Trickle Charge EV Batteries to Power an Off-Grid Solar System: A Feasibility Analysis

Desiring an off-grid lifestyle that leverages the potential of renewable energy without the added cost of conventional battery systems can be achieved through innovative methods. One such method involves the use of a vehicle's battery to power an off-grid solar system. This article explores the feasibility and technicalities of using an electric vehicle (EV) battery as a source of power for an off-grid solar setup.

Charging an Off-Grid Solar System: The Role of an EV Battery

While a conventional off-grid solar power system necessitates the use of batteries for energy storage, the use of an EV battery presents a unique and more cost-efficient alternative. The key to this system lies in the concept of trickle charging, where the EV battery acts as the storage unit for the solar power generated.

There are several reasons to consider using an EV battery:

Cost-effectiveness: EV batteries are often cheaper and can last longer than traditional solar batteries. Compatibility with solar power: Most EV batteries are capable of handling regular charging cycles, making them a suitable choice for solar power. Scalability: Over time, the solar setup can be expanded, utilizing more EV batteries to increase the power capacity of the system.

Technical Specifications and Practical Examples

The system described in this article relied on a golf cart battery, which was initially chosen due to its affordability and durability. According to the author, a single deep-cycle battery (215 USD from Costco) was capable of providing enough power for the off-grid system. Multiple batteries (3 in this case) were used to ensure sufficient energy storage for peak demand periods.

For a more detailed look at the technical aspects, consider the following example:

210 amps per day were sufficient to run the system, but 3 deep-cycle batteries (each providing 315 amps) were installed for redundancy and additional capacity. The system was designed to use no more than half of the battery's capacity per charge cycle to prevent damage to the battery.

Efficiency and Performance Metrics

The concept of using an EV battery as a storage unit for solar power demands a thorough understanding of efficiency metrics. An MPPT (Maximum Power Point Tracking) controller is recommended over a PWM (Pulse Width Modulation) controller:

MPPT controllers allow for more power extraction from solar panels, with an efficiency of up to 98 percent. PWM controllers, however, are less efficient and can only achieve about 80 percent of optimal power extraction.

Other components of the system include a 10-gauge power cable, a breaker between the inverter and batteries, and grounding techniques to ensure safety and optimal performance.

System Examples: RV and Small Home Setup

For an RV application, the system was designed to be efficient and compact. The setup included 400 watts of solar capacity, which provided a daily run of 20 amps for 5 hours, totaling 100 amps. The system was able to power a freezer, fridge, lights, a TV, and a small heater. Medical equipment was also run with a small power draw.

A more extensive system for a small home (600 sq. ft.) can be calculated with the following parameters:

Total solar system power: 7.5 kW Total daily amp draw: 144 amps for a single night (8 hours at 18 amps plus some for the inverter) Additional system costs: $21,000 (without batteries, $14,000, with batteries, $21,000)

When considering large appliances like an oven, house heater, dryer, or hot water heater, a regular electricity source must be used. This highlights the limitations of a small solar system and the need for a combination of solar and conventional power sources for a full household setup.

Conclusion

The use of an EV battery for an off-grid solar power system presents a viable and cost-effective option for those looking to reduce their reliance on conventional power grids. By carefully designing the system and utilizing efficient components like an MPPT controller, it is possible to create an off-grid solar power system that can significantly reduce power costs and reliance on traditional energy sources.