P W HAPGOOD

Radiant Energy Systems
2nd November 2004
 
 

System Outline

The system proposed consists of an array of 6 to 10, 160 watt solar modules mounted on the North facing roof of your house or shed; working in with a diesel or petrol generator.
The majority of the energy requirements of the dwelling is provided from solar modules but during the months of April to October the petrol/diesel generator will be run at least weekly to keep the batteries fully charged.
The system can provide approx. 2 -7 kwatt hrs of energy per day during summer.  If more energy is required, the generator will need to run for longer periods of time.

The system proposed is a trade-off between system cost and generator run time.

It is normal practise to have a back-up generator to ensure that the batteries never get below 50% discharged to ensure extended battery life.
It is also useful to have another source of 240v power in case the inverter/battery system should fail or require servicing.

System Components

Load Profile
The design of your system is normally based on your actual energy requirements and is the only basis on which a quotation can be made.  I will base this proposal on an imaginary load figure of 3kWhr/day
The average load for a house in the city running modern appliances is approx. 10kWhrs/day.  If you are running a remote system, expect to trim that back to between 1-4 kWhrs/day through running energy efficient lighting, 24v fridges, gas or wood stove cooking, solar water heating and keeping all heating type loads on the system to a bare minimum.

Solar Modules
BP Solar 160 watt modules have been selected as they are made from the highest quality materials and come with a 25 year warranty. Other brands are also available

Mounting
The modules are mounted on a North facing roof.  They are attached to a 50 x 50 x 3mm galvanised steel angle frame which is bolted to the roof battens.  A strip of PVC between the steel roof and the angle steel prevents corrosion.

Array Inclination
The array can be set at a fixed angle to the horizontal, 55 degrees is recommended to allow for maximum solar input during winter and 25 degrees for summer.  However, for practical purposes your roof angle may dictate the array angle.  Alternatively, and in order to optimise performance, provision can be made for simple seasonal adjustment of module angle.

Solar Regulator
A Plasmatronics regulator is used to control the charging current to prevent the batteries from being overcharged.  A PL40 type is used for up to 7 modules and a PL60 for 10, 160 watt modules.
It has a three-stage controller that ensures the highest state of battery charge.
Built-in sensing allows a higher battery voltage to be obtained for 2 monthly battery equalising,  i.e. a higher charging voltage.  The unit comes with a 24 month warranty.
This unit also forms the basis for system monitoring. (see later section)

Battery Bank
A system voltage of 24 volts (12 x 2volt cells) is normally chosen to reduce inverter input current and therefore system power loss.
The BP Solar PVstor batteries chosen for this system are specially designed for solar systems.  Their main features are:
• long life and low maintenance
• high charging efficiency
• deep cycling capacity - 7500 cycles to 10% discharge
• large electrolyte reserve.
The BP Solar PVstor batteries are regarded as the best solar battery on the market and have a lifetime of at least 15 years if properly cared for.
A 4-day energy reserve is designed into the battery bank to allow for cloudy days and low solar output during winter.
The battery bank capacity has been sized for a maximum discharge of 50% to ensure longer battery life.  These cells have a 5-year, full replacement warranty.
Other battery brands are Raylite, GNB Energystore and Century Yausu.
Sealed Gel batteries made by Sonnenschein are virtually maintenance free and, at the moment, are a similar price to a set of 785 Ahr BP pvstor.

Battery Shed
A separate area in a corner of a workshop or equipment shed can be used to accommodate the battery bank, control panel, inverter and diesel generator.  The batteries are mounted on wooden steps made from 30mm x 100 planks to support the rather heavy battery load.  This set-up raises the batteries off the concrete floor to prevent them from becoming too cold in winter.  We can supply suitable layout plans.
Battery ventilation
*Warning – Explosive Gases*
The battery storage area is vented to outside air to ensure that hydrogen vapours given off during charging, do not build up to explosive levels.  Two vents of minimum 240 x 240 mm are used in the outside walls to provide an adequate airflow.

Diesel Generator
The back-up power source comes from the 240 v AC electric start generator.  A diesel type is recommended because of the longer service life and less maintenance required compared to a petrol generator.  The diesel is not as noisy and does not produce any radio frequency interference.  Petrol generators are cheaper to buy initially but are more expensive to run.
While the generator is running, jobs requiring larger power such as ironing, vacuum cleaning, washing and welding can be done.
The generator can be started either manually from the generator room or via a inverter or system monitor that senses low battery voltage and automatically trips the starting circuit.  The inverter can be programmed to not start the generator during any pre-set night-time period so as not to annoy the neighbours!!
Generator Room
A partitioned area next to the battery area is set-aside for the diesel generator.  The room must be well ventilated to outside but also sealed from the neighbouring battery area and workshop or storage area.

Battery Charger
A 240-volt AC to 24volt DC battery charger allows the batteries to be charged while the generator is running.  A 24v, 80A model has been recommended.  The charging voltage and therefore current is adjustable.
This unit is wired so that as soon as the generator is started, the charger begins to charge the battery bank.  The unit has a 12 month warranty.

Automatic Changeover Relay for 240 v circuits
As soon as the generator is started, a circuit automatically senses generator voltage and disconnects the inverter output after a pre-set delay of around 60 secs to allow for generator warm-up.  It then connects the generator to the house circuits and allows battery charging if the charger is turned on.

Sine Wave Inverter
The inverter is the heart of the system.  The inverter transforms 24 volt DC from the battery bank to 240 volt AC for the house circuits.  A number of good quality, Australian made sine wave inverters can be chosen from to run most household appliances including microwaves, mixers, pumps, and power tools except high wattage heating appliances.
The most popular ones are:, Selectronics 2.4 kwatt & 1.7 kwatt, SEA 2.2 kwatt & 1.7kw and a ranger of inverter-chargers. Trace 2.5 kwatt inverter/charger.
Features
All inverters have built in high and low voltage, short circuit, reverse polarity and over-temperature protection.
The inverters have a 2 (SEA) or 5yr (Selectronics) warranty if the unit is installed according to the manufacturer's requirements.

System Monitoring
The Plasmatronics PL40/60 solar charge controller has a digital display that monitors battery voltage, charge current (both solar and charger), load current (dc loads and inverter loads separately), as well as the energy used (Ahr OUT) and the energy put into the battery bank (Ahr IN).
The regulator logs daily max battery voltage, minimum battery voltage, total Ahr IN, total Ahr OUT, % state of charge (SOC) and float time (if reached) each day for 30 days.  This information can be useful in determining if the state of charge of the battery bank is being kept high enough to ensure optimum battery life.

Electric Fridges
Refrigerators use a large amount of energy to cool and freeze food and drink.
Most people that are “off-grid” have in the past, generally chosen a gas fridge.  Recently, very efficient fridges have been produced which use a “Danfoss” sealed compressor type cooling system run by a 24v DC electric motor.
Below are cost saving calculations which demonstrate that in about 4 years of use, the savings will completely cover the purchase cost of the 3 solar modules required to run the fridge and the extra battery capacity required.
Over a 15yr period, the savings can easily amount to the replacement cost of a new set of batteries for the whole system as well.  Thus keeping down the running costs of the total system to very low values.

Advantages of the 24v dc electric fridge compared with a gas fridge
• Keeps food colder and freezes better during high ambient temperatures in summer.
• The higher summer energy needs are matched with the excess solar energy available.
• Produces far less green house emissions than a gas fridge.
• Purchase price of 300 litre fridge cheaper than a similar sized gas fridge by $275.
• More convenient - Reduced changing of gas bottles.

Cost savings using a 24v electric fridge
Gas fridge running costs
Assume 1, 45kg bottle of gas per 3 months for 320 litre gas fridge $82
Total yearly gas cost will be    $368

Extra equipment costs for electric fridge
1.5 x 160 watt modules
Cost of modules @ $1600 ea but with rebate, cost is 60%                                         $2100

Cost of extra battery capacity $520
Reduced purchase price of 310 litre electric fridge  - $275

  Total extra cost   $1520

Approximate Cost of System Items
 
 

Solar modules 6 x 160w	10200	Solar modules 20 x 80w	15000
Array frames x 2	600	Adjustable Array frames x 4	900
Batteries BP Pvstor 785Ah, 24v	6336	Batteries 1100Ah, 24v	7656
Batteries Sonnenschein 600Ahr 24V	6100
SEA Inverter 1.7kw sine wave	2450	SEA Inverter 2.2kw sine wave	3100
PL40 Solar controller	440	PL60 Solar controller	690
System monitoring	224
Pre-wired control panel	520          with fusing, switching & metering
Battery charger 24/80A	1250
Electrical wiring/install	950          (variable depending on system)

The equipment can be altered according to system design and the ratio of solar to diesel power generated.  Various equipment items can be selected on cost alone.

System Manual
A system manual is provided which contains system description, block diagram, wiring diagram, maintenance schedule, System Serial Nos., battery safety guide & equipment manuals.

System Warranty
The system wiring and fitting is warranted for a period of 2 years from completion of installation.
The quoted price also includes a site visit 4 weeks after installation to check on satisfactory battery and system operation.
Normal equipment warranty (as specified) applies to individual system components.

Stage payments
To begin the job, a first stage payment of 40% is due before equipment is ordered.  The balance (60%) is due upon completion of the installation.
 

Load Summary Worksheet

Date:
 
 

Area	Wattage	Hours of use	watts x hrs of use
Bedrooms
Bedroom 1
lights
Bedroom 2
Lights
Bedroom3
lights
Kitchen
Radio
Foodmixwe
Microwave oven
Lights
Lounge
stereo
lights
television
video recorder/DVD
Other
vacuum cleaner
Computer
sewing m/c
exhaust fans
electric tools
washing machine

 DC Loads
 

 Total energy   kWH/day
 
 

 Home Page | About Radiant | Products |Contact Radiant| Index this page|