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When solar panels first became available to the mass market their wattage rating was fairly small. Around 2009 a large panel was 185 watts but as time went by the size of the panels steadily increased.
Within the commercial solar sphere panels of around 450 watts seem to be the most popular but currently there is a shortage due to high demand and other factors.
This presentation will look at the viability of using a lower wattage panel, say 370 - 380 on the assumption that the $cost/watt is lower than the larger panels.
The Question continued
Obviously a larger panel will take less time to install than a smaller panel to achieve a desired system size and the smaller panels will require more:
- Panel framing and associated fixtures
- More DC cable
- More cable tray
- More time on the roof
At the end of the day we need to assess the material:install cost ratio taking into account as many factors as possible.
The differences between the size of the panels becomes apparent from a DC perspective, not so much from the AC side as in the example we are about to discuss it is assumed that the inverter component and the number of DC strings is the same.
This is because with the smaller panels the VocMax figure is lower than say a bigger panel and this results in longer strings, say 20 x panels compared to 16 x panels
What the analysis is based on
The basis of the comparison revolves around a framing spreadsheet that calculates:
- How much rail is required and requisite fittings
- Per row
- Associated total area that the panels take up
We will be assuming the same cost for materials for each example and allocate further costs including:
- Cost per panel to install
- Cost per metre to install the rail
- Cost per metre to install the cable tray
- Cost per metre to install the cable
The panels and system size
We will be looking at two panels:
- 450 watt, JAM78510-450MR, high VocMax, so 16 x panels per string
- 370 watt, TSM-DE14A (II), lower Vocmax, so 20 x panels per string
The system size we are looking at is 468 kW composing of 65 rows for the larger panels and 64 for the smaller ones*
* This is due to the difference in string lengths, 20 x panels for the smaller footprint compared to 16 x panels for the larger one.
With the smaller panels this results in more frames being used and of course the amount of associated fittings, feet, rail joiners etc.
*4000 mm rail
Price for materials is on a per metre basis and install cost is also based per metre BUT install for panels is based per panel. Cable and cable tray costs were derived from the total area each of the designs encompassed.
Now let’s assume that the pricing given is fairly accurate so one question is how much does the smaller panel price per watt need to be to = the overall cost of the larger panel design?
Now, Excel has an interesting set of functions that fall under the What if Analysis mantle and one of these functions is Goal Seek and by using this we get an answer.
The smaller panel has to be $0.387/watt compared to the larger panel at $0.41
Now I have assigned a value of $20/ panel to install so what if I halve this to $10/panel and ask the same question again?
The answer this time is $0.385/watt to match the larger panel design so a very slight decrease compared to when panel install cost per unit is $20.
So how much is this $ terms? The number of larger panels is 1040 x $10 = $10,400.
The number of smaller panels is 1,265 x $10 = $12,650
As solar panels become even larger they start to stray into the ‘two person lift’ area. If this is the case the viability of smaller footprint panels may be a good option.
This presentation has assumed a roof mount scenario and with GM things start to change. The framing proportionally is higher than with roof mount panels so the larger footprint wattage panels may be the go for these systems.
Another thing to remember is that the really large panels may need a third rail system due to the belly effect when installed on a fairly flat commercial roof so take this into consideration when making your assessment.
When assessing the viability of particular panel dimensions and associated wattages the designer must take into account the material: install cost ratio of the various components involved as well as labour fatigue, time spent onsite, the amount of packaging rubbish, roof mount versus ground mount and more.
The larger wattage panels appear on paper to be the better option but if there is a substantial $/watt differential then maybe a smaller panel is the go.
With any project costing all has to be taken into account. Good luck on your next project.
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