Basic Renewable Electricity Question

[bealers]

As I mentioned on @eatyourownver's thread re: Rayburns we're currently planning a self-build.

One thing on my list is to design the electrical system and I've been considering the following:

--Grid connection on its own main. We'll use this for high drain items like kettle (if stove not on) & cooker as well as a supply to the workshop.

--PV/inverter main for lower drain items but also efficient Fridge/freezer. A battery bank of some sort is likely but cost/maintenance is a concern.

--12v circuit for phones, laptop, lights etc.

I had assumed I would use different plug sockets for each main so there was no chance of plugging in to the wrong source.

We'll be cooking & heating the house with wood and in warmer months the water will be solar heated. I want to keep heating as low-tech as possible though I assume I'll need a pump of some sort? (2 floors).

As we'll have PV (I can get a decent set-up at cost through work) then I may as well take advantage of the FIT, but this is still optional and in some ways it may be better not to bother. Am I right that grid tie set-ups are not allowed to consume locally if the grid goes down?

Am I overcooking things here? 12v circuit seems a no-brainer.

[RenewableCandy]

Am I right that grid tie set-ups are not allowed to consume locally if the grid goes down?

Yup. G83 and all that.

You can get switchover-type inverters geared to the boat community ("Ship" and "Shore" settings on one inverter) but I don't know owt about them, they've been mentioned elsewhere on PS, though.

[vtsnowedin]

As I mentioned on @eatyourownver's thread re: Rayburns we're currently planning a self-build.

One thing on my list is to design the electrical system and I've been considering the following:

--Grid connection on its own main. We'll use this for high drain items like kettle (if stove not on) & cooker as well as a supply to the workshop.

--PV/inverter main for lower drain items but also efficient Fridge/freezer. A battery bank of some sort is likely but cost/maintenance is a concern.--12v circuit for phones, laptop, lights etc.

I had assumed I would use different plug sockets for each main so there was no chance of plugging in to the wrong source.
We'll be cooking & heating the house with wood and in warmer months the water will be solar heated. I want to keep heating as low-tech as possible though I assume I'll need a pump of some sort? (2 floors).

As we'll have PV (I can get a decent set-up at cost through work) then I may as well take advantage of the FIT, but this is still optional and in some ways it may be better not to bother. Am I right that grid tie set-ups are not allowed to consume locally if the grid goes down?

Am I overcooking things here? 12v circuit seems a no-brainer.

If cost/maintenance is your concern you will just stick with the mains power. The question is how much will you be willing to pay for a KWH when the mains are down and how often do you expect them to be down.
Different plugs probably won't make code. Here a double pole ,double throw switch is the minimum. With the first throw you disconnect the mains and with the second throw you connect your power source to the house wiring. You can't do one without first doing the other. Automatic transfer switches are also available that accomplish the same thing for stand by generators that start when they sense a loss of mains power.
Need a pump for wood heat? Why? Gravity is very reliable and some well planed heat registers and cold air returns will do the job nicely for even the largest house.
At present I have a four bedroom 2000ft^2 two story house that is heated totally by gravity circulated wood heat. The plumbing is also gravity fed so the only thing I have to worry about in a power outage is the fridge and freezer. I have a 4000 watt portable generator for that and I just unplug the freezer from the wall socket and plug it directly into the generator. Another cord to the fridge and I'm all set and the line crew is safe.

[emordnilap]

A pump is necessary in most set-ups - getting the water to move round the system can be tricky, especially if it goes through a coil in the cylinder first, before the radiators.

If it's going straight to radiators, I advise a suitably wide diameter piping from the stove to the first radiator, which must be as near directly above the stove as possible. The first pipe run needs to be vertical and to a large radiator.

In an power cut with no wired off-grid electricity, a good back-up for a circulation pump is a battery and inverter, suitably sized of course. The pump rarely has to run for long and you can damp down the fire to lessen the chances of it kicking in anyway. Rake the fuel to the front of the stove, away from the back boiler. Never leave the house if there's a strong chance of a power cut and you have a good fire going!

As vt says, a convection system in a two-storey house is eminently possible and he also suggests a generator. Remember adam2's sig. about them, though.

[mobbsey]

It occurs to me that this thread is all about providing backup electricity -- not finding ways around the problem of having to use electricity in the first place. E.g. we use a large (6") pessel and mortar instead of a food processor (does the job better, quicker, without lots of washing up and electricity to make it work); whilst we have a fridge and a small freezer, much of our food is stored as dried goods/non-refrigerated containers; and most importantly we have books and practical hobbies instead of electrically-powered entertainment.

You can do a lot to provide power to the absolute necessities (mostly lighting) in the event of a power cut, but by far the more effective option is lifestyle change in advance of that happening -- and that serves your needs better from the point of view of power-down rather than the technological substitution of power supplies.

[emordnilap]

It occurs to me that this thread is all about providing backup electricity -- not finding ways around the problem of having to use electricity in the first place.

We could do with a PS cookbook - alternatives to using fossil energy, as in your pestle and mortar example. We have a 'human-powered machines' thread I suppose but it seems to have died. Maybe a sticky?

[kenneal - lagger]

Tarrel, we've got a heat store cylinder from Gledhill which will do what you want. It has a coil for domestic hot water supply at the top, a coil for a boiler input just below the middle and a solar hot water input coil at the bottom. It has tappings direct into the vented cylinder for a Rayburn/Wamsler type hot water boiler at top and bottom and also direct tappings for a central heating take off at middle and bottom.

Ours was made specially for us at no extra cost to replace another thermal store but they have standard ones as well. Although the supplied insulation is very good I would advise additional insulation. We have supplied this by building a polystyrene box around the heat store, top as well, and filling it with loose broken bits of polystyrene packaging. All the joint in the polystyrene box are taped to make it airtight. This gives an additional 150mm of insulation to the original 60mm on the cylinder. If you think about the thickness of insulation in a house wall, for a Passivhaus you would typically have 300mm of Rockwool for a 21deg C temperature difference, and compare it with the temperature difference between cylinder and house, 40deg C, 60mm of insulation seems more than a bit sparse.

Our previous house had a gravity fed central heating system to supply a maximum heat load of about 3kW to the upstairs. This used a 22mm riser and horizontal to first floor ceiling level with 12mm down pipes from this to the rads, fitted with TRVs, at first floor (we had a pumped underfloor system on the ground floor). The 22mm horizontal return pipe was in the ground floor ceiling/first floor. To supply ground floor rads this return pipe would have to run under the ground floor.

For a larger heat requirement you would probably have to go for 28mm rise and return pipes and possibly use some 22mm radiator feed pipes for the larger rads. The riser could be fed through the thermal store tappings with the thermal store at first floor level above the boiler. The top heating tapping would be the riser and the bottom one the return.

[Tarrel]

Thanks very much for the info. I've just had some feedback from Grant, the makers of our oil fired combi boiler, saying it would be possible to use the "central heating" side to contribute to a thermal store. I'm guessing the thermal store you describe would need an additional coil for this purpose.

The reason I want to retain the oil boiler is that we will be leaving the house for the odd 2-3 weeks, sometimes in the winter, and we'll need to provide frost protection. The boiler is there anyway, so makes sense to use it. Could also be useful in the "shoulder season", when we don't really need heating, but will need hot water and the solar heating may not

Do you still need a separate cyclinder for domestic hot water, or does it work more like a combi boiler, where the wateris heated on demand as it passes through the coil in the heat store?

Regards

Tarrel

[kenneal - lagger]

I'm guessing the thermal store you describe would need an additional coil for this purpose.

It has "...a coil for a boiler input just below the middle..."

........ Do you still need a separate cyclinder for domestic hot water,

No.

or does it work more like a combi boiler, where the wateris heated on demand as it passes through the coil in the heat store

Yes. "It has a coil for domestic hot water supply at the top"

[Tarrel]

Cool. (or should I say "warm"!)

Thanks for the info.