If you locate your cabin in a remote location, you may be faced with finding a source of water. We are able to carry in our drinking water, however it is convenient to have an additional source available for showering, washing dishes, watering plants, etc. One way to aquire water passively is to collect rainwater in a cistern.
A cistern is a tank (usually underground) for storing hauled water and/or rain water which has been collected from a roof or other catchment area. A cistern may be a good choice in several situation. If you are in an area with no water service, you want to avoid the cost of digging a well, you have no spring, stream, or other ground water source. A cistern can also serve to supplement water from other sources.
To harvest rain water the gutters and downspouts of a home, barn or other building are routed thru a device to divert the first portion of rain water from entering the cistern. This keeps the dirt, dust, etc. that has collected on the roof and in the gutters from entering the cistern.
Once an adequate amount of water has been diverted, the device then shunts the rain water into the cistern.
Below is the formula for calculating the maximum amount of water that can be harvested from a given structure.
Once you know the area of your roof and the annual rainfall for your area, you can visit http://www.greenbuilder.com/sourcebook/Rainwater.html to see a chart to convert this info into gallons per year that may collected by your system.
For example, the foot print of our roof measues 12'x 28'. We recieve about 40" of rainfall per year in our area. Using the chart we calculate that under perfect conditions we could collect up to 7490 gallons per year.
If you lived in our cabin full time and were very carefull with your water usage, you might use about 25 gallons per day per person. Say there were four people living in the cabin, each using 25 gallons per day times 365 days per year, the total demand would be about 36,500 gallons per year.
So under these conditions we would be able to supply about 20% of our total demand by harvesting rain water. Note however that this is a rather small structure, 336 square feet per floor. If you are collecting water from a roof with 1500 square feet you could expect to collect 33,708 gallons per year or about 92% of the water demand for a family of four.
Rainwater harvesting can be done with any roofing material if it is for non-drinking use only. For potable use of rainwater, the best roof materials are metal, clay, and cement.
Asphalt shingles can contribute grit to the system and need a pre-filter for the water before it enters the cistern. Lead materials in any form should not be used in the system (i.e. lead flashing).
A 1500 galllon polyethylene storage tank like the one pictured here sells for about $700. Rain water diverters to keep the intial flow from washing dirt and debris into the tank can either be homemade or commerical purchased.
Once the water is in the cistern or tank you can use either gravity or a pump to move it from the tank to the point of use.
Using a 12 volt demand pump such as is used in an RV may work well if 110 volt electricity is not available. This model sells for about $70.
The combination of a solar panel and a deep cycle battery can provide enough power for the pump as well as some lighting.
A Siemens 12 volt, 50 watt solar module sells for about $300. This units have a 10 to 25 year warranty. These solar modules are self cleaning, made with ultra-tempered glass that provides excellent light transmission and protects from wind, hail, and impact.
These panels are constructed with high efficiency single-crystalline solar cells that deliver excellent performance even in low light conditions.
Deep Cycle Batteries for Photo-voltaic Storage
Deep cycle batteries are designed to be discharged down as much as 80% time after time, and have much thicker plates. The major difference between a true deep cycle battery and others is that the plates are SOLID Lead plates - not sponge. Unfortunately, it is often impossible to tell what you are really buying in some of the discount stores or places that specialize in automotive batteries.
The lifespan of a battery will vary considerably with how it is used, how it is maintained and charged, temperature, and other factors.
A charge controller is a regulator that goes between the solar panels and the batteries. Regulators for solar systems are designed to keep the batteries charged at peak without overcharging. These units are fully automatic. These chargers can be left permanently attached to batteries for true "connect and forget" operation. They sell for about $175.