DayNightElectricity

Day Night Electricity

Measurements

Gauging the benefit and ideal size of a battery is complex.
One measure is the number of days when the day time export exceeds the night time consumption, so that the tomorrow morning charge in the battery exceeds this morning's charge.
To gauge this, I downloaded the data for the church from United Energy. In this file B1 is export and E1 is import. We do not have any other monitoring of our panels. In particular, we have no measure of total daytime consumption, the sum of import and self consumption.
The kWh in each 5min interval were summed for 6am to 6pm (Day) and 6pm to 6am (Night). As expected the night time export was zero except for small numbers during early morning in mid summer. Night time import therefore equals night time consumption.
Daytime export in green. Nighttime import / consumption in red, against the day in the year measured, ie March 2023 to March 2024
Daytime export versus night time consumption. On days above the 45 degree line, the exports diverted to a battery would cover the night time consumption
A battery of 30kWh capacity would cover 61% of those nights. That is on 61% of days, the export was enough to fully charge the battery and the battery would be large enough to supply the evening load.
A 20kWh battery would be fully discharged virtually every night, but only fully charged on 78% of days.
Estimated saving would be about 61% x 365days/year x 25kWh/day x 27c/kWh, or $1500/yr for a 30kWh battery. Some extra use would occur on intermittently sunny days, when the battery could supply energy during cloudy spells.
The minimum overnight consumption of 20kWh surprised me, but it is consistent with the United Energy data for last January, which shows an average daily import of 36kWh, the sum of day and night, when most of the day time load would be met by solar and evening activities were few. Note that "Energy used" is actually energy bought.

Day Night Electricity

Measurements

What accounts for the night time consumption?

Boiling water unit (Urnie)

Refrigerator

Freezer