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  • Re: Advice on buying a good used laptop?

    Make sure to have good backups (if needed).

    SSD drives are reliable, but usually do not give any warning before they die.

  • Re: Advice on buying a good used laptop?

    Linix Mint (or Cinnamon?) is not bad (or others). Very easy to install (easier than Microsoft products). And use Open Office or LibreOffice are good alternatives (for Linix or Microsoft OS). Linix will allow you to boot and run from USB memory stick to see if you like or not (dual boot possible too). I suggest that ~2 GBytes of main memory is about the minimum to run the modern OS (Windows XP shipped with ~250-500 MBytes minimum--Amazing. Don't even bother to try and run modern OS with that small of memory--Will barely install and not really run any useful programs).

    All free and stable. Pretty compatible with MS Office (newest file types not always "convertible" between Open/Libre and MS office--I just save in an older file version to be sure).

  • Re: Mistake in Startup Construction Project


    Yep, that is correct. When you have panels on a moving structure (mechanical, wind, ice, etc.)--You want to make sure the copper wire does not work harden and break (finely stranded cables are used in areas where lots of flexing occurs--Such as line cords, welding cables, locomotive wiring, etc.). Solid and coarse stranded cables where they are not subject to moving/bending--House wiring, fixed wiring in cabinets, etc.).

    You don't (for example) want a run of cable that can sway in the breeze--The constant motion will work harden the copper and possibly crack the insulation at fixed points (random wire tie, gland nut entry, etc.). And plastic wire ties generally do not do well in full sun (there are UV/Outdoor versions, but I would still suggest metal bands/ties). Your electrician may have some alternatives/advice.

    Entrance of flexible/moving cables into "the box" or panel j-boxes will focus strain and flexing right at the gland nut (or whatever you are using).

  • Re: Equalization with Victron 75/15 MPPT controller

    Need to see charging voltage and current closer to solar noon.

    Bulk = all available power from solar panel
    Absorb = hold charging voltage ~14.75 volts for 2-4 hours (estimated) then drip to float voltage around 13.4 to 13.8 volts.
    Float = around 15.0 volts for 1-2 hours typical

    On a sunny cool day neat noon with panel pointed at sun, a battery below ~80% state of charge (oor good size dc load), i would expect a typical best case Bill charging of

    220 watt panel × 0.77 panel+controller derating = 169 watts into the battery

  • Re: Mistake in Startup Construction Project

    You are in a tough situation... you might be better with two panels flat (or 5 degree tilt for cleaning)--That would give you nearly 3.8 hours of sun in December (with two horizontal panels).

    So, two panels flat, December average sun (this is long term average, if you have one or more days in a row of really dark storm clouds, you could get at little as 1% to 5% of "predicted output" those days:
    • 200 Watts * 0.77 panel+controller deratings * 0.90 battery eff (assuming LI ion or AGM battery) * 1.90 hours of sun per day (Dec) =  263 Watt*Hours per average December day

    Assuming 2watt+8watt+8watt running 24 hours per day:

    • 18 watts * 24 hours per day = 432 Watt*Hours per day
    During winter, I do not see how two panel back to back (with random sun orientation) or even two panels flat without shading can keep up with December sunlight (let alone during bad weather).

    I suggest 10% to 13% rate of charge for a "full time off grid power system" as a starting point... If you have 18 watts of load and limited solar panels, you may need to up your panel size/number to get enough power to both fully charge the battery bank and run your daytime loads... Also, I think your battery bank AH (Watt*Hour rating) is a bit on the small side (about 1 day storage--suggest at least 2 days of storage and 50% maximum discharge--Most rechargable chemistry batteries will die if taken to zero or negative state of charge)

    Something like this would be a suggestion (two days of "no sun" operation and not too hard on battery banks--Note that some battery banks using various LI Ion chemistries really need a Battery Monitor System to keep the batteries in an acceptable operating voltage range for safety and good battery life--Another post):
    • 432 Watt*Hours per day * 2 days storage * 1/0.50 max discharge * 1/12 volt battery bank = 144 AH minimum battery bank @ 12 volts
    And to charge such a battery bank from solar:
    • 144 AH * 14.5 volts charging * 1/0.77 panel and controller derating * 0.05 rate of charge = 136 Watt array minimum (weekend/non-winter operation)
    • 144 AH * 14.5 volts charging * 1/0.77 panel and controller derating * 0.10 rate of charge = 271 Watt array nominal
    • 144 AH * 14.5 volts charging * 1/0.77 panel and controller derating * 0.13 rate of charge = 353 Watt typical cost effective array maximum
    Because you are running loads during the daytime/during charging, I would suggest taking the above results and adding:
    • 18 Watts * 1/0.77 panel+controller derating = 23 Watts additional panel (charging while running system--Not a big deal in this case).
    And then there is sizing the array based on your loads... Note that most off grid systems have variable loads (don't do wash/pump well water during bad weather or run genset if needed). The typical maximum load from "predicted numbers", I would suggest ~65% to 75% of predicted numbers... For example:
    • 432 Watt*Hours per day * 1/0.65 "continuous load fudge factor" * 1/0.61 typical solar derating for off grid DC system * 1/1.90 hours of sun per day (December) = 573 Watt array minimum (December flat array)

    You may have some charging current issue (depends on battery type, charge controller type/model, etc.)--But I would be suggesting a minimum of 573 Watt minimum "flat mounted" array for the minimum amount of field maintenance/irritated customer calls.

    Anyway, the above is just a starting point based on a lot of assumptions on my end... Your thoughts George?