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Off Grid Thoughts

SteamyTea

Entry posted by SteamyTea in Off Grid

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Off Grid Challenges

 

Recently, there has been a few people talking about off grid living. This is an admirable and romantic idea, and something I would like to do myself.

Then reality kicks in.

First we must agree what we mean by off grid. To me it means not connected to main services, but usage of public services i.e. roads, domestic rubbish, healthcare, education, policing, food, clothing etc is allowed.

Basically it comes down to water, waste and power. I have come to these limitations because I cannot live without the others. No one want to see me in handmade clothes and washed only in spring water.

 

So the first thing to look at is how much energy I actually use, and when I use it.

Luckily I take a keen interest in this and log my electrical data every few seconds (a mean of 8.5 seconds). Internal temperature data is also logged.

 

Initially, to keep things simple, I work with monthly data, but will drop down to weekly, daily and half hourly data when needed.

The chart below is the big picture of what I use.

 

image.png.e7418f78914928dafb6bea8f79998931.png

Chart 1

 

 

 

I am generally quite happy with my overall usage and internal temperature. This winter I am experimenting a bit with the temperature as my working hours have changed after 15 years of working evenings I have gone back to working days.

As Chart 1 shows, January to April shows I have my storage heaters on and use a Mean Power of between 0.7 kW and 0.4 kW, then it drops to 0.36 kW in March, then down to 0.25 kW until the end of October.

As you will have noticed, there are two Mean Power lines. One is the ‘normal’ interpretation of the Mean i.e. the sum of all readings, divided by the number of readings. This obviously includes the minimum readings, which are 0 kW and sustained maximum 4.33 kW. ‘Sustained’ in this instance means for at least half an hour. There are times where the Maximum Power peaks at 13.16 kW when looking at half hour data, but this may be for just a few seconds or minutes.

By filtering out the 0 kW times, one gets a more realistic idea of what is actually being drawn and when it happens. This is important as it can help when choosing storage and delivery systems.

Without changing anything, including usage behaviour, I could get an inverter that has a maximum power delivery of 14 kW and know that all my usage would be covered. Storage, for one day, without any inputs, would need to be at least 26 kWh once 20% efficiency losses are taken into account. The 20% losses are based on a ‘best guess’ as this is a very variable percentage based on different power draws, battery charging and discharging temperatures and the state of charge they are at.

 

So what do I use my energy for. Luckily, being on E7, I can easily see what is used for water heating and what is everyday usage.

By looking at my April to November night usage, I can get a fairly good estimate of my domestic hot water usage.

 

 

image.png.1b99dd6bbb8b6933b367c9b843613967.png

 

Chart 2

 

Chart 2 above shows the half hourly usage between April and up to November, when there is no space heating on.

The mean usage over that period is 4.2 kWh, so apart from the washing machine usage and the fridge switching on, it is fair to assume my daily water energy usage is around 4 kWh/day. This is bourne out my my higher than average water usage. One of my many failing is that I like a bath, every day, and would have two a day if I did not curb my enthusiasm.

 

If I fitted a heat pump, to heat the water, I could probably reduce that down to 2 kWh/day. Or if I took showers, less than 1, but I dislike having a shower, though they are good at getting the day’s fat, blood and grizzle off my body after work.

 

image.png.3f1c1b17ca8590c5fc8cab82af75fd78.png

Chart 3

 

 

Chart 3 shows the same data, but for January and February when the storage heaters where on. The daily mean, for space and water heating, has increased to 12.25 kWh/day, so 8 kWh/day are for space heating. This works out as a power delivery, for my house, of 27 W.m-2. Using a heat pump could reduce that by a factor of 3, so less than 2.6 kWh/day or 9 W.m-2.

 

Looking at the mean internal air temperature, I see they are within 0.5°C. This is good as it shows that my heating regime is working well and does not need adjusting.

 

So having got my usage figures, and estimated some usage figures if I changed to a heat pump, what can be done about generating energy on site to cover approximately 8 kWh/day.

 

My house is small, and the roof will only support, at the very most, 3 kWp of photovoltaic. It is also less than ideal facing with the optimal side facing South West.

Looking at PVGIS to get an estimate of what I could generate, highlighting December because it is the worse month and with similar usage to January, it shows that there would be a total generation of 24 kWh.

 

 

 

That works out as around 0.75 kWh.day-1

 

It is not until April that I could cover my usage, and by October a deficit would be showing.

 

The deficits are in the table below.

 

Month

Usage /kWh

PV Generation /kWh

Deficit

January

248

31

-217

February

232

58

-174

March

248

129

-119

October

155

83

-72

November

180

38

-142

December

248

24

-224

 

Whiles the above energy deficits are not that large, they need to be covered.

Even if a battery storage system was installed, without the generation capacity, regardless of how spasmodic the generation, it would still not be covered.

The only realistic generation method is to use a small generator.

Using December’s data, as it is the worst month overall, on average, a 2 kW generator would have to run for 4 hours a day once efficiency losses where taken into account. During these 4 hours, a battery system of 26 kWh capacity, could be efficiently charged with 8 kWh of energy. By having an oversize battery storage system, more effective charging and discharging can take place, and the system will have a longer lifespan. It also allows for some days to probably not run a generator at all depending on the weather.

 

My choice for a generator would be bottled gas (LPG). While diesel may offer a small improvement in efficiency, they are noisy and if the stored fuel gets some water in it, can be expensive to rectify or repair. Gasolene to LPG is a tried and tested conversion.

 

Ideally a combined heat and power (CHP) unit would be used as these offer the best possible efficiency with about 30% of the fuel input turned into usable thermal energy and 20% into electricity. Unfortunately there are no easily available small CHP units or around 5 kW total output.

This would mean that a DIY solution would have to be made. This would be an interesting project. There are some small capacity, water cooled, twin cylinder motorcycle engines that may lend themselves well to this application. There are also cheap, permanent magnet, low speed, direct current current motors that can be driven as a generator.

Noise would be the biggest problem with a generator, but as it may only run for a few hours a day, then it can be used during the daytime. It can also be buried in an earthen bank, with secondary inlet and exhaust systems fitted. Modern cars are very quiet at low revolutions, no reasons that a modern motorcycle engine should be any different. My car, and old diesel is quite quiet at tickover, and it is using 1 kWh of fuel per hour.

 

So to conclude, while it is not possible for me to be ‘off grid’, with a larger, more isolated property, and the use of a generator, and about £25,000 of investment, I could be off grid.

 

Edited by SteamyTea

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Marvin

Hi @SteamyTea

 

wonderful stuff. I have also looked at this but from a different angle. I realised pretty quickly that there are about 5 main areas associated with going off grid electrically.

 

Decisions on how your going to live (candles or going to bed when it gets dark. How your going to cook, wash and so on.)

Total energy used per year.

Peak power requirement

Production source

Energy Storage.

 

We only have electricity. no gas or oil or wood burner. 

We have PV, ASHP and MVHR and Electric car.

We produce about 6000kWh per year

We use about 4500kWh per year

We buy in about 3000kWh per year

 

Just over November we purchased 500kWh

If we could go off grid by storing all our PV energy whilst producing the peak power requirement and not have to generate any extra over the winter and do that for about £20k and keeping our existing life style I think we would. 

 

Problems we face are 

Size and cost of energy storage

Supporting peak power demand

Storing long term, the energy produced in the summer, for the winter.

 

Saying all this things would dramatically change if the building would hold it temperature over the winter and we stopped using high power equipment in the kitchen

 

M

 

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SteamyTea

@Marvin

I think I have just about done all the reduction measures I can (except baths).

I intend to add a bit more insulation here and there, but it will only make a marginal difference.

An EV would make the biggest difference, but at the moment it would not be practical (or affordable) for me.

I could get a lodger again, which would pay for an EV, but I like living in my own.

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mike2016

I'm ordering a Japanese Ofuro bath and plan to heat it with a 2kW electric in line heater for about 2.2 hours per day (21oC->39oC) but keep the water all week. Their approach is to shower first and then bathe and the whole family can enjoy the bath at different times. They then use the warm water for washing clothes at the end of the week. I like the idea of a daily soak and while I could integrate with the hot water heat pump I'm not sure I'll do that up front until I'm sold on daily soakages which is an aspirational project only at this stage for me! 

Anyway, you only drain your hot tank once and after that top up the heat. With some insulation and a cover it reduces the heat loss and saves starting from scratch each time. Some hot tubs even come with heat pumps, a nice outdoor investment if you have a view to enjoy?

 

For the rest of the loads, winter is the real issue. You could do Vehicle to load via an EV to your house but you have to charge the car somewhere and fast charging is a lot more expensive than off peak which you wouldn't have use of without nice neighbours! 

 

It's about transferring energy in it's easiest, cheapest form to maintain the lifestyle you want. Any rivers nearby you could stick some hydro on?! Maybe a community SMR scheme down the road?! Or move to Iceland near a fissure? 

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Bramco

Interesting read - like lots of us on here, I'm always working out ways to reduce our usage and make the most of off peak electricity prices.  Like @Marvin we're all electric, with PV, ASHP and in our case batteries not an EV. Now we're in the new year, I'm just working out what we've used this year.

 

At one point in your analysis @SteamyTea, you say a 20% efficiency loss on batteries would be a best guess.  This is one thing I was concerned after I'd installed our batteries.  What I've noticed is that at low wattage the losses are higher. If this is the case, then there's probably a base loss due to the inverter being 'on' so to speak and then a %age of the actual wattage being delivered. 

 

An example from this morning, with a house load of 323W the inverter was actually drawing 397W from the battery, so 19% - which is about your best guess.  Later in the morning with the ASHP drawing power, the house load was 2953W and the inverter was using 3187W from the battery (2452) and PV (735W), so about 7%.

 

Unfortunately for all battery users the lowest loads will be the most common and higher loads more intermittent, so losses would be closer to the 20% than the 7%.

 

I'll have to try to dump data from the inverter to get more data points, for example when the batteries are being charged, either from the grid or from the PV etc.

 

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SteamyTea
5 hours ago, Bramco said:

 

I'll have to try to dump data from the inverter to get more data points, for example when the batteries are being charged, either from the grid or from the PV etc

That would be really useful data.

I often think people are over optimistic about the efficiency they can get from almost every bit of equipment they own.

Reducing parasitic loads is an area I really focused on a decade ago, it is why I show two different 'means'.

In my larger spreadsheet I can look at the half hourly data and see what is happening.

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Marvin

Goodness me!

 

I have estimated our running energy use (no, not all metered, but a lot of history over the last 5 years and testing on items like the MVHR fridge and freezers, internet, ASHP, TV fire detectors, water softener, telephones, clocks, items on standby and so on)

 

Heating         1,674    28.74%
Hot water      1,460    25.07%
Running         2,190    37.60%
Car                   500    8.59%
Total              5,824    100%

 

I'm going to have to do something about this.......
 

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Bramco
22 hours ago, SteamyTea said:

That would be really useful data.

I often think people are over optimistic about the efficiency they can get from almost every bit of equipment they own.

Reducing parasitic loads is an area I really focused on a decade ago, it is why I show two different 'means'.

In my larger spreadsheet I can look at the half hourly data and see what is happening.

OK @SteamyTea, here's some data for you....

 

Not sure about the 28% line!!  But this shows in general that a low draw in the inverter runs at about 20% loss, while a high draw runs at a much lower loss in the region of 6/7%.  Quite low, the last line is still 11%.  So given your maniacal focus on parasitic loads, batteries will never be for you!!  😄

 

Obviously, these need to be taken as a general rule of thumb, I don't think the data from the inverter on the grid is v accurate for example.

 

Also apologies for the shift in the headings - this is as it came across from Excel.  First 3 columns are what is what is being generated, next 3 columns are what is being consumed.

 

      Total       Load less      
  PV Battery Delivered   Grid Load Grid   Loss %age
Battery to house 0 397 397   17 340 323   74 19%
Battery to house + ASHP 735 2452 3187   18 2971 2953   234 7%
PV to battery and house - low PV 1529 -1139 390   58 374 316   74 19%
PV to battery and house -high PV 4237 -3862 375   55 325 270   105 28%
PV to diverter with export 4747 -17 4730   -1107 3353 4460   270 6%
PV to diverter low PV 932 -21 911   -49 759 808   103 11%
                   

 

 

 

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