Looking for battery back-up on GT system

Re: Looking for battery back-up on GT system

Thanks all for your constructive comments so far.
I admit I am an idiosyncratic scientist and do things that are not mainstream and against common accepted wisdom and dogma (thats why I'm a scientist)!

SO to clarify for some who have raised emminently reasonable concerns and criticisms:

1. I want to have a back up capability. Its not really feasible with a fixed installed generator. Our town only allows LPG tanks, and due to my small irregular property lines ad neighbors I'd never get permission for one or both. For insuarance reasons I can't store more than a few gallons of gas for a small portable generator on teh property. (Believe it or not I had to fight with our town to put up PV on myback roof!). So if I want resilience in teh case of grid down and interruption in fuel supplies - that leaves me with teh admittedly expensive adn less than perfect battery back with ?second inverter option. Swapping out the fronius for the Outback Radian and rewiring is an interesting thought... I know this may get expensive, but as I am pessimistic about our political class on either side, and that our savings will be eventually vaporized in inflation/hyperinflation, I think its at least reasonable to plow money into a long lived back up system that protects us in case of catastrophic events, and in the event it all works out and I'm just a hopeless pessimist....adds to the resale value of the house.
2. I chose parallel PV design due to significant shade issues from east and west. Instead of microinverters I chose Eiq vBoost which is a DC-DC converter. Like Enphase, they have on line single panel monitoring, but provide much more data including historical data, Pi, Po, Vi, Vo, Ii, Io, and temperature ! You can literally scan the 24 hour profile of the whole array or any individual panel in real time or historically. Looking at the data I can really see how this has benefited me. I achieve the full theorectical 80% yield. I'd guess a set of two or three serial strings wouldnt have gotten better than 30%. Anyone interested, PM me and I'll send you the link to see the data. Interestingly, they are so busy they don't sell residential anymore - only commercial installs. So I'm lucky (I also finagled....).
3. Solar thermal: I'm a big believer in that. THe comments here are spot on. A dedicated panel is by far the most efficient way to go. Unfortunately we had limited roof space and esthetically mixing the panels wouldnt have looked nice either. I chose admittedly a new technology - Sundrum (Sundrumsolar.com). I have no commercial link to the manufacturer or owner. After seeing his system in actuality I decided to take THE RISK of trying it. He claims 50% solar yield as solar thermal energy which translates to a stagnation temp maxof 130F in summer, and probably is on the order of 70-90F in winter. Clearly this is not as efficient as dedicated ST - BUT you dont waste space. You go get BTUs that are useful, but you have to supplement them. Again being the iconclast scientist that I am I have gambled and oversized my system and installed 28 Sundrum SDM 100 panels underneath my 40 Sanyos. SInce I have my Eiq vBoost monitoring - I will be able to monitor the actual advantage (if any of a PV panel with or without the SUndrum. THeoretically it should cool the panels and increase output. If it does that - I will have on site proof. I have seen SUndrum installations of smaller systems and they seem to work well. The owner tells me he has installaed large systems where hot water demand is substantial - ie. hotels, water distillation plants etc. SO the technology while new is not entirely untested. I admit I am taking a gamble here. I sort of view this whole experience as a grand science project and hope to share the info with others so they can learn and learn from my mistakes...

Re: Looking for battery back-up on GT system

Inetdog-
everything you say is correct. I accept that. Accepting that a battery back up is the most expensive (least cost effective) option, what do I need to know to get it done?
Evidently that persistence on my part despite my acknowledging this reality, was not appreciated by some. Since I know you inhabit both spaces, hopefully you saw the exchanges.
In any case its clear this is a helpful community where disagreement doesn't have to be disagreeable. Thanks and feel free to criticize anything I might say or suggest. I've certainly learned alot, but am the first to admit I can and do get things wrong. Providing a good dose of reality is always a good thing.

Re: Looking for battery back-up on GT system

Inetdog, 'Coot and others with experience-
it seems more evident to me that performing ac-coupling will be difficult and expensive (at best) given my present fronius GTI. Perhaps the best option would be to bite the bullet and go with a proven integrated solution such as SunnyBoy8000 with the Sunny Island 5048, and sell the fronius despite it being but a few months old. Unfortunately I got bad advice that the fronius would be compatible with battery back up when I originally ordered it. Does anyone know how noisy the SunnyBoy is compared to the Fronius? Its in my wife's workshop so that is a consideration.
How much energy does one lose in terms of efficiency when you combine a second battery connected inverter when the grid is connected?
Thanks.

Re: Looking for battery back-up on GT system

Cariboocoot wrote: »

This is where it gets complicated.
If your second, battery-based inverter is a hybrid type (that is also able to feed the grid) there is no appreciable efficiency difference between half your GT power coming from it and half coming from a standard (no battery) GT inverter. (Somebody is bound to jump in here and contradict me over a few % efficiency. :roll: )
If your second inverter is for stand-by power only (doesn't or can't feed the grid) it will not actually be connected when the grid is up. It will take AC IN from the grid and keep the batteries charged, but otherwise just sit there doing nothing.
This is why I suggested replacing the Fronius with the Radian. If you have to buy a second inverter anyway, you might as well have it doing something all the time.

Not sure how loud any of them are. Loudness is somewhat subjective; some people may hear and object to the inevitable transformer hum. For others it will just fade into the background like so much white noise.

Thanks 'Coot.
Two comments/questions:
1) The site for batteries (in our crawl space) is about 20-25 feet from where the Fronius now sits. Alternatives would be have the Radian sit next to the batteries (wall available), but then DC from the PV would need to go that 20-25ft. If it replaced the Fronius, it would be next to the breaker and subpanel, but DC from the batteries would have to go back that same 20-25 feet. DOes that change the financial calculation substantially (due to the cost of heavy guage wire) as compared to buying a SunnyBoy/Sunny Island and doing ac coupling?
2) I guess if I did replace teh Fronius for Radian I would be losing 6% of yield as the CEC is 96 vs 90%. SMA SB/SI are both rated at 96%.

Re: Looking for battery back-up on GT system

SolaRevolution wrote: »

I have AC coupled a Fronius IG into an Outback dual FX system in an off-grid situation. It works but not ideally. This system operates well as a whole because there is also a DC coupled PV array/MPPT charge controller to provide regulated charging. (I do not, as yet have any experience with the Outback Radian.)

The Fronius/dual FX system would probably work quite well as a grid-tie while the grid is available. The main trouble comes when the grid is down, the batteries reach absorption voltage and there is no grid to back-feed into. If you don't have an adequate PWM diversion load you do not have regulated battery charging. An "adequate" PWM diversion load would be capable of handling 100% of the Fronius' output and the diversion controller would need to be capable of handling 125% of the Fronius' output. I don't know of any readily available product that can handle this. Of course there is the temptation to use multiple smaller controller/ load combinations but in my experience there is great value in keeping things as simple as possible. (I may be talking to the wrong person on this point.;))

Another problem which has shown up is that many surge loads (garage door opener, motor driven tools, etc...) cause the AC output power of the dual FX system to fall out of the allowable specs of the Fronius which causes it to disconnect until the power remains acceptable for 5 minutes. This same 5 minute "grid monitoring" time is required by the Fronius if it is "regulated" by any frequency shifting of a battery based inverter.

This would be a good reason to consider the SMA Sunny Island system with SMA Sunny Boy inverters. The SBs can be programmed to throttle down rather than disconnect thus providing full multi-stage battery charging. If you wish to make use of "diversion" loads this can still be done with auxiliary relays to switch some desired AC loads. (Some homework would be required to figgure this out but I'm pretty sure it could be done with some finesse with the right settings and loads.)

It would be best to use dual Sunny Islands to have a 120/240 without the need for a transformer (24 hr phantom load). While the grid is available they will tend the batteries with programmable periodic boost charging and when the batteries are full they would enter "silent mode" and use relatively little energy (more homework) and make less noise. When in off-grid mode or while boost charging they do make a hum typical of most battery inverters. I'm not sure how the sound level might compare to a Fronius IG Plus.

Too bad for your solar thermal system your Sanyos are not the transparent ones.


-Alex Aragon

Thanks Everyone for your extremely helpful suggestions!

An installer acquintance of mine is very partial to Apollo Solar battery back up systems, albeit not yet grid interactive. He was wondering if we could link that via ac coupling to the Fronius. Any comments?

Alex - while I plead guilty to complixifying things (must be the integrative physiologist in me coming out), I do agree there are times when simpler is better and less likely to fail. Thus all the recent suggestiosn are great for me to think about. As to the Sundrum panels, the manufacturer claims about 40% of solar yield as thermal capture, and teh panels are SRCC certified. I have seen a couple of working systems and they clearly do capture thermal energy. They sit flat against the back of the PV panel and are essentially glorified aluminum heat sinks (The inventer was a CPU cooling expert in the computer industry!). On a sunny day, my Eiq vBoost DCDC converters monitor everything going on under/in the PV panels. THey also monitor temp and they routinely show temps going up to 65C on a hot sunny day. When we have cooler days and intermittent clouds, I can see output jump easily 10% based on PV panel temps of 35C. Thus if the SUndrums cool the PV panels by 30C I would hope to see that difference consistently. Well only time will tell once I have the data. If this group is not familiar with the DCDC product (Eiq), feel free to PM and I'll send you a link to my account so you can see for yourself how neat the data look. Much superior in my opinion to that from Enphase. It has just one little technical bug which is that the Po algorithm is faulty and gives readings greater than Pi. I assume being a small company they haven't fixed it yet. Their "new" monitoring system which is fixed, doesn't show the individual panel data, thus in my opinion is much less useful and interesting. Other data look very consistent with reality, and Fronius production. Temps certainly consistent with independent monitoring.

Re: Looking for battery back-up on GT system

Thanks TechnTrak. I already have a kill a watt meter, and have used it selectively to find phantom loads. Haven't done yet as you suggested, but very sensible suggestion.