TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Components: The battery control unit comprises: a first output; a second output; a discharge protection circuit electrically connected to the first and second outputs, the lithium-ion battery unit and the solar cell unit; and an overcharge protection circuit electrically connected to the lithium-ion battery unit and the solar cell unit. The lithium-ion battery unit has: a cut-off discharge voltage, where the discharge protection circuit breaks the electrical connection between the lithium-ion battery unit and the second output, and shorts the first output and the second output when an operation voltage of the lithium-ion battery unit is equal to or smaller than the cut-off discharge voltage, so that the lithium-ion battery unit and the solar cell unit ceases supplying power to the external load; and a cut-off charge voltage, where the overcharge protection circuit breaks the electrical connection between the lithium-ion battery unit and the solar cell unit when an operation voltage of the lithium-ion battery unit is equal to or greater than the cut-off charge voltage. The lithium-ion battery unit and the solar cell unit supply power to an external load via the first output and the second output when the operation voltage is greater than the cut-off discharge voltage. The battery control unit comprises: a sensing circuit detecting an operation voltage of the lithium-ion battery unit; a control circuit electrically connected to the sensing circuit, where the control circuit compares the operation voltage with the cut-off charge voltage and the cut-off discharge voltage to generate a comparing signal; an overcharge protection circuit electrically connecting to the control circuit; and a discharge protection circuit electrically connected to the control circuit, where the overcharge protection circuit controls the lithium-ion battery unit being charged by the comparing signal, and the discharge protection circuit controls the lithium-ion battery unit discharged by the comparing signal. The overcharge protection circuit that: electrically connects to the solar cell unit and the lithium-ion battery unit when the operation voltage is equal to or smaller than the cut-off discharge voltage so that the solar cell unit charges the lithium-ion battery unit; and breaks the electrical connection between the lithium-ion battery unit and the solar cell unit when the operation voltage is equal to or greater than the cut-off charge voltage such that the solar cell unit ceases charging the lithium-ion battery unit. The battery control unit further comprises a diode electrically connected to the solar cell unit and the lithium-ion battery unit, where the solar cell unit is unable to be charged by the lithium-ion battery unit via the diode. The lithium-ion battery unit comprises a lithium-ion battery positive output and a lithium-ion battery negative output. The solar cell unit comprises a solar cell positive output (122) and a solar cell negative output. The battery control unit comprises a lithium-ion battery positive input, a lithium-ion battery negative input, a solar cell positive input, and a solar cell negative input, where the lithium-ion battery positive input is electrically connected to the lithium-ion battery positive output, the lithium-ion battery negative input is electrically connected to the lithium-ion battery negative output, the solar cell positive input is electrically connected to the solar cell positive output, and the solar cell negative input is electrically connected to the solar cell negative output. The solar cell unit comprises many solar cells connected to each other in series or in parallel, where the solar cell unit comprises at least one solar cell including a monocrystalline silicon solar cell, a polycrystalline silicon solar cell, an amorphous silicon solar cell, a multinary compound thin film solar cell, a polymer multilayer modified electrode solar cell, a nanocrystalline solar cell or an organic solar cell. The lithium-ion battery unit comprises at least one lithium-ion battery including a lithium iron phosphate battery, a lithium cobalt battery, a lithium manganate battery or a lithium cobalt manganese battery. The inverter: comprises an inverter positive input, an inverter negative input, an inverter positive output, and an inverter negative output, where the inverter positive input and the inverter negative input are electrically connected to the solar power storage modules in series, and the inverter positive output and the inverter negative output are electrically connected to the external load; and is a direct current (DC) to DC converter or a DC to alternating current inverter.