Gradually Going Off-Grid (Battery Backup and Solar)

[Mark (Basspig) Weiss]

With electric bills approaching $800 monthly, and with the frequent long duration outages after a storm, I decided to supplement my generator with LifePo4 battery backup (starting out with 14kWh, 16 280 Ah cells) and a 6kW/18kW inverter so that we can keep the electricity on overnight when the generator is off.

I ordered 40 240W solar panels (which would have been here today on two palettes, except for the snow happening) and plan to charge the batteries with solar.

Future expansion plans if this works out are to triple the battery storage and get the larger 18kW/54kW inverter, which should have us close to mains quality power.

Plan in the spring is to deploy the solar panels at all sunny locations on the property and wire them into combiners and an MPPT solar charger.

I did some preliminary testing, and the batteries and inverter hold most of the smaller loads and some of the bigger ones fairly well. The submersible well pump has a high starting current of 86 amperes, but this handles it well. I even powered up the 20kW sound system, but with no signal, just to see what the load factor looks like. That got the load up to 45% of the inverter, along with all the computers and studio equipment in the house. Ran for about 90 minutes and only lowered the battery voltage from 54 volts to 52.2 volts in that time. Overnight with just the fridge and furnace, should have no problem going 14 hours.

Eventually, I hope to have enough solar input to avoid use of the generator at all.

 

[Mark (Basspig) Weiss]

Update in May:
Solar array #1 has been running for 3 weeks. We've been able to transfer to the inverter from about 11am to 8pm most days. With less use of electric stove, some days I get to midnight and still have 30% battery left.

This week, I ordered 28kWh more LifePo4 batteries and a metal cabinet to house the batteries from Treeline Power Systems.

Array #2 is under construction this week. I just brought in about 25 yrds of fill to make a level area for the next array.

The final step will be upgrading to the 18kW inverter, which will enable us to run normally as we do on mains power.

During the day, the solar panels charge the batteries. Our generator is hooked into the inverter, so if it is running, it powers the battery charger that is in the inverter.

The only issue I have at the moment is RFI, tons of it. HF band is unusable with 30 over S9 buzz. Even 100' of underground cable has enough hash on it where it connects to panels to act as antenna.




Footings in place for array #2, which will catch the morning til 1pm sun.

 

[Alrainbow]

Does your panel array move to stay aligned to sun automatically ?
if I may ask how much have you invested so far
not labor just all supplies. ? I’m not being crude I’m a contractor and curious
down south I have a 22kw generator due to frequent power outages
but the electric bill is about 200 a month with 4000 sq foot living space
3 HVAC units heat pumps with electric aux heat coils
the best improvement was getting propane for gas hot water lowered bill by 70 per month
gen is gas powered too.
the gen can do all but does have a load shed panel just in case
can you use a load shed panel on a system like yours ?

 

[BlueFox]

I have had solar for about ten years with no issues. Power is stable here so I haven’t given backup power much thought. Baring a major earthquake knocking out power for weeks I am pretty content with the current setup.

 

[Mark (Basspig) Weiss]

No, these are fixed arrays. I've built the frames with lumber and they rest on blocks.
This system is off-grid. I shut off the main breaker and then run off the inverter. The inverter is backed up by a generator. Our electric bill started to top $700 monthly two years ago. Eversource is getting another big rate increase this year, so it will be unaffordable for many folks soon.

I've got $11K invested in 42kWh of Lifepo4 batteries, BMS'es and a battery cabinet.
Another $2000 in used solar panels (40 240W panels) from Santan Solar.
$1100 in a 6kW pure sinewave inverter. About to spring $3900 on the 18kW model after I've finished upgrading the battery bank. About $500 invested in copper wire from panels to house.
In the photo below, the array on the right was built a month ago and the array on the left is under construction. The one on the left will get the morning to early afternoon sun, while the one on the right starts to produce peak power from 11am to about 4:30pm. One array maintains the battery voltage with baseline loads, that being four computers, my recording studio gear, intermittent use of well pump, and light cooking during daylight hours.
The additional panel should give us enough juice to charge the bigger battery bank and give us 30 hours of battery power.

 

[Alrainbow]

So a total minus gen is 15k ? not bad at all really
top quality batteries
I use Lipo for my rc stuff
your batteries are better and needed for deep cycle needs.
ty for your reply

 

[Mark (Basspig) Weiss]

Counting every nut, bolt, copper wire and a third solar panel array installed in late June, we are at $22K now. Most of it financed with Paypal credit.

Here's the current state of it:

 

[Alrainbow]

A question do the panels have heaters ? how do you deal with snow and ice ?
explain your home a bit in details
heat type and hvac
hot water type
gen set fuel
what is the Avg kWh needed to keep things running
and what’s max needed compared to your supply of batteries
I’m not picking I’m very interested in this

 

[Mark (Basspig) Weiss]

A question do the panels have heaters ? how do you deal with snow and ice ?
explain your home a bit in details
heat type and hvac
hot water type
gen set fuel
what is the Avg kWh needed to keep things running
and what’s max needed compared to your supply of batteries
I’m not picking I’m very interested in this

All excellent questions!
We're all oil heat with hydronic heating. Water heater is new. The old one finally ruptured after 17 years. Burner on that thing was over 28 years old. I found out it was using more power than both our A/C units combined. The ignitor was running full time and pulling 750W. I replaced the tank and burner last month with a Carlin that uses far less electricity with electronic ignitor that shuts off after 30 seconds. Takes only 3 minutes to heat the water now, as opposed to 9-10 minutes for old heater/tank.
HVAC: downstairs is 18000 BTU Mr Cool DiY minisplit. Upstairs is a new LG dual inverter A/C. Each take around 250W running on their quiet modes. A bit more when it's very hot outside.
Generator (not used) is a Northstar 13000, V-twin gas engine.
Baseline load is around 2.5kW day, just under 1kW overnight.
Intermittent loads with high surge, well pump.
When it's sunny and hot outside and A/C is in use, our 42kWh battery bank (LifePo4) will deplete to around 35% by morning, if it charged to 100% the previous afternoon.
On cooler dry days with no A/C, we end up with 69% battery by morning and hit 100% by 12:40pm.
The middle array I have no stats for as it's internal MPPT charger in the inverter. I only have an ammeter and volt meter that tells me the instantaneous and cumulative kWh, which I have to log on paper manually. That center array typically makes a kWh more than the East facing array.

This inverter setup with a 54kW surge for 20 seconds capacity handled my 20kW sound system playing at high volume levels quite easily. It's about the same as grid power in terms of voltage regulation for big loads.
BTW, one hour of high volume listening used 2.25kWh of electricity.

Here is the graph for one of the 4800W arrays, this one is south facing and you can see that it stopped charging when the batteries hit 100% at 12:40 today:



East facing array: