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Peter,
There's also a significant earthing issue - the ground at the top of the hill almost certainly isn't at the same potential as the ground in the electrical wiring in your house. It has two consequences.
Firstly there is a risk of a touch potential between the stuff earthed at the hill, if you are at the remote end (ie in the house); at 1km this could easily give you a shock.
The second is more invisible and a long-term issue. Connecting the two without an isolating transformer creates an earth loop and the result is electrolytic corrosion of whatever metal bits are stuck in the earth - starting with the earth connections and very often your plumbing. It may also corrode steel reinforcing in concrete (if you have a slab).
1 current of 1A per year equates to 1kg of metal dissolved so consider what that could do to weaken things or make pinholes in pipework.
One solution is to have all the components at the house which are connected to the hill double-insulated, and in such a way people in the house cannot come into contact with anything metallic wired to the hill. That's not so easy.
The proper solution is to use alternating current in that cable and isolate the hill from the house with an isolating transformer, so that the earth of the hill is separated from the earth at the house, and the secondary side of the transformer (active and neutral) supplying the house are also electrically isolated from the hill.
PS if you don't have an isolating transformer what you have currently is already hazardous and possibly in breach of the wiring rules.
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