NOVELTY - Preparation of vanadium battery solution comprises using electrolysis unit comprising electrolytic cell packet, anode electrolyte storage tank, cathode electrolyte storage tank, liquid conveyor pipe and pump. The anode electrolyte storage tank is connected with anode electrolyte inlet of electrolytic cell module through liquid conveyor pipe. An anode electrolyte outlet of electrolytic cell module is connected with anode electrolyte storage tank through liquid conveyor pipe. The cathode electrolyte storage tank is connected with cathode electrolyte inlet through liquid conveyor pipe.    USE - Method for preparation of vanadium battery solution (claimed).    DETAILED DESCRIPTION - Preparation of vanadium battery solution comprises using electrolysis unit comprising electrolytic cell packet, anode electrolyte storage tank, cathode electrolyte storage tank, liquid conveyor pipe and pump. The anode electrolyte storage tank is connected with anode electrolyte inlet of electrolytic cell module through liquid conveyor pipe. An anode electrolyte outlet of electrolytic cell module is connected with anode electrolyte storage tank through liquid conveyor pipe. The cathode electrolyte storage tank is connected with cathode electrolyte inlet through liquid conveyor pipe. A cathode electrolyte outlet of electrolytic cell module is connected with cathode electrolyte storage tank through liquid conveyor pipe. The anode electrolyte in electrolysis unit is aqueous solution containing supporting electrolyte. The cathode electrolyte is a solution or suspension of vanadium compound. The vanadium in vanadium compound is pentavalent, tetravalent and/or trivalent. Anode and cathode electrolytes flow through anode and cathode of electrolysis unit cyclically through forced convection by maintaining temperature and pressure of continuous liquid phases of anode and cathode electrolytes. A voltage is applied between anode and cathode to generate direct current that can generate oxygen and reduce vanadium compound. After finishing electrochemical oxidation and reduction reactions, the anode and cathode electrolytes, flowing through anode and cathode of electrolytic cell packet respectively, return to anode and cathode electrolyte storage tanks, respectively. The anode and cathode of electrolysis unit are conductive porous materials which are inert to acid and vanadium compounds. The anode is made of material with activity catalyzing oxidation. The cathode is made of material with activity catalyzing reduction of vanadium ion. The electrolytic cell packet is provided with electrolytic cell module(s). The electrolysis unit is continuous flow electrolysis unit. INDEPENDENT CLAIMS are included for:    (1) off-line capacity regulation of vanadium battery;    (2) on-line capacity regulation of vanadium battery; and    (3) an electrolysis unit used for preparation or capacity regulation of vanadium battery solution.