Solar A/C Hack: Zero Out Your Bill with a Golf Cart Battery

I tackled one of the biggest energy hogs in my home: the central air conditioner. By combining a powerful Hoymiles microinverter with a Temgo LiFePO4 golf cart battery and my portable solar array, I managed to offset 100% of my A/C unit's power consumption. The best part? This setup is incredibly efficient and cost-effective.

What I Built

My setup consists of a central air conditioner unit, a Hoymiles high-powered microinverter, a Temgo 51.2V 100Ah LiFePO4 golf cart battery, and four 370-watt bifacial solar panels. The solar panels are connected in series to an MPPT solar charge controller, which then feeds power into the Temgo battery. The battery, in turn, supplies DC power to the Hoymiles microinverter. The microinverter then converts that DC power to AC and feeds it directly into my A/C unit’s contactor. This allows the microinverter to only produce power when the A/C unit is actively running.

Why It Works

The core of this system is intelligent power management. Instead of directly hooking the microinverter to the solar panels (which is an option, as shown in my Version 2.0 video), I routed the solar power through a charge controller to a battery. This allows me to store excess solar energy when the A/C isn't running. The Hoymiles microinverter is special because each of its four inputs has its own MPPT controller, meaning it can efficiently pull power from multiple sources without them interfering with each other. When the A/C unit turns on, its internal contactor signals the microinverter to start producing AC power. This ensures that the solar power is consumed directly by the A/C unit, preventing unwanted backfeeding to the grid.

Parts & Specs

• Hoymiles High-Powered Microinverter: 2000-watt capacity.
• Temgo 51.2V 100Ah LiFePO4 Golf Cart Battery: Over 5 kWh of storage. Weather-resistant. Comes with an 18A AC wall charger and a smart LCD monitor. Price point at time of video: around $800.
• MPPT Solar Charge Controller: 20-amp unit (a 40-amp version is now available). Has a Bluetooth app for monitoring.
• Solar Panels: Four 370-watt bifacial solar panels from Payoff Solar. Purchased for just under $100 each. Mounted on adjustable stands.
• Micro-Air EasyStart: (Optional) Soft starter for the A/C compressor, reduces startup current.
• In-line 20-amp breaker: Protects cabling from the A/C unit to the microinverter.
• Bus bars: Used to distribute DC power from the battery to the microinverter inputs.

Math & Run-Time Numbers

Before connecting the solar and battery, my central A/C unit drew about 6.72-6.77 amps of AC power. When running the A/C solely off the Temgo battery and microinverter (without solar input), the battery was discharging at 37 amps (DC). Once the solar panels were connected and actively charging the battery, the discharge rate dropped significantly to about 18 amps (DC). The MPPT solar charge controller was putting in approximately 20.61 amps from the solar panels, equating to around 1086 watts of charging power. This effectively shows how the solar input directly reduces the load on the battery, stretching its runtime considerably.

Pros & Cons

Pros:

• Zero A/C Bill: Can completely offset A/C power consumption during sunny hours and even at night with battery storage.
• Scalable: Easily expandable by adding more batteries, charge controllers, or microinverters (up to three Hoymiles in parallel).
• Portable Solar Array: Panels are on adjustable stands, making them easy to move or pack up if relocating.
• Weather-Resistant Components: Both the Temgo battery and its charger have weather resistance ratings, allowing outdoor use.
• Smart Monitoring: Temgo battery includes a built-in monitor and Bluetooth app for detailed stats.

Cons:

• Backfeeding Risk: Without a grid-tie agreement, producing more power than consumed can backfeed to the grid, which is unsafe and often illegal. It's crucial to appropriately size your system or have a grid-tie agreement.
• Fusing Required: Proper fusing is essential for safety, especially on the positive side of each microinverter input and for the overall battery system, to protect against short circuits or overcurrents.
• Initial Setup Complexity: Requires some electrical knowledge for safe installation, particularly when dealing with AC unit wiring.

When To Use This vs. Alternatives

This setup is ideal for homeowners with central A/C looking to significantly reduce or eliminate their cooling costs, especially if they have access to affordable solar panels and prioritize energy independence. If you have a smaller, more efficient A/C unit, this system might be more than enough. For larger, older A/C units that consume 4000+ watts, you could easily scale up this system with additional batteries and microinverters. If you don't have a central A/C, you could use a portable power station to run your indoor furnace blower, offsetting that consumption too. It's important to note that mini-split heat pumps with advanced computer controls are generally not compatible with this microinverter setup due to their lack of a traditional contactor.

Bottom Line

This solar A/C hack, leveraging a powerful microinverter and a robust LiFePO4 golf cart battery, is a fantastic way to achieve energy independence for your home's cooling needs. It’s a smart investment that provides tangible savings and peace of mind against rising energy costs. The scalability and component quality make it a compelling option for those ready to take control of their power consumption.

Final Wrap-Up

What do you think of this setup? Let me know your thoughts and questions in the comments below – I love hearing from you! Your questions often inspire new content. Don't forget to like this video, subscribe to the channel for more DIY solar and energy independence hacks, and share it with anyone looking to cut their power bill. You can also check out my YouTube channel for other versions and related content.