Old solar house with Walmart and "other" batteries..

Re: Old solar house with Walmart and "other" batteries..

Welcome to the forum CB.

First, do not spend anymore money until you have nailed down your needs (other than cleaning up the mess and making it safe).

CBear42 wrote: »

Hi all -

I purchased an off-grid home two years ago. I haven't been able to live there because the battery bank was discovered to be a disaster after I moved in. They had used a hodge-podge of Walmart and other batteries, deep-discharged them to 0% (because 'that's what you're supposed to do"), let them dry out for a year while they sold the house, etc. They didn't know where the charge controller was and the inverter is an antique. They burned through multiple generators every year. There is an operating solar panel bank of 6 80w panels that seem to be the only thing worth salvaging.

Yea, there is not much left to salvage... Even the current 480 watts of solar array is, probably, not worth salvaging (at best, perhaps you can add it to your system with a decent controller, but I would not go out of my way to do that just yet).

All of this is my own fault. I bought stupidly without educating myself. Lesson learned.

Been there, done that. :roll:

I have calculated my potential electric use (with a little growth room allowed) at approximately 200kwh per month. Refrigerator, on-demand hot water and stove/oven are all propane.

A 200 kWH per month system is fairly large for an off grid home (although, with today's prices, it has never been more affordable). I would suggest seeing if you can adjust your needs (i.e., conservation, new energy star appliances, insulation, etc.) towards 100 kWH per month (at least for a starting point). You are in an area that does not get large amounts of sun (especially in winter), so keeping energy use to a minimum is going to save you lots of money.

Note, energy usage is a highly personal choice--If you need more energy, more than happy to help the best we can.

Trying to size my battery bank is the biggest headache so far. From what I have read, I want 12 volt 105 AmpHour AGM lead acid batteries,

The "ideal" lead acid battery is AGM--But they tend to cost 2x as much and may not last as long as other types of lead acid batteries.

In any case, I highly recommend that you get large AH capacity batteries (or cells) so that you do not need to parallel strings of batteries (or two to three parallel strings maximum). Anyway, more on battery bank design later.

A couple of Battery FAQs:

Deep Cycle Battery FAQ
www.batteryfaq.org

a Xantrex 2500 Pure Sine Power Inverter, a 3 stage 40 amp Charge Controller, and a good monitoring tool. I need to have the batteries accessible - the house is in very northern New York state - so cold is an issue. Therefore, sealed AGM batteries were recommended to me. I realize that I am probably under-paneled, but it may need to be that way for a while...(I'm working in Europe to make enough to get this puppy into a liveable state!).

Instead of picking hardware, lets look at a design from the bottom up. Say you need 200 kWH per month, fixed array near Massena NY, and some basic rules of thumb for initial design (deratings, flooded cell battery bank, AC inverter, charge during day, power usage at night--i.e., typical worst case assumptions).

For a battery bank, 200 kWH per month (assume 48 volt battery bank), 1-3 days of no sun (use 2 days here), 50% maximum planned discharge (longer battery life), 85% efficient inverter, we get:

• 200,000 WH * 1/30 days per month * 1/48 volt battery bank * 2 days no sun * 1/0.50 max discharge * 1/0.85 inverter eff = 654 AH @ 48 volt battery bank

For batteries, perhaps 16x Trojan L16RE-B 370 AH Deep Cycle Battery (~$5,600 plus shipping and handling and taxes) or 2x Crown Industrial Battery - 24 Volts, 745 Amp-hours (~$7,000 forklift type)

Inverter wise, you need to look at your peak (starting) loads and average loads... With a ~600 AH 48 volt battery bank, you are looking at a practical maximum of 6kW (6,000 watts) of inverter. Note, there are many Inverter/Chargers out there too--The inverter/chargers tend to work very nicely with genset (are usually power factor corrected--again more later as we discuss). A Xantrex (Schneider) or Magnum 48 VDC 4kW to 6kW True Sine Wave Inverter/Charger will run around $2,200 to $3,000 plus.

Solar array sizing... Massena NY, using PV Watts with 0.52 system derating, fixed 1kWatt array tilted to latitude (probably near vertical in winter if you have snow):

"Station Identification"
"City:","Massena"
"State:","New_York"
"Lat (deg N):", 44.93
"Long (deg W):", 74.85
"Elev (m): ", 63
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 44.9"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:","14.5 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 3.13, 53, 7.69
2, 4.28, 64, 9.28
3, 4.97, 81, 11.75
4, 5.12, 76, 11.02
5, 5.02, 74, 10.73
6, 5.55, 76, 11.02
7, 5.55, 78, 11.31
8, 5.23, 73, 10.59
9, 4.44, 63, 9.13
10, 3.67, 55, 7.98
11, 2.44, 36, 5.22
12, 2.32, 37, 5.37
"Year", 4.31, 766, 111.07

My suggested starting point is assume that 3 months of the year, you will need generator backup, the 4th lowest month for your area is October at 3.67 Hours of Sun per day or ~55 kWH per month per 1kW of solar panels. For 200 kWH per month:

• 200 kWH per month * 1/55 kWH per month per 1kW of panels = 3.636 kW (3636 Watts) or solar array for 9 months of year without generator use

Of course, you can pick different numbers for your needs (perhaps you don't use 200kWH/month in winter, or don't need 270 kWH per month in summer--your choice).

A 3,636 Watt array will output, on average, a maximum of:

• 3,636 Watts * 0.77 panel+solar charger derating * 1/59 volts batt charging = ~47 Amps

There are a many 60+ amp solar charge controllers, look at Midnite (Classic), MorningStar (TS MPPT family), Xantrex, and Outback (FM80)... Note, I am suggesting a 48 volt battery bank and MPPT type charge controllers. Not cheap ($500-$600 or so), but for your requested size system, usually the best functional choice overall.

Two questions:
1. How many batteries do I need at a minimum to get myself going? (I am buying a new Generac GP7500 Electric Start Portable Generator as backup - but would prefer not to burn it out like my predecessors did.)

Before purchasing a genest, do some more research (and size your PV system)... 7.5kW is not a bad size (oversizing genset will cost you a lot in fuel), but there are only a few 1,800 RPM generators these days that are even warranted for off-grid home use (and many of the newer gensets do not seem to last long--Generac has some good and some not so good units--from what I have read). Have you picked a fuel (propane, diesel, gasoline?). Also, Generator Fires are not uncommon--Recommend keeping generator and fuel supply separate from home/battery/solar array shed. Battery bank safety is important too (appropriate sized wiring/fuses or breakers where needed, etc.).

It is difficult to recommend a minimum bank and then adding batteries later (I don't like paralleling batteries if you do not have too, and adding new batteries to an old battery bank can cause charging/overall battery life issues). If you don't know what you want... Get "cheap" flooded cell lead acid batteries that will last you 3-6 years, then replace them with a new set (frequently we call these training batteries because people do frequently kill their first battery set (over discharging, improper watering, over charging, family member left pump/hair drier on and left home, etc.).

2. Can I add other panels to the existing 80w panels without damage to the existing panels. Or do I need to replace them all at the same time?

You can add more panels--but frequently the Mix and Matching of old+new panels is difficult. The "modern" 200+ watt panels do not usually "mix" well with older/smaller panels (unless you use a second charge controllers for the old panels and parallel with new charge controller to battery bank). In your case, you are saving about $480 in panels, adding another charge controller+wiring... May not be worth it.

Battery Monitors (Victron, another good brand), I highly recommend (not perfect, but they do a good job of letting you know what is happening with battery bank).

I am sure I've forgotten something here .. please let me know if you need any other info.

Inverter FAQs:

All About Inverters
Choosing an inverter for water pumping

-Bill

Re: Old solar house with Walmart and "other" batteries..

Kill-a-Watt meter for 120 VAC 15 amp appliances (or equivalent).

-Bill