Method for conditioning a fluid at a target temperature (T.target) within a desired usage time (t.target), by means of a device that controls a conditioning element adapted to condition a fluid in a storage where said device is powered by electrical energy, and is part of an electrical user facility wherein it shares the deliverable power (P.em) with other electrical loads, - where said deliverable power (P.em) is defined as the sum of the contractual power (P.contr) that is the maximum power deliverable by the grid and, if present, of power coming from a renewable source (P.pv), - and where in said user facility there is the restriction that the overall used power (P.used) by said loads does not exceed said deliverable power (P.em) for more than a limited time interval (Δt.max), - and said user facility being equipped with means capable of detecting at least whether said used power (P.used) is greater than said deliverable power (P.em), - and said device being equipped with a control card adapted at least to: - detect the storage temperature (Ta) in said storage, - keep in a memory parameters comprising said target temperature (T.target) and said usage time (t.target) and perform calculations on said parameters, - modulate a conditioning power (P.cond) of said conditioning element; the method being characterized in comprising the following steps: - determine an activation time (t.ON) such that said fluid reaches said target temperature (T.target) within said usage time (t.target) and said conditioning power (P.cond) is a forecast power (P.f) lower than or equal to the nominal power (P.nom) of said conditioning element - at said activation time (t.ON) start a conditioning step and set the conditioning end temperature (T.end.cond) equal to said target temperature (T.target); - during said conditioning step, periodically carry out the following checks: - if said used power (P.used) plus a tolerance value (P.toll) not lower than zero exceeds said deliverable power (P.em) then - detect the time of over consumption (t.sovr) at which that occurs and - reduce said conditioning power (P.cond) until said used power (P.used) added to said tolerance (P.toll) no longer exceeds said deliverable power (P.em), within said limited time interval (Δt.max) from said time of over consumption (t.sovr), defined in the memory of said control card and as long as said conditioning power (P.cond) remains greater than zero; - if said conditioning end temperature (T.end.cond) is reached, end said conditioning step. - where said deliverable power (P.em) is defined as the sum of the contractual power (P.contr) that is the maximum power deliverable by the grid and, if present, of power coming from a renewable source (P.pv), - and where in said user facility there is the restriction that the overall used power (P.used) by said loads does not exceed said deliverable power (P.em) for more than a limited time interval (Δt.max), - and said user facility being equipped with means capable of detecting at least whether said used power (P.used) is greater than said deliverable power (P.em), - and said device being equipped with a control card adapted at least to: - detect the storage temperature (Ta) in said storage, - keep in a memory parameters comprising said target temperature (T.target) and said usage time (t.target) and perform calculations on said parameters, - modulate a conditioning power (P.cond) of said conditioning element; - detect the storage temperature (Ta) in said storage, - keep in a memory parameters comprising said target temperature (T.target) and said usage time (t.target) and perform calculations on said parameters, - modulate a conditioning power (P.cond) of said conditioning element; - determine an activation time (t.ON) such that said fluid reaches said target temperature (T.target) within said usage time (t.target) and said conditioning power (P.cond) is a forecast power (P.f) lower than or equal to the nominal power (P.nom) of said conditioning element - at said activation time (t.ON) start a conditioning step and set the conditioning end temperature (T.end.cond) equal to said target temperature (T.target); - during said conditioning step, periodically carry out the following checks: - if said used power (P.used) plus a tolerance value (P.toll) not lower than zero exceeds said deliverable power (P.em) then - detect the time of over consumption (t.sovr) at which that occurs and - reduce said conditioning power (P.cond) until said used power (P.used) added to said tolerance (P.toll) no longer exceeds said deliverable power (P.em), within said limited time interval (Δt.max) from said time of over consumption (t.sovr), defined in the memory of said control card and as long as said conditioning power (P.cond) remains greater than zero; - if said conditioning end temperature (T.end.cond) is reached, end said conditioning step. - if said used power (P.used) plus a tolerance value (P.toll) not lower than zero exceeds said deliverable power (P.em) then - detect the time of over consumption (t.sovr) at which that occurs and - reduce said conditioning power (P.cond) until said used power (P.used) added to said tolerance (P.toll) no longer exceeds said deliverable power (P.em), within said limited time interval (Δt.max) from said time of over consumption (t.sovr), defined in the memory of said control card and as long as said conditioning power (P.cond) remains greater than zero; - if said conditioning end temperature (T.end.cond) is reached, end said conditioning step.