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aw 17-02-10

Dear reader,

we hope that you will find the most important questions about the solar electric hot water here.  If not, please contact us: info@awasol.com

1. Planning
1.1. How does it work, the SELACAL-solar electric water heating?

The PV solar panels on the roof provide the power to heat the store. The control SELACAL control transfers the solar power to 230 V DC and injects it into the compact electric hot water tank. The power supply is completely disconnected from the power mains.

If the maximum storage temperature is reached, the controller switches off the power supply.

1.2. How many modules can be connected?

The SELACAL solar system can be operated from approximately 120 to 200 V DC from the PV-modules. Maximum feed line: 1000 W. Typically therefore  3, 4 or even 5 solar modules with approx. 260 Wp in series can be connected. At more than 1000 W solar input the SELACAL controller regulates the feed-in power to 1000 W down. A power from 5 modules with more than 1000 W is very rarely, so that the energetic losses remain low.

1.3. What happens with solar surpluses?

When the max. storage temperature has been reached, the controller switches off the PV-energy supply, like it is by solar themal systems.

Overheating of storage or solar modules is thereby excluded.

1.4. Which hot water demand can be covered by the SELACAL system?

The SELACAL solar storage tanks are available from 80 to 200 litres. Accordingly the need for hot water ranges from approximately 80 to 170 l / day, relate to 2-5 people, depending on the use habits. Maximum DHW flow rate is approx. 12 l / min. The SELACAL storage tank typically operates with higher temperatures as a solar thermal plant, as there are no additional heat losses of the solar circuit.  


1.5. How much space do I need for storage and PV module field?

The Selacal storage tank be wall-mounted and connected from below.

Typical dimensions are 50 or 60 cm in diameter and 1-1.5 m height (see technical information).

The solar modules are approx. 1 x 1.65 m tall. Depending on requirements, 3 to 5 are about arranged side by side or stacked in pairs.

1.6. What angle should I choose for the solar panels?

Because of surpluses in the middle of summer, the inclination angle should be designed for optimal irradiation conditions in the colder period. As a rule of thumb the angle should be in the range of 20 to 45°. But it depends on the degree of latitude.

1.7. How does the reheating works?

If indoors eg. gas heating is available, usually a reheating of this boiler is recommended. The SELACAL tank with 150l or 200l is available with integrated heat exchanger for the boiler (type “HX”).

Otherwise, the all SELACAL tanks have also an electrical auxiliary heating.

1.8. Will the Legionella guidelines be fulfilled?

Due to the compact design of the tank (under 400 l) and the mostly short distances to the taps (less than 3 l tube content) usually no additional technical measures are required.  Because of the often very high operating temperatures up to the bottom of the tank, a multiplication of legionella is generally suppressed.

1.9. How does the tank corrosion protection looks like?

The SELACAL solar storage tank is a steel container which is enamelled. Additionally there are two Mg protection anodes, which provide additional corrosion protection. In addition, the functioning can be checked via the Mg-protection indicator.

1.10. Is a hot-water heat pump with PV modules more efficient?

A hot - water heat pump is in clock mode. This means that the heat pump requires a constant electric power for a specific time, which the sun is not able to supply. The solar modules deliver very different current performance values. The overlap of current solar power and energy consumption is very low, so that only a very low portion of solar electricity can be used for the heat pump.

The SELACAL solar system, however, uses all solar energy, no matter at which irradiation (up to 1000 W). And only when the storage is charged (max. 85 ° C) the controller switches off.

2. Application

2.1. For how many persons SELCAL is sufficient?

Depending on the storage size and hot water demand SELACAL can supply enough hot water for about 2 to 5 persons (see also 1.4.)

2.2. What do I save?

Depending on the location and hot water demand, you can save approximately 55 to 85% of the hot water energy demand (see technical information).

2.3. What do I do with the equipment during periods of long absence?

Also in case of prolonged absence, no particular measures have to be considered. Only for high lime content in tap water, it is recommended to lower the maximum storage temperature, for reducing the deposition of lime. The solar modules can tolerate a standstill easily even in the height of summer.

2.4. How long does a SELACAL system lasts?

The SALACAL system has no moving parts and consists of high-quality components. Regular monitoring in particular of the tank is to be expected with a life span of more than 20 years.

2.5. What do I do, if high lime content is in the tap water?

High lime content in tap water of over approximately 12 ° dH leads to higher limescale on the heating elements. But because they are enamelled in the SELACAL tank, the lime formation is much less compared with simple electric hot water tanks. If necessary, a descaling of the heating elements should be done. For very high lime content is recommended to lower the max. storage tank temperature to approx. 60 – 65°C.

2.6. Connecting the hot water with dishwasher / washing machine is worth?

Generally Yes. Short conductor paths to consumers are important, as the hot water dispensing quantities in several small cycles and cooling in the pipe must be taken into account. Dishwasher can be connected directly. A washing machine should only be connected via a special 3-way valve, so that only the sequences of the program with warm water are fed with solar hot water.

2.7. Where can I install tank and controller?

The tank can  be installed at the wall even in narrow chambers.

The controller is preferably attached to the tank, alternatively it can also be fastened on the wall (as the cable length allow).

3. Installation

3.1. What are the costs of  the installation?

The installation consists of three sections:

- PV module assembly eg. on the roof

- storage tank attachment, connection to water pipe & blow-off line  

- wiring PV-module cable to the storage and grid – connection

Compared to solar thermal systems many installation steps are not necessary, such as solar piping, insulation or solar liquid management. So the installation time is reduced by min 50%.

Especially for wall mounting tanks there are compact security groups that facilitate the connection for the water installation.


3.2. Is there enough space for a hot water mixer?

A domestic hot water mixer automatically adjusts the hot-water tap temperature to a desired value. As the storage temperature may be very different, such a mixer offers a high comfort of hot water.

Specially for wall-hung storage there are special security groups including domestic water mixer which are very compact. They can easily be screwed directly on the in- and outlet of the tank.  

3.3. How to install the safety installation group?

The safety installation group is connected in the inlet of the hot water tank to prevent over-pressure and it protects against infection by suction effects.

Depending on the country-specific requirements, a small combined safety valve (standard equipment in storage accessories) is sufficient or a security group according EN 1567 is required (see accessories in the price list). Water can drip on the safety valve during temperature rise. Therefore, the valve must be connected with a blow-off line.   

3.4. Which cable cross section for the solar power supply?

The maximum solar capacity of SELACAL plant is 1000 W. For this, the very flexible cable cross-section of two 2.5 mm is sufficient. The connector on the controller has therefore been designed. Different wire colours for plus and minus cable secure a reverse polarity at the controller.   

4. Environment / Ecology

4.1. How much CO2 do I save?

Depending on the location and design of the SELACAL plant saves up to approx. 1300 kWh/a. That refers to approx.  780 kg of CO ² per year compared with electrity and compared with a gas heater 338 kg of CO ² per year. At the site of Rome, the savings is up to 1155 kWh/a or 693 kg per year. (see also "SELACAL system test")

 4.2. What is the energetic payback time?

The energetic amortisation of poly-crystalline solar modules is at 1.5 to 2 years.

4.3. How can I check the efficiency of my plant?

The SELACAL controller displays the cumulated kWh that have fed the solar modules into the tank. This value corresponds to relatively precisely the net savings, compared with a conventional water heater.

Dividing the net savings through efficiency eg. a gas boiler (e.g. 75% according to DIN EN 12975) then you will get the gross energy savings.

4.4. Which auxiliary heating system is recommended?

If there exists  a modern gas- or oil-boiler, generally it is recommended to combine it with the SELACAL tank. Otherwise, the the electric auxiliary heating in the SELACAL-tank can be used.

4.5. Energy / ECO - labelling required?

An energy labelling for water heaters has been introduced throughout Europe since September 2015. However, the legislature has left many gaps in the implementing of the regulations. Accordingly, only those heat generators for which there is a corresponding technical regulation are marked. At the moment it is still open, as they will look like for thermosifon systems as well as for solar electric hot water systems.

SELACAL Solar System Frequently asked questions (FaQ)