Battery solar charging system for a 2KW home as backup

Re: Battery solar charging system for a 2KW home as backup

More or less--Identify loads (typically smaller ones) that you critically need at any time or 24x7 (always on power) per day... That would be some LED/CFL lighting, laptop computer, cell phone charger, battery charger (flashlight/radio batteries), perhaps a small water pump (if you have a well or storage tank) and such...

Get 2-4 6 volt golf cart batteries, a smallish MorningStar TSW 300 watt 12 VDC Inverter (300 watts/600 watts for 10 minutes, remote on/off, "search mode" for low power standby). Get a 20-40 amp or so AC battery charger (grid or generator), and a Honda eu2000i (1,600 watt) or Honda eu1000i (900 watt) inverter/generator (these use very little gasoline to run your loads--400 watts will run ~9 hours per gallon; 1,600 watts will run about 4 hours per 1.1 gallons of gas--Also, they can be connected to a 5 gallon fuel container so you have several days of fuel without refueling the small internal gas tank--of course, you need to watch oil levels).

You can get a larger genset--But storing fuel and trying to find fuel for a generator that may consume 1/2 to 1 gallon of fuel per hour to power your whole home can become a big issue (12-24 gallons per day vs 1-3 gallons per day for a smaller Honda genset).

So, say you want 4x 6 volt 220 AH "golf cart" type batteries (cheap, plentiful--there are better, but for a start and learning without dumping a heck of a lot of money--a good way to gain experience without emptying your wallet).

Lets say you choose 4x 6 volt 220 AH batteries (series/parallel connected for a 12 volt @ 440 AH battery bank). The recommended solar array would be around 5% to 13% of battery capacity (you can go to ~25% charge rate--But not usually recommended unless you have special needs):

• 14.5 volts charging * 440 AH battery bank * 1/0.77 panel+controller derating * 0.05 rate of charge = 414 Watt array minimum
• 14.5 volts charging * 440 AH battery bank * 1/0.77 panel+controller derating * 0.10 rate of charge = 829 Watt array nominal
• 14.5 volts charging * 440 AH battery bank * 1/0.77 panel+controller derating * 0.13 rate of charge = 1,077 Watt array "cost effective maximum"

The daily power usage from the battery bank would be 1-3 days of storage and 50% maximum discharge. A good sized system, lets say 2 days of storage and 50% maximum discharge, or 25% discharge per day:

• 12 volts * 440 AH * 0.85 eff inverter * 0.25 discharge = 1,122 Watt*Hours per day of 120 VAC power (estimate)

To make things easy, say you are in Atlantic City NJ, using PV Watts with a 1kW array (simple round numbers), fixed array, and 0.52 end to end system efficiency would be:

"Station Identification"
"City:","Atlantic_City"
"State:","New_Jersey"
"Lat (deg N):", 39.45
"Long (deg W):", 74.57
"Elev (m): ", 20
"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:"," 39.5"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:","11.2 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 3.61, 59, 6.61
2, 4.20, 62, 6.94
3, 4.78, 74, 8.29
4, 5.23, 76, 8.51
5, 5.44, 80, 8.96
6, 5.48, 74, 8.29
7, 5.55, 77, 8.62
8, 5.41, 76, 8.51
9, 5.23, 73, 8.18
10, 4.60, 68, 7.62
11, 3.59, 54, 6.05
12, 3.17, 50, 5.60
"Year", 4.69, 824, 92.29

You would average around 50 to 80 kWH per month. At this time of year, November averages around 54 kWH per month or:

• 54,000 WH * 1/30 days per month = 1,800 WH per day (average) of 120 VAC...

Just to give you an idea, a standard energy star refrigerator uses around 1-2 kWH per day (1,000 - 2,000 WH per day).

For an AC battery charger, you can pick a "simple" AC charger for ~20 amps maximum for the Honda eu1000i generator, and the eu2000i would support 40 amp or larger... For a 440 AH battery bank with 5% to 13%/25% rate of charge, the suggested chargers would range:

• 440 AH * 0.05 rate of charge = 22 amps minimum
• 440 AH * 0.10 rate of charge = 44 amps nominal
• 440 AH * 0.13 rate of charge = 57 amps peak "cost effective"
• 440 AH * 0.25 rate of charge = 110 amps not to exceed (can overheat battery bank--remote battery temp sensor, etc. suggested)

If you are in the technical side of the "most efficient" battery charger/small genset combination, here is a good thread:

Question about battery charger selection with EU2000 generator.

There are some nice options for charge controllers in this size array... Simple and less expensive PWM type charge controllers--But you probably will end up with MPPT charge controllers which are ~3x as expensive as the PWM types. MPPT controllers are more flexible and support arrays with longer wire runs from array to battery shed. Looking at ~$150 to $500+ for charge controllers.

Note, the above system is really too small for powering a refrigerator--I would use a genset to power that (running the genset ~12 hours per day to keep cool/frozen). At the same time, the generator can also help recharge the battery bank (assuming you have bad weather and poor sun at the same time).

For a ~1,000 watt solar panel system + batteries + equipment--You are probably looking at $5k to $10k+ or so (you install, vs somebody else, bells and whistles, etc.)... (Honda eu2000i ~$1,100 or so over the Internet).

Some vendors (including our host--above links) can even configure/build/wire/test a system if you need it now, delivered.

The links I have provided are suggested starting points for good quality equipment. You are welcome to purchase anywhere--We support all.

I am a big believer in conservation and "balanced" system design. Too big of battery bank need a larger solar array+backup genset. A larger genset uses more fuel, etc...

-Bill