Sizing a Solar Panel System

[Zen83237]

I have been asked to get some estimates for a solar panel and battery system to power lights and fans for a tourist development in Thailand, so no shortage of sunshine. Not allowing for losses and expansion I estimate aload of about 3.4kw. Say I allowed 50% for expansion that gives a load of

5.1kw. How would I now estimate the number and size of panels and battery storage. Seems quite a lot to me so I imagine that there would be a fair number of panels and batteries for storage. I stress that I am not designing this I just want to know what questions to ask suppliers to get the esimates off of them.

Kevin

[Dave Liquorice]

5kW from battery. Ouch. Say 50 lead acid cells at a nominal 2v each that gives you 100v. 5kW at 100v = 50A. Thailand is closeish to the equator so if you want your 5kW through the night you are looking at 50 * 12 = 600A/Hr *minimum*. A 600A/Hr wet lead acid cell I should imagine is a foot or so square and a couple of foor high, you have 50 of these and big hefty copper busbars joining them together.

Then you need to charge the things in the 12hrs of daylight (ha ha) you'll need solar panels capable of supplying the demand *and* charging the batteries so at least 10kW...

How much did you say you had to spend?

[Zen83237]

[Mogga]

Make it an eco development properly and say only power when the sun is shining.

[Dave Liquorice]

Does it have any spare capacity? Though it seems a bit silly to run an engine to generate electricity to drive a motor to drive a pump. Drive the pump directly...

You could use any spare power from it to charge your batteries, it'll be a lot more reliable than the sun.

2300 is late enough for a "lights out" tough, get used to it, approach. Have some small low power solar lighting so you can see to move about but you don't need much more than 1 LED to do that once your night vision developed.

5kW is doable, just rather expensive both for the batteries and the solar panels to charge 'em. The big problem with solar is that it's rather unpredictable, OK you could fit panels that can supply the load and enough charge for the batteries on a bright dawn to dusk sunny day but what about when it's cloudy? How much do you need to factor up the panels to take that into account? 1kW just needs less panels and smaller battery bank...

[meow2222]

The very first thing you need to do when going solar PV is cut consumption to the bone. Why dont you tell us a lot more detail about what youre running. Once this exercise is done its often workable.

NT

[meow2222]

Accounting for dull days is just part of the design process.

While awaiting more details, there is another way to cut costs further: use a smaller capacity battery system that supplies only loads that need 24 hr supply, and put other loads on an invertor run direct from the panels.

This way you get adequate power 24 hrs a day, but can only run the less necessary loads (eg washing machine) when the sun's out.

There are lots of tricks and options.

NT

[RobertL]

if those loads are average loads then my estimate is:

200 square meters of solar panel and 600 big leisure batteries.

You get about 0.1kW per square meter of panel in bright sunshine with the panel perpendicular to the sun.

Assuming you have direct bright sunshine for 1/4 of the day that means you need about: 4*5.1/.1 =3D about 200 square meters of solar paneling.

You need to store n*24 hours worth of electricirty where n ios the longest number of days without sunshine you need to cover. If n=3D5 then Thats 5*5.1*24 kwHr =3D 610 kWHr. A big 12 volt leisure battery will store about 1 kWhr. So you need about 600 Batteries.

Cost? at =A350 per battery and =A3400 per square meter that's =A3110,000.

But maybe "load" meant "peak load" not "average load"....

Robert

[Peter Lynch]

If you do choose the solar route, you will need a generator for days when the sun don't shine (beleive me, there will be some). If you decide to use a generator instead, seriously consider getting a spare one, too. Your primary will need occasional maintenance and will inevitably go wrong at some point, esp. if it's running 24*7. Oh yes, the sort of genny you get at B&Q won't hack it, get proper industrial, long-run, tropicalised kit.

Depending on the profile of the load(s), one solution would be to have batteries feeding an invertor for small/momentary loads and only have the generator fire up for bigger loads, or after the invertor has been running a while. This is a fairly normal configuration.

For solar panels, think about where you can place them so that trees and plants won't obscure the view of the sun at it's lowest point. Don't forget: plants grow. There have also been cases I've heard of in Spain of baddies coming into an area and nicking all the solar panels, think about physical security, too!

Pete

[AJH]

How often does it run? Has it spare capacity to run household electrics and charge a battery when it is running? Can use be made of the waste heat.

Whilst you aren't likely to compete with grid electric from a diesel genset if you have to run one anyway the marginal cost of the extra fuel is still likely to beat PV.

You say 80W per bungalow but for how long, 8hrs? .64kWhr with a 50% depth of discharge looks like about 1.28kWhr storage per bungalow.

AJH

[Dave Liquorice]

But thats at 12v. 5kW at 12v means a current of 416A not exactly that easy to handle... Also you wouldn't be using 12v leisure batteries in this application as they really don't have the capacity required. Think proper batteries:

link to decent sized batteries I could persuade google to cough up.)

Enersol T series with a capacity of 1282A/Hr per cell. As I previously posted to bring the current down to manageable levels you need to have a battery voltage around 100v or more (5kW = 50A, 1282/50 = 25hrs) so at

2v/cell you'd need a bank of 50. Or there is the OPzS series going up to 4600A/Hr.

The 1282A/Hr cell is about 8" square, 21" high and 52kg, the 4600A/Hr one

9" x 23" x 32" high and weighs 217kg (both weights inc acid). Housing these sort of cells requires a proper, well constructed to take the weight, ventilated, battery room, ie acid proof.

[Dave Liquorice]

Two panels about 2' x 5' (700W ish) went walk about up here. Don't under estimate the requirement for physical security of lots of expensive silicon.