Solar Powered Water Heater: Cut Your Electric Bill Now!

Saving on your electric bill, especially for high-draw appliances like a water heater, is easier than you think. I recently tested a straightforward method to power an electric water heater with solar panels, and the results were surprisingly effective and incredibly simple to implement. The biggest takeaway? You can significantly reduce your grid consumption for hot water without complex net metering or expensive battery banks.

What I Built

For this proof of concept, I set up a temporary solar array in my yard consisting of four 370-watt bifacial solar panels. These panels were mounted on adjustable stands, allowing for optimal angling to catch the morning sun. Underneath, two APsystems DS3-L microinverters were connected, each handling two panels. These microinverters convert the DC power from the panels into AC power compatible with my home's electrical system.

The AC power from the microinverters was then routed through an in-line breaker for protection. The core of the system involved a current sensing relay and a contactor. The relay was clamped over one of the wires feeding the electric water heater, and its output was connected to the contactor. The contactor itself was wired to receive both grid power and solar power, with its state controlled by the current sensing relay. For the water heater, I used a Camplux TEW08 tankless electric model, which was generously provided for testing.

Why It Works

The magic behind this setup lies in the current sensing relay. The water heater is always connected to the grid, ensuring it can pull power whenever needed. When the water heater turns on and starts drawing a significant amount of current from the grid, the current sensing relay detects this demand. Once the current draw exceeds a preset threshold (which I adjusted to be slightly more than what my solar array could produce), the relay closes.

This closure sends power to the 240V coil on the contactor, activating it. The activated contactor then allows the microinverters to see the grid power, prompting them to boot up and start producing electricity. As the solar power comes online, it immediately feeds into the household circuit, directly offsetting the power being drawn by the water heater from the grid. Crucially, the solar power only engages when there's an active load, preventing any backfeeding into the grid. As soon as the water heater shuts off (or the load drops below the threshold), the relay opens, and the solar power is disconnected from the circuit.

Parts & Specs

Here's a breakdown of the main components used in my setup:

• Solar Panels: Four 370W bifacial solar panels from Powered Portable Solar. These panels capture sunlight from both sides.
• Solar Panel Stands: Adjustable stands from Powered Portable Solar, allowing for angle adjustments and securing with earth anchors (though not used in this temporary setup).
• Microinverters: Two APsystems DS3-L Microinverters. Each unit accepts up to two panels and provides a maximum continuous output of 768VA (approximately 760W). I sourced these, along with the panels, from Payoff Solar.
• Trunk Cable: Used to daisy-chain multiple microinverters together.
• Electric Water Heater: Camplux TEW08 Tankless Electric Water Heater. This unit operates at 240V/60Hz, has an 8kW power rating, and draws 33.3A. It requires 8 AWG/2 wires with a grounding wire and a 40 AMP double pole circuit breaker. Minimum flow rate to activate is 0.475 GPM (1.8 L/min).
• Current Sensing Relay: A 50A rated AC current switch. This device detects the current drawn by the load and triggers the contactor.
• Contactor: A 50A rated contactor with a 240V coil. This acts as a switch, connecting the solar power to the load when activated by the current sensing relay.
• Ground Bus Bar: A simple bus bar used to tie all ground wires together in the temporary setup.
• APsystems Wi-Fi Bridge: An optional component that allows you to monitor your solar power generation via the APsystems app.

Math & Run-Time Numbers

Before connecting the solar, the Camplux water heater was drawing approximately 27-29 amps from the grid. Once the solar array was online and the microinverters booted up, I measured the current coming in from the grid at around 25-26 amps. This shows a direct reduction in grid consumption, confirming the solar offset was working as intended. The solar array itself was contributing approximately 3.48 amps per microinverter. Considering I have two microinverters, the total solar contribution was around 7 amps.

It's important to note that microinverters typically have about a 5-minute delay before they start producing power after detecting the grid. This means there's a brief period when the water heater will draw fully from the grid before solar kicks in. The Camplux unit's display, though hard to capture on camera, shows the water temperature and allows for adjustment of the set temperature via a simple knob.

Pros & Cons

Pros:

• Significant Savings: Directly offsets electricity consumption from a major appliance, leading to lower utility bills.
• Easy Implementation: The wiring is relatively simple, and the components are readily available and inexpensive.
• No Backfeeding: The current sensing relay ensures solar power is only used when there's an active demand, preventing unwanted export to the grid.
• Grid as a "Thermal Battery": With a tank-style water heater, you can essentially use your tank as a thermal battery, heating water with solar during peak daylight hours and drawing from it at night.

Cons:

• Undersized Array: My current solar array (approximately 1.4kW total) is undersized for an 8kW water heater, meaning it can only partially offset the load. A larger array would be needed for full offset.
• Variable Solar Output: Performance is subject to sunlight conditions (clouds, time of day), which can lead to fluctuations in offset.
• Initial Investment: While less complex than full grid-tie, there's still an upfront cost for panels, inverters, and control components.

When To Use This vs. Alternatives

This setup is ideal for homeowners who want to reduce their electricity bills by directly offsetting the power consumption of their electric water heater without engaging in complex net metering agreements with their utility company. It's particularly effective for tank-style water heaters, which can act as a "thermal battery," storing solar-heated water for later use. You could set a timer to run the water heater during peak sun hours, maximizing solar self-consumption.

If you have a large electric water heater and consistent sunlight, this system can provide substantial savings. Alternatives include traditional grid-tied solar systems with net metering (where allowed), or switching to more efficient appliances like heat pump water heaters or gas-fired units if available in your area.

Bottom Line

This solar-powered water heating conversion is a winner. It's a remarkably simple and inexpensive solution to tackle one of the heaviest electricity consumers in most homes. By leveraging a current sensing relay and microinverters, you can effectively use your solar panels to reduce your grid reliance for hot water, ensuring that power is consumed directly when generated. It's a practical step towards greater energy independence and lower utility costs, especially if you have an existing electric water heater.

Final Wrap-Up

I hope this detailed look at solar-powered water heating has given you some valuable insights. What do you think of this setup? I'm always keen to hear your thoughts and observations in the comments below. If you found this content valuable, please consider giving the video a like, subscribing to the channel for more DIY solar and energy independence projects, and sharing it with anyone who might benefit. You can also check out the gear page for links to all the components used in this build. I've got some more great content coming up, and I'll catch you all next time!