need some help

Welcome to the forum Bravo1,

When we size battery (and solar) powered systems, the dividing point between a "small" and a medium size system is the addition of a Refrigerator as a load.

For starting a single refrigerator, you would usually need a 1,200 to 1,500 Watt minimum AC inverter (and run some other lights, laptop, cell phone charger, etc.). A 3 kWatt inverter may be a bit larger than you would need or want... But I am not sure--As you say, a standard AC induction motor/compressor has a lot of starting surge--In the US (and already present in many non-US countries), are "inverter compressor" (or sometimes linear compressor) refrigerators that have almost no surge current on starting.

Getting a Kill-a-Watt type meter will help you measure/understand your daily energy needs (in Watt*Hours or kWatt*Hours--K-a-W meters do not measure surge current)--But lets start with assuming you have energy star rated refrigerator of moderate energy draw--Roughly 2 kWH per day for the fridge in hot weather, and 1 kWH per day for the freezer (these are conservative numbers, but if you have a large fridge with all of the bells and whistles, and it is getting a bit old--2 kWH per day is common).

For the battery bank, assume 24 volt battery bank and 2-2.5 kWatt inverter, 2 days of battery storage, and 50% maximum discharge. The battery bank would be:

• 3,000 WH per day * 2 days * 1/0.50 maximum discharge * 1/0.85 AC inverter eff * 1/24 volt batter bank = 588 AH @ 24 volt battery bank

Do not use "marine" batteries... Use deep cycle batteries. Marine batteries will not last very many deep cycles.

Just to give you an idea of how big of battery bank that is--4x golf cart batteries (6 volt @ 200 AH) in series x 3 parallel strings gives you a 600 AH @ 24 volt battery bank (12x G.C. Batteries total). While you can build a battery bank out of 3 parallel strings--I would suggest you get larger AH rated batteries and try to do one string or two parallel strings... It is a pain to check / water 36 cells and all of the parallel battery strings.

Solar panels--You need around 5% to 13% rate of charge--5% is good for a weekend/seasonal system--10% or larger for a full time off grid system:

• 600 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 1,130 Watt array minimum
  
• 600 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 2,260 Watt array nominal
  
• 600 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 2,938 Watt array "cost effective" maximum

And then there is sizing the array based on your load... If you have ice storms/winter outages--Sizing the array for no genset and average weather:
http://solarelectricityhandbook.com/solar-irradiance.html

Pittsburgh
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 35° angle from vertical:
(Optimal winter settings)

Jan	Feb	Mar	Apr	May	Jun
2.98	3.49	3.83	4.20	4.07	4.32
Jul	Aug	Sep	Oct	Nov	Dec
4.40	4.38	4.45	4.13	2.86	2.59

So, if you want 3,000 WH per day for an average December (2.59 hours of sun per day):

• 3,000 WH * 1/0.52 system eff * 1/2.59 Hours of sun (ave Dec day) = 2,228 Watt array minimum
  

That is not a small solar array--That is 10 of the "large" solar panels (~225 watt, takes two people to move around safely each panel) or ~20x ~120 Watt panels (that you can move by yourself)--Plus you need to mount the panels so that they do not get blown over in a wind storm/buried by snow, etc (and they do not get hit by rocks from a lawn mower, kids, and such).

Anyway--As you can see, if I was to "guess" your power needs and design a nominally worst case system that can keep your fridige+freezer running 24 per day without a genset (deep dark winter storm, you will need a genset or shed loads--Solar panels do not generate a useful amount of power in dark weather).

If your outages are short/few times a year--A genset (natural gas/propane available?) is usually a better backup system (unless you are in an apartment/condo or other place you cannot use a genset). Solar Power + Battery Bank is usually better where there is no utility power and the power needs are not that great (lots of conservation).

The system above is enough to run a full time off grid home (LED lighting, fridge, washer, well pump, TV, laptop, cell charger--A very conservation minded home) and the system I have suggested above, is probably way over kill for your needs (or at least your expectations).

Some of your needs may be different--For example, if it is winter power outages, a freezer in a cold space will use much less power than in a sunny kitchen during summer.

Anyway--An initial stab at your problem statement. Questions and comments?

-Bill

With 10-20 gallons of stored gasoline (and fuel stabilizer, change 1-2 times per year) for a small/quiet Honda eu2000i--Run during the day, and get 2-4 golf cart batteries and a small AC inverter (300 Watt 12 volt TSW inverter) to run LED lighting, cell phone charger, laptop) at night (when the genset is not running).

The fuel should last you 5-10 days. And the inverter gives you power 24x7 for the small loads. 2 or 4 golf cart batteries:

• 2 * 6 volt * 220 AH golf cart batteries * 0.85 * 1/2 days storage * 0.50 max discharge = 561 WH per day
• 4 * 6 volt * 220 AH golf cart batteries * 0.85 * 1/2 days storage * 0.50 max discharge = 1,122 WH per day

5% to 13% rate of charge--Choose 10% as a good full time off grid power system:

• 2 * 7.25 volt charging * 220 AH golf cart batteries * 1/0.77 panel+controller derating * 0.10 rate of charge = 414 Watt array
  
• 4 * 7.25 volt charging * 220 AH golf cart batteries * 1/0.77 panel+controller derating * 0.10 rate of charge = 829 Watt array

Assume February at 3.49 hours of sun per day, 9+ months of the year as the break even month (generator for darker days when needed):

• 414 Watt array * 0.52 system eff * 3.49 hours of sun per day = 751 WH per day
  
• 829 Watt array * 0.52 system eff * 3.49 hours of sun per day =1,504 WH per day
  

Replace the batteries every 3-5 years. Get yourself a Hydrometer (to monitor battery health) and a DC Current Clamp DMM (Digital Multi Meter) for maintenance/debugging.

Get an ~20-40 amp Iota Battery charger with optional smart charger module (for bad weather AC line/Genset charging).

You can use 4-8x ~140 Watt (Vmp~18 volt) solar panels (not cheap, but smaller panels, easier to move around and ship) plus inexpensive PWM solar charge controller. Or get 2-4 ~220 Watt (Vmp~30 volts) panels (cheaper) plus not cheap MPPT type solar charge controller.

Solar panels should last you ~20+ years easily. Electronics (charge controllers, AC inverter) should last around 10+ years. Honda should last 2,000 to ~6,000 hours with recommended oil changes.

Do you have a well pump? Many AC well pumps will take a 4 kW minimum inverter (or genset) to run (unless you go with a "solar friendly well pump)... Run a genset and pump to cistern/tank (elevated tank ~40 feet or more above point of use--Or an RV type 12 volt water pump to pressurize home).

I would suggest avoiding oil lamps. LED lighting + AC inverter (or even LED flashlights) are much safer (fire)--And avoid the heat/fumes of oil lamps.

That would be my suggestions as a starting point.

-Bill

Sorry, I got a few sentences mixed up and missing information in my previous post (Fixed).

Basically, assumed 3.49 hours of sun, not 4.0 hours minimum (Pittsburgh is not that sunny).

And I intended to have a link for a Hydrometer and a, "good enough" DC current Clamp DMM (Sears):

http://www.solar-electric.com/midnite-solar-battery-hydrometer.html
http://www.sears.com/craftsman-digital-clamp-on-ammeter/p-03482369000P

Don't buy any equipment just yet... We first try to back of the envelope design for the system (rough battery bank capacity, solar array, AC inverter, etc.)... Once you have a system that meets your estimated needs, then start selecting equipment (or at least "classes" of equipment)--And when you have the list of compatible hardware--Then finalize pricing to ensure that you are not spending beyond your comfort zone (solar power is not cheap).

I would suggest that you look around our host's store (Northern Arizona Wind & Sun). They have good pricing and service.  Note, I do not work there and I am purely volunteering my time here. NAWS founded this forum and is funding and maintaining it. You are under no obligations to purchase your hardware from them--And we will still work with you no matter where you buy from (virtually everyone here are volunteering their time. We have a few folks from NAWS from time to time, and some mfg. that have answered questions here

You may find that batteries are cheaper/easier to get locally (batteries can be hazardous), and solar panels can be expensive to pack and ship in less than full pallet quantities---So make sure you get shipping and insurance costs too.

So--Have you decided on a Battery Bank and AC inverter capacity (i.e. 2-4 golf cart batteries, 300 Watt AC inverter, etc.)? Once you have the overall system sizing penciled in, we can talk about details for hardware.

For Solar panels, there are two "classes"--The ~120-140 Watt that are relatively small and have Vmp~18 volts (~$2.00 Watt, easier to ship and a single person to move around/install)--But they tend to be more expensive. And then there is the >200 Watt panels that tend to be Vmp~30 volt panels (~$1.00 per Watt, large, usually need two people to move around safely, can only ship by truck, etc.).

https://www.solar-electric.com/residential/solar-panels.html

But you need to pick a charge controller to support these panels. PWM (Plus Wave Modulation--Basically a simple "on/off" switch) are inexpensive and work well with Vmp~18 volt panels.

The other choice are MPPT (Maximum Power Point Tracking) type charge controllers which are ~3-6x more expensive than PWM--But can take the higher voltage from the large solar panels and efficiently down convert to the low voltage/high current needed to charge the battery bank (think like the DC version of a variable AC transformer).

One place that MPPT controllers do well at is to allow you to run high voltage solar array (~100 VDC Vmp-array for many controllers and upwards of 400 VDC Vmp-array for a few)--This allows you to install the solar array a 100 feet or more away, while the PWM controllers (especially for 12 volt battery banks) should have very short cable runs (10's of feet).

Also, if you like to "computerize" your stuff... Some of the newer/high end MPPT controllers have Ethernet connectivity and others may have other computer interfaces to let you download the daily/monthly data (and remote monitoring). Some people love this, others do not.

Battery banks--There are flooded cell batteries which are cheaper, typically more forgiving, and easier to monitor/understand (measuring specific gravity of each cell). AGMs are an option, but tend to be much more expensive and a bit less forgiving.

And there are LiFePO4 batteries--Not cheap, but have some advantages over lead acid--And some complexities...

Basically, most people end up "murdering" their first (and sometimes second) battery bank--And getting a cheap "training bank" for the first time or two (i.e., golf cart batteries or similar) is a good way to save some money. Here are some battery FAQs:

http://www.windsun.com/Batteries/Battery_FAQ.htm
http://www.batteryfaq.org/
http://batteryuniversity.com/

And there is thread with lots of basic information and links to other projects, etc.:

http://forum.solar-electric.com/discussion/4426/working-thread-for-solar-beginner-post-faq

-Bill