Most home storage systems that disappoint their owners were not badly built. They were sized on a bill rather than on a load. A monthly kilowatt-hour figure tells you the average; it does not tell you how much of that load the battery has to carry after sunset, how long it must carry it when the grid stays down, or what happens at 7 p.m. on the hottest evening of the year, when the air conditioners and the pump start together.
This is the order in which to work out the numbers, whether the installation is a grid-tied system with backup o r a true off-grid one.
Start with a load list, not a bill
List every load you intend to keep running during an outage: lights, fans, refrigeration, the pump, the router, and separately the air conditioning. For each, note the running watts and the hours per day. Then note which of them start with a surge — compressors and pumps typically draw several times their running current for a second or two — because that figure, not the running total, sets the inverter size.
Two numbers come out of this exercise. The first is nightly energy: the kilowatt-hours the battery must deliver between sunset and sunrise. The second is peak power: the highest simultaneous load, with surge. Systems are usually undersized on the first and oversized on the second, which is expensive and still uncomfortable.
Decide autonomy before you choose capacity
Autonomy is how many days the battery must carry the critical load with no sun and no grid. One night is not autonomy; it is the normal duty. In most of South Asia and Sub-Saharan Africa, two nights is a reasonable design target for a hybrid system, and three is not unusual for a site where the grid fails for days at a time. Off-grid systems in the monsoon belt need a week of generator cover, not a week of battery.
Capacity follows: nightly energy × autonomy days ÷ usable depth of discharge. A LiFePO4 pack run to 90% depth delivers about nine tenths of its nameplate; a lead-acid bank run to 50% delivers half, and needs more capacity for the same job. That single difference is usually larger than the price gap between the two technologies.
Then size the array against the worst month, not the best
Photovoltaic yield in the worst month can be less than half the annual average in latitudes with a pronounced dry and wet season. Sizing on an annual average produces a system that is fine in March and short in August. Use the worst-month daily yield for your location, add the charge and discharge losses (typically 10–15% combined for a lithium system), and check that the array can refill the battery and carry the daytime load in that month.
Weak grids need three things that a plain hybrid inverter does not give you
- Wide input tolerance. Voltage that sags to 170 V and returns at 250 V will trip a narrow-input inverter into constant grid/battery switching, which wastes the battery on a problem the grid caused.
- A defined transfer time. Ask for the switching time in milliseconds, and check it against what your loads tolerate. A desktop computer rides through 20 ms; some pumps do not.
- Generator input with a current limit. Where a diesel set is the fallback, the inverter has to accept a limited, dirty supply and stop charging when the set is loaded, rather than trip it.
The installation questions that get skipped
Where will the battery live, and what is the temperature there in July? A pack in an unventilated utility room at 40 °C will age faster than the datasheet suggests, and a pack in an unheated outbuilding in a cold climate will refuse to charge on winter mornings unless it has heating. Is the critical-loads panel actually separated, or does the whole house drop when the grid does? Is there a maintenance bypass, so the inverter can be serviced without cutting the house? And is the monitoring reachable by the person who will act on it — an alarm on a phone in another country is not a maintenance plan.
How Origin Drive Future supplies it
We build LiFePO4 storage packs and systems for the residential and commercial & industrial ranges, from wall-mounted units to stackable cabinets. Our packs are built and tested against the target standards UN38.3 and IEC 62619, and the file set for a model — including the cycle-life test conditions — is confirmed in writing with the quotation. Send the load list, the autonomy you need and the worst-month yield for the site, and we will return a capacity proposal rather than a catalogue page. Request a quote.
Most home storage systems that disappoint their owners were not badly built. They were sized on a bill rather than on a load. A monthly kilowatt-hour figure tells you the average; it does not tell you how much of that load the battery has to carry after sunset, how long it must carry it when the grid stays down, or what happens at 7 p.m. on the hottest evening of the year, when the air conditioners and the pump start together.
This is the order in which to work out the numbers, whether the installation is a grid-tied system with backup or a true off-grid one.
Start with a load list, not a bill
List every load you intend to keep running during an outage: lights, fans, refrigeration, the pump, the router, and separately the air conditioning. For each, note the running watts and the hours per day. Then note which of them start with a surge — compressors and pumps typically draw several times their running current for a second or two — because that figure, not the running total, sets the inverter size.
Two numbers come out of this exercise. The first is nightly energy: the kilowatt-hours the battery must deliver between sunset and sunrise. The second is peak power: the highest simultaneous load, with surge. Systems are usually undersized on the first and oversized on the second, which is expensive and still uncomfortable.
Decide autonomy before you choose capacity
Autonomy is how many days the battery must carry the critical load with no sun and no grid. One night is not autonomy; it is the normal duty. In most of South Asia and Sub-Saharan Africa, two nights is a reasonable design target for a hybrid system, and three is not unusual for a site where the grid fails for days at a time. Off-grid systems in the monsoon belt need a week of generator cover, not a week of battery.
Capacity follows: nightly energy × autonomy days ÷ usable depth of discharge. A LiFePO4 pack run to 90% depth delivers about nine tenths of its nameplate; a lead-acid bank run to 50% delivers half, and needs more capacity for the same job. That single difference is usually larger than the price gap between the two technologies.
Then size the array against the worst month, not the best
Photovoltaic yield in the worst month can be less than half the annual average in latitudes with a pronounced dry and wet season. Sizing on an annual average produces a system that is fine in March and short in August. Use the worst-month daily yield for your location, add the charge and discharge losses (typically 10–15% combined for a lithium system), and check that the array can refill the battery and carry the daytime load in that month.
Weak grids need three things that a plain hybrid inverter does not give you
- Wide input tolerance. Voltage that sags to 170 V and returns at 250 V will trip a narrow-input inverter into constant grid/battery switching, which wastes the battery on a problem the grid caused.
- A defined transfer time. Ask for the switching time in milliseconds, and check it against what your loads tolerate. A desktop computer rides through 20 ms; some pumps do not.
- Generator input with a current limit. Where a diesel set is the fallback, the inverter has to accept a limited, dirty supply and stop charging when the set is loaded, rather than trip it.
The installation questions that get skipped
Where will the battery live, and what is the temperature there in July? A pack in an unventilated utility room at 40 °C will age faster than the datasheet suggests, and a pack in an unheated outbuilding in a cold climate will refuse to charge on winter mornings unless it has heating. Is the critical-loads panel actually separated, or does the whole house drop when the grid does? Is there a maintenance bypass, so the inverter can be serviced without cutting the house? And is the monitoring reachable by the person who will act on it — an alarm on a phone in another country is not a maintenance plan.
How Origin Drive Future supplies it
We build LiFePO4 storage packs and systems for the residential and commercial & industrial ranges, from wall-mounted units to stackable cabinets. Our packs are built and tested against the target standards UN38.3 and IEC 62619, and the file set for a model — including the cycle-life test conditions — is confirmed in writing with the quotation. Send the load list, the autonomy you need and the worst-month yield for the site, and we will return a capacity proposal rather than a catalogue page. Request a quote.