Howe to Size a 55KWH daily Capacity system?

Hello Dan,
Good day, i am interested to understand the basics of sizing a system.

I want to make a system that is off the grid during daytime and can be hooked to the grid when needed.( no evening operation - this means i am charging while i am using the system)
i am doing a feasibilty to power up a school:

i tried to calculate using the following but i end up with so much
batteries and panels which i feel that there is something wrong with my
calculations.

daily consumption: 55KWH (all from lights, computers and fan)
questions are:

how many panels do i need if i will use a 220V PV?
how many days back up is reasonable? one? 2 or three days?
50% factor for my battery.
battery size : can you recommend for these sizes of capacity?
what is the best system voltage 12? 48vdc or what and why?
how many batteries do i need?

when they say 5KW system, does it mean that the PV can deliver 5KW of power inclusive of the losses?

i am here in a tropical region of southeast asia so sunshine of 5 hours
is normal.

please help me understand how to size such capacity
respectfully and hoping for your kind sharing!
more power!

Dindo

Tags: PV, capacity, large, system

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Permalink Reply by Dan Kuthy on May 6, 2010 at 12:47pm

Hi Dindo,

Your question is somewhat complicated, but let me help you understand some basics. From there, I'm happy to put you in touch with one of our solar experts to get into the details.

First off, I'd recommend you choose either grid-connected or off-grid. When you install the system you're going to want to connect it to the grid, even if you have battery backup if you intend on using grid-power at any point in the future.

Sizing the system really depends on your needs. Are you trying to offset 100% of the electricity you're using or are you going to always be supplementing with grid-energy?

As far as your questions go, you'll need to determine the number of panels based on a few things:

1. How much roofspace do you have?
2. What's your budget?
3. How much of the electricity has to come from a PV system vs. the grid?

Regarding batteries, your days of backup all depends on the needs of the school and the reliability of the grid. Are there long periods of time where power isn't available via grid?

This is going to be a pretty large system if you're trying to offset 100% of your usage, so you're going to need a lot of very large batteries.

A 5KW system means that in "standard testing conditions," the system will deliver 5kw of power per hour. You're going to experience de-rating as well from the panels, inverter, transmission of electricity via wires, etc.

When is the project scheduled for? What's the budget? We're happy to help you work through all of these problems and design a system that will work for you.

We can't ship internationally, so we'd have you arrange shipping from a North American port city. We can ship to the port city.

Looking forward to working with you,
Dan