Best way to use electricity from solar panels

Discussion in 'Eco Talk' started by Unclebirt, Nov 5, 2020.

  1. Unclebirt

    Unclebirt New Member

    Hello,

    I have just had solar panels fitted together with a battery and i am thinking about the best way to use the
    electricity once the sunny days return. My first thought was to fit a cistern with an immersion heater - the old cistern was removed when the combi boiler was fitted some time ago. Then use the hot water for bathing and washing-up. However, since the solar panels were fitted some two weeks ago there has only been two days when there has been enough sunshine to fully charge the battery. So for most of the winter i would be using bought electricity to power the immersion heater, if the heating was purely done by the immersion heater rather than the boiler.
    One possibility is to have a valve to decide where the hot water comes from - the cistern or the boiler, presumably controlled by the temperature of the cistern, another possibility is to have the inlet to the boiler from the cistern. The boiler is a Worcester Greenstar Highflow 550CDI , anybody have an opinion as to what effect it would have on the boiler receiving possibly hot water to the inlet.

    thanks
    Unclebirt
     
  2. Creek

    Creek Member

    I have been using a solar immersion controller for the past 5 years to heat a 210L tank.
    It's been really good as all the surplus solar electricity the house is not consuming goes to heating water. Only after the tank is fully heated, is when I export surplus electricity.
     
    Notnowvicar likes this.
  3. Unclebirt

    Unclebirt New Member

    Hello Creek,

    Thanks for the reply, i have a question -
    when the water in the tank (which has been heated by the surplus electricity) is not hot enough for say a shower or bath - where does your hot water come from ?
    thanks
     
  4. masterdiy

    masterdiy Screwfix Select

    birt, It sounds like you are not charging enough from your panels to even charge your batteries.
    You have a Combi Boiler, that will feed hot water to whatever tap, & will also provide for a shower. (have you an electric shower? or what?)

    So with Solar, the idea of adding batteries is to give you some electric power when the sun goes down.

    Forget the other cistern with an immersion heater, as you will be adding expense & not saving.

    Can you tell us, what system solar & Kw batteries you have??
     
  5. Bob Rathbone

    Bob Rathbone Screwfix Select

    Use a pressurized hot tank and feed the hot outlet into the cold water inlet of the combi. Then the water going to the combi will be pre heated or even hot enough and you will save gas. No need for complicated control systems.
     
    stevie22 likes this.
  6. Creek

    Creek Member

    I also have a timer set up to use Economy 7 electricity to heat the water early morning. (We all have showers by 9.00am so the tank has cooled waiting for the solar immersion to reheat the tank. I occasionally use an oil boiler to heat the water. Mostly December/January when not much solar is being produced.
     
  7. Unclebirt

    Unclebirt New Member

    Hello Bob,

    This was my thinking as it was the only method that i could think of that will use the excess electricity produced during sunny days, and only use the gas boiler to heat
    the water up to the temperature required for the shower/bath and washing. I just needed any comments on the do's and don'ts (if any) of connecting the HOT outlet of the
    cistern to the COLD inlet of the boiler - will it have any effect on the boiler apart from the saving on gas used.

    masterdiy - it's a Solax system with 18 panels and a 5.7kWh battery

    I have been looking at the Telford tempest cylinder range - any reviews ?

    thanks
    birt
     
  8. masterdiy

    masterdiy Screwfix Select

    birt, Right OK.
    You might find unless south facing, that your system might not be able to push much into an immersion heater & to cope with charging the batteries as well.??
    I think you would need to ask some experts on that matter. But charging up the batteries would be the best option in the first place. Otherwise you'll have flat batteries, which isn't a lot of good.

    I have a 4Kw solar system, that is producing enough for battery storage as well.
    Currently looking at 5Kw battery storage, as most days in the winter I can charge sometimes 5Kw a day.

    Quote "I have been looking at the Telford tempest cylinder range - any reviews ?"
    I don't know enough about that to comment. But good luck on that one.
     
    Last edited: Nov 5, 2020
  9. Unclebirt

    Unclebirt New Member

    Hello masterdiy,

    The house is an extended semi - the majority of the panels are on the front roof which faces due south with the remaining panels on the west side.

    The system has been fitted for about 2 weeks, on two of those days the battery has been 98% charged but from a 10% base - it has only gone down to 0% on one occasion,
    any ideas why it is not routinely going down to 0%.

    Yesterday, the 4th November it was very sunny and when the battery got to 90% - we had the electric cooker on - cooking all sorts of food to use up the electricity, and then
    switched on an electric heater. I am waiting for an EPC before requesting the Feed In Tariff.

    Two things have surprised me - 1) how quickly the battery becomes fully charged on a sunny day, 2) how little charge there is on a cloudy but reasonably bright day
    - direct sunlight without cloud is the thing

    So - come the spring i want to be in a position of using the electricity to heat the water rather than using the gas boiler alone.

    birt
     
  10. masterdiy

    masterdiy Screwfix Select

    Is there any feed in tariff anymore??? I thought that stopped last year??

    Quote "any ideas why it is not routinely going down to 0%".
    Sorry no idea.
    You could ring your installer & ask them.
    Did they give you an estimated charge rate per year?
     
  11. Bob Rathbone

    Bob Rathbone Screwfix Select

    It was something I had considered with our Worcester combi, not sure what the maximum input temp of the water should be, but their is only a flow sensor on the input side of the heat exchanger, then it is all hot from there. Good luck with the project. I may be looking at solar off grid for a workshop next year but I do expect to have so supplement the solar with a diesel generator in the winter, but that will give hot water for the central heating, so not so bad. It would cost £15k to get the grid connected so solar and batteries look attractive.
     
  12. Ronaldmc

    Ronaldmc New Member

    I've had my solar panels installed three years ago. I pay about $40 per year for my power. I will pay a small amount for power during December and January.
     
  13. Bob Rathbone

    Bob Rathbone Screwfix Select

    Hi Ron, in the US you have 'nett metering' I believe. They will not do that in the UK:(
     
  14. Ronaldmc

    Ronaldmc New Member

    Agree with you.
     
  15. Alex0908

    Alex0908 New Member

    I'm considering of installing solar plants. But I heard that people say they are too expensive, and doesn't really help to save up money on electricity bills. Can someone share their experience?
     
  16. masterdiy

    masterdiy Screwfix Select

    Alex, as there is little to no feed in tariff now, the fitting of solar is to reduce Your use of electric via the grid.
    Savings will be had on a monthly basis, but as for paying for itself within 4-5 years will not happen.
    So the only saving you will have, is to use what it charges during daylight hours.
    Think of it as a green measure, & not to make money. But as they say, every little helps.

    Battery storage is also available, & that would help in the evenings, when the solar isnt charging.
     
  17. Notnowvicar

    Notnowvicar Screwfix Select

    Well my solar off grid install was £5.2k for a self install of 4.2kwp (rated- actual 4kwp) + 6kw of battery storage (yes i know blah blah self install the electricity po po will be round to drag me off), we added a tank in the loft as a thermal store later. Was it worth it hmmmm kind of..our average electricity use is average of 10kw a day 3720kw last year.

    standing charge is payable no matter what so is ignored

    On grid costs are 3720kw at 31p a unit + vat =£1210.65

    with solar of 4kwp summer was great no bills from may to august, battery charged and enough to run the house 24/7

    Wahooo but average cost are a silly thing with solar, monthly costs are the real deal as the sun sinks in the sky the light spreads out and solar efficiency drops, cloud cover turns off solar with a bang.

    By october we are getting on average 4 full batteries a week but here is the but that's it, it is either charge battery or run the house for 4 hours max. As we are out a lot we went for batteries first. The issue we found was there is an inverter overhead to change 12v to 240v its not immediately apparent when you run during the summer as there is a glut of electricity .. basically we got on average 21kw a week from 24.3kw stored.

    In terms of costs we get nearly free electricity during the summer may to august so a saving of 950kw or 237kw pm ( its summer we are out...) or £294 but again that's not the whole picture as the size of the inverter for our 4kwp is 3.5kw max so whilst all the background stuff is covered tv, computers fridge etc our 7.2kw hob or 5kw fan oven are not and we still draw from the grid for those. There is no battery boost that output has to go through the same inverter, if you want to have the battery and the panels you need another inverter @ £700 a pop.

    sept and april we get get roughly 1/2 our electricity from solar...our usage has increased to 320kw so we save 160kw @ 0.31 = £49.60pm

    October to march..95kw is about it per month can go up but it can sit a nothing for a month Jan this year we got 8kw... our electricity usage shoots up to 2200kw for the period oct/march.

    so 2200 - 6 x 95 = 570 kw solar = 1630 drawn from the grid. So our saving is £176.6

    So over the year we have a leccy saving of £578...so that gives us a a break even at £5200 / 578 = 10 years..assuming that the panels do not degrade or anything goes bang... which it has for us the inverter gave up the ghost at 3 years ( the warranty was 2 years so no surprise

    Basically that size of system will give 4000 kw a year but at precisely the time of year that you do not need it....

    We fitted a thermal store , which has increased our return by about £90 a year over electricity.

    I now wish that we had spent the cash on large rads for a heat pump....
     
    Last edited: Apr 18, 2023
  18. matbram

    matbram New Member

    If you aren't filling your batteries, then I would just leave it as is. Your batteries then can be used to power anything at night etc.

    If you find on sunnier days that you are filling your batteries, rather than trying to heat water etc (which will then lose hear over time if not used), I would recommend fitting more batteries. This is really the most flexible way to collect and use electricity in any way - so if your needs change throughout the year (let's say aircon in summer and water heating in winter) then the electricity can be used in anyway.
     
  19. Abbadon2001

    Abbadon2001 Screwfix Select

    I assume this is on a thermal store then?
     
  20. Jimbo

    Jimbo Screwfix Select

    Can be used on any tank.

    Standing losses from DHW cylinders make them rubbish batteries though.
     

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