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.


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 per day)
        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 battery bank
        230V for home use from a 3.5kW inverter

3. B. M., Onekaka
    Solar Water panels – SolarPeak technology glass tube system
    Each glass tube produces 80 Watts power (manufacturer specs),
        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 bank
        230V for home use from a 1.8 kW inverter
    PV Electric Solar Panels – Total 260 Watts (manufacturer specs)
        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.


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.)

Example 1:
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 energy.

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 kWh
(At 20c per kWh, you would pay $4.80 per day for this energy)

Example 2:  
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!)

Example 3:
How about electric lights?
A 100 Watt light bulb, left ON for a time of 24 hours – let's work out the Energy:
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.

Example 4:
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 per month)


The average household electricity bill can be divided into four main components:
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 lifestyle considerably!

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 40 years!



The Sun shines with an average power of 1 kW per square meter on the earth's surface.
This is for an average NZ Summer's day, between 10am and 3pm, i.e. for 5 hours.
(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 pumped)
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 (e.g. Bath)
6. Stir, and measure the temperature again.  Calculate the Rise in Temperature.

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.)


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


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.

Good Luck!


Definitions and Formulae:

Powerjet = power at the jet, based on jet Flow and jet Pressure with valve open
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 = 1000 W)

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 Watts    
Poweract (= Volts x Amps)    28 x 0.9 = 25.2 Watts    
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     


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 (summer)
Powersun = 0.7kW per square metre of surface area exposed to the sun (winter)

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 (winter)

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 min    
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 degrees    
Poweract (= Flow x Temprise / 857)    150 x 42 / 857 = 7.4 kW    
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!)    


PV panels have a “Power Rating”, e.g. You can buy a 75Watt or a 120Watt panel, etc.
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 (in Watts)
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 (winter)

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 Watts)
Powerrating (total for all panels)    4 x 80 = 320 Watts    
Poweract (= Volts x Amps)    24V x 10 A = 240 Watts    
Efficiency (= Poweract / Powersun)    240 / 2400 = 0.10 (or 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 course participants:

IDEA NO. 1 - SOLAR HOT WATER  (Stolen from L. R., Awaroa)

Throw 100m of 15mm black polyethylene pipe onto a flat, black butyl roof.  
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 off.
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.
Happy Person

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 started thinking....

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.

It Worked!

Slight modification:
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.

Hot Air from Roof

Ok, that's it.  Hope you get some good ideas from this offering.