Going off grid

[openspaceman]

Two very good posts Alec and Stere and much to think about. I would like to hear from those actually off grid rather than my situation. Personally don't want to be a slave to the system and constantly worry about how much energy I am using but I am careful.

 

In my case the refrigerator/freezer does use a fair amount but as we cook for two we often need to keep food a few days. I suspect I could do without a freezer. It would make sense to set a freezer to run on off-peak electricity, possibly with a deeper thermostat for off peak but currently there are no off peak tariffs and truly off grid have no choice.

 

While I like the idea of Stirling engines in practice they seem to have difficulties. Kockums had a very high tech submarine installation that made good use of the advantages but for domestic use there are problems:

 

1) Stiring cycle favours a small molecule and working under high pressure but the system can be sealed, the microgen uses helium at pressure and the whispergen nitrogen, which is 6 times denser. You cannot use air at pressure as it will react with any common lubricants and burn them.

 

2) Conversion efficiency is low compared with internal combustion (most efficient ic engine is a high pressure gas turbine as used in aircraft)

 

3) Low volume production must affect pricing so for true off grid a diesel or spark ignition engine remains best choice.

 

The LiPo battery entering the arena means a small genset running a constant optimum load and heat recovery makes sense.

 

I have been investigating a DIY thermo electric system as this fits better with log burning that the rest but conversion efficiency is low and the problem is having to pass all the heat flux through the Seebeck device AND be able to use the heat.

 

I'll see what others have to say and then try and respond to individual points made by Alec in individual posts.

[Haironyourchest]

I lived off grid for 8 years. Very basic set up though, so not of much interest I suppose. 100 watts of PV and 120 amp hours in dump salvaged gel-cell Panasonics. Was ok for charging a phone, running a car CD player and a couple of car bulb lights (before the days of LED). Still have the panels but the batteries are long perished. Same system would be more useful nowadays actually, as I have more rechargeable gadgets and the latest led tech is just wow....the problem isn't entertainment comms and lighting, it's heating (kettles, cooking, water heaters, washing machine, dishwasher, toaster). Heating with electricity requires enormous currant. Workshop machines is another problem, but that can be worked around with a generator... 

[Billhook]

I built my house in 1983 with no electricity supply available 

My cousin married an ex RN submariner who was then working at Listers in Tetbury

He organised a Lister Startamatic diesel 3.5KW generator, the sort that goes pleasantly chugg chugg chugg rather than brrrrrrrrrrr!  He also found me some ex sub nickel cadmium batteries which I could charge up when the generator was going and then use them for lighting at night with a 2 kw inverter.  This was ok for lights but because the inverter was square wave as opposed to sine wave there was a loud buzz on tv and hifi 

Together with a Bosky 90 wood stove ( what happened to them?) I managed quite well…………. Until I got married!

Doesn’t life change!!!

[openspaceman]

46 minutes ago, Billhook said:

I built my house in 1983 with no electricity supply available 

My cousin married an ex RN submariner who was then working at Listers in Tetbury

He organised a Lister Startamatic diesel 3.5KW generator, the sort that goes pleasantly chugg chugg chugg rather than brrrrrrrrrrr!  He also found me some ex sub nickel cadmium batteries which I could charge up when the generator was going and then use them for lighting at night with a 2 kw inverter.  This was ok for lights but because the inverter was square wave as opposed to sine wave there was a loud buzz on tv and hifi 

A chap from the BBC TV bought a cottage next to the estate I worked on and had a startomatic and Victorinox inverter in 1974. His mate worked at the CEGB research place 5 miles away in Leatherhead. Bob used to attract loads of helpers, including me, to build his model railway and help out in his workshop, I wish I still had access to his myford 7 lathe.

 

All went well till a house guest got up after Bob had gone to work and had a shave. None of us could figure why the lister kept starting up and stopping a few seconds later, so we disconnected circuits till it stopped happening.

46 minutes ago, Billhook said:

Together with a Bosky 90 wood stove ( what happened to them?) I managed quite well…………. Until I got married!

Doesn’t life change!!!

I've got a Bosky in my garage, bought second hand and never fitted. Along with a rebuilt 2.3 pug 504 diesel engine and a envirofire  pellet stove should anyone be interested for donation to charity.

 

What happened after you married, did you get power laid on?

[agg221]

On 13/12/2021 at 09:56, Canal Navvy said:

Good read (as always) Alec.

Interested in your views on Phase change materials 😉🙂

 

Thanks - there is so much information around on these subjects that posts have a tendency to get rather long, but hopefully not too boring!

 

I did a bit of work on phase change materials in around 2012, working with Northumbria University and a company which worked on Stirling engines at the time (run by a man called Drummond Hislop - who coincidentally went on to be involved in the establishment of HIETA which is one of the leading powder bed additive manufacturing companies these days, but the original interest was in the use of additive for advanced heat exchangers to improve heat transfer). We also had a partner up in Northumbria which makes heat pipes.

 

Phase change materials have several useful properties - one is that you can store a lot more energy in a given volume which is particularly useful if you have limited space. What we were looking at was the ability to reduce energy use in domestic water heating so this was important for fitting it in to flats or small houses. The principle was that people usually run their boilers in the evening to heat the house which efficiently generates hot water at the same time, but whilst a well insulated house will hold its temperature through to the morning, the hot water tank has probably cooled down too much by the morning to be used for showers so the boiler gets fired up again which is very inefficient. If you could hold the temperature steady then you wouldn't need the boiler. This is where the second advantage of phase change materials lies - the energy input changes the phase rather than the temperature, so it is very consistent. You would need a very efficient way to get the heat out of the thermal store and into the water supply, which is what the heat pipes were for. In practice you need a much higher temperature thermal store than the water you are trying to heat, and again a phase change material is one way to achieve this, although of course you could just heat up anything so long as it doesn't vaporise (pressure management is not desirable).

 

In practice, whilst what we were doing worked, it made it so far down the line, the funding ran out and there wasn't enough impetus to keep it going commercially (aka the Valley of Death in innovation terms).

 

These days, the big advantage I can see is as a high grade heat store. For example, if you are generating power and have a high temperature exhaust, putting the heat into water limits you to space heating and hot water. If you can keep the temperature higher there may be more uses for it, such as cooking - imagine plumbing a high temperature fluid loop through a phase change heat store and around a converted Rayburn or Aga. Here, phase change materials help as they give you more compact storage so it's easier to insulate, let you get to higher temperatures so it's more efficient, and give you a very stable temperature which only starts to drop once the phase change has fully reversed.

 

There is a substantial challenge though. Most phase change materials are not too convenient to handle. They are either low melting temperature salts which tend to be very corrosive, or organic waxes which are highly flammable. This makes the plumbing rather expensive. That said, recent advances in coating technology may make the molten salt route more viable.

 

Alec

 

 

[Billhook]

9 hours ago, openspaceman said:

A chap from the BBC TV bought a cottage next to the estate I worked on and had a startomatic and Victorinox inverter in 1974. His mate worked at the CEGB research place 5 miles away in Leatherhead. Bob used to attract loads of helpers, including me, to build his model railway and help out in his workshop, I wish I still had access to his myford 7 lathe.

 

All went well till a house guest got up after Bob had gone to work and had a shave. None of us could figure why the lister kept starting up and stopping a few seconds later, so we disconnected circuits till it stopped happening.

I've got a Bosky in my garage, bought second hand and never fitted. Along with a rebuilt 2.3 pug 504 diesel engine and a envirofire  pellet stove should anyone be interested for donation to charity.

 

What happened after you married, did you get power laid on?

I rather fell on my feet, as I discovered that the main North Sea gas line passes 100 yards from my remote house along the lane going from the main sub station to the local town.  My initial enquiries were fruitless but later they relented and offered a connection for £90 but I would have to supply, bury and be responsible for the 2 inch metal pipe going to the house.  Or I could have the high pressure pipe brought to the house for £200 as long as I dug the trench, so the latter was a no brainer!

For electric I managed to buy some second hand armoured cable for not a lot and trenched it half a mile to the farm but  because of the diameter and length of the cable I was limited to about 6 kw.  This did not matter as I had the gas for heating.

The gas was so cheap for years but as it became more expensive I bought the Aarrow Stratford and linked it to the gas via a Dunsley Neutraliser.  I do not use the gas at all now for heat,  just cooking.

The final part of the story happened about five years ago when Western Power decided to renew their main 33,000 Kw line that runs over the farm, but they wanted to also change the route which meant putting poles in different fields which was a pain to farm around and the whole project was very disruptive.

What would I like in compensation?   Three phase line trenched to my house please!   Grumble grumble grumble, but they caved in at the finish.  So I am not threatened with divorce (over the electric supply anyway!)

[Billhook]

10 hours ago, openspaceman said:

 

I've got a Bosky in my garage, bought second hand and never fitted. Along with a rebuilt 2.3 pug 504 diesel engine and a envirofire  pellet stove should anyone be interested for donation to charity

I see that they still are making Bosky stoves.  Does anybody here run one?

 

Bosky F25-F30

THERMOROSSI.CO.UK

---

Thermorossi Bosky F25-F30

 

[openspaceman]

On 10/12/2021 at 23:08, Watercourse management said:

As per title, with our electricity prices jumping from 15 p per kWh to 27 kWh and not looking like it’s ever going to get a lot cheaper is it time to consider going off grid. 

I have been looking at systems which combine battery solar and wind backed up with a diesel generator to charge the batteries ( lead acid ) when they are discharged to 50 percent, also the genni would be 3 phase to run the workshop instead of using single phase inverters.

anyone have any experience of these systems?

 

I've started back at the beginning as yours is a different case from those people without a grid connection at all. Also you are looking to run a 3ph generator to do tasks your current electricity supply will not manage. Apart from the generator bit you are similar to me in wishing to reduce costs.

 

I don't know what your standing charges are but mine are about £100 for gas and £100 for electricity per year, this is low enough for it not to be worth doing without a connection, even at 3% ROI that would only justify investing £7k in an alternative  and you're not going to get much for that.

 

I cannot comment on the powerguard system as I haven't dealt with generators for 30 years apart from small ones for power tools and welding, which are petrol powered and only used occasionally and briefly where the fuel cost isn't worth considering. @Justme gave a figure of 0.6litre of diesel  per kWh of electricity produced IIRC, as a litre of gasoil contains 10kWh so a conversion of 6kWh of heat to 1kWh of electricity doesn't seem so good.

 

No one other than I has admitted to trying to make use of some of the waste heat.

 

 

What I do have experience of is the inefficiency of running a generator all the time electricity is required  and this tends to be inefficient because the generator is seldom loaded to its optimum. This is where inverters and battery systems  make more sense. Yes run the generator when there is a load but  bring that load up to the optimum for the generator by charging a battery. I hope @Canal Navvy can give us some real world experience especially about Victron and open source because I am a bit disappointed in the proprietary  system running my inverter-charge and 6kWh battery (BTW the PV output has bombed since 6 December when  the solar PV output fell below my consumption from the grid and since then has averaged only about 15% of my usage).

 

Small scale generation tends not to have a good rate of conversion to electricity but if my demand were more than 6kWh/day, such as charging an EV, and given I have a gas connection, I would be looking at running  a little 3cylinder SI engine on gas, recovering the heat for the house and charging car and house battery  at optimum load, and this should use about 270grams of gas per kWh, so just over half the energy of the example above. Yes a thermal store would be needed and the genset may need to run a couple of times a day. In terms of efficiency I feel this would be more economic than running my little diesel car but capital cost of an EV means I'll stick. Also the capital cost of replacing the generator engine every few years would be less than depreciation and O&M cost of a conventional car.

 

At present  I am interested in just reducing my electricity imports a bit more, especially for these few months when the solar PV is not enough. I could invest in more PV panels but want to investigate a better winter production. This is why I liked some of the ideas in the link @Stere cited. The drawback of TEGs is they don't convert a lot of the heat passing through them into electricity but there is a decent match with home heating and potentially from wood. The high (ish) temperature TEGs from the example operate up to 300C (cheaper ones seem similar devices but the solder fusion temperature lowers their top temperature to below 200C and hence lowers the conversion rate). As wood burns at up to 1600C but typical firebox temperatures are around 800C  some though needs to be given for exposing the devices to over high temperatures, this will tend to make a woodstove running at 4kW (e.g. the size I use) considerably larger. This big problem is to get the required delta Temperature will mean a coolant will have to extract all that 4kW at around 30C. To use heat at 30C for house heating means you are almost bound to have underfloor heating. In practice I expect I would like to see my fire and enjoy the radiant heat coming through the glass so 2kW passing through the TEG may be more realistic, it means only 100W of electricity would be available at best  and the cost for the TEG alone would be £750 before the stove manufacture costs were added in. However 100W for 16 hours is 1.6kWh although only a fifth of what I need to be independent of electricity imports at this time of year and I wonder how much the water pump would use.

[Billhook]

Just wondered what became of Taylor Wilson and his ideas.  Might be a solution for a village or small town

 

 

[Justme]

19 hours ago, openspaceman said:

I've started back at the beginning as yours is a different case from those people without a grid connection at all. Also you are looking to run a 3ph generator to do tasks your current electricity supply will not manage. Apart from the generator bit you are similar to me in wishing to reduce costs.

 

I don't know what your standing charges are but mine are about £100 for gas and £100 for electricity per year, this is low enough for it not to be worth doing without a connection, even at 3% ROI that would only justify investing £7k in an alternative  and you're not going to get much for that.

 

I cannot comment on the powerguard system as I haven't dealt with generators for 30 years apart from small ones for power tools and welding, which are petrol powered and only used occasionally and briefly where the fuel cost isn't worth considering. @Justme gave a figure of 0.6litre of diesel  per kWh of electricity produced IIRC, as a litre of gasoil contains 10kWh so a conversion of 6kWh of heat to 1kWh of electricity doesn't seem so good.

 

No one other than I has admitted to trying to make use of some of the waste heat.

 

 

What I do have experience of is the inefficiency of running a generator all the time electricity is required  and this tends to be inefficient because the generator is seldom loaded to its optimum. This is where inverters and battery systems  make more sense. Yes run the generator when there is a load but  bring that load up to the optimum for the generator by charging a battery. I hope @Canal Navvy can give us some real world experience especially about Victron and open source because I am a bit disappointed in the proprietary  system running my inverter-charge and 6kWh battery (BTW the PV output has bombed since 6 December when  the solar PV output fell below my consumption from the grid and since then has averaged only about 15% of my usage).

 

Small scale generation tends not to have a good rate of conversion to electricity but if my demand were more than 6kWh/day, such as charging an EV, and given I have a gas connection, I would be looking at running  a little 3cylinder SI engine on gas, recovering the heat for the house and charging car and house battery  at optimum load, and this should use about 270grams of gas per kWh, so just over half the energy of the example above. Yes a thermal store would be needed and the genset may need to run a couple of times a day. In terms of efficiency I feel this would be more economic than running my little diesel car but capital cost of an EV means I'll stick. Also the capital cost of replacing the generator engine every few years would be less than depreciation and O&M cost of a conventional car.

 

At present  I am interested in just reducing my electricity imports a bit more, especially for these few months when the solar PV is not enough. I could invest in more PV panels but want to investigate a better winter production. This is why I liked some of the ideas in the link @Stere cited. The drawback of TEGs is they don't convert a lot of the heat passing through them into electricity but there is a decent match with home heating and potentially from wood. The high (ish) temperature TEGs from the example operate up to 300C (cheaper ones seem similar devices but the solder fusion temperature lowers their top temperature to below 200C and hence lowers the conversion rate). As wood burns at up to 1600C but typical firebox temperatures are around 800C  some though needs to be given for exposing the devices to over high temperatures, this will tend to make a woodstove running at 4kW (e.g. the size I use) considerably larger. This big problem is to get the required delta Temperature will mean a coolant will have to extract all that 4kW at around 30C. To use heat at 30C for house heating means you are almost bound to have underfloor heating. In practice I expect I would like to see my fire and enjoy the radiant heat coming through the glass so 2kW passing through the TEG may be more realistic, it means only 100W of electricity would be available at best  and the cost for the TEG alone would be £750 before the stove manufacture costs were added in. However 100W for 16 hours is 1.6kWh although only a fifth of what I need to be independent of electricity imports at this time of year and I wonder how much the water pump would use.

I think I might have remembered wrong on the 0.6L per kWh.

More like 0.36L per kwh on smaller units but still bad.

 

From memory diesel engines loose 1/3rd to wet heat, 1/3rd to dry heat & noise & 1/3rd to rotational force. Then add in the electrical efficiency & you can see why its not very efficient to use a genny.