Planning a house solar system, considerations

[Tice]

Dear solar enthousiasts,

After lurking on this board for quite some time, I decided to finally join.
I’m currently looking into options to add solar power to my house in France.

I have three reasons to do this:

• Cost reduction
• Stabiilzing a voltage drop under load which is caused by the utility company transformator distance to my house that they won’t fix because it’s still above their 207V limit. This is quite annoying with the led lighting in my house as it causes dimming now and then when heavy loads switch on.
• Having a backup when grid is down (which happens a few times a year here due to extreme winds we can face)

Getting an export agreement with the utility company here in France is quite a pain with a self installed solution and I have a fancy feed detecting smart meter. So after reading for some hours on this forum it’s clear to me that the double conversion route is the way to go for me.
The double conversion will give me stabilized power for my critical loads, will reduce the power bill at plenty sunny days at the expense of conversion loss for moments the solar and battery are not sufficient. As a bonus I have a limited power backup for power outages.

I’m planning to use all Victron gear, because I want the components to be of high quality with good support.
I’ll need around 5kw of inverter power for my critical loads and will add a sub panel at the inverter output for these loads. The rest will remain grid fed via the main panel. The grid will only be indirectly connected via the charger, so no backfeed will be possible.

For now I selected a EasySolar-II 48/5000/70-50 with 2 pylontech US5000 batteries and 4kW of solar for the main inverter part and a Victron multiplus-II GX 48/5000 as a charger when the solar and batteries can’t keep up with the demand.

I also considered using an automatic transfer switch that switches to grid when the inverter/battery has not enough juice to power the critical loads panel instead of the chargeverter solution. Because there are two mini splits connected ,that seems to introduce problems with the split compressors that don’t like the transfer times of the ATS (resulting reverse operation of the compressors; a rabbit hole that I don’t want to dive into).

It’s going to be kind of costly, but still it will be a far more cheaper and more satisfying option than letting an utilities-company-approved solar company come over to install 5kw of solar with some micro inverters for 10.000-12.000 euros.

What do you experts think of this selected solution? Am I missing out on better, more logical options or does it seem like nice solution for the 3 reasons mentioned above to add this system to my house?

 

[kommando]

Before you commit to your chosen route speak to these guys who are in France. I have the UK version and it works very well but for France it needed some mods as the French meters are different.

Accueil -

MK2 PV Router Maitriser et optimiser la consommation de votre installation PV en pilotant votre flux d’énergie au cours de la journée … Le MK2 PV Router est l’accessoire indispensable lorsque l’on souhaite optimiser son autoconsommation. Particulièrement adapté à l’alimentation de résistances...

mk2pvrouter.com

It won't overcome your low V feed issues but at least gives you some other options for diverting excess production and it not feeding back into the grid.

I too work between on grid and off grid using a Transfer switch but I switch manually but my grid supply is stable so I do not have your low V issues.

I DIY'd the battery build and got the price halved against the fully made Pylontech price, there are other pre built batteries with less premium pricing than pylontech.

 

[DIYrich]

With double conversion, you need a bypass vs ats. Harder to do if not built into the inverter. Ats senses grid loss. Bypass senses load is exceeding inverter capability.

 

[Tice]

Before you commit to your chosen route speak to these guys who are in France. I have the UK version and it works very well but for France it needed some mods as the French meters are different.

Accueil -

MK2 PV Router Maitriser et optimiser la consommation de votre installation PV en pilotant votre flux d’énergie au cours de la journée … Le MK2 PV Router est l’accessoire indispensable lorsque l’on souhaite optimiser son autoconsommation. Particulièrement adapté à l’alimentation de résistances...

mk2pvrouter.com

It won't overcome your low V feed issues but at least gives you some other options for diverting excess production and it not feeding back into the grid.

I too work between on grid and off grid using a Transfer switch but I switch manually but my grid supply is stable so I do not have your low V issues.

I DIY'd the battery build and got the price halved against the fully made Pylontech price, there are other pre built batteries with less premium pricing than pylontech.

Thanks, I will look into that solution and wether it could work out for me. I looked into DIYing a battery but I think it's not worth the hassle for me (finding quality cells seems quite challenging) and I like a neat solution of rack based or wall mount.

 

[Tice]

With double conversion, you need a bypass vs ats. Harder to do if not built into the inverter. Ats senses grid loss. Bypass senses load is exceeding inverter capability.

Thanks, not really sure if I understand the bypass solution correctly. Do I have to see that as a kind of relais that switches to grid only when it senses an excess load (kind of how some of the off-grid inverters work)?
For the ATS route I had in mind was to set the solar inverter-battery scenario (not grid connected but separate critical loads panel) as primary source and let it switch to grid if the inverter switches off due to low voltage. No double conversion would be in place in that scenario. It would not bring a solution to my voltage drop problem in case it switches to grid.

 

[DIYrich]

For the ATS route I had in mind was to set the solar inverter-battery scenario (not grid connected but separate critical loads panel) as primary source and let it switch to grid if the inverter switches off due to low voltage. No double conversion would be in place in that scenario. It would not bring a solution to my voltage drop problem in case it switches to grid.

Inverter -> Primary of ATS
Grid -> Secondary of ATS
ATS output -> Main panel

If inverter is overloaded, inverter will cut output, and the ATS will switch to grid. So far, so good.
Assuming the Inverter resets itself (vs manual reset), it will power the output (which now has no load).
ATS will see power on the Primary, and will switch back to Primary (maybe after a 5 minute delay, depending upon the ATS).
Assuming no reduction in Load, the Inverter will immediately overload again, and repeat.

Note: Some ATS have a delay when switching to Secondary to allow the "Generator" to stabilize. You will be out of power during the transition.
Note 2: No frequency synchronization during switchover.

Basically, not an optimal solution.

Inverters with built in built in bypass handle all the logic, and some my be synchronize to the "gen/grid", allowing for a better switchover.

 

[Tice]

Inverter -> Primary of ATS
Grid -> Secondary of ATS
ATS output -> Main panel

Assuming no reduction in Load, the Inverter will immediately overload again, and repeat.

Thanks clear. It would have been a bit different in my case as the ATS-output would power a sub panel that has only critical loads connected matched to the output of the inverter avoiding that overload loop. The main panel would be completely seperated for loads that would always use the grid. In that way it could have been a good solution as opposed to the double conversion one, but I read too many issues with mini-splits in an ATS scenario that seem quite hard to find a proper solution for.
[edit]
I realize now that the loop will also occur when the loads will pull down the battery voltage to a level that the inverter switches off when no solar input is present, but will get back to a voltage where it will turn on again once the loads are switched to grid --> loop. This will probably not work indeed, or needs a clever inverter disconnect voltage in place which takes into account the pull down. I think double conversion will be the route to go to avoid these problems.

 

[Tice]

Before you commit to your chosen route speak to these guys who are in France. I have the UK version and it works very well but for France it needed some mods as the French meters are different.

Accueil -

MK2 PV Router Maitriser et optimiser la consommation de votre installation PV en pilotant votre flux d’énergie au cours de la journée … Le MK2 PV Router est l’accessoire indispensable lorsque l’on souhaite optimiser son autoconsommation. Particulièrement adapté à l’alimentation de résistances...

mk2pvrouter.com

I looked into that solution. It seems to work like product from a company in the Netherlands( https://www.solyxenergy.nl/product/solar-iboost/). It measures the overproduction and can steer the surplus to resistive loads like a electronic water heater. I think with these kind of solutions there still will be the possibility of back feeding which is not allowed here in France without the export agreement as it will be still grid connected.

 

[kommando]

I looked into that solution. It seems to work like product from a company in the Netherlands( https://www.solyxenergy.nl/product/solar-iboost/). It measures the overproduction and can steer the surplus to resistive loads like a electronic water heater. I think with these kind of solutions there still will be the possibility of back feeding which is not allowed here in France without the export agreement as it will be still grid connected.

The one you have pointed to is a commercial version without the option for programming and calibration.

This is the original version used in UK developed by Robin Emely and now made in France with software tweaks that Robin did to help out his French customers who has issues with small exports.

Mk2PVRouter - Introduction

A DIY Constructor’s project to build a Mk2 PV Router system for surplus energy diversion.

openenergymonitor.org

Its programmable plus the x-cross over point between import and export can be calibrated to suit your exact location.

Mk2PVRouter - Improved Calibration

Instructions for calibrating the Mk2PVRouter energy diverter against a domestic electricity meter for optimal performance.

openenergymonitor.org

 

[zanydroid]

Is this diverter for people with interconnection agreements that get bad to no credit for export? Or is it for people without interconnection agreements that want to stay undetected? The latter IMO is pretty risky to try to sustain. Especially if the reason to do so is unfavorable DIY gridtie regulations in the first place.

 

[Tice]

The one you have pointed to is a commercial version without the option for programming and calibration.

This is the original version used in UK developed by Robin Emely and now made in France with software tweaks that Robin did to help out his French customers who has issues with small exports.

Mk2PVRouter - Introduction

A DIY Constructor’s project to build a Mk2 PV Router system for surplus energy diversion.

openenergymonitor.org

Its programmable plus the x-cross over point between import and export can be calibrated to suit your exact location.

Mk2PVRouter - Improved Calibration

Instructions for calibrating the Mk2PVRouter energy diverter against a domestic electricity meter for optimal performance.

openenergymonitor.org

Thanks for the more detailled explanation. I'm kind of a microcontroller programming fan, so I will dive into that. Also in a off-grid situation this can be useful when batteries are full and the solar gets cut. I'm heating with an electric heater and it would be nice to adapt that to a triac fed load for the extra watts that could be used.

 

[Tice]

Is this diverter for people with interconnection agreements that get bad to no credit for export? Or is it for people without interconnection agreements that want to stay undetected? The latter IMO is pretty risky to try to sustain. Especially if the reason to do so is unfavorable DIY gridtie regulations in the first place.

In France, people look into ways to avoid the agreement because it's quite a hefty administrative process which requires Consuel approvement once you go over 800 watt balcony plug and play systems. Even when you use grid-tied inverters that safely shut off when the grid goes down. Also the power network is quite a bit more unreliable than for instance in the Netherlands and heavy wind areas can have frequent power cuts because all the lines are above ground in rural areas.
So one of the reasons I want to detach my system from the grid by means of an ATS or double conversion is to make sure no utility company workers will get hurt when they are working on the lines. Second I don't want to get my inverter to shut off with the power outages because I need the power to do my work. Third reason is to spare me the headaches involved with the extremely bureaucratic procedures here in France. You are kind of forced to hire an Utilities approved company to do all the administrative and installation work for you at ridiculous high pricing.
The credit is not too bad for now in France, but in the Netherlands the government and utility companies really let solar investors down with new policies that even charge people now when they feed to the grid at peak hours (just when you harvest the most power). That's why these routers for maximizing self consumption are becoming lucrative for existing panel owners. I see the penalties for exporting happening in France too in the near future because here solar is just getting started as opposed to the Netherlands which already has high density solar on roofs. In France you are allowed to place 3kw of solar on the ground (max height 1.80m) without any administrative process. To put more on your roof is not very hard too by means of a permit. It starts getting more complicated when you want to connect that solar to the grid with agreements and taxing.

 

[kommando]

Also in a off-grid situation this can be useful when batteries are full and the solar gets cut.

No, its uses a CT to detect export and off grid is no export. What I do off grid is monitor frequency as my Sunny Islands control PV inverter output using frequency shifting. I then turn the same immersion heater on and off based on frequency of the internal grid.

 

[Glock24]

@Tice I think you may be overcomplicating the situation. The Victron inverters have built-in ATS and bypass. You can power your critical loads with solar and battery all the time, if the battery gets low it will automatically switch to grid in a seamless way as the output is always synced with the grid. When the battery is charged it will switch to battery again seamlessly. You don't need an additional charger, the inverter is also a charger. You can charge from the grid in case you don't have enough solar.

If you're still worried about the issue with the compressor of the AC or fridge, then you can install a voltage protector on each device, it'll cut the energy for a set amount of time if it detects abnormal voltage or frequency. Something like this but for your region:

Voltage protector 900J/1800W, 1 outlet, 350° plug, RJ45-220V| ForzaUPS

The handy on/off switch helps reduce standby power consumption.

www.forzaups.com

 

[Tice]

No, its uses a CT to detect export and off grid is no export. What I do off grid is monitor frequency as my Sunny Islands control PV inverter output using frequency shifting. I then turn the same immersion heater on and off based on frequency of the internal grid.

Yes I understand, but couldn’t you use the CT principle to measure the amount of current used in your off-grid setup and compare that with the solar input current (read from the viltron data bus) so that you can divert the difference to the heater and prevent wasting the possible solar overproduction? It also could prevent the heater taking up it’s maximum current which as a bonus leaves headroom for the inverter’s capacity especially if you always limit it at a max current use by default.

I will look into the frequency shifting solution you mention.

 

[LydMekk]

Just my 2 cents: 5kw inverter sounds SMALL for a normal EU house.
Not much more money to go to f.ex. a 8 or 10kw model.

 

[kommando]

As the Victron also uses Frequency shifting, I do not waste any PV off grid unless the Water tank is up to 80C and the immersion says not to supply it anymore which would happen regardless. For the switching I use Shelly 16A wifi switch controlled by Node-red on a Raspberry Pi which also gets the frequency info. You can run Victron Venus on a Pi and Node-red at the same time.

I use two SMA SI's giving 10kw peak power but I could get away with 5kw by scheduling washing machines and cooking to different times.

 

[Tice]

@Tice You can power your critical loads with solar and battery all the time, if the battery gets low it will automatically switch to grid in a seamless way as the output is always synced with the grid. When the battery is charged it will switch to battery again seamlessly. You don't need an additional charger, the inverter is also a charger. You can charge from the grid in case you don't have enough solar.

If you're still worried about the issue with the compressor of the AC or fridge, then you can install a voltage protector on each device, it'll cut the energy for a set amount of time if it detects abnormal voltage or frequency. Something like this but for your region:

Voltage protector 900J/1800W, 1 outlet, 350° plug, RJ45-220V| ForzaUPS

The handy on/off switch helps reduce standby power consumption.

www.forzaups.com

I read about that functionality on the Victron community. I think I read there that because it syncs it will not guarantee small amounts fed back to the grid when switching, but I could have missed something there. Thanks for the tip about the voltage protector. You can easily get them here in France.

[edit]

This thread on the Victron community site explains about the same requirements that I have minus the voltage drop issue on mains.
It seems that using Ignore AC mode is what I have to use. But Victron tech support states at the bottom of this thread
"Ignore AC is the closest you can get to reducing the chance to zero, while still having the benefits of an inverter/charger"
I interpret that comment not as a solid it will never export in that mode. But that might be the language barrier and my misunderstanding of that phrase.

https://communityarchive.victronenergy.com/questions/43171/mixing-grid-with-solar.html

 

[Tice]

Just my 2 cents: 5kw inverter sounds SMALL for a normal EU house.
Not much more money to go to f.ex. a 8 or 10kw model.

The past year I monitored my maximum current draw for the critical loads that I want to feed with solar. It never exceeds around 4kVA. I will start with a 5kW and if that will give problems in the future upgrade by adding one in parallel.