Solar efficiency

Discussion in 'Eco Talk' started by DIY womble, Mar 1, 2019.

  1. MGW

    MGW Well-Known Member

    The solar panel has a sweet spot where with a set amount of sun light it gives maximum output so both the volts and amps vary with the sunlight, so in the morning the volts and amp will be less than at midday.

    If you fix the volts then the panel will start producing later and will not produce as much at midday.

    As to the immersion a 220 volt immersion heater at 110 volt will still work but with 1/4 of the output, so there is not reason why one element should be connected in the morning as as the day progressed more and more elements are added, the problem would be if an element failed then the voltage would rise to the rest, so it would need some safety system, but if the panel at midday will only produce 230 volt then using elements at that rating would not be a problem even if voltage drops to 50 volt or less.

    However some way would need to be found to control how many elements are connected and close down if there is an error, and as far as I am aware this does not exist.

    So at the moment there is a device which measures the panels output and if more than 3 kW is being exported it switches on the immersion heater as in the early systems you were paid for having the solar panels rather than actually measuring what they produced, as far as I am aware the new meters actually measure in both directions so this is not longer as lucrative.
    DIY womble likes this.
  2. DIY womble

    DIY womble Well-Known Member

    Great had a look at forum ( unable to post )
    Think I understand mppt but couldn't google anything in depth , converts to ac and transforms to suit load and back to DC , to have manual or controlled switching for multiple loads to ease a better power match for different times of the day and year would seem sensible
    I agree with your motives although I have extra incentive as I'm sort of going off grid , houseboat , and would like not to be in the marina unless its to moor to go to plaster the occasional house ( 2 months a year ) .
    So I need occasional power for boat engines to move up and down the river
    And was considering solar charging batteries and hot water tank with option of two elements
  3. JustPhil

    JustPhil Active Member

    Ah well if you’re planning to charge batteries then mppt battery chargers are readily available and not expensive - because they’re very popular (camper vans etc) there’s plenty of cheap options on eBay. Because I’m looking at solar->heater there’s few mppt controllers available for this specific case. You’ll have to spend a bit on batteries - lead acid is still the cheapest option here, rather than lithium - but you can use that to also run a water heater.
  4. DIY womble

    DIY womble Well-Known Member

  5. DIY womble

    DIY womble Well-Known Member

    That seems like a clever piece of kit delivered from all the way from China for such little money
  6. JustPhil

    JustPhil Active Member

    Yep, point well made these are a lot cheaper. Although that’s cheaper than I was thinking! Some reputable brands around the £50 mark. Also agree about small add on systems, I’d gladly spend 300 quid on 300 watts of panels if I could get a cheap controller to run my hot water, taking out a chunk of heating oil. Annoyingly, as an electronics engineer I can see how I’d design one, but quite another matter to guarantee a market for a company to bother and test/approve such a product.
  7. JustPhil

    JustPhil Active Member

  8. big all

    big all Screwfix Select

    ok my thruppence worth
    dont waste your money
    at best you will get enough energy to overcome the heat loss at body temperature in a couple off litres off water
    in other words at most on a cloudy day perhaps 2 or 3 % off the energy needed to heat an emersion
    remember on gas it costs you about 6p for a 1000w
  9. DIY womble

    DIY womble Well-Known Member

    Yes couldn't get any data off the cheap ones to compare and would need to probably start at the battery end and wiring configurations to choose a suitable controller so not wasting time looking at the moment.
    As I'm that way inclined I will go for simple programmable switching circuit to keep batteries topped , dumping excess into hot water tank for showering / heating and perhaps under sink 12v heater for any remote taps .
    Are you considering solar tracking or manual adjustment in a
    understand your point , solar is never going to get close to fossil fuels but want to live off grid and gas / oil isn't for me ( I currently live in a transit in a field and didn't have any heating throughout the winter out of choice )
  10. DIY womble

    DIY womble Well-Known Member

    I have a slight advantage , I need more power in the summer for my boat engines , so when not travelling ( winter ) I will have 2KW system being idle for just led lights , radio and shower
  11. MGW

    MGW Well-Known Member

    Controllers like these [​IMG] are designed to combine solar and wind power for small boats and caravans and charge a battery. With a boat or caravan one huge problem is how to charge a battery in a short time without over charging it or under charging it.

    A standard stage charger has 2 or more stages starting with bulk stage where it charges as much as it can, and ending with a float stage or off. The problem is they use the current going into the battery to work out when to reduce the charge voltage, 14.8 volt on a 12 volt battery is fine when it's 20% charged but can wreck it when 90% charged.

    Since the battery is being used while being charged it can hold the charger in the bulk charge stage, so a different type of fast charger is required. What it does is store the power in capacitors and send pulses to the battery, then it works out battery state by the volt drop between pulses.

    Often narrow boats have two sets of batteries, one for engine only, and then some more for domestic, even cars do this today, my wife's Jaguar XE has two batteries and an inverter to ensure a steady voltage, and charging controlled by the engine management.

    With narrow boats it was normal to have two alternators one for engine battery and one for domestic, to get extra power for the domestic you can get a special inverter which takes the two alternator supplies and combines them so some can charge at 400 amp and This controller will work on panels of up to 150 volt open circuit so there are loads of controllers out there.

    However it is rather specialised so I would suggest you go to a narrow boat forum where these items are normal for them.
    DIY womble likes this.
  12. DIY womble

    DIY womble Well-Known Member

    Lots to read up about many thanks to you all , my immediate instinct is a seasonally and daily configured set up with overload to charging batteries being heating elements , will do some research and let you know if I find anything interesting , busy with work this month and got to get the money when I can, not on the forum as much recently due to brexit fever causing so much bad feelings , be pleased when things calm down , once again , many thanks for all your comments
    chippie244 likes this.

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