Solar Panel Mirror Concentrator – Do Mirrors Increase Solar Panel Output?

Do Mirrors Increase Solar Panel Output - post top

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Do Mirrors Increase Solar Panel Output - post top

Improving solar panel efficiency of commercial solar panels has long been the Holy Grail of DIY solar enthusiasts, both for PV electrical systems and also thermal water heaters.


Mirrors and solar concentrators or reflectors can increase solar panel output up to 30% if care is taken to dissipate the extra heat generated. The best configuration is to place a mirror on the ground in front of the solar panel in line with the panel vertical axis.

Place mirror in front of solar panel to increase power output

Before moving on to working tips, it’s worth pointing out why solar panels aren’t that efficient and the best way to use them. Monocrystalline solar panels are the most efficient at about 22% maximum for commercially available panels. Basically it means that for every 1000 watts of sunshine energy falling onto it’s surface, the panel will produce 220 watts of electrical energy.

Most small systems use so-called 12 volt models, which have 36 solar cells connected in series. The open circuit voltage off such a panel, or Voc, is about 21 volts. However, this is never the voltage seen once it’s connected to a load. The maximum power output (Pmax) from a 12 volt panel occurs at approximately 18 volts.

The exact point at which the panel generates its maximum watts is called the Maximum Power Point. Solar panels are almost never used without a solar charge controller, either a PWM type (Pulse Width Modulation) or MPPT (Maximum Power Point Tracking).

MPPT solar charger more efficient than PWM for charging batteries

As its name implies, the MPPT type regulator tracks the point at which the panel generates most power and maintains its output voltage at that point. If the load, usually a charging battery, needs less voltage, then the charger converts the extra voltage into current, thereby maintaining optimum power output.

The PWM type is less sophisticated and drops the panel output voltage down to that need to charge the battery, which severely reduces the panel’s output.

This is an important point:

Unless you have a very small system, in most circumstances and conditions an MPPT solar charge controller is the most efficient way to manage the power generated from solar panels.

Author’s Solar Panel Mirror Test and Observations

Test 1 – Flexible 100 Watt Monocrystalline (MPPT Controller)

Curiosity prompted me to carry out a simple test using a flexible 100 watt monocrystalline solar panel with a domestic mirror positioned in front of it, aligned with the sun. The panel faced the sun (South), angled so that the sun’s rays hit the surface at about 90 degrees for optimum incidence of irradiance.

Solar panel mirror test - 30% more power

I did consider mounting two mirrors, one either side of the panel but research into other experiments led me to think that one mirror was the best option.

Although I monitored the panels surface temperature with a non-contact infra-red thermometer, I didn’t expect high temperatures as the test was carried out in February with a measured  irradiance value of 330kW/m2.

An increase in current of 30% was measured using the MPPT solar charger remote monitor. I was surprised! It seems reflectors are well-worth the effort for small solar energy systems and would definitely consider it for fixed installations.

Test 2: Dokio 80 Watt Folding Solar Panel (PWM Controller)

I set up the mirror in exactly the same position at the same time of day but the results were disappointing at 8% gain. I’m guessing that the PWM solar charger is not using the extra irradiance falling onto the panel’s surface.

PWM regulators are less sophisticated than MPPT and don’t make use of all the power available generated by the panel – they pull the panel voltage down to the that required to charge the battery and use whatever current is available at that voltage.

Note: I’ll update this post in Summer 2021 to re-check panel surface temperature with the same test parameters and to measure any difference in output gain between the seasons.

How To Increase Solar Panel Output – Increasing Solar Panel Efficiency With Mirrors

10 years ago solar panels were 3 times more expensive than they are now and it made complete sense to work out ways to improve their efficiency. It isn’t so critical now, but of course gaining extra power is always an attractive proposition.

So can a solar panel booster using reflectors, concentrators or mirrors actually work? In fact, they do to various degrees and with certain provisos. Luckily, there are always groups of ‘mad scientist’ citizens out there willing to publish the results of their experiments, which can save the rest of us a lot of time!

The video below illustrates the point, and describes boosting the output of a small solar panel using a fresnel lens. A fresnel lens is a type of flat magnifier that is suspended above a panel to focus the sun’s rays onto its surface. They can be very powerful but often bring overheating problems – check it out:

10 Tips Related To Increasing Solar Panel Output Using Mirrors or Reflectors

1. Always use MPPT instead of PWM solar charge controllers

I already covered this, but it’s a great point. I published a post recently gathering the results of several real practical tests of different sized solar panel installations using these two type of controller and MPPT came out on top every time.

The tests showed an improvement of around 25% over PWM. The weather conditions were various and it’s worth noting that MPPT technology can give good gains in cloudy conditions when panel voltage falls. Go to test post.

2. Wire Solar Panels In Series When Using MPPT Controllers

These regulators work best when the solar panel voltage is significantly more than the required load voltage. Connecting two standard ’12 volt’ panels together with Voc of 21 volts will give 42 volts, as the volts are added together and the current stays the same.

Solar panels connected in series for MPPT battery charging

Two panels in parallel give 12 volts while the current doubles. With larger arrays it’s generally a good idea to connect multiple panels in series to give higher voltages and a low current.

This is because power losses inn the form of heat are generated by the square of the current multiplied by the cable resistance. This means that keeping the current low can bring substantial savings in cable costs.

3. What type of solar panels are most efficient?

Rigid mono panels can be up to 23% efficient, while their closest competitor, polycrystalline, come in at about 18%. Of course, it may be more cost effective to buy more panels, as poly are cheaper, but it really does depend on the installation so a cost analysis exercise is needed.

Different types of solar panels for domestic use

Flexible mono panels are just as efficient as rigid, but the very flexible thin-film variety (amorphous) are very poor at 12 to 15%. They can be useful for special purposes for fitting in very difficult physical situations but in general are too expensive for large areas.

4. What is the best angle for solar panels mounting?

There are two axes to consider when mounting solar panels, the vertical and the horizontal. The best angle across all season is about 60 degrees from the horizontal, but it’s worthwhile adjust manually for Summer and Winter in automatic tracking mechanism is used.

In the summer the correct angle is your location’s latitude -15 degrees, while in Winter it is the latitude +15 degrees.

Solar panel best angle in summer and winter

4.  Is Solar Panel Orientation Important?

Structured tests show that gains from the use of mirrors are substantial when used on solar panel arrays that are not mounted in the optimum orientation, that’s to say, not facing due South if living in the Northern hemisphere.

Panel arrays facing South-West or South-East enjoyed output gains up to 40%, while installations facing due South tended to be around 25%

5. Solar Panels Are Less Efficient At Higher Temperatures

Heat is a problem with solar panels in general, the average panel losing up to 5% for every temperature increase of 10 degrees C.

Even if a well-distributed heat rise doesn’t give problems in the short-term, I don’t know of any studies that have monitored panel efficiency over the 25 to 30 year warranty period offered by most manufacturers. For this reason, suppliers will often not guarantee arrays using solar reflectors.

Industry standards indicate that 4% to 5% should be allowed for overall losses due to high temperatures across seasons.

Mirrors vs extra heat for solar cells

One of the concerns for installers is the possibility of hot-spots that quickly and radically degrade the individual solar cells, rendering some useless or breaking the connections between them. However, a recent study in India indicates that this effect is minimal and is of no real concern.

Nevertheless, as overheating reduces solar panel output, it seems prudent to have some kind of cooling system to keep the temperature lower. The same study carried out in the mountains recorded output gains of between 20 to 30% overall.

6. What is a hybrid solar panel?

An obvious by-product of any cooling system is heat. If water was used to cool PV panels then the heat could be recovered and incorporated into the building’s heating or water system

Several commercial products exist to do just that, but the cost analysis is not clear – perhaps over the longer term they are viable but they are expensive, for now. Solar thermal panels are much more efficient than PV at 70 to 80%, so heat recovery is a real option. It also makes complete sense to use mirrors and reflectors in solar thermal systems.

7. Is it Cost Effective To Use Reflectors or Mirrors on PV Panels?

A quick calculation will soon tell us.

  • Assume a solar panel of 1m2 generating generating 4kWh per day
  • Tests show that we can expect an increase in output of 25 to 30%
  • At 30% we would gain 4×0.3=1.2kWh/day
  • Cost of 1.2kWh at average US cost of $0.13 per kWh = 1.2 x o.13 = $0.156
  • Assume 10 year life of mirrors, saving in recovered elec = 0.156 x 365 x 10 = $569
  • Cost of mirrors and maintenance must be less than $569

If we consider the cost of more panels to augment the existing system, it may not worth the effort.

8. Panel Maintenance and Regular Cleaning

Regular cleaning is known to improve efficiency by up to 25% and can generally be relied to improve things by 10%.

9.  What material is best for reflecting more light onto solar panels?

We tend to think of glass mirrors in this context. They are the most reflective after all, but it’s been found that white surfaces like glossy plastic sheeting reflects about 90% of the amount of light reflected from glass mirror surfaces.

This cuts down the cost considerably,  but there’s another, even more eco way – using natural resources. It’s advised to mount solar panels on roofs at an angle but sometimes this just isn’t possible. Mounting panels vertically is frowned upon but if fixed on a wall facing South in front of a white-painted concrete surface, the gains in output can be considerable.

In some Northern locations that have snow for 6 or 7 months of the year, natural reflection can be a huge boon to the annual electricity output.

10. Advantages of solar tracking systems

Automatic sun tracking is a well-established method of increasing solar output and is commercially available. It needs to have cost-analysis carefully carried out to find out if it’s worthwhile for your own particular situation.

That said, single-axis tracking can bring gains of up to 40% while dual-axis systems have been recorded at up to 65%, which is obviously well worthwhile – but is it worth an extra $10000?

It would seem that some kind of reflection system combined with auto-tracking might optimize panel output but I haven’t seen any studies for this combination. In theory, if mirrors give 25% extra output and then tracking provides 45% more, the equation would look like this:

  • 100 watt becomes 125W with mirrors, becomes 175W with single axis tracking.

Now there’s a thought!

Related Questions

Can solar panels store energy?

Solar panels are an energy conversion device consisting of silicon wafers. They have no means of storing energy in any form.

Will hail damage solar panels?

A properly installed solar panel array will not be damage by hailstones, rain or high winds.

Will solar panels get cheaper?

Solar panels have reduced in price by 80% since 2010. Although they will continue to get cheaper, the rate of price reduction will not be as steep.


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