Idiot's guide to a self build battery

[Krill]

Energy storage is awkward because unless you know exactly where the energy stored in it came from, what is it you are trying to find out? If I have a chimney brest that stores energy from burnt wood, why would that be counted the same as if it were heated from RE?

I mean, I could count the number of bricks in my walls but it isn't exactly useful information, how much is heated by incidental solar, how much by gas, how much by electric heating (My laptop is an electric heater), how much by the exothermic reactions of respiration...

[Joeboy]

Energy storage is awkward because unless you know exactly where the energy stored in it came from, what is it you are trying to find out? If I have a chimney brest that stores energy from burnt wood, why would that be counted the same as if it were heated from RE?

I mean, I could count the number of bricks in my walls but it isn't exactly useful information, how much is heated by incidental solar, how much by gas, how much by electric heating (My laptop is an electric heater), how much by the exothermic reactions of respiration...

Burning wood is RE, click, throw.

[Oldgreybeard]

Energy storage is awkward because unless you know exactly where the energy stored in it came from, what is it you are trying to find out? If I have a chimney brest that stores energy from burnt wood, why would that be counted the same as if it were heated from RE?

I mean, I could count the number of bricks in my walls but it isn't exactly useful information, how much is heated by incidental solar, how much by gas, how much by electric heating (My laptop is an electric heater), how much by the exothermic reactions of respiration...

I think it's still useful to know how much useful heat is stored in stuff, though. For example, our concrete floor slab is well insulated from the ground, both underneath and around the edges, so almost all the heat going into it is stored until it moves from the floor into the house, by conduction and convection (and an extremely tiny bit of radiation). It's heated by electricity, so knowing the ratio of renewable generation to non-renewable generation allows the RE bit to be estimated.

When it comes to people and pets, then it's reasonable to assume that their heat output is renewable, as most food comes from a renewable source (albeit with a bit of energy during processing that may be partly from non-renewable sources). People output around 80W each on average, children a bit less, and pets an amount depending on their volume, but roughly in a linear relationship to humans, I think.

As an aside, one of the greatest sources of useful heat storage in our house is the plasterboard. Gypsum has a pretty high energy density, so there's a good case to be made for using doubled up plasterboard on walls to increase the heat stored inside the house.

[Joeboy]

Energy storage is awkward because unless you know exactly where the energy stored in it came from, what is it you are trying to find out? If I have a chimney brest that stores energy from burnt wood, why would that be counted the same as if it were heated from RE?

I mean, I could count the number of bricks in my walls but it isn't exactly useful information, how much is heated by incidental solar, how much by gas, how much by electric heating (My laptop is an electric heater), how much by the exothermic reactions of respiration...

I think it's still useful to know how much useful heat is stored in stuff, though. For example, our concrete floor slab is well insulated from the ground, both underneath and around the edges, so almost all the heat going into it is stored until it moves from the floor into the house, by conduction and convection (and an extremely tiny bit of radiation). It's heated by electricity, so knowing the ratio of renewable generation to non-renewable generation allows the RE bit to be estimated.

When it comes to people and pets, then it's reasonable to assume that their heat output is renewable, as most food comes from a renewable source (albeit with a bit of energy during processing that may be partly from non-renewable sources). People output around 80W each on average, children a bit less, and pets an amount depending on their volume, but roughly in a linear relationship to humans, I think.

It's a fair question. 'What are you trying to find out'?
The simple answer is the standalone capacity of Camelot Inc if a big switch was thrown. The muddy area of where the line is for RE I leave to the individual.

The usefulness for me came from becoming aware of how far I could extend today's heat into tomorrow's cycle with stored energy and close a loop. I'd like to think that this discussion will help a lightbulb moment for a household now and then.

[Krill]

Energy storage is awkward because unless you know exactly where the energy stored in it came from, what is it you are trying to find out? If I have a chimney brest that stores energy from burnt wood, why would that be counted the same as if it were heated from RE?

I mean, I could count the number of bricks in my walls but it isn't exactly useful information, how much is heated by incidental solar, how much by gas, how much by electric heating (My laptop is an electric heater), how much by the exothermic reactions of respiration...

Burning wood is RE, click, throw.

Yeah yeah, if you have your own land that you coppice I'd buy that but in general, no chance, and for a list like this? Sure, save the data, it doesn't mean much. It's like when nurses way peoples faeces to check how much food has been absorbed for people with eating disorders, why does anyone really want to have that data?

[Joeboy]

Energy storage is awkward because unless you know exactly where the energy stored in it came from, what is it you are trying to find out? If I have a chimney brest that stores energy from burnt wood, why would that be counted the same as if it were heated from RE?

I mean, I could count the number of bricks in my walls but it isn't exactly useful information, how much is heated by incidental solar, how much by gas, how much by electric heating (My laptop is an electric heater), how much by the exothermic reactions of respiration...

Burning wood is RE, click, throw.

Yeah yeah, if you have your own land that you coppice I'd buy that but in general, no chance, and for a list like this? Sure, save the data, it doesn't mean much. It's like when nurses way peoples faeces to check how much food has been absorbed for people with eating disorders, why does anyone really want to have that data?

Can't say I appreciate your yeah yeah attitude or your negativity. Also it's weigh not way and I didn't know that was a thing. Each to their own though.

[Oldgreybeard]

It's a fair question. 'What are you trying to find out'?
The simple answer is the standalone capacity of Camelot Inc if a big switch was thrown. The muddy area of where the line is for RE I leave to the individual.

In my case I wanted to calculate the thermal time constant of the house, before I built it, as a part of the design process. I wanted the house to stay warm for a long time with no heat input, so as well as knowing how much heating power I needed, I also needed to know how much sensible heat was stored in the materials inside the house.

The heating power needed was easy enough to estimate, just by calculating the fabric and ventilation heat losses and accounting for the incidental heat gains from the occupants and appliances etc. That gave me this plot of heating power needed:

Heating power.jpg (67.22 KiB) Viewed 1074 times

I then wanted to know how much sensible heat the internal structure of the house could store. For example, every sheet of plasterboard stores about 22kJ of heat (about 6Wh) for a 1°C temperature difference, so if the plasterboard warms up during the day (from solar gain) then each sheet (and there are hundreds of them) can store heat to give out during the night when the temperature starts to drop. 100 sheets of plasterboard could provide about 600Wh of useful heat for every 1°C increase in its temperature above room temperature.

[openspaceman]

Can't say I appreciate your yeah yeah attitude or your negativity.

I suddenly had an image of Joeboy as Donald Sutherland laid back sipping red wine.

My view was simply that the thermal mass in a dwelling and its heat storage is difficult to quantify, let alone where the heat comes from; solar gain, hot bodies, wood stoves etc.

An electric powered storage heater is more straightforward.

[Joeboy]

Can't say I appreciate your yeah yeah attitude or your negativity.

I suddenly had an image of Joeboy as Donald Sutherland laid back sipping red wine.

My view was simply that the thermal mass in a dwelling and its heat storage is difficult to quantify, let alone where the heat comes from; solar gain, hot bodies, wood stoves etc.

An electric powered storage heater is more straightforward.

I just fell over! I was actually thinking about a glass of red and I am also fully reclined watching Billions. I didn't know remote viewing had come on so far, impressive!

Agree on difficult to quantify yet its there and working. It was only a thought from a morning cuppa. We'll see how it shakes out.

[Joeboy]

Not sure what's really meant by thermal mass, TBH, it seems to be something often quoted but quite hard to really define. I think the key thing to know is the heat capacity, i.e how much useful heat energy is stored in any particular thing, either in Joules or Wh, perhaps. The mass is a bit irrelevant, I think, as energy density only uses volume and energy. For example, concrete stores about 2,122kJ/C° of heat per cubic metre.

You don't need to know the mass of a cubic metre of concrete to work out how much useful heat it contains, you only need to know the difference in temperature between the volume of the lump of concrete and the room temperature.

It's easy to measure or estimate the volume of something and easy to measure its temperature, so just using the energy density for common building materials allows the useful heat stored to be quickly calculated. I've listed below the energy densities for some common materials (taken from the Engineering Toolbox site). To convert these numbers to kWh/m³.°C divide them by 3600:

Brick = 1,813kJ/m³.°C

Granite = 1,896kJ/m³.°C

Concrete = 2,122kJ/m³.°C

Fireclay = 2,200kJ/m³.°C

Cast iron = 3,889kJ/m³.°C

Water = 4,190kJ/m³.°C

You must be that clever guy I was speaking about, nicely done and an excellent set of figures for longterm reference. Very cool OGB, cheers!