30*330 = 9900 Watts is the system's size. While, PV's efficiency varies between 8-30. Also, the location's solar radiation is important in the calculations.
Therefore, if they say 8774 kwh, you have no choice but accept it because you do not have efficiency and solar radiation info and panels' area.
1 year equals to 8765 hours. If you want to do some calculation:
8765 h * 30* 330 Watts = 86,773.5 Kwh! in a year.
Where you know that it is not correct because Sunlight is not available 24/7.
Locations radiation is available online you can access but that gives you energy received in a unit area. You can use it to calculate PV output if you have the efficiency and area values.
For Example:
This is data from Ontario, London station using Google Maps (click on a place to get the location) then CLIMWAT(Select stations in a country and extract data) and then CropWat (open extracted data to see graphs, etc.) software.
You can also use HOMER Pro 1 month free trial to do some calculations.
Mj convert to KW using online tools.
Month | Sun | Radiation |
| hours | MJ/m² (per day )
(can be converted to KWh
using online tools) |
January | 2.3 | 5 |
February | 3.4 | 7.7 |
March | 3.9 | 10.9 |
April | 5.7 | 15.8 |
May | 7.3 | 19.8 |
June | 8.3 | 21.9 |
July | 8.7 | 22 |
August | 7.5 | 18.7 |
September | 5.4 | 13.4 |
October | 4.2 | 9.2 |
November | 2.4 | 5.4 |
December | 1.7 | 4.1 |
| | |
Average | 5.1 | 12.8 |
| | |
Thanks again, Mr Eng.
I have been given a copy of the documents provided to the vendor when they proposed the system. It is pretty comprehensive with charts showing the effects of partial shading throughout the day from the neighbouring building, their own house's 'ridge' etc etc, and it was on that basis that they detailed the anticipated generation. Eg there are three panel zones, with one being of 6.6kWp size, a KK (postcode, roof orientation and pitch) of 959 and an SF (shading factor) of 2. This is repeated for the other two zones. From this is they anticipate a total annual Kwh of 8,773.
In addition, the system is signed up for 'Social Energy' and I understand this essentially means that when the home's PV and stored energy capability exceeds the domestic requirement, the energy provider can take that excess energy for the grid. Eg, in this current period of high sun and low use, the battery is almost always fully charged, so they'd anticipate the energy company would pinch some of that excess power during, say, the early morning and tea-time grid demands. In return, when little energy is being produced by the PV system and the domestic energy demand is high - as it would be on cloudy days in cold weather - the energy company will sell it's power at times of low demand at a much cheaper rate. Eg it would charge up the battery overnight at a low cost.
They have estimated that this 'SE' benefit is not far off the main benefit from the actual PV generation; £990 pa for solar-generated savings, and £516pa for the SE-generated savings.
Yes, we need to take these calculated figures on trust to some degree and I know that various elements can affect its performance such as each year's climate and the living conditions of the occupiers. What I am trying to figure out, tho' is if it's possible to anticipate what
additional benefit can be gained by adding a further, say, two batteries, given that the single one fitted is only 4.5kWh, and has been spending these last few weeks in a state of near permanent full charge.
I did phone up the installers - Project Better Solar - to ask them if they could re-run their initial calcs with 2 additional batteries fitted, but they - pitifully - cited 'data protection' as their reason for 'no'. They are happy to do this
after we buy the hoosie...
The vendor did admit that they'd been advised at the time to install more batteries, but their renovation costs had already reached a point where they decided to say 'enough'.
My sis would like to have an idea - before considering making an offer - if an additional outlay of around £6k (for two batteries) should be on the cards.
Basically, assuming the figures given are accurate enough - annual generation of 8,773kWh, PV savings of £990pa, SE savings of £516pa on a single battery - is it possible to estimate the additional benefits of a second or third battery?
Many thanks.