Solar lighting system in our school

[Mike90250]

And about halving the 250 W-hr energy, what's that for? PV array inefficiency? Thanks.

It's a rough # for all the losses, PV efficency, battery losses (another 20%) charge controller losses......

[pastmaster02]

It's a rough # for all the losses, PV efficency, battery losses (another 20%) charge controller losses......

Oh I see. How about the losses due to wire resistance? Is it already included or is it another part of the story? How would I know which type of wire, size and length is ideal for our circuit? Is there any formula to calculate that?

[Mike90250]

Oh I see. How about the losses due to wire resistance? Is it already included or is it another part of the story? How would I know which type of wire, size and length is ideal for our circuit? Is there any formula to calculate that?

Wire losses are pretty complex, here's a link to a spreadsheet you can download, and input your system info into, and get a result.

Normal electrical systems allow 5% loss, but with solar, you want no more than 3%

http://www.solar-guppy.com/forum/download/voltage_drop_calculator.zip

[pastmaster02]

Wire losses are pretty complex, here's a link to a spreadsheet you can download, and input your system info into, and get a result.

Normal electrical systems allow 5% loss, but with solar, you want no more than 3%

http://www.solar-guppy.com/forum/dow...calculator.zip

Thanks for the link. I already downloaded it and I'll try it tomorrow.

I'll post my calculations again tomorrow and see if it will work. It's really difficult to engage in solar energy if you're really low on budget. It's quite a heavy investment for us. I just hope that we could get the most out of our available materials. Thanks for your answers and advice. Gonna get some sleep. Tomorrow I'll share to my classmates what I've learned from this forums. Thanks again.

[axis11]

Since its for a school project and you are low on budget, you dont have to make your system designed for 25 years. Just make it last until the end of the semester. You can make panels to last a year at a much reduced cost. You can use second hand batteries,either deep cycle or whatever you can find. You can design the batteries for a deeper discharge, smaller capacity. Over all, you will pass with flying colors at a much reduced price. That's your goal right?

[john p]

Finding the cells to make the panels may be difficult and soldering the tabs if they do find them . Another problem maybe getting a good sealant to even last the year out.

Its hard to give a good answer as to how long your batteries will last. As it will depend a lot on the quality or lack of it on the battery /ies you can buy. Try to get a true deepcycle battery not a "marine" battery.If you are not in or near Manila that may be difficult. only buy "truck " battery/ies if you are really desperate and cant find anything else.. if you buy one of these get the #100 size cost about p4000. they will last if discharged 20% about 3 years and in your case would be more than adequate.

[john p]

One post says you will have shorter sun times in winter ????? Dec and Jan. Well as you know that is not ever going to be the problem. Work on 4 hrs a day all year round. My panels in Visayas putout same every sunny day of the year. Yours will do the same.

Daylight in central Phils is from 4.30 am to 5.30 pm every day of the year. twilight is about 10 mins every day( this is NOT the sun hours for solar panels)
temperature is day 25 to 38 deg C night 18 to 25 deg c

[axis11]

Ebay have lots of cheap grade B cells. I think these students are in a trade school or other electronics course, it wont take them long to solder the cells. There are lots of Dow corning silicon products in the hardware stores.Silicon on the edges of glass-cell-glass arrangement would pass the one year mark. There are ways to keep the acetic acid from corroding the wires. Its a lot easier to buy the panels, but as they say, they are low on budget. I bet these students will share the cost of their project.

[john p]

Axis 11 they may be doing an electronics course but first time soldering cell tabs is not easy. I have seen many that failed almost instantly that were done by people that said they could solder..buying from ebay may be a problem as there will be no one selling them most likely in phils? and they may not have a credit card to do purchasing with. As you would know not many students or teachers have credit cards.
They could use natural cure silicone . its available from places like Ace hardware.

[axis11]

It really is hard to solder the tabs. But im sure they can do it.They should! That's the reason they are in school. There are available cells locally, more than a dollar/watt. Ready made panels, 4+ $/watt.Im sure they can find a way to order the cells online.Anyway, its for them to decide which route to take, the difficult route or the not easy route.

[john p]

They can read here all the ideas offered then make some decission them selves. As in some plases some parts easy to find and others very hard to find even if in western countries easy to buy. That is why its hard to give exact information.

[Mike90250]

A vendor could be approached regarding blems or scratch & dent panels, that could be donated.

STUDENTS - get creative - ask around.

Soldering cells, it's actually pretty demanding, and not likely a place to invest $ and time into. And solder has lead, and lead is BAAADDD! Lead free solder may not stand up to the thermal stresses.

[john p]

Mike its NOT USA they are in.. In Phils if you ask for discount on damaged or blemished item you may get if you very very lucky get 2%.
There if yopu ask price of an item and its 250peso then you ask discount if you buy 50 of that item you might if you lucky get 5 peso off each one..
example I bought a damaged case freezer normal cost 11600 peso got 400 peso off it..
reason... most places only have very small stocks of items and need to sell them at full price or no profit.. believe it or not people there will often accept some damage on a new item.

A vender will not donate even giving you the time of day.(mabe if you offer a cigerette)

[pastmaster02]

Since its for a school project and you are low on budget, you dont have to make your system designed for 25 years. Just make it last until the end of the semester. You can make panels to last a year at a much reduced cost. You can use second hand batteries,either deep cycle or whatever you can find. You can design the batteries for a deeper discharge, smaller capacity. Over all, you will pass with flying colors at a much reduced price. That's your goal right?

Problem is our school director (through our professor) is the one who suggested this project. The purpose of that project it to cut the electric expenses of the school by a little. So even if we left school, it'll still be there for other students to use.

And by the way, I forgot to mention, we're not students in electronics. I know this may not make any sense but we're studying mechanical engineering.

[pastmaster02]

Total load rating: 50 W
Operating time: 4 hours
Total energy consumption: 50 W x 4 hours = 200 W-hrs

Battery capacity: 100 Amp-hr (fixed)
Depth of discharge: 20%

PV Array rating: 100 W peak (fixed)
Sun hours: 4 hours
Total energy produced: 100 W x 4 hours = 400 W-hrs
Energy delivered from panels to battery (at 50% eff. including PV, charge controller, etc) = 400 W-hrs x 0.50 = 200 W-hrs

Solar charge controller capacity: 30 A (is this just enough or overkill?)

##########################
With the above info, do you think our system will run just fine? Some are fixed, meaning we've already bought those components. I've excluded losses from wiring. Probably it will be less because the wire runs are not that long. Or is it? Our catwalk is about the same length as a basketball court. Thank you.