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  • FIRST POST
    • LB?
    • By LB? 12th Feb 18, 3:13 PM
    • 12Posts
    • 7Thanks
    LB?
    Failing to understand my PV diverter
    • #1
    • 12th Feb 18, 3:13 PM
    Failing to understand my PV diverter 12th Feb 18 at 3:13 PM
    Hi - hoping someone can help me understand what I've got wrong with my Solar PV + diverter.
    I've lurked for a long time, and saught advise from some very helpful members a good few months ago - but now I'm stumped.

    I have had Solar PV for several years, and at the end of last year my gas boiler was at "end of life" so I looked at the options for a replacement and decided not to go for a Combi but have a "standard" Gas boiler and an immersion tank with an electric element and a Solar iBoost+ to allow me to divert surplus PV generation during the day.

    The new system was installed and the iBoost+ was briefly tested, but being just about the worst time of year for Solar the diverter has been getting very little use (coupled with the fact that we've been using the Gas boiler to heat the water on a timer).

    At the weekend we had a particularly sunny morning so I was eager to see the system work in the way I expected! We had showers (the shower takes the Hot water from the tank) and let the shower run to the point where the water temperature dropped noticeably. The H/W timer was not on at this point so I expected the iBoost+ to kick in but the display said "Tank Hot" (or words to that effect) and no diverting took place. I haven't worked out what was going on - and a short while later I ran a Hot tap and the water was indeed hot!

    So I'm rather confused at this point - Why would the shower have gone cold if the Water tank was still Hot (which is what the iBoost+ was indicating)?

    I know the diverter does work - because a few weeks ago I emptied the hot water (ran the Hot taps until they went cold) and saw the diverter kick in and heat the water as expected. Also there has been a small amount of "Energy saved" shown on the iBoost+ display over the past few weeks!

    Does this make sense - I suspect there is something fundamental that I have misunderstood but I just can't see it at the moment.

    Any help appreciated.

    Thanks all.
Page 1
    • ASavvyBuyer
    • By ASavvyBuyer 12th Feb 18, 7:05 PM
    • 672 Posts
    • 1,682 Thanks
    ASavvyBuyer
    • #2
    • 12th Feb 18, 7:05 PM
    • #2
    • 12th Feb 18, 7:05 PM
    Does the hot water tank have two elements in it?

    If it does, is the iBoost connected the top or bottom element?

    If it is connected to a top element, the top of the tank may already be hot enough.

    But, I would assume it is connected to the bottom element, where it should be.
    Rhondda Cynon Taf, 4kWp, W roof, 30° pitch, 16 x 8.33 Eternity 250w E+10 panels, Solar Edge SE4000-16A Inverter + P300 Optimisers & REUK Diverter
    + Toshiba RAS-10G2KVP-E Ultra High Efficiency Air Conditioner/Heat Pump
    • DREKLY
    • By DREKLY 13th Feb 18, 1:16 AM
    • 147 Posts
    • 111 Thanks
    DREKLY
    • #3
    • 13th Feb 18, 1:16 AM
    • #3
    • 13th Feb 18, 1:16 AM
    It could be that the internal thermostat inside the immersion heater element is set too low, so the i-boost thinks it's reached temperature
    and the contacts have opened.. perhaps ?

    Check it is set at 60 to 65 C by removing the cover, and adjust as
    necessary, with the power off, of course !

    My Immersun shows exactly the same "HOT" display once water has
    reached the set temperature, the element is in the top, and it does not
    take much diversion to reach that required temp, there's just not a lot
    of hot water compared to if it had a lower element - it could benefit from some sort of stratification pump to circulate the water inside the tank, but that's another topic altogether !
    16 x Enhance 250w panels + SolarEdge Inverter + TREES
    • silverwhistle
    • By silverwhistle 13th Feb 18, 9:03 PM
    • 1,706 Posts
    • 2,243 Thanks
    silverwhistle
    • #4
    • 13th Feb 18, 9:03 PM
    • #4
    • 13th Feb 18, 9:03 PM
    Keep an eye on how much the iBoost is putting to the tank to get a better idea of the situation. Today the sun came out very briefly and I managed 0.07 kWh, but yesterday it too 4.00kWH and I got the HOT display.

    You could have a problem with stratification and hopefully one of the physics experts will be along soon. Try increasing your thermostat level too. Perhaps experiment with drawing some hot water to maybe induce turbulence and mixing within the tank. Finally, wait for the sunnier weather and longer days: mine does all my hot water from around March!
    • LB?
    • By LB? 14th Feb 18, 8:36 AM
    • 12 Posts
    • 7 Thanks
    LB?
    • #5
    • 14th Feb 18, 8:36 AM
    • #5
    • 14th Feb 18, 8:36 AM
    Thanks for the comments and suggestions.

    I think I need to repeat the experiment in a slightly more "controlled" way to make sure the gaps between my observations weren't longer than I thought - hopefully this weekend.

    There is only one element, I wasn't aware of the internal thermostat - I assumed it was all controlled by the external one (on the side of the tank).

    How does the iBoost+ determine that the water is "Hot" - clearly it takes a temperature reading but I don't know how or at which part of the tank. Talk of stratification makes sense to a certain point (with a reading being taken at the hottest part of the tank?) - but the shower running cool would seem to indicate that the water is being drawn from the coolest part of the tank while the reading is still "Hot" for the iBoost+.

    We are currently over-using the Boiler for the Hot water until we can reach the point where the iBoost+ can do all we need (March?)
    • Dave Fowler
    • By Dave Fowler 14th Feb 18, 8:55 AM
    • 458 Posts
    • 810 Thanks
    Dave Fowler
    • #6
    • 14th Feb 18, 8:55 AM
    • #6
    • 14th Feb 18, 8:55 AM
    The iboost doesn't measure the temperature of the tank, it relies on the thermostat in the immersion heater. When it opens, the iboost gives the indication 'water hot'.

    Dave F
    Solar PV System 1: 2.96kWp South+8 degrees. Roof 38 degrees. 'Normal' system
    Solar PV System 2: 3.00kWp South-4 degrees. Roof 28 degrees. SolarEdge system
    EV car
    Location: Bedfordshire
    • LB?
    • By LB? 19th Feb 18, 12:29 PM
    • 12 Posts
    • 7 Thanks
    LB?
    • #7
    • 19th Feb 18, 12:29 PM
    • #7
    • 19th Feb 18, 12:29 PM
    Thanks Dave - I guess that makes sense

    I've noticed the readout on the iBoost+ has "Saved n.nn Kw" several times over the past few days, so it is clearly kicking in at some point. I'll wait until we have better Solar before re-testing - I think the eventual aim is to have the water heated almost exclusively by Solar over the good months (Mar/Apr to Sep/Oct?) with a bit of help from the Gas Boiler for approx. 15 to 20 mins early morning (showers are often around 05:30 so if the water temp has dropped overnight this should top it up a little?).

    Thanks all for the comments
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