LIVING OFF THE GRID – DREAM OR REALITY?

One of the main ideas we are pursuing at present is the ability to live and work off the grid but without giving up on the niceties of modern life.  No compost toilets here then, nor washing your smalls in the nearest stream - not that there is anything wrong with that sort of lifestyle - it just doesn't suit most of us in the 21st Century.  This means no concession is given to replacing normal mains equipment, that is 240V AC with low voltage or DC replacements.

Now there are many installations that can be described as "independent of the mains" and these arise for a variety of reasons from choice of  environmental lifestyle to simple geographic location, mobile installation,  un-manned sites in remote locations, marine or leisure application etc.  In most cases we find that occupiers / developers make immediate concession to modern living and drop off the requirement for major items of mains powered equipment.  Naturally this has the effect of massively reducing total kilowatt demand, and in so doing, reduces the need to produce any serious quantity of useful electrical energy.   Our design philosophy has created a Hybrid system combining various forms of energy production.  This allows mixed voltages to feed into a common control and load distribution network.  

Lets look at current traditional alternative energy systems - an average small wind turbine and solar collector operating on 12 or 24V DC.   These small load systems are capable of producing 240 volts AC from an inverter, but they are subject to heavy DC current drain, due to very low input voltage - in other words the batteries go flat very quickly.  The average small wind turbine and solar collector rarely produces more than 2000 watts of sustainable output at 240 volts AC.   This small output capacity is incapable of running even the smallest domestic appliances let alone a kettle or fridge/freezer.  

So what do we do that is so different?  We've designed an energy storage system based on a much higher input DC voltages – 96 volts, 120 volts, 180 volts and 240 volts.   This is coupled to very high storage capacity of up to 2000 A/Hours, which means that at least 10 – 15 kW of sustainable power can be delivered from a fairly small unit, with outputs of 60 – 100 kW readily available. This type of system has already been proven a viable alternative to conventional standby generators for a variety of essential services such as heating and domestic hot water plants for nursing homes.

We have our first commercial installation going in this month to a 60 bed elderly care home in Elgin in Scotland - not in this case designed for alternative energy living because their location in the middle of a small city does not permit this – no planning consent for a large wind turbine for example and frankly there are limited supplies of sunlight.   However it does allow them to take advantage of low night-time tariffs  – they draw electricity at night into a DC storage system and as soon as the day rate tariff comes into play the system switches on to DC power and all services are run on the back-up battery system – everything,  70kW boilers, all lighting, catering and ancillary services – these all run on battery power for the 16 hours of expensive electricity.  We believe this to be unique in the UK and are now looking at a small Hotel in the Scottish Highlands for our next installation – they benefit from better location because they can have both solar and wind turbines integrated.

In rural / remote locations or environmentally friendly domestic installations requiring 10 – 15 kW of sustainable power at mains voltage, a typical system will produce energy from the following separate but integrated sources: 

• Small scale wind turbine   

• Solar panel collectors 

• Micro-CHP

• Wave generator  

• Water driven turbine

• Small scale wind turbine

A unit of any size from 500 watts upwards can produce energy at low voltage, ie 12–24V DC nominal, and feed into the common energy storage system through a continuously automatic selective switching system which allows the total storage battery of up to 240 volts to be progressively charged in 12 or 24 volt segments.    A similar progressive and rotating charging system is applied to solar electric units, (photovoltaics), which allows any number of units to be added or removed from service, and allows completely safe mixing of otherwise different voltage output equipment.  

We are also building Micro CHP.  Standard generators powered by diesel / LPG / Biogas etc.   We build them as small as 10 kVA output. Their primary task is to supplement 240 volts AC production, but with very precise instrumentation to monitor the load any surplus energy is rectified, stored and then used through the AC inverter when the engine has switched off.   Also – and this is where they can replace boilers in conventional operations - up to 60% of total engine capacity is recovered through heat at 400°C from the exhaust manifold. This heat is immediately usable for domestic hot water or normal space heating through a heat exchanger or underfloor heating or simply piped into the central heating pipework.  Surplus heat – of which there is usually plenty - can also be stored underground in large capacity insulated water tanks.  Our small scale CHP systems operating from Biogas / Methane are particularly aimed at dairy herd operators. It is well known that cattle produce vast quantities of gas, much of which is trapped in the slurry and bulk stored on site.  Our design team are developing a small digester plant to extract the gas, and use it to power a small micro-CHP to produce and store electricity.  Extracted heat from the exhaust pipe is used primarily for heating the cow’s drinking water and by providing free warm drinking water for milking cows we raise the cow’s milk yield.  

The AC inverters have proven control circuits that permit the safe use of the most delicate electronic equipment, such as computers, digital audio and television appliances, clock radios etc. However,  our primary objective is to develop a modular system for expanding inverters and operating in parallel arrangement. We are currently working on a design and build range of matching components to form the basis of an inventory of tried, tested and very reliable plant which can be placed on the market at a reasonable price, where investment recovery can be transparent and readily justified.