Living Off Grid with Renewable Power - It's
easier than you think!
One of the major considerations
when looking at Renewable Energy as a power source is the need to
completely review your use of energy and to admit that you are never
going to have the unlimited access to energy that you have been used
to. Having thrown that bucket of water over you, it is not all bad.
By following a few simple recommendations you can be totally self
sufficient and have a very comfortable life with most of the
facilities that we have become accustomed to.
To start with we have to dispense
with all the high power consumption items found in a normal
household, meaning anything that produces heat electrically, which
includes electric kettles, ovens, hobs, immersion heaters, dish
washers etc, however washing machines are a very important aid that
cannot easily be replaced and can be used either in hot fill from
your water heating system (wood burner etc) or cold fill (with built
in heater) subject to rationing its use with regard to your
available power. Luckily most modern washing machines will wash at
very low temperatures which helps keep energy consumption low. Most
of the items mentioned above can be substituted with gas or
alternative powered equivalents. Although it is obvious it is still
worth mentioning that lighting should be low wattage where possible,
some old dimmer switches are not compatible with low energy
lighting, especially the fluorescent types and some of the original
type LEDs, they are however compatible with some of the newer LEDs, check out what is available
before spending any money! All electrical
equipment should also be as efficient as possible, look for A rated
models - especially fridge/freezers as they are one of the biggest
drains on your renewable power, as they operate (on & off) 24hrs a
day!
Having done a survey of your
electrical items to weed out the greedy ones, we now have to
consider what power requirements you will need to run your home.
Most off grid systems will be battery based, using the renewable
sources to keep them charged and an advanced inverter/charger to
supply the power you need. It may also be necessary to consider
having a diesel generator as a backup for battery charging/supply if
required, this can be automatically controlled by the inverter and
also in the event of having something like a borehole pump that
requires a lot of power on a regular basis, you can set the inverter
to start and stop the generator on a suitable timetable.
A “normal” small household will use approx 8-15kWh per day, we would expect an off grid system to
survive on approx 3 to 5kWh per day if you are being frugal, this includes fridge freezer,
TV, lights, computer etc. When looking at the size of the battery
bank, we would expect it to give you a minimum 2-3 days power from
the battery bank alone without any input.
Batteries
We normally recommend using Rolls
Deep Cycle Batteries as these are industrial quality (made in
Canada) batteries that have been around for a long time and have a
good reputation, although if you are looking to save some money it
would be worth considering ex fork lift truck batteries if you can
find them, check out any fork lift servicing companies in your area…
Batteries come in a variety of voltages and amp hours (AH).
The amp hours (usually measured over a 20 hr discharge called “c20”)
give you the storage capacity of the battery at its voltage. The
common voltages are 2v, 4v, 6v and 12v, you use a combination of
these to arrive at the bank voltage and AH you require*. We would
normally recommend a minimum of 400AH @ 48V (8 x 6v/400 AH
batteries) giving a bank of 19.2kW, of which we usually allow 50%
discharge giving 9.6kW available, which would give you just over 3
days supply at 3kWh per day.
* When working
out Amp Hours (AH) for battery banks, if you have a single battery
(let’s say a 12v one) that is rated at 100AH, then if you have 4 of
these in series to make 48v, you will have a bank of 100AH at 48v.
But if you had 4 in parallel at 12v, you will then have a bank of
400AH at 12v. If you multiply the volts by the amps, you will notice
they provide the same amount of power i.e. 4.8kW, although not all
of this is available, as you must never completely drain your
batteries.
Renewable Sources
In order to keep your batteries
in fine fettle they will need charging at a rate that exceeds the
power that you draw from them, this can be accomplished from a
number of different renewable sources, three of the main ones being
Wind, Solar and Hydro generation. Two of the three sources are
usually readily available, Wind and Solar. In the above example of a
48v/400 AH battery bank we would suggest having at least a 1kW Wind
Turbine and a 2kW Solar Array in order to give
you a belt and braces approach to your power supply, if the sun
isn’t shining, the wind is usually blowing! (although you can
survive on solar or wind only if the other is not suitable, just
make sure you have enough production capacity to cover your needs).
In this instance you should get enough power from the Wind Turbine
and the Solar Array to keep your battery bank fully charged.
Obviously there will be times when due to our delightful and
unpredictable weather the batteries may be a little short changed,
but that is when you find out why you bought that generator, however
you may find you hardly need your generator, but it is an emergency
standby, should it be necessary. It is also worth
mentioning that having a generator allows you to maintain your
battery bank in top form by allowing the charge routine to be run in
equalization mode (a special high voltage charge) periodically which
helps keep the cells de-sulphated (the build up of lead sulphate on
the battery plates will reduce the efficiency and eventually kill
your battery).
Solar Panels are very reliable,
require very little maintenance and are getting cheaper year on
year! (Under £800 per Kilowatt) They are best mounted on South
facing roofs (north if in southern hemisphere) using a special roof
mounting kit, an average 250w panel weighs around 20kg each, so bear
that in mind when deciding where to put your panels. Panels can also
be sited on frames on the ground which can be beneficial as it would
allow you to change the pitch angle of the panel to suit the time of
year, but you may run into planning problems with ground mounting,
check with your local authority.
Wind Turbines obviously need to
be in an area that is not surrounded by trees and buildings,
preferably with a clear view to the south west (or your prevailing
wind direction), they do better on a rising hill which tends to
accelerate the airflow as it approaches the turbine. We do not
recommend mounting turbines on domestic houses as the gable ends of
UK houses are notoriously weak and they would also transmit any
noise or vibration into the living accommodation (we generally
discourage people from mounting them on any building because of the
turbulence caused by the airflow over the building) . One of the
simplest and cheapest mounts for the smaller turbines (1kW) is a
guyed scaffold pole (these do not generally need planning permission
as they are considered as temporary structures, but if in doubt
check it out!) At the moment the cost of (small) Wind Power per watt
is pretty well level with Solar Power, however as Solar
manufacturing technology and quantities improve due to the demand
for them, then Solar will become cheaper. The main advantage of wind
is that it blows at night as well as during the day, so has a
distinct advantage over solar in that regard.
Hydro Power is one of the best
sources of renewable energy if you have it available on your land.
One of its best properties is that it is usually fairly predictable
and you usually have more of it in the winter when you need the
power. If you have a stream on your property and the difference in
height (head) between the highest and lowest sections of your stream
is more than 10ft then you may have a chance of generation, although
with such a small head you usually need a high flow rate. It is
worth noting that Hydro will produce between 10 and 100 times more
power than PV or wind for the same capital investment - if your
water source is good, it runs 24 hours a day, 7 days a week,
providing lots of off-grid energy for as long as the water flows…..
Inverters
Inverters come in a variety of
sizes and usually two types, the cheapest are usually modified sine
wave, which will run most items but may cause problems with washing
machine motors or microwave ovens depending on the quality of the
waveform. The best inverters to use are the pure sine wave type
which will give you a wave form as good if not better than a
standard grid supply. They do tend to be more expensive but are
usually programmable and also parallelable meaning you can add
modules for increased power capacity and to even use 3 to give you 3
phase power (one inverter becomes the master, the others are the
slaves). They come as either inverter
only or inverter/chargers, we find the addition of the charger to be
very useful in an off grid situation as it allows you to have a
generator as a backup if required, which can be autonomously
controlled by the inverter. To judge what size of inverter you need,
look at what your maximum power demand at any one time is likely to
be, we usually recommend a minimum of 3kW to allow for washing
machines, however a 5kW would give you a little extra should you
ever require it. Most of the inverters we recommend allow you to
combine the power of the inverter with the generator to give almost
double the power of the inverter alone for occasional high demand
situations (the inverter will automatically start the generator to
add its power to its own). The modern inverter is very efficient
usually in the region 95% and will automatically go into standby if
no power is required. I would just mention that all the inverters we
recommend are from Europe or the US (Victron, Studer, SMA and
Outback).
Feed in Tariff
(in the UK) can be available to you even though you are off grid, as
it pays for any power that you produce whether connected to the grid
or not and also whether you use it or not! However it is a bit of a
minefield as all the items have to be MCS (Microgeneration
Certification Scheme) accredited, many of the small turbines
(wind/hydro) are not accredited due to the accreditation fee of
around £80,000 per model required…… This is just not a viable
proposition for the smaller turbine manufacturers as to recoup that
amount would price them out of the market. However a solar
installation would usually qualify as long as it is installed by an
MCS accredited installer, You would need to get advice on this as
there are a number of “wrinkles” that you need to be aware of.
Generators
Generators come in all shapes and
sizes, a basic rule of thumb is that they should be at least the
same capacity as your inverter or able to supply your maximum demand
at any one time, they should preferably be Diesel
(bio-fuel/red diesel) or BioGas and run at no more than 1500rpm, and as quiet
as possible! One other point is that water cooled are usually
quieter and you may be able to harvest the heat from the generator
to supply your property.
Hope this helps those of you
considering dipping your toes into the OFF-GRID renewable energy
world, feel free to email/call if you need any further advice.
