Some say that photovoltaics don't work in winter...
Yes, it works less...
BUT it is better to heat water with mains electricity from 36 degrees to 50 degrees
than from 12 degrees to 50 degrees, right? ;-)
FAQ
1. I need a new electric water heater with a 125-liter storage capacity. Later, I would also like to heat water with photovoltaics. What do I need to add to or convert a conventional water heater?
You won't need anything if you buy a Logitex water heater. Logitex water heaters are equipped with two separate circuits. One (the standard circuit) operates on mains power, the other is powered by photovoltaic panels. The photovoltaic circuit is switched off by simply turning the thermostat knob. The water heater is then powered by mains power and functions like a normal hot water tank. You can connect two DC cables from the photovoltaic panels to the water heater. Then, by turning the thermostat knob, you activate the photovoltaic circuit, which allows you to heat the water with green electricity. And most importantly, this electricity is free. However, if you buy a standard water heater from another manufacturer now, you won't be able to convert it later.
2. What is the difference between water heating using regular solar panels and Logitex photovoltaic water heating?
3. Isn't it better to use a regular AC water heater to heat the water and connect the panels to the inverter?
Statistics show that connecting a water heater to the grid is more economical than connecting it to a direct current supply from photovoltaic panels. However, this only applies when solar radiation is less than 70% of the specified power. At 70% irradiance, the balance is balanced, and at irradiance above 70%, photovoltaic direct current is significantly better. One condition for this is that the resistance of the heating coil must match the resistance of the panels at maximum power. For this reason, we only recommend 250 W panels with 30 V. Modules with a lower connected load will produce a correspondingly lower output. Many of our own measurements and measurements from independent institutions show that supplying power from the public grid or from photovoltaic panels results in the same consumption. However, the inverter incurs direct current conversion losses of 30 to 50 W per hour. When converting direct current to alternating current, manufacturers state a loss of 3 to 4%. Therefore, if all of the inverter's losses are taken into account, the annual balance is truly 1:1. If the sky were cloudy throughout the year, the inverter would obviously be better, and vice versa. And another key difference: A normal water heater is heated with grid power only when it needs it—for example, in the morning after a shower. Later, when the water heater could have used the electricity generated by the sun, it may no longer be needed. The difference then is that you have to pay for the grid power. The electricity from the photovoltaic modules is free. If you connect the inverter to the photovoltaic modules instead of the water heater, the inverter supplies the free electricity to the home grid.
A few practical tips: Heating and water heating using photovoltaic panels is a supplementary system to the main heating system and is especially recommended for transitional periods. In these cases, it can work like this: from a 2 kW system, 1 kW can be used for direct current heating or underfloor heating and 1 kW for the water heater. Once the heating has reached the desired temperature or the room thermostat has switched, 2 kW will automatically be used for water heating. The system can also be connected in reverse.
4. Is it possible to connect the Logitex storage tank with the photovoltaic modules directly to a heat pump?
While it is possible to connect the Logitex hot water tank directly to a heat pump, we do not recommend it. Heat pumps have a temperature limit of between 55 and 60°C. The heat pump would heat the water in the hot water tank to this temperature. The photovoltaic modules would then be virtually unable to supply any energy, as the water would already have been heated above 60°C, which would automatically cause the heat pump to malfunction. There are several dozen installations where the Logitex system has been connected to the heat pump as follows: A DZD storage tank is installed at the cold water inlet to the heat pump tank. This tank either preheats the cold water or heats it to a maximum temperature of 75°C. A mechanical mixing valve transfers the heated water to the heat pump tank. This reduces the heat pump's activation frequency, saving you money on electricity and increasing the heat pump's service life by at least 30%. The increased service life of the heat pump plays an important role in calculating the return on investment. It makes a big difference whether you need to replace the pump after 10 or more than 13 years.
5. Can I connect a normal water heater to photovoltaic modules?
No! Absolutely not. If you were to connect a regular water heater to the photovoltaic panels, as some DIYers have already done, the thermostat and thermal protection would burn. There's a fire hazard! To ensure the system operates safely and reliably, Logitex has developed and patented a solution that's unique worldwide.
6. Can I connect photovoltaic modules to a coil that is already installed in the water heater and is intended to feed in power from the grid?
No! Almost all heating coils are submerged in water. If they were connected to direct current, electrolysis would occur, gradually damaging the hot water tank. To prevent this, Logitex uses dry heating coils that were specially developed to be powered by direct current from photovoltaic modules.
7. What care and maintenance does the Logitex system require throughout the year?
None. Two weeks after installation, you'll be curious to see what the temperature is in the hot water tank. After that, once you've confirmed that the system is working properly, you'll only stop by the water heater when you walk past it, and even then, you'll only check the water temperature.
8. Can I order a 1kW photovoltaic system from you and install it myself?
What about the guarantee then?
Basically, yes, if you are both a certified electrician and a plumber. The warranty begins on the date of purchase. The warranty covers electrical components for 2 years, and the warranty covers the storage tank for 5 years. If a claim is made that the system was not properly connected, the claim cannot be accepted. We recommend having the system installed by a certified company. A list of certified companies can be found on the Logitex website.
9. Where is the best place to place the photovoltaic modules?
Anywhere the sun shines and there is no shade. If, for example, the shadow of a chimney or tree casts a shadow over one of the panels, the performance of all the panels will decrease because they are connected in series. A south-facing orientation of ± 20° is always the most favorable. If you have to choose between a southeast and southwest orientation, southeast is always better, although it is usually colder in the morning. The sky is clearer in summer, and clouds form around midday. During the rest of the year, fog can form in the morning and often lasts until late morning. For this reason, a southwest orientation is less favorable. Photovoltaic modules do not like heat; they work much better in cold temperatures. For this reason, the performance can be much higher at -30°C on a sunny day than on a hot summer day. The panels therefore operate year-round, which is an undisputed advantage of the panels. The panels do not have to be installed solely on the roof.
10. How is the consumption of hot water in the household calculated?
In the past, when calculating the volume of hot water in a household, it was assumed that an adult consumed 50 liters of hot water heated to 42°C. Nowadays, people are more economical, and 36 liters are used in the calculation. Another significant difference is whether you bathe in the tub or just shower. If you prefer bathing in the tub, the storage tank volume must be increased by at least 50%. A larger storage tank volume is not necessary with gas water heating, as this method of water heating is much faster than with electricity.
11. What do the photovoltaic modules do when the water in the storage tank has reached the desired temperature and the panels are switched off?
In such a case, the photovoltaic modules do not supply any power. However, the voltage remains. However, it would be a shame not to fully utilize the modules' capacity. For this very reason, Logitex has developed a new "M" model that transfers the energy after the water in the storage tank has been heated. This energy can then be used to heat water in the next Logitex water heater. The model can also be connected to an inverter, and the electricity can be used in the home's electrical system.
12. Can Logitex products also be used in a prefabricated building that has its own gas boiler room?
Yes, Logitex products can be used anywhere there's a need for hot water. In prefabricated buildings, apartments, schools, government offices, workshops, houses—in fact, anywhere. However, in prefabricated buildings, the roof area without shade is a limiting factor. The photovoltaic modules are connected to Logitex water heaters using only direct current cables, which can be installed in a shaft. In your case, the water heaters would preheat the cold water, which is then fed into the central storage tank.
13. When heating water with the LX ACDC 125 using mains power, you recommend setting a heat limit in case of persistent bad weather. In the manual, you also recommend heating the water to 75°C or more using photovoltaic modules. However, you also recommend installing a mixing valve. But how do you calculate the volume of water that can flow through the mixing valve if, for example, it is set to 40°C and the water in the water heater is 75°C?
The calculation is based on the formula below:
x ÷ yxz = k
x - volume of the storage tank in liters
y - temperature set on the mixing valve in °C
z - temperature of the water in the storage tank in °C
k - available water quantity, temperature according to y
So in your case it is:
125 l ÷ 40°C x 75°C = 234 l
From the calculation above, it follows that you can get 234 liters of water with a temperature of 40 °C.
14. I purchased your hybrid water heater with photovoltaic panels. The water heater works very well, but why does water occasionally drip from the pressure relief valve?
Water is not compressible, and therefore every system that heats water must be equipped with a pressure relief valve. Any drops from the pressure relief valve must be drained into the nearest sewer. Another option would be to install an expansion tank to equalize the pressure in the system. The capacity of an expansion tank suitable for 100- and 125-liter water heaters is 5 liters. For 160- and 200-liter water heaters, the expansion tank should have a volume of 8 liters. However, the air pressure in the expansion tank must be taken into account. The air pressure must be higher than the water pressure in the pipes and lower than the value set on the pressure relief valve (0.6 MPa).
15. How much hot water does an adult use per year?
This is very individual. It is generally assumed that an adult uses an average of 15 liters per shower. This is estimated at 36 liters of hot water per person per day. This translates to 13,140 liters of hot water per person per year. In energy terms, this amounts to 870 kWh per person per year. If the 2 kW system from Logitex generates approximately 2,400 kWh per year, it should be sufficient for 2.76 people (2,400 ÷ 870).
16. What is the output in kW of a tube heat exchanger in the M+K water heater?
24 kW at 80 °C and flow rate of 720 liters per hour.
17. What is the difference between connecting photovoltaic modules directly to the Logitex water heater and connecting photovoltaic modules directly to an inverter that converts direct current into alternating current, which can then be used to supply the home grid to which a normal water heater can be connected?
The difference is significant. A conventional water heater draws power from the grid when it needs it, not when the sun is shining. The Logitex water heater draws free electricity from photovoltaic panels when the sun is shining, and only when this energy is insufficient is the difference drawn from the grid. This results in significant savings on grid power. If you were to feed the electricity from your small power source directly into the grid, you would receive three times less from the utility company than the price you pay for grid power. So, to answer your question, connecting photovoltaic panels directly to our water heater is three times more economical.
18. How are the panels attached to the metal roof?
Very simple. Special screws are screwed into the roof truss, sealed with a rubber gasket. Guide rails are attached to the screws via plates, and the panels are then mounted to the guide rails.
19. After a year of operation, only cold water flows through my system, even though the photovoltaic modules heated the water in the Logitex water heater to 70°C. I installed a mixing valve at the water heater outlet and set it to 49°C. We have very hard water. What could be causing the problem?
If a problem arises with thermostatic mixing valves, limescale deposits are always the cause. The formation of limescale on the mixing valve sensor causes it to become isolated, resulting in improper mixing. As a safety precaution, the mixing valves are designed to block the hot water supply if the sensor malfunctions, thus preventing health risks. An immediate solution is to turn on the hot water, lift the mixing valve cover, turn the tap left and right at least three times until it stops, and then close the cover.
20. I have a condensing boiler with a solar heating system, with the appropriate piping, of course. I would now like to switch to your system. Is this possible?
Ideally, the solar heating system could be separated from the condensing boiler and operated as a standalone system. The boiler could then be connected to the Logitex M+K or M+KW storage tank (a special version for gas boilers). The preheated water from the solar heating system would feed the Logitex storage tank, where the water would then be further heated by photovoltaics. If the sunshine were too weak, the gas heating system would kick in. Naturally, this would result in excess electricity production in the Logitex storage tank. However, this does not pose a problem for the Logitex system (unlike conventional solar heating systems). The excess electricity is fed into the house's grid via inverters. In this case, gas consumption for water heating would be minimal. You can generate enough electricity for your own use and actually don't need to throw away or replace anything.
21. I have a 1,000-liter storage tank connected to a solid fuel boiler, which stores heat for both space heating and domestic hot water. To ensure I have hot water outside of the heating season, I always have to heat the boiler in the morning. How could I install your hybrid water heating system so I don't have to heat it every day?
Very simple. The Logitex LX ACDC/M water heater is connected to the hot water outlet from your large storage tank, which in turn is connected to the photovoltaic modules. The Logitex heater will accumulate solar energy. If the weather is unfavorable for a long time, the water can be additionally heated using mains electricity. During the heating season, the preheated water from your large storage tank flows into the Logitex water heater. There, it is either further heated or—if it is warm enough—it simply flows through. If the system is connected as described above, you don't need to heat the boiler every day and will only heat during the heating season.
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