Tony Paul Martin

I cannot recommend masonary stoves enough. Slow safe warmth that is very efficient and comfortable and low maintenance. Also good for cooking preserving, water etc. https://www.mha-net.org/

If you use a larger diameter pipe it will improve flow and reduce the amount energy needed to pump.
You might find this article on sizing of hosepipes of interest.
http://www.what-is-permaculture.co.uk/articles-by-tony

See here for more on legionella
http://www.hse.gov.uk/healthservices/legionella.htm

Hydrogen peroxide will only work for a certain time depending on conditions as it degrades to water and oxygen

Power is in watts, energy storage is in watt hours. 1 ton of water (1 cubic metre) stores about 1 Kwhr/oC rise

http://www.what-is-permaculture.co.uk/wp-content/articles/water-temperature-moderation-permaculture-design-greenhouse-GGI-33.pdf

Best wishes to you.

Hi, adding containers of water will keep daytime temps down a bit and then slowly release that energy overnight and keep the temperatures up. Watch out for round bottles unless the liquid is coloured or they can act as magnifying lenses and burn the plants.
See here for some more details.
Using water to maintain even temperatures in greenhouses.  Appears in Growing Green International Issue 33
http://www.what-is-permaculture.co.uk/articles-by-tony

Sounds an amazing place! Some pics when you have finished would be welcomed.
Worst case scenario. Fan, the trouble is that whilst it may seem always windy, sods law says that on the hottest days when you need the wind it will stop and it doesn't take long to fry plants so I think a windmill would be risky.
At least with the sun, no sun = no heat. You are guaranteed power for the fans without any fancy control circuitry. Yes computer fans are popular and cheap. It might be good to have at least 2 on separate circuits and solar panels in case of failure. A simple protection device for the fans would be a suitably power rated 12volt zener diode. This will stop your fan getting extra voltage and which would reduce their life expectancy or completely burn them out. Hope this helps.

Hi Pearl, sounds great, of you are blocking the light will the plants get enough? Would instead a thermal chimney help move enough air through to keep the temps down?
This sort of idea http://sustainablesources.com/images/passsolar6.gif or maybe solar powered fan, the more sun the more air. Best of luck with this.

Sounds like a lot of effort which should be well rewarded. One thing that will also help. Heat is lost through conduction, air currents but also radiation. Night time reflective blinds automatically drawn over could make a huge difference (even if you are using double glazed panels in your green house)
Also if you get any condensation you may be able to channel it somewhere useful. Exhaust gases from your house will contain a small amount of extra carbon dioxide which may make a small difference. Above all have fun and experiment

Hi Elizabeth,  "the thermal lag of water is very short". The rate of discharge and charge will be effected by the volume of water, container material and thickness of material and the temperature differential between the air and the surface of the container.
To slow down the thermal transfer speed of water whilst retaining it's high specific heat capacity you could add a preservative and a gelling agent then it would act more as a solid, or even add some sponges to reduce convection currents.

Secondly whilst the slabs would store some heat you might be better off adding insulation around the edges of the greenhouse and thermally connecting the slabs to the mass of soil below. You may also get some heat gain in the depths of winter from the ground as per earth sheltered greenhouses.

Hi Pearl, I did some experiments a while back because I was also interested in what sized containers would work best. It was published in Growing Green International (Magazine of the Vegan Organic Network) but I have made it available here as a PDF. Hope this helps. Tony
http://www.what-is-permaculture.co.uk/wp-content/articles/water-temperature-moderation-permaculture-design-greenhouse-GGI-33.pdf

Hi Burra, thanks for best wishes. where abouts did you live then?