WetEV said:
SageBrush said:
WetEV said:
I don't see any reason to doubt that he sold them. Don't need to understand all the details to sell.
*All* the details, no.
But a half-assed salesperson would ask about PV generation and home consumption in order to size the battery.
In case it is not obvious, PV generation is akin to charging and consumption to range
Batteries are queues for energy.
A larger battery means that less PV generation can supply the same loads. The real trick is finding the minimum total cost.
Need to understand? Get a program that spits out an answer, don't need to understand the calculation, just plug in the numbers and read the result(s).
Well, sometimes. What is often the driving force in off-grid systems is days of autonomy you can meet the demand, usually 3 to a maximum of 10 (when I was designing these systems), and being able to replenish that autonomy given the solar/wind resource before it was next needed would determine the amount of generation required. Cottages and the like used only on weekends could use bigger battery packs and smaller PV arrays, because they had enough time in between demand to recharge for the next demand period, and you can usually cut out a few optional loads with minimal impact if you occasionally come up short. Full-time occupancy is a different matter - you've got to design the system so the PV generates an excess of the daily load, so it can replenish the batteries are while continuing to meet the daily demand after a period of low production.
At the time I was doing this, PV was 7 to 10 times more expensive per Wp than it is now, so we told customers to first spend money on buying the most efficient lights and appliances and, to the extent they were willing to do so, accommodate their activities to the system's needs; doing so was by far the least expensive option, rather than simply throwing money at the problem by buying more PV and batteries. Since the typical off-grid customer was a DIY type who had a strong environmental motivation and a belief that small is beautiful, plus limited funds, almost all of them were willing to make the necessary accommodations - things like waiting to do laundry until the pack was full on a sunny day, paying $2,500 for a refrigerator (that only required the output of 4 panels to run it vice 10-15 for a standard refrigerator), etc.
The economics have shifted considerably since then, most systems are on-grid now, and the typical mainstream customer is far less willing to learn how their system works, maintain it, or make the kinds of accommodations that my early adopter customers would, so system designs need to adapt to mainstream customers' expectations. Exactly the same process is needed to make BEVs mainstream - early adopter behavior and expectations are significantly different.
BTW, we did all our demand and generation calcs by hand or with a calculator, as such programs weren't available at the time. As there were typically far fewer and individually smaller loads, often DC rather than AC, this wasn't a problem. Actually, we encouraged our customers to do those calcs for themselves (but we'd check them over for errors, and make suggestions for options), because the more they knew about how the parts of their system worked together, the less expensive it would be to buy and operate.