OffGrid Home - 30kW too much?

SimonTT

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Going to preface this with I am fresh out the box to power generation but willing to learn and being a programmer feel the logical mindset will help me process info.

I am looking to build an off grid passive house in northern England (54.0270887, -2.825434). I have been looking at the best way to do this, Solar, Solar/Wind, Solar/Hydrogen, Wind/Hydrogen and I believe that pure solar maybe the best way to go.
Edited: I do not want to use a generator.

In my current property I am using ~18Kwh a day (6,570Kwh per year), this is purely appliances and hot water, we don't require heating and in the new build I expect this to be very low due to passive standard. I would like to over spec the system compared to what is required now to future proof us, allow for EV's etc and thinking about 12,000kwh would be a good number.

Using the links that @snoobler has provided I calculate that to cover my 18Kwh a day now in the winter months (36° tilt, 180° Azimuth) I would need a system size of 30kW. This would just cover my usage in December now. This obviously does not take into account any batteries.

Reading the forum in the summer months I 'am potentially going to be producing dangerous (at least to systems) amounts of power.

I am just struggling to work out how much I can expect to store and critically for how long?
I am stuck on how/where to go next to properly size the system components?

I am in the fortunate position that space (on the ground) is not an issue, there is no shading and orientation can be any which way is needed. I have budgeted around £50k ($70k USD) but if any components can be bought from China ideal.

Thanks in advance for the help.
 
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toms

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There is no such thing as too much PV.

If you have the ability to run a generator, size your batteries for your maximum overnight consumption.
Size your PV to fully charge your batteries at least 75% of the time.
Run your generator when required.

I’ve never seen a domestic system that can reliably produce 20kwh/day without occasional generator use.
 

SimonTT

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There is no such thing as too much PV.

If you have the ability to run a generator, size your batteries for your maximum overnight consumption.
Size your PV to fully charge your batteries at least 75% of the time.
Run your generator when required.

I’ve never seen a domestic system that can reliably produce 20kwh/day without occasional generator use.
Hi Tom,

I do not want to use a generator. I would like to be completely carbon neutral. Which I know can be achieved in a number of ways but for my definition I would prefer no carbon use at all. That was why I was looking at the addition of hydrogen fuel cells but the cost of electrolysis maybe the stumbling block here.
 

upnorthandpersonal

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Are biofuels an option? You could run a generator on reclaimed cooking oil, or other vegetable oil.
The biggest draw you have is the hot water heater. If you can replace this with something else, e.g. wood, other renewable, or maybe in combination with a heat pump, you can probably get there. 18kWh a day is a lot to do with just solar in winter months - you'd really want to lower that.
 

toms

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I do not want to use a generator. I would like to be completely carbon neutral.

At 20kwh/day, i’d wager running a biodiesel generator as i described will be the closest to carbon neutral you will get.

You do realise every component used in typical off-grid power system (PV/inverter/battery/cabling etc) has a significant carbon footprint?
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
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Oct 29, 2019
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Rural NE Ontario Canada
Solar Powered Offgrid with self-designed & built Net Neutral High-efficiency home.
Radiant Heating within a Frost Protected Slab Insulation, Over Insulated to R20 / RSI 3.52.
NB: This also acts as a Thermal Regulator & Maintainer in summer. It has been 40C outside & has never gone beyond 26C inside, I gave away my AC system which I kept "just in case" it was moot.

A) Conservation is FAR Cheaper than Generation & Storage.
B) For any respectable EV, you will want a 220VAC/30A up to 220VAC/50A if you want to do fast charge. Several options exist but wire bigger to your charge point when doing the construction, you can always use less but upgrading after the act = a royal PITA and much more costly.
C) Do consider BioGas from Waste, it can run LPG (Propane) Based appliances such as On-demand Water / Radiant Heating cookstove etc... If it works in Alaska, Yukon, Nunavut and other parts of Canada it WILL work for you provided it is done accordingly to your region.
D) Passive Cooling can be accomplished several ways, much of it by "Home Design" actually. Same for Passive Heating.
E) Solar Heating of Water, either by Solar Water Heaters, or using Dump Loads (even combinations) is quite possible and works well,
F) Roof Design / System is a BIGGY for both heating & cooling, never underestimate that, it IS HUGE ! Preventing the heat from getting in during summer and of course keeping it in during winter will save obscene amounts of energy.
G) Use TREES, plant some for Shade onto the home and strategically located to act as Wind Breaks, it adds up fast and makes a massive difference.
H) Consider a Heat Pump / Mini-Split System for heating cooling, they are quite efficient and solar power friendly.

DO NOT FORCE your house onto the land, use nature & work with it. Observe where the wind blows, where snowdrifts, where water settles. What areas on the property are "Naturally" sheltered from the elements like windbreaks etc... Take advantage of what Nature does and does not do on your property. Do as all our ancestors did in the past, work with the land & nature. The folks in the Bronze age and back figured it out, it was the Roman's who came and decided to "force" themselves onto lands and to reshape everything to their will, with their inneffient square buildings.

*Round Houses win for many reasons not readily apparent. There are no corners that create Vortices against walls in wind storms. There is no "Catches" for things to get hung up on like peaked roof's and much more. BTW: Archeology & history buff, so....
 

svetz

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Welcome to the forums!

Let's check those numbers....

  • ...(54.0270887, -2.825434)....
  • ...current property I am using ~18Kwh a day (6,570Kwh per year) (appliances and hot water)
  • ...future proof us, allow for EV's etc and thinking about 12,000kwh would be a good number.

If you're currently using 18kWh/d, I suspect the 12,000 kWh is a typo.

How far away is the EV purchase? I wouldn't future proof by buying all the gear until I was ready, by the time you get EVs the prices might go down on solar panels and efficiencies up. Future-proofing is a good idea, but you can do that with microinverters so they're easy to add to, or string inverters with a parallel capability.

So, looking up the nearest city in a calculator and adjusting tilt for maximum winter power we get the insolation at 21° tilt in December is 0.99. So, if you want 18 kWh/d you'd need enough solar to cover that, the round trip losses in the batteries, and the inefficiencies of the gear. Lets say those are 90% for the RTL, and let's say you went with Enphase for a 96% efficiency in the inverter/mppt.
1613136343592.png

So, 18 x 0.99 / .9 / .96 = 20,625 watts of solar panels.

30 kW of panels should produce: 30,000 x .96 x .9 / .99 = 26 kWh/d.
If your EV consumes 200 watt-hours per mile, then 26 kWh/d produced -18 kWh/d residence consumes = 8 kWh left over for EVs.
8000 Wh/ 200 watt-hours/mile = 40 miles per day range.

You'd probably also want a few days battery backup. There are example calculation in the FAQs that can help with all that. But, if you wait long enough you'll eventually be able to use your EVs (assuming you don't need to travel while the power is out).

...Reading the forum in the summer months I 'am potentially going to be producing dangerous (at least to systems) amounts of power...
The insolation at July at 21° tilt is 3.8. So, 30 kW of panels x 3.8 / .9 / .96 = 132 kWh/d. Your power company might not like that, especially as you have a nuclear plant just down the road (I know you're off-grid, thinking about the competition when you start up your summer EV charging business with all that excess power ;-). Even if you went vertical the insolation only drops to 2.82 in July (98 kWh).

You can get a lot more accurate numbers using SAM or PVWatts as they'll take your local weather into account. If you have a lot of winter storms you'll need more panels (or possibly wind).

Hope that helps some.
 
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SimonTT

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Feb 12, 2021
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Welcome to the forums!

Let's check those numbers....



If you're currently using 18kWh/d, I suspect the 12,000 kWh is a typo.

How far away is the EV purchase? I wouldn't future proof by buying all the gear until I was ready, by the time you get EVs the prices might go down on solar panels and efficiencies up. Future-proofing is a good idea, but you can do that with microinverters so they're easy to add to, or string inverters with a parallel capability.

So, looking up the nearest city in a calculator and adjusting tilt for maximum winter power we get the insolation at 21° tilt in December is 0.99. So, if you want 18 kWh/d you'd need enough solar to cover that, the round trip losses in the batteries, and the inefficiencies of the gear. Lets say those are 90% for the RTL, and let's say you went with Enphase for a 96% efficiency in the inverter/mppt.
View attachment 36930

So, 18 x 0.99 / .9 / .96 = 20,625 watts of solar panels.

30 kW of panels should produce: 30,000 x .96 x .9 / .99 = 26 kWh/d.
If your EV consumes 200 watt-hours per mile, then 26 kWh/d produced -18 kWh/d residence consumes = 8 kWh left over for EVs.
8000 Wh/ 200 watt-hours/mile = 40 miles per day range.

You'd probably also want a few days battery backup. There are example calculation in the FAQs that can help with all that. But, if you wait long enough you'll eventually be able to use your EVs (assuming you don't need to travel while the power is out).


The insolation at July at 21° tilt is 3.8. So, 30 kW of panels x 3.8 / .9 / .96 = 132 kWh/d. Your power company might not like that, especially as you have a nuclear plant just down the road (I know you're off-grid, thinking about the competition when you start up your summer EV charging business with all that excess power ;-). Even if you went vertical the insolation only drops to 2.82 in July (98 kWh).

You can get a lot more accurate numbers using SAM or PVWatts as they'll take your local weather into account. If you have a lot of winter storms you'll need more panels (or possibly wind).

Hope that helps some.
Thanks @svetz thats really helpful. Perhaps not thinking too far ahead is better.

Having considered the figures I think I can perhaps look at the solar/hydrogen option again. Use it to produce hydrogen which I can keep longer and cheaper than excessive batteries and use that top up the reasonable battery bank over fallow periods. More expensive than a traditional generator but keeping inline with my efforts.
Still a long way to go but super helpful thanks.
 

svetz

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What are you thinking about for hydrogen? If you burn it in a generator you might as well avoid the expense and do a gasoline generator. AFAIK, fuel cells are still prohibitively expensive.

The real problem is the sun is so low in Nov thru January to get the full power you want from solar leaves you with a glut of summer energy (which wouldn't be a problem if you were on-grid with net-metering). Even optimizing for December (~20° tilt, 36° optimizes you year-round) it gives you a low insolation so you've little power in winter and far more than you can use later. If you had something to augment you in those months it wouldn't be too bad. I took a look at the numbers in PVWatts, and with an 18 kW array it predicted you'd only get ~< 9kWh/d, so thinking you get a lot of storms in December. It also predicted an 18 kW array at that tilt would generate the most power (76 kWh) in May. But, according to PVWatts, and 18 kW array would get you > 18 kWh/d of power for every month other than December and some of November. A 12 kW array would leave you short November thru February.

Quite the solar farm at the lat/long you specified, they might be able to provide you historical data for the most accurate estimates. They might also have wind-speed data (a SAM resource file would be ideal) - if you do get a lot of winter storms in November through January and the wind forces aren't too high it might make a good winter supplement.
 

SimonTT

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What are you thinking about for hydrogen? If you burn it in a generator you might as well avoid the expense and do a gasoline generator. AFAIK, fuel cells are still prohibitively expensive.

The real problem is the sun is so low in Nov thru January to get the full power you want from solar leaves you with a glut of summer energy (which wouldn't be a problem if you were on-grid with net-metering). Even optimizing for December (~20° tilt, 36° optimizes you year-round) it gives you a low insolation so you've little power in winter and far more than you can use later. If you had something to augment you in those months it wouldn't be too bad. I took a look at the numbers in PVWatts, and with an 18 kW array it predicted you'd only get ~< 9kWh/d, so thinking you get a lot of storms in December. It also predicted an 18 kW array at that tilt would generate the most power (76 kWh) in May. But, according to PVWatts, and 18 kW array would get you > 18 kWh/d of power for every month other than December and some of November. A 12 kW array would leave you short November thru February.

Quite the solar farm at the lat/long you specified, they might be able to provide you historical data for the most accurate estimates. They might also have wind-speed data (a SAM resource file would be ideal) - if you do get a lot of winter storms in November through January and the wind forces aren't too high it might make a good winter supplement.
I do intend to see if I can get any information from the solar farm as that’ll help greatly.

It is windy and the area is actually designated by the council as a suitable area for wind turbines however when I was first looking at turbines perhaps I was looking at too large a system and as such the cost was rather high. I’ve also read quite a few articles saying that residential turbines are rubbish or at least not to be trusted for a great deal.

With the hydrogen the thought was to distill/deionise (depending on requirements) water from a borehole, through a pem electrolyses stack, store h2 for use with fuel cell when needed, fuel cell connected to batteries to charge.
Given the over production of power in summer I could conceivable produce as much hydrogen as I wanted/had space for and there for there is a lot more security for extended fallow solar/wind periods ( although granted it’s unlikely).
The hydrogen is also in part to help with planning. It is a para 79 project so there is a very high bar for innovation and design. The local area has a strategy for the next 10-15 years to really push hydrogen. I therefore, thought it would be a 2 birds 1 stone situation. I’m also less likely to face objections without a big ol’ turbine.
 
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alex68

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if you are interested in hydrogen then have a look at "HPS System – picea" it's a germany based company, but spoiler alert: it is more then your 50k for a system which would cover your needs
 

SimonTT

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if you are interested in hydrogen then have a look at "HPS System – picea" it's a germany based company, but spoiler alert: it is more then your 50k for a system which would cover your needs
I have already spoken to them. They aren’t selling outside of Germany at the moment. Had they, perhaps there would be a conversation to have and some moving of number as it’s a one stop shop but unfortunately not to be.
 

Pyke13

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I have been living in Northumberland for the last year relying completely on solar for all my electrical use. I have a lot lower consumption than you have stated you will have, I live in a converted truck my heating is from a wood burner and cooking is from a gas cooker. Between the two of them that also covers all my hot water. My electricity use is very limited on solar thru winter as there’s just not enough daylight hours, December and January I would reckon about 6 hrs a day of solar and many days where there’s not that much power in it due to rain and clouds. I have 650w of solar powering 300ah AGM batteries, I have to turn my fridge if at the end of October as I simply cannot generate enough from the solar until March to run it again. I run 6 led lights, normally only 2 on at a time, charge a phone and tablet and have the router on 24/7. Apart from that I charge a vape every day, 2x 18650 batteries to power it and charge 4aa batteries twice a week for a radio.
I understand I have no place near the solar or storage your looking at but I also have no place near the usage you have. It’s almost impossible to live on solar alone in the uk. 3 or 4 days of rain in the summer and I struggle for power. I ended up having to buy a generator this year and running it once a week thru the winter just to top up the batteries. It’s only been the last couple of weeks I have seen the batteries fully charged by solar and still yet might need to run the genny if there’s bad weather.
build your system to be able to power the house in the middle of winter and expect it to struggle in bad weather. I would think you will need a back up generator if some sort for the time when the solar just can’t keep up.
I would also over spec the battery bank so you have the storage to last a few days.
hope this is of some use
 

Pyke13

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In winter out of 650w solar my batteries charge at about 2-5amps depending on conditions.
 

svetz

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...when I was first looking at turbines perhaps I was looking at too large a system and as such the cost was rather high...
Turbines, with moving parts, have wear and can be quite noisy (I suspect excessive noise is a plea for service). While I've never seriously looked into wind turbines myself, I know there are good ones that work fine. A lot of sailors use them and recommend them, they didn't look over sleep-deprived. ;-)

But, I also know from reading the forums there's a lot of cheap snake-oil out there in the land of wind-turbines that give them a bad name. This is a link I usually recommend folks considering them: www.solacity.com/small-wind-turbine-truth/ (although mainly it's to scare them off the tech, but it sounds like your site might be appropriate). If you work with a reputable reseller (someone with a good reputation for service (e.g., altE) they'll generally work with you to make sure you're happy with your purchase. Although, definitely do your research on them. You might find that it's cheaper and more reliable to just add extra panels and throw out the excess power.
 
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JakeinCanada

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I know you said you didn’t want a generator, but have you considered the V5 autogen it’s a 70 amp 48 volt battery charger. It monitors the batteries and automatically starts at the programmed level. Only 5 HP available in tri fuel at just over $ 2000 US dollars.
 

creeky

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Jake, do you have one of these? What's the lowest voltage it starts at. I'm repurposing NMC from LG Chem. It would be nice if I could set 42v to start and 48 to cut off.
Upnorth. Diesel can be a pain when its cold.
 

JakeinCanada

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No I don’t, I was doing some research and came across this auto start generator which seems perfect for going off grid. There are a few videos on YouTube and it appears that it can be set to any starting voltage, I emailed the supplier for information on warranty and they replied within a day. I really like that the generator is also the starting motor, almost seems to good to be true at that price.
 

toms

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With the hydrogen the thought was to distill/deionise (depending on requirements) water from a borehole, through a pem electrolyses stack, store h2 for use with fuel cell when needed, fuel cell connected to batteries to charge.

That would be awesome! Let me know where i can get that setup?

PS, i have a borehole, that will be a challenge to drill without burning fossil fuel.
 
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