Photovoltaic direct current hot water production

[not C]

Wishing to equip my house with photovoltaic energy, I asked myself the question of buying only the necessary. My first goal was to replace the domestic hot water production of my gas boiler with an electric cumulus powered by panels. So I installed 6 panels of 270 W on the ground in my garden. I also bought an electric cumulus. The acquisition of an inverter appeared to me as an investment as high as useless (but I will come back to it because I changed later of opinion, finally in part ...). Why not simply use the DC power provided by the panels? Only one problem my cumulus thermostat is made to switch only the alternative. In direct current, it will prime and grill. Solution quickly found, put on my cumulus a thermal contactor and switch the power by means of a transistor (coupled with a manual circuit breaker, to switch the power also manually). For safety, no differential, the panel voltage is left floating, no adverse consequence of a lack of insulation. That's the installation works since 4 months. At the rate of savings on the gas bill, the installation will be paid on 3 years.
Direct current, the solution for small domestic installations?

[izentrop]

Hello and welcome Pasc,
There is already a topic on it solar-photovoltaic / cumulus heater-with-the-photovoltaic-t6792.html

One problem my cumulus thermostat is made to switch only the alternative

Normally a cumulus resistance is only weakly inductive, so no arc problem at break.

[not C]

Thank you for the welcome message.
In fact, the arc problem is not directly related to the inductive nature of the load. In direct current, the current does not cancel as AC, so the arc is maintained by Corona effect. Moreover on my cumulus, I wanted to make sure of the thing and the cumulus thermostat has started well. In fact it has a kind of bimetallic thermal protection that prevents it from burning. Electromechanical systems do not work, but transistors switch very well.
The interest of the direct current is double in this kind of application. On the one hand the price of the installation on the other hand the overall efficiency of the installation. First there is no loss of energy by conversion (they are today very low given the performance of modern transistors), but especially by not regulating the voltage, the power supplied to the load, 'follows the power available at the panels, and thus the efficiency of the installation is considerably improved. We can do the same thing by not regulating the alternative (I did it elsewhere and I will return) but it's more complicated. In fact the principle of regulated voltage is essential for a collective distribution of electricity, but for an individual production / consumption, it becomes a considerable handicap.

[not C]

The previous subject on the production of hot water: solar-photovoltaic / cumulus-heating-with-the-photovoltaic-t6792.html
date a little, in my opinion. Since then, the economic data have changed, especially the price of solar panels. I think that photovoltaics can be considered today in a cost-effective way without the cost and complexity of fluid exchanger systems.

[izentrop]

the power supplied to the load 'follows' the power available at the panels and thus the efficiency of the installation is considerably improved.

A regulator like MPPT, I suppose? Can we see the diagram?

The yield can not be better than solar thermal.

Not so old, the subject solar-photovoltaic / cumulus heater-with-the-photovoltaic-t6792-20.html # p338444

[not C]

No, there is no MPPT type regulator. For this type of use that wants to be the most rustic. But it is necessary to specify what I mean by 'yield'. The optimum point of use of a panel is at the angle of its rectangular voltage characteristic. This point fluctuates depending on the solar flux. Roughly speaking, the voltage is roughly constant, but the current generator varies greatly. So if we have a resistive fixed load (U = RI, a straight line, therefore), the operating point of the set is easily found by drawing the load line on the characteristic of the panel provided by the manufacturer. In the absence of MPPT (no battery either, why store the energy in chemical form while the goal is to store it in the water of the cumulus, which would duplicate), this point deviates from the optimum (the upper angle of the current voltage rectangle) when the current drops, but the heating works nevertheless. On the other hand, if a regulated voltage system is put between the panel and the load, then it can only provide a constant power P = V ^ 2 / R and as soon as the solar power falls below this threshold he's going to break up. That's what I mean by 'yield loss'. The removal of this voltage regulator allows the use of power that would be lost (I do not speak of a system coupled to the network).
In conclusion, the regulated 220 V standard is not optimal for using solar panels for self-consumption.

[not C]

Actually I had not seen the last page: solar-photovoltaic / cumulus-heater-with-the-photovoltaic-t6792.html

Yes, it's at the heart of the subject actually. I agree with the general direction and the idea that the operation is quite profitable. On the other hand, a heating resistor seems a little complicated and in any case the reliable switching of direct current requires modifying the cumulus, but an electronic switch is much easier to make a heating resistor immersed.

[izentrop]

if we put between the panel and the load a regulated voltage system then, it can only provide a constant power P = V ^ 2 / R and as soon as the solar power falls below this threshold, it will break up. That's what I mean by 'yield loss'.

For me, the resistance must be calculated at the point of maximum power. Then indeed, it is necessary to adapt the voltage to the terminals of the resistance according to the point of power and what better than a MPPT for that? https://fr.wikipedia.org/wiki/Maximum_p ... nt_tracker

[thibr]

it is a pity to take photovoltaic panels to heat water
it is more logical to make self-consumption and possibly to heat the water only with the surplus that is not self-consumed

[GuyGadebois]

it is a pity to take photovoltaic panels to heat water

Especially since there are excellent inexpensive solar water heaters and can also be made (DIY):
https://www.hellowatt.fr/chauffe-eau-so ... -thermique