Who obtains permits, books inspections and confirms utility requirements?

Before you sign anything

Decide what must stay on, find out whether your cooling and heating fit under the battery’s start rating, and reserve the rebate before any work begins. Then compare proposals on circuits, runtime and paperwork rather than on the headline label.

Book a free assessment or call (301) 953-4140 to talk through the circuits you want backed up.

Solar savings and incentive eligibility depend on your roof, your usage, your utility, and your tax situation. Incentive programs change and some have limited funding. We are not tax advisors — we will review your bill with you and tell you what you may qualify for. Confirm any tax credit with a qualified tax professional.

Program rules decide who qualifies. Ask any installer whether it is on the program’s contractor list.

Sources (16)

1. National Renewable Energy Laboratory (now National Laboratory of the Rockies), Will Solar Panels Help When the Power Goes Out? Planning for PV Resilience, March 2020, https://docs.nlr.gov/docs/fy20osti/75704.pdf; read October 25, 2026. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

2. Pacific Northwest National Laboratory, PV Battery Storage for Power Outages, last updated September 29, 2021, https://basc.pnnl.gov/information/pv-battery-storage-power-outages; read October 25, 2026. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸

3. Maryland Energy Administration, FY27 Residential and Commercial Energy Storage Program Funding Opportunity Announcement, issued September 24, 2026 (sections 2, 3, 7, 11 and 15), https://energy.maryland.gov/SiteAssets/Pages/EnergyStorage/FY27%20RCES%20Funding%20Opportunity%20Announcement%20-%20Issued%209.24.pdf; read October 25, 2026. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³

4. U.S. Department of Energy, Solar and Resilience Basics, undated current page, https://www.energy.gov/cmei/systems/solar-and-resilience-basics; read October 25, 2026. ↩ ↩² ↩³

5. Soleil Energy, Battery Storage & Retrofits, undated current service page, https://soleilenergycorp.com/renewable-energy/battery-storage/; read October 25, 2026. ↩

6. Pacific Northwest National Laboratory and Florida Solar Energy Center, Emergency Air Conditioning and Food Refrigeration, last updated December 16, 2022, https://basc.pnnl.gov/resource-guides/emergency-air-conditioning-and-food-refrigeration; read October 25, 2026. ↩ ↩² ↩³

7. Enphase Energy, IQ Battery 5P data sheet (document DSH-00010-11.0-EN-2025-05-06), May 6, 2025, https://enphase.com/download/iq-battery-5p-data-sheet; read October 25, 2026. One manufacturer’s sheet, used as an example of the figures to look for. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸

8. Illustrative calculation, run October 2026: 5.0 kWh of usable energy divided by a 1.0 kW load is 5.0 hours, before conversion losses and any reserve, with the inputs sourced at ⁷. ↩

9. National Laboratory of the Rockies, Residential Battery Storage, Annual Technology Baseline 2025 edition, current page, https://atb.nlr.gov/electricity/2025/residential_battery_storage; read October 25, 2026. A cost-model page; its system size and lifetime are modeling assumptions. ↩

10. Howard County Department of Inspections, Licenses & Permits, Let’s Get Started: Resources & Fees, undated current page, https://www.howardcountymd.gov/inspections-licenses-permits/lets-get-started-resources-fees; read October 25, 2026. ↩ ↩²

11. Montgomery County Department of Permitting Services, eSolar Residential Rooftop Solar Panels, undated current page, https://www.montgomerycountymd.gov/department-permitting-services/all-permits/residential-permits/esolar-residential-rooftop-solar-panels; read October 25, 2026. ↩ ↩²

12. Baltimore Gas and Electric, Quick Reference Guide: BGE Technical Interconnection Requirements, revision dated June 4, 2024, https://www.bge.com/cdn/assets/v3/assets/blt71bfe6e8a1c2d265/blt86b5a443d3247ab7/66630c7f522922000dd37333/Quick_Reference_Guide_to_Technical_Interconnection_Requirements_%28QRG-TIR%29.pdf?branch=prod_alias; read October 25, 2026. ↩ ↩²

13. Maryland Office of People’s Counsel, “Your Local Electricity Companies,” https://opc.maryland.gov/Consumer-Learning/Electricity/Your-Local-Electricity-Companies; current page, undated, read October 25, 2026. ↩

14. Maryland General Assembly, Utility RELIEF (Reducing Energy Load Inflation for Everyday Families) Act, Chapter 353, approved May 12, 2026, amending Public Utilities Article Section 7-306(d)(5), https://mgaleg.maryland.gov/2026RS/chapters_noln/Ch_353_hb1532E.pdf; read October 25, 2026. ↩

15. Maryland General Assembly, State Government Article Section 9-2012 (Energy Storage System Grant Program), subsection (f), current text, https://mgaleg.maryland.gov/mgawebsite/Laws/StatuteText?article=gsg&section=9-2012&enactments=false; read October 25, 2026. ↩

16. Maryland Energy Administration, Residential and Commercial Energy Storage Program, current page (funding table last updated October 19, 2026), https://energy.maryland.gov/Pages/Energy-Storage-Grant-Program.aspx; read October 25, 2026. The table’s column heading on the page reads “Total FY26 RCES Grant Program Budget”; the table sits under the page’s FY27 anticipated-budget paragraph. ↩ ↩²