Solar Power system

[gizmo]

In another thread I mentioned my solar power system which powers our home. I have started a new thread so as not to hijack the discussion about older houses.

here are some pics:

This is our mudbrick home which we owner-built over the last few years. Some details still to finish...

The panels on the roof are solar hot water panels, the hot water tank is in the peak of the roof. The heated water from the panels rises naturally to the tank, no pumps required. (thermosyphon)

 

[gizmo]

8 x 120 watt solar electric panels mounted on garage roof:

 

[sudsmaster]

Nice looking home.

Mud brick? You mean adobe?

You must be near the coast, I see evidence of moisture ;-)

 

[gizmo]

battery bank 24 volt 1330 Amp-hour:

 

[gizmo]

control panel -contains breakers, charge controller, inverter.

 

[gizmo]

inverter 1500 watt continuous, 3600 watt peak:

 

[gizmo]

nanny state signs required by law:

 

[gizmo]

my home-made 24 volt DC generator:

Briggs and stratton Vanguard 6hp engine, twin v-belts drive to Bosch 24 volt 55 amp automotive alternator, internal regulator removed and replaced with basic brush set and external adjustable voltage regulator, set to stop charging when batteries reach 30 volts.

Under normal use battery voltage ranges from 24.0 to 25.5 volts, under charge voltage rises slowly to 30 volts when fully charged. When charging is stopped the voltage drops to 25.6 volts fully charged. Once a month voltage is increased to 31 volts for about 15 minutes, this stirs up the electrolyte in the batteries, which prevents stratification and so extends battery life. This is done automatically by the solar charge controller.

 

[gizmo]

two 24 volt DC fans in the wall provide a flow of cool air when the generator is running.

The battery bank is in one room; the generator, inverter and controls are in another room. The rooms are sealed from each other so no spark in the generator room will ignite gases from the batteries when charging.

 

[gizmo]

Hi Sudsmaster,

Yes, the house is adobe. The common term for that here is mudbrick, though our home isn't true mud brick as the walls are not made of bricks, but the mud was poured into formwork clamped between the big cypress posts you can see at each corner. The walls are 250mm (10 inch) thick poured mud, comprising about 110 mm (4.5 inches)of mud inside, centre of 35 mm (1.5 inches) of polystyrene sheet, and another 110 mm approx of mud outside. This was a new method of construction I devised myself, splitting the mud wall into two skins with a core of insulation. I got the idea from a magazine article, but the original design used wheat straw between the two skins of mud, I thought the polystyrene would better suit our damp climate.
I got the styrene for nothing - it was foam vegetable boxes from nearby restaurants which I cut into slabs to go into the walls.
The issue is this - a wall has two thermal properties, insulation and thermal mass. Insulation is resistance to heat passing through the wall, thermal mass is its ability to absorb excess heat from its surroundings during the day and release it back during the night. Mud walls have poor insulation but good thermal mass.

In areas where you have high day temperatures and cool night temperatures, the excellent thermal mass properties of adobe help provide comfortable internal temps by evening out the highs and lows. Its poor insulation value isn't an issue.

In areas which have prolonged periods of low day and low night time temperatures, there is no "recharge" of warmth into the walls and their low insulation value becomes a problem - your heat being generated inside leaks out through the walls. By combining thermal mass of the mud with the excellent insulation of the polystyrene, we get walls that even out daytime high temps and evening low temps during sunny periods, and contain warmth from heaters during cold periods.
I'm happy to say the theory works - we have only a tiny 2-burner lpg heater for the whole house at present, and it is fine. The amount of heating we need is so tiny it is amazing. we are putting in a wood-burning heater soon, but it is a very small one and should only need to burn for 3 or 4 hours on the cold days. It will also boost out solar hot water.

We are not far from the coast - I think about 10 km as the crow flies, about 30 km by road. It is a VERY damp area, we have 2 metres per year rainfall. That's about 40 inches I think. The old locals say it rains for nine months of the year, for the other 3 it drips off the trees. So I'm not surprised you can see evidence of water. The house isn't quite finished but it needs some touching up already - the the upstairs windows need more coats of sealer on the timber, and some of the mud has been damaged by driving rain. None of the mud has had a sealer coat yet - it needs a couple of years to stabilise first, then it gets a lighter coloured waterproofing coat which it hasn't got yet. The local soil is very resistant to water damage though. (any soil which wasn't resistant to rain washed away aeons ago!)

Chris.

 

[hydralique]

Very Interesting, Gizmo!

That's clever with the isolation of the interior and exterior walls and I can see it working quite well from a thermal standpoint. I am curious how your engineer dealt with the structural issues though. Thin layers of mud don't have much strength - did you add any binders or fibers to the mud mixure? A post every so often would take care of vertical loading if you connect them with beams, but that doesn't address lateral or shear loads. Are there any moment frames or steel "flagpoles" set in the slab to address this, or do you have sections of non-mud wall in strategic locations?

 

[gizmo]

Hi Hydralique

The mud walls are non-loadbearing. There was no "engineer" involved, we hired a building designer to draw up the plans, he turned out to be hopeless, his plans failed council permit application, so I bought copies of the Timber Framing Manual which gives span and load calculation tables, and worked it out for myself.

The post and beam frame takes all loads, except the mud wall provides some bracing, and there are also several internal studframe walls which provide further bracing.

The post and beam structure does the real work, a local architect who specialises in designing this type of home for inexperienced owner-builders famously says "you could build the infill walls of chocolate boxes if you want, the frame takes the loads."

The two mud skins are very strongly tied to the posts and window mullions with four galvanised ties at each mud-to-post intersection, at each pour. Each mud pour was 250mm (10 inches) high, so you can work out we used LOTS of galvanised wall ties, plus at each pour the two mud skins are tied together with heavy plastic mesh.

Here's the process for a pour:
1. attach 2 galvanised wall ties at each intersection of mud skin to post. (2 skins = 4 ties per post per pour)
2. clamp 250m x 50mm (10 inch by 2 inch) sleepers between posts.
3. Stand up the pieces of polystyrene in the centre of the formwork.
4. pour pre-mixed mud/straw mix into the formwork, almost to the top. The mud/straw mix needs to be worked in well around the ties to make sure there are no air gaps or weak sections.
5. fit a length of heavy duty plastic "gutter guard" mesh across the whole wall, spanning the two skins and crossing the centre polystyrene. Bed it well down into the mud. (The mesh comes on a roll which is slightly less than the width of the wall, which is very convenient.) Add a layer of mud/straw mix to cover the mesh, and fill the forms to the top.

Once the mud has set enough to support itself ( few days in warm weather, up to worst of 10 days in wet weather) you can remove the forms and re-fit them higher up for the next pour.

The walls could also be built using dried adobe bricks of the same thickness of about 110 mm, but the poured-in-situ method saves a lot of heavy handling. The disadvantage of poured-in-situ is slower drying, and a greater risk of shrinkage cracks while drying. Our soil is very reactive (it shrinks a lot when drying) but we were able to prevent that problem by using a very wet mix and a real lot of wheat straw. We built several test walls using a variety of mixes and assessed them over a year before deciding on a suitable recipe. The best walls were undamaged after a year with no protection at all (no roof over), the worst had almost disappeared.

We still have some rendering to do inside, a couple of walls have fine surface cracking which will be covered by a render layer whch gives a smoother surface and lighter colour.

Chris.