Hybrid Off Grid Energy Feasibility

[Iceverge]

We went on hols for a week and I monitored the energy use in our absence. Our house is all electric. Passive class, no heat pumps or woodburner. 

 

I turned off everything except the following. 

MVHR ,Fridge/Freezer ,Biocycle septic tank. Total  3.68 kWh/day. (153 watts)

Heat Loss from the immersion powered 300l UVC @70deg. 1.64 kWh/day (68 watts equivalent load) 

 

Total background load 221 Watts or 5.3kWh/day of which 30% is heat loss from the cylinder. Granted everything except the septic tank is inside the heated envelope so it contributes to the heat load for the 3-4 months of the year it's needed. 

 

Our daily electricity use is 20kWh of which normal use is about 11kWh DHW (including tank heat loss) 3.68 kWh background load and 5.32 kWh everything else. 

 

I reckon we could half our electricity use with a few straightforward steps.

Burn something ( wood/oil/gas/diesel) to heat water and provide space heating. 

Replace the tumble dryer with an MVHR vented drying cupboard. 

Hot fill washing machine and dishwashers. 

Fill the kettle from the hot tap. 

 

 

That would leave a conservative 3kWh/day electricity demand with 153w base load.  

 

I considered what if our house was where yours was in Scotland with a 15kW array and a 20kWh battery storage system. ( Best installed price I reckon would be about £30,000) 

According to PVGIS you would still be short for about 1/4 of the days in december. 

 

You would have to make further lifestyle compromises like cooking on solid fuel, restricting appliance use etc during the winter. An electric vehicle would be out of the question Nov- Feb. 

 

If you were to consider the same case in Brighton, with a 12kW array and a 7kWh battery you would short less than 7 days a year.

 

 

I think in your situation the electricity connection is your only option unless you want to live a country lifestyle of 100 years ago. Perhaps consider your petrol cost saved by changing to an electric vehicle as part of the equation when getting a grid connection. 

 

 

 

[SteamyTea]

6 minutes ago, Iceverge said:

Perhaps consider your petrol cost saved by changing to an electric vehicle as part of the equation when getting a grid connection

That is a valid point, we are going down the EV route and home charging will be expected to happen.

[ProDave]

We use about 10kWh per day powering "stuff" that is not heating or DHW and that is pretty constant throughout the year. Some day I will do an appliance by appliance measurement to try and see if there is anything we can save on, but at the moment short of watching less telly I can't see an easy saving.

 

Re the tumble dryer.  the compromise we have is it is NOT a "dryer" it is a "towel fluffing machine"  Certain things like towels, socks and underwear "must" have a spell in the fluffing machine so they end up soft and fluffy.  If they dry entirely naturally they fail the "fluffy" test and get described as "cardboard".

 

So just half an hour un the fluffing machine does it, they don't come out dry, but then when hung on the airer in the utility room under an mvhr extract vent, when dried by that they do pass the fluffy test, as long as they have had the short time in the fluffy machine.

 

One day I will pluck up the courage to see a a period in the fluffy machine on "cold" will have the effect of making them fluffy.

[SteamyTea]

1 hour ago, ProDave said:

it is a "towel fluffing machine"  Certain things like towels, socks and underwear "must" have a spell in the fluffing machine so they end up soft and fluffy.  If they dry entirely naturally they fail the "fluffy" test and get described as "cardboard".

I have got used to the rasping feeling.

Like tomatoes, I quite like it now.

(I stopped wearing underwear as a new year resolution back in 2010, and have saved literally a few kWh of marginal energy since)

[Curtis]

On 02/10/2021 at 10:21, pdf27 said:

https://www.bere.co.uk/assets/NEW-r-and-d-attachments/Lark-Rise-Self-consumption-study-by-Energelio-160429.pdf is worth reading deeply if you're seriously considering going off-grid. It's the calculations for how close to autonomy you can get with a ~200m² Passivhaus in the southern UK with 13kW of PV and a battery of varying sizes.

Even with a very big battery (40 kWh in this case), in December it's still importing ~60% of electricity demand from the grid.  Per PVGIS for Aberdeen, you'd need at least a 30kW ground-mount system to meet demand in December, which is the hardest month to handle - in the process producing 27,000 kWh nearly all of which would go to waste. You could probably downsize a bit as you're looking at a smaller house, but given how well insulated the example given is you're going to struggle with getting a 50% reduction without going full Passivhaus. Going off-grid with only PV and batteries in the UK is exceptionally hard.

 

Assuming you need 500 kWh in December to give you some margin (most of the power coming from PV throughout the year), you only need a steady-state power of 700W to keep things going which isn't huge. Small wind turbines are very site-specific and a bit of a lottery though - average capacity factor seems to be in the 15-20% region (inferring you'd need ~5kW installed power), but can be very high or low.

 

One interesting note - heating demand is 1000 kWh of electricity a year in this model and DHW another 800 kWh/year. Take that away and over an **average** year, you'll be able to run everything else 100% on PV. In the model the COP is assumed to be 2.8, so heat demand is 5100 kWh/year => equivalent to about 400 kg of Propane. So an LPG boiler plus standby propane-fuelled generator in case you get a week of miserable weather might be a decent option in your case. As noted the power draw will be very low from it - it's only there as a backup for the few times a year that the batteries run out and need a top-up, so fuel burn and running hours will be relatively low.

 

Resale value is going to be higher on-grid and running costs a bit lower, but not shockingly so. It's really important that the house is very low-energy though - the cost per kWh of off-grid energy is much higher than on-grid. If it was my build, at £30k I'd go for a grid connection (mostly considering resale and the faff-factor), but if it ended up being a lot more (£50k+) then off-grid is feasible.

 

 

Thanks for the links and the in depth info, much appreciated.  I've been speaking to the locals over the weekend and there may be a closer pole that we can connect to and the local farmer has said that he would be willing to dig the trench through his field so we are now hopeful that we can lower the 30k estimate to somewhere closer to 20k so current thinking is that we go ahead with the grid connection and we also install a solar array and battery bank so rather than use wind as a back up to the solar we will use the grid as a back up to solar. 

 

One of the locals we visited had a wood burning stove which had a back boiler which fed a large holding boiler which gave them hot running water and also hot water for their radiators to heat the whole house so this is something we are going to look into as well at least for hot water but i'm not sure whether this would also service our underfloor heating as well but something for us to look into.

[Curtis]

21 hours ago, Iceverge said:

We went on hols for a week and I monitored the energy use in our absence. Our house is all electric. Passive class, no heat pumps or woodburner. 

 

I turned off everything except the following. 

MVHR ,Fridge/Freezer ,Biocycle septic tank. Total  3.68 kWh/day. (153 watts)

Heat Loss from the immersion powered 300l UVC @70deg. 1.64 kWh/day (68 watts equivalent load) 

 

Total background load 221 Watts or 5.3kWh/day of which 30% is heat loss from the cylinder. Granted everything except the septic tank is inside the heated envelope so it contributes to the heat load for the 3-4 months of the year it's needed. 

 

Our daily electricity use is 20kWh of which normal use is about 11kWh DHW (including tank heat loss) 3.68 kWh background load and 5.32 kWh everything else. 

 

I reckon we could half our electricity use with a few straightforward steps.

Burn something ( wood/oil/gas/diesel) to heat water and provide space heating. 

Replace the tumble dryer with an MVHR vented drying cupboard. 

Hot fill washing machine and dishwashers. 

Fill the kettle from the hot tap. 

 

 

That would leave a conservative 3kWh/day electricity demand with 153w base load.  

 

I considered what if our house was where yours was in Scotland with a 15kW array and a 20kWh battery storage system. ( Best installed price I reckon would be about £30,000) 

According to PVGIS you would still be short for about 1/4 of the days in december. 

 

You would have to make further lifestyle compromises like cooking on solid fuel, restricting appliance use etc during the winter. An electric vehicle would be out of the question Nov- Feb. 

 

If you were to consider the same case in Brighton, with a 12kW array and a 7kWh battery you would short less than 7 days a year.

 

 

I think in your situation the electricity connection is your only option unless you want to live a country lifestyle of 100 years ago. Perhaps consider your petrol cost saved by changing to an electric vehicle as part of the equation when getting a grid connection. 

 

 

 

 

Yea i think you are right, we are now hopeful we can get the electric connection down somewhere closer to 20k so a combo effort of grid electric and solar is the current thinking, thanks very much for the info much appreciated

Edited October 4, 2021 by Curtis

[Curtis]

20 hours ago, SteamyTea said:

I have got used to the rasping feeling.

Like tomatoes, I quite like it now.

(I stopped wearing underwear as a new year resolution back in 2010, and have saved literally a few kWh of marginal energy since)

 

I'm with you on this, i prefer the cardboard towels, towel fluffing is a fine balance too much fluffing and you can't actually dry yourself with the blooming thing!!

[Ferdinand]

I mentioned micro-hydro before, and it has got lost on this thread.

 

If there is that possibility even 80-100w can make a hell of a difference in winter, and is complementary to solar.

 

The blog I mentioned before has a lot on there buried quite deep.

 

[Curtis]

On 08/10/2021 at 19:51, Ferdinand said:

I mentioned micro-hydro before, and it has got lost on this thread.

 

If there is that possibility even 80-100w can make a hell of a difference in winter, and is complementary to solar.

 

The blog I mentioned before has a lot on there buried quite deep.

 

 

Sorry i missed your message, no meaningful water on the plot unfortunately, there is a dribble of a stream along the boundry but when i say dribble i mean dribble, barely enough water for the birds!

[Smallholder]

On 02/10/2021 at 11:23, Iceverge said:

@pdf27

 

An excellent post. I will dissect the full PDF later

 

One point I would caution though with this is they had their array at 10deg (due to architectural/planning constraints I assume). 

 

If they were able to mount them at 75deg they would have been much more optimum for winter production. Annual production would have only dropped slightly 10.9MWh to 10.4 but their December production would have doubled from 237kWh to 487kWh. 

 

 

 

I wonder if this would have resulted in significant shading? They would need a lot more surface area to spread out the panels to prevent shading at this angle.

[Iceverge]

Any shading is bad news for solar panels.

 

Have a look at the below picture and graph. Panel 5 is considered a reference unshaded panel.

 

 

For a ground mount array you should assure that all panels are unshaded from 09:00 to 15:00 local solar time on the winter solstice. Practically this may preclude setting them out in multiple rows at your latitude as the spacing will be very large. 

 

 

https://www.hindawi.com/journals/ijp/2014/763106/

 

[Iceverge]

At your latitude, with 2m high panels mounted 1m high on level ground you would need 30m spacing to ensure minimal spacing. 

 

 

Unless you plan to burn something for winter heat/DHW or live like a narrowboater you're better off getting a grid connection.

 

As someone else commented persons often spend more on a kitchen. 

[Marvin]

I too have looked at this and we don't have anything like enough land, or money to buy batteries, to make this work. 

 

Interestingly our system, over a year, will produce enough power for all our demands, just not at the time when we need it....