solar battery sizing

P Peter Lu Energy Storage Product Manager, GreenMore There is no single correct battery size for every home. A system that is too small runs out during the evening or a long outage; one that is too large costs more than it will ever save. The right number comes from three things: how much electricity the loads you care about actually use, how long you want them to run without the grid, and how much of that energy the battery can realistically deliver. This guide walks through all three and ends with a simple worked example. Step 1: Build your load profile Start from your electricity bill, which states daily or monthly kilowatt-hours, rather than guessing from a list of appliances. Then separate the loads you want to keep running during an outage or overnight from the ones you can do without. Refrigeration, lighting, internet, a fan or a small heat-pump circuit usually make the essential list; an electric oven, clothes dryer or whole-house air conditioning often do not. To make this concrete, read the nameplate power of each essential appliance and multiply by the hours it runs per day. A 150 W refrigerator cycling for 8 hours, for example, uses about 1.2 kWh. Add the essential loads together to get your daily critical load. A small efficient home might land near 5 kWh, a typical family home around 10 to 15 kWh, and a large home with electric heating considerably more. If your main goal is savings rather than backup, also check your utility's time-of-use schedule. Under a plan with a clear peak and off-peak gap, the battery should be large enough to shift a meaningful share of your evening consumption; where rates are flat all day, size mainly for backup and solar self-consumption. Treat any quoted prices as illustrative — tariffs differ by utility and change over time, so use your own plan. Step 2: Decide your backup target Next, decide how long the essential loads must run on their own. Most homes aim to cover one evening and night until solar returns, which is effectively a one-day target. Off-grid and weak-grid homes may want two days or more to ride through cloudy weather. Backup days multiply the energy you need, so this single decision has the biggest effect on cost. Basic backup — lights, refrigerator and communications for a short outage; roughly 3 to 5 kWh of usable energy. Comfort backup — adds heating or cooling, a water heater and kitchen circuits; commonly 8 to 15 kWh. Whole-house or off-grid — running the full home for a day or more; usually 20 kWh upward and often a generator for long stretches. Step 3: Apply depth of discharge and efficiency You cannot use 100% of a battery's nameplate capacity repeatedly without shortening its life. The usable share is set by the recommended depth of discharge (DoD), and some energy is lost in the inverter, cabling and battery itself. Lithium iron phosphate (LiFePO4) systems commonly allow about 90% DoD and run at a round-trip efficiency near 90%, but the exact figures come from the product datasheet, and it is sensible to leave a small margin rather than cycle at the limit every day. Battery capacity (kWh) = daily critical load × backup days ÷ (DoD × system efficiency) Worked example Suppose the essential loads total 12 kWh per day. For one night of backup with a DoD of 0.9 and efficiency of 0.9: 12 × 1 ÷ (0.9 × 0.9) ≈ 14.8 kWh Rounding up leaves headroom, so a system around 15 to 20 kWh fits a one-night target. If the same home wanted two days of autonomy, the requirement doubles to about 30 kWh — a decision worth comparing against adding a backup generator, which is cheaper for rare multi-day events. Note the distinction between nominal and usable capacity: a battery sold as a certain kWh delivers less to the wall, so always size from usable energy. Home situation Typical usable capacity Configuration Apartment or small house, short outages 5 to 10 kWh Single wall-mounted battery, single phase Family home, one-night backup 10 to 20 kWh Wall or stacked system, hybrid inverter Large home or villa, three-phase loads 20 to 30 kWh Stacked modules, three-phase inverter Off-grid or two-day autonomy 30 kWh+ Multiple modules, often with a generator Leave room to grow A modular battery lets you add capacity later, but only if the inverter and communication bus support it. It is common to start with enough storage for the essentials, add modules when an electric vehicle or heat pump arrives, and integrate solar on the same system. Confirm the expansion limit and that new modules are compatible before buying; not every wall-mounted battery can be extended, and mixing different generations can be restricted. GreenMore energy storage batteries support parallel expansion of up to 15 units What to check before you buy Match the battery and inverter. Their voltage windows, power rating and control protocol must be compatible. A battery is only as useful as the inverter it pairs with, so confirm the combination works rather than buying them separately on price. Check real certifications. Ask for the documents relevant to your market, such as CE and IEC for many regions, plus UN38.3 and MSDS for transport and handling. Safety testing such as IEC 62619 is a good sign; verify the certificate rather than relying on a logo. Compare usable capacity and warranty, not sticker size. Two batteries with the same nominal kWh can differ in usable energy, cycle life and warranty terms. Read the cycle definition and warranty period — GreenMore covers non-tile storage components for 3 years. Avoid undersizing on price. A battery that is regularly flattened or pushed past its limits will not reach its rated life. If budget is tight, protect the essential loads and expand later rather than running a small unit at its limit. You can see the residential range on our home energy storage category page and the home energy storage system product page. If you send us your bill, appliance list, country and backup target, we can work through the sizing with you — use the contact page or email export@gmsolarkit.com. FAQ Is a 5 kWh battery enough for a house? For a small efficient home that only needs to keep lights, a refrigerator and internet through a short outage, around 5 kWh of usable storage can be enough. It will not run heating, cooling or the whole home overnight, and it is tight where outages last more than a few hours. What is the most common home battery size? Most grid-connected family homes land between 10 and 20 kWh of usable capacity, which covers the essential loads through one night. The right point within that range depends on your evening consumption, whether you heat with electricity and how long local outages tend to last. Should I use nominal or usable capacity when sizing? Use usable capacity. Nominal capacity is the battery's full rating; usable capacity is what remains after the DoD and efficiency limits. A 12 kWh nominal battery might deliver around 10 kWh to your appliances, so sizing from usable energy avoids coming up short. Is it cheaper to add a battery or a generator for long outages? For frequent short outages and daily savings, a battery is clean, quiet and automatic. For rare multi-day events, a generator — or a hybrid system that uses a battery first and a generator for extended bad weather — usually costs less than buying enough storage for several days of autonomy. P Written by Peter Lu — Energy Storage Product Manager, GreenMore Peter works with distributors, installers and system integrators to size residential and commercial storage around real load profiles. He focuses on LiFePO4 systems that match the inverter, grid rules and backup needs of each destination market.

P Peter Lu Energy Storage Product Manager A 51.2V 200Ah battery stores 10.24 kWh of energy. You get there by multiplying voltage by ampere-hours and dividing by 1,000: 51.2 × 200 ÷ 1,000 = 10.24 kWh. This is one of the most common capacities in 48V-class home storage, and it is typically built from 16 LiFePO4 cells in series (16 × 3.2V = 51.2V nominal). A popular science illustration of residential energy storage battery capacity and kilowatt-hours The calculation explained Ampere-hours (Ah) describe how much current a battery can deliver over time, while volts (V) describe its electrical pressure. Multiplying the two gives watt-hours (Wh), and dividing by 1,000 gives kilowatt-hours: Energy (kWh) = Voltage (V) × Capacity (Ah) ÷ 1,000= 51.2 × 200 ÷ 1,000= 10.24 kWh The same rule works for other sizes. For example, a 51.2V 100Ah battery holds 5.12 kWh, and a 48V 200Ah battery holds roughly 9.6 kWh. If you only know the Ah figure, you cannot find the energy without the voltage, which is why both numbers appear on the specification label. Nominal vs usable capacity The 10.24 kWh figure is the battery's nominal energy. In real use you may not be able to draw all of it. Most systems reserve a small amount at the bottom to protect the cells, and some energy is lost in the battery and inverter during conversion, so the usable energy delivered to your loads can be slightly below 10.24 kWh. When comparing batteries, check whether the quoted figure is nominal or usable, because two units labelled "10 kWh" are not necessarily equal once conversion losses and reserves are counted. What 10.24 kWh covers in a home How far 10.24 kWh goes depends on your household. As a rough guide, it can carry efficient essentials — lighting, a refrigerator, communications and some electronics — through an evening or an outage, while heavy heating, cooling and electric cooking draw it down quickly. Average daily consumption varies widely by country and home, so the most reliable estimate comes from your own electricity bills rather than a generic figure. Configuration Nominal energy Typical role 1 × 51.2V 200Ah 10.24 kWh Evening self-consumption and essential backup for a small to medium home. 2 units in parallel 20.48 kWh Larger evening load and longer backup runtime. 3 units in parallel 30.72 kWh Higher-consuming home or extended off-grid use with solar recharge. Why capacity is given in kWh It matches the bill. Electricity is charged in kWh, so stored kWh directly tells you how much evening or peak-tariff energy the battery can replace. It matches the inverter. Inverter and solar-array sizing is done in kW and kWh, so the battery's energy figure shows whether the system is balanced. It is required for certification. Standards such as IEC and UL expect the energy rating to be clearly marked so safety and compatibility can be checked. Expanding with parallel modules Modular 48V-class batteries can often be added in parallel to increase total energy while keeping the same voltage, which lets you start with one unit and add more later. The exact number of modules supported and the cabling rules depend on the model and its BMS, so check the specification rather than assuming any number can simply be connected. Adding modules in stages is often more practical than buying the full capacity up front, provided the inverter and wiring are rated for the final size from the start. GreenMore supplies home energy storage batteries built around 51.2V LiFePO4 modules with a BMS for monitoring, balancing and protection, together with compatible inverters. We size the number of modules against your actual usage and backup needs rather than quoting a fixed package. Browse the home storage range or send us your recent electricity bill for a recommendation. Frequently asked questions Is 51.2V the same as a 48V battery? Essentially, yes. A 16-cell LiFePO4 battery has a nominal voltage of 51.2V but is commonly called a 48V system because it works with 48V inverters. Its actual voltage moves with state of charge, from roughly 40V when empty to about 58.4V fully charged. Is the full 10.24 kWh available to use? Not always. The figure is nominal; systems typically reserve some energy to protect the cells, and conversion through the inverter causes small losses. Check the stated usable capacity when comparing models. Can I add more batteries later? Usually, if the model supports parallel expansion and the inverter and cabling are rated for the larger size. Confirm the maximum number of modules and the installation requirements before you buy, so the system can grow without being replaced. How many 10.24 kWh units does a home need? That depends on daily usage and backup goals. Many homes start with one unit for evening self-consumption and essential backup, adding a second or third if they use more power or want longer runtime. Your electricity bills give the most accurate starting point. P Peter Lu Peter is GreenMore's Energy Storage Product Manager. He helps homeowners and installers convert battery voltage and Ah figures into usable kWh, size parallel modules against real load profiles, and understand the difference between nominal and usable capacity. Reach him through the contact page or at export@gmsolarkit.com.