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Friday, 19 December 2014



This report is to design a power supply system for an autonomous house by combining renewable energy device and auxiliary electricity generator. Before the work of designing, an economic evaluation for different types of system are provided, in order to convince client that proper designed power supply system will cost less on energy consumption. Later, the system design is based on the type of lowest cost evaluated previously, and begins with energy consumption estimation. 

In order to design a suitable power supply system for client, the household electricity consumption and hot water requirement will be firstly estimated, and the consumption will be minimized to enhance the energy usage efficiency by reducing the using hour, which can help to determine the minimum energy that the power supply system needs to generate. The power supply system will be designed according to the energy consumption estimation, which consists of inverter, AC petrol generator, battery bank, battery charger, PV panels. 

This post also provides a plan to optimize the system, for elongating life of component, enhance system efficiency and hot water supplying. Finally, the analysis and calculations for the power supply system designing will be provided in appendices. Also, a catalog of appliances is attached at the end of the post. 

Power Supply System Options

This chapter is to approximately evaluate the cost of different power supply system. Assuming that the daily electric consumption is 4.5 kWh, what type of system has the lowest cost on energy consumption for 25 years life cycle? 

This post provide client with three practical options, and evaluate them in initial investment cost and cost on every kWh of electric energy by assuming house daily electric energy of 4.5 kWh, and the life cycle is 25 years. According to the table below, grid connection has the lowest initial investment, but the cost for 1 kWh is the highest. 

The hybrid system consists of petrol generator, battery bank and PV panel having the lowest running cost, but the initial investment costs over 25000 dollars. The option of petrol generator has moderate cost of initial investment, while it is not convenient as grid connection and the cost on 1 kWh of energy is not as cheap as the last option.

Investment Item
Cost in dollar(Present Worth of the System)
Cost in dollar per kWh
Grid Connection
Connection Fee
Petrol Generator & Battery Bank
Petrol Generator
Battery Bank
Petrol Generator & Battery Bank & PV Penal
Petrol Generator
Battery Bank
PV Panel

                       Economic Analysis of Three Power Supply System Options

Aero generators are not suggested to use for house energy consumption, since the yearly average wind speed of Melbourne is 3.25 m/s, which is very low speed to run an aero generator. The report evaluated the average output of aero generator as an example by using data of Air Breeze Marine 24 Volt 200 Watt Wind Turbine, which the aero generator can produce power of barely 7.2 W. in Melbourne. 

Because of the low wind speed and power generation, aero generator is not a part of the systems evaluated above. This report suggests the third options to be the power supply system for the house, because of lowest cost on 1 kWh of energy. The arrangement of placement for the system is provided in the appendices of the report.

Equipment used to evaluate systems

Petrol generator: Powerlite 3.3 KVA Recoil Start Petrol Generator
Battery: Solar Block Sealed Gel Battery 12 V 130Ah
PV panel: Sanyo 230 Watt Poly crystalline Solar Panel

Powerlite 3.3 kVA Recoil Start Petrol Generator (first one); Solar Block Sealed Gel Battery 12 V 130 Ah (middle); Sanyo 230 Watt Poly crystalline Solar Panel (third one) 

Energy Consumption Auditing 

Electricity Consumption Estimation
The estimation will collect data, power consumption and using hours, for every electric household, and hence to determine the daily electric energy consumption. This estimated daily electric energy consumption is fairly much, which the daily consumption is 10.40 kWh, and some of the consumed energy is actually wasted. 

The power supply system will not be designed based on the estimated daily electric consumption, since wasting energy will cause the system to be over sized, so that this consumption must be minimized by reducing running hours of those household, and the system is only designed to cover effective energy. Because some of appliances are sometimes not being used in running hours, and thus those using hours can be reduced and even eliminated to optimize the energy consumption effectiveness.

The minimization of electric energy consumption of the house is mainly by reducing microwave oven, washing machine, kettle and computers using hour, because those appliances have relatively high power consumption and hence to reduce the running hour of those appliance can decrease the daily energy consumption efficiently. The optimized electric energy consumption is 5.78 kWh, which is much lower than the original estimation.

Hot Water Consumption

In this house, hot water is mainly used to take shower, and the energy resource to heat the water for shower is electricity providing by the power supply system. In this report, the volume flow rate of shower nozzle is measured as around 1.7 L of water flowed out in 6 seconds, and hence the volume flow rate can be take 0.283 L/s. 

Estimation for energy to heat water will take that the 4 people taking shower for 10 minutes per day, and the hence the hot water consumption is 679.2 L. This report will reduce the hot water consumption as much as possible so that the hot water usage for each person will be re-managed.  

Firstly, water is not necessary to continuously running out during taking shower, and thus the time of water flowing for each person taking shower can be decreased to 5 minutes. Secondly, people living in this house are not taking shower everyday so that this report assumes that everyday two people take shower. According to the re-managed hot water usage, the total volume of hot water consumption is 169.8 L.

Design of Power Supply System 

The power supply system consists of motor, AC generator, battery charger, battery bank, inverter, transfer switch and water heating equipment. The Water heating equipment will be independent from other devices, which will collect solar radiation and convert solar energy to electricity to heat water for daily usage independently.

Inverter and Battery Bank

As the Catalogue of Appliance shows that the total power consumption of all of the electric household will be 8771 W, the inverter should has a capacity of half of the total power consumption, which is 4385.5 W. This report will select 8 ZED 24 V 5000 W Power Inverter for the house, which has a continuous max power capacity of 5000 W, efficiency of 90%, input voltage limit of 24 V and output voltage range of 220 V to 240 V.
                                                           8 ZED 24 V 5000 W Power Inverter

The battery bank voltage should be design based on daily electrical energy consumption of the house and the input voltage limit and efficiency of the selected inverter. The electrical energy consumption is, according to the auditing, 5780 Wh for summer and 5980 Wh for winter. 

Thus, the battery bank has to provide electrical energy of at least 6422.22 Wh (or 267.59 Ah) for summer daily consumption and 6644.44 Wh (or 276.85 Ah) for winter daily consumption. Since the system must ensures that the battery bank can provide electricity for two-days consumption without recharge, the daily depth of discharge will be assumed as 0.5, and hence the battery bank should have an electricity energy saving capacity of 553.70 Ah. 

This report will select Raylite MIL 17 Sbattery bank as the electrical energy storage equipment for the house, which has voltage of 24 V and capacity of 600 Ah. Assuming that the battery bank has allowable depth of discharge of 90%, so that the battery bank can support the house consumption without recharge 1.95 days, determined by the product of the depth of discharge efficiency and the energy storage capacity of the battery bank (in amp-hour) divided by daily energy consumption.
 Ray lite MIL 17 S battery bank

Battery Charger

In this report, it is expected that the battery bank can be recharged electrical energy of half of the capacity of the battery bank (the daily energy consumed)in few hours. This report will select Stunbury NG12/70G as the battery charger of the system, which has battery voltage of 24 V and maximum output current of 70 A with efficiency over 90%. Thus, the maximum output power is 1680 W. This charger can recharge the battery bank in 4.29 to 5 hours by the output current range of 60 A to 70 A.
Stunbury NG 12 /70 G Battery Charger

Petrol Generator Set

In this system, the petrol generator is designed to recharge the battery bank without directly connecting to household. Since the battery bank has maximum output power of 1680 W and the 90% efficiency of AC to DC conversion, the AC input power to the battery bank charger should be above 1866.67 W. 

This report suggests selecting Honda 2kVA Domestic Generator Kit as the generator for the system, which can provide 2000 W power of AC current in 240 V. The generator runs in power of 2000 W for 4.29 hours will recharge the battery bank for one-day energy consumption, or recharge the battery bank from empty to full in 8.57 hours.
Honda 2kVA Domestic Generator Kit

Solar Power Equipment (Solar Array) 

In this report, PV panels will be used to build solar power equipment, which will be designed based on the summertotal global radiation data of Melbourne and placed at latitude angle facing to north, since the solar power equipment is expected to recharge energy for one day consumption to recharge the battery bank, and the battery bank will be recharged mainly by generator in winter. 

The peak sun hour of summer (January) is 7.08, which means the number of hours needed at peak sun radiation condition to have an equal amount of energy from sun for one day. This report selects Suntech 140W 12V Monocrystalline Solar Panel for the solar array, which can provide maximum output power of 140 W with voltage of 17.6 V, current of 7.95 A, and efficiency of 14%.  

Therefore, the PV panel can provide 991.2Wh energy in a winter day. As mentioned in previously, the daily electrical energy consumption of the house is 5780 Wh, so that the number of panel the that the house needs is 6. Since the panel has operating voltage of 17.6 V and operating current of 7.95 A, it is suggested to arrange the panels to be 2 series connected in parallel and each of the series consists of 3 panels.Therefore the solar array will provide normally 35.2V to fit the system voltage of 24 V.

Suntech 140W 12VMonocrystalline Solar Panel

Let us go to the next post which is remaining part of this article
Remote area power supply system second part
Difference between pressure reducing valve and pressure relief valve

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