Hybrid Off Grid Energy Feasibility

[Curtis]

Hi folks, new to the forum.

 

I'm in the process of purchasing a remote 5 acre plot of land in the north east of Scotland, the cost of getting electricity to the plot is at least £30k so before i commit to that I want to find out whether a hybrid off grid system of solar and a wind turbine with a backup battery bank is actually practical and would actually service the energy demand of the house power & heat.

 

We are planning to build a relatively modest 3 bedroom 110sqm house which we intend to make as energy efficient as possible, added insulation, triple glazed windows etc. so we are estimating our energy demand would be up to 15,000 kWh per year, hopefully closer to 12,000 kWh.  The heating would be either electric radiators or underfloor heating but would be supplemented by a wood burning stove in the living area.

 

From what I’ve read on Solar (not an expert) we could potentially service most of our energy for 8 to 9 months of the year but come winter time especially but also at other times throughout the year we would need an alternative source, because the plot is 700ft above sea level and we are in the North East of Scotland I hoped that a wind turbine could make up the difference that solar couldn't provide but I am not sure if this is realistic or not.  From what I’ve read on here and other forums getting a good reliable and efficient wind turbine is not easy. 

 

So basically I am just looking for some guidance as to whether a hybrid system is even a practical solution or whether I’m wasting my time and i should just suck up the £30k electricity connection.

[markc]

At 30k over the lifetime of the property I would say it’s money we’ll spent.

if it was a temporary supply then a combined diesel, battery, solar and wind set up would be feasible and economical(ish).

I was at a trade show last week and some of the new generator/battery power modules look really good

[Conor]

First thing to do is see what your local planning policy is regarding turbines. I know of somebody near me that was building a house to be fully off grid, but was dependent on a wind turbine for winter. He's not been able to get permission and has had to connect to the grid. Find out how likely you are to be able to have a turbine before committing.

[SteamyTea]

I think your energy usage seems high. What are you basing that on?

You can, with some careful design, get down to 50 kWh/m². 

 

Small wind turbine tend not to be very good, and are expensive. PV, though pretty poor in the winter is the way to go.

With 5 acres of land, and assuming you can get planning permission, you would be better off spending £15k on a ground mount system.

But as that is half the cost of a grid connection, I would go with that because another £15k will go on battery storage.

 

Or just get a small CHP unit and get your heat and power from a diesel tank.

[Ferdinand]

Read this blog:

 

https://lifeattheendoftheroad.wordpress.com/

 

Do you have any streams? 

[TonyT]

What happens in a fault?

what happens if you are not technically minded to maintain equipment

what happens when you get old?

only you can answer what’s right for you

you can get someone else to excavate to save some costs and get the DNO  to run cable, they don’t have to do all the works

[A_L]

2 hours ago, Curtis said:

so we are estimating our energy demand would be up to 15,000 kWh per year, hopefully closer to 12,000 kWh

 

1 hour ago, SteamyTea said:

I think your energy usage seems high. What are you basing that on?

 

Agree with @SteamyTea. Given good but not quite Passivhaus standards, walls/ceiling/floor to about 0.12W/m^2.K, windows below 1.0W/m^2.K, infiltration less than 1.0ach (with MVHR)  annual space heating not more than 1000kWh, hot water 2500kWh (a lot less if WWHR installed on showers). Appliance electricity should be below 3650kWh/yr, current electricity use could give a guide here. So total of no more than 7150kWh/yr unless you are including an electric car. With further conservation measures perhaps the total could be reduced by 2500kWh/yr.

Edited September 30, 2021 by A_L
minor typo

[Thedreamer]

1 hour ago, Curtis said:

We are planning to build a relatively modest 3 bedroom 110sqm house which we intend to make as energy efficient as possible, added insulation, triple glazed windows etc. so we are estimating our energy demand would be up to 15,000 kWh per year, hopefully closer to 12,000 kWh.  The heating would be either electric radiators or underfloor heating but would be supplemented by a wood burning stove in the living area.

 

If it helps our three bedroom on Skye is using between 10-11 kWh a day for electricity. I have no heating system, apart from a electric oil heater that gets wheeled out on special cold frosty occasions for a morning boost.

 

The rest of heating is provided by a centrally placed wood burning stove which usually runs from Octoberish to March for a a few hours in evenings.

 

Might be worth sharing a bit more information on your electricity connection? There are ways I got mine down a lot with SSE.

 

Also bear in mind that members come from all over the UK and beyond so do consider advice in the context of your location.

[SteamyTea]

20 minutes ago, Thedreamer said:

The rest of heating is provided by a centrally placed wood burning stove which usually runs from Octoberish to March for a a few hours in evenings

Ignoring my dislike for wood burning, how many kg/day do you burn?

Knowing that, and PV performance for Skye, it should be easy to work out what size PV system would be needed to offset it.

[Thedreamer]

7 hours ago, SteamyTea said:

Ignoring my dislike for wood burning, how many kg/day do you burn?

Knowing that, and PV performance for Skye, it should be easy to work out what size PV system would be needed to offset it.

 

Sorry, but I don't know the weight, as I own no scales. The wood is very well seasoned and light, the home grown alder especially.

 

It's no more than a garden trug basket at the very coldest points of the year.

 

A bright cold frosty day will provide sufficient solar gains to keep the house nice and warm without the need for the stove.

 

 

 

 

 

 

[Curtis]

Thanks for all the responses, much appreciated!!

 

I am hopeful my usuage will be around the 10,000 kWh mark but my thinking was if i size the system for 15,000 kWh then i should never have blackouts unless obviously something goes wrong with the equipment.  

 

I haven't spoke to planning yet as there's no point in doing that if a hybrid system isn't a good idea, my architect seems to think planning would be fine under existing planning rules for Moray council and also due to the fact i have the space for the equipment with no immediate neighbours and there are others within a few miles radius.  

 

The estimate of 30k is due to the fact i have to upgrade the initial pole i am coming off as this needs a transformer upgrade, i then have to pay for 2 additional poles for part of the way and then i have to lay the rest of the cable underground to cross a neighbours piece of land and then cross under the farm track road which leads down to my plot and 2 other plots past mine, so the entire 700m ish route is part overground and part underground. 

 

[Ferdinand]

22 hours ago, Ferdinand said:

Read this blog:

 

https://lifeattheendoftheroad.wordpress.com/

 

Do you have any streams? 

 

They are on Raasay, and have had a (Proven, I think) 2.5kw wind turbine up for more than 15 years.

https://lifeattheendoftheroad.wordpress.com/about/ 

[Curtis]

3 hours ago, Ferdinand said:

 

They are on Raasay, and have had a (Proven, I think) 2.5kw wind turbine up for more than 15 years.

https://lifeattheendoftheroad.wordpress.com/about/ 

 

Thanks i haven't looked much into Proven turbines yet, I have looked at the R9000 from Britwind but it's 5kw and the best part of 25k to install but based on my average wind speed of 6m/s per year i'd get around 13,000 kwh of energy from the R9000, so even if that was high and i only got about 60% ish of that so around 8,000 kwh and i then have a solar array and battery bank in my simple head i should be able to do this but it's hard to find proper case studies of peopole doing this so thanks for the link.

[Ferdinand]

7 minutes ago, Curtis said:

 

Thanks i haven't looked much into Proven turbines yet, I have looked at the R9000 from Britwind but it's 5kw and the best part of 25k to install but based on my average wind speed of 6m/s per year i'd get around 13,000 kwh of energy from the R9000, so even if that was high and i only got about 60% ish of that so around 8,000 kwh and i then have a solar array and battery bank in my simple head i should be able to do this but it's hard to find proper case studies of peopole doing this so thanks for the link.

 

I don't know if they still exist.

 

But the point is that 700ft in Scotland is probably more like Siberia than Cirencester for wear on a wind turbine, and experience is everything.

 

I'd suggest being in touch, and taking a trip to talk to them. I think one of his points is that he can repair it himself. 

 

It's only 6 hours in Scottish Miles ?.

[Curtis]

12 minutes ago, Ferdinand said:

 

I don't know if they still exist.

 

But the point is that 700ft in Scotland is probably more like Siberia than Cirencester for wear on a wind turbine, and experience is everything.

 

I'd suggest being in touch, and taking a trip to talk to them. I think one of his points is that he can repair it himself. 

 

It's only 6 hours in Scottish Miles ?.

 

Cheers will reach out to him and maybe go for a jolly to see the turbine

 

 

[SteamyTea]

58 minutes ago, Ferdinand said:

I don't know if they still exist.

Went pop a decade ago (about the same time as most of the small turbine manufactures went, including the one I worked for).

They were bought by Kingspan (who bought up a few RE companies), but pretty sure they have pulled out the market.

 

As a rule, small turbines are pretty poor on performance and reliability.  You will need a large battery system to smooth out the constantly changing output.

PV is easier all round.

[Curtis]

18 hours ago, SteamyTea said:

Went pop a decade ago (about the same time as most of the small turbine manufactures went, including the one I worked for).

They were bought by Kingspan (who bought up a few RE companies), but pretty sure they have pulled out the market.

 

As a rule, small turbines are pretty poor on performance and reliability.  You will need a large battery system to smooth out the constantly changing output.

PV is easier all round.

 

Thanks for the info ?

[joe90]

Whilst I applaud being self sufficient I agree that £30k is not a big portion of a build cost, having mains connection will be a selling point if you should ever want to sell (we all do eventually) and as we get older maintaining kit gets more difficult and a worry. I built a large conservatory on the South side of my  build and this contributes greatly to the warmth of the house for a large part of the year. I also have a wood stove for burning local sourced wood as much fir the “cave man” effect and it works well.

[Iceverge]

We use 20kWh per day but that’s heating water for 4 , boiling the kettle regularly, electric cooking, constantly running biocycle unit, tumble dryer, constantly running MVHR, and powering a borehole pump. Yet to see what that escalates to with the winter.

 

My parents live in a drafty house next door with literally no insulation. Everyday the rayburn cooker is lit. It heats the water, boils the kettle, cooks dinner, heats the house, dries the clothes and, by stack effect, ventilates the house. Old fashioned septic tank. They do have an electric shower. They use about 10kg per day of dried oak in the summer. (roughly 50kWh)

 

Our electricity use is double theirs although their energy use is triple ours. Probably at least 10 times to achieve the same comfort levels. 

 

You can go off grid easily if you are willing to cook, heat and DHW on Wood/gas/oil.

It won’t be the freewheeling energy on tap lifestyle that most of us rightly or wrongly enjoy however.

 

 

 

 

 

 

[pdf27]

20 hours ago, Curtis said:

Thanks i haven't looked much into Proven turbines yet, I have looked at the R9000 from Britwind but it's 5kw and the best part of 25k to install but based on my average wind speed of 6m/s per year i'd get around 13,000 kwh of energy from the R9000, so even if that was high and i only got about 60% ish of that so around 8,000 kwh and i then have a solar array and battery bank in my simple head i should be able to do this but it's hard to find proper case studies of peopole doing this so thanks for the link.

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.

[Iceverge]

@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. 

 

 

[joe90]

Oo. er, this thread and the lekky price hike thread have got me thinking twice about self installing PV. I know @ProDave did his own (mind he is an electrician but how hard can it be ?‍♂️.). I have a South facing garage roof or South facing field nearby.

https://www.ebay.co.uk/itm/164775013949?var=0&&mkcid=1&mkrid=710-53481

Edited October 2, 2021 by joe90

[SteamyTea]

1 hour ago, pdf27 said:

worth reading deeply if you're seriously considering going off-grid

 

50 minutes ago, Iceverge said:

will dissect the full PDF later

Me to as I have been working on a similar project recently.

[pdf27]

57 minutes ago, Iceverge said:

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. 

The building has a flat roof, so they were trying to hide the array behind the parapet.

For the calculations I did to get to a 30kW system, however, I used PVGIS and an optimally-orientated ground mount array to work out how much PV was needed for 600kWh in December near Aberdeen. That was for year-round optimisation to be fair - if I give it a near-vertical orientation to optimise for winter (tricky for ground-mount on a windy site) you can get it down to ~24kW or so. It's still very weather-dependent though so you probably want generator back-up anyway.

 

6 minutes ago, SteamyTea said:

Me to as I have been working on a similar project recently.

https://www.bere.co.uk/assets/NEW-r-and-d-attachments/Lark-Rise-Interim-Monitoring-Report-171201.pdf is also worth a read here - details of how actual performance compares to modelled.

FWIW I think the main thing they missed out on was hot fill for the dishwasher and possibly washing machine - clothes washing and dishwasher is about 12% of total demand, and is pretty easy to shift to DHW from a heat pump. Most dishwashers will take hot fill (and clean better for it, at least in my experience), washing machines are a bit less clear but given the lengths they're going to in order to minimise electrical demand it's a very cheap way of making a sizeable saving.

[DamonHD]

In case it is useful as a data point, my family of four in London uses per year ~2MWh electricity (gross, ie ignoring our PV, import is about half that), ~2MWh space heat and ~1MWh DHW both currently gas.  Heated floor space 76m^2.  So to me 12MWh total, even just using crude electric resistance heating, feels high, allowing for London vs up north (I haven't lived north of Edinburgh though).  Conservation is by far the cheapest energy source.

 

Rgds

 

Damon