function f = load_profile(t)
% LOAD_PROFILE  Returns fractional SG heat demand at time t.
%
%  Output is in [0, 1] where 1.0 = 100% of nominal power P0.
%  Multiply by P0 to get Q_sg in watts: Q_sg = @(t) P0 * load_profile(t)
%
%  Default profile (load-following):
%    0  - 30s:   hold at 100%
%    30 - 130s:  ramp 100% -> 80%
%    130 - 350s: hold at 80%
%    350 - 450s: ramp 80% -> 100%
%    450+:       hold at 100%

    if t < 30
        f = 1.0;
    elseif t < 130
        f = 1.0 - 0.2 * (t - 30) / 100;
    elseif t < 350
        f = 0.8;
    elseif t < 450
        f = 0.8 + 0.2 * (t - 350) / 100;
    else
        f = 1.0;
    end

end