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Cheap domestic energy storage/ time shifting

edited 30 November -1 at 1:00AM in Green & Ethical MoneySaving
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JKenHJKenH Forumite
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edited 30 November -1 at 1:00AM in Green & Ethical MoneySaving
Now I have solar panels and also Economy7 I am looking for cheap ways to store free or low rate electricity. I have a small (3kwh) battery already. Storage radiators are too expensive in terms of payback time in my view but I like the idea in principle.

I have been considering a 20L tea urn/hot water boiler as a storage radiator in the kitchen. I could, using a timer, heat this up until 7.30am using Economy7 then allow it to cool down over the next few hours. If I have got my sums right it would use about 2 kWh of energy to raise the water temperature from 14* to 100* and then give out about 1.8 kWh as it cooled down to 20*.
(In practical terms I might only heat it to 90* to reduce evaporation.)

In spring and autumn using Economy7 it would give the kitchen, which is on the north side, a boost without having to put the oil fired c/h or a convector heater on. Possibly, if there was excess solar available during the day it could “recharge” to give us a warm kitchen at teatime.

At the moment on cool days we are using convector heater on a 750w setting to soak up spare PV but I quite fancied the idea of being able to store some heat for later.

The cost of our night rate electricity is 7.6p/kWh or 15p to heat up the urn and I would get back 25p’s worth of electricity at day time rates. The cost of a new 20l urn/boiler on eBay is about £45 so it would need 450 morning cycles to pay for itself or 180 PV top ups.

Does anyone else use hot water storage for heating or have any other good energy storage tricks I might try?
Northern Lincolnshire. 7.8 kWp system, (4.2 kw west facing panels , 3.6 kw east facing), Solis inverters, Solar IBoost water heater, Mitsubishi SRK35ZS-S and SRK20ZS-S Wall Mounted Inverter Heat Pumps, Nissan Leaf (plus some ICEs:) )

Replies

  • Martyn1981Martyn1981 Forumite
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    Have you considered a heat pump? This way you get 3-5 times as much heat for your leccy (during the daytime) and the building mass becomes a heat battery.

    Even if you are paying for all the leccy, it'll still beat the normal leccy heater, and most likely the oil fired c/h on cost, but of course not on volume if you need lots of heat.

    Discussion ... ASHP(Air/Air) with Solar pv ....

    With your size system you may well find that you have around 500-700W of spare leccy for the ASHP (giving you 1-3kW of heat) and still be charging the batt.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
  • JKenHJKenH Forumite
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    Martyn1981 wrote: »
    Have you considered a heat pump?

    Thanks Mart, I had been looking at ASHPs/a/c units and am making enquiries in that direction. I had not however considered deploying one in conjunction with the thermal mass of the house for time shifting. In the summer on hot days we do fling all the windows open at 6am and close up again about 9am to exploit thermal mass for cooling.
    Northern Lincolnshire. 7.8 kWp system, (4.2 kw west facing panels , 3.6 kw east facing), Solis inverters, Solar IBoost water heater, Mitsubishi SRK35ZS-S and SRK20ZS-S Wall Mounted Inverter Heat Pumps, Nissan Leaf (plus some ICEs:) )
  • GreatApeGreatApe
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    I would advise against a hot water tea urn lots of people burn themselves quite badly with hot water I have known two over the last two years who have had very very bad burns from kettles/stoves/trips etc. You are just adding a risk needlessly to your kitchen.

    Not really worthwhile but you could shift some refrigeration demand

    Assuming your economy 7 kicks in at midnight to 7.30AM you could set the timer to turn the fridge off at 9pm and then back on at midnight. Then set it to turn off at 7.30AM and then back on at 10AM

    The first time shift will move 0.125KWh of electricity to off peak and the second will hopefully shift upto 0.105KWh from a lower PV output time to a higher PV output time

    Would save you ~£3 a year

    You would get more out of just upgrading a few appliances/lights etc or check that everything is working as it should.

    My neighbor boiler pump was on 24/7 as the storage tank was asking for a temperature higher than the boiler was set to. For arguments sake the tank was asking for 65 centigrade and the boiler was set to 60 centigrade. So the boiler was always on and the pump always on. It was an easy fix just reduce the tank temp to 60 centigrade and increase the boiler temp to 70 centigrade. So the pump is on maybe just 1 hour a day rather than 24 hours a day. Saving is ~2KWh a day in electric and perhaps 10KWh a day in natural gas (pipes between boiler and tank were at 60 centigrade 24/7 rather than 1 hour a day). Something close to £200 annual saving with ~3-4MWh of gas saved and ~700KWh of electricity saved.

    I wonder how many of the UKs ~25 million boilers are set up like this?
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