Simulate home battery from Home Assistant data

battery_sim.sql

drop table tmp_battery_sim;
create table tmp_battery_sim (start timestamp without time zone, energy_in_battery numeric, energy_not_consumed_from_grid numeric, savings_from_battery numeric);

do $$
declare
    -- Variables
    t record;
    vn_battery       numeric :=  0.0;
    vn_battery_prev  numeric :=  0.0;
    vn_grid_savings  numeric :=  0.0;

    -- Constants
    cv_feedin_sensor varchar := 'sensor.stromzahler_energie_einspeisung';
    cv_grid_sensor   varchar := 'sensor.stromzahler_energie_bezug';
    cn_grid_price    numeric :=  0.3085;
    cn_feedin_comp   numeric :=  0.0694;
    cn_invert_max    numeric :=  4.0;
    cn_efficiency    numeric :=  0.9;
    cn_battery_cap   numeric := 26.0;
begin
    for t in (
        select
            to_timestamp(s.start_ts) at time zone 'Europe/Berlin' as start,
            -- Rename sensors as to and from grid
            case m.statistic_id
                when cv_feedin_sensor then 'to_grid'
                when cv_grid_sensor then 'from_grid'
            end as direction,
            coalesce(round(s.state::numeric-lag(s.state) over (partition by m.statistic_id order by s.start_ts)::numeric,3),0.0) as energy
        from statistics s
        join statistics_meta m
        on s.metadata_id = m.id
        -- Energy sensors from meter for both directions
        where m.statistic_id in (
            cv_feedin_sensor,
            cv_grid_sensor
        )
        order by start, direction desc
    )
    loop
        -- Maximum Power of Inverter
        if t.energy > cn_invert_max then t.energy := cn_invert_max; end if;
        
        -- Charge Battery
        if t.direction = 'to_grid' then
            -- Charge/Discharge efficiency combined in one factor
            vn_battery := vn_battery + t.energy*cn_efficiency;
            -- Battery cannot be charged higher than max capacity
            if vn_battery > cn_battery_cap then vn_battery := cn_battery_cap; end if;
        end if;
        
        -- Save battery state before discharge
        vn_battery_prev := vn_battery;
        
        -- Discharge Battery
        if t.direction = 'from_grid' then
            vn_battery := vn_battery - t.energy;
            -- Batttery cannot be discharged below 0
            if vn_battery < 0.0 then vn_battery := 0.0; end if;
        end if;
        
        vn_grid_savings := vn_battery_prev-vn_battery;
            
        if t.direction = 'from_grid' then
            insert into tmp_battery_sim (start, energy_in_battery, energy_not_consumed_from_grid, savings_from_battery)
            values (t.start, vn_battery, vn_grid_savings, vn_grid_savings*(cn_grid_price-cn_feedin_comp));
        end if;
    
    end loop;
end$$;

-- Show all calculated data
select start, energy_in_battery, energy_not_consumed_from_grid from tmp_battery_sim;

-- Savings per month
select extract(year from start), extract(month from start), sum(energy_not_consumed_from_grid)
from tmp_battery_sim
group by extract(year from start), extract(month from start)
order by 1,2;

-- Savings per year in Euro
select extract(year from start), sum(energy_not_consumed_from_grid), sum(savings_from_battery)
from tmp_battery_sim
group by extract(year from start)
order by 1;