A solar water heater can significantly reduce the electrical energy you consume for domestic hot water. However, it does not reduce your entire electricity bill by the same proportion: the benefit primarily concerns the electrical heating element, which will operate for fewer hours. The actual savings depend on water consumption, location, shading, sizing, and the quality of the installation.

Therefore, for a smart purchase, comparing liters and prices is not enough. You need to calculate what the solar system is replacing, how much energy it can cover, and what tasks are included in the quote.

1. How much electricity and money do you save?

Energy for water heating is approximately calculated as: liters × temperature difference × 0.001163 = kWh. This is the heat required by the water, excluding storage and distribution losses.

For example, four people using a total of 160 liters of water per day at 40°C, with cold water at 15°C, require approximately 4.65 kWh daily. This corresponds to about 1,700 kWh annually. Including losses, an indicative baseline for calculation is 2,000 kWh per year. Temperatures and usage vary seasonally, so this is a simplified example.

Example of annual savings

Let's assume a properly sized solar system covers 65% of this annual demand. This percentage is used as a calculation assumption, not a guaranteed yield for every home.

  • Annual reference consumption with an electric element: 2,000 kWh.
  • Energy substituted by the sun: 1,300 kWh.
  • Indicative avoidable electricity cost: 0.20–0.25 €/kWh.
  • Annual financial benefit before maintenance: approximately 260–325 €.

For your own calculation, use the charges that actually decrease when you consume fewer kWh. Standing charges and fees independent of consumption are not saved. If hot water is already produced by a heat pump, the financial benefit is usually lower than with an electric heating element.

In summer, you may need almost no electrical backup, while in winter, during continuous cloudy weather, it will be required. Savings are evaluated on an annual basis, not from a single sunny week.

2. How many liters and what type of collector do you need?

The tank capacity is not the same as the liters of water you use in the shower. Water is usually stored at a higher temperature and mixed with cold water before use. As a starting guideline for a standard home:

  • 1–2 people: approximately 120–160 liters.
  • 3–4 people: approximately 160–200 liters.
  • 5–6 people: approximately 250–300 liters, with a corresponding collector surface area.

The final choice changes if there are large showers, a bathtub, frequent guests, or concentrated evening consumption. Indicatively, for 160–200 liter systems, we often see a total flat plate collector area of about 2.5–4 m². The appropriate combination is derived from the system's performance data and local conditions.

What to compare

  • Certified performance tests, such as Solar Keymark certification, not just marketing labels.
  • Net aperture area and collector performance with comparable data.
  • Tank insulation, corrosion protection, and maintainability.
  • Availability of spare parts and clear warranty terms.

Selective flat plate collectors are a common solution for Greek homes. Vacuum tube collectors may have advantages in specific conditions, but they are not automatically the most economical choice. Also, oversizing can increase summer overheating when the house remains empty.

3. Purchase cost and payback time

For domestic thermosyphon-type solar water heaters, indicative total amounts including VAT and basic installation can range around 1,000–1,700 € for 160 liters and 1,300–2,200 € for 200 liters. These are budget ranges, not binding purchase prices. Location, equipment, and access difficulty significantly influence the final offer.

Ask to have it written down if it includes:

  • Transport to the roof or use of a hoist.
  • Dismantling and removal of the old water heater.
  • Piping, external insulation, and a special mounting base.
  • Safety valves, thermostatic mixing valves, and any pressure regulator.
  • Electrical connection and restoration of roof waterproofing.

Simple payback is calculated as net investment cost ÷ net annual savings. With a 1,600 € installation, a gross benefit of 260–325 €, and a hypothetical annual maintenance reserve of 50 €, it takes approximately 6–8 years. The reserve is an accounting assumption, not the price of a specific service.

If you have to buy a new electric water heater anyway, consider the additional cost of the solar system versus that alternative for a comparative evaluation. Any subsidy is taken into account only after eligibility has been confirmed.

4. Installation and maintenance: critical points

Southern orientation without shading is usually the preferred starting point. An inclination of about 35°–45° is a common choice for year-round use but is adjusted based on location and needs. Chimneys, parapets, and neighboring buildings should be checked, especially for winter shading.

  • Support: Check the weight of the full system, surface strength, and wind loads. Anchors must not create water leaks.
  • Piping: Needs short runs and insulation suitable for high temperatures and external exposure.
  • Closed circuit: Use appropriate thermal fluid, with concentration according to the manufacturer and local frost risk.
  • Pressure and safety: Required relief and expansion devices must be installed. The safety valve outlet should be led to a safe point and never blocked.
  • Electrical backup: The element needs proper grounding, residual current protection, and inspection by a licensed electrician.

A thermostatic mixing valve limits the risk of scalding, as the tank can reach very high temperatures. Storage around 60°C, where provided by design, helps with sanitary control, with safe mixing toward consumption points. In case of prolonged disuse, follow the manufacturer's restart and thermal disinfection instructions.

Maintenance includes checking the magnesium anode where present, thermal fluid, valves, tightness, and insulation. The interval is determined by the manual, water quality, and operating conditions. In an apartment building, also check the bylaws and the possibility of using the common rooftop.

5. Frequently Asked Questions

Does the solar water heater work in winter?

Yes, when solar radiation is available. Lower ambient temperature and shorter daylight hours limit production, so backup heating is needed more frequently.

Is it worth it for one person?

It can be, but lower consumption usually extends the payback period. You need a small, properly selected system and a comparison with actual current hot water costs.

What is the difference between dual-energy and tri-energy?

The dual-energy system uses sun and an electric element. The tri-energy system has an additional heat exchanger for connection to an appropriate heating source. Compatibility, especially with a heat pump, requires checking the exchanger surface area.

Can I perform maintenance myself?

Limit yourself to safe visual inspection from an accessible point. Work at heights, electrical parts, and circuits with hot fluid or pressure require a suitable technician. Do not open plugs or connections.

6. Conclusion

A solar water heater is particularly useful when it replaces systematic water heating with an electric element. Calculate the savings based on your own consumption, select the right capacity and collectors, and ask for a detailed installation quote. Good positioning, correct safety measures, and consistent maintenance are worth more than a low purchase price without clear specifications.