poisondwarf wrote:
Dont forget ....... my plan was initially to power about 750W of equipment for about 5 or 6 hours EVERY night.
Thats a total of, on average, of about 4KW EVERY night.
If I have, lets say 8 x 90Ah batteries, (just as Andy H has) then would they produce nearly 4Kw of power every night?
I have no idea how to do this calculation, maybe some of you can help?
Your usage is measure in kWh, not kW. So, your usage is 0.75*6 (worst case), so that's 4.5 kWh.
To store 4.5kWh, or 4500Wh, in batteries at 12V, you need 4500/12 = 375Ah. But, even assuming you get batteries that are able to cope with a deep discharge, you should only take them down to 80%, or even 50% if you want them to last really well. So lets say 50%, then you need 750Ah of storage. So Andy's set of 8*90Ah will near enough do it.
The next step is to work out how much PV you need to gather the energy. The first thing to remember is that charging and discharging the battery is only about 80% efficient (approx) each way, so lets say 65% efficient. We'll ignore the effect of this on battery capacity, as we've over-specified anyway, but you have to take note for power generation. so we don't need 4.5kWh a day, we need almost 7kWh a day. And we've not allowed for losses in the cabling, inverter, dirty panels, etc. Lets ignore them for now...
In the summer, southern UK might get about 4.5kWh of sunlight per square meter every day. So, (without going into the detail) to get 7 kWh you need PV rated at just over 1.5kWp (kWp = kilowatt-peak).
In the winter, it's another matter, as we might only get 0.5kWh/m2/day of sunlight, and you'd need 14kWp of PV panels.
If you take an annual average of 2.5 kWh/m2/day (at a rough guess), you need 2.8 kWp, which would give you bags of power in the summer, but not as much as you want in the winter.
As a completely random, but reasonable, figure, I've just looked up a 240W panel on ebay for ?700. so if you bought them to get to about 2.8kWp, you'd need to spend about ?8,000. I guess if you were buying from a supplier in bulk you'd get them a bit cheaper though. As you can see, if you wanted to have your 6 hours supply in the winter, you'd need to spend 4 times as much! And there's the cost of the inverter and batteries to add, which would be a good few hundred at least, if not 1 or 2 thousand.
And last of all, all of the above only works if it's sunny every day. If you want capacity to last through a cloudy day, you need to double the battery capacity, and add a fair bit to the PV amount. And if you want to last for several cloudy days...
I hope that's helpful?
I guess you can see why if saving money is the objective, it makes sense to cut demand first, because solar PV is actually very expensive. Which is why I'm watching films on a laptop using 40W!
Of course, if you get a grid-connected system, you can apply for a 50% grant on the panels, but then you wouldn't have your battery system. Not sure about the issues of getting a grid system installed and then hacking it around yourself later...?
poisondwarf wrote:
Multi-crystalline solar panel....Quite efficient for a given area but doesn't perform well on a gloomy day.
Amorphous solar panel.....Performs better than Multi- crystalline panels and MUCH better than the aforesaid panels on a cloudy day.
Mono crystalline solar panel.......Supposed to be better than any other type of solar panel. Performs well for a given area and also performs quite well on a dull day
Finally, I'll clarify this.
- Mono-crystalline are most efficient, followed by multi-crystalline, followed by amorphous (or thin-film, as they're more commonly known).
- However, efficiency is in power per unit area. If you're concerned about power per unit cost, then thin film panels are better.
- Crystalline panels work best with direct sunlight, but still generate power in ambient light. Thin film panels are very good with ambient light, though of course direct sunlight is better still.
- There is some evidence that crystalline panels will last longer than thin film, but I don't know how true this is.
Yes this is sooo true!!!!