% of annual power supplied.

[jmackle]

I have a south facing garage (40 deg. inc.) - 4m x 2.5m - my meterboard is
on the garage. If I put on 4 no 110w p/v Navitron panels- roughly what percentage
of my annual power would it supply given that my ann. unit usage is about 9600 units?.
Any tips on how to connect them also appreciated(using SunnyBoy inverter.)
The info. supplied is probably insufficiently detailed but I'm only looking
a rough estimate.

[switchoffthelights]

I would say you would only be looking at around 10%

going by what you say you use twice as much power per year as i do !

[Ian]

OK, if you are looking for a ball park only...

4 * 110 watt panels = 440 watts maximum PV power deliverable.

If, on average, there are 8 useable hours of sunlight a day throughout the year, and if, on average, there was enough incident sunlight to excite the panels to 50% of maximum, then you would have the equivalent of 4 hours of "good" panel excitation each day. This equates to 4 * 440 = 1.76 kW hours per day from the PV panels.

In 1 year you therefore get 365 * 1.76 = 642 kW hours of solar power.

You say you use 9600 kw hours per year so the PV panels would provide 642 * 100 / 9600 = 6.7 % of your requirement.

If it was me, I would further derate this to 5% to allow for crud on the panels, inverter inefficency, line losses, etc.


9600 units a year sounds like a lot to me - but not so unreasonable. This would currently cost you around £960 per year in electricity and is equivalent to using about 1 kW constantly 24/7.

If you were to use all of this electricity at night, then no benefit would acrue and you would still use 9600 units from the grid.

Now because you have decided upon 4 x 110 watt panels, using the right inverter is critical.

I will assume that the panels have a Voc of 22 volts, and a Vmax of 17 volts. (I have made this up but I think it is in the right ballpark - it depends on which panels you get your hands on).

Well, there is only ONE SMA Sunny Boy that you can use! It is the low voltage version (SB110LV) and this is also one of the most expensive in £ / watt terms (expect to pay around £1350). This has a minimum input voltage of 23.8 volts and a maximum of 60 volts.

You can only configure your panels for this inverter in one way; 2 strings of 2 panels per string. Each string will give you 44 Voc, and around 34 Vmax. With this sort of configuration, the inverter will not be operating anywhere near its peak efficiency. Efficency curves are available; I have not bothered to look at them for this inverter recently, but I guess you would be lucky to get the inverter working at the 80 - 85% efficiency level.

Again, if it was me, I would be looking at a different inverter. The real pain is that very few of them are G/83 approved so far (if this is important to you).

I hope this helps.

Regards,
Ian

[jmackle]

Thanks for an informative answer Ian - P/V obviously isn't going to be the solution
I thought it might be  - what about the German 240v Panels?

[Ian]

jmackle - I think you mean the German 240 WATT models.

If so, the German 240 watt models (I have not seen personally) will have the same sort of conversion efficiency as other panels (at around 13- 16%) - so to generate 240 watt - they will just be bigger.

I think I now understand your thinking. You are restricted by space. If this is correct, then PV may be for you - but you just need to find more space from somewhere (like your main roof).

If 4 panels can supply 5% of your annual power requirement, then 40 panels can supply 50%. To use 9600 units you have a large house and therefore you probably have the roof or garden space to accommodate these panels - they do not all have to be physically situated close together.

Larger numbers of panels will give you a much better option of inverters.

I hope this helps.

Regards,
Ian