PV solar panels + electric water heater + VDE inverter

[coccigro]

Hello,

Why not double feed the water heater? You keep the day / night contactor for the night top-up and you connect the PV directly on the water heater (via the inverter of course).

Your panels are sized for the water heater, which prevents it from receiving too much. If he receives less, well, it's just resistance, right?

Between the inverter and the water heater, you install a very simple daily clock which sends the current to the water heater between 12:30 and 17:30 p.m. (the times you have chosen) and which switches to the rest of the house outside these times.

In this way, you mechanically manage your production to avoid giving too much to EDF

Naturally, you should consume hot water first in the morning ...

To use the PV and EDF current at the same time, it's a synchronization story. I do not know more.

Good luck,

[vbenistant]

Thank you for your reply,
The problem with this inverter is that it does not inject current if it does not detect the presence of EDF current.

[coccigro]

Well seen,

The search continues ...

[lilian07]

Has anyone experimented with this idea or even improved this principle by injecting into the DHW only in case of surplus?
I think it is possible to have such a device by keeping it simple but with the use of a programmable uP.

[izentrop]

it is possible to have such a device by making it simple but with the use of a programmable uP.

+1
And rather than supplying the water heater via an inverter, plan to supply the resistor directly with PVs connected in series ... taking into account the characteristics of the different elements so as not to make bullshit;)

[lilian07]

The idea seems to me not bad, but the system becomes less simple and less easy to transpose to all. Eventually I will tend to use a low voltage immersion heater but with a cost too high for my taste.

Really, the trick of regulating the power to the immersion heater by cutting the voltage seems to me the most suitable knowing that the main function is not to lose the energy which has already passed through the inverter which becomes relatively cheap for our days.
I see 3 interests, we store the surplus lost in a large battery, the DHW, without significant modification of the electrical installation, we are no longer 'outside the law' with respect to EDF while being d 'autonomous advantage and finally we can significantly increase the number of panels without losing ROI (return on investment) by overwhelming the overall consumption of the home.
With this trick it is possible to exclude batteries by performing the installation itself, you just need an injector inverter and a mounting with Up before the installation. It remains to test the feasibility and practical operation.

[izentrop]

I'm afraid you're going wrong.
Without going into the calculations,

1. Heating water is much more efficient from thermal solar
2. The pressure drop of an AGM lead battery is 2% month
3. That of a standard 200l flask is 5% per day
4. With 9 kWh of hot water, you don't run an electric motor

And yes, you have to consume 2 kwh per day to only keep the water at 60 °.
We can go down to 700 wh / d by over-insulating it.
We are still far from the performance of the battery.

After calculation, a 200l balloon varying from 20 ° to 60 ° corresponds to 5 12 V / 150 Ah batteries.

[izentrop]

erratum: losing 2 kwh per day to maintain the temperature of a 200 l (9kwh) tank is 22% / d

[lilian07]

Yes, I fully agree that to make hot water it is better thermal sensors whose efficiency is 70% vs 17% there is no more photo we stay on the same type of energy therefore less degradation of yield by change of physical state.

Of course, I start from the principle that we use the PV to "crush" in the simplest possible way, the most profitable moreover a maximum the direct electrical consumption of the home so by simply using PV and an injector inverter. The corollary we all know, we must inject into the network in a wild way so as not to have to use an unprofitable system (Battery, PV, specific subscription, inverter specific to the ERDF standard and very expensive two-way meter which leads the ROI to 15 years...).

I'm talking about a system with a ROI at 3 years (without any comparison with what we know in a standard way).
Why?
Because the injection is no longer wild (in the sense of the law and a pure loss for the producer) it becomes an asset when you have a simplified system with more PV on the roof (the injector inverter allows you to be satisfied with having only the essentials are cables + Pv + inverter on standard socket).
The system of wild injection without recovery of the lost energy is reasonable only with low power (1 or 2 PV 100 to 200 W) which is content to simply crush the background noise of the habitat ( refrigerator, standby of devices, computers .....) out there with this trick you can very significantly increase the number of PV to crush consumption more because the surplus is no longer wildly injected into a network but come directly to interest our daily need.
Without however sinking on an overproduction which would come to make thermal in the great majority.

Some had already in principle mentioned the diversion in a heating resistance in pure loss .... here I speak of a system already gaining in use but with a diversion of losses to our profit.

Why then in this logic we do not put a battery at the end of the chain rather than at the beginning as we traditionally see and well I will say that it is the same problem, beginning or end same fight, we move away from the ROI by adding batteries because as your calculation showed it takes 5 large polluting lead batteries and very expensive to replace a storage of hot water which in any case will be used even before having lost its output destocking either the same evening (this need represents 75% of our electric bill).
If the DHW tank is a solar tank with electric backup as is traditionally the case, it works even better because we combine the best of thermal and the best of solar electric.