Utility of Solar Panels

We have had solar panels since the start of the 1980’s. The original panels were only about 10% efficient, so converted about 10% of the light that fell on them.

But we are really dependent on the irradiance of the area you have the panels situated. The average for the world is about 4KWh per square metre, but ranges from 0.7 to 7.5KWh per square metre a day, so where you live an alter this by as much as 10 times larger or 10 times smaller.

A typical solar panel will roughly cover about 2 square metres, so 20 panels will be around 40 square metres and weigh 20Kg each.

So actual power ranges from 2.8KWh per day for and installation of 20 very old panels at a very high latitude to 75KWh for a perovskite panels in a very high irradiance area such as northern central Australia.

A typical set of 20 average panels in the UK midlands would be about 20KWh per day, enough to keep 2 average electric cars topped up or a day’s household use.

For the new perovskite panels, you may get as much as 27KWh per day, so you are close to an electric car and the household. If it was a working household, then in both cases you would probably need two Tesla Powerwall’s for storage. So, the price would be between £30-50,000. Siting in the Cornwall area could increase the panel outputs by as much as +20%, so reducing the full system costs by this amount, the Highlands of Scotland reducing it by as much as -30%, so increasing the full system costs by this amount.

It you thought of them having a 20-year life then they would probably cost about £60,000-£100,000 over that period. The current cost of electricity is about 16p per KWh, so for 20 years it would cost somewhere near £24,000-£32,000. The break-even point without subsidies would about 40 years for a standard system or 65 years for a perovskite one. If you took away the Powerwall’s then the break-even points without subsidies would be 22 years to 24 years. This is a midlands UK figure, Cornwall could be 80% of the timings, the Scottish Highlands 130% of the timings.

The current average solar panel is about 16-19% of the radiance that falls on them. The very latest monocrystalline modern panels come out at about 22%. The world record for silicon-based panels is 28%, but the new perovskite ones have reached a record efficiency of about 29.15%.

The record rate is currently increasing at about 0.5% per year since 2010 when the world started changing from polycrystalline panels at 13-16% to the more efficient monocrystalline panels at 15-20%, then onto perovskite at 22-25%. A change from polycrystalline to monocrystalline panels is about 25% improvement. From monocrystalline to perovskite ones should be a further improvement of about 33%. So, where a set size panel about 1980 would produce about 200W, a standard panel could produce 300W, the very latest 370W and a perovskite around 490W. The difference in cost would be an old second-hand panel about £50, a standard one about £100, the very latest around £200 and a current perovskite one around £500, so there are a few power return vs. cost problems at the moment.

For same size panels:

20 old second hand panels producing 4KW would cost £1000

14 standard panels producing 4.2KW would cost £1400

11 Latest model solar panels producing 4.1KW would cost £2200        and

9 perovskite panels producing 4.4KW would cost £4500

All would provide similar power but as you go down the list, take up less space.

A typical house using 20 same size panels would be:

Second hand panels producing 4KW would cost £1000

Standard panels producing 6KW would cost £2000

Latest model solar panels producing 7.4KW would cost £4000        and

Perovskite panels producing 9.8KW would cost £10000

We will ignore the costs of inverters for the moment, which start at around £1000 up to £10000 for the latest high-power ones needed for a top end system.

But the key to use is storage. It’s no good having a massive amount of power generated unless you can use this throughout all the time that you need it.

One option is to use an electric car for storage during the day, but it’s likely that this is the time that you will need to use it, and when you aren’t using it there are a lot of hours of darkness. Also, if you run down the cars batteries then you will have less opportunity and duration when you need to use it. So, the likely option is to use storage batteries of some sort, such as a Tesla Powerwall, currently about £7,000 for 13.5KWh of use. A typical home uses about 1.5KW per hour when solar power isn’t available, except in much higher and colder latitudes when it can reach 2KW per hour. This gives between 7 and 9 hours use.

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