How To: Choose A Solar Panel

 

Help! How do I choose a solar panel?


 

There are several things to consider in choosing a panel:

  • How much power (wattage) do you need?

  • Does the panel need to fit in a particular space?

  • What is your budget?

  • What accessories does it come with and how easy is it to mount?

  • Does it need to be portable, lightweight, flexible; is it a permanent or temporary installation?


 

How much power do you need?

The wattage of solar panel you need is perhaps the most important thing to get right. If you underestimate the amount of power you need you could be very disappointed, but if you overestimate you might end up spending more than you need to. Unless you are sizing for an uninterruptible power supply (UPS) system, the panel needs to be sized according to how much power you are using, not according to the size of battery you are charging. The battery is a store of power – to maintain that store at a constant level the panel needs to put in to the battery the same amount of power as is going out of the battery.

As a general rule, if you have a caravan you'll need a panel between 20-60W, whereas most motorhomes are fitted with panels of 80W and above.

For laptop charging you need at least 25W to provide a useful trickle charge.

See 'Sizing your system' for more details.


 

Does the panel need to fit a particular space?

One of the reasons we like to supply a range of different manufacturers panels is to provide lots of different sizes. You can also add panels together to get the overall size you need. Remember that for the equivalent wattage a crystalline panel will be smaller than an amorphous panel. For large orders we can have panels made to your specifications.


 

What is your budget?

Put simply, the more powerful the panel, the more it will cost. Rigid panels cost less per watt than flexible and folding panels. There are also differences between equivalent panels that may reflect the quality of the junction box and frame, packaging and instructions, cables and other accessories that might be included, and how good a deal we can get from the manufacturers!


 

What accessories are included?

Think about what accessories you'll need and how confident/competent you are with the wiring, and whether you would be better getting a kit. Some panels come with cables already fitted to the junction box (all flexible and rollable panels, smaller Kyocera panels), or with plug-and-go connectors (Sunsei range). However many will require you to fit cables and sometimes blocking diodes, both of which we can supply. Consider also whether you need additional cables like a 12V cigarette lighter socket or extension cables, and if these are available for your chosen panel. Finally, how will you mount the panel? Sunsei panels come with integrated mounting feet, but most rigid panels will have an aluminium frame that needs to be raised off up by about 10mm to allow the air to circulate underneath. We can supply simple mounting brackets, but if you require something more complex (a pole mount, or angled mount) please contact us.


 

Does it need to be portable or is it a permanent installation?

Generally speaking if weight and portability is your main concern then you need a folding or rollable panel. However, if you're not trekking/canoeing/cycling or doing some other extreme sport that requires you to carry all your kit, then you might like to look at our kits for Caravans. These are based on a rigid panel, so are less costly, but include a carry bag and stand.

For permanent installations on motorhomes, sheds, boats etc it generally makes sense to use a rigid framed module. However, if you need to walk on the panel, or need it to fit on a curved area, you might consider either a rollable Powerfilm panel or a Solara semi-flexible kit.


 

Sizing a system

 

In sizing a system, the aim is to balance the power going in from the solar panel with the power going out of the battery over a period of days or weeks (depending on how it is being used). A 10W panel will give 10W (0.6A @ 16.5V) over an hour under standard test conditions (1000W/m sq and 25oC). In the UK allow around 4 hours equivalent sunshine in summer and 1 in winter. In Winter a 10W panel will give 10W over a whole day, whereas in summer it will give 40W. These are fairly conservative figures – some companies use up to 6 hours in summer. You can do the same calculations with the Amps.

 

Some simple steps for sizing a 12V system:

 

  1. Find the Wattage of your appliances. List all the 12V electrical appliances you’ll use in a typical day, and find out how many Watts they each consume. Usually this is on the appliance or in its handbook. If you can only find a figure for Amps, simply multiply this by 12, to convert it to Watts.

  2. Calculate your daily total Watt-hour requirement. Estimate how many hours you would use each appliance for over a typical week, then divide by 7 for a daily rate. Multiply each appliance’s wattage by the hours you’ll use it for in a day. Then add all the totals together to get the final daily total Watt-hours you require

 

 

  1. Next calculate your panel size. Simply divide the daily total Watt-hours you require by the hours of usable light you expect in an average day. This will give you your minimum panel wattage. In the UK, allow 1 hour of light in winter, rising to 4 hours by mid-summer.

 

 

  1. Then your battery size… Multiply your daily Watt-hour requirement by 7 to create a weekly requirement, and divide this by 12 to convert back to Amp Hours, which batteries are rated in. Multiply by two to give the correct battery size.

  2. And finally, your charge controller. Size your charge controller according to the Amps produced by your panel. Calculate the Amps produced by dividing the panel wattage by 16.5.

 

 

  1. A worked example. In one week you want to run a 65W television for 4 hours, and an 8W light for 5 hours. Your daily Watt-hour requirement for the TV is 65 x (4/7) = 37Wh; and for the light you require 8 x (5/7) = 6Wh. Your total daily requirement is thus 43W. You only intend to use the system in summer, so you need a panel that is 43/4 = 11W or more. Your battery size needs to be (43 x 7 x 2)/12 = 50Ah. And you need a charge controller suitable for a solar input of at least 11/16.5 = 0.7A

Feedback Form
Customer Feedback