To make a long story short, think in terms of averages. If you calculate an alternative energy source such as wind or solar to exactly what it appears you will need, chances are it will fall short from time to time. As well there will be a surplus from time to time. Better to have a surplus more often. Espcially if off grid and the load is a critical one.
You state that your wind resources are minimal although its averages are governed by the same factors, I will leave it out and stick primarily to PV.
As I am sure you already know, the output of your power supply, in this case; PV and wind, is an estimate based on averages depending on several factors but suffice it to say, the weather? Each season has its own extremes as far as weather goes. Summer brings more hours of intense solar radiation and heat as Winter brings less with cold. The geographical location and local terrain as well as local flora can have an impact on those averages.
All of these work hand in hand to create what is known as, "The number of hours of equivalent full rated power from a PV module." Its not an uncommon practice to have to, increase the size of a PV array by a certain factor after its size is calculated. Even doubling it in some extremes.
The link below provides, in my opinion, a fair estimate of those number of hours of equivalent full rated power from a PV module when the lowest denominator is used. But its still not an absolute. The exact, intended site most also be taken into consideration as well.
http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/Myself, I like to use no less than a factor of 5 when sizing a battery bank. My figures would have been -
100 watts / 24 volts = 4.17 amps
4.17 amps x 24 hours hrs. = 100 amp hrs.
100 amp hrs. x 5 = 500 amp hrs. (No less!)
(Not that much different than yours so far.)
To replace that with PV -
I would go to that site and choose; "Average", "Annual" and, "Flat Plate Tilted South at Latitude." (Even if I were contemplating the use of a tracker and mppt controller I would use this.)
In my area the lowest number of hours would be 3. So -
2.4 kWhrs. / 3 = 800 PV array (No less!)
Again, since you stated that wind power is minimal I left those figures out. Think of that as an unexpected "wind fall" when the wind does blow.
Site specifics such as but not limited to; mountains, hills, trees, buildings may cause one to increase this by a certain factor.
So, no less than 500 amp hours of battery capacity and 800 watts of PV (in my area) all at 24 volts nominal.
As for wind -
http://rredc.nrel.gov/wind/pubs/atlas/maps.htmlUnfortunately, I live in one of those areas that show, on a yearly average, a big fat 0. Even though we do, from time to time see a signifcant amount of wind, because of; tall trees, local terrain, soil conditions and, the general rule of thumb that states, "the bottom of the swept area of the rotor should be no less than 30 foot above anything within a 500 foot radius' keeps wind from being a cost effective alternatinve for me. I spent those thousands of dollars on more PV instead of a guyed steel tower and tons of concrete.
