Starting/growing a system

Another lurker coming out - I hope you guys don't get tired of the newbie questions. This may be a bit different, or maybe not. I'll try to be brief, but that's easier said than done :-)

Situation: 40 Acres in southern Colorado, which if it doesn't get wiped out by drought or fire will be wonderful. We're on a ridge that runs east-west, so we have all the southern exposure we care to use and then some. Currently the land is undeveloped, and we'll follow what is probably the usual progression: a) storage shed(s) for temporary infrastructure (one to house power systems), b) cabin for weekends/vacations etc c) (maybe/hopefully) full-time residence, which may or may not include expanding the cabin. Power is 1/4 to 1/2 mile away, and our feeling is that it's not worth bringing in - better to put the equiv $$$ towards RE over time. No well yet, and since we're probably looking at 500-700', we may simply put in a cistern and haul water for now - this will obviously have a huge impact on the ultimate makeup of the system.

We're planning to do the bulk of the work on building ourselves, so the near-term need is primarily capaity to run tools for construction - small pancake compressor, circular/table saws, charging cordless batteries etc. We'd likely rent gas-powered stuff for big jobs. We'll have some lights etc, but for weekend cabin use this will be pretty minimal and should fit within the other constraints. So, high peak requirements, but relatively low average requirements. We could go weeks between visits, and probably won't visit at all from Nov-Mar.

What I think I know:
- I already have a Xantrex SW4024. Somthing of an impulse buy, but at just over $1k used, it didn't make any sense to spend $500+ on a stopgap, plus the Xantrex will work for charging the batteries from the generator (from what I've read the setpoints will accomodate either flooded or AGM cells) The 'generator support' mode would also seem to be a very very valuable feature for our needs, as it allows very high surge capacity from more moderate sized systems. I don't expect to need to replace the Xantrex unless we go full-time, and maybe not even then.
- system will be genset + solar. No point investing in solar capacity for our peak needs now. OTOH I don't want to run the generator too much, so some solar is needed. I'm hoping to ultimately get set up with a slow-speed deisel running off veggie oil, but my line on a ChangFa fell through and the EPA thing has dried up supply. Probably go with an EU2000 for now, since quiet is important, and 1600 W continuous seems adequate if we can take advantage of generator support mode..
- AGM batteries seem to be the way to go. Being remote the lower maintenance by itself is enough reason, but since the generator will be a main charging source initially, the higher charging currents are also a plus. No venting requirements is also nice, although the cost isn't so nice.
- no solar panels this year, one or two panels installed next spring. charging from the generator in the interim.
- we discovered over Memorial day that we can get a ton of wind, but it may be seasonal. Unsure yet whether wind power is something we'll look at

What I don't know:
How to get from here to there, particularly on the battery plan. This is mostly due to cost - by the time we pay for all the other startup costs like land clearing, sheds, generator etc, paying for a 'good' AGM battery bank up front looks a bit steep, particularly since our average draw will be small. However, the thought of a 'throwaway' starter set isn't too palatable either. Seems the options are
1) go ultra-cheap to start. Assume the genny will handle the bulk of the work, and get something like the Stowaway 'deep cycle' units at sams club that'll last a year or so, and get real batteries when we put the solar panels in. (~150-300)
2) go with T-105's which should give 'several' years use if we are careful and bring them back to the city for the winter (~300-350)
3) small AGM bank - say two Concorde ~120Ah. (~400)
3a) do 3, but 'hope' our usage is low enough that we can add two more next year and they won't have aged too much
4) take the hit and get ~250 Ah@24V AGM now, and don't worry about it again until/unless we become full-time residents. (~800)

Since the difference between 3 and 4 is 'only' $400 or so, it may be crazy to try a shortcut for that amount of savings, but this is all hitting at once so anywhere we can save is welcome. I'm particularly interested in how much use we'd need to put on the batteries before 3A becomes impossible. It makes me feel cheap and sleazy, but if option 1 was to ever make sense for anyone, it seems to fit OK here since we can manage the depth of draw closely and would mostly use them in surge capacity.

The panels would be the next question. Since we'll have tons of sun and sporadic use, almost anything should keep the batteries charged when we aren't there. Sizing would be more determined by what the battery bank needs as a minimal charging source.

So, I guess any general feedback on the approach is welcome, including things I may have overlooked and/or options I haven't considered. (ie get an EU3000 instead and forget batteries until you put the panels in). Thanks for reading this far, and for any advice/help that you can provide.


  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Starting/growing a system

    to start you can look over this thread about batteries.
    if it's a circumstance of charging all week to be there on the weekend go with more battery capacity, but don't go with a charging source that is lower than 5% of the battery capacity total. an example might be using the concorde pvx-2580l agm battery which is an 8d size battery. this is rated 255amphrs so at 5% for charging would mean 12.75amps. going with 2 kyocera kc-130s would yield at max 2x7.39amps or 14.78amps and that's about 5.8%. you must use caution if you know the week was cloudy and rainy/snowy as that means the battery may not have come to a full charge. know that you also can't run a battery all of the way down as most lead acid batteries should not be drained below 50%. for the concorde agm i recommend no lower than 60% discharged(dod) even though i've seen 70% from the company. this is only an example for you and not a recommendation as you will weigh what you want and need. the batteries brock and crewzer have are good batteries too and you may be able to get them cheap as they did.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
    Re: Starting/growing a system

    I like the eu2000i (bought one as a home backup generator), however, the eu3000i (or some other) might be better for you if you need to run several tools at once and/or want electric start down the road. However, if you are going to haul the tools back and forth for the first year or so, the smaller genset is probably better (and at less than full power loads, the eu2000 is supposed to be more fuel efficient than the eu3000).

    From looking at the costs of solar/wind/battries/etc., the numbers have always seem to come out that if you are not using power at least 6+ months a year (day in and day out), that a good quiet generator is more cost efficient than a part time use solar (for anything more than a couple storage batterys/panels supplying a few lights and a TV in the evening a couple days a week).

    So, at most for solar, I would tend towards a few inexpensive storage batteries with enough panels to charge them during the week for a weekend's use of a few lights/appliances. And plan on a nice (probably portable) generator for heavy loads (power tools, and such). This keeps the costs low, still gives you quiet days/evenings when you are not working. And does not leave too much out there for damage/theft/etc. over time. And no wind generators as they are fragile and may attract "vistors" to you site. During the winter, I would plan on the few solar panels as being enough for maintenance charging of the batteries (1%-2% charge rate) just to keep them happy and from freezing (if you don't take them home in the winter).

    One way to justify the genset over large solar--estimate how may kWhr per weekend for 8 months per year you will need. Add up all of the costs for panels/batteries/etc. What will its useful life be (for you). As an example:

    Compressor (1kW * 3 hours), circ. saw + table saw (1kW * 1 hour), plus lights for even work (0.5 kW * 2 hours) = 5kWhrs/day
    Cabin/Camper lights / TV / Radio / Fan = 2kWhr per day (SWAG)

    If you assumed that you have enough batteries for 3 days, plus the solar can charge (during 6 months of the year) over 7 days:

    Assume tools used 2 days per week, "camping" 3 days per week (get there Friday evening, leave Sunday eve).

    kWhrs = 5kWhr*2 + 2kWhr*3 = 16 kWhrs per week

    Batteries = 16 kWhrs (1 cloudy weekend of work) * 1/50% = 32 Kwhrs of storage

    Panels = 0.035 KWhr panels per kWhr week * 16 kWhrs per week * 1/80%= 0.7 kW peak (700 watts of panels).

    Battery costs for a T-105 is $86 447 amp*hour (447ah*6m= 2.682 kWhrs of storage per battery).

    $Bat = 32 kWhr / 2.682 KWhr => 12 batteries * $86 = $1,032
    $panels = 700 watts * $5 per watt = $3,500
    $Charge Controller = $500 Outback MX60 (wind-sun on sale).
    Assume panels have 25 year life, and you will only use for 5 years then recycle. Assume Charge controller 10 year life. Do not include shed, wiring, inverter (which you have)...

    $/kWhr = ($1,032 + $3,500 * 5yr/25yr + $500 * 5yr/10yr) / (5yrs * 16kWhr * 26 weekends/yr) = $1,982 / $2,080 = $0.95/kWhr (pure solar, weekend use, 26 weekends per year).

    Generator: Honda eu2000i at low power, from Honda web site, (most inefficient) uses 1.1 gallons per 15 hours @ 25% * 1.6 kWatts =>

    kWhrs/gallon of gas = 15hr*0.25*1.6kW/1.1gals = 5.45 kWhrs/gallon of fuel
    Generator ~$1,000.

    $/kWhr = (1 gal *$3.50/gal) / (5.45kWhr/gal) + $1,000 gen / (5 years * 16 kWhr * 26 weeks/yr) = $0.642/kWhr + $0.481/kWhr = $1.123 per kWhr (generator only).

    Just for the heck of it, what would it cost for a power line.... Assume $100,000 / mile, 1/2 mile, 30 year useful life to you (capital costs), and $0.10 / kWhr. And the period of use is 5 years. (fixed equation, was 20, should be 30 years

    $/kWhr = ($100,000/m * 0.5m * 5yr/20 30yr) / (5 years * 16 kWhr * 26 weeks/yr) + $0.10 per kWhr = $6.094.01/kWhr + $0.10/kWhr = $6.19 4.11 per kWhr for a powerline dropped into your building site (boy, that was a surprise to me!).

    OK, we now have some costs. I admit, that I have done some SWAG's here--but you can do the same calculations with your numbers (for example, the weekend usage works about to, roughly 125 kWhrs per month if fully occupied, the solar was based on my 1 year average of 400 kWhrs per month for a 3.5 kWatt array south of SF CA, if you assumed 6 moths a year--probably pretty conservative--should power you from early spring through late fall, assumed battery only for 3 days, etc.). Play with the numbers and see if there is any better combination for you.

    By the way, have you gotten a quote on utility power to your site? I have been reading of $100,000 per mile since deregulation separated the utilities distribution from generation charges.

    One possibility to justify batteries through the winter is to allow you to set up some sort of remote alarm system. Don't know about your area, but in California between the squatters (who can get protection by the law and require formal eviction instead of being lead out at the point of a ...) and theft (pulling up entire well/pump sets, and even dismantling kit homes--its something that may need to be considered. Full Quote below
    Kay Kugler and her husband B.J. Miller bought 40 acres in California's El Dorado County and erected a 10-by-20-foot prefabricated cabin on the property, which they used as a vacation home. In July 2003, they arrived at their property to discover that the cabin was gone. In their absence, someone had stolen the cabin, a shed, a generator, an antique bed, a well pump and a 2,600-gallon water tank. (more details)

    That is proably enough typing for now... :|

    Sounds like a great home to be!
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Brock
    Brock Solar Expert Posts: 639 ✭✭✭✭
    Re: Starting/growing a system

    I would agree go with the cheaper Sams batteries. It will also allow you to "get your feet wet" in the battery area and if you use them to death you will learn and be better off when you buy your next set. Although even Sams carries a T105 type battery (tell them it's for a golf cart) I have found they are better then the stowaways in marine use and cheaper per watt as well. 4 should get you going.

    I would lean towards the EU2000i for portability reasons and if you ever need more it is a great backup as well.

    I would also suggest maybe 120w or so of solar just to keep them topped off when your not there, this will also get your feet wet in the whole solar area and give you a better idea of what kind of solar you will actually get at your location.
    3kw solar PV, 4 LiFePO4 100a, xw 6048, Honda eu2000i, iota DLS-54-13, Tesla 3, Leaf, Volt, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • System2
    System2 Posts: 6,290 admin
    Re: Starting/growing a system

    Sorry for the delay in following up. Thanks for responses, particularly BB - that was a lot of work. You actually touch on a lot of topics that I was referring to when I said I'd try to keep it brief.

    Your cost analysis is right on, although it's not always about the short-term cost calculations. However, it does make me realize that I need to carefully consider my solar needs, as a couple panels and a decent charge controller may run ~$2k, which is a pretty steep price to pay for a few kWh per month if we're going to be running the generator anyway. This is particularly true considering the rebates currently in play in CO for installed systems - after rebates, we can put 1kW grid-tie on our house in the city for about $4500, so it seems to me we would be far better off investing our solar money there than spending a few $k on a system whose output will largely be spent maintaining a $250 battery bank.

    As for the powerline cost, you're way high, but it's not cheap. We haven't gotten an official quote, but it would probably run $15k or so, depending on the details. This would be on poles, and I'm not sure how you account for the cost of having to deal with @#$# ugly poles running up the road. No clue about whether bringing it in buried is an option, but that would certainly cost even more. So, it simply makes zero sense unless we decide to live there full time (or we are looking at resale value, which we currently are not), so for the moment it's not on our radar.

    On the battery front, after reconsidering I picked up 4 GC2 golf carts from Sams, figuring that writing them off in a year or two is an acceptable price for getting into the game. It leads to my next question/area of research, which is charging strategy. Seems to be three main options:
    a) haul them back to town every trip, and keep them charged up from the grid
    b) put a small (1-2%) solar charger in place. Ensure that they're charged up from the genny before we leave, and hope the panels keep them somewhat topped up without killing them.
    c) disconnect them when we leave, and let them self-discharge while we're not there. Hook them up and recharge via the generator as soon as we arrive each trip

    a) is a royal pain, and I'd like to avoid it. So the question is whether a 1-2% charge source would be worse than no charge source at all. Assuming that we could give them a full charge and/or eq charge via the generator each trip, would the 'trickle' be more damaging to the overall life than simply disconnecting them and letting them sit idle? Seems like all approaches are less than ideal, but that's what we'll be facing in the near term.

    Thanks again for the responses.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Starting/growing a system

    "a) is a royal pain, and I'd like to avoid it. So the question is whether a 1-2% charge source would be worse than no charge source at all. Assuming that we could give them a full charge and/or eq charge via the generator each trip, would the 'trickle' be more damaging to the overall life than simply disconnecting them and letting them sit idle? Seems like all approaches are less than ideal, but that's what we'll be facing in the near term."

    it can be worse if you elect not to put some regulation on the pvs. even a simple controller would help in preventing damage to the batteries while you aren't there. with no regulation you run risk of overcharging and boiling out the electrolyte leading to premature battery failure. at the same time leaving them without the pvs the batteries are being left to self discharge without a mainainer on it which also leads to damage and premature failure if done for long lengths of time and often enough. many simple and cheap leadacids can lose 7% a month. with the maintainer from pvs and a controller you may find those batteries could last many years as oposed to a year or so that you may be counting on them lasting. other factors will come into play for just how long they will last for you in addition to the maintainer circumstance, but i'll not get into the other areas at this point as i've answered your question hopefully well enough for you to make a good decision on.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
    Re: Starting/growing a system

    Boy, you guys are spoiled up there in Colorado... $15K for a power line 1/4-1/2 mile... My brother-in-law (San Jose, CA) paid this year around $10k+ just to bury (in dirt) his utility feed 30' from his newly remodeled home to the power pole right on his fence line. Most of that was city "fees" (not even a new utility customer)...

    Trying the "cost" of power line calculation again (note that there is a miss-statement in my earlier post, the utility power was based on 20 years instead of the 30 year that I stated--Fixed above calculation:

    Assume $15k, 1/2 mile, 30 year useful life to you (capital costs), and $0.10 / kWhr. And the period of use is 5 years.

    $/kWhr = ($15,000 * 5yr/30yr) / (5 years * 16 kWhr * 26 weeks/yr) + $0.10 per kWhr = $1.20/kWhr + $0.10/kWhr = $1.30 per kWhr for a powerline dropped into your building site and light usage (better price).

    May be worth looking around to see what power on property is worth vs those properties that do not have power (I know, power lines are ugly--can you run phone/cable/Internet wires at same time and share costs?)... Any possibility that, if, somebody wanted power 10 years from now and get stopped because of environmental issues and/or "high" developer fees that make it horrendously expensive (developer fees are famous around California Cities--it's for the children)...

    Regarding using batteries... I would only use them if you want some silence (especially in the evenings). However, trucking them around every weekend (depending on how far you have to drive) may cost you more in fuel than the batteries can even store...

    One GC2-H-6V battery rated at 245 ah @ 20 hour rate or 245a * 1 hr * 6 V * 50% (battery discharge level) = 0.735 kWhrs (or about $0.07 worth of home utility electricity--or 0.735 kWhrs / 5.45 kWhrs/Gal = 0.135 gallons of gas in the generator--or little more than 2 cups of gasoline equivalents per battery). 4 batteries, 2.9 kWhrs of storage.

    If you are developing the land... you will slowly be leaving more and more of your property up there. 4 batteries in a locked container/shed with 30-60 watts worth of panels and a cheap charge controller to keep them topped off is probably fine. Or, to charge them after a full weekend of use--drained and 5 days of charge time would be around 175 watts worth of solar panel(s)--based on an average May day of production for me and charging losses... 175 watts of Solar panels would, at least, give you the best bang for your buck if they charged for 5 days between weekend trips... Save at least a 1/2 gallon of full and 2-4 hours of generator runtime just to charge the batteries from a weekend of use... Assuming that none of this becomes a "target" during the week.

    Me being me... I would go for option d)... I would make a small solar/battery/inverter/AC bat charger maintainer backup kit for my home and see if I can still get the rebates... (design ability to switch grid-tied solar panels (at least a few) to a backup MPPT charge controller/bat/inverter for emergency use). You can always move the entire setup to the cabin when you are ready for it (again, as emergency power or evening lighting/radio loads). Use the MPPT charge controller (like Outback MX60) because you can still use 80 VDC -- not the usual grid tie voltage of 200-550 VDC--but much easier to wire the panels to be "switchable" in an emergency. But, still more of batteries looking for a use--than not... Some folks even mount the whole thing on a trailer for portable "clean/quiet power"...

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Starting/growing a system

    in hearing these outrageous fees has anybody ever went ahead and bought poles on their own and put them in? it has to be cheaper than the utility, but not necessarilly easier. why not one step further and put the wires on the poles too leaving the hookup to the utility after inspection? in any case i believe it would still be very expensive to do leaving solar/wind a more viable solution.