planning stage

ok folks here's another newb with delusions of grandeur

known so far home usage 2005 -3210kwh per 30 days 98 per day
2006 - 2209kwh per 30 days 76 per day
location victoria texas 77901 (south central)
average solar insolation is listed at 6 hours
due to tempature issues (lucky 65 degree californians -green envy smily-)
and financial issues i have decided to utilize unisolar shr-17's as high tempature performance will be an issue with many over 100 days also financially speaking they allow for the callanged to purchase them slowly since i did find a price of $130 each (dont rember where but was a dealer and i kept the link in my over filled solar links file)
as my budget/credit is massively limited i plan the following as a tentative outline

note ALL of these goals are long term
1 3 kw system grid tie
2 3 kw system (above ) with battery backup grid tie
3 dual 3kw system with battery bank and grid tie

goal point purposes
1 reduce electric bill
2 prepare for becoming grid independent and having power during outages and smoothing the #### poor power from the local utility
3 becoming grid independent and selling back as much as possible to the grid to recover costs once costs are recovered pay for replacements (texas puc code utility has to pay actual money not just a credit they can wipe out iirc)

1 begin purchasing of shr-17's at the point of 60 watts (6 shingles)
2 purchase and install a grid tie inverter with possibility of battery addition later on to that end and keeping in mind a goal of a 3 kw system presently the xantrex 3.ogt (just from lurking the forums for a few days) appears to be the controller for the purposes desired (im a computer nut so monitoring is a definite plus to me)
3 as i continue to add to the system wattage will go up and more investment will become available

please note i have read about conservation and some measures are being implemented others are not feasible and everything isn in planning however no matter what conservation measures end up providing a pv system will be installed

the decision on the pv panels to use was most decided due to extremely low cost per item/panel compared to other panels requireing a panel purchase cost of 600$ each and by the fact that high tempatures are less of a problem
also a minimum of weight since they woulld replace the presently installed shingles thus having an effective additional weight of near zero

ok i think maybe i have given enough information in my ramblings so have at me folks :-D


  • RoderickRoderick Solar Expert Posts: 253 ✭✭
    Re: planning stage

    Hi, and the best of luck in your noble adventure.

    I just wanted to make sure that the decimal places were right on your usage. Admittedly, we live in the city, but our house isn't super insulated or anything, and we seem to use about 10 kWh a day. If your number is really 9.8 or 7.6, then the 3 kW system sounds about right. Otherwise, you will probably need more photovoltaic than will fit on your roof. If this is a ranch, maybe Wind power makes sense, at least for a portion of it.

    I'm unfamiliar with the rebate strucutre in your area. Where I live, I would not be eligible for rebates each time I bought a few more tiles - the rebate is only good for a full system install, not an upgrade. The rebate is a significant fraction of the cost for me, so it was worth paying attention to.

    On pricing, if the $130 was for 60 watts of tile, then that's fantastic. If you can get a steady supply at that price, then I'd say go for it. If it was $130 each, then that's $780, and you can get twice that many watts, including mounting system, by going with an ordinary PV module designed for grid-tie.

    Your idea of adding panels as you go will influence the choice of inverter. I would pick one with a wide range of acceptable input voltage, so I would be able to scale up in voltage first, which should be simpler for wiring, then later scale out in amperes. I don't know inverters well enough to make a specific recommendation, though.
  • System2System2 Posts: 6,290 admin
    Re: planning stage

    something im not sure about yet is the strings thing i see on the xantrex website setup calculator

    also i see on the clculator a listing of minium 26 modules does this mean i am incapable of powering the inverter with less than 25 shingles/modules

    also i note the shading issue spoken of in some other threads and thus concludei need to learn these string things in order that i may be able to design a connection scheme that will provide a minimum susceptibility to that problem

  • System2System2 Posts: 6,290 admin
    Re: planning stage

    oops missed rodericks post (been up to long)

    texas does not have a rebate that i can find according to the dsire (spelling ???) website so that does not affect me
    however even if it did the financial situation will not lend itself to any expenditure of that magnitude and yes i understand i could get (6 shr-17's at ptc 15 watts and $130 each = 780) 60 watts cheaper if i was able to purchase at the higheer outlay per module of the monocrystalline also another factor is that the 60 watts of monocrystalline actually comes to a 10 to 20% loss of capacity in my tempature zone also a lower life expectancy due to a much higher incidence of the factors that cause delamination specifically high humidity year round and high tempature oh and beinfg 25 miles from the gulf we get a fairly high salt concentration (not as important considering california proving of panels in high salt areas )

    re decimals the corect values were posted this is a 4 bedroom 3 bath home (or 3 bdrm plus fathin law suite ) with lv dine play and 2 car garage (1 car being 27 feet long) its an old house that been added onto 4 times already

    my conservation efforts have allowed the reduction of energy usage from 3210.0 total kilowatts per month per reliant energy at an average daily usage of 98.0kw
    to a monthly kw of 2209.0 kwh and an average daily usage of 76kwh pwer reliant energy bill
    note the cost per kwh is approx .09 to .11 cents (depending on fuel factors ) and has remained so since well long as i can remember wwhich i think was september 1997 (cheap costs i know weird huh)

    it is an in town home however considering that one shingle in 15 w ptc and is 86 inches long by approx ....7 inches exposed the available ssurface area of the roof should be suffecient though i do plan on verifing that with hard numbers instead of my present estimates based on presently installed normal shingles (just the garage roofing area (south facing ) should provide space for 360 watts the rest of the roof that is south facing should provide (very rough estimate ) room for easily 1920 watts of shingles the rest can be madeup by other areas that dont get south facing sun but will easily provide the additional watttage

    if the system does not provide the elimination of a normal electric bill at least it will reduce the bill to a managable level

    also additional conservation measures are in process of being implemented which should reduce usage even further but present usage provides sufficent data to start planning
  • System2System2 Posts: 6,290 admin
    Re: planning stage

    OVER 75 KWH PER DAY ??!! And that AFTER conservation measures were implemented!
    That amount of power would almost run the whole village where I live !
    Here in Nova Scotia, that would give you a by-monthly bill of about $600.00

  • BB.BB. Super Moderators, Administrators Posts: 32,599 admin
    Re: planning stage


    Actually, I believe that is 2,200 kWh / month (still 10x mine--but that is another story). Seems to not be out of the ordinary for KWh/month in the South with a good size house (AC and what not) from some of the other people's posts I have read.


    A couple of points to think about...

    1) The 80 mph rated shingles sounds pretty low--do you have wind storms in your area? What does code require (or owners association if town homes) in your town (if any).

    2) Try to have all panels exposed to south sun. A few pointing in other areas, or with local shading can really kill your output (especially, if you are paralleling strings).

    3) I understand the issue of costs... However, if I have the numbers right, ~2.9 kW peak rated Xantrex GT 3.0 Unisolar will cover about 600 sqft of roof space (40 tiles x 5 strings).

    The BP 4175's (also 2.9 kW peak rated) I have cover about 272 sqft (10 panels x 2 strings). --granted the panels probably don't stack as tightly as the tiles, but you are using 2x the roof space for the same power.

    3) I am not sure I trust the Unisolar claim of better high temperature performance from what I have read... They seem to be about the same temperature deratings as other good quality panels.

    Using the Xantrex calculator (voltages at several temperatures):

    Ratings for 40 panels x 5 strings:

    PTC: 2967 watts peak
    32 F: 5170 watts peak
    104F: 2690 watts peak [seems to be less power at high temp than BP 4175]

    Ratings for 10 panels x 2 strings: (BP 4175)

    PTC: 2933 watts peak
    32 F: 4704 watts peak
    104F; 2714 watts peak [should be slightly more power at high temp--probably not noticable in real life]

    Also, it is possible that the shingles may run at a higher temperature than a set of "racked" standard panels due to better airflow--leading to reduced power output due to higher temperatures.

    4) Walking on shingles--nobody would think of walking on your glass panels--but I would worry that folks may walk on your shingles and damage them (although they might holdup OK).

    I have been running my Xantrex 3.0 GT system now for almost 1 year here just south of San Francisco (SF Bay side of coastal mountain range) and my 10 panels x 2 strings of BP 4175 (20x 175 watt = 3,500 STC panel rating) panels seems on track to give me about 4,800 kWhrs for the whole year (or an average of 400 kWhrs per month and 1 year net metering law). My panels don't face south (~153 degrees true), are rack mounted to a 30 degree pitch roof--a little morning/evening shading in winter. However, this last winter, I did have a lot of rain/cloud cover where I got only 134 kWhrs for December.

    Your electricity charge is quite low--In my area, it has been $0.11/kWhr for a decade--but that is only for the first ~300 kWhrs per month. We are hit by a $0.35/kWhr for any use over 1,200 kWhrs for the month.

    I am using time of use metering (peak is noon-6pm Mon-Fri)--and it works well for me (avoiding power use during that time and any generated kWhr are paid to me at $0.29/kWr summer peak rate--off peak is $0.09). --assuming baseline of 300 kWhrs/month.

    Lastly, if you don't have enough solar panels in series, then as the array heats up, the output voltage falls--and if it falls enough on hot days, then the inverter will shut down and not deliever any energy at all.

    I am into computers too--but I decided to just log the readings once per day... I am not sure what I would do with all of those numbers... Also, running a computer 24 hours per day is a significant usage of electricity. As an example, if I try really hard, I can get down to 175 kWhrs per month which works out to:

    24x7 kW load = 175 kWhr/month / 30 days * 24 hours = 0.243 kW load or 243 watt load on all the time...

    243 watts probably equals the power of an average desktop system. That one desktop computer left on 24x7 would double my power use just to log my solar generation!

    My old laptop averages around 20-30 watts. And, I am sure that you could find a small industrial computer that uses less power and sleeps when the sun is down.

    So me, being cheap, I just decided not to waste the power on running a standard PC to log the data that I did not really need anyway.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: planning stage

    wayne and bb re 2200kwh /month 76 per day average yes that is typical for large houses in south texas ours is second largest in our block and we are in a lower middle class neighborhood the LARGE houses in the upper neighborhoods are usually much more example an elderly terminal lady my mother helped out with household maintenance had a 3 bedroom and her bill regularly runns $300 in the summer months and for you people who dont realize what summer is thats march through november with daily highs running 80+
    unlike the executive in ohio who apologized for the heat wave (dad at a traing course) when my dd and another texan went outside to warm up in 78 degree weather (tha damn office building was at 68 degrees and he a very large 350 lb 6'5" texan was freezing cold so yes if i was anywhere near nova scotia i'd probably be in winter coat mode and if it like chicago illoinis latitude then probably haver to get to a store and buy the second pair of longjohns i ever owned (i was in navy boot camp in winter -yucch- )

    todays tempatures the night time low was 74 degrees for about 2 hours the daytime high was a very warm 94
    the texan tempature scale
    <10 brrrrrrrrrrrrr
    10's """""
    20's @#$% very bad winter
    30's !@#$%^&amp;* northerner (cold front)
    40's damn cold
    50's very cold
    60's cold
    70's comfortable
    80's warm
    lower 90's very warm
    upper 90's hot
    lower 100's darn hot
    upper 100's dmn it cookie put out that fire
    >110 siesta time

    ( multipe messages
    computer crash loss prevention program
    yep my computer tends to crash alot sometime in febuary i'll get an update and fix it all i hope (im a ex puter shop owner i do knwo whats wrong its a matter of timing and finance for the fix thanks for the thought though )
  • System2System2 Posts: 6,290 admin
    Re: planning stage

    ok to address bb's points

    1 80 mph shingles hmm could end up a factor i'll have t check standards and windstorms not really though we are due a hurricane sine we missed out for the last 10 or 20 years im sure that is a factor in satandards but i don't know what te minimum standard is have to check

    2 south facing yep i got that one

    3 spacew is not that much of an issue the roof is j shaped long side is east west
    bottom (dining room and garage is south at over 400 square feet north side of garage roofing is interrupted by short side of j so could be used but not necessary
    long side of j east facing side is over 675 sq feet and has been getting full sun since 730 am and will continue to get near full sun until 3 pm ( i roofed it believe me i know :-D )
    note these measurements are completly square taken from the ground and not taking into account the extra space available frm the rise of the roof which here in the south is approximatly 40 degrees or less for older homes (newr construction seems to be using a higher pitch putting steeper roof on homes possibly due to the 150 year snow we had in 2004 (20 years ago we had minor snow 1 to 3 inches for a day the 2004 snow was first in 150 years to be more than 3 inches iirc)

    4 tempature performance while important and you have shown that uni-solar has claimed better than reality performance however the financial part is still a primary factor that for a performance differencee of less than 100 watts total (in a approx 3 kw system) can be lived with

    5 wallking on shingles well to be truthfull they have to be capable of handling that the very act of installation requires the installer to stand/kneel on the previous row of installed shingles ( i did shingle my roof my self once already)

    6 heat up causes voltage drop which can reduce or eliminate any power generation ah haa that why you series them like batteries to increase base voltage to a minium necessary for operation thus making the voltage you need like a set of batteries (2 x AA = 3.0v ) thus series sufficient shr-17's get 12 24 or 48 vdc thus a string is effectively a battery gen pack [term works for my brain a battery generator pack matching the voltage of the batteries it would charge thus reducing loss due to voltage matching circuits (mppt ????) ]
    and multipe srings just increase the total amps
    notes strings are susceptible to shading reduction thus fewer strings means less shading losses but higher voltages mean less power loss from resistance so balancing umber of strings vs resistance power los against max voltage of the inverter is the purpose of the xantrex calculator viola the light dawns (maybe :wink:)

    7 computer use well thats a conservation measure and i do thank you for the tip

    8 power usage cost
    believe me i know its real nice here's acouple of nicety comparisions
    1 california electtricity costs are on a sliding scale more use more cost starting a 11cents per kwh to a peak time use of 35 cents
    texas electricity costs are usually a flat rate from .09 in winter to up to .16 cents in places in summer (business however are demand metered for any usage over 3000 kwh per month
    2 californis law provides overtime for any worker who works more than 8 hours per day
    texas law only provides overtime if a worker exceeds 40 hours per week whether they work 4 8 10 12 14 or 16 hours in a day and double shifts are common practice in texas (no wonder im tired :-D) also rotating schedules with 8 hours or under offtime are common

    texas has things i believe are not correct however it also has things that are uniquely beautiful and just plain texan
    thus i stay in the !@#$%^&amp;*()_!@#$%^&amp;*() one horse p### ant s%^& town (65000 pop)

    yup i love my fellow victorians course i'd love em better if i could hang the stupid ones but hey then we'd have a pop of 5 and i'd be swinging from a rope :-D
  • BB.BB. Super Moderators, Administrators Posts: 32,599 admin
    Re: planning stage


    I like Texans--but sorry, I don't read Texan very well. :wink:

    I think you got all of the points of my post... Just a couple of clarifications...

    The Xantrex GT is designed only for 240 VAC output. So, they chose an input voltage range that worked best for their efficiencies and costs. So, their low input is 195 VDC and their high is 550-600 VDC. They don't have to worry about keeping the solar panel output voltage in some relationship to standard battery bank voltages.

    According one of the design engineers (Solar Guppy), the absolute best efficiency is down towards the 200 VDC input range. However, I would tend to just make sure that my Solar Panel output voltage range covers the 200-550 VDC range--and I would tend to keep it higher voltage to keep the current (and I^2*R losses) lower (plus fewer parallel stacked connections, issues with solar panel fuses, etc.).

    Lastly, the MPPT (Maximum Power Point Tracking) type solar controllers (battery and Grid Tie) use a DC to DC switch mode power supply internally to "transform" the DC intput into the appropriate DC (or grid tie AC output). Other than operation losses, DC-DC converters don't have resistance losses or bang/bang type (simple DC Solar Controller) losses (where 22 VDC is simply dumped to a 14 VDC battery where P=IV--I is constant, V could be 22 VDC but is clamped to 14 VDC by the battery).

    The MPPT units transfer constant power from Solar to Load... I.E., P=constant, and if V is less, then I is increased in direct proportion--keeping power transfer optimal. This is great for areas where there is a significant different in solar panel temperatures between hot and cold weather... However, in more moderite climates and with smaller systems, the "extra power" gathered by the MPPT units is frequently mostly consumed by the Switch Mode Power Supply overhead losses--leading to little gained by the more expensive MPPT controller.

    Anyway--today your are talking about Grid Tie inverters--and I believe that all of the commonly available units are relatively large (and efficient) and are MPPT designs.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: planning stage

    IS there an issue with hot temp's on panels? This discussion makes a references to that from the guy in Texas. I too live in Texas (south Texas!) and I'm in the process of looking for a solar PV system for my house. It is normally 97 to 104 here in the summer. Do I need to consider this when purchasing PV panels?

  • BB.BB. Super Moderators, Administrators Posts: 32,599 admin
    Re: planning stage

    Best starting point would be to look at the Xantrex support site... They list a whole bunch of solar panels and give you charts of how much energy they will produce and at what voltages the panels (DC side of system) will run at.

    Even if you don't purchase their inverter, you can figure out the rough ratings for your system (panel voltages/currents and power output).

    But basically, the hotter the panels, the Maximum Power Voltage drops as the temperature increases... So, two issues.

    1) you have to make sure that the low temperature (high panel voltage) and the high temperature (low panel voltage) fall within the operational range of the controller (too high, damage the controller). And on the low side, the controller will either not be able to output to the Grid or will not be able to properly charge the battery.

    For example, if you want to float your 12volt battery near 15 volts, most controllers will need to have about 1-2 volts over battery charge voltage to operate... So, the minimum panel voltage (on a typical hot day) will need to be about 17 volts DC... Any less, and you will not be able to fully charge your battery. And anything much more is loss energy.

    2) Panel ratings issued by the manufacturer are wildly over stated unless you are in a very cold climate (work great during winter).

    For example, my 3,500 watt peak panels, really generate for me (south of San Francisco CA) about 3,000 watt peak (on cool day--usually not for a long time)--but most of the time during summer, I get about 2,500 watts (or slightly less peak--including ~150 watts inverter overhead loss).

    So, the hotter the weather, the less power generated (roughly ~20-25% less peak power vs a cool day before/after summer). For example, my system, which averages about 400 kWhrs per month, will in a wet winter month generate about 134 kWhrs for December to about 500-550 kWhrs during the late spring through early fall months for me... It is not that the long/hot days of summer reduced my monthly totals much--it is really that, on average, it did not generate any more than the cooler months with slightly shorter days of sunshine because of the averge higher tempratures of the panels...

    I can give daily numbers for my system... but it probably would not help you much in south Texas.

    So, yes, you will need to calculate both the min and max solar panel voltages and compare them against your charger controller or Grid Tie Inverter's requirements. And understand your actual power usage requirements (daily, monthly, seasonly, yearly) and the type of system you will be installing (Grid Tie or Battery, monthly or yearly net metering, etc.) to purchase the optimum number of panels (series/parallel configured appropriately) for your system

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • FrankFrank Solar Expert Posts: 54 ✭✭✭
    Re: planning stage

    It's none of my business, but what type of conservation measures have you implemented? If you ever hope to become grid independent you're going to have to reduce your consumption a lot more. Hopefully you've done all the obvious things like compact fluorescent lights and more efficient appliances. Do you use timers or programmable thermostats for the A/C? You have to look at every little bit of consumption and figure out how to reduce it. If you don't you'll never have enough roof space, battery space or $ to accomplish your goals. You should think about which essential services you'll want to provide during a power outage (I understood that was one of your goals). Those have to be gathered together into a subpanel to be powered separately by an inverter.

    Sounds like an interesting project!
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: planning stage


    Average annual solar irradiation for a fixed south-facing array tilted up at Latitude (~29 degrees) in Victoria, TX is 4.9 hours/day. Assuming 80% effective efficiency for a grid-intertie system without batteries, you’ll need a PV array rated at (76 kWh/day / 4.9 hours/day) / 80% = 19.4 kW STC. That’s a massive PV array, and you’ll need seven GT 3.0’s to handle the power and be able to net zero your energy consumption.

    A 3 kW system will lower your average energy consumption by ~15%, and, at your present consumption level, it will never result in net selling back to the utility. It will, however, reduce your net energy consumption, as well as your utility bill, to some degree.

    Note that the Xantrex GT utility-intertie inverters do not provide any back up capability to your home when the grid is down. Zip, zero, zilch, nada. In fact, the GT’s disconnect from the grid (a UL requirement) and they do not provide for a direct means to connect to a battery bank. If you’re looking for a grid-intertie inverter with battery backup, you’ll need to look at something like the Outback GVFX inverters.

    Finally, as Wayne suggested, the place to start is with an investment in conservation. I sympathize with your environmental challenges (my mother-in-law lives near Austin), but 2,209 kWh/month is still a lot of energy.

    I’d be happy to continue this discussion with you, but I suspect that at this point you may wish to review your plans. This site may help you find information on rebates in TX, and don’t forget the federal tax credits available this year and next.

    Jim / crewzer
  • BB.BB. Super Moderators, Administrators Posts: 32,599 admin
    Re: planning stage

    One thing that I forgot to address was the issue of off-grid/battery backup...

    Unfortunately, right now, the electronics and panel wiring for Grid vs Battery based systems almost exactly requires 100% different materials, wirings and has other issues too. About the only thing the same is the solar panels themselves between Grid Tie and Off-Grid applications.

    1. Wiring: Battery systems generally operate at lower voltages... For example the MX60 (a very good MPPT Solar battery charger/controller) max voltage is ~150 VDC (IIRC). The Xantrex GT 3.x is 195-550VDC (600 VDC max). So, changing controllers would require rewiring your panels (or bringing extra panel connections down to a box where you can rewire from the ground--more copper, more costs).

    2. Solar Grid Tied inverters (like the Xantrex GT 3.x) do not run if there is no AC to the house... If you lose AC mains from the utility company, the solar panels are just dirty pieces of glass on the roof. Certainly a drawback for emergency use...

    3. Inverter/Charger wise, the equipment is pretty much expandable as you grow... If you add a new string of panels, just adding another inverter (if Grid Tied) or Solar Charger (if off-grid battery), is pretty straight forward and usually does not involved any major issues.

    4. Batteries: A big issue in off-grid/inverter backup applications... First, they require maintenance, and depending on what you purchase--you will have to check/add water every month or three. They are also dangerous... Hydrogen gas, battery acid spills and leaks, battery connection failures, high current shorts, and battery aging (replace, roughly every 7-15 years, depending on price, usage, maintenance, luck, etc.). Also, because batteries age, it is not recommended to add to an old battery string with new batteries... The new batteries will carry most of the load and quickly age into performance (and over all life time) to that of the original batteries (weakest link issue). You also have to size the battery bank to your needs... Generally, a good place to start is assume that you will have 3 days of battery storage--no sun (and since you only want to use 50% of battery capacity for good life, that is really:

    6days * (2,000kWhrs/30days) * (1/50%) = 800 kWhrs of storage--equivalent to 800 car sized storage batteries (of course, you would use larger batteries--but this is still not a small installation.

    Also, you will need 10-20% more solar panels with a battery system because of the extra losses in the inverters/battery charging too with respect to a Grid Tied system.

    5. Going off grid can handle any size load you wish to throw $$$$$ at... However, it could be quite a bit of money. As a guess, to supply your home usage of 2kW/month during the sunny months would be on the order of $150,000 +/- 25% (not including any rebates)... And for weather conditions (winter), if you have clouds and/or sun obstructions (which tend to be worse in the winter for many folks), you will probably need a backup power source--gas/diesel generator, wind generator, and/or grid.

    Again, you can throw money at an off-grid solution... But realistically, a Grid-Tied system (if your state supports good net metering rules) is the best bang for your buck. And, if you want off-grid for emergencies, if you have propane or natural gas or a good place to store fuel, use a small solar/battery system for a few lights/fans/tv and get a good quality (1,800 rpm) generator (for ~$15,000 plus installation) to power your AC during hot weather--and/or if you want to be able to run everything full bore during outages.

    Otherwise, use a small solar/battery backed system, and a window AC unit for 1 room + a Honda 2kW (or 3kW if you get a larger AC unit) that only uses a gallon of gas every 4 hours (running AC) or 1 gallon every 15 hours (1/4 load running fridge/a few lights/TV) and store 20 gallons of fuel (enough for 4 days running AC in evening or 10 days w/o AC).

    For myself, even though I use 1/10 the energy you use (no AC, natural gas appliances)--my power has historically been very reliable (~45-50 years ago was last multiday outage in our area). So a full size off-grid capable system just did not seem to be worth the expenses and where to put the batteries issue. Also, with going off grid, I would need a generator for winter use (my 400 kW/month system generated about 134kWhr last December). Doable--but why?

    I just picked the Honda eu2000i at ~$900 plus 5 gas cans (and a syphon for the cars). I was mostly concerned about earthquakes, so a natural gas powered generator was something I did not trust in a major natural disaster. Using the factory numbers, the Honda eu2000i (family of 1,000, 2,000, and 3,000 watt) seemed to be the most fuel efficient per kW (as good, if not a little better than the smaller 1,000watt unit). The only way, I have seen, to get better fuel efficiency per kWhr is with bigger units (like a 20kW diesel or natural gas)--however, given that I only need 300-500 watts (fridge, freezer, a few lights) to run my home on average--the 20kW genset would be, basically, idling at $1.50 per hour of natural gas to supply electricity for my home. The Honda would operate a 400 watt load for 15 hours on 1.1 gallons of gas... Only ~$0.25 per hour for gasoline).

    Also I could take the Honda with me--a 20kW generator set is not really portable plus uses huge amounts of fuel to operate, even at reduced loads).

    In the end, as Crewzer (Jim) posted while I am typing this--conservation is the way to go... For example, looking at conservation as an investment. Assume you can save 1,000kW per month for AC and other energy costs with remodel/new equipment and your home costs an average of $0.13/kWhr over 1 year and you can get 5% interest on your money in a savings account (use what ever number you like):

    Amount to spend on Conservation:$0.13*(1,000kWr/month)*(12months/year)*(1/0.05 cost of money)=$31,200 capital investment

    So, if you spent $31,000 to save 1,000kWhr/month, you would break even (assuming cost of money is 5%).

    To power 1,000 kWhr per month (using my Grid Tied system as an example). 400kWhrs/Month (average over 1 year) *$29,000 retail installed cost (excluding rebates):

    Solar Costs: $29,000 * (1,000kWhr/month)/(400kWhr per $29k) = $72,500

    So, to get a Grid Tied system you would need to spend on the order of ~$36,000-$72,000 to offset the 1,000 kWhr/month load (assuming Texas has 1 year net metering contracts available).

    You can play with the numbers (for example, sunny 1/2 of year solar generates more power, and Texas charges more for electricity--so the savings with solar are probably better--but you don't us AC in winter(?), so to save 1,000 kW/month average will require other measures too--which may not be practicable) any way you wish. It is very interesting to look at cost of installation, vs cost of money, where you expect prices to head, Time of Use Metering, and on and on... At some point though, you do have to pay your money (either in monthly power bills, or somewhere else).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Patman3Patman3 Solar Expert Posts: 62 ✭✭✭✭
    Re: planning stage
    BB wrote:

    5. Going off grid can handle any size load you wish to throw $$$$$ at... However, it could be quite a bit of money. As a guess, to supply your home usage of 2kW/month during the sunny months would be on the
                                     ^^2MEGAwatts not kW
  • BB.BB. Super Moderators, Administrators Posts: 32,599 admin
    Re: planning stage

    And, Patman3, you are correct... My typo--2kW should have been 2,000 kWhr/Month. I believe the rest of the numbers where typed correctly...

    I try to not throw too much stuff at others... I will never be perfect myself either. And, I have not walked in their shoes either (don't know home, area, life style, available cash for conservations/solar, site suitable for solar, etc.).

    Keeping it friendly and educationally, and we can all learn. Open conversations about Solar on another Board (Brock is there too), helped me take the plunge I am now probably 1,200 kWhrs on the Green Side (credit with utility) for 11 months with my installation. (I changed windows to double pane, new appliances, insulated the walls of my 67 year old home, and blessed to live in a very temperate climate).

    I will be the first to say that going Solar Electric Grid Tie was more expensive for me than staying on-gird utility. I took the rebates/tax credits offered, and am looking towards the day a Prius size/type all electric or hybrid electric becomes available in the next couple of years--My tiered utility service goes from $0.09-$0.11 (at less than 300kWhr/month to $0.50 per kWhrs over 1,200 kWhr per month). So, I took this as an investment in the future. Solar costs me around $0.14-$0.17 today (forgetting interest costs and the fact that I am only using about 2/3's of the energy I am generating today--the rest is free power to my utility company).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Sign In or Register to comment.