Heating for a small shed/outbuilding

[fungus]

I am planning to have a shed/ workspace in my back garden where I can move all my electronics stuff. I'm planning to have a 40 to 60 watt solar panel charging batteries and then running through an inverter to power my soldering iron/other stuff and with a small light. My question is how will I be able to heat this place for periods when it is cold? It will be quite small, only a few metres across so I want it to be small, non-obtrusive and safe. I have 14 watts of solar panel that I can mess around with(1 4watt amo and two 5 watt polys) already but I'm not sure if that'd be enough power.

[johnlm]

I could spend about 10 minutes calculating all your heat losses in a shed that size but I would have to make a bunch of assumptions.  The quick answer is that your 14 watts you have from your panels will not provide any significant heat (48 BTU/Hr) while the panels were putting out 14 W.   Even if you had the shed super insulated, say R50, on all the six faces (4 walls floor and ceiling asuming a 3M x 3M X 2M tall room) of the building the 14 watts would not work.  The heat coming off your body would provide much more to heat the building than 14 watts would.  If you want any kind of more indepth answer you need to provide more info, such as what kind of outside temps you have, what is the required inside temp, are there any windows, how airtight will the structure be, what R value do you anticipate to insulate the walls and ceiling, what kind of floor and will it be insulated.  

Johnlm

[ElSenator]

From HomePower magazine - Thermosyphon Solar Heater

http://www.builditsolar.com/Projects/SpaceHeating/solar_barn_project.htm

And you could scale it down a bit, too..

L

[BT Humble]

I'm planning to have a 40 to 60 watt solar panel charging batteries and then running through an inverter to power my soldering iron/other stuff and with a small light.

Dick Smith Electronics here in Australia sells a couple of quite good 12V soldering irons (the $19.95 one is very nice to use, and has a much better tip).

http://www.dse.com.au/cgi-bin/dse.storefront/43f108b80bf6e39c2740c0a87f9c0755/Product/View/T2102

http://www.dse.com.au/cgi-bin/dse.storefront/43f108b80bf6e39c2740c0a87f9c0755/Product/View/T2100

I've also been successful in rewinding a burnt-out mains (240V) iron for 12V operation.  Your small workshop is almost exactly what I'll be setting up at a school in Fiji in a few weeks, except that I've gone for 12V soldering irons, drills, etc. to avoid the inverter.  My reasoning was that if the inverter stops working and all your tools run off it, you're sunk. ;-)

As for heating your shed, forget about doing it with solar PV.  Maybe a hot-air collector, or if you can get one an old flat-plate hot water heater running a loop of antifreeze to an indoor radiator?

BTH

[fungus]

 Thank you for that. I'd probably opt for the Thermosyphon and the 12 volt soldering iron. One more question, what sort of capacity battery should I use for this?

[Volvo farmer]

Don't forget to do some passive solar, it will take a load off whatever you decide to use for your primary system. I'd think a little wood stove in a shed like that would be nifty. You only fire it when you need heat and if you do it right, wood is practically free.

I built this little shed, I think it's 20'x8' and just put a couple of windows in the south side. I went in there a few weeks ago in the early afternoon and was quite surprised how warm it was in there compared to the outside. It was probably 35-40F outside and it felt 20 degrees warmer in the shed. This is with zero insulation too.

 

[BT Humble]

Thank you for that. I'd probably opt for the Thermosyphon and the 12 volt soldering iron. One more question, what sort of capacity battery should I use for this?

That depends.  You need to know spell out a few things:

1. What will be your average power usage per day (in Wh or kWh)?
   
2. What size of solar panel do you and your wallet have in mind?
   
3. On average, how many hours of clear blue skies and full sun will your panel see per day?
   
4. Will you have generator/mains backup for this system, or will it be solar-only?
   
   

If you can answer those, I can give you a more meaningful reply.

For what it's worth, the answers for the Fiji workshop are:

1. ~120Wh;
   
2. 40W;
   
3. 5 to 6;
   
4. Solar only.
   
   

BTH

[dudevato]

What about a small wood burning stove.  'Something made from one of those small throw away freon bottles.  Cut a door in it with a saw and put a hinge on.  The smoke stack could be some old muffler pipe or mayb fence posts.  You'd be all set with a hand full of twigs.

[fungus]

Okay then:

1. anywhere from 50 to 200.
   
2. 40w
   
3. from 2 to 4(I live in Scotland)
   
4. preferrably solar only.
   

[GaryGary]

Hi,

The BuildItSolar thermosyphon heater mentioned above is mine, and I will say that after a couple years I still like it very much, and it has been zero maintenance.

On my attached garage shop, I use this solar heater:

http://www.builditsolar.com/Projects/SpaceHeating/garcol.htm

The nice thing about this one is that you get terrific day lighting -- which is nice in a shop where you are doing close work.  Using the rollup door as moveable insulation really cuts the night heat loss.

The solar passive solution that was mentioned above is also a good one.  If you go this way, I would try to incorporate overhangs above the windows that shade the window from the high summer sun, and prevent overheating.  Also, some type of thermal shutters will greatly reduce night heat loss, and allow the shop to carry over some heat to the next day.  

In the end, you need to have good insulation and good control on air infiltration.  Solar solutions just don't work very well on poorly insulated and drafty buildings.

Good Luck!

Gary

PS -- I just put up a great book on building solar batch water heaters on the website -- I think its the best book ever written on the subject -- download it here: www.BuildItSolar.com

[BT Humble]

Power Usage: anywhere from 50Wh to 200Wh.

Solar Panel: 40w

Daily insolation: from 2 to 4(I live in Scotland)

preferrably solar only.

OK, let's work through it a little.  

A 40W panel in the real world will give you about 2.5A into a 12V battery.  

   2.5A x 3hours = 7.5Ah per day

   7.5Ah x 12V = 90Wh per day

There are losses involved in putting power into the battery and taking it out again (a useful analogy is a water tank with a slow leak) - I usually count it as 10%.

90Wh x 90% = 80Wh (approximately).

So with a 40W panel you'll need to use less than 80Wh per day, on average.  If you're using an inverter you'll have another 15% (or thereabouts) loss in the 12VDC->230VAC conversion, so you'd only be able to use  60Wh.

The usual rule of thumb is to size your battery  at the C/20 rate (meaning Capacity / 20 Hours), which in this case means you multiply 2.5A by 20 hours, and get 50Ah as the right battery size.  That said, I've never had any trouble charging my 1000Ah battery bank with a 20A solar array, which would be the C/50 rate.

So I'd suggest a 70Ah flooded-cell battery.  Given your short daylight hours if you keep a close eye on the water level you might not even need a regulator.  They're pretty cheap to build though, if you're a very DIY kind of guy:

http://www.homepower.com/files/hp70-40.pdf

You can find the MOSFET and Schottkey diode for it in an old PC power supply.  Here's a PCB I've designed for the circuit:

http://www.otherpower.com/images/scimages/236/switchreg.PNG

BTH

[ElSenator]

Nice work there, GaryGary! Well thought out.

[GaryGary]

Hi,

Thanks!! :-)