The Reservoir Control Law: How EWISER EDM Shaves Maximum Demand

What you're paying for: the single half-hour

The meter integrates power into a 30-minute average, and a C&I demand charge is set by the one highest such average in the whole month — a single half-hour can define the bill. Shaving that half-hour is the entire game; the rest of the month is watching for it.

A battery can flatten that peak, but it holds only so much energy. The reservoir control law is what decides how fast to release it: enough to shave the peak, never so much that the battery empties before the real peak arrives.

The reservoir, live

Picture the battery as a reservoir of water. As the site's demand rises toward the target ceiling, the battery discharges to fill the gap and hold grid demand down — and the reservoir level drains. As the peak nears the ceiling, the release tapers: the reservoir stops draining freely and holds a reserve for a genuine breach.

This forecast-light discipline is what separates a battery that reliably lowers Maximum Demand from one that empties on an early, minor peak and has nothing left for the half-hour that actually sets the bill.

Three lines the law lives between: Floor, Guard, Ceiling

Every site is calibrated to three levels from its own history, turning one battery into a strategy that behaves differently on a quiet day than on a dangerous one.

Floor — how low it will push: the deepest the target ever goes. On a quiet day the peak is shaved down toward the floor and no further; going lower just burns cycles on demand you were never going to be billed for.

Guard — the 'this could be a big one' line: when the running peak crosses the guard, the day is flagged as a potential spike day. The law stops draining freely and starts pacing, because the real peak may still be ahead.

Ceiling — the line held at all costs: the highest demand the battery commits to defend at full power. Between guard and ceiling the release tapers to zero, so the reservoir arrives full — with everything in hand for a true breach.

Why taper, not freeze

The release rate scales down smoothly as load climbs from the guard to the ceiling — the shave equals a dynamic rate multiplied by (1 − approach), where 'approach' runs from 0 at the guard to 1 at the ceiling.

It keeps shaving the whole way up, so nothing is wasted if the feared breach never comes; yet it self-preserves energy near the ceiling, so a real breach is still met at full power. One rule, with no thresholds to tune.

Valley recharge: refill in the lulls

Between peaks the demand dips into a lull. The controller uses that headroom to top the reservoir back up — but always kept below the floor, so recharging can never lift the billed 30-minute peak — leaving more energy for whatever comes next.

Predictive reserve (lambda λ): save for the peak it can see coming

The controller carries a forecast of the rest of the day and ring-fences the energy a later peak will need. An early peak can spend only what is truly spare, so a bigger one later is never left undefended. The lambda (λ) parameter sets how hard it rations.

Beyond the core idea

In production the same reservoir runs with more on top: it diverts surplus rooftop PV into the battery instead of curtailing it, derates power on temperature, and anchors a recharge to the floor. These details are left out of the core explanation so the central idea stays legible — but they run the same reservoir logic.

The reservoir control law is the dispatch engine behind EWISER's demand-shaving results, and it is what Live Shadow runs against a site's real load to prove the Maximum Demand saving before any hardware is bought.

Frequently asked questions