Joining the Group!

[radoir]

Hi all,

I joined this forum because I have a few questions that I just can't seem to find a solid answer for, even within this forum. Also, I feel as though I have a fairly solid understanding of renewable energy systems so I'm hoping I can also contribute to this collaboration between solar enthusiasts. It's great to see so many people being proactive and taking large stride towards renewable energy generation.

As for my main inquiry that someone reading this post may be able to answer:

Everything I have read concerning the sizing of PV systems indicates the first thing you do, once you determine your load, is to size your array. This has always left me somewhat baffled because this cannot be true in many cases (in my mind anyway). Lets say for a weekend cottage where the system would only be loaded on Sat and Sun and the odd Fri/Mon holiday. Wouldn't it make more sense to size the battery bank to your load first (with 2-3 days autonomy, max 50% DOD), then determine the array size to be able to charge the battery bank over the days you are not there? So if you needed a 1kW array to meet the daily load and charge the battery bank during daily use, couldn't you charge the batteries over four days with a 250W array as long as you had the required voltage/amperage for the battery bank?

Why size the array to meet a daily load when you don't need to charge the battery bank daily? Could save you at least a little bit of money on PV modules if thats the case.

Hopefully some of you have some insight on this, thanks!

[inetdog]

Hello radoir, and Welcome to Solar Panel Talk!

It is usually best to post specific (or general) questions in specific topics once you have introduced yourself.
The sizing of an array for an intermittent load like you describe is different from the usual full time occupancy, as you suspect.
But the batteries need to be brought back to full charge as soon as possible after discharge for best cycle life.
I would not have a problem designing for recharge in an additional day or two, including what recharging will be done on the days of use.
But planning for a five day recharge would be foolish and risk the health of your batteries.
Note that the array size needed will vary from month to month as the number of sun hours per day changes.
If the site will not be used at all in the winter, you can also scale back the array size based on the summer isolation numbers.