How to Convert an Electric Water Heater to Solar
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How to Convert an Electric Water Heater to Solar 🌞
Heating water is one of those household costs most people barely think about until the bill arrives.
You use hot water for showers, washing dishes, laundry, cleaning, hand washing, and everyday comfort. But behind the scenes, your electric water heater may be quietly eating up a big chunk of your energy use.
That is why more homeowners, homesteaders, off-grid dreamers, and money-saving DIYers are asking the same question:
Can you convert an electric water heater to solar?
The answer is yes, but there is an important catch. You do not usually turn the electric heater itself into a solar panel-powered appliance by simply plugging it into solar. Instead, the smartest setup is often to use solar energy to preheat or heat the water, while keeping the electric element as a backup.
That means free energy from the sun does the hard work whenever possible, and your electric heater only steps in when needed.
Solar water heating systems use collectors to capture heat from the sun and transfer that heat into a hot water cylinder or storage tank. Energy Saving Trust explains that these systems are normally used with a conventional boiler or immersion heater because solar output changes through the year. (Energy Saving Trust)
So, before you start cutting pipes or wiring anything, let’s break down how it works, what you need, and what you must be careful about.
First, What Does “Converting” An Electric Water Heater To Solar Mean? 🔧
When people say they want to convert an electric water heater to solar, they usually mean one of three things:
- Solar thermal conversion
This uses solar collectors to heat water directly. It is often the most efficient way to use sunlight for hot water. - Solar PV with an immersion heater
This uses solar panels to generate electricity, which powers an immersion heater or water heating element. - Solar preheating system
This preheats cold water before it enters your existing electric water heater, reducing how much electricity the tank needs.
For many DIY-minded homeowners, the preheating method is the most realistic because it lets the existing electric water heater stay in place as backup.
The U.S. Department of Energy explains that some solar water heaters preheat water before it continues into a conventional backup water heater, giving you reliable hot water even when the sun is not strong enough. (The Department of Energy’s Energy.gov)
Why Convert An Electric Water Heater To Solar? 💰
There are a few big reasons this idea is getting so popular.
✅ Lower energy bills
Water heating can be one of the biggest energy users in the home. Energy.gov says water heating accounts for about 18% of home energy use in the United States. (The Department of Energy’s Energy.gov)
✅ Use free sunshine
Once the system is installed, the sun does part of the work for free.
✅ Keep your existing backup
You do not have to lose the convenience of your electric water heater. It can still heat water on cloudy days, winter days, or heavy-use days.
✅ Great for off-grid and homestead setups
Solar hot water can be a smart step toward reducing reliance on the grid.
✅ Less strain on your electric heater
If incoming water is already warm, the electric element has less work to do.
How A Solar Water Heater Conversion Works 🌞🚿
Here is the simple version.
Cold water enters the system. Instead of going straight into your electric water heater, it first passes through a solar heating setup.
The sun warms the water, then the preheated water flows into your electric water heater tank.
If the water is already hot enough, the electric element may barely need to run. If the water still needs a boost, the electric heater tops it up.
In a solar thermal setup, solar collectors heat a liquid that transfers heat into the water cylinder through a coil or heat exchanger. Energy Saving Trust describes this process as solar collectors heating a fluid, which then moves through pipework in the cylinder to warm the stored water.
Think of it like this:
Solar = main helper
Electric heater = backup safety net
That is what makes this setup so useful. You are not relying on perfect sunshine every single day.
What You May Need For The Conversion 🧰
The exact parts depend on the type of system in your video and your home setup, but common components can include:
- Solar collector or solar thermal panel
- Storage tank or existing electric water heater
- Circulation pump
- Solar controller
- Temperature sensors
- Heat exchanger or coil
- Check valves
- Pressure relief valve
- Expansion tank
- Insulated pipework
- Tempering valve or mixing valve
- Backup electric heating element
- Correct electrical disconnects and wiring
- Pipe insulation
- Mounting brackets
⚠️ Important safety note: Water heaters involve electricity, pressurised hot water, plumbing, and sometimes roof work. This is not the same as building a raised bed or painting a shed. Mistakes can cause leaks, burns, electrical shock, tank damage, or dangerous pressure build-up.
For anything involving mains wiring, consumer units, pressure systems, or code compliance, use a qualified professional.
Step 1: Decide Which Solar Setup You Want
Before buying parts, decide how you want the system to work.
Option 1: Solar thermal hot water
This is designed specifically for heating water. It is efficient and commonly used for domestic hot water.
Option 2: Solar PV to immersion heater
This uses electricity from solar panels to power a heating element.
Option 3: Solar preheater before the electric tank
This is often the easiest concept to understand. The sun warms the water first, then your existing water heater finishes the job if needed.
For most people looking to convert an electric water heater to solar, solar preheating with electric backup is the most practical route.
Step 2: Check Your Water Heater
Not every water heater is ideal for modification.
Look at:
- Tank age
- Condition of the tank
- Size of the tank
- Access to pipework
- Existing thermostat and element
- Pressure rating
- Available space nearby
- Whether the tank already has extra ports or fittings
If your tank is old, rusty, leaking, or already inefficient, it may make more sense to replace it with a solar-compatible cylinder instead of modifying the old one.
Step 3: Choose A Sunny Location For The Collector ☀️
Solar collectors need good sun exposure.
A south-facing roof is often ideal in the UK, but the best location depends on your property, shading, roof pitch, and available space.
Avoid areas shaded by:
- Trees
- Chimneys
- Other buildings
- Dormers
- Roof vents
- Fences or walls
Solar thermal performance drops when panels are shaded, so placement matters more than people think.
Step 4: Add The Solar Loop Or Preheat Line
This is where the real conversion happens.
In a basic preheat idea, cold water goes through the solar heating section first, then enters the electric water heater.
In a closed-loop solar thermal setup, a heat-transfer fluid runs between the collector and the heat exchanger, warming the water inside the tank without mixing with your domestic water.
The right design depends on your climate. In colder areas, freeze protection is extremely important. Energy.gov notes that certain direct solar water heater designs should only be installed in mild-freeze climates because outdoor pipes can freeze in severe conditions. (The Department of Energy’s Energy.gov)
This is one of the biggest mistakes beginners make. They build something that works beautifully in summer, then winter arrives and the pipework freezes.
Step 5: Keep The Electric Heater As Backup
One of the best parts of this setup is that you can keep the electric water heater as a backup.
That means:
- Hot water on cloudy days
- Hot water in winter
- Hot water after several showers
- Better reliability
- Less worry if solar output is low
Energy Saving Trust says solar water heating usually provides roughly half of hot water needs on average, with more contribution in summer and less in winter. (Energy Saving Trust)
So do not design the system assuming the sun will do everything every day. A backup is not a failure. It is what makes the system practical.
Step 6: Add A Mixing Valve For Safety 🌡️
Solar-heated water can sometimes get very hot.
That sounds good, but it can also be dangerous. Water that is too hot can cause scalding.
A thermostatic mixing valve blends hot water with cold water before it reaches taps and showers. This helps keep water at a safer usable temperature.
This is especially important if you have:
- Children
- Elderly family members
- Guests
- Very sunny summers
- A high-temperature solar setup
Do not skip this part.
Step 7: Insulate Everything
If you heat water with the sun, then lose that heat through uninsulated pipes, you are wasting the benefit.
Insulate:
- Hot water pipes
- Solar loop pipework
- Tank connections
- Outdoor exposed lines
- Storage tank where suitable
This small step can make a big difference.
It is one of the cheapest upgrades and one of the easiest wins.
Step 8: Test The System Carefully
Once installed, the system should be checked for:
- Leaks
- Correct flow direction
- Pump operation
- Temperature sensor readings
- Pressure levels
- Relief valve operation
- Thermostat settings
- Backup heater function
- Safe water temperature at taps
Do not rush this part.
A solar water heater conversion is only useful if it is safe, reliable, and easy to live with.
Common Mistakes To Avoid ⚠️
❌ Removing the electric backup too soon
Solar hot water is amazing, but weather changes. Keep backup heat unless you have a very well-designed off-grid system.
❌ Ignoring freezing risk
Outdoor pipework can freeze and split. Use the right system for your climate.
❌ Forgetting pressure relief
Water expands when heated. A safe system needs correct pressure protection.
❌ No mixing valve
Very hot water can be dangerous at taps and showers.
❌ Poor panel placement
Shade can ruin performance.
❌ Not checking local rules
Planning permission, building regulations, plumbing codes, and electrical rules can vary by area.
❌ Trying to do mains electrical work without experience
Electric water heaters can draw serious power. This is not a place to guess.
Is It Worth Converting An Electric Water Heater To Solar? 💡
For many people, yes.
It can be worth it if:
- You use a lot of hot water
- You have good sun exposure
- Your current electric water heater is expensive to run
- You plan to stay in the home long term
- You enjoy DIY energy-saving projects
- You want more self-sufficiency
It may not be worth it if:
- Your roof is heavily shaded
- Your tank is near the end of its life
- Installation costs are too high
- You only use a small amount of hot water
- You cannot safely install the system
A solar water heating system can reduce water heating costs, but the real savings depend on your hot water use, location, system size, and backup energy costs. Energy.gov states that solar water heating bills can drop by 50% to 80% on average after installation, depending on those factors. (The Department of Energy’s Energy.gov)
Pro Tips To Get More From Solar Hot Water 🌞
- Use the most hot water during sunny parts of the day when possible
- Insulate your hot water pipes
- Fix dripping hot taps
- Use low-flow shower heads
- Set your backup heater timer wisely
- Do laundry with cold water when possible
- Keep solar collectors clean and clear
- Check the system before winter
- Service pumps, valves, and sensors as needed
Solar hot water is not just about the equipment. It is also about how you use it.
Common Questions About Converting An Electric Water Heater To Solar
Can I connect solar panels directly to my electric water heater?
Sometimes solar PV can be used to power an immersion heater, but it must be designed correctly with the proper controls, wiring, safety devices, and electrical protection. Do not simply connect panels directly to a standard water heater element without a proper system design.
Is solar thermal better than solar PV for hot water?
Solar thermal is often more efficient for heating water directly, while solar PV is more flexible because it can power other appliances too. The best choice depends on your home, budget, and goals.
Will I still have hot water at night?
Yes, if you have a storage tank and backup heater. Solar heats water during the day, and the tank stores it for later use.
Can this work in winter?
Yes, but output is lower in winter. That is why most systems keep an electric immersion heater, boiler, or other backup.
Can I use my existing electric water heater?
Possibly, but it depends on the tank, plumbing layout, age, pressure rating, and whether it can be safely integrated. In many cases, a solar-compatible cylinder may be better.
Do I need a professional?
For most homeowners, yes. You may be able to understand the system and do some planning yourself, but plumbing, pressure safety, roof mounting, and electrical work should be handled by qualified tradespeople.
How much money can it save?
Savings vary widely. They depend on your hot water use, local sunlight, energy prices, system size, and how much backup heating you still need.
Final Thoughts: Solar Hot Water Is A Smart Step Toward Lower Bills 🌞🚿
Converting an electric water heater to solar is one of those projects that sounds complicated at first, but the idea is actually simple.
Let the sun heat the water first.
Let the electric heater finish the job only when needed.
That one change can reduce energy use, lower bills, and make your home feel a little more self-sufficient.
Just remember, this is not a project to rush. Hot water systems involve pressure, heat, plumbing, and electricity. Done correctly, a solar water heater conversion can be brilliant. Done badly, it can be dangerous and expensive.
So use the video above as a helpful guide, learn how the system works, plan carefully, and bring in a qualified professional for the parts that need expert hands.
Would you ever convert your electric water heater to solar, or would you rather start with solar panels for electricity first? Let us know in the comments. 🌞
