San Diego Solar Panel Cleaning Research - How Does It Compare To The UK?

San Diego Solar Panel Cleaning Research - How Does It Compare To The UK?

Recently, there has been some research into the financial benefits of solar panel cleaning in San Diego, California. Here, we will compare the findings in the U.S. to see if it is comparable to solar panel cleaning here in the UK.

We have studied the scientific benefits of solar panel cleaning for the last 5 years and in the early days, we spent a lot of time researching the American and Spanish solar panel cleaning industries. We quickly found though that comparing the UK to such places was not feasible, due to the difference in climates. This led us to look closer at the German solar panel cleaning industry. The German climate is similar to that of the UK.

Because of our findings, our opinion on why San Diego findings cannot compare to solar panel cleaning in the UK are as follows:

Climate Difference

Rainfall in San Diego
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Total rainfall in MM 45.7 38.9 45 20.1 4.8 1.8 0.5 2.5 6.1 9.4 36.8 39.9
Data supplied courtesy of
Rainfall in London
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Total rainfall in MM 53 36 48 47 51 50 48 54 53 57 57 57
Data supplied courtesy of

While the rainfall in San Diego and London is comparable in January, February and March, there is a considerable drop off in rain in San Diego from April.

The panels only lost 7.4% in 145 days during a drought, in California. The Californian climate differs greatly from the UK. A comparison is unfair.

Because of the drought, we doubt people washed their cars as often either. It does not mean that cars do not need cleaning though. In the UK, we get our fair share of rain. It is the RAIN here which puts dirt on the panels, it does not clean them. If you left your car on the drive for 12 months and let the rain water clean away the dust that had accumulated, what state would your car windscreen be in? It would certainly not be clean. Why would solar panels mounted at a similar angle be any different?

Dirt Accumulation

The test was a nearly six-monthly test on residential arrays. A 7.4% loss on a residential 4 KW array will equate to roughly £30.00 over a six month period. However, scientific tests have shown that dust accumulation on surfaces is accumulative. It takes time for a layer of dust to accumulate on a surface, but when a dust layer is present, it attracts dust at an increased rate. On the San Diego test, if the panels were left longer, the percentage increase would have more than doubled. This would have meant the arrays losing over 15% over the course of a year. In the UK, this equates to a £127.50 loss.

The San Diego researchers calculated that panels would lose about 0.05% output each day. Without even taking into account the accumulative effect of dirt accumulation, that still mounts up to 18.25% over a year! If you do not clean your panels for 2 years, you could potentially be losing 36.5% of your electricity generation! Is this the case in the UK? Yes. We have monitored output from arrays on farms and frequently find an increase of 20%-40% in output after having the panels cleaned. On one industrial site where there was a lot of air-borne dust due to the products they manufactured, an increase of 58% was reported!

Relative Solar Panel Cleaning Costs

Jan Kleissl says “You definitely wouldn’t get your money back after hiring someone to wash your rooftop panels.” That is a very relative statement. Value for money depends heavily on how much you are paying. In the UK, some companies, not ours we hasten to add, charge up to £175.00 for a 16 panel roof mounted array. That cost would prove Mr Kleissl to be correct. But £175.00 is a very inflated price to just clean 16 panels. Our solar panel cleaning costs are nowhere near this price.

Solar Panel Situation

"Engineers also found that at a few sites, photovoltaic panels were dirty enough to warrant cleaning due to very specific and localized circumstances. For example, being directly next to and downwind of a highway, factory or agricultural field may generate enough dirt to warrant cleaning." This must represent 90% of all solar panels mounted in the UK. Where were these panels mounted in California if not next to a road, the sea, a factory or in a field? If it were the desert, the panels would have been very dirty. The vast majority of solar panels are indeed mounted near roads, where they are exposed to traffic film, the sea, where they accumulate salt deposits or in a field where there is a lot of dust, especially during harvest time.


In conclusion, we can see that recent San Diego findings regarding solar panel cleaning were carried out in unusual circumstances, a drought. They were very localised, specific to that area and were based heavily on the weather in that part of the world. The findings are also relative as it depends great what you paying for your solar panel cleaning and whether this gives a good return on investment. there is no point spending £100 p/a on solar panel cleaning if the extra electricity generated is £75. Because of these factors, it is clear to see that the recent findings of San Diego researchers are not representative of the value of solar panel cleaning as a whole.

Clean Solar Solutions Ltd have done much number-crunching over the last few years in order to make our solar panel cleaning service a financially viable option for residential and commercial clients. Our cleaning service will help your solar panels produce extra electricity and provides excellent value for money. If you would like a free quote for your solar panel cleaning, please feel free to contact us.