What do you think is best arrangement for "grid assisted off-grid" setup for Costa Rica

[l00semarble]

Hey I'm new here. Hello to the group.

I am building a medium sized 3 bedroom "luxury" home in the jungle in Costa Rica. We have US spec 120/240v split phase power here. I have done a load inventory but it is somewhat hypothetical based on all the appliances and such that I will buy and spec for the home. I do have real data from my current house where we have averaged around 1,000kwh/mo during occupancy.

One of the killer loads in current house is a single speed pool pump that is used 365 days/year. The new house is a bit larger and will have a garage/workshop but we will spec all LED lighting, highest efficiency appliances including the best possible variable speed pool pump and we will spec a rooftop non-electric solar water heater. The new house will have mini-split air conditioners in the 3 bedrooms but they would not be regularly used as the house has an open air design and is at an elevation that makes it unnecessary but they may be used for humidity control if/when we are away from the house or to briefly cool/duhumidify a bedroom bedtime if it had been closed up and stuffy. Cooking can be either electric or I could do a propane stove but I have to hump my own propane bottles if I do this which is not a deal breaker but this is an hassle and an energy cost that I would like to avoid if possible.

I'm still working the spreadsheet but I figured I will need about 900 kwh/mo.

Electricity here is expensive at about $0.15/kw so part of the goal is to reduce energy costs to at/near zero for my retirement but the other problem is that the grid at our remote location is unstable and causes constant problems with appliances. We are constantly replacing "motherboards" and "control boards" and small appliances due to damage from voltage fluctuations and frequent momentary outages.

So we want a system that provides cost savings but also protects us from the unstable grid. Exporting to grid is complicated/bureaucratic here and you don't get the full benefit back of the power you export. I'd rather store it and forget export.

I own a a marine electronics/electrical shop and we are a dealer for VIctron Energy but my Victron experience is limited to marine applications. Because I am very familiar with the products and because I can get Victron at wholesale I plan to spec an all Victron system including batteries.

I am working on sizing of solar array and battery bank but I think I will end up with about (at least) 10kw of solar and at least 30-40 kwh of batteries and that much battery basically only gives 1 day of autonomy but I will use the grid like a backup generator and use the Victron system with their Energy Storage System (ESS) setup to use grid if necessary but always optimize self consumption and maintain zero export. Victron has some very flexible/configurable options for their ESS systems and I believe the inverters can act quickly enough (maybe using UPS mode?) to avoid passing through any voltage flucuations or other grid instability anomalies.

i need to consider what Energy Storage System topography and what Victron equipment is going to make the most sense. I was planning a 48v battery bank as it will be exclusively for the ESS system so seems that would be most efficient. To get split phase I plan to use a 230v inverter and a Victron autotransformer but I will also spec as many of my appliances as 240v as possible to keep the AT balanced as possible. I am thinking this is better than using two inverters to make split phase 120/240v but open to any thoughts on that.

So the main choice regarding overall topography is do I use a AC PV "grid tie" inverter (Fronius) on the output side of the Victron inverter or do I just use Victron MPPT controllers and put all PV into the DC side. With the later I stay virtually all Victron. I guess I can check the cost difference and go based on that but I am wondering about the performance difference or what relative advantages/disadvantages there are. I assume direct consumption off an AC PV inverter is technically more efficient than going through an MPPT and a DC to AC inverter so maybe that is the main difference. I guess I would have more total AC wattage available during daylight so I can also make a point of running certain heavy loads like the pool pump or dryer during daylight.

Thoughts?

OR

 

[FilterGuy]

I own a a marine electronics/electrical shop and we are a dealer for VIctron Energy but my Victron experience is limited to marine applications. Because I am very familiar with the products and because I can get Victron at wholesale I plan to spec an all Victron system including batteries.

1) I envy you!!!! I am a big fan of everything Victron.... except the cost!
2) The marine applications are a bit more complicated because of a combination of DC Loads and AC loads. Your application will be a simpler version of a large marine application.

To get split phase I plan to use a 230v inverter and a Victron autotransformer but I will also spec as many of my appliances as 240v as possible to keep the AT balanced as possible. I am thinking this is better than using two inverters to make split phase 120/240v but open to any thoughts on that.

There are pros and cons to the autotransformer. The big pro is that it tends to be a lot less sensitive to load imbalance between the two hot lines.
The con is that it is less efficient than two stacked inverters. If you are going to have plenty of PV and can afford to waste some energy, I would go with the autotransformer.

One other advantage to stacked inverters is that if one goes out, you can re-configure the remaining one and limp along on just 120V, till you get the other fixed.

So the main choice regarding overall topography is do I use a AC PV "grid tie" inverter (Fronius) on the output side of the Victron inverter or do I just use Victron MPPT controllers and put all PV into the DC side.

Unless the cost difference is huge, I would just put all the PV into the DC side.

 

[l00semarble]

Thank you for the reply.

I have thought about redundancy and there is something to be said about being able to limp with 1 leg of power if one Victron component fails vs. being totally dead in the water if one components fails. The system will be in remote area that UPS does not deliver. In fact getting a replacement would be a complicated matter with a lot of delivery cost.

In my draft schematics if inverter fails I can just go to grid which isn't a hardship other than paying a utility bill. If the AT fails I would have a problem. I could bypass it and have my 240v loads only which would not be very helpful because refrigeration, lights, receptacles are everyday survival things and are all 120v.

Going to two 5kw vs. 10kw Quattro+AT would increase my cost about 16% on those pieces. Noticable but not a deal breaker if the stacked configuration is better. But the AT does have advantages in balancing loads across the inverters and less copper needed for my run from solar shed to house.

Actually the 16% difference is about the cost of an AT. I could have a spare AT on hand for same price as doing system with two inverters. So many things to consider.

I like putting all PV into DC side as I can stay all Victron. There will be a lot of DC current moving around but I can size everything appropriately.

I also thought about putting one series string of panels on MPPT to DC and one series string on AC PV inverter. Kind of split the difference and do a little of both.

 

[Tecnodave]

Question...

In your layout #2 with the Fronious inverters how are you going to charge the batteries?

I do have some expereince with Victron but far more with Midnight, Magnasine, Outback, Schneider, etc.

It looks like you plan to do the AC coupling to the output of the Victron. I do not beleive that the Victron will charge the batteries from the inverter output? None of those that I mention above can do that.

The main transformer in most inverter/chargers is used for both functions...When inverting it cannot charge and when charging it cannot be inverting.......will be using grid pass through power when charging to provide AC grid to Fronious but the charger will be off on grid failure

Extensive experience in electrical engineering at G-E pretty good understanding of electronic systems

 

[l00semarble]

The Victron inverter/charger will allow excess AC watts made by PV inverter and not consumed by the house to "backflow" into the AC output to charge the batteries essentially reversing the process of inverting. In fact it can ebb and flow as PV output and loads change with the Victron sometimes inverting and sometimes charging.

Victron has a very flexible set of Energy Storage System (ESS) options which are very configurable including options to have grid available to use but no export to grid which is what I am hoping to set up.

1. ESS Introduction & Features

www.victronenergy.com

 

[Tecnodave]

So when the Victron is using the excess power developed by the Fronious to charge the batteries where does the Fronious get the AC power to sycronize to?

 

[l00semarble]

The invert function of the victron is necessary to start the system but once its started the victron will do what's necessary to maintain voltage on its output side either invert if necessary or allow back feed to charge if possible. As long as the voltage is there on the PV input of the PV inverter it thinks there's a grid present and will work normally.

I'm just regurgitating what I've learned in my research and through victron dealer training. I have not actually built a setup like this.

 

[Tecnodave]

OK, good explanation, Im strictly off grid. I do have grid power here but I rarely use it. I prefer to make all my own power from clean sources. Just personal preference. My local POCO will shut off power for very long periods for public safety, California’s PSPS program. Directly due to the fact that my local power company has done no high voltage maintaince for far too long creating wildfires at every windstorm resulting in loss of life in far too many instances.

The Camp fire killed at least a hundred directly due to a transmission line falling in a windstorm.

Ive had one power outage in over 20 years due to a Tiawan/Chinese inverter giving up after 10 years. Less than 10 minutes Im back up on the other inverter.