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1. POWER CONSUMPTION DATA Enter the power consumption information for your equipment. Modify the default values as needed.
Select Battery Voltage
Select the battery voltage used in your system. The program automatically recalculates the Ah for the selected battery voltage.
Enter
Average
Watts Enter average Watts in this column OR average Amps in the Amps column
Enter
Average
Amps Enter average Amps in this column OR average Watts in the Watts column
Enter
Daily
Hours Enter the total number of hours that the equipment runs each day
Daily
Ah
[Totals] This column gives the calculated Ah for each equipment and the total Ah for each area
Select
day
night Select if equipment is operated day only "D", both day and night "D/N" or night only "N". Night includes sunset and sunrise periods when little is generated by the solar system.
Fridge (upgright/large)Enter average power or average current for your fridge or freezer. If you are not sure of the power consumption, click on "KITCHEN" for a list of the most common models of fridge/freezer used in Australia. Set the daily usage hours to "24" - this has been set as default.
Fridge (portable, freezer setting)Enter average power or average current for your fridge or freezer. If you are not sure of the power consumption, click on "KITCHEN" for a list of the most common models of fridge/freezer used in Australia. A fridge/freezer on a freezer setting will consume roughly double the power compared with a fridge setting. Set the daily usage hours to "24".
Fridge (portable,fridge setting)Enter average power or average current for your fridge or freezer. If you are not sure of the power consumption, click on "KITCHEN" for a list of the most common models of fridge/freezer used in Australia. Set the daily usage hours to "24".
Range HoodEnter average power or average current for your range hood. A typical value is 15Watts. Enter the running time in hours.
Type in the name of any other appliance and enter Watts or Amps and the running hours.
ELECTRONICSLaptop computers may have a significant impact on the sizing of solar and battery capacity, the default values should be varied as needed.
Other electronic items such as tablet computers, phones, cameras and GPS have a minor impact, so a reasonable assumption can be made about the daily power consumption need. The default values here are reasonable assumptions for sizing purposes.
Laptop ComputerEnter average power or average current for your laptop. This may range from 15Watt for a Macbook Air up to 30W for an older or higher spec'd laptop. An allowance should be included of 10% for power losses in an inverter or a DC adaptor. Running multiple older spec laptops for long periods places a big demand on solar power capacity, and if used after the sun has "gone down" can place a big demand on battery capacity. The most recent machines will have the lowest power consumption, with appropriate computer settings the power consumption can be further minimised.
If the machine is further run on its internal battery, then an allowance for charging the battery must be added. For example, a 54Wh battery (2014 model 13.3" MacBook Air) will require 4.5Ah, plus losses, say 5Ah to fully charge its battery from flat.
Tablet Computer (recharge)It is assumed that power is required only to charge the tablet battery. An Ipad 2 has a 25Wh battery, and an Ipad 3 has a 42.5Wh battery. A full recharge every day is unlikely, however, a high charge rate assumption of around 50% charge daily is reasonable for solar and battery sizing. Therefore, for the Ipad 3, a daily charge of 24Wh, or 2Ah at 12V is reasonable.
Mobile Phone (recharge)As with the laptop, it is reasonable to assume a 50% charge is required daily. A 2014 Samsung Galaxy S5 has a 11.78Wh battery, therefore a 50% charge daily requires 0.5Ah at 12V.
Camera (recharge)As with the phone and tablet, it is reasonable to assume a 50% charge is required daily. A mid-range Nikon DSLR camera has a 7.5Wh battery, therefore a 50% charge is 0.3Ah at 12V.
Type in the name of any other equipment and enter Watts or Amps and the running hours.
PUMPSWhen free camping, minimising water usage is normally a priority, therefore pump usage will similarly be minimised.
Water Pressure PumpA pump fitted into a caravan having a shower consumes around 60W (5A at 12V) at maximum flow. Check your pump rating and adjust as necessary.
Type in the name of any other appliance and enter Watts or Amps and the running hours.
ENTERTAINMENTDefault values are typical for equipment used in caravans. Adjust as necessary.
TV
Antenna / Satellite
Radio
Type in the name of any other equipment and enter Watts or Amps and the running hours.
MEDICALEnter data for any medical devices requiring power.
CPAPCPAP machines can significantly impact the solar and battery sizing. Mid-range default values have been provided which must be amended by the user.
Type in the name of any other equipment and enter Watts or Amps and the running hours.
LIGHTINGAdd up the average wattage (or amperage) for the lights used. A reasonable estimate may be 20W for 3 hours. This is is equivalent to 3 to 4 downlights for 3 hours.
Although LED lights are very efficient, strip LED lights can be quite power hungry. The strip LED lights above the kitchen bench in a caravan consumed 24W and the outside LED light 16W. Therefore, careful management of lighting is needed to avoid unnecessary power usage.
Average lighting consumption
VENTILATIONAdd up the average wattage (or amperage) for any fans used. A portable fan suitable for a caravan fan will consume 3-4 Watts.
Fans
240V via INVERTERPower consumption on the 240V circuits is mostly discretionary, such as microwave usage, and the running load should not drive the solar and battery sizing.
The inverter must be selected in accordance with the manufacturer's guidelines so that it is able to accommodate both the starting in-rush current and steady state running current. To meet the start-up in-rush current requirements, the guidelines for battery capacity in the inverter manufacturer's manual must be observed - this may necessitate an increase in the battery capacity.
Inverter
2. PV & BATTERY PERFORMANCE DATA Enter the performance information for the components in your system. Modify the default values as needed.

PV Solar Panel
% Efficiency at STCThis value is the PV solar panel efficiency as stated by the manufacturer.
%/oC Temperature Coeff of Power The PV Panel Temperature Coefficient of Power will be stated on the PV Panel datasheet. It defines the rate at which the output power reduces as the solar cell temperature increases. This coefficient is multiplied by (PV Panel Operating Temperature - Temperature at STC(25oC)) to yield the reduction in power output compared with the panel specified output at Standard Test Conditions (STC). The parameter "PV Panel Operating Temperature" should be set to 45oC. The panel will of course run hotter on sunny hot days, however on these days an appropriately sized system will generate surplus power.
oC Operating Temperature Refer to the help under "PV Panel Temp Coeff Power"
% Efficiency at Operating Temp This is the PV cell efficiency at the operating temperature of the PV panel.
% Useable Peak Sun Hours
Insolation is the amount of solar energy received on a given area measured in kilowatt-hours per square meter (kwh/m²). This value is equivalent to peak sun hours. The Useable Peak Sun Hours, disregards the sunrise and sunset periods when the irradiance is below the threshold for the solar system to generate power.
% Extra solar generating margin This is an allowance for underestimation and/or future growth in the power consumption.
Note that the solar power sizing includes a margin for this.
Cable - PV Panel to SCC
% Loss - PV Panel to SCC This is the power loss in the cable from the PV panel(s) to the solar charge controller (SCC). The objective is that total cable losses should be less than 3%.
Solar Charge Controller (SCC)
% Efficiency This is the efficiency of the Solar Charge Controller (SCC). For an Maximum Power Point Tracking Controller with a 2 or 3 stage charge characteristic, an efficiency of 95% can be assumed.
For a PWM SCC an efficiency of 75% can be assumed, or less if it a single stage float voltage for charging the battery.
Cable - SCC to Battery
% Loss - SCC to Battery This is the power loss in the cable from the Solar Charge Controller (SCC) to the Battery. The objective is that total cable losses should be less than 3%.
Battery
% Charge Efficiency This is an allowance for the inefficiency of the battery. For a LiFePO4 battery, this is around 90-95%. For lead-acid around 85%. Note that the solar power sizing includes a margin for this.
Hours Autonomy (no sun) The hours of autonomy includes the overnight period plus further time when, due to shading or poor sun, there is little or no solar power being generated.
Note that the solar power is sized for the overnight usage, plus a spare margin.
% Non-useable Minimum SoC This is the minimum charge that must remain in the battery to avoid impacting battery lifetime. This varies with battery technology. For AGM repeated discharge below 30% will reduce battery life. For LiFePO4, the minimum SoC should be set to 10% to avoid the possibility of total discharge.
3. PV SOLAR SIZING CALCULATIONS This frame shows the calculated PV Solar Power capacity required for your system.

PV Panel(s) Sizing
Watts-peak at STC This is the calculated PV Panel capacity required to generate the daily Amp-hour load plus the extra solar generating margin.
Watts-peak at Operating Temp This is the calculated PV Panel rating at the operating temperature (normally set to 45oC).
Wh/day at output The cable from the PV Panel(s) to the Solar Charge Controller (SCC) loses a small amount of power, hence the Wh/day at the PV Panel(s) output is marginally higher than at the SCC input.
Solar Controller Sizing
Amp Rating (Amp) This is the amp rating of the Solar Charge Controller.
Power Rating (Watt) This is the power rating of the Solar Charge Controller.
Wh/day at SCC Input The Solar Charge Controller (SCC) is not 100% efficient, hence the Wh/day at the SCC input is marginally higher.
Wh/day at SCC Output The cable from the Solar Charge Controller (SCC) to the battery loses a small amount of power, hence the Wh/day at the SCC output is marginally higher than at the battery terminals.
Charge required from PV
Ah/Day used by loads This is the total Amp-hour consumed by the loads.
Ah/Day Extra solar margin This is the Amp-hour allowed to account for underestimation of the load daily load and/or allow additional loads.
Ah/Day Battery charge efficiency This is the Amp-hour required to compensate for the inefficiency of the battery. Losses are primarily due to the internal impedance which results in a heating of the battery during charge and discharge..
Ah/Day req'd from Solar This is the total Amp-hour (Ah) required daily from the PV Solar System to replenish the battery. i.e:
Total Ah/Day = Ah/day consumed by load + Ah/day allowed for error/spare + Ah/day allowed for battery inefficiency
Wh/Day req'd from Solar This is the total Watt-hours (Wh) required daily from the PV Solar System to replenish the battery . ie
Total Wh/day = Total Ah/day * Battery Voltage
4. BATTERY SIZING CALCULATIONS This frame shows the calculated battery capacity required for your system.

Ah - Total battery capacity This is the total Amp-hour size required for the battery. This size equals: Ah used overnight + Ah for use in the battery. This reserve can be used overnight or used if insufficient sunlight for solar power generation.
Ah - Used Overnight (no sun) This is the total Amp-hour used overnight - this includes the dusk period before sunset, and dawn period after sunrise, when there is insufficient sunlight for solar power generation.
Ah - Useable Reserve This is the reserve Amp-hour available for use in the battery. This reserve can be used overnight or used if insufficient sunlight for solar power generation.
Ah - Non-useable Minimum SoC This is the total Amp-hour used overnight - this includes the dusk period before sunset, and dawn period after sunrise, when there is insufficient sunlight for solar power generation.
Hrs-Battery Endurance (no sun) Assuming an initial full battery, this is the duration in hours that the battery will supply the load without any incoming charge. i.e it uses the capacity allocated for overnight use, plus the useable reserve.
Maximum Charge Rate (C) The "C" parameter defines the charging current relative to the battery capacity, eg, 0.2C is 0.2 x 100Ah for a 100Ah battery, i.e 20Amps. The charge rate must be within the range recommended by the battery manufacturer.
6. CALCULATION RESULTS This frame provides a summary of the PV system size, solar charge controller and battery capacity that, for average solar insolation, will support continuous free camping.
PV Panel(s) Required (Watt) This is the total PV Panel Wattage required.
 
Solar Charge Controller Capacity This is the required capacity of the Solar Charge Controller. Power above about 400W will likely require (suitable) multiple SCC's connected in parallel, due to power limitations of available equipment. A 24V batter system is also recommended.
Amps This is the capacity of the Solar Charge Controller (Amps).
Watts This is the capacity of the Solar Charge Controller (Watts).
 
 
Battery Capacity Required (Ah) This is the total Amp-hour size required for the battery. This size equals: Ah for the hours of autonomy (Ah required overnight + useable reserve) plus the normally non-useable minimum state of charge (SoC).
7. YOUR CURRENT / PROPOSED SYSTEMEnter your proposed PV system and battery sizes. For the selected location and season, the calculator will estimate how many days your battery will last.
Watts-peak PV Panel(s) current/proposed Enter the total PV Panel Wattage installed or proposed.
 
Ah/Day from the current/proposed PV System This is the Ah per Day is or will be provided by the current or proposed PV system.
 
Ah/Day shortfall in charge from PV System This is the shortfall in Ah/Day of the Solar System with respect to the Ah/Day used by loads.
 
Ah Battery current/proposed Enter the total Ah of the battery current or proposed.
 
Number of days before the battery SoC is diminished to the "% Non-useable Minimum SoC" The battery SoC will reduce as the Solar System is not capable of topping up the battery each day. Starting with a fully charged battery, this value indicates the number of days before the battery SoC will reduce to the "% Non-useable Minimum SoC".
 
Number of days before the battery reaches 0% SoC This is the number of days before the battery is completely flat. Note that this is based on a basic SoC calculation. The actual number of days will likely be less than this.
5. SELECT LOCATION AND SEASON For the selected location and season, the program will show in frame 6. the PV P anel Watts(peak), Solar Charge Controller (SCC) Size and Battery Size required.
The text overlaid onto the map shows this same information for selected locations around australia.
P: = Watts-peak at STC - PV panel rating
S: = Amps - Solar Charge Controller Rating **
B: = Amp-hours - Battery Rating
**: SCC rating is based on maximum PV panel output, not achievable. ie. winter in the more southerly latitudes, eg Hobart, will generate much lower power and current. Future updates to this tool will implement changes to reflect this.

Feedback:

We are keen to improve the SPEC so value your feedback.  Please email info@solar4rvs.com.au       or complete and submit the feedback form below.

IMPORTANT:

If a box has a yellow background you can manually change the figure.  It may have a pre-populated amount which is a general assumption that is changeable.   If the box has a black background the figure that appears has been automatically calculated.

How to use the SPEC

There are 7 sections (left to right and top to bottom):

  • Sections 1-6 will identify what system you need
  • Section 7 will let you input the wattage of panels you currently have/propose so you can see how long you can free-camp based on the battery capacity that you enter here.

​Some boxes require input whilst others automatically re-calculate:

  • If a box has a yellow background you can manually change the figure.  It may have a pre-populated value which is a general assumption that is changeable. 
  • If the box has a black background, the figure that appears has been automatically calculated.


Section 1: Power Consumption Data
From the drop down menu select battery voltage - 12V, 24V, 36V or 48V.  Then enter either watts (column 1) OR Amps (Column 2) of items that will consume power plus the daily hours the item will generally be used (column 3). Column 5 lets you select whether the item is used day and night, just day or just night time.  This section is pre-populated with some example data that should be checked and modified by the user for their specific needs.

Section 2: PV & Battery Performance Data
This section is pre-populated using real equipment data.  The data, particularly the battery performance data should be checked and modified by the user if necessary.

Section 3: PV Solar Sizing Calculations
This section automatically calculates the required PV solar system size based on data in sections 1 and 2.

Section 4: Battery Sizing Calculations

This section automatically calculates the required battery capacity based on data in sections 1 and 2.

Section 5: Select Location and Season

This section allows you to choose a location and season from the drop down menu.  This may be a regular travel destination or area where you will use the solar power the most e.g. Tropical North Queensland in Australia’s winter (dry season up north). Once chosen, the location on the map will display the peak solar panel power, the solar charge controller capacity and the battery capacity required for that location.

Note: The map shows annual solar radiation levels from lowest (dark blue) to highest (red) across Australia. (Source: http://www.energyfutures.qld.gov.au/solar.cfm)

Section 6: Calculation Results

This section displays your solar power system component requirements based on the data entered.

Section 7: Current/Proposed system

Since the calculation results in section 6 are only a guide, this section gives you the opportunity to choose a smaller system. You just need to enter your current/proposed panel wattage and battery Ah.  The automatic calculations then display how long you can be independent without mains power based on the amount/size of panels you have/propose and the battery capacity you have/propose.  

​Only available on desktop.

​If you have difficulty using the SPEC on an Apple Mac then try an alternate web browser (Chrome or FireFox).  We are in the process of sourcing an alternate hosting platform to resolve the formatting issues on some PCs.   

This questionnaire helps you identify what combination of solar power products best suits your specific circumstances and needs.

Solar Power Estimate Calculator (SPEC) for caravans and other RVs

The calculator takes into account the power consumption you use in your caravan/RV and your travel destinations.

The SPEC is copyright © Solar 4 RVS 2014 so please read the copyright information below.

Feedback form

What is a PV System? 

A Photo-Voltaic (PV) system is the solar panels together with the solar charge controller.