Energy Matters Forums

[470rigby]

Heat Banks as we know are so "last century" and rebates are available for for their removal when fed off the Grid.

But what about the prospects for providing or simply augmenting heating in an Off-Grid SAPS???

On most Winter days, my Batteries sytem goes into FLOAT and unless some heavy appliance, such as the Wife's Hairdryer is fired up all that PV energy potential is simple wasted.

So, it occurred to me...maybe I could find an old Heat Bank to charge up during the day...and settle down to a cosy evening beside the Heat Bank!!

Has anybody thied this???

[munter]

I don't see why not. I don't know anything about the old style units but don't see why you couldn't just put a resistor into a large thermal mass object and place it within your living space. Dry heat banks would probably have the advantage of lower risk of shorting out than would arise in a water based system though I'm sure both could work.

You're lucky to have an excess of power in winter!

[Diamond]

Hi
From my experience with off-grid systems, when your charger goes to float what it does is shunt the energy into a load resistor. This can be disabled if you have somewhere else to put the ergs - now I haven't had ANY experience with Heat Banks but it makes perfect sense to me that you could use that power in a suitable version of such a thing.
I've always been meaning to divert it to heat water for showers etc but I'm not at my site often or long enough to get that done.
I'd be interested to know how you go...
Cheers

[470rigby]

I
You're lucky to have an excess of power in winter!

Here in NE Victoria the weather pattern is either overnight frosts followed by sunny days or overcast days with relatively mild overnight temperatures. The PV energy collection is “chalk and cheese”. By midday on a sunny day my batteries are in float and roughly 6kWH goes missing. But this is just the time that overnight heating is useful, so it is on these days and nights that the Heat Bank idea might provide cost-free heating for a small area such as a Bedroom.

In overcast conditions, the PV energy collected is so low that the 6.5 kW Genset gets a daily workout. With about 3.5 kW required to run the Charger in Bulk Charge mode, there is surplus energy available to heat up a Heat Bank, and the additional fuel cost is minimal, so the concept might just work at those times too.

Now all I have to do is find a Heat Bank going cheap!

[Gordon-Loomberah]

Resistive heating is a waste of potential space heating energy, unless you can do it for minimal cost and maybe even then... Using a heat pump should gain you 3+ (with a conservative COP of 3.0) times your expended energy, ie you have 2kW to spare once the batteries are in float, a heat pump will give you 6+kW of heating. Assuming of course that your inverter can start a suitably sized compressor. Even a 1kW HP to give 3+kW is better than 2kW of resistive heating.

[470rigby]

Resistive heating is a waste of potential space heating energy, unless you can do it for minimal cost and maybe even then... Using a heat pump should gain you 3+ (with a conservative COP of 3.0) times your expended energy,

The point of considering using Heat Banks in a Solar SAPS is to store energy that can only be collected during daylight hours, for use at night for heating. Obviously not the only way, but potentially a low cost way if an old pensioned-off Heat Bank could be obtained for minimal expense. Yes, a Heat Pump could be used and energy stored in a Thermal Mass of some sort, but at what capital cost to set up? I had thought that an “off the shelf” domestic Heat Pump HWS could be used to run a Hydronic System but the Radiator surface area needed to transfer heat energy rapidly to the space to be heated would be substantial and thus impact on the utility of the living space. Again, the cost would be an impediment.

I am off course, interested in hearing about other strategies for storing energy for heating purposes (other than the obvious use of batteries), preferably one that my long suffering Wife can get her head around to operate, or does reqiure one to subscribe to the “tinkerer” mentality that seems to be prerequisite for an article in magazines such as “Renew”.

[Mr5cott]

In reading this post, I am wondering why you don't incorporate the use of a passive solar collector? Easy to build with minimal materials. You can also incorporate the use of a solar powered fan with a thermostat to pump more air through the unit. Some argue that while it provides some great heat during the day, it is not much use at night.

I have built a solar heat collector myself and I have it vented underneath my home. To make use of the heat at night, simply build a box of rocks so to speak(like a battery) to store the heat. Build a large wooden crate, fill the crate with rocks and vent the heat from the solar collector into the bottom of crate. As the heated air flows into the crate the heat rises. As the heat rises the rocks absorb the heat all day long (Thermal mass) then it is slowly released during the evening. Obviously the larger the crate of rocks the more storage you will have.
This design could also be implemented in your home or building if you have the Solar collector venting in through a window or even a wall. Just some ideas that might help. It works for me in the mountains of Colorado at 8,500 feet above sea level.

[Tracker]

.
The old "School Heaters" used to be a big box of bricks, with resistive heating, and blower-fans.
ie.. a small mass of bricks, heated to a high temperature..

The heaters came on at night (Off-Peak), and the blowers, during the day..

A typical PV array might have a DC Voltage of 300V.. This will be a basic Constant-Voltage source (variable Current)..., meaning that it could be used to heat a bank of bricks, for night time usage.. eg.
My house system generally produces about 10KwH.. That is a deal of heating, but nothing like the same power run into a heat-pump..

We recognise that what Gordon says is correct, that resistive heating ... IS ... the most wasteful, but I wonder just how serious a sin it is, when running on OFF-PEAK power..
Some would suggest that we are doing the generators a favour by using their power at 2AM..

Heat pumps are only so good, but generally can't raise a temperature too high, as it has deleterious effects on compressors etc. I think that the limit for my heater is 60c.

You can naturally implement Gordon's idea, if you have a very large mass to be heated to a lower temperature..

A passive solar collector has much the same issues, in that you can't heat to much more than boiling point, and again, unless you start using salt solutions and then I would wonder what the cost would be for the associated equipment.

I find it ALL so frustrating.. So many way of doing things, but technically, many pitfalls for doing it correctly..

Gordon - Did you ever get Phase-Change heat storage working ?
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[Gordon-Loomberah]

Gordon - Did you ever get Phase-Change heat storage working ?

The experiments I did certainly demonstated the large latent heat of fusion, ie the liquid wax cooled to just under 60C and stayed there for a long time before dropping again. It was clear that it is a poor conductor though- the core stayed molten until the outside was not too far above ambient, but I was using a rather large single mass of it.
I was out riding the mountain bike this morning and thinking I should extract the digit and finally put the wax to use- so I'm going to put most of it into my 1000 litre hydronics storage tank, and save some for the tank that's going into the roof space above the wetback (when I finally get around to installing it).

I'm going to put it in copper pipes with an air space, and a bit more weight in one end so they orient themselves with one end up in the water, so they should also distribute the heat through the water more evenly due to copper being such a good conductor.

[Tracker]

I'm going to put it in copper pipes with an air space, and a bit more weight in one end so they orient themselves with one end up in the water, so they should also distribute the heat through the water more evenly due to copper being such a good conductor.

I must admit that I do like that concept.. I had never thought of that most obvious use..
I too had been troubled by the low conductivity and could not see an easy way around it.
The floating tubes is brilliant.
We are now talking about a practical "Heat-Bank", where Solar Energy could be used to advantage.
As far as hardware is concerned, you could really cheat and use a normal resistive HWS, by removing the Galvanic-Protection rod, and just slip your sealed copper tubes into the tank.. (so you don't damage the lining)
I think that the Galvanic-Rod-Retaining head is about 30mm, so you could get fair sized wax-tubes in there..

The concept is even better as the tubes could be bulk manufactured (OS) and sold to ANYONE who wants to store more energy in an existing storage system (of any type).. eg. Off-Peak electric.
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