24 to 64-Years
NB Please note this article only relates to solar photovoltaic systems installed and operated without the Feed-in Tariff government incentive scheme and only looks at the true economies of the technology. Please refer to the energy saving trust for the latest on The FITs scheme as they do make a significant difference making solar PV economically viable.
The terms solar energy and solar power are often used to describe technologies which collect the energy of the sun and redistribute it for our use. These terms are however a little ambiguous. For example, solar energy effectively drives our whole planet, wind, wave and fossil fuels could ultimately be regarded as solar energy. For the purposes of this site our only concern is for solar energy that can be collected directly by our dwelling and used to, for example, heat water or to drive our electric devices. For this article only Solar Photovoltaic power generation is considered. Please follow the link to take a look at Solar hot water.
| If you are interested, all light is made up of photons, which might be best described as tiny little packets of energy. There is a whole range of different energies or “packet sizes” which if you put them all together from small to large would constitute the spectrum of light. |
| Solar Hot Water... |
To collect solar energy a method is required to collect photons of light and to convert the energy in this light into another form of energy for storage or use.
In photovoltaic’s this energy is directly transferred into electrical energy using solar cells, the energy may then be stored in a battery, used immediately in your house or sold back to the grid.
| In solar cells the light photons are absorbed by transferring electrons in a semiconductor to higher energy levels. They are transferred to what is called the conduction band of the semiconductor, where they can flow through a circuit and provide electrical energy to your property. Semiconductor physics is a bit much for this site; there is a good wiki on the subject. http://en.wikipedia.org/wiki/Semiconductor. |
Is it worth it?
On the face of it, it should be quite straight forward to calculate how sensible an investment in photovoltaic power generation is likely to be. The number of variables is however extraordinary, here are the more important
- How sunny is it where you live.
- The orientation of solar panel, (North, South, East, West).
- The angle of the panel.
- The size of the intended panel.
- The efficiency of the solar cells.
- Efficiency of the electrical systems, (invertors and power storage)
- The cost of the installation.
- The cost of mains electricity.
The first term that you generally come across when looking into solar modules is the term Kilowatt peak (kWp) or peak power. This value specifies the output power achieved by a Solar module under solar radiation under set standard test conditions. Standard test conditions use a solar radiation level of 1,000 watts per square meter (W/m2).
As an example, an 8m2, 1kW peak system (1 kWp) is often specified as an entry level system. This means that under test radiation conditions of 1000 W/m2 this 8m2 panel is capable of producing a 1kW power output. A general consensus of suppliers indicates that such a unit should produce 750 kWh of electricity per year in the UK, if correctly oriented. (As physically smaller 1kW peak system would produce the same but would have more efficient solar cells.)
The tables below give an indication of how these values might be derived and considers different radiation level across the UK, but it is very rough. If you are interested there is also a solar radiation map of Europe at the bottom of the article.
N.B. FITS and government incentives are not included in these calculation
| Light energy avaiable to you see graphic kWh/m2 per year* | 900 | 1000 | 1100 | 1200 |
| light energy incident on a 8m2 panel * kWh per year | 7200 | 8000 | 8800 | 9600 |
| Light capture efficiency, or Gross efficiency over full area of solar collector | 12% | 12% | 12% | 12% |
| Energy converted to electricity 8m2 collector kWh per year | 864 | 960 | 1056 | 1152 |
| Electrical efficiencies, storage and invertor | 75% | 75% | 75% | 75% |
| Useable electrical energy kWh per year | 648 | 720 | 792 | 864 |
| Equivalent standard rate mains electric price of this energy per year | £ 94 | £ 104 | £ 115 | £ 125 |
| Example 1 Installation Cost (price per kWp) More typical of a small install | £ 6000 | £ 6000 | £ 6000 | £ 6000 |
| Example 1 Payback period (years) | 64 | 57 | 52 | 48 |
| Example 2 Installation Cost (price per kWp) | £ 5000 | £ 5000 | £ 5000 | £ 5000 |
| Example 2 Payback period (years) | 53 | 48 | 44 | 40 |
| Example 3 Installation Cost (price per kWp) | £ 4000 | £ 4000 | £ 4000 | £ 4000 |
| Example 3 Payback period (years) | 43 | 38 | 35 | 32 |
| Example 4 Installation Cost (price per kWp) More typical of a large install | £ 3000 | £ 3000 | £ 3000 | £ 3000 |
| Example 4 Payback period (years) | 32 | 29 | 26 | 24 |
| *The value for the light energy availiable assumes that the panal is optimally inclined at about 38 degrees and is south oriented. | ||||
To determine if a system is financially viable in the UK it is instructive to use the installers own figures, however the installers do not generally state which part of the UK their figures are applicable to, probably Cornwall! So be wary.
The calculations in this article so far do not allow for the Feed-In Tariff (FITs) incentive schemes for renewable energy systems in the UK. They show raw calculations based on the true cost of grid electricity which is being replaced by the renewable energy system. With the FIT's scheme you are essentially paid by the government via electricity companies much more than the electricity is worth, even if you are using what you have generated. With the Feed-In Tariff solar PV looks a lot better, use this website, Energy Savings Trust to get more details and to determine the current rules regulations and eligibility.
If further add-up for shipping, imports duties, VAT, cabling&inverter and labour cost and all other can not be in extreme case more than 80% additional. Further adding margins at 20% it can not be more than double. i.e. German panels can not be more than 2 Euro and Chinese panel 1.6 USD per watt.
So for 1KW (i.e. 1000 watt) system can not cost more than 2000 Euro (1600 GBP) for German & 1600 USD (1000 GBP) for Chinese.
Further efficiency of inverter are in range of 95% to 99% depending on manufacture. In extreme case balance of systems (i.e. excluding panels) efficiency can not be less than 80% (and not 75% as highlighted)
The cost of storage (i.e. batteries) is very high, but not that high also, such that the cost of system can be 3 to 5 times above calculated cost (i.e. it make the cost of 1 KW system in the range of 5500 GBP). Further the use of storage is optional, depends on the applications and size/calculation varies significantly.
I also agree, FITS and subsidies are not sustainable solutions and need to be taken into considerations since it is nearly impossible for any government to sustain such freebies in present economic climate or in long run.
So ROI and payback period is definitely not in the range that has been highlighted over here. Further well balanced systems (irrespective of orientation) can be easily in the range of 5-7 years. Which is not bad, compare to YoY bank interests rate are in range for 7-9% for loan or 3-5% for fixed term deposits.
A main cost is install labour, it is never a trivial expense, get a quote and find out for yourself, I can barely understand any of the rest of your comment
cheers
Richard
Have a look at this link
http://www.navitron.org.uk/forum/index.php?topic=16066.0
Most seem to be quoting about 3 kWh per day on average for a 3ish kWp system. This is entirely consistent with the article above
Your daily average power gen is so much better than most of these. We find that the efficiency difference of solar cell with temperature across the UK is very small sub one percent, and at the very most light conversion efficiencies are 14% for a reasonably priced system.
Sincerely do you have some tips for others??
Also we cannot find an install cost as cheap as you suggest, nearest we can find is £16,000 for 3.5 kWp. But we agree they have come down in prices and we have added a new price to the article £5,500 for 1 kWp.
We keep being told the payback quoted here is too long, but no one provides any evidence. We like facts.
Can you send me some hard facts and a full study on this and I will be happy to do a full case study on this using this data, provided that it is verified and factual. How efficient do you say the cells are?
my data suggests a 3.5kWp system will provide 2268 kWh per year. so if the true number is 3100, based on more efficient cells and with the install cost is £10,000, then yes the article needs to be revised. I look forward to the data.
All the best
Richard
Other discrepancies
1. Solar PV panels are more efficient when colder (20 degree optimum), so although there is less light they are more efficient in the north
2. The EST calculator takes no account of RPI (guaranteed for FITs) or energy price increases over 25 years. A bank would not be allowed to give such misleading figures.
please quantify what you are saying, are your comments based on solar technology or on the feed in tarriff scheme in the United Kingdom. The Feed in tarriff scheme does indeed provide a much better payback time and it probably is about 8-10 years as you say. But it is a market distortion and is likely to be tempory, it pays 5 times (about) the market rate for the green electricity. The article above is based only on the physics of solar cells, invertor efficiency, the sun, your geography installation cost and the standard electricity tarriff. In this context the only thing that can make the above out of date is much more efficient solar cells, from 12% efficient to over 50%. This has not happened.
all the best
Richrad