BigQuery Calculating Battery State of Charge - sql

Question

I'm trying to calculate the battery's State of Charge (SoC) given energy usage and PV energy production. I'm using BigQuery and can't solve the puzzle correctly.
When the energy is produced (negative value) can be stored in the batter hence it should increase the SoC of the battery. When the energy is consumed (positive value), it should reduce the SoC of the batter. The SoC of the batter can't go below 0 or above 200. See the table below.
Energy in/out
Battery SoC
4.57
0
2.5
0
0.29
0
-2.29
2.29
-6.00
8.29
3.29
5
6.65
0
-2.15
2.15
The "Energy in/out" is given (calculated based on other values). The SoC has to be a rolling value changing from row to row showing SoC at a given moment (15 mins intervals).
I tried using the following and few other functions with no luck.
SUM(energy_usage) OVER (ORDER BY usage_at)
Yet I can't incorporate the condition that SoC can't be less than 0 and more than 200.
The same setup and formula look in Excel as in the attached image.
How can this be represented in BigQuery query language?

Answer 1

You might consider below approach.
CREATE TEMP FUNCTION value_cap(v FLOAT64) AS (
LEAST(GREATEST(v, 0), 200)
);
WITH RECURSIVE sample_table AS (
SELECT * FROM UNNEST([4.57, 2.5, 0.29, -2.29, -6.00, 3.29, 6.65, -2.15]) in_out WITH offset AS usage_at
),
SoC AS (
SELECT *, value_cap(-in_out) soc FROM sample_table WHERE usage_at = 0
UNION ALL
SELECT t.in_out, t.usage_at, ROUND(value_cap(s.soc - t.in_out), 2)
FROM SoC s JOIN sample_table t ON s.usage_at + 1 = t.usage_at
)
SELECT * FROM SoC ORDER BY usage_at;
Query results