Storage of heat underground is attractive because the heat losses are less as the ground stays at roughly 7-8 degrees C most of the year. That's the plus side. I thought it might be feasable to use an old oil tank and some oil-drums insulated with straw and water-proofed with plastic sheet. The minus side is that it is difficult to stop moisture from getting in and taking away your hard-earned heat, O, and the other thing, just about every small animal in creation thinks that nice warm straw underground is a perfect home!. I shan't try that again in a hurry. (Click on picture to enlarge)
This was an earlier flow test to find out how easy it was to push water slowly through several different oil-drums at the same time. It was very ticklish to get it right, I now think it is better to use electric valves to turn the water on and off to each container in turn. That way the flow to each tank is predictable and not prone to slight changes that have a large effect. I have now come to the view that the best heat-store is in an insulated shed above ground. Every renewable project should have one if possible as there are many times when there is just too much heat to use straight away. With what I have learned I have now hit upon what I think is the perfect solution, I'll let you know if I'm right when I have built it. (Click on picture to enlarge)
This shows the bare frame of a 16 cubic metre wood-chip store (that's about enough fuel for 100 days). The floor is v-shaped so the wood-chips fall to the middle as they are removed. However, wood-chips do not flow and active agitation is required to make them move. They also 'bridge', so it is not possible to remove chips at the base and expect the ones above to fall down into the space, generally they won't. (Click on picture to enlarge)
Same again. (Click on picture to enlarge)
Now with the plastic coated steel cladding to keep out the rain. This store has worked very well and stayed beautifully dry no matter how violent the storms have been. The next stage is to make an automated transport system to get the wood-chips from the store to the boiler. I'm not a great fan of conveyor belts, besides, I believe there is a much simpler solution - more later. Any wood-chip store must be away from where the chips are burnt for obvious reasons. Ideally there should be at least two 'drop-zones' to inhibit the passage of sparks or flames and prevent the possibility of a fire in the larger store. (Click on picture to enlarge)
