Spatial planning of renewables system

[Rendall]

Hi All

 

I need to knit together a few components for our offgrid renovation and am just thinking about the spatial 'certainties' and would appreciate thoughts on the permutations and things to bear in mind with this.

 

The plan is to have a solar/generator/battery combination plus either LPG or oil fired rayburn with backboiler for DHW and CH.

 

The access track along the side of the house will limit oil or LPG deliveries to the rear of the property as it is only 2.4m wide, and the closest point the tanker would get to will be more than the 40 or 45m distance it appears most operators state as the length of the hose (or are there operators out there who deliver with extra long hoses?).

 

Therefore the space that then appears to work best for deliveries plus planning regs to site the tanks for both the LPG or kerosene for the Rayburn, plus the red diesel for the generator, is about 70 meters south from the house (and about 2m lower in height). Are there issues with this distance? 

 

We could locate the generator near the location of the tanks too, or else locate this up closer to the house itself - I suspect the latter be easier operationally and is my current thinking.

 

The wider solar aspect of the system has two possible locations in relation to this. Option 1 is about 120m SW of the proposed site of the tanks. Option 2 would be about 50m north of the house (slightly shadier early morning and needs agreement with farmer).

 

Added to all of this there is a future possibility of a pico hydro in addition to help support the renewables side of all of this, funds & permissions permitting, so I want to bear in mind how that might graft onto all of this. The penstock would come down an old smooth incline to a turbine house adjacent to the proposed fuel tank location 70m SW of the house.

 

Suspect a map may be useful (!), but any thoughts or whatouts in the first instance?

 

[Russell griffiths]

Just as a side thought that may not be relevant at all

is this a property that is already there, or are you trying to get planning 

the reason I ask is that track seems a bit narrow for a fire engine so may effect planning. 

[Rendall]

1 minute ago, Russell griffiths said:

Just as a side thought that may not be relevant at all

is this a property that is already there, or are you trying to get planning 

the reason I ask is that track seems a bit narrow for a fire engine so may effect planning. 

 

Good question I'd not thought of. It's an existing property though, so presume they'd take the 'already that way' view  - and I'd guess tender hoses have longer reach than the 40/45m length the delivery tankers have and they'd be able to get that same point as the tanks and from there its around 55m from the front of the house/70m to the back.

[Ed Davies]

Where will the batteries be? In or adjacent to the house?

 

Normally off-grid PV arrays are run at significantly lower voltages than on-grid ones - the maximum input voltage to an MPPT charge controller is typical 150 or 250 volts whereas grid-connected ones usually work around 600 volts or so. This means you usually want the PV array quite close to the battery otherwise you need a lot of copper wire; low voltage means higher current so thicker wire for a given amount of power transferred.

 

Alternatively, you can AC-couple your system. You have a normal on-grid style inverter by the PV array then connect it to the house and battery via 230 volt AC lines, typically SWA buried in the ground for this sort of system. At the battery you then have an inverter/charger which establishes the 50 Hz mains frequency for your mini-grid and can even tweak the frequency up and down to control the amount of generation the PV's inverter puts out depending on the loads the house is taking and the state of charge of the batteries.

 

There are not a lot of AC-coupled systems around. Paul at the end of the road has one.

[scottishjohn]

why so many fuel types? --you could get an lpg conversion on generator .

no problem with tank being lower for lpg ,as its pressure ,but oil will require a pump at tank ,so that also means electric supply to it ,which means generator has to be going . or use a 12v car fuel pump ,but battery will need charging or its own solar pv system .

for hydro to be viable you need a water supply that can run a 6" pipe all the time , and have minimum of 40 ft drop from water supply to turbine --that should give 3-5kw depending on how big a drop --more is better

 

Edited February 16, 2019 by scottishjohn

[Miek]

8 hours ago, scottishjohn said:

 

for hydro to be viable you need a water supply that can run a 6" pipe all the time , and have minimum of 40 ft drop from water supply to turbine --that should give 3-5kw depending on how big a drop --more is better

 

Not entirely.. 

 

Even a 500w small hydro scheme will give you 12kWh per day which is enough for most domestic usage (assuming no heating loads) . If you had a 5kW system that would be great, no need for oil at all then since you could run a decent ASHP for space heating. 

 

What is your power budget? How many kWh/day in mid winter for electricity? You need this figure before deciding on a system. 

 

A map would certainly help. 

 

 

 

Edited February 17, 2019 by Miek

[Jeremy Harris]

Worth looking at Paul Camelli's hydro setup at his off-grid house up on Raasay: https://lifeattheendoftheroad.wordpress.com/

 

IIRC his micro-hydro system is around 500 W, and it's fed by a long length of MDPE pipe, scrounged from a fish farm and towed by boat to Raasay.  The pipe he used was 750m long, 90mm diameter MDPE, the entry about him getting it in place is here:https://lifeattheendoftheroad.wordpress.com/category/hydro/page/36/.

[PeterW]

Sounds like you have a couple of options.  You’ve talked about a Rayburn - is that existing currently and what fuel ..? It’s an existing build - is it being replaced or are you looking at improving or extending it ..?

 

In line with what @Ed Davies has said, I’d look at using mains rather than DC, but also if you have a “power house” location then I would combine everything there. Batteries, generator, PV and hydro feeds and then feed this via a single SWA cable to the house. 

 

In terms of heating oil, there is nothing stopping you moving the oil yourself when it’s been delivered - I’ve seen on one farm an oil line that’s inside an MDPE pipe buried across the yard and it pumps uphill to the house about 120m away. The house has a separate 250 litre oil tank and there is just a simple timer and float switch from memory that activates the oil pump from the lower tank. 

[dpmiller]

A standard pressure jet burner (duno what Rayburn use these days?) shouldn't have a problem with 2m lift. The oil pump will happily pull from an underground tank. Pipe restriction/ entrained air may be more of an issue but there's ways round that.

[Jeremy Harris]

22 minutes ago, dpmiller said:

A standard pressure jet burner (duno what Rayburn use these days?) shouldn't have a problem with 2m lift. The oil pump will happily pull from an underground tank. Pipe restriction/ entrained air may be more of an issue but there's ways round that.

 

Very true.  I fitted an in-wall-mounted oil boiler to our house in Scotland, with the tank just sat on concrete blocks in the garden, with the oil level perhaps 1.5m or so below the boiler.  The pressure jet pump never had any problem in lifting oil up that high.

 

Rayburn's used to have to have a small head of oil, though, as back when we had one in the 1980's the burner used a thing like a carburettor on the side to control the oil flow to the evaporation-type burner.

[Onoff]

Oil level lower than the burner? Isn't this is is what a tiger loop is for?

[Miek]

12 minutes ago, JSHarris said:

 

Very true.  I fitted an in-wall-mounted oil boiler to our house in Scotland, with the tank just sat on concrete blocks in the garden, with the oil level perhaps 1.5m or so below the boiler.  The pressure jet pump never had any problem in lifting oil up that high.

Do pressure jet burners have posiitive displacement pumps capable of sucking air, or would they need priming in this instance? 

[Jeremy Harris]

Just now, Miek said:

Do pressure jet burners have posiitive displacement pumps capable of sucking air, or would they need priming in this instance? 

 

Mine all those years ago (early 1990's) had a positive displacement pump, that just pulled oil up from the tank.  It worked fine, but did need to be run for a while during commissioning to pull oil through for the first time.  It also needed good joints on the feed pipe, as I remember having a problem initially with a joint that was oil-tight, but which allowed air to be sucked in (the boiler didn't have either a return pipe or tiger loop fitted).

[Onoff]

The outlet on my oil tank must be a good 2m above the (Riello)      burner. Guaranteed though if I run out completely I have to disconnect the feed pipe at the fire valve (level with the burner) and "suck" the oil through with one of these:

 

 

 

[Miek]

16 minutes ago, Onoff said:

The outlet on my oil tank must be a good 2m above the (Riello)      burner. Guaranteed though if I run out completely I have to disconnect the feed pipe at the fire valve (level with the burner) and "suck" the oil through with one of these:

 

 

 

That doesn't sound right surely? I'd expect the oil to flow freely once you bleed the air out. 

[Onoff]

14 minutes ago, Miek said:

That doesn't sound right surely? I'd expect the oil to flow freely once you bleed the air out. 

 

Don't know. The tank level drops below the outlet and the burner must suck through what's left in the pipe. The pipe is now empty. I then get +2000L of oil delivered. You'd expect it to flow freely through the pipe (about 25m long). Not a dribble without some help.

It's a copper pipe maybe 8-10mm, not coated or anything. Maybe kinked by a root? 

[scottishjohn]

3 hours ago, Miek said:

Not entirely.. 

 

Even a 500w small hydro scheme will give you 12kWh per day which is enough for most domestic usage (assuming no heating loads) . If you had a 5kW system that would be great, no need for oil at all then since you could run a decent ASHP for space heating. 

 

What is your power budget? How many kWh/day in mid winter for electricity? You need this figure before deciding on a system. 

 

A map would certainly help. 

 

 

 

I would say the operative word in what i said regarding hydro   was viable --long term

-not some mickey mouse turbine that not going to last  with sod all output ,but  with all the complications 

-a real turbine will last 50 years  or more 

pressure increases with more drop --if not big drop then you need bigger flow .its all about the weight of water  and or force (pressure ) to turn it  

I have done the numbers and  3-5kw per hour is where it becomes viable to consider it as  a power supply .

how big a generator were you going  to run ?-

[Jeremy Harris]

16 minutes ago, scottishjohn said:

I would say the operative word in what i said regarding hydro   was viable --long term

-not some mickey mouse turbine that not going to last  with sod all output ,but  with all the complications 

-a real turbine will last 50 years  or more 

pressure increases with more drop --if not big drop then you need bigger flow .its all about the weight of water  and or force (pressure ) to turn it  

I have done the numbers and  3-5kw per hour is where it becomes viable to consider it as  a power supply .

how big a generator were you going  to run ?-

 

 

Paul Camelli's experience with his (very definitely not "Mickey Mouse") hydro installation, plus that of his neighbours at the Old Schoolhouse, Torran, seems to indicate that small turbines of around 500 W can be very useful and reliable long-term ways of providing constant power to an off-grid house.  His has been running for several years now (I gave the link earlier).  As mentioned by @Miek, 500 W of continuous generation is 12 kWh per day, enough to meet the needs of an off-grid house that has heating and hot water provided by another means.

[Triassic]

I agree with Jeremy, Paul’s set up is not Micky Mouse, to the extent that he has to have heat dumps in his workshop to dump the excess generation.

 

He has a backup generator that he only ever runs when he’s welding!

Edited February 17, 2019 by Triassic

[Miek]

1 hour ago, scottishjohn said:

I would say the operative word in what i said regarding hydro   was viable --long term

-not some mickey mouse turbine that not going to last  with sod all output ,but  with all the complications 

-a real turbine will last 50 years  or more 

pressure increases with more drop --if not big drop then you need bigger flow .its all about the weight of water  and or force (pressure ) to turn it  

I have done the numbers and  3-5kw per hour is where it becomes viable to consider it as  a power supply .

how big a generator were you going  to run ?-

But we are talking OFF GRID, so any generation in mid winter is very valuable, even a few hundred watts if constant. Bigger schemes like a 5kW turbine would make far more sense with a grid connection IMO as the capital outlay is considerable and you could likely get some FIT payments (though I'm not sure on the current deal) for your export, which would likely be around 90% of your production. 

[Ed Davies]

2 hours ago, scottishjohn said:

and  3-5kw per hour

 

You're still getting this wrong. Please have a read of this.

 

I agree with the others, 500 W continuously, even if only during the winter, would be very valuable. It would reduce the size of both batteries and PV required significantly and mean so much less generator use that you could get away with a relatively cheap petrol or LPG one rather than needing a beefier diesel.

[TerryE]

2 hours ago, JSHarris said:

As mentioned by @Miek, 500 W of continuous generation is 12 kWh per day, enough to meet the needs of an off-grid house that has heating and hot water provided by another means.

 

You would also be better using a hot+cold fill washing machine and dishwasher, but even 12 kWh / day is not to be sneezed at.  With PV + micro hydro + battery, the number of times that you'd need to fall back to using a generator would be very small.

Edited February 17, 2019 by TerryE

[Rendall]

1 hour ago, Miek said:

Even a 500w small hydro scheme will give you 12kWh per day which is enough for most domestic usage (assuming no heating loads) . If you had a 5kW system that would be great, no need for oil at all then since you could run a decent ASHP for space heating. 

 

What is your power budget? How many kWh/day in mid winter for electricity? You need this figure before deciding on a system. 

 

 

I'm looking at designing for 20kwH per day.

 

ASHP I'm not sure on - its an older house so feel it will always be relatively leaky and I worry about the effectiveness? The Rayburn was a fixed ask from my wife. It was originally an aga ask but she's happy with a Rayburn, so my thinking is that as we're putting that in anyhow we could go for a Heatranger and thereby use the back boiler for the DHW and CH rather than have/fund another component for those elements.

 

A hydro could have up to a 100m fall, but 20m in on our land/80m on a neighbours. My 'bucket tests' suggested flow of around 15lps even at the height of last summer's dry spell, but a wider initial desktop survey by a hydro firm suggests a mean flow of around 27lps. They calculated potential of a 14kw system so around 45000kwh per annum generation off this but that came with high costs - c£50K - and we'd definitely not need something of that size of generation (and can't export). I want to get a lower cost for a smaller system that is closer to our domestic needs, but ultimately this is all dependent on agreement for the weir and penstock to be installed on the neighbour's land. Having a conversation with them in next couple of weeks, but even then speed of consents or our budget may constrain when we could move on this. If we did do this though a pelton turbine or something like http://www.scotthydroelectric.com/ which could give us 500w or 1kw or so would make a big chunk of the need for a good proportion of the year and be balanced/supplemented by the solar and backup generator.

 

 

[Miek]

I think I would aim for oil for all my heating requirements, and bottled propane for cooking. 

 

You could go for LPG throughout, and possibly use an LPG genny? 

 

Assuming a diesel genny, could you run this on heating oil? Possibly with additives for the fuel pump longevity? Seems annoying to have two separate tanks. 

 

Sounds like you have great potential for hydro

 

 

[Rendall]

I did wonder about LPG for both the rayburn and backup generator. However, I was pointed in the direction of a few horror stories from the shortages last year which has shifted my mind back to oil as potentially more reliable in terms of supply.