"off-grid systems where the loads are enormous," i realize this is not popular now in these days of "solar is so cheap", but i will not work for people who wont conserve or be efficient. as we all know, pv contains lots of embedded energy and to my thinking... having it power waste is simply greenwashing... so the "race to the bottom" will have to happen without my help.
i start every job (on or off grid) with an energy audit. the result is radically lower consumption levels, more conscious customers, a smaller system (so less resource use and less economic investment). this yields a win-win for the customer and planet. with propane/wood powering the water and space heating loads (and sometimes refrigeration), line drying laundry... generally the maximum consumption i see is in the 5 to 6 kWh/day area. around here, with our seasonal precipitation it is nearly impossible to do off grid without generator use in the winter. here again, conservation helps as it reduces the overall load, battery cycling (and wear) and generator use. i realize you were asking about battery cycling, but with lower consumption profiles, this becomes less of an issue. thats my "old school" .02 todd On Friday, August 16, 2013 10:53am, "William Miller" <will...@millersolar.com> said: Friends: We have been receiving a flurry of requests for design of off-grid systems where the loads are enormous, relative to normal off-grid requirements. It is obvious that the size of PV and battery arrays to power these loads is beyond what is practical. We have dubbed these systems Generator/battery with PV assist, or PV assist for short. These systems will cycle batteries multiple times per day. It is my understanding that the extra battery cycels will shorten battery life. Since generator run is expected, we are willing to increase generator run time in order to prolong battery life. The parameters I suggest are an aggressive load start and a very high battery start parameter. This will prevent deep discharge of the battery bank. I know shallow discharge is not the norm, but I don't believe shallow cycling is a problem as long is it as at the top of the voltage window, i.e. the batteries achieve absorption at least once per day. We know a load start ciuld result in an abbreviated run time, curtailing absorption period, but we are assuming there will be a battery votage start at least once per day allowing full absorption. Has anyone else considered these issues, and what conclusions did you make I am looking forward to a spirited discussion as usual. I throuroughlyenjoy and beneift from them, even thought the advice is usually conflilcting. Thanks in advance. William Miller Sent from Finest Planet WebMail.
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