Questions about Solar Power hookup.

hillbillydudeman · February 2012

I live in the woods of Arkansas, and the power drops constantly.
I would like to run
-full size refrigerator/ 2 smaller fridges
-computer
-fans
-lights
-for 2 person household

I plan on getting a few 12v solar panels.

I understand there is a linking from the-

Panel --> Controller --> Battery --> Inverter --> Household (IF my understanding is correct.)

So my questions begin.

1. Would a few 12v solar panels power a series of deep cycle batteries sufficiently for a household ?
2. What type of controller would be best ?
3. What type of inverter would be best ?
4. What type of battery would be best ?

I have a professional who can wire, but is not experienced with solar power. All the numbers up and down for controllers and inverters baffled me, and i figured it would be in my best interest to ask a few questions before embarking on this solar quest.

Thank you for all help!
Again, all MY knowledge has merely come from speculation, and slight investigation.

-J. E. C. Smith

BB. · February 2012

Re: Questions about Solar Power hookup.

Can you get your loads better defined... Use a Kill-a-Watt meter or similar and estimate how many hours per day (or how many days) of power outage you are preparing for.

More than likely, you would be looking at a 24 volt or even a 48 volt battery bank.

Regarding solar panels--If this is a "UPS" for your home--just a few hours a day--I probably would suggest getting a nice Inverter/Charger (maybe something like one of these). And only add solar panels+charge controller when/if you decide solar panels would be useful for your situation/cash flow (yes, solar panels are pretty cheap historically speaking right now--But a small array is not going to really do much, and a large array is "wasteful" of cash if you don't use much of the power generated.

At some point, there may be the trade off between a generator or solar array for longer outages... Longer than a few days or a week--probably solar panels are a good answer (depending on weather/location and how much sun you get during "outage" season).

No right or wrong answers--just what you think will work best for your needs.

-Bill

icarus · February 2012

Re: Questions about Solar Power hookup.

As Bill suggests,, all calculations start with the loads. Any other plan is simply "ready, fire, aim!

As a general rule of thumb, a simple generator is a MUCH cheaper alternative for short term power outages. The equation would change if your grid is really unreliable. For example, a Eu 1000 honda (~$900) will run for hours on a couple of quarts of fuel, and will run for days on end at 80% load.

Another rule of thumb for off grid PV. Take the name plate rating of the PV, divide by 2 to account for all CUMULATIVE system loses, then take that number and multiply it by 4 to account for the average hours of GOOD sun you can reasonably expect, on average, per day, over the course of the year.

So, for example, a 1000 watt PV system might look like this,, 1000/2=500*4=2000 watt/hours/day.

So, define your loads, then figure out how to power them. Typical off grid system, might run ~$5-8/watt installed, so that same 1000 watt system might cost $5000+ all in. (compare that to the $900 for the Eu 2000) You also have to realize that the life of batteries are limited, 5-10 years, and represent ~1/2 the cost of the system.

Also realize, that while PV prices have come down dramatically, the prices for wire, electronics and batteries have risen significantly.

Welcome to the forum, hope this helps, and keep in touch,

Tony

hillbillydudeman · February 2012

Re: Questions about Solar Power hookup.

Wonderful Answers!
Much better than I could have came across from research, or asking neighbors!

With the inverter/charger in mind $$ and the batteries in mind $$, I have a ways to go, to get all my funding together.

Thank you for pointing out i need to find the optimal zone for the amount of panels needed. (Not too few, or too many, to overshoot cost.)

"Typical off grid system, might run ~$5-8/watt installed," This is very useful for me!

I would prefer to get full energy use, year round in the long run. We use about 5kwh a month. Would i need a 6500watt sytem for year round?

Again, thank you so much for your input.
Being free, I will not turn down your advice.

and does PV stand for PhotoVoltaic? The best i could assume......

-J. E. C. Smith

icarus · February 2012

Re: Questions about Solar Power hookup.

PV is,, photo voltaic.

My guess is that upon mis typed,, do you only use 5 kwh a month? Perhaps 5 kwh/day? ( which would be very good!)

You PV dollars are much better spent in general on grid tie, rather than battery based. Grid tie comes at about half the cost, with twice the efficiency. Spend $10k in grid tie, reduce your utility bil to near zero, take the savings and buy a stand by generator,, would be my suggestion.

Gone to PV watts, plug in your location, and your potential system size, and it will give you a pretty good idea of how much you can harvest,, and the value of that powe given your kwh rate. (irrespective of rebates, tax credits etc.)

Tony

BB. · February 2012

Re: Questions about Solar Power hookup.

Without understanding your loads and requirements--We cannot really give you a "good answer" that does not just tend to confuse the situation... However here is some generic information you can start with:

PV Watts (Tony's recommendation) for Fort Smith Ark (just guessing), you have "two solutions" to start your design with. One is a pure Grid Tied system (with UPS or Generator backup separate from system) or a pure off grid system (solar panel to charge controller to battery bank to UPS to your loads).

A 2kW GT system with defaults (assuming fixed array with 0.77 derating factor):

"Station Identification"
"City:","Fort_Smith"
"State:","Arkansas"
"Lat (deg N):", 35.33
"Long (deg W):", 94.37
"Elev (m): ", 141
"PV System Specifications"
"DC Rating:"," 2.0 kW"
"DC to AC Derate Factor:"," 0.770"
"AC Rating:"," 1.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 35.3"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 7.4 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 4.13, 195, 14.43
2, 4.84, 203, 15.02
3, 5.13, 235, 17.39
4, 5.67, 243, 17.98
5, 5.77, 247, 18.28
6, 5.97, 242, 17.91
7, 5.85, 239, 17.69
8, 6.08, 252, 18.65
9, 5.34, 218, 16.13
10, 5.07, 222, 16.43
11, 4.42, 196, 14.50
12, 3.62, 170, 12.58
"Year", 5.16, 2662, 196.99

You can see such a system will supply around 170-253 kWH per month (depending on season) in good sun (no system will produce usable power if shaded, and not much power if under clouds/fog/behind a mountain).

The same system using 0.52 derating for an off grid system:

"Station Identification"
"City:","Fort_Smith"
"State:","Arkansas"
"Lat (deg N):", 35.33
"Long (deg W):", 94.37
"Elev (m): ", 141
"PV System Specifications"
"DC Rating:"," 2.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 1.0 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 35.3"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 7.4 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 4.13, 129, 9.55
2, 4.84, 135, 9.99
3, 5.13, 156, 11.54
4, 5.67, 161, 11.91
5, 5.77, 162, 11.99
6, 5.97, 159, 11.77
7, 5.85, 157, 11.62
8, 6.08, 166, 12.28
9, 5.34, 143, 10.58
10, 5.07, 147, 10.88
11, 4.42, 129, 9.55
12, 3.62, 111, 8.21
"Year", 5.16, 1757, 130.02

Note that the same system off grid will produce much less power--Around 111 kWH to 162 kWH per month.

There are also Hybrid Systems--Grid Tied fed back to utility when power is up (efficiently), and will run off-grid when the utility power is down. Similar to designing an Off-Grid system with a Hybrid inverter to perform both functions (you can even use a Hybrid inverter off grid--price is not much different).

Very roughly:

$0.10 per kWH is your grid price (or less)
$0.15-$0.30 per kWH for Grid Tied power (can make economic sense for California and others where we are >$0.52 per kWH at times)
$0.45 per kWH (for hybrid power when running from grid)
$1-$2+ per kWH for pure off-grid power

If you have not "done the conservation dance" yet--Take a long/hard look at your current power usage.. The Kill-a-Watt and other tools (whole home monitoring systems--Links provided for further research--not recommending a specific product for your needs) can really help you reduce your power usage.

Multiple refrigerators/freezers, desktop computers, any form of electric (resistance) heating, A/C and dehumidification, lack of insulation/double pane windows, etc. improvements can save many people upwards of 50% of their power usage (if they have not addressed conservation before).

Also, remember that your battery bank may last around 6-10 years, your "electronics" (charge controllers, inverters, etc.) probably will need to be repaired after 5 years, and replaced after 10 years (upon failure). All of this adds up.

To give you an idea of power usage to aim at:

100 kWH per month or less--Typical off-grid cabin or home
500 kWH per month or less--Pretty easy for folks with natural gas and no A/C requirements
1,000 kWH per month--North American average power usage per home
~2,000+ kWH per month--Not unusual for people with heavy A/C needs and electric hot water, etc.

It is almost always cheaper to conserve a Watt*Hour than to generate a Watt*Hour.

In the end, power usage is a highly personal choice. We do not push conservation as being "green" or kind to the Earth... We push conservation here because (most of us here) are CHEAP.

-Bill

Questions about Solar Power hookup.

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