Solar Water Heaters for Home: An Introduction


A solar water heating system is a good start for those looking to become energy independent and/or environmentally friendly. It’s one of the cheapest alternative energy systems you can install, and in most cases it’s clearly a long term money saver (check out this article for more detail on the cost of installing a solar water heater). It really is a no brainier, so let’s get started and learn what they’re all about.

Solar water heating (SWH) systems use solar energy to heat the water a household uses. Some cheaper systems can cover 50-70% of the water heating needs, while some of the more efficient and expensive models can cover over 90%. Considering that around 25% of the average household’s energy consumption each year is on water heating, this can lead to large savings on your energy bill.

Types of Solar Collectors

There are various forms of solar collectors that can be used in a SWH system.

Flat Plate Collectors: Metal boxes with a clear glass or plastic top, and a dark-coloured, sunlight-absorbing bottom which heats a series of pipes containing the heat-transfer fluid. This model is simpler and cheaper.

Evacuated Tube Collectors: A series of tubes within tubes. The outer tube absorbs and locks in heat, while the inner tube contains the heat transfer fluid. This model is more efficient, especially in colder climates, but is more expensive.

Batch Collectors: A water tank that serves as water storage as well as a solar collector, located within an insulated box to maximize heat absorption.

solar water heater systems

Types of Solar Power Systems: Active vs Passive

There are also two types of SWH systems available: Active systems and passive systems.

Active Systems

Active (or pumped) systems use a pump to move water through the heating cycle, requiring a second power source. They allow much more flexibility in design, allowing the water tank to be located inside and hidden from view. They also may be a necessity in climates that experience freezing temperatures.

An active system stores the water tank inside of the house, with a tube running through it containing a non-freezing liquid (usually propylene glycol). The non-freezing liquid is pumped out to the heating panels, where it is warmed. It flows back to the water rank, warming the water, which can then be used for washing and bathing.

Active systems are more expensive than passive, but are more efficient, more reliable, and can be used in climates that experience freezing.

Passive Systems

Passive (or compact) systems use no pumps or secondary electrical sources. They use natural convection currents to move warm water to the water tank and cold water to the collector to be heated. They are generally cheaper than active models, and due to their simpler nature last longer, but are less efficient, less reliable and sometimes require setting up a water tank on your roof. They are better suited for warmer climates, where freezing isn’t a concern.

There are two types of passive systems:

Integral Collector-Storage Passive Systems (ICS): In this model, the batch collector is used, making it simpler and cheaper than other model. It works best in warmer climates and households with daytime/early evening demand for hot water. It requires the water tank to be stored on the roof, though, so the roof must be able to support the weight (400-700lb) of the water tank.

Convection Heat Storage Systems: In this model the tank and collectors are separated, and natural convection currents are used to allow heated water to flow into the water tank, and cold water to flow to the collector to be heated. As warm water flows up, the water tank must be located above the collector. This model is more expensive than ICS’s, but is more efficient and reliable.

Other notes:

At times when there isn’t enough solar power (at night, or overcast days), your traditional water heater will switch on the heat the water.

After installation, maintenance is a must. Consider having an active system inspected every couple years, a passive system ever 3-5 years.

Solar water heating is becoming more popular worldwide. China is the largest user overall, with 3/4 of the world’s units. Israel is the highest per capita user, with 85% of households having a solar thermal heating unit, and was the first country to require the installation of solar water heating systems. Spain was the second.

solar water heater

DIY: How to Build a Solar Water Heater for Home

A solar water heating system is the low hanging fruit of energy independence and reducing your carbon footprint. It’s relatively cheap, compared to other alternative energy systems. It is clearly profitable in most cases, paying for itself in only a few years. And if you’re handy and feel like building the solar collector yourself (as this article will teach you to do), you can cut your costs by 2/3rds and make a solar water heater even more of a no-brainer. A homemade solar water heating system will likely be able to supply you with ~50% of your hot water needs, roughly on par with all but the best models available on the market.

What You’ll Need

In order to build our own panel we will need some supplies:

  1. Cedar planks, 5m+ per panel you plan on making, 80mm in width.
  2. Plywood board, larger than 1.5mx1m for each panel you plan on making
  3. 1.5mx1m aluminum sheet. Decent thickness/quality to avoid warping.
  4. 40’ of 10mm annealed copper tubing
  5. Primer
  6. Black spray paint
  7. Insulation foam
  8. 1.5 x 1m 4mm float glass plate
  9. Aluminum foil

Tools

Some tools we’ll need:

  1. Drill
  2. Wood screws

Building the Pieces

1) Wood Tray

We’ll start by preparing a wooden tray to house our panel. You’ll want to use a good hardwood that after being coated will last long and resist warping/deterioration. Cedar should work well. Best to pay a bit more for quality now to ensure the life of your unit. Cut the planks into two 1.5m pieces, and two 1m pieces. Use these pieces to create a rectangular frame, and use the drill and wood screws to connect them together. When finished, coat with a wood preservative.

Nail a plywood board to one side of the frame, creating a tray.

2) Copper Tubing

Next we’ll prepare our copper tubing. Copper is soft and easy to shape, but do this slow and carefully as any kinks in the metal will reduce your efficiency. That can cost you A LOT of money over 20-30 years, so take your time. You can use a round object to bend the tubing around, a beer bottle works great. Shape the copper tubing into a zig zag pattern that maximizes filling the space within the frame, but still has the tubing moving slightly outward after each bend.

Here’s an illustration to demonstrate what I mean:

My incredible artist rendering. If this isn’t clear, do an image search on Google for DIY Solar Water Heater, that should clear things up.

When you are finished, apply primer and spray paint black. Let paint dry.

3) Aluminium Absorber Plate

The next step is to build an absorber plate. Take your aluminum sheet, and clean it thoroughly. Apply the primer to the shiny side. When ready, spray paint it black, and let dry.

Putting It Together

  1. Take your wooden tray, and put a thin layer of insulation foam on the inside.
  2. Put a piece of aluminum foil, shiny side up, on top of this.
  3. Place your absorber plate on top of this, black side up.
  4. Place your copper tubing in top of this, lying on the absorber plate. Drill 2 holes in the wood frame for the copper tubing to come out of.
  5. Put the glass plate on top of the open end of the frame. There should be less than inch between the glass and the copper tubing. Attach to the wood frame with a good adhesive and sealant.

Connecting to the System

Once your panel is finished, you will be ready to connect it to your water tank, and from there it will be accessible from your home. You’ll need to connect the ends of your copper tubing from your solar panel to rubber tubing or pipes that run to your water tank. This will complete your convection circuit. Each 1.5mx1m solar panel will require ~15 gallons of water tank space, so plan accordingly.

The way it works: the panel warms the water, which flows into the water tank, and cooler water flows from the tank to the panel to be warmed. There are two ways to accomplish this- natural convection, or using a pump system.

If you live in a warm climate where your pipes are unlikely to freeze, and you can place your water tank close to and at a level higher that your solar panel, you may be able to get your system to work through convection alone. When the solar panel warms water, it naturally rises to the top of your convection current. If your water tank is higher than your solar panel, then the top of the current is the top of your water tank. Cold water is pushed from the tank to the bottom of the convection cycle (ie your solar panel) where it is warmed, and the process begins again.

If you need to place your water tank far from your solar panel, or need to place your tank at a level lower than your solar panel, you may need to add pumps to help the process along. Pumps require their own energy source, so will need to be connected to the grid or have their own source of power (ie their own solar panel).

If you live in a region where your pipes may freeze, you may need to create an indirect heating system. In such a system, you still have your panel and still have your water tank. But inside the water tank is a coiled tube that connects to the solar panel, and it contains a freeze-proof heat transferring fluid. The convection cycle remains the same, but the fluid that moves is freeze proof, and carries the heat to the tubes in your water tank, warming the water. The water never leaves the tank and can stay indoors.

Such a system will be less effective for 3 reasons: 1) it is winter, so there’s less direct sunlight, 2) there is another step of heat transference added, where heat is lost and efficiency is reduced, and 3) You’ll also likely need a pump system, which will require energy and thus require more power in to produce power out. In a cold climate, however, there isn’t much of a choice, and it can still be an effective one, even in the winter season.

The angle of your solar panel should match the angle of your latitude. So if you are 12 degrees North of the equator, your panel should face south at a 12 degree angle to maximize the sunlight it receives.

Additional Items

Some additional items you may want to consider adding to your solar water heating system:

Temperature sensors: Can tell you the temperature of the water in the water tank and pipes, and maximize efficiency.

Controller module: – if all the water in tank is hot, water running through pipes would just cool it. A module can keep it in place and maximize efficiency.

A pump system- as covered above, some systems may require a pump system to keep your current moving.

Air/pressure release systems: to release air and/or pressure that has built up within your system. Some systems may require this, definitely look into it if your building a system yourself.

Let me know if you choose to build a solar water heater and how it goes!

If DIY isn’t your thing, check out this article on the costs of installing a solar water heater.

Good luck and stay prepared!

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