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Dan's 57Kw Build
#11
I was thinking more of a small pellet stove to to put in a central room to reduce the power consumed by your GSHP.
Something like this: http://www.woodpelletstove.co.uk/content...llet-stove
It should cost no more than 2~3k. Of course, this might require near daily manual refilling, but will still be much less hassle than burning logs of wood.

Also, note that all of Tim's calculations are based on monthly averages. You have to consider the possibility of having a perhaps 2 week long blizzard, during which even a 30kWp PV array will produce nothing. Once you run the batteries dry, not even the pellet stove will work. Also, a supersized PV is likely prohibitively expensive and will be a waste of money and resources the rest of the year.

My suggestion would be to install a large-ish, but still reasonable PV array.
Keep an eye on the weather forecast and turn on the wood/pellets/gas stove on consecutive cloudy days to supplement the GSHP and thus reduce battery drain.
And have a diesel generator (test before season; drain & store after season; use/give away old fuel) to provide emergency powerwall charging. I believe a low voltage auto-start can be implemented fairly easily. You'll want to have a detached generator shed for safety and noise reduction.
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#12
Hi Wardy,

Forgetting heating for a moment.

If you are off grid, you shall absolutely need a generator. As AWJ22 says, periods of poor weather that deplete your battery storage are common, unless you massively over specify the generation. As I said in my earlier post, covering your peak usage is expensive. Covering periods of prolonged low generation is also expensive, and compounds the issue.

You say you have a lot of space, and I hope that this is truly the case. 15kWp array using 300Wp panels of the standard 1.6m x 1m size requires 50 panels. That's 80m²! So if you were making a wall of them at 75° arranged as 2x25 panels you would end up with a structure 3m high and 25m in length. Quite a formidable structure that will act like a wind break, so the structure shall need to be anchored down well. They will also weight 900KG excluding mounting brackets and the mounting structure. I expect double when you include the mount. So taking them down in the summer would be quite an undertaking. You'd need an 8x6' shed to store them in too.

On the winter solstice the sun peaks at just 15° above the horizon in the UK so any structure can cast a very long shadow and reduce your generation potential. A small tree for example that is 10m high and directly to the south of the array would need to be at least 38m distance to the array in order not to cast a shadow at midday when the sun was highest. The 38m value becomes far longer when the sun is not so high in the morning and afternoon. So a ground mount array in winter needs to be on the north side of a farmer's field essentially, or side of a nice south facing hill.

The good news is that a 15kWp array starts generating significant power levels quite early in the year, so you really only need to worry about the darkest two months. The amount of top-up you'd need from the generator would be fairly small. Just as well as red diesel is about 65p + VAT (5%) per litre. It contains about 11kWh per litre gross, but you shall realise only about 25% efficiency to electricity so your 1 litre will yield no more than 11kWh * 25% = 2.75kWh. Or 65p / 2.5kWh = 26p/kWh + VAT. Double the cost of natural gas CHP I spoke of earlier. Quadruple the cost of cheap rate grid electricity.

Heating in those coldest months must be from non-electrical sources. You may generate enough in the shoulder months to run heat pump for space heating though, but is it worth the cost and complexity? In the summer you shall have so much excess solar generation that using a heat pump for hot water is not required. 5 - 10kWh per day for hot water depending on family size will cover your usage. In fact looking at my previous number you should be able to cover your electricity and hot water needs from end Feb to mid Nov with a 15kWp array just using a standard immersion heater.

So basically if you are set on going off grid then you need to spend a lot of time in Excel working out the best ratio of equipment for your needs. Yes, a 15kWp array would cover your average usage for electricity only year round, but you will need an amount of generator power. A 30kWp array combined with life style changes in winter to conserve energy would probably see you use no generator power. But that additional 15kWp array would cost you another £10k or so and only be of use for 2 months per annum for 20 year life of the panels. So the cost per winter would be in the region of £500. Conversely you may decide that 15kWp array is too large and you could live with something smaller, but expect to use generator power far more in the winter, but not for the summer 50% of the year. You have to model each scenario with real world costs, and bear in mind the phsical reality of your plans too (not forgetting planning permission).

The battery storage element is actually the easy bit... I know, I've looked myself but I cannot find suitable reason to ditch the grid unless you live far from civilization. I even contemplated taking just gas, and not electricity or water, and making CHP. Still doesn't work out financially. So it really comes down to what you *want* to do. I like the idea of being able to stick two fingers up at energy companies and being self sufficient. So I shall remain grid connected, but just not import electricity for a good part of the year, and when I do need to import in winter I shall do it over night on the cheap rate.

-Tim
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#13
(11-17-2018, 02:02 PM)Hey ajw22 Wrote: I was thinking more of a small pellet stove to to put in a central room to reduce the power consumed by your GSHP.
Something like this: http://www.woodpelletstove.co.uk/content...llet-stove
It should cost no more than 2~3k.  Of course, this might require near daily manual refilling, but will still be much less hassle than burning logs of wood.

Also, note that all of Tim's calculations are based on monthly averages.  You have to consider the possibility of having a perhaps 2 week long blizzard, during which even a 30kWp PV array will produce nothing.  Once you run the batteries dry, not even the pellet stove will work.  Also, a supersized PV is likely prohibitively expensive and will be a waste of money and resources the rest of the year.

My suggestion would be to install a large-ish, but still reasonable PV array.
Keep an eye on the weather forecast and turn on the wood/pellets/gas stove on consecutive cloudy days to supplement the GSHP and thus reduce battery drain.
And have a diesel generator (test before season; drain & store after season; use/give away old fuel) to provide emergency powerwall charging.  I believe a low voltage auto-start can be implemented fairly easily.  You'll want to have a detached generator shed for safety and noise reduction.

I like the look of them pellet stoves, especially the inset ones! Way more efficient than logs and less mess with clean ups. Never seen them before. I’ve put log burners in my last 2 houses and they are a faf. With only a 3” flue as well as opposed to 6” ones I’ve been putting in. 

Yeah I think that’s the most practical and realistic option mate, large PV array a stove, possibly a wind turbine (if I can find a practicable location for it) and a generator for back up / emergencies.
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#14
Exept for the wind turbine, thats exactly how i do it.... and i do have also a heat-pump for in the mornings.
___________________________________
18x 300Wp solar off grid and 10x 180Wp solar tracker grid-tie
10KW 3phase hybrid inverter. 40Kwh 18650 storage (for now)
My setup: https://secondlifestorage.com/t-Instant-powerwall
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#15
You may also want to look into solar water heating. It should drastically reduce the demand placed on your PV+battery system. Evacuated pipe systems reportedly work somewhat even on a cloudy winter day, and will probably be much more effective (both roof space and financially) than heating via PV+heatpump.

Also, you may want to install multiple large hot water tanks- it's a much cheaper form of energy storage than using batteries. Probably best to use this pre-heated water to feed your heat pump water heater to ensure stable hot water supply for showers etc.

AverageJoe has a working system scraped together from junk parts. Very easy to understand how such a system works.
I believe he circulates some of that hot water under his kitchen to provide some floor heating.
https://www.youtube.com/watch?v=xXoCIegCjzY

If I had the opportunity to build my house, I would insulate and fill the entire basement with hot water tanks. Use all summer+autumn to heat up the tanks, then use that stored heat through winter. Come to think of it, most of the tanks could be replaced with an insulated box filled with gravel. Or perhaps paraffin wax (melting point 37degC).
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#16
(11-18-2018, 08:34 PM)ajw22 Wrote: Or perhaps paraffin wax (melting point 37degC).

Phase change materials are certainly interesting. If they can get the cost down it could make a useful thermal store. I saw these guys on the Fully Charged YouTube channel.

https://www.sunamp.com
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#17
(11-18-2018, 10:00 PM)w0067814 Wrote:
(11-18-2018, 08:34 PM)ajw22 Wrote:  Or perhaps paraffin wax (melting point 37degC).

Phase change materials are certainly interesting. If they can get the cost down it could make a useful thermal store. I saw these guys on the Fully Charged YouTube channel.

https://www.sunamp.com

What a great bit of kit they are!.. I will have to do some more research on them. If you had a couple of them running it would rerun the use of the GSHP massively!. What’s to stop you substituting the GSHP all together and install a few of these instead?. Would certainly be a lot cheaper and easier to install.

Ajw22 what do currently have running in your home for heating & hot water?.
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#18
What I have now:
17kWp PV grid tied (6 more years of FIT at 32UScents / kWh)
2kWh battery storage
ASHP for summer cooling and space heating.
3x small kerosenes stoves for deep winter space heating.
Piped gas for on demand hot water.

What I'm planning to have by the time FIT runs out:
23kWp PV grid tied (no idea what the feed in rate will be)
60+kWh battery storage. During winter, charge to 50% using 1/3 price night rate.
ASHP for cooling and space heating
3x small kerosene stoves for deep winter space heating. Possibly replace one with pellet.
ASHP with 500L tank for hot water. Considered solar hot water, but I'm often away on business, and the excess energy would go to waste during that time.
Piped gas for hot water during winter.

I want to stop using kerosene/gas and go all renewable, but it does not make sense in my situation, because my excess clean PV electricity offsets inefficient burning of dirty coal.
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#19
Really interested in this site, I know property is cheap in Wales but its terrible weather haha Smile

Are you building it from scratch? Did you get planning permission?
Arrow  See My DIY PowerWall Build here Arrow
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#20
(11-26-2018, 12:46 PM)zag2me Wrote: Really interested in this site, I know property is cheap in Wales but its terrible weather haha Smile

Are you building it from scratch? Did you get planning permission?

Hey we have our own micro climate up on the North coast..  Undecided
I'm yet to submit planning mate, the plan is to submit that spring time hopefully.
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