Saying hello!

Re: Saying hello!

Cutting power needs back to a single refrigerator + a few lights + small radio/TV and possible well pump--You can do OK with a Honda eu2000i (1,600 watt) inverter generator or equivalent and run it on a couple gallons of gas a day... All of a sudden, 20 gallons of gas (storage with fuel stabilizer rotated once a year into the car, siphoning a the gas tanks of a couple family cars, etc.) is real practical to run for 10 days (basically a camping like existence). By that time the fresh food is gone and you will be looking for longer term living issues. Genset is only 50 lbs and very portable... A large solar system is not portable at all. And a small solar system does not produce that much energy.

Solar PV for purely emergency use is expensive (system is expensive, batteries still need replacing every 3-8 years or so typically). You can run a few optional loads off of solar to keep things exercised and get back a few kWH per day from your investment.

Or you can look at a full Hybrid GT/Off Grid system. Basically a giant UPS with solar power, generator backup, that can do Grid Tied solar back to the utility so you can use the power for your whole home. Very practical and almost cost effective--especially if you have lots of outages or risks of weeks of blackouts (rural area, ice storms, hurricanes, etc.).

-Bill

Re: Saying hello!

I understand... You are in Nevada, so even a smallish system can supply a lot of energy year round.

A good way to start is use a Kill-a-Watt meter (or equivalent) and measure the daily loads of what you want to keep going...

Typically:

1 kWH per day for refrigerator
0.500 kWH per day for laptop+satilite modem
0.500 kWH per day for lighting/radio/small tv
================================
2kW per day...

A nice sized small but life life pretty normally is around a 2-3kWH per day system (remember loads like refrigerators use more power in hot weather/summer than winter).

Using a website like PV Watts. For Las Vegas NV, assume 1kW of solar panels (round number), and 0.52% end to end system derating (solar panels to charge controller to battery bank to AC inverter), fixed array:

"Station Identification"
"City:","Las_Vegas"
"State:","Nevada"
"Lat (deg N):", 36.08
"Long (deg W):", 115.17
"Elev (m): ", 664
"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:"," 36.1"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 9.7 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 5.19, 79, 7.66
2, 5.98, 80, 7.76
3, 6.57, 98, 9.51
4, 7.32, 103, 9.99
5, 7.42, 105, 10.18
6, 7.35, 96, 9.31
7, 7.37, 98, 9.51
8, 7.29, 97, 9.41
9, 7.31, 96, 9.31
10, 6.56, 94, 9.12
11, 5.75, 83, 8.05
12, 5.05, 77, 7.47
"Year", 6.60, 1106, 107.28

Will produce a minimum "typical/average" of ~79kWH per month in January or:

• 79 kWH per month / 30 days = 2.63 kWH per day

So, at a minimum, you would like around:

• 3 kWH per day / 2.63 kWH per day per 1,000 watts of solar panels = 1,139 Watts of solar panels

Battery bank wise, assume 2 days of no power (1-3 days is recommendation) and 50% maximum discharge:

• 3,000 WH per day * 1/0.80 battery eff * 1/24 volt battery bank * 2 days * 1/50% maximum discharge = 625 AH @ 24 volt battery bank

The "nominal" nice to have recharging current for a battery bank is around 5-13% with 10% being a nice number to hit for a flooded cell battery bank (AGM numbers are slightly different--AGMs are more efficient).

• 625 AH * 29 volts charging * 1/0.77 solar panel+charger derating * 0.10 nominal charging current = 2,354 Watts of solar panel

So, for the above "balanced" system design--Having an array of 1,200 to 2,400 watts would be recommended for an average of 3 kWH per day "maximum" load in January (you probably would need to use a genset to keep up if you really used 3kWH per day).

Plan on using about 50% to 75% of your daily predicted solar output to allow for bad weather, increasing loads, etc. ... Don't plan on using 100% of predicted power per day (long term averages can vary by 10-20% or more due to weather variations).

The above is an off grid set of calculations--If you go Hybrid (like a Xantrex XW hybrid inverter system)--you can adjust sizes to supply grid power back into your home and even turn the meter backwards (assuming your utility allows Grid Tied systems).

An off-grid system probably costs around $10 to $20 per watt (yea, big range of guessing) to install (yourself vs turnkey). So you are looking at $10-$20k or so for such a system. And new batteries every 3-15 years (depending on battery price/quality and how well you take care of them).

-Bill