235 watt panel for battery charge

Re: 235 watt panel for battery charge

How much loads...

10 bulbs * 10 watt * X? hours = ABC Watt*Hours per day.

How many days of "no sun" do you want (typical is 2 days, reasonable range 1-3 days of storage and 50% maximum discharge).

With a single 30 volt Vmp panel, you are looking at a 12 volt battery bank unless you do something "special".

-Bill

Re: 235 watt panel for battery charge

In general, conservation will be your friend.... If these are "security lights", motion detectors will help a lot (and like them better than lights on overnight). And if general lighting, perhaps you can use 1/2 the wattage of LEDs and people will hardly notice (if at all). Our eyes can just perceive around a 2x or 1/2x change in lighting intensity.

• 10 bulbs * 10 watt * 18 hours = 1,800 Watt*Hours per day (not a "small" system).

A healthy system would have a battery sized for 2 days of storage and 50% maximum discharge. Are these going to be 12 volt or 120/230 VAC light? Assuming 12 volt direct:

• 1,800 WH * 1/12 volts * 2 days of storage * 1/0.50 maximum discharge = 600 AH @ 12 volt battery bank

You might get away with 1/2 that size battery bank... Have to look more at the charging details (you need a certain amount of time per day to fully recharge a battery bank... The deeper you discharge, the more time you need--Why a slightly larger battery bank, in this case, may be a help (for longer battery life).

Looking at charge rates for battery bank using 5% to 13% rate of charge:

• 600 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 565 Watt array minimum
• 600 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 1,130 Watt array nominal
• 600 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 1,469 Watt array "cost effective" maximum

Using solar electric handbook, for
Santo Domingo
Average Solar Insolation figures

Measured in kWh/m²/day onto a solar panel set at a 72° angle (18 degrees from horizontal):
(For best year-round performance)

Jan
Feb
Mar
Apr
May
Jun


4.88
5.28
5.65
5.61
5.47
5.68


Jul
Aug
Sep
Oct
Nov
Dec


5.59
5.14
5.11
5.15
4.88
4.74


We see around 4.74 hours minimum. If no generator, use 4.0 hours for a margin of safety:

• 1,800 WH * 1/0.61 DC system eff * 1/4.0 hours of sun minimum = 737 Watt array minimum

So, a single 235 Watt panel is not going to be enough.

Before we pick hardware, your thoughts on my guesses on your power needs and amount of sun?

-Bill

Re: 235 watt panel for battery charge

andersondiaz wrote: »

is 110 AC (according to your knowledge, is better (12 or 24vdc) or (110 or 220 vac))

In general, the higher the base voltage, the farther you can send power... I.e., sending 120 watts of 12 volts is 10 amps of current, and you can only have ~0.5-1.0 volts of drop before the load cuts out/runs too low of voltage.

At 240 VAC (or 230/120/110/etc. whatever is standard for your region), you only have 0.5 amps and can have 7+ volts of drop without any problem. So you can use much thinner wire and send it many times farther than 12 volts.

So--figure out the location of the battery bank (and AC inverter, if used), and then how much power (volts/current) and how far you need to send it... That will help you decided if 12/24 VDC or 110/230 VAC makes more sense.

the LED bulb are 10w, but in the tests only consume 7 watt.
I have another led bulbs 7 watt, and consume only 3W in the tests.

Partially, it depends what is available locally (LED lights that meet your needs). 12 volt are common for RV's, 24 volt units can be found for marine vessels and trucks, and 120/230 VAC for homes.

Also, you can find "interesting" LEDs too... For example some folks here have had good luck with low voltage track lighting lamps (designed for 12 VAC) and running them from DC.

http://www.ledlight.com/12-volt-led-track-lighting.aspx (just an example, I know nothing about vendor or lights)

You always have to be a bit careful... Some lamps may have electronic ballasts and be very efficient and stable lamp output regardless of "bus voltage". Others may have a simple resistor and be sensitive to voltage variations (10.5 to 15.0 volts is a very wide range for many "12 vdc" devices--And they may not be very happy with wide voltage ranges--strobing / overheating / etc.).

And you can get lamps that support almost any standard AC voltage:

http://www.buy-led-bulb.com/10w-cool-white-led-flood-light-outdoor-landscape-lamp-110v-220v-p-79.html

With any LED solution, getting a few lamps from different vendors in varying styles/voltage ratings and doing some testing may be helpful.

Many times, there is no "right or wrong" answer--Just shades of grays.

if the system fails, then I can load it from the electric grid (I do not need more than 1 day in my battery bank). anyway i've another panel, we can do the calculations with two.

In many places in the world, there is a need for a system that can run loads for 4-8 hours on afternoons/evenings due to rolling blackouts. Setup a battery bank and AC battery charger and enough battery/inverter/etc. with an automatic AC transfer switch--Basically a UPS (uninterpretable power supply) that you design to meet your needs.

You can then add solar arrays later, if you wish, to support longer blackouts (hurricanes, etc.) and backup generator (as needed).

Until we "nail" your loads/power needs, it is really not too helpful to focus on the hardware--Although, sometimes you have a given (i.e., 2 solar panels, or ABC Amp*Hours of YZ volt batteries, etc.)... So, we can start with that, and rough out a system and see how much power it can provide.

AC inverters are nominally around 85% efficient--However there is another issue with AC inverters--Just to "turn on" and inverter, they will draw something like 6 watts (for a smaller AC inverter) to 10's of watts (larger AC inverters)... So depending on loads; i.e., running a 10 watt AC lamp on an inverter with 6 watt tare load means a total load of:

6 watts tare + 10 watt lamp*1/0.85 = 17.8 watt total DC load on battery bank

So, in this (dumb) example, just running a single 10 watt 110-240 VAC lamp with a 300 Watt TSW AC inverter on a 12 volt battery bank uses 78% more power because of the AC conversion...

Now, if you had 30*10 watt lamps on the AC inverter, then the losses are much less (as a percentage of "useful load"):

6 watts tare + 300 watts * 1/0.85 inverter eff = 359 Watts from DC battery bank (20% more power needed or a bit less as tare is usually included in 85% eff)

Getting a meter (this AC/DC current clamp DMM from Sears US is "good enough" for testing) or a small DC AH/WH meter like this. Or for measuring AC loads, a 120 VAC or 240 VAC Kill-a-Watt type meter.

Note: Links are examples of what I am suggesting--Most of the vendors/products I know nothing about--Just a starting point for your research.

Sorry to be avoiding "answering" your questions directly. I really want your system to support your needs--And not my guesses of what I think your needs are.

-Bill