Small things matter

Wood stoves, pellets and other bio-fuels
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Joeboy
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Small things matter

#1

Post by Joeboy »

We were out and about and passed through Rothes at the weekend. Found an excellent wee junk shop. Bought an upgrade kettle for the woodstove. I estimate that at about 3 minutes per boil and 8 cups a day saves us around 0.879kWh E per day. Over a 7 month stove run (Scottish off season) that's about 1/4 MWh. Crazy eh?
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Seems odd that an essentially inert bit of kit can make such a difference? I'm still on the hunt for a small copper back boiler to mount external on the stove and run a rad off it just to see. If the result was good I'd run the pipes upstairs to a rad to extend the stoves reach.

Edited due to horrendous man maths.
Last edited by Joeboy on Tue Jun 08, 2021 11:11 am, edited 1 time in total.
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Paul_F
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Re: Small things matter

#2

Post by Paul_F »

Specific heat of water is 4200 J/kg.K, and a mug is usually 0.3 l (0.3 kg of water). Assuming that the water comes in at 10°C on average over the year, and you're drinking 8 cups a day that's:

(8 x 0.3) x 4200 x 90 = 907,200 J/day
1 kWh is 1000 J/sec for 1 hour = 1000 x 60 x 60 = 3,600,000 J

So your actual energy consumption (expressed as hot water) is 907,200 / 3,600,000 = 0.252 kWh/day -> 92 kWh/year

Two possibilities here - either your estimate of 3 minutes to boil a kettle is wrong (and it sounds very long to me for a cup of water) is wrong, or you're drastically over-filling it and the rest of the boiled water is going down the drain or contributing to space heating as it cools in the kettle.
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Joeboy
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Re: Small things matter

#3

Post by Joeboy »

Jings, man maths only 2.2kWh/60×3x8x7months = 0.187MWh. Paul, your working is more impressive (and accurate)! I am making 2 cups at a time (me n Her) and we like a big mug. :)

Also not including the pre heats of water for cooking which diet depending can be large. Fire on being closer to 8 months than 7 would push the figure North.

Although that doesn't defend that my Man maths was WAY out. :)

I guess I just like the idea that an already outputting resource (the stove) can have such a knock on effect. The lowering of gas volume burned was the first and most obvious knock on.
In this case the switch not being thrown to burn or draw from battery stack in marginal times, the whole alchemy of woodstove heat converting to electric not used impacting on battery charge not depleted which with a bit of luck was charged by some Winter Sun which might get us through a night without grid grabbing is just too cool not to draw attention to. :shock: :D

I am continuing to claim a 1/4MWh as its too good a figure not to. Its an 'angels dancing on head of pin' type deal. :lol:
Last edited by Joeboy on Tue Jun 08, 2021 11:10 am, edited 2 times in total.
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Bugtownboy
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Re: Small things matter

#4

Post by Bugtownboy »

Paul hasn’t taken into account the mass of the kettle. Sure that’ll get you to the magical 0.25mW Joe

;)

Must admit, stew/crumble/pie tastes better cooked on the stove.

That extra umami of cooking it for ‘free’.
spread-tee
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Re: Small things matter

#5

Post by spread-tee »

Tea doesn't count in the UK, it is totally essential to life as we know it, even 50 brazzzillion trillion PWhrs a day!! it's a small price to pay

Perhaps Paul-F doesn't drink tea....................... :shock:

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Paul_F
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Re: Small things matter

#6

Post by Paul_F »

spread-tee wrote: Tue Jun 08, 2021 6:17 pmPerhaps Paul-F doesn't drink tea....................... :shock:
Assam for preference, but I can't do maths properly without it. With it, however, I can actually count how much energy is required to make it...
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Joeboy
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Re: Small things matter

#7

Post by Joeboy »

Temperatures dropping, rain is on. It's with great delight that I have my 1st test run for the rice. Wee pot now earning it's keep! :)

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SWMBO & I have been discussing how satisfying this life is. WAY more interesting than just throwing a switch and pulling from the grid?
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Ripple 7kW WT & Gen to date 15MWh
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Joeboy
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Re: Small things matter

#8

Post by Joeboy »

I thought this was Summer, where'd it go? Past few days we have been generating 'only' around 16kWh between both systems. Luckily with the woodstove doing the cooking, heating and drying and the extended battery stack taking all the power produced we are easily managing to run the house as normal, chuck an hour of power into the HWT and charge the EV a bit, without touching the grid.

This would not have been possible last year, as alluded to before in my horrendous man maths post. The woodstove is taking up a lot of the electrical load (kettle, cooker, tumble dryer) and the extra battery capacity means I have the headspace to chuck power about in the evening (HWT&EV) knowing we'll be good to go the next morning with remaining capacity until time and meager flow of electrons tops em back up.

This experience coupled with a thought the other day about the varying shades of off gridding made me wonder what you guys do to exclude the grid from your daily life?

I also bought a small back boiler off the back of an excellent post last year by Biff and will be having a crack at using it externally on the stove in a strap together test which is guaranteed to aesthetically horrify SWMBO.

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18.2kW PV SE, VI, HM, EN & DW
Ripple 7kW WT & Gen to date 15MWh
42kWh LFPO4 storage
95kWh Heater storage
12kWh 210ltr HWT.
73kWh HI5
Deep insulation, air leak ct'd home
Zoned GCH & Hive 2
WBSx2
Low energy bulbs
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Stinsy
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Re: Small things matter

#9

Post by Stinsy »

Are you trying to effect a lava lamp with your stove?
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Joeboy
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Re: Small things matter

#10

Post by Joeboy »

Stinsy wrote: Thu Jul 08, 2021 10:45 am Are you trying to effect a lava lamp with your stove?
No mate, good thought though. Just where it lives! :)
18.2kW PV SE, VI, HM, EN & DW
Ripple 7kW WT & Gen to date 15MWh
42kWh LFPO4 storage
95kWh Heater storage
12kWh 210ltr HWT.
73kWh HI5
Deep insulation, air leak ct'd home
Zoned GCH & Hive 2
WBSx2
Low energy bulbs
Veg patches & fruit trees
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