Off Grid Systems

Reedbed sewage water treatment

Why Off the Grid? ___________________________________________________________________

In order to supply a household with the basic infrastructural needs, we tend to use centralized networks for power, water, waste and waste water. This centralized approach seems to be more suitable in densly populated areas that are characterized by a short distance from input to input or output to output. 
The plot of the Ecolodge Project is far away from these kind of supply networks. Thats why off-grid solutions became very attractive, on the one hand because we believe that  under circumstances like this, they can do a better, cleaner, cheaper and more sustainable job and on the other hand it became, due to the location, a necessity. 
We implemented: Power supply, Rain water collection, Rain water storage, Rain water to fresh water, Waste water treatment, Composting of human manure, recycled treated waste water , Natural light design and Solar thermal design.  
All these different parts come together to form a highly sustainable infrastructure for modern living.    

Electric Power ___________________________________________________________________

We had to consider wether wanted access to the power grid or if we wanted to try to design an autonomous system powered by photovoltaic and wind generators. 
The first choice would have meant paying the DEH (Greek Power Company) to lay overland cables from the nearby village as far as the plot. Considering the cost and the effect on the landscape (visual pollution) caused by the posts and cables, the network outages and the general problem of energy generated by burning fossil fuel, we came to the conclusion that we should go for an autonomous solution.

So we started to calculate the consumption of all the electric units needed for the plot. We calculated that we would need a photovoltaic system of 1.5-2 kW peak power and a small wind generator (100cm diameter) of 400 W. The combination of the two different power sources seems to be optimal because of the varying strength of wind and solar radiation throughout the year. In summer the photovoltaic system has its maximum production rate while the wind speed is generally low, whereas in winter solar radiation decreases but wind speed increases, so that the lower power production of the photovoltaic system is supplemented by the wind generator. For winter time with very little power production we calculated a battery bank with 600 Ah at 48 V wich gives us 2 days of power. For periods of heavy power usage such as during construction work we have a 7 kW diesel generator that functions also as a backup system in case of system failure. The overall cost including installation comes out at about 15,000 euro.
9 panels of 2.2kW power was installed

Water summarized__________________________________________________________________

Like most Islands in the Cyclades Tinos has an average anual rainfall of around 400mm which makes water a scarce local resource. Therefor we put a lot of effort into the design and planning of the water system. The goal was to design a system that can harvest and store enough rainwater to supply the needs for 6-8 people over the 4 completely dry summer months. 
So we estimated our actual water usage in order to calculate the size of the surfaces that we will need to collect the rainwater and the size of the cistern reqiuered to store the water throughout the summer. 
We calculated that we will need 240 sqm of hard surface to collect around 100,000L of rainwater for 6-8 people and for irrigating the gardens.

Water analyzed_____________________________________________________________________

We started to calculate or potential water requierement by looking at the average daily water consumption for of a single person in the European Union . With an average of 160 L we came quite quickly to the conclusion that it will be very hard to find a way of satisfying such a demand. So we started to look at the numbers more closely. These showed clearly that the flush toilet represents one of the largest demands on the water suply.
We found that the best solution for saving water is the compost toilet, because there is no water used at all. We decided against it because:
  • we have to treat grey water from the kitchen and shower anyway
  • the compost tank has to be placed underground which would require a small basement
  • the need of maintenance for every unit is higher
  • users have to be shown how to use the system
But we kept the composting possibility in mind. So we decided that a ultra low flush toilet (2.5L//4L) is the way to go. Actually, it is not easy to source them on the market.

In an "off grid" sewage system you have to treat the sewage water on your land in order to extract the pollution. There are vast several premanufactured products on the market that can do the job. For us most of them had drawbacks such as:
  • fairly high consumption of electricity
  • need fo constant usage 
  • high maintenance that can only be done by a technician  
  • proprietary sophisticated equipment
  • most of them need to be cleaned out
  • most of the treated water is still not sufficiently purified to reuse for garden irrigation
For all the above reasons we went for a reed-bed filtration plant. The advantages of this system are that you can construct it in a DIY approach, it is very robust in coping with usage fluctuation, it requieres very few electronic components and it can be designed to be a beautiful part of the garden. Furthermore the purification power is so high it is one of the few systems that allow you to reuse the treated water.

With the option of reuse we came up with the idea of using the treated water for the toilet flush and beneficial water for non-edible garden irrigation. This action saves us 4,500 L per month for 6 people. So over the summer period we can reduce our water storage capacity by 16,000 L.  

Water treatment____________________________________________________________________

As mentioned above our system of choice was the reed-bed filtration plant.  There are mainly two kinds of systems that are widely used and well documentated, the vertical and the horizontal flow system. We decided on the vertical flow because of higher filtration rates per square meter and a more robust overall design with less possibility of clogging in the sand filter. As a general size we calculated with 4-5sqm per inhabitant. This figure is defined in the standard literature on black water.

A 3x8 hole was digged in the end for the reedbed.

In order to provide enough treated water for the toilet flush we had to modify the existing design aproaches because they do not take into consideration that in our climatic region most of the water intake will be evapotranspirated (consumed) by the reeds. To reduce this effect we had to reduce the size which also necessitated the reduction in the pollution of the black water.
To achieve this reduction we came back to the composting solution. We designed a system that splits black water from grey water at the source. This reduces the pollution in the first stage. Then we incorporated a centralized composting mechanism into the black water stream. This means that all the solids such as manure and paper are filtered out of the stream before it reaches the reed bed system. By doing this the black water has pollutant levels that are close again to those of grey water. This approach leads to a size reduction of the reed bed by 40% and comes to a theoretic water output gain of 30%.
There are many more customisation details in our design that still have to be evaluated in real life, so we will report back at a later stage.
The centralized composting unit is a Swedish product called Aquatron. The solids need around 5 months to compost. This compost can be used for non-edible garden plants. If a 12-month hot composting process is added theoraticaly the compost would be suitable for edible plants. By taking out the solids from the sewage water stream the size of the sedimentation tanks is reduced. The sedimentation sludge that you have to get rid of every once in a while is also reduced to a minimum by this design.
The Aquatron toilet seperator of solids

Solar thermal design ________________________________________________________________

At the beginning of the project we were dreaming about a completely passive house design. Due to a lack of experience, time and other consideration we had to give up this approach. But when we where dreaming about it we read and saw a lot. So we kept some basic guidlines in mind while designing the houses and the landscape. 

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