Need help planning my off-grid system

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Need help planning my off-grid system

I am strongly thinking about going off-grid on my new house that we are building. The cost to bring PG&E to the house will be 15-20K. I have estimated my energy use of the new house to be about 10kW per day (4-5 of that is for reef aquarium and turtle pond). I have a kill-a-watt meter on the way and will be find out more then. We are a young growing family (3 yr old and one in the oven) with not too much for income (I am a public school teacher). I plan on my income increasing in the future as I have plans to work as an administrator.

I would like to do a hybrid system, using a medium sized solar array, a diesel or propane generator, a decent sized battery bank, and most likely wind power. Due to my limited funds right now I plan on (if needed) having the generator due my bulk charging every three days or so. I am having problems sizing my system and deciding what products to use.

PLANNING:

I am having problems sizing my system. I figure my battery bank needs to hold 2750 amp hours @ 24 volts or 66000 watt hours for 3 days of backup. That would be 28 L-16 batteries in 7 strings (not sure if I will use these or larger Rolls batteries). I can get the high capacity L-16’s through my dad at $225 a piece.

I really do not know where to go from here.

My current thinking is getting 10 190W Evergreen plans from Sunelec.com. I was planning on using the UL listed blems, in case I ever need to resell. Solar panels seem to be the expensive for what the produce. I will mount these on a fixed panel rack that can adjust for seasons. I will make this myself. My zip is 96013 and plan on about 4.5 sun hours a day and I have full exposure to the S, SE, & SW.

I plan on using an auto start diesel or propane generator. I would like to spend the extra money on an 1800 rpm generator. I have no clue what size needed (how fast will it bulk charge batteries?) or which brands are good. I want to use the generator every 3 days or so to bulk charge. My preference would be to run it as little as possible, but I have no problem using it.

As far as wind, I believe my site has good potential. I have visited two bergey 1kW generators. They were kicking butt, but way too loud for my liking. This concerns me. I would like to research further or here comments on the Skystream or the Pacwind Delta I. How loud is the skystream? I am awaiting the new performance charts from pacwind (been in touch with them). I still do not understand how to size hybrid system and what to realistically expect out of the wind generator. The wind generator is the one reason I have been thinking of running my batteries at 24 volts and not 48 volts. Can wind be ran efficiently at 48 volts?

My powersystem will most likely be a MidNite E-Panel, magnum invertors, and hopefully (if it is out soon) the MidNite CC. I was thinking about the MS-4448, but have been thinking that have two invertors might be wise for redundancy. Any other sizing thoughts need here? Comments?

As you can see, I have some work still to do, but I have been learning a lot in the last few weeks. One thing that is confusing is getting different answers and ideas on how to do this kind of setup. It seems every company does things differently. Any help or ideas for me?

thanks,

michael

Comments

  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
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    Re: Need help planning my off-grid system

    Your most pressing issue will be financing, If the home doesn't have grid power, getting conventional loans is problematic at best ... so make sure this is resolved before anything else
  • System2
    System2 Posts: 6,290 admin
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    Re: Need help planning my off-grid system

    I have identified a few mortgage companies that do off grid financing. I still have my mortgage broker looking into some of the "special" details needed, such as teacher programs. It looks like it will not be a great problem finding financing. Both off-grid homes I visited were also bought/built using convential mortgages.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,471 admin
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    Re: Need help planning my off-grid system

    Reality wise, you probably would be best off paying $20k for the power lines and, when you are ready, installing a grid-tie solar system (and I would suggest that solar hot water for domestic and space heating possibly should be installed before solar electric--in terms of the best bang for the buck).

    From very rough numbers I have played with before comparing the cost per kWhour between Grid Tie and a true off-grid system roughly 3-4 times the cost per kWhr (between $0.25 vs over $1.00 per kWhr).

    You appear to be near Reading California, so you should have good sun most of the year--good for solar.

    Also, I believe the current California rebates only pay for Grid Tied systems--not for off-grid systems. It is very possible that you could pay for the Utility lines with the money you save in batteries and inverters, and the extra money you qualify for in Grid Tie rebates (worth around 1/3 of the total system costs--installed, retail at ~$10 per watt of solar).

    Connecting power lines, I would hazard to guess, is only going to get more expensive and more difficult (permits, growth limits, zoning, etc.) as time goes on.

    I understand the pull for a true off-grid existence... But the price of maintenance (generators, batteries every 5-15 years, fuel, etc.) will probably equal, or cost more after all of the accounting is done, than bringing utility power in and using Grid Tie solar. If you will need emergency power (storm, grid failure, etc.)--Generally, it is cheaper to install a backup generator for those few times it would be needed (keep fridge/freezer/aquariums running) than to create an entire off-grid home/installation.

    In any case, your #1 job should be conservation in building the structure to take advantage of the sun, shade, lighting, thermal mass, and new technology equipment (heat, cool, appliances, conservation life-style, etc.).

    Reading through Home Power Magazine and working with your architect/designer to avoid some very basic mistakes made by many people (i.e., too many windows, improper use of thermal mass) will be worth it with respect to future costs and livability.

    My 2 cents worth anyway. ;)

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
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    Re: Need help planning my off-grid system

    Bill, I completely understand what you are saying. I have looked into being on the grid also and still have some more looking to do.

    What I really need right now is more knowledge.

    How am I supposed to know which is more cost effective in the long run, if I do not fully understand what my off-grid system will look like and what it's costs will be?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,471 admin
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    Re: Need help planning my off-grid system

    The off-grid system becomes more complicated because of the nature of the beast--storing and providing energy based on the needs of the batteries and the appliances. The addition of a generator anyway for winter weather, and the inefficiencies of conversions from solar to DC to battery to DC to AC (typical system).

    The Grid Tie Inverter can be around 95% efficient converting DC solar to AC utility power--but so can the charge controller... However, with the Grid Tie the power goes either directly to your appliances and/or out through the meter (spinning it backwards) out to the grid--with just a little loss in the wires.

    With the Off-Grid system, much of the solar power goes from the panels, to the charge controller, and then into the battery--that battery (if wet cell lead acid) costs you about 20% in losses right there. Then, there are the losses of re-converting the energy back into AC--another 10-20% loss there... And lastly, since you can only store about 3 days of usable power, any extra power generated (during summer, you guys on vacation, etc.) is forever lost--beyond that what the battery can store (Grid Tied, you can "store" up to one year's of energy--depending on your net metering plan--you can even "pre-use power" in one season and make it up back in another system--something that a battery system cannot do). You add up the losses because of battery/inverter losses and other issues--the solar panels have to be 1.5x to 2x as large with a off-grid/battery system.

    And, there are the variation between summer and winter generation--for you system (see below for exact numbers), from a 3kW system, you can get ~500 kW during the "sunny months" and down into the ~150 kWhrs in the "dark months"... So, you need to make those losses during the winter--either by cutting back on energy usage (OK, if you have heavy summer loads, like A/C), or, more likely by a fuel driven generator (and maybe alternatives like some wind power too)...

    Generator power (gasoline) will probably cost you on the order of $0.50 to a $1.00 per kWhour just for fuel--let alone the costs for wear and tear.

    You add the costs for batteries (and their replacement every hand full of years), the extra equipment required (chargers, inverters, generator, maybe wind-turbine), and long periods of cloudy weather (fuel costs).

    I went through one winter 23 day period where my system, which could generate ~10 kWhrs per day (on sunny winter day) average just 3 kWhrs per day, and I went 3-4 days with less than 1 kWhr per day--that December I only generate less than 1/2 the predicted amount of electricity because of bad weather (and I live in a realtively sunny area of the state).

    Can you build an off-grid system--sure. It is neat (and) expensive project. Is is cost effective--less clear.

    Over the years, I have read many articles (back when solar panels and the electronics were much more expensive than today), and there seemed to be a sweet spot at about 100 kWhours per month, if you can get your monthly usage down to that level (or below), the equipment is not that expensive and the maintenance (cleaning batteries, watering, size of the wiring, etc.) is reasonable... 10 kWhrs per day is a pretty large system--especially if that system needs to generate 10 kWhrs per day winter and summer.

    From the link I posted in another thread (solar calculator), a 3 kW rated system system for 96013...

    kWH Month
    ==============
    163 January
    247 February
    370 March
    421 April
    495 May
    501 June
    550 July
    519 August
    450 September
    344 October
    168 November
    133 December
    4,363 TOTAL

    On average, you needed 10 kWhr/day = 3,600 kWhrs per year... A 3 kW grid tied system with net metering can do it pretty nicely.

    However, if this was an off grid battery system, you average uses at 10 kWhr/day because 15+ kWhr/day or 450 kWhrs/month or 5,400 kWhrs per year...

    Your off-grid 3kW system (with about ~3.5kW of solar panels) could (at best) only supply 100% of your power needs from April through September and just 30% of your needs during December (or less in bad weather)...

    Again, depending on your actual seasonal loads, the numbers may be better (or worst)--and these are averages. The real numbers for any particular period can be much worst (or somewhat better).

    IMHO, the 1.9 kW of solar panels would not be enough power for a 10 kWh/day (really 15kWhr per day) load. And seven strings of "smallish" batteries would be a cabling/maintenance/operational nightmare (again, in my humble opinion--using much larger batteries would help here).

    Wind-Sun's store has price listings for all of the basic components, and good FAQ's in the various categories (charge controllers, inverters, batteries, etc.) where you can read up on their suggestions...

    In the end, comparing 20 years of off-grid solar costs (cost of purchase and maintenance) vs 20 year amortization of utility line + power costs (with optional grid tie solar to reduce exposure to ever increasing electric rates)--I would be hard pressed to ignore that utility feed...

    One way to look at the utility feed costs... assume 20 year payback period and 10 kWhrs / day usage...

    $20,000 / (10 kWhr/day*365d/yr*20yr) = ~$0.27 per kWhr + $0.12/kWhr electric rate PG&E E1 rate @ 300 kWhr/month
    effective rate of = $0.39/kWhr (for 20 years)

    $0.39 per kWhr is not cheap--but it is still cheaper than anything you can generate with an off-grid system.

    Plus a 3 kW $30,000 grid tied system will be eligitable for ~$8,000 in CA state rebates (plus another ~$2,000 in Fed tax credits). Something that a off-grid system (at something like twice the installation and maintenance costs--SWAG) is not even eligible for.

    I hope that this helps give you some ideas.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
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    Re: Need help planning my off-grid system

    Bill, I understand that you really really favor being grid tied,mainly for logical reasons. I see you post in most threads saying such. Once I understand what my off-grid system looks like, I will be able to do a cost analysis.

    Still looking for some understanding in how to figure in my wind production and the how the generator plays into this. Most folks I talk to about sizing off-grid systems, ignore the generator and wind.

    I can understand wind, as it is hard to calculate what it will put out (at least it is for me). I know that some corp is planning a fairly big commercial wind farm about 10 miles west of us, but on a ridge. I have what I think is a good site for wind, but I am unsure what the turbines will produce.

    Is it a bad plan to want to use the generator every three days or so to bulk charge the battery bank?

    In regards to the battery bank; Lets say I want to take my battery bank to 50% DoD. If my battery bank has three days worth of storage. What happens with the energy my solar/wind is producing during those three days.

    Lets say I use 1/3 of my storage the first night. The next day my solar produces more energy than my current load uses. Does the rest go back into the battery bank? How does that effect my 50% DoD? (This is just one example of my lack of understanding)

    ?? Any help??
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
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    Re: Need help planning my off-grid system

    It's winter, you have the furnace fan on, and the rain/sleet has been coming down for 2 days. Windmill blades are iced up, and have no "bite", no sun and batt's have approached 50% You can't turn the furnace off, or the pipes will freeze. Now's the time you have to fire up the generator, and rapid charge the batteries. And it's a 80' walk in the rain/ice to get to the power shed to start it up, because the auto-start relay died last year.

    You likely wouldn't be any better off with grid tie, 'cause all the power went down when the ice took out the wires.

    There are lots of scenarios brought up here, give it a week to get lots of replys, feedback, and and see what others are asking about too. I understand you want to price out your system, but till you have a firm handle on what your loads are, you don't know what size to set your battery bank at. Most folks settle at 3 days, and assume they have to run genset a couple times a year. 2 Days battery, and you may have to run twice a month, was 10 gallons of fuel less expensive than a 3 bank of cells in the battery farm ?
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
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    Re: Need help planning my off-grid system
    Mikeyvon wrote: »
    Lets say I use 1/3 of my storage the first night. The next day my solar produces more energy than my current load uses. Does the rest go back into the battery bank?

    How does that effect my 50% DoD? (This is just one example of my lack of understanding)


    1st night/2nd AM = 80% capacity (20% discharge)

    Daytime
    excess recharges batteries. now at 90% cap (10% dis)

    then 4 day storm settles in.

    Winters have short days, and less sunlight available for recharging, your PC/TV is on more, and the coffee pot runs to keep hot.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.
    BB. Super Moderators, Administrators Posts: 33,471 admin
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    Re: Need help planning my off-grid system

    Sorry Mike--I guess I sound like a broken record here at times.

    One way to think about solar (or any complex engineering system) is to look at everything as a block... The batteries--a block of energy storage. The inverters, a DC to AC conversion block. The Charging block, several sub sections--one that draws and regulates power from solar panels, another one that draws power from a fuel powered generator, and others--like Wind Turbine). And there are losses as power passes through each of these blocks (battery ~20%, solar charger ~5%, inverter ~10-20%, etc.).

    Realistically, the only block in this setup that can be damaged by improper use is the battery itself. The other parts (charging block, inverter block, etc.) will operate based on available energy and storage space--but will not be damaged by these normal operations.

    So, focusing on the lead acid battery... The issues are; 1. battery is temperature sensitive, 2. produces hydrogen gas and is filled with sulfuric acid, 2. should not be deep discharged (typically, below 50%), and 3. should be "fully charged" ideally within a day or three of being discharged.

    So:

    1. The batteries ideally run around 70-80F-- if it is too cold, they can freeze (and break the case). A battery freezes at lower temperatures if it is fully charged. Battery charge voltage is temperature sensitive--so having a charge controller that monitors the temperature is important. In general, for every 10 degree Celsius increase in temperature, the battery life is cut in 1/2. A battery forms sulfates as it discharges, and these sulfates begin to harden after approximately 1 day and hardened sulfates do not recover during recharging (from what I have read). So recharging a battery after use is very important.

    So, that gets back to how you use a system. Discharging and charging the batteries within these limits, and they should last pretty well. That would mean that if you have more that a few days of no sun--then you would have to fire up your alternate charging source to recharge the batteries and power your daily loads during the time the sun does not shine.

    2. The battery storage area needs to be ventilated to prevent hydrogen build up and explosions. The hydrogen gas is formed during the equalization charging (converting the water in the cell to hydrogen/oxygen--electrolysis--during the last bit of the charging--and especially during equalization).

    3. Monitoring the battery change by just watching its voltage is prone to errors... The battery should sit for several hours, without loads/charging currents, then the voltage accurately measured (against a temperature correction chart). The better method is to use a battery monitor that measures current into and out of the battery bank. It is much more accurate and can be read for capacity at any time (under load, charging, etc.).

    I am more of the school that a few, very large batteries in series, is preferable to a bunch of "smaller" batteries in multiple parallel strings. Filling fewer/larger battery cells, less cabling, higher voltages (lower current--12 volts vs 48 volts systems).

    Getting a bunch of parallel batteries to current share can be pretty difficult. Cables, connections, etc. should all be identical for each of the parallel banks for the batteries to properly load share. One battery manufacturer I read said that they found series connected banks to last longer than parallel connected banks.

    Wind-Sun, the owner of this site, themselves said they don't see any life difference between parallel and series connected banks in terms of life--so, if properly designed, either will probably work OK for you.

    The inverter (DC to AC conversions). There are many good suppliers out there that have many options for true sine wave inverters (vs modified square wave)... But they are not cheap. You best need to define the loads you have first, then pick the units that might meet your needs (120, 240, low standby loads, efficiency, connections with charge controllers and generator controls, etc.).

    The charger block--now that you know the downstream requirements (load, inverter, batteries, losses), you can size the charger. Solar panels are probably the highest cost per watt--but if you have good sun and a place to mount them, they are probably the least maintenance/lowest long term cost component of the system. But, there is a ~4:1 output between summer and winter months in your area (and mine). And it can be made worst if cloudy weather (or recently, major brush fires) reduce your capacity.

    And only you can decide if you want the solar panels to supply 100% of your load during the summer, but 25% of the load during the winter--or if you have seasonal/optional loads... A/C during the summer and lower electrical use during the winter. Optional loads--washing, drying, vacuuming, TV, etc., that you can load shed during periods of low sun..., will all help you reduce the absolute size of your solar array.

    Solar panels themselves have issues--voltage (and power) drops during hot weather (need good air flow for cooling, more panels if in hot area). Voltage changes between cold and hot weather--need to look at the extremes to ensure that charger/grid-tie inverter can accept the range of voltages.

    Wind Turbines, if you have the land to mount them, and the ability to service them are a good backup to solar--in many areas, the wind is high when the sun is not shining (stormy weather). They are mechanical units so there is more maintenance required (getting the turbine down off a hundred foot tower has always been my question--renting a crane vs a tilt up tower and those issues/limitations--but I don't have the land or wind--so it is not something I am real familiar with).

    Generators--your choice, gas, diesel, propane, natural gas... Look at the fuel flow rates vs kWhours generated. A good Generator/Battery system is probably the most efficient. Running a 10 kW generator to run a 200 watt TV is not great. Running TV on batteries for a few days, and running the 10 kW generator to pump 7.5 kWatts back into the batteries (bulk charging) and using the solar to do the final charging/equalization (where currents/power use are relatively low)--a good thing.

    You have visited a few off-grid homes in your area--so you have seen the equipment required.

    Do you have specific brand of equipment you like/dislike? Many of the manufacturer websites have pretty good diagrams/explanations of how it all fits together.

    Also, building a small solar system first (1/2 - 1 kW of panels, a few good sized storage batteries--or even golf cart batteries, with charge controller, battery monitor, inverter) and getting some runtime under you belt (use it like a generator for your home construction site, or to power part of your existing home), would help too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
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    Re: Need help planning my off-grid system
    Need help planning my off-grid system

    I have estimated my energy use of the new house to be about 10kW per day


    I would like to do a hybrid system, using a medium sized solar array, a diesel or propane generator, a decent sized battery bank, and most likely wind power. Due to my limited funds right now I plan on (if needed) having the generator due my bulk charging every three days or so. I am having problems sizing my system and deciding what products to use.

    I figure my battery bank needs to hold 2750 amp hours @ 24 volts or 66000 watt hours for 3 days of backup. That would be 28 L-16 batteries in 7 strings (not sure if I will use these or larger Rolls batteries). I can get the high capacity L-16’s through my dad at $225 a piece.

    My current thinking is getting 10 190W Evergreen plans from Sunelec.com. I will mount these on a fixed panel rack that can adjust for seasons. I will make this myself. My zip is 96013 and plan on about 4.5 sun hours a day and I have full exposure to the S, SE, & SW.

    I plan on using an auto start diesel or propane generator. I would like to spend the extra money on an 1800 rpm generator. I have no clue what size needed (how fast will it bulk charge batteries?) or which brands are good. I want to use the generator every 3 days or so to bulk charge. My preference would be to run it as little as possible, but I have no problem using it.

    My powersystem will most likely be a MidNite E-Panel, magnum invertors, and hopefully (if it is out soon) the MidNite CC. I was thinking about the MS-4448, but have been thinking that have two invertors might be wise for redundancy. Any other sizing thoughts need here? Comments?

    Mikeyvon,

    Knowing your location (96013 = Burney / Redding) and your estimated average energy requirement (10 kWh/day) gets you off to a good start. It would be helpful to standardize on one system voltage for the batteries. A 24 V battery bank is not compatible with an MS-4448 (48 V) inverter.

    Your estimate for a 66 kWh battery bank looks pretty good. That would require a battery bank rated at 48 V X ~1,390 Ah. You could build this from one-, two-, three-, or four strings of batteries, depending on specs. I’m OK with parallel battery strings, but I think four strings is the practical limit.

    Off-grid PV systems are typically ~60% efficient. To net 10 kWh/day from 4.5 hours of “full” Sun, you’ll need a system rated at (10 kWh/4.5 hrs)/60% = ~3,700 W STC.

    A 1,900 W STC PV array would supply ~50% of your stated energy requirement. You’d have a 15 kWh deficit every three days. Assuming 90% charging efficiency and the 60 A charge current spec, the MS-4448 would require a 120/240 VAC generator rated for at least 4,000 W continuous duty. Allowing for modest altitude derating, other AC loads, manufacturers’ puffery, and the long run time, I suspect a generator rated at between 6,000 W and 7,500 W continuous duty would work dependably at ~2/3 to ¾ load with the charge in bulk mode.

    60 A of charge current is probably good enough (~4.3%) for a 1,390 Ah battery bank if the generator is powering downstream loads. The inverter/charger’s 60 A charging limit will pretty much define how long the generator will have to run. Assuming 80% recharging efficiency and absorption stage current limiting, I estimate it’ll take the generator between 8 and 10 hours to fully recharge the batteries.

    I recommend you carefully consider your loads before deciding that a 4,400 W inverter will be big enough. It doesn’t take long for a microwave, a hairdryer, a well pump, and other loads to add up to a big number. You may find that you need a pair of inverters stacked for 120 or 120/240 operation. Besides redundancy, such a configuration could increase battery charge current by 50% and cut recharge time by ~1/3. You’d need a bigger generator, though.

    Decisions, decisions…

    The attached link suggests to me that wind is not a viable RE option in your area. See: http://www.eere.energy.gov/windandhydro/windpoweringamerica/maps_template.asp?stateab=ca

    HTH,
    Jim / crewzer