onward with the counterpoint
ok, i guess i missed the 3.4kw solar setup, however i thought i read he figured to get 9kw/hrs per day? iirc , this is probably right for an average and maybe that over what? 5 hours per day sunlight?
i understand that i neglected to account for the fact that the hours of incoming power might out generate his hourly needs for that power and as such he needs to have some place to go with it.
it would appear that he cannot conserve, because he is not living there, this tells me that once he is there the hourly useage is likely to go up during the daylight hours, or most certainly could be made to do so via the use of things like washing machine, food prep, entertainment, cleaning etc.
i am betting that if his daily consumption is 25 plus kw/hrs that during the peak hours of the day, he is likely to consume the better part of 2kw per hour, leaving very little to charge a big bank of batteries reliably. and as we all know being able to recharge reliably is more important than covering most loads for most people that are trying to get the most out of their battery banks.
i am still of the opinion, start with a small buffer A bank, and then later as you get your head around just what you have to work with then, buy the B bank....remember the B bank could be another 8 batteries, 16 or whatever multiple you want... if the B battery is then sized to do the job, the A battery could be put in float for emergency work, and only used periodically to keep it from stratifying.
going with a dump load to make hot water makes infinitely more sense in such a system than does buying more batteries, at least to me... we all use domestic hot water and the vast majority will need to pay for that heating... as Chris states electric heating is very efficient, much more so than taking the hard won solar power, controlling it (with its attended losses) charging batteries (more losses), powering an inverter(more losses) to power the load (which has more losses than heating water directly)
if it were me, i would take a hard look at my loads, and determine which are most efficient to power with the proposed system,
things like deep well pumps might well be out of the question and better served by grid power, if only because of the large surge current requirement and the fact the need is very intermittent and short duration. same would go for things like electric cooking appliances, shop equipment like welders and compressors, and other power tools.
removing these loads, leaves us generally with other heavy loads such as airconditioners, electric dryers etc that take a large amount of current, usually 220-240vac and run for extended periods of the day, at least during some portion of the year... these loads too might be better served by the grid, no real sense in sizing a system to cover them especially when talking about the airconditioning system where the need is probably not much more than 1/3 of the year.
now what are we down too? things like refridgeration, lighting, the washing machine, tv, stereo, small appliances in the kitchen, microwave, (ok, its late and i am drawing a blank on other loads).
of these loads generally speaking about half of them are either are used or can be used exclusively during the daylight hours. this leaves us with a handful of reasonable loads to power over the course of a 24hour period.. things like lights, refrigeration, and entertainment come to mind.. these also are the loads most likely to be in use after the sun goes past the panels each day.
just spitballing here, can't sleep, so i am working on getting my head around this question.
i think long before i spent a substantial amount of money on a big battery bank, i would want to prove beyond a reasonable doubt that i really had the excess capacity available to maintain them properly, further i would want to have a very intimate knowledge of my real needs once i lived there full time. i would want to chart my load usage over the 24 hr day, and my power production over the year,
at this point suggesting a large bank just seems like putting the cart before the horse, especially given this is not an offgrid application.
being ongrid means effectively having an extremely large battery bank and inverter system that delivers power at a bargain price compared to what is proposed. if one has this option he might as well exploit it to its best use, this allows one to develop a very efficient alternate system that will compete favorably with the utility company if the loads to be driven are chosen carefully after having monitored them long enough to know which are best supplied by an alternate system.
gww will do as he feels is best for him, the operative word here is "feels". what feels right often is not right, most especially for those that don't have a very good understanding of the subject at hand. i mean no slight to gww in this regard! its a very rare person that knows enough about a subject that is not part of his vocation, to be able to make decisions on instinct (feelings) that turn out to work anywhere near what is hoped.
this is why i suggest moving forward with some level of caution, after all he is going to soon retire, and as such likely will need to get the most out of each and every dollar spent. i guess i want no part in suggesting something that i am not very very sure is going to work, and work well...
from my perspective, what harm will be if i am wrong? he ends up not utilizing some part of the pv power available to him... this is fine as it really does not cost him anything, he has already bought the panels and their lifespan is largely unaffected if they are not fully utilized. the buffer batteries however would be fully utilized, up to the maximum extent that he allows them to be used... so he is out nothing save for lost opportunity which is hard to quantify in dollars just yet.
while he is losing out on opportunity, he has time then to get up close and personal with his real needs and also the real charging capability he has... armed with this info he can then make a good decision as to when and how many extra batteries he might like to buy...
while it might be argued that battery prices are going up everyday, the very real likelihood is that depreciation of a large bank during the same time frame will be more in real dollars than what the eventual price difference might be..
just thinking out loud here
bob g
