As I understand it, the supply water of a municipal water tower is primarily gravity feed only. The water draining down from the reservoir above has never, to my knowledge, been considered an alternative source of energy. Water pumps, lighting, maintenance facility needs are all fed from a electric utility grid. Their is no "net-grid" hook up in a cookie cutter water tower operation.
Me being me, I've seen that the emperor has no clothes and I say - put some impellers on, y'all! I consider every water tower ever built to be a source of gravity fed power generation. Granted, one is not going to get as much energy back as it takes to put the head of water above - but one could expect SOME energy recovery, especially during electrical peak demand when the commercial rates for power is at a premium. A savey public works administrator would make it a policy to charge the tank with water only at night after the rates for electricity are at their lowest; the gen-set would make up some of the cost of electricity during the day when the rates are highest. Over the life of the tower an impeller/transmission/gen-set would more than pay for its capital outlay and save tons of carbon emissions in the process by way of savings of some fraction for electric water pump demand, local lighting, power for municipal repair shop tools, etc.
The pedestal of a water tower is a shroud. Inside and they are a steel strut and box truss structure covered for support. They add resistance to wind loading and angular bracing and to make it look more pleasing to the eye of neighbors. Inside are more than one water pump, for redundancy and maintenance. Older water towers still have their struts and girders exposed and are often the target of adverse city council complaints by individuals that have encroached into the suburbs where they were placed.
The point is that there is room to work on improved infrastructure, such as a scavenging impeller, inside a discharge pipe, inside of the shroud, out of sight. If the pedestal is too small, a small building attached but offset from the base could contain a transmission and generator set with automatic synchronization controls and a contactor, to connect it to the load side of the net-grid (on the load side of the electric meter.). One assumes from the start that this auxiliary alternative system will not make all the electricity that it will need for its pumps, local lighting, etc. Ergo, it has to be tied into the net-grid. The target is to reduce operational cost (and by so doing, reduce the water tower's carbon footprint). It is not about commercial or economic profit. It very well IS about reduced operational cost.
The purpose of putting the water up into the air in a water tower is to create both a reservoir and to create head pressure, especially when the demand for water exceeds the water pump maximum make up capacity.
An impeller coupled to a variable speed transmission, fed by the draining water, can then automatically maintain the 60 Hz r.p.m. needed by net-grid synced generators to remain online, permanently. As the head pressure drops during peak demand periods, the impeller will gradually start to slow somewhat. The transmission will adjust up wards and the generator will just make less than its capacity of electricity, but still be able to produce it at a steady 60 Hz. The impeller will be in a set aside supply pipe of course, not in a refill pipe up to the reservoir above. As the generator produces less and less power, the net-grid will make up the facility's water pump and lighting shortfall; spinning the meter forward faster, in so many words. But the amount of electricity purchased from the utility company will be significantly less than if there were no scavenging generators in the loop.
Add in the wind turbine, too, and you may (just maybe) see the meter turn backwards on occasion - who knows? The point is - here in a zone 2 area - there is no plausible way to make back all the costs of operation of a wind turbine system. However - Addison's city council can still look their tax paying constituents in the eye and say the cost is justified in that this water tower will cost less to operate than any other of its capacity, anywhere and it will save TONs of CO2 emissions in the bargain. And oh, bye the way? It will be a knockout crowd stopper to watch in operation, anytime, day or night.
Chris, as to your last question, I am sole owner and webmaster of www.green-metroplex.com If you or anyone has questions about the definitions of any of the terms above - use my websites' search tool for terms like net-grid, carbon footprint, etc., and you'll find definitions to these terms and hundreds of other, cross referenced, alternative and eco friendly words, resources and issues and further links to information and solutions related to our planet's citizens common need to go green. There are also off-topic web pages related to anecdotal interests and rants - but you have to look hard to find them. The full-sized pictures linked by thumbnails posted on the CR4 threads are stored there, too.
