Small Sys. Requirements--Back up/Solar System

Re: Small Sys. Requirements--Back up/Solar System

Some of the equipment you may want:

Kill-a-Watt (120 VAC 15 amp power/energy measurement--great for conservation and AC off grid power estimates)
DC amp*hour/watt*hour meter (good for smaller DC applications)
Battery Monitor (and Victron brand) (good for monitoring the charging/discharging of your system--almost a necessity for sealed/AGM type batteries)
DC Current Clamp Meter (here is a cheap/good enough meter for debugging solar)

Regarding using the smaller genset (I am a big fan of small/inverter-generator systems--can be very fuel efficient if you keep your daily power needs low):

Question about battery charger selection with EU2000 generator.
Propane conversion for Honda EU6500i?
Auto Choke/ Propane Conversion
Selecting the correct backup generator
which generator is best

-Bill

Re: Small Sys. Requirements--Back up/Solar System

The answer is in Watt*Hours:

• TV ---70W X 3 hrs =210 Watt*Hours

It is a very common mistake--we are all used to Miles per Hour, Gallons per Hour, etc. as being a "Rate". And multiplying by hours gives us mile, gallons, etc.

Watts is array a "rate" (Joules per Second)

So, with the above, Watts~Miles per gallon, multiply by time we get Watt*Hours (~gallons used).

Using PV Watts for Youngstown OH, at ~41 degrees from laying flat:

Month    Solar Radiation (kWh/m 2/day)
1      2.17     
2      3.05     
3      4.12     
4      4.61     
5      4.95     
6      5.20     
7      5.21     
8      5.21     
9      4.21     
10      3.84     
11      2.24     
12      1.93     
Year      3.90      

For 9 months of the year, February at 3.05 hours of average "full sun" per day, and ~52% end to end system efficiency, to keep even you will need:

• 640 WH per day * 1/0.52 system eff * 1/3.05 hours of sun per day = 404 watts of solar panel minimum (February-October)

We also like to size the solar array to the battery bank... Anywhere from 5% to 13% of rated charge is OK. AGM work well towards 5% rate of charge (and up to 13% or higher). Flooded cell should be greater than 5% for various reasons. 10% is a good healthy amount of charging current:

• 108 AH * 14.5 volts charging * 1/0.77 panel derating * 0.05 rate of charge = 102 watts minimum
• 108 AH * 14.5 volts charging * 1/0.77 panel derating * 0.10 rate of charge = 203 watts nominal
• 108 AH * 14.5 volts charging * 1/0.77 panel derating * 0.13 rate of charge = 264 watts max cost effective

You are using a fairly small battery bank (1 day of autonomy)... So, the size of the solar array needed to keep up with the battery bank charging is smaller than your daily power usage. For an emergency system, using a smaller battery is OK because you are not after cycle life--So if you discharge to 50% or even 20% state of charge in an emergency--it is not going to cause the battery to die an early death for a few outages a year (your battery will likely "age out" instead of cycling out).

Also, normally, we use ~4 hours per day of sun, but in Ohio, it looks like you don't have great sun, so you need a larger array to keep up with your loads.

-Bill

Re: Small Sys. Requirements--Back up/Solar System

Note that the "600 Watt Backup Kit With 56 Amp-hour Battery" does not include solar panels (of course, you can add panels+charge controller to the order or later when funds permit).

Also, a 35 amp 120 VAC to 12 VDC charger may be too big for an eu1000i (900 watt) generator.

And I would review the size of AC inverter you wish to use... A 600 watt inverter will drain a 56 AH battery bank in less than one hour at 600 watts. OK for short/heavy loads (running an electric drill or as a UPS allowing to to finish up your work and shut down the computer)--But a bit overkill if you want to run lights/radio/charge small battery devices over a 10+ hour period (closer to 60 watt load than 600 watt load).

-Bill