ALBIE'S ALTERNATIVE ENERGY SEMINAR
22 April 2007
These are the notes which were handed out at the seminar - hopefully
they will be useful for other people as well.
I've changed names of some people - just in case they'd rather not have
their names mentioned on the internet.
PART 1: PLACES WE VISITED
1. Fill and Albie's farm, Kotinga
Hydro – very small, uses a GE washing machine motor
as a generator
Power: 25 Watts (for 24 hrs
Energy produced: 0.6 kWh
per day (0.025kW x 24hrs)
Storage in 24 Volt lead acid
battery bank (2 x 12V batteries)
24V Lighting in house direct from
battery – 6 x 20Watt reading lights
Solar Water Heating – large, home-made, low
efficiency but high effectiveness.
Power: 5 kW to 8 kW (for 3 hrs
winter, 5 hrs summer)
Energy produced: 15kWh (5kW
x 3hrs) to 40kWh (8kW x 5hrs) per day
Solar Oven – 1.5 sq.m. of glass area
Power: 1kW (for 5
hours per day)
Energy produced: 5 kWh per day –
enough to roast a leg of lamb!
2. B.W. , Kotinga
Hydro – uses a Fisher & Paykel Smartdrive
washing machine motor,
Power: 250 Watts maximum, 150
Watts average (for 24 hrs)
Energy produced: 3.5 kWh
per day (0.150kW x 24hrs)
Storage in 48 Volt lead acid
230V for home use from a 3.5kW
3. B. M., Onekaka
Solar Water panels – SolarPeak technology glass tube
Each glass tube produces 80 Watts power
Power: 80 x 24 tubes = 2 kW (for
6 hrs in Summer, 4 hrs in Winter)
Energy produced: (summer) 12 kWh
per day (2kW x 6hrs)
Energy produced: (winter) 8 kWh
per day (2kW x 4hrs)
4. A.M., Onekaka
Hydo – uses a very small amount of water because of
a high head!
Power: 140 watts Winter, 80 watts
Summer (for 24 hrs per day)
Energy produced: 3.3 kWh per day
(Winter) 1.9 kWh per day (Summer)
Storage in 24V lead acid battery
230V for home use from a 1.8 kW
PV Electric Solar Panels – Total 260 Watts
Actual Power: 9 Amps at 24V = 216
Watts (for 5 hours per day)
Energy produced: (0.216 x 5) =
1.08 kWh per day
(Charges up the same battery bank
as the hydro system above)
Solar Shower – Black painted copper tank on roof.
Provides 2 or 3 warm showers in
the afternoon, after a day of sun.
PART 2: WHAT IS POWER? WHAT IS ENERGY?
Power is defined as: the “Rate of consumption of Energy”, which
is a little confusing...
I like to think of it as: the “Ability to do Work” (where Work is
the same as Energy consumption), or as: the amount of “Muscle” in
the machine or the appliance...
(The more “Muscle” the appliance has, the faster it uses up energy)
We'll measure POWER in KiloWatts (kW)
Energy consumed is the application of POWER for a certain TIME
Therefore, Energy = Power x Time - remember this formula! We'll
use it often.
We'll measure ENERGY in KiloWattHours (kWh). i.e. kW x Hrs
(This is the same “unit” the electricity companies use when they charge
you for the electrical energy you consume.)
A 1-bar electric heater has a Power rating of 1 kW.
If you use it for 3 hours in a day, you'll consume 1 x 3 = 3 kWh of
Let's say you use the 1kW heater ALL DAY (24 hours) because it's cold.
The 1-bar heater has a Power of 1 kW, used for a Time of 24 hours:
Energy = Power x Time = 1 x 24 = 24
(At 20c per kWh, you would pay $4.80 per day for this energy)
An electric jug (used to make four cups of coffee each day)
The Jug has a Power of 2.4 kW, used for 8 minutes each day: (that's
0.13 of an hour)
Energy = Power x Time = 2.4 x 0.13 = 0.312 kWh
(At 20c per kWh, that's 12c per day for this energy)
So, an electric heater left on all day consumes MUCH more energy per
day than the jug! (nearly 100 times as much, in fact – so you
could make nearly 400 cups of coffee for the same energy cost!)
How about electric lights?
A 100 Watt light bulb, left ON for a time of 24 hours – let's work out
100 Watts is a Power of 0.100 kW (1000 Watts = 1 kW, remember?)
Energy = Power x Time = 0.100 x 24 = 2.4
kWh per day
(That's 48c per day, or 4 times as much as 4 cups of coffee per
day!) But still only 1/10 of the cost of the heater.
A fridge or freezer is similar to a light-bulb, around 100 Watts.
But they cycle on and off with a 50% “duty cycle” approximately.
This means they are ON for only half the time on average. So a
fridge uses around 1.2 kWh per day = $0.24 ($7.20 per month)
1-Bar electric heater for 24 hours: 24kWh per
day $4.80 ($144 per month)
Electric Jug for 4 cups of coffee: 0.312kWh
per day $0.12 ($3.60 per month)
100 Watt light bulb for 24 hours:
2.4kWh per day $0.48 ($14.40 per mth)
Fridge or freezer:
1.2kWh per day $0.24 ($7.20
PART 3: HOW MUCH DO WE NEED FOR OUR HOME?
The average household electricity bill can be divided into four main
1. Availability charge (line charge) about $40 per month (not related
to energy use)
2. Hot water heating – about 5 to 10 kWh per day
3. Space heating (heaters, heat pumps, etc) – about 0 to 30 kWh per day
(0 in summer, 30 in winter)
4. Everything else (lights, stove, computer, fridge/freezer, etc) – 5
to 10 kWh per day
Item 3, Space heating, is by far the highest use, about $0 to $180 per
month. It is also the most variable – from $0 in summer to as
high as $180 per month in winter.
Item 2, Hot water heating, is the next most expensive single item at
$30 to $60 per month
Item 4, Everything else, also costs around $30 to $60 per month.
How can we reduce these costs using alternative energy sources?
Item 1, Availability charge – can't be reduced, except by going
completely “off grid”.
Item 2, Hot water heating, can be completely eliminated (Albie's
example) fairly cheaply.
Item 3, Space heating, can be reduced by burning wood in a
well-designed firebox, by insulating your home, by using heat pumps
instead of electric heaters, and by simple tricks like moving hot air
from the roof-space into the house (J. S.'s example).
Item 4, Everything else, can be reduced by using Hydro generation (most
effective and cheapest method), or Photovoltaic Panels (very expensive
and not practical if grid power available)
Or you can choose to go completely “off grid” - but you really need a
good hydro source to do this, unless you're prepared to change your
The average all-electric home (what's “average” anyway?) needs about 10
to 20 kWh per day in summer (that's $60 to $120 per month in summer),
or 40 to 50 kWh per day in winter (that's $240 to $300 per month in
winter) – PLUS the $40 availability charge.
Installing a solar hot water system providing 15 kWh per day in winter
(much more in summer) can save $30 to $60 per month, for a cost of
around $1000 (Albie's DIY system) or $4000 (a commercial system)
The payback period can be calculated easily – between 2 years (Albie)
and 8 years (commercial).
Installing a hydro system providing 5 to 10 kWh (for “Item 4” above)
per day can save $30 to $60 per month, for a cost of around $3000 to
$6000 (generator, piping, batteries, inverter, etc) The payback
period is between 5 and 10 years. But this assumes you have a
constant, reliable water source for the hydro system.
Installing a Photovoltaic system providing 5 to 10 kWh per day (as
above) can also save $30 to $60 per month, but this will require about
twenty x 100 Watt panels at $1000 each to do the job, as well as a
fairly large battery bank – another couple of thousand dollars.
The payback period for a capital outlay of over $20,000 would be around
PART 4: CALCULATING POWER AND ENERGY FOR ALTERNATIVE SYSTEMS
A: SOLAR HOT WATER SYSTEMS
The Sun shines with an average power of 1 kW per square meter on the
This is for an average NZ Summer's day, between 10am and 3pm, i.e. for
(For Winter, you can work on 0.7 kW per square meter for 3 hours)
This means that if you can collect it with a 100% efficiency,
each square meter can produce 1kW x 5 hrs = 5kWh of energy
per day in Summer, and 0.7kW x 3 hrs = 2.1kWh of energy per day in
Winter. (Remember, Power x Time = Energy)
A 4-person family requires about 10kWh of hot water heating per
day. This can be provided by a 2 sq.m. solar panel in Summer, or
by a 5 sq.m. panel in Winter. (This assumes that the panel is 100%
efficient! - which is impossible!) This is why, when purchasing a
solar hot water panel, you need to know how big it is, and how much
energy it will produce per day – or you may find yourself disappointed
with the performance...
Calculating the Power - “Single-Pass” solar hot water systems:
You need to know the Flow of water through the panel in Litres per
Hour, and the Rise in Temperature from the inlet to the outlet
end. The Power is then calculated by this formula: Power =
Flow x TempRise / 857 (The answer comes out in kW)
Calculating the Power - “Recirculating” systems: (both passive and
This is more difficult, because you can't empty the storage tank
easily... but you need to know the Volume of water in the storage
tank, and the Rise in Temperature of that water over, say, a Time of 6
hours in the middle of the day. Here's a method which I haven't
actually tried – but I believe it makes sense...
1. Early in the morning, cover up the solar panel (e.g. with a sheet of
plywood.) and turn off any electric booster.
2. Run off the entire volume of the tank (e.g. 150 litres) from the hot
tap to waste.
3. Measure the temperature of the (now cold) water in the hot tap.
4. Uncover the solar panel from 10am to 4pm (6 hours of heating).
5. Run off the 150 litres of (now hot) water into a larger container
6. Stir, and measure the temperature again. Calculate the Rise in
Calculate the Power of the solar panel: Power = Volume / Time x
TempRise / 857
(Please note that this will be an underestimation, because of the
partial mixing of incoming cold water with the hot water when you drain
the tank at 4pm... but that's what happens anyway when you're using the
system normally, so the slight underestimate is probably ok.)
B: MICROHYDRO SYSTEMS
You need to know the JetPressure (dynamic, i.e. with the jet running,
in kiloPascals) and the JetFlow (in Litres per Second) This
formula gives the Power (in Watts) available at the Jet:
JetPower = JetPressure x JetFlow
The Actual Electrical power (in Watts) available to charge your
batteries is calculated by:
ElecPower = Volts x Amps (Measured at the batteries, when they
are not fully charged, of course)
The Energy provided by the system is Energy = ElecPower x
24 (it runs 24 hrs a day)
(This gives energy in Watt-Hours per day. You need to divide by
1000 to get kWh per day)
The dynamic efficiency of the system is the actual electrical power
produced, divided by the power available at the jet
Efficiency = JetPower / ElecPower
C: PHOTOVOLTAIC SOLAR PANELS
The manufacturers give specifications e.g. 85 Watts, for each
panel. This would be under ideal conditions, full sunlight, flat
batteries, etc. The actual power produced (in Watts) is
calculated as: ElecPower = Volts x Amps (measured at the
batteries, with the batteries NOT fully charged - i.e. they are taking
everything the panels can throw at them)
We can take 5 hours in Summer and 3 hours in Winter as a rule of thumb
for energy production: Energy = ElecPower x Time
(This comes out in Watt-hours. Divide by 1000 to get kWh.)
So, using A. M.'s setup as an example:
ElecPower = 24 Volts x 9 Amps = 216 Watts (measured with the batteries
about half charged)
In Summer (5 Hrs), this gives Energy = 216 x 5 = 1080 Watt-Hours (1.08
kWh per day)
In Winter (3 Hrs), this gives Energy = 216 x 3 = 648 Watt-Hours (0.648
kWh per day)
Their Hydro system provides 3.3 kWh per day in winter, and 1.9 kWh per
day in summer
The hydro produces more in winter, less in summer, and vice versa for
the PV panels. This makes for a good combination! But they
still have only about 3 or 4 kWh per day to work with. The key
for going “off grid” is not to try and generate enough energy to supply
all your “on grid” requirements, but rather to adjust your requirements
to suit the energy available...
I hope these notes can act as a reference for you when you're thinking
about installing or building your own alternative energy system.
WORKSHEET 1: VITAL STATISTICS OF A MICROHYDRO SYSTEM
Definitions and Formulae:
Powerjet = power at the jet, based on jet Flow and jet Pressure with
Powerjet = Jetflow x Pressure
Poweract = actual electrical power available to charge batteries etc.
Poweract = Volts x Amps
Energy generated per day = Power x 24hrs (a hydro system works
for 24 hrs per day!)
Energy generated is measured in WH (WattHours) or kWH (kiloWattHours)
Jetflow is in litres/second
Pressure is in kiloPascals
Power is in Watts (or kiloWatts, where 1 kW =
Example: Albie and Fill's minimicrohydro system.
Jetpressure (with valve open) 100 kPa
Jetflow 1 litre per sec
Charging Current 0.9 Amps
Battery Voltage 28 Volts
Powerjet (= Jetpressure x Jetflow) 100 x 1 = 100
Poweract (= Volts x Amps) 28 x 0.9 = 25.2
Efficiency (= Poweract / Powerjet) 25.2 / 100 =
0.252 (or 25.2%)
Energy generated per day (Poweract x 24) 25.2 x 24 =
605 WattHours (or 0.605 kWh)
Energy generated per year, at 20c per kWh “unit”
0.605 x 365 x 0.20 = $44.17
WORKSHEET 2: VITAL STATISTICS OF A SOLAR HOT WATER SYSTEM
Definitions and Formulae:
Powersun = Sun's radiation on the surface of the earth at midday
Powersun = 1 kW per square metre of surface area exposed to the sun
Powersun = 0.7kW per square metre of surface area exposed to the sun
Poweract = Actual power absorbed into water, determined by measuring a
rise in temperature of the water flowing at a certain number of litres
per hour through the panel.
Poweract = Flow x Temprise / 857
Energy generated per day = Poweract x no. of hours of full sunlight
Energy generated per day = Poweract x 5 (summer) or Poweract x 3
Example: Fill and Albie's maxi-solar hot water panel
Area of panel in Square Metres 30 Sq m
Powersun (summer = area x 1) 30kW (summer)
(winter = area x 0.7) 21 kW (winter)
Flow in Litres per Minute 2.5 litres per
Flow in Litres per Hour (L/min x 60) 2.5 x 60 = 150
litres per hr
Water inlet temperature 18 degrees C.
Water outlet temperature 60 degrees C.
Temprise (outlet temp – inlet temp) 60 – 18 = 42
Poweract (= Flow x Temprise / 857) 150 x 42 / 857 =
Efficiency (= Poweract / Powersun) 7.4 / 30 =
0.25 (or 25%)
Energy generated per day in summer (= Poweract x 5 hrs)
7.4 x 5 = 37 kWh (“units”)
Value of energy generated each summer at 20c per kWh, for 180
days 37 x 180 x 0.20 = $1332.00
($1332? REALLY???? - Ah, but remember that the energy Generated
isn't necessarily the energy Saved - otherwise the payback period would
be less than 6 months for this system!)
WORKSHEET 3: VITAL STATISTICS OF A PHOTOVOLTAIC SOLAR PANEL
PV panels have a “Power Rating”, e.g. You can buy a 75Watt or a 120Watt
Usually this rating refers to the “Full Sunlight” condition in
midsummer. You can expect less than the rated power in winter and
at times much earlier or later than midday.
Powersun = 1 kW per square metre (summer)
Powersun = 0.7kW per square metre (winter)
Powerrating = Stated power of the panel, by the manufacturers (in Watts)
Poweract = Power actually delivered by the panel at any particular time
Poweract = Volts x Amps
Energy generated per day = Poweract x hours of full sunlight
Energy generated per day = Poweract x 5 (summer) or Poweract x 3
Example: Four x 80Watt panels, delivering 10 Amps into a 24Volt
battery bank (NOT fully charged)
Total Area of panels in Square Metres 4 panels, each
1m x 0.6m = 4 x 1 x 0.6 = 2.4 sq metres
Powersun (summer = area x 1) 2.4 x 1 =
2.4 kW (or 2400 Watts)
(winter = area x 0.7) 2.4 x 0.7 = 1.7 kW (1700
Powerrating (total for all panels) 4 x 80 = 320
Poweract (= Volts x Amps) 24V x 10 A = 240
Efficiency (= Poweract / Powersun) 240 / 2400 = 0.10
Energy generated per day in summer (= Poweract x 5)
240 x 5 = 1200 WattHours (Or 1.2 kWh “units” per day)
Value of energy generated each summer at 20c per kWh, for 185
days 1.2 x 185 x 0.20 = $44.40
Here are descriptions of a couple of really good ideas from two of the
IDEA NO. 1 - SOLAR HOT WATER (Stolen from L. R., Awaroa)
Throw 100m of 15mm black polyethylene pipe onto a flat, black butyl
Fill the pipe with water from the garden hose, then let it lie there on
the roof, for 20 minutes in the sun.
Fit a shower rose to the other end of the black pipe, turn on the
garden hose, and ...
You've got a 1 minute hot shower! (10 litres of piping hot water
(pardon the pun) because 100m of 15mm pipe holds 10 litres of water.)
Slight modification (because the water is usually too hot!)
Connect a cold water line with a tap between the garden hose and the
shower head, to let in some cold water so you don't burn yourself...
There are 2 disadvantages:
1. There's just enough time to get yourself soaped before you run out
of hot water and have to wait another 20 minutes before you can rinse
2. This only works while the sun is actually shining. There's no
storage of hot water.
There is one advantage:
1. It's simple.
IDEA NO. 2 - HOT AIR (Stolen from J. S., Waitapu Road)
J was doing some plumbing up in his roof space, one cold, sunny winter
afternoon. He came down in a bath of sweat, because it was so HOT
up there! (And the house down below was COLD!) So he
Install a duct pipe from the top of the roof space (where it's hottest)
down into the lounge.
Put a duct fan into the pipe, and use it in the cold winter afternoons
to blow the hot air down from the roof space into the lounge.
So that you don't have to remember to turn the fan on and off, install
a thermostatic control system as follows:
Thermostat no 1: In the roof space, near the inlet of the
duct. Set to turn ON when the temperature goes ABOVE 25 degrees
C. (You'll need one of those air-conditioning thermostats, which
work the other way round from a normal one)
Thermostat no 2: In the lounge. Set to turn ON when the
temperature goes BELOW 20 degrees C. (This is a normal type of
wall thermostat for heating)
Now comes the clever bit...
Connect the two thermostats in SERIES, so that the fan only comes on
when BOTH of the thermostats are ON at the same time! The fan
goes OFF when either thermostat is off.
This means that the fan will only turn ON when the temperature in the
roof is high enough to do some useful work, and the temperature in the
lounge is low enough to need warming up.
Ok, that's it. Hope you get some good ideas from this offering.