Off Grid Home Forums Technical Discussion Solar power – help/advice needed please

  • This topic has 10 replies, 5 voices, and was last updated 13 years ago by Anonymous.
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  • #62871

    Hi all

    Firstly let me brief you on my off-grid project. I have a small static caravan/mobile home on some land in Greece. I want to provide most of my power via solar and have the following approx daily power needs:

    6 x 7w light bulbs x 4 hours

    1 x 60w 12 v TV x 2 hours

    1 x 70w LCD laptop x 2 hours

    I have been quoted by a Greek solar supplier and told that I need a total of approx 600WH for this

    They have suggested that I use:

    1 x 125 W panel

    1 x 166AH battery

    1 x solar controller

    1 x 700 w inverter

    My lighting circuit is currently on the caravans 220v ring – supplied via the main electricity hookup point to the caravan (hence the inverter)

    I intended to run a 12v cable to supply the laptop and TV

    My questions are:

    1) Would it be more beneficial (in terms of power usage) to take my light circuit off the mains 220v hookup and try to power via 12v? (the lights are all currently 220v 7w bulbs) – how much would I gain if so?

    2)I have considered upgrading the system quoted slightly to give me more redundancy by:

    a) Upgrading the panel from 125w to 175w

    b) Adding a second battery wired to the other

    Do you think this is worth doing? How would I connect the two batteries together to give me the most benefit? (ie in series or parallel)

    3) Would I take the feed for the 12v system from the load output of the charge controller or from the battery terminals?

    4) I intend to take the 12v off to a car quad lighter adapter (as thats the plug fitting that all my 12v appliances use) – is there any loading issues I should be aware of? (eg can I use my 12v TV and kettle at the same time)?

    5) Is it the case that I need to keep the cable run as short as possible for the 12v system? How much power per meter of cable do I loose approx?

    Sorry for all the questions – completely new to all this!

    If you can answer any I would be most appreciative


    Your last point about keeping the 12V DC wiring as short as possible gives the hint for most of your other questions. Shifting from the 220V mains to direct DC is going to be lossier. Power loss in a cable or wire is a linear function of current flow in amps. Generally one of the small inverters running around 80% loaded can reach conversion values above 90% efficiency. Your wiring losses could be much greater. Connect your charger controller to battery terminal and take your 12V feed from the battery. You need the presence of the battery in order for the charge controller to work effectively. since this is a 12V system adding extra batteries must be connected in parallel. Given your location in Greece adding extra panel capacity if you are not increasing your load may simply result in the charge controller disconnecting earlier due to lots of sunshine. You may be better off using the area to install a solar hot water collector.


    I’m currently trying to learn as much about DIY solar installations myself. If anyone can recommend a simple, jargon-free website or book I’d be grateful, and hopefully that would also help the original poster answer their questions too. Cheers.


    Reading up on solar power installation is a must. I first read the Solar Living Source Book, then the Independent Home. That was back in the late 90s, and there are more current books like here;

    I wish I had known about using thick aluminum foil underneath the sheet rock between the inverters and phone lines and stereos, amps, etc. separating the inverter locale from these things. The prolific EMI/RFI does cause problems.



    I can understand your frustration with the EMI issue. While I worked for Xantrex we conducted some tests. We ran spectral emission tests on both a MSW and pure sinewave inverter. same capacity and same loads.

    ther was a huge difference. The guy who ran the tests was a ham operator and his special peeve was the hash emitted by must inverters. ham radio guys call the noise emitted in specific frequencies ‘birdies’ and are most annoyed when these birdies happen to sit in their part of the radio spectrum.

    The prosine model completely squelched them. Bose rado also like the prosine model because it did not produce any clicks or noise in their hign end reiever such as our competitors did.

    Are you using a pure sinewave inverter?


    Hi, elnav, My main house system is twin DR2424s com linked for my well pump and in a special split shed add on vented with a separate compartment for 8-L16Ss below, also vented and weather sealed. The exterior wall is uninsulated to warm the insulated attached shed, and has 5/8″ fire rock on the outside of the wall in the compartments. On the inside is the 220 standard 100 amp circuit breaker box and 1/2″ drywall. I used two 5/8 x 96″ ground rods, one for the box and one for the batteries, then used a 6 gauge wire to link them for potential equalization. They are just over 4′ apart and should have been at least 6′ apart. The phone line comes in 2′ away. Originally I had regular dial up and the computer right under the circuit breaker box. It slowed the computer down and put a buzz in the phone. I got an EMI meter and it read unhealthful 1′ and closer. I moved the computer across the room, went to DSL and the filters keep the buzz out from my phone line and the phone line to the satellite TV. Originally, I stapled thick aluminum foil to the wall, which was really tacky. If I would have known, I would have put the thick foil on the wall under the rock!!! THAT wasn’t in the Independent Home or the Solar Living Source Book!

    When I added on another system in the garage I used a Puresine 1000 for my guitars and a selectable MSW for use with the Staber washer and power tools and lights. I still lined the inside of its cab with thick Al foil. However, the MSW, when on, still interferes with my amps, with both inverters on, because of gaps at the hinges and under and over the compartment. The EMI/RFI escapes easily through any gap.

    In my Earthship I use a Puresine 180 which gives no noise to my smaller amps and guitars out there unless I am using the CFLs and a single coil guitar, which I don’t do, even in the garage with its CFLs. If I’m playing with the lights on I only use humbucker guitars.

    If I would have known, and the prices were like today, the original system would have been an SW2440 with step up transformer. Back then the two DR2424s w/o cover piece were 2K. The price of the SW2440 w/transformer was close to 5K. Now, it is down to around 3K while the new designation 2424s are about 2.5K a pair.

    Idle current usage was also a concern. The Trace/Xantrec with the search mode is low power use at idle (.1A) and so is the original MSW inverter I had in the garage. A UPG1300/6000 mounted vertically, which wore it out after 8 years, now replaced with an 800/2500 w/remote switch (higher idle than the UPG’s .09A). I had left the UPG1300 on all the time because of its low idle, it was $100, now up to $300, and mount the inverters with cooling fans horizontally!!!



    Part of that EMI is conducted by the power wiring, not radiated as you supposed. In other words the MSW waveform in the power lines contains enough harmonics that harmonics of the fundaamental frequency is radiated from each power line carrying the MSW power to lights and appliances.

    Even chokes will not totally eradicatee it.

    The cheap solution is to shut off the MSW power when you want clean sound or else find a buyer for your non sine wave equipment then go buy sinewave inverters to replace them. ( expensive solution)

    BTW that twin DR2424 design approach is terribly expensive. Unless you really need a huge surge power for a deep submerged well pump a simpler approach is to use a step up transformer and a soft start module on the water pump.

    Franklin the well pump people sell a soft start module for around $175.

    The Trace/Xantrex model inverters with a laminated iron core transformer can only handle surges of 2X but the high frequency switch mode like th Prosine can handel surges even greater. When large enough cables are uses and they are short I have measured 3X surges wwithout the inverter shuting down. Right now I find Victron and Mastevolt products superior to Xantrex products.


    Yes, at the time, the twin DR2424 approach was much cheaper than a large sine wave inverter with step up transformer. It was for the huge power surge and use of the 470 ft. deep well pump (220VAC, 1 HP), 120 feet away. Half of the original house system was just for that!! I also used the house power for the addition and Earthship tools like Skilsaw, table saw, cement mixer, big router for trim and cabs, and 22.5 lb. Bosch Demolition Hammer with 5″ compactor face for tire and ground compaction.

    I turn off the MSW for the addition with the remote switch when not in use. The Prosine 1000 is used without that MSW on for buzz free amp sound. However my little Puresine 180 does put out some buzz in my Earthship on its Marshall MG15MSZW. I’ll have to refoil its area, but it still hits the lead wire to the three outlets and lights. It was only $80, and the requirements out there do not justify the huge expense of a Prosine. I just play loud, instead.


    I’m not familiar with a Marshall MG15MSZW.

    Sounds like the puresine180 is not so pure

    You might try some ferrite chokes right before the outlets to see if that will knock down the buzz. Corcom is a long established filtermaker that may also have a solution. Last time I checked they were not expensive.


    Thanks elnav, I had forgotten about them. I used to have a couple on my extension cords to the amps, and lost them when everything was taken out for painting. I just bought 5-10mm, 2-12mm, & 2-9mm ones for $13.05 total on ebay.


    A book I like is from the 1970’s called “Producing your own Power”, I have some articles about producing your own electricity at Home Energy Production-Electricity

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