Off Grid Equipment Replacement

[Near Reno Off-Grid]

Greetings. I purchased an off grid second home 10 years ago approx an hour out of Reno. The system was well constructed. However, we are having to run the generator now 2X per day in the cold season when we have the radiant floor heat on. I purchased the "Mobil Solar Power" guidebook to check to see if the system is sized correctly. It appears to be. What I really need is an expert to consult with on battery options as I fear the Rolls deep cells are nearing the end of life. Also, I would like to not to have to travel 400 miles every 30-45 days to water the batteries. While I do most things myself (registered civil engineer and not afraid to get my hands dirty), I would like to find someone who would work with me to make sure that the appropriate equipment is purchased and ultimately installed.

Will - I see clearly that you are not in the consulting business (I think your guidebook is fantastic!), but maybe able to point me in the right direction? Much appreciated. Gary

 

[E. Cho]

You have told us barely anything.

All the equipment you have and want and energy used needs to have all their numbers listed so the math can be done to see what all needs matching, power in to power out and storage capacity needed, basically.

You MUST do an energy audit using the spreadsheet found in this Forums Resource section. Look at some other threads where people ask for advice. No info provided makes advice difficult to give. More info is better and much faster for you to receive help. Making others keep asking you questions about your set up will have many lose interest or give up trying to help.

List your present energy production components, with names, models and their rated capacities. Eg: Solar panels, inverter, solar charge controller, fuses, generator size and fuel type, breakers, etc..

Maybe look at the Victron Cerbo monitoring equipment, which can monitor equipment and be controlled remotely via an internet connection. Cheaper than driving 400 miles.

Others will have more ideas.

 

[Rednecktek]

Also, I would like to not to have to travel 400 miles every 30-45 days to water the batteries.

I have the same problem with my camp. The Equalizing Charge timer should be changeable so my plan is to just up that to 180 days and don't bother with it boiling the batteries when it's not being used for 6+ months at a time. I'll top them off when I get there.

 

[MichaelK]

Have to agree with EC. Next to no information. Without meaningful information, no meaningful answers can be given. As an engineer, you should have intuitively understood that.

I have Rolls batteries also, and I find that I'm adding water to them quarterly, so expect to be there every three months instead of monthly.

Electric heat in winter has got to be the single worst application that can be applied to solar. Can your heating system be programed so it only comes on during daylight hours?

 

[Near Reno Off-Grid]

Thanks for the replies. I did not know that folks would want to help me with analysis. I appreciate that a bunch. My name is Gary Darling. I can be reached at gary@darlingh2o.com or (925) 382-4350.

Loads: I have a ton of information. I have tried to share an image from the Mate 3 of 3 days last December (did it attach?) so you can see how much the generator ran on those days which were both short days and not a high producer (maybe 3 hrs at 3Kwhrs and then much less). The radiant floor heat uses between 400 and 600W continuously to heat a 3000 sq ft, 4 zone home. It is a solar thermal system from Radiant Floor Co in Vermont with a Takagi flash heater back up. The other household load is typically 100W (refrigerator is high efficiency Samsung, small device charging and sparing use of lights which have all been changed to LED; and sparing use of microwave, hair dryers and dishwasher only when the sun is producing. The auto gen start is set at 47.6V 2 min or 4.8V 24 hrs. With these setting I find that he state of charge never drops below 80% (is that too conservative?). The house went through a foreclosure 10 yrs ago. I have reason to believe the batteries were not filled during several months. I have since watered every 30 to 45 days. Again, I have lots of data and pictures, but it is hard to convey that in this space.

System: Installed in 2007, 4.9kW solar system consisting of 28 X 175 watt Sharp panels mounted on 3 poles, 2 Outback inverters (VFX3648), charge controllers (MX60) , Flexnet DC, and 12 Rolls 4V batteries Deep Cycle Solar Series 5000 (4 KS 21PS) in series with a 20 hr capacity of 1104 CAP/AH at a SP of 1.265 (note: I have tracked the SP over time and it has degraded to 1.2 on some cells). Back-up generator now has 3000 hrs and is an Onan 12kW with a Honda engine.

Here is another screen share from Dec 3, 2021 where we did not get much sun and you can see the generator automatically turned on around 4 am and ran for 2.5 hrs. At 6 gal of propane/hr that can add up.

 

[MichaelK]

Those were very nice batteries! I have the 4CS17P version myself. I believe you don't have adequate solar to charge those batteries at the rate that Rolls recommends. Rolls recommends charging at 1/8th of C, or 13%, so with 1104Ah that comes out to be 1104Ah X 0.13C X 50V charging X 1.175fudgefactor = 8432W, or almost double what you have now. Since you usually don't see more then 85% of total output from panels, I use a fudgefactor (an engineer could call it the efficiency conversion factor) of 1.175 (reciprocal of 85%)

For comparision, my battery is 568Ah, about 1/2 your size, and I am charging with 4500W of panels. I haven't had to run a generator in three years now. So, the very first thing I would do is add an additional 3000-4000W of solar to bump your charging rate up to what Rolls expects. You'll have to add another charge controller to handle the extra amps.

Look on Craigslist to find local deals on panels. Buy local instead of having them shipped. Here is a seller in Sparks that has prices less than 1$/W

265W Jinko Poly Solar Panel $165 - general for sale - by owner

Don't get stuck without power in time of need. Get reliable clean energy. Several panels in stock. Brand new, Jinko never used, 265W 60 cell polycrystalline solar panels for sale. Great for off grid...

reno.craigslist.org

In the short-term, I'd recommend starting the generator in the wee morning hours, and get the batteries mostly charged by sunrise, then let solar top them off, then equilize for a couple of hours to try to bring those low cells back up. Maybe twice over a weekend. Then check the SG again and see if you've improved?

Don't know if that will work though, because it appears to me that they've barely been getting enough charge for years now.

You can install even more solar if you put them on rotating mounts that you can point East or West. You can maximize charging by having arrays facing in different directions so you dampen down the noon peak, but broaden the overall solar curve.

 

[OzSolar]

The radiant floor heat uses between 400 and 600W continuously to heat a 3000 sq ft, 4 zone home. It is a solar thermal system from Radiant Floor Co in Vermont with a Takagi flash heater back up

Is the 400 to 600 watt continuous just the controls and pumps? If the Takagi is the back up what is the main heat source?

 

[OzSolar]

12 Rolls 4V batteries Deep Cycle Solar Series 5000 (4 KS 21PS) in series with a 20 hr capacity of 1104 CAP/AH at a SP of 1.265 (note: I have tracked the SP over time and it has degraded to 1.2 on some cells)

1.2 as in 1.200? That's ~50% state of charge. You ~may~ have some serious equalizing to do.

I switched over to refractometer for measuring SG and really like it.

Here's a link to the Rolls Battery Manual in case you don't have it. Lot's to be gathered there.

 

[Near Reno Off-Grid]

Solar thermal heat source comes from the Sunda Seido 1-5-16 evacuated tubes as shown in the picture.

 

[MichaelK]

Is the home kept just above freezing in winter, or at room temp for any weekly visit? Using that much propane to keep the house powered seems like it might be better utilized being burned directly instead of using it to power the generator. Assuming you rate of conversion is only ~1/3rd, I'd expect you to be able to heat the home 3 times as much by just burning the propane inside?

With a home left just above freezing to keep the pipes intact, I'd expect your daily electrical demands to drop greatly, to maybe only 2-3kWh of power per day, depending on how much electrical stuff is left on. Your arrays should be able to make that much power even in the rain.

 

[OzSolar]

Solar thermal heat source comes from the Sunda Seido 1-5-16 evacuated tubes as shown in the picture.

View attachment 100493

Hopefully that shading doesn't start until after 4 pm.

It looks like a few evac tubes have lost thier vacuum. If so they actually could be taking heat out of your system so they need replaced or removed and capped off if you can't get replacements. Not familiar with the specifics of that as I haven't worked on solar hot water for a long time.

If your radiant in floor system really is pulling 400-600 watts just for the controls and pumps 24/7 something is amiss. I have 6,000 ft2 of house and shop combined on my radiant in floor system. It draws a few watts when nothing is pumping and right at 300 watts when all 5 zones are calling. That includes the pump to my boiler and the injection pump for my outdoor reset.