How To: Choose A Solar Panel

Help! How do I choose a solar panel? This is one of the most frequently asked questions.

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When selecting a solar panel, several factors are essential to consider:

We will explore these factors broadly (the actual power calculation will be addressed in Q6).

Q1. How much power (wattage) do you need?

The wattage of the solar panel you choose is arguably the most crucial aspect.

Why? If you underestimate the needed power, you might not achieve the desired results. (Similar to expecting a small car to tow a large caravan).

On the contrary, overestimating could lead to unnecessary expenses. (Most people wouldn't purchase a luxury Ferrari for a quick drive to the store).

A solar-powered system has three primary components:

1. Power generation (the solar panel)
2. Power storage (the battery)
3. Power usage (the devices you want to power with solar energy)

To determine the correct wattage, the panel must be sized according to your power consumption. (You'll also need information on each electrical item to be powered by solar energy).

Batteries act as storage for solar power collected during the day for immediate or later use. Without a battery, a solar-powered flashlight is practically useless in the dark!

Keep in mind that to maintain constant power storage, the solar panel must supply to the battery the same amount of power that is drawn from it now (or anticipated later).

For this stage, you don’t need to worry about the battery size unless sizing for an uninterruptible power supply (UPS) system. Just remember; one is necessary.

Quick power rating guidelines:

Typically, a caravan requires a panel rated between 20-60W, while most motorhomes use panels rated at 80W or more. (Motorhomes usually have more power-consuming gadgets than caravans).

For laptop charging, you need at least 25W for an efficient trickle charge.

Refer to Q6 - How to size a system for further details.

Q2. Does the panel need to fit a particular space?

We provide a variety of solar panels from different manufacturers to accommodate various sizes, including width, length, thickness, and power rating.

You can also connect panels together to achieve the desired overall size. If a 120W panel is too large for your space but you can fit two 60W panels side by side, that option works too.

Remember, for the same wattage, a crystalline panel will occupy less space than an amorphous panel. (If these terms are unfamiliar, consider reviewing our Glossary).

For large orders, we can even manufacture panels to your specifications.

Q3. What is your budget?

Simplistically, the more powerful the panel, the higher the cost.

Rigid panels usually cost less per watt compared to flexible and folding panels.

There are also differences in quality across equivalent panels, which can include:

• The quality of the junction box and frame
• The packaging and instructions
• Cables and other included accessories

(Prices might also depend on the bargains we can secure from manufacturers!)

Q4. What accessories are included?

Consider the necessary accessories and your wiring skills. Would it be better to purchase a complete kit?

Some panels come with pre-fitted cables (all flexible and rollable panels, smaller Kyocera panels), or plug-and-play connectors (Sunsei range).

However, many panels require you to install cables and blocking diodes, both of which we can provide.

Think about whether you may need additional cables (like a 12V cigarette lighter socket or extension cables) and if those options are available for your chosen panel.

Lastly, how will you mount the panel? Sunsei panels include integrated mounting feet, while most rigid panels possess an aluminum frame requiring around 10mm clearance from the surface for air circulation.

We can supply basic mounting brackets, but for more complex installations (like pole mounts or angled mounts), please reach out to us.

Q5. Does it need to be portable or is it a permanent installation?

If weight and portability are top priorities (maybe you are a touring cyclist), then a folding or rollable panel is ideal.

However, if you aren't engaged in extreme sports requiring you to transport all your equipment, consider our solar kits for Caravans. These feature a rigid panel, making them less costly, but they come with a carry bag and stand.

For permanent installations on motorhomes, sheds, boats, etc., using a rigid framed module is sensible. Yet, if you need to walk on the panel (like on a boat deck) or have it fit into a curved surface, you might explore using either a rollable Powerfilm panel or a Solara semi-flexible kit.

You may also want a rollable panel for temporary placement using bungee cords (for example, on a boat or tent). Rollable or flexible panels are quite convenient for such purposes. You can browse our flexible panels according to their power rating or in specific solar kits.

Q6. How do you size a system?

Sizing a system means balancing the power flowing into the solar panel with the power leaving the battery over days or weeks (based on your usage).

A 10W panel provides 10W (0.6A @ 16.5V) for each hour under standard test conditions (W/m² and 25°C).

A quick sunshine hours guide for the UK:

On a summer's day, you can expect around 4 hours of sunlight. A 10W panel will therefore generate 40W during that day.

On a winter's day, you might get about 1 hour of sunlight, yielding only 10W from a 10W panel that day.

These figures are conservative; some companies assume up to 6 hours in summer. The same calculations can be made using Amps.

Some simple steps for sizing a 12V system include:

1. Identify the wattage of your appliances. List all the 12V appliances you'll use in a typical day and find their wattage, usually indicated on the appliance or its manual. If only the Amp rating is available, multiply this by 12 to convert to Watts.
2. Calculate your daily total watt-hour requirement. Estimate how long you'll use each appliance over a week, divide by 7 to determine the daily rate, then multiply each appliance's wattage by the hours you’ll use it in a day. Add all totals for your final daily watt-hour requirement.

3. Calculate your panel size. Divide your daily watt-hour requirement by the expected hours of usable light in an average day to find your minimum panel wattage. In the UK, assume 1 hour of light in winter, rising to 4 hours by mid-summer.

4. Determine your battery size. Multiply your daily watt-hour requirement by 7 for a weekly requirement, then divide by 12 to convert back to Amp Hours (the battery rating). Multiply by two for an accurate battery size.
5. Lastly, size your charge controller. Determine your charge controller based on the Amps produced by your panel, which can be calculated by dividing the panel wattage by 16.5.

6. A worked example. If you intend to run a 65W television for 4 hours weekly and an 8W light for 5 hours, your daily watt-hour requirement for the TV is 65 x (4/7) = 37Wh; for the light, it's 8 x (5/7) = 6Wh. Thus, your total daily requirement is 43W. If using the system only in summer, you need a panel rated at 43/4 = 11W or above. Your battery requirement will be (43 x 7 x 2)/12 = 50Ah, and you need a charge controller suitable for at least 11/16.5 = 0.7A input.

For more information, please visit Hongyuan International.