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It’s natural to assume that the question arises from concerns about the total weight of a solar panel array and the impact on the average home roof. Although becoming more and more common, house roofs are not the only place solar panels are being used.
There are almost as many types of solar panels as there are uses for them, so the weight of each different kind will obviously vary quite a lot. However, domestic solar panel arrays are by far the most common usage, so I’ll answer this first.
A typical 280 watt rigid solar panel used for domestic installations weighs 37.9 lbs (17.2 kg). The average US home solar system of 5.32 kW uses 18 panels of 280 watts each weighing 37.9 lbs, so the roof supports a total weight of 682 lbs (309.5 kg) plus framing, cables, string inverters and junction boxes. Load spread can be up to 4 lbs/sq ft (19 kg /sq meter).
- Why are solar panels so heavy?
- Will my roof support solar panels?
- What are 4 types of solar panels?
Why are solar panels so heavy?
The working part of a solar panel, the actual solar cell, is very thin and doesn’t weight much at all, but the crystalline structure is brittle, as are the bus-bars connecting them together. If they crack, or the connection breaks away, that cell will become useless, reducing the efficiency of the whole solar panel.
Standard rigid solar panels have a number of solar cells connected together in the form of a thin, flat plate. The size and the number of the cells can vary, but most residential panels have 60 cells which generate an open circuit voltage (Voc) of about 40 volts.
Large solar farms tend to have larger panels and these have 72 cells, therefore producing higher voltages. However many solar cells are used, the same manufacturing process is used to encapsulate a thin cell framework into a rigid panel.
Solar Panel Construction
The ‘fingers’ of conductive material mounted across the solar cells and the bus-bars connecting them together are quite delicate and need to be protected against the elements and rough usage.
What is EVA encapsulant in solar panels?
The solar cells are encapsulated above and below with EVA, which stands for ethylene vinyl acetate. The cells are compressed between EVA layers at 150 degrees C under pressure, effectively sealing them from contaminants. It also acts as a shock absorber on both sides of the delicate crystalline structure.
The Relative Density of EVA is 0.92 to 0.94 g/cm 3, so it is lighter than water, with a RD of 1. EVA doesn’t contribute much weight to the panel at all, just a few ounces at most.
In the early days of mass production tempered glass was used for the top and the back sheet, but in the interests of shedding weight a semi-rigid plastic back sheet was introduced. This is heavier than EVA but a fraction of the weight of glass.
Solar panel glass material – what is tempered glass and how is it made?
Tempered glass is another name for ‘toughened’ or ‘safety’ glass. With a Relative Density of 2.5 it makes up most of the weight of a solar panel. Put in another way, a cubic meter of glass weighs about 2500 kg (5511 lbs)!
The standard requirement for solar panel glass is that it can withstand the impact of a hail-stone 25 mm (1 inch) in diameter travelling at 23 meters per second (50 miles per hour).
The glass is ‘tempered’ by re-melting and re-forming ordinary glass, making it up to 5 times tougher. The process also re-structures the glass crystals so that it doesn’t shatter if broken, but crumbles into small pieces. There are no shards to injure people.
The glass cover alone for a typical 250 watt solar panel weighs 20 kg (44 lbs) and has a nominal thickness of 4 mm. Tempered glass is heavier than normal or ‘float’ glass as it is compressed at high temperature.
Will my roof support solar panels?
The typical US house roof built with 2 inch x 6 inch rafters is designed to support an extra 20 lbs per square foot. If you prefer metric measurement, that’s almost 98 kg per square meter! As solar panel weight is spread across aluminium mounting rails. The maximum weight will be less than 4 lbs ft2 (20 kg m2). There is no danger with a properly constructed roof.
Flat roofs do support less for the same construction timber size and this should be factored in accordingly. I have never heard of a house roof collapsing under the weight of a solar panel installation! The table below gives the power, size and weight of some popular solar panels:
Popular solar panels by brand and their weights
65.47 x 39.29 x 1.38 inches
17 kg /37.9 lbs
1567mm x 1567mm x 40 mm
17.9 kg (39.5 lbs)
1666mm x 1002mm x 35mm
18.5 (40.8 lbs)
15kg (33 lbs)
1686mm x 1016mm x 40mm
21 kg (46 lbs)
1559mm x 1046mm x 40mm
24 kg (53 lbs)
Hanwha Q-Cells (Q-plus.G4.3)
1670mm x 1000mm x 40mm
18.5 kg (40.8 lbs)
REC Solar (REC290TP2)
1675mm x 997mm x 38 mm
18.5 kg (48 lbs)
CSUN (300-60 35)
1640mm x 992mm x 35 mm
18.3 kg (40 lbs)
Canadian Solar (Biku - CS3U-375MB-AG)
2022mm ˣ 992mm ˣ 30mm
25.9 kg (57.1 lbs)
1956mm x 992mm x 40mm
1650mm × 992mm × 35mm
18.6 kg (41 lbs)
What are 4 types of solar panels?
Up until now I’ve been talking about the heaviest solar panels, the rigid type with a glass top, but there are others. There are many ways to use PV solar and different applications need a different type of construction.
For example, one of my pet projects was an inflatable solar kayak with electric motor. The problem is with a kayak or canoe is there isn’t much room to mount solar panels. Although they can be hung out the side or at the back, the very best place is overhead creating a kind of ‘bimini’.
Inflatable kayaks are very tough and difficult to tip over, but even so, mounting rigid solar panels overhead would have made it dangerously top-heavy. We were also limited by size. The final sizing was with two 100 watt panels – rigid panels of this wattage weigh about 15 kg (33 lbs) each, so it was out of the question.
The solution was to use flexible solar panels and mount them on a DIY aluminium frame to give some rigidity. The above structure weighs 5 kgs (11 lbs) in total.
The four main types of solar panels in common use are:
- Monocrystalline (rigid, glass covered)
- Polycrystalline (same weight as mono)
- Flexible (mono or poly sealed and covered in flexible clear plastic
- Thin film or amorphous (very light and flexible but low efficiency)
Flexible solar panels are about one fifth of the weight of rigid panels and I use them for mostly everything as I often create DIY projects that are mobile.
Thin film are even lighter but with an efficiency of between 5 and 10% personally, I don’t find a lot of use for them.
Powering An Rv With Solar – How Much Weight Can An RV Roof Support?
It’s an urban myth that an RV can be totally powered by solar panels, although some manufacturers, like Dethleff above, like us to think it’s possible.
In my camping van days I had a Pilot model built on a Ford Transit. It had just two batteries, one for the engine and one for the living cabin. I just needed enough solar to keep both topped up, so opted for an 80 watt rigid solar panel and a simple PWM controller.
Boondocking is becoming more and more popular and owners are opting for more powerful solar systems on their RVs. Even so, there really isn’t much room for more than 300 to 400 watts on the roof – but is that too heavy for a fiber-glass roof?
Rest easy. RV roofs are good for up to 115 kgs (150 lbs).
Web Story – Can A Solar Panel … FAQ
Are solar panels heavy for roof?
The weight of a solar panel array is spread across a roof by mounting at either end on aluminium mounting rails. The average weight is never more than about 4 lbs per square foot. The typical professionally built US house roof using 2 inch x 6 inches trusses can hold up to 20 lbs per sq foot.
What is the average solar panel weight per watt?
A common size of domestic solar panel is 300 watts which weighs about 40 lbs. Dividing 40 lbs by 300 we get o.133 lbs per watt. The average US solar installation is 5.5 kw which would weigh 5500 x 0.133 = 733 lbs or 332.5 kgs.
What is the average commercial solar panel size?
The average commercial solar panel size for domestic use is 285 watts with dimensions of 1656mm x 1005mm x 40mm. Solar farms use bigger panels up to 400 or 500 watts, which have proportionately bigger dimensions. The biggest solar panel commercially available is the Sunpower 415 watt and 22.5% efficient.
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