Rain Water Recovery

All new builds must by law, have a water meter, I have been used to paying a flat rate for water so I have no idea whether we are high or low water users. I expect we are high – my youngest will clean her teeth and leave that bathroom tap running, or the older one will “accidentally” run a bath full of cold water. I am not keen on having run-away costs associated with water use, and frankly as we are told, water is a scarce commodity and we should do what we can to conserve it.

Somewhere between 35-60% (depending on who you talk to) of domestic water use goes on flushing toilets and washing machine use, and as the quality of water needed for these activities doesn't have to be drinking standard an alternative to mains-sourced water can be used. One of the most popular sources for this is rainwater. A rainwater recovery system links the guttering system of the building to a large storage tank (in our case 6000 litres) which is usually buried underground. There is a filtration system that removes debris in the water and then it is pumped around a discreet piping system to the utility room and toilets.

I expect that given the rainfall levels these days in the UK, this system should never run dry but if the level in the tank falls too low then mains water is introduced to supplement. 

I can’t imagine retro-fitting such a system, but for a new build it is pretty simple. I believe the whole system is around £4000 for supply and fit. Now I know that the payback period for such as system will be pretty long, but as with all this ecological stuff, you have to balance the payback with the ecological benefits, so you can feel smug about doing your bit to save the planet. The other aspect is that low running costs, particularly for a large house is surely a good selling point when the time finally comes to move on.

Heat from the Ground

Some things that you see or read about seem too good to be true. Geo-thermal heat pumps, in my humble opinion fall into that category. When I first researched this topic I was gob-smacked.

In layman’s terms this is how these things work. The sun heats up the earth, and the earth takes a long time to give that heat back again, especially when you get below the surface, even a meter of two. This technology exploits that differential between the ambient temperature and that underground. A loop of plastic coil is buried a metre below the surface and water is pumped through it, the water in the tube is heated by the earth and that heat is then gathered by the heat pump and by a heat exchanger system is used to warm up your domestic hot water system. The running costs are for the electricity to drive the system – there is no gas or other fuel burnt in the process (apart from the power station that supplies your electricity – see the note about Solar PV for a solution to that too!).

The system works the whole year around, domestic water is heated to the same temperatures as a boiler system whatever the weather, and the source of heat (i.e. the sun) will hopefully last for a few years yet.

Obviously this approach to heating is very environmentally friendly, and right now the Government will give you a grant towards the costs of the supply and fit of such a system.

So where is the catch? There are two actually. Firstly the length of pipe that has to be laid underground. In our case this is about 1 kilometre, so the whole back lawn will be dug with a long winding trench to accommodate this much pipe. This is expensive and time consuming, and will need remedial landscaping work.  A borehole is also possible for those without enough land for a shallow loop. The depth would need to be 80m or more and is dependent of geological conditions, again this is expensive.

The other catch is the capital cost. The plant for a heat pump is not much bigger that a boiler, but it is very much more expensive. There is a bit of a chicken and egg situation here – if the systems are to become more economical then greater mass production is required, for that to happen these systems would need to be installed in mass produced housing, and from my experience, plumbing and electrical systems in most new housing is remarkably rudimentary and cheaply done.

For self-builders there is a choice – if you plan to stay in your new house for 7 years or more (on current prices) you will begin to see the financial benefits of a geo-thermal heat pump, but it will take that long. Low running costs will obviously be an attractive option if you plan on selling the house after it is complete, but I suspect that a heat pump or other green technologies will fall lower on a prospective buyers list of priorities compared to location, garden, schools, the kitchen etc.

Solar PV

Solar heating has been around for some time – it is not unusual to see those boxes mounted on the roof of houses and public buildings. This system is used to heat up water with sun light. There are a number of obvious drawbacks with this; firstly and most obviously the sun in this country does not shine every day – so solar water heating can be redundant quite a lot of the year. Secondly they are just pig ugly, big boxes sitting on your roof. The mechanisms inside these systems exploit new materials these days and are robust, long lasting and a lot less prone to leaking antifreeze laden water over your roof, however there surely must be something around a little more modern?

We there is – solar photovoltaic (PV) systems. This means “sun light electricity”, and like many modern materials is a product of space exploration. Many space craft have solar PV cells either on their flanks or on special vanes than are extended when the craft is in space. The cells convert sunlight directly to electricity. The earthbound versions do the same thing, but are now even more efficient, being able to generate electricity from any amount of light, i.e. unlike solar water cells, solar PV will generate electricity even on a cold, cloudy day.

Solar PV systems can be mounted on frames a little like solar water heaters, and you can see them more and more on traffic signals and other transport signs and signals to supplement either mains or battery power. One of the most recent developments of solar PV is so-called “Solar Shingles”. These are the same size and shape as standard roof tiles and replace tiles rather than sit on top of them. This allows you to convert whole roof elevations into a giant solar PV matrix which generates electricity as long as there is daylight.

One recent innovation in the use of solar PV in the UK is the ability to link to the incoming electricity meter from your supplier. The power generated by solar PV is not usually stored, so anything that you create in excess of your own needs is fed onto the National Grid via your electricity supplier’s meter, and they have to buy it from you at so-called “green energy tariff”, this is the price that companies charge for electricity that is generated from sustainable energy sources. So the theory is that if you can sell to the electricity company enough surplus during daylight hours, you can subsidise the power you use from them after dark.

And like geo-thermal heat pumps, the government is currently providing a substantial incentive for those who are willing to invest in this technology. In our case we could secure a grant of 50% of the supply and fit costs of the system, this would amount to £14,000! However there is a fixed pool of funds for this and according to our supplier it is going fast.

There are of course some catches – firstly, the solar PV cells are a blue/black translucent colour – great swathes of this over your south facing elevations will certainly not be to everyone’s taste, and then there is the capital cost and payback period. You still need all the usual electricity equipment you do without solar PV. Unlike a heat pump there is no equivalent savings on a boiler, so all the payback would come on a reduction of electricity bills, and that could take a very long time if the capital cost is £14,000 (or £28,000 without the subsidy!!) – This may be longer that the working life of the PV cells. 

I am not sold on this technology for both of the reasons above, although getting £14,000 in a government grant is very alluring. I have asked our potential supplier to do some real analysis on the likely cost savings compared to normal electricity, so that I can calculate the payback period – I will put the results on the web site when I have them.