4 weeks of batts will do the job... From: Sean Heskett Sent: Wednesday, June 21, 2017 11:13 AM To: [email protected] Subject: Re: [AFMUG] Vendor for super high efficiency (Sunpower,etc) PV panels
When it snows for 4 weeks straight (not kidding) there's no amount of panels and batts that can save you. On Wed, Jun 21, 2017 at 7:27 AM <[email protected]> wrote: 90 kWh/mo load is a 123 watt load. (123*24*30.4) 123 * 20 = 2460 watts My rule of thumb for Utah. Assuming you have 2 weeks of batts that is all you will need. You have 4140 watts of panel. That is 33X. No doubt it will work. Probably produces usable current in moonlight. Certainly overcast power. During a light overcast you get 5% power. If you are 20x load, you are fully powering the load during overcast. Now, in my case, that extra 1680 watts of panel that I would not have installed would have paid for the generator and propane tank. So, 33X in WA and BC, 20X in Utah no generator. 10X in Utah with generator. (and that is cutting it thin). From: Eric Kuhnke Sent: Tuesday, June 20, 2017 9:34 PM To: [email protected] Subject: Re: [AFMUG] Vendor for super high efficiency (Sunpower,etc) PV panels I have to respectfully disagree, in WA and BC the mid winter sunlight hours are even fewer. But 12 x 345W panels tilted at 80 degrees facing directly south will produce far more than enough kWh/mo for a particular type of site's calculated needs, in December and January. Battery voltage monitoring systems are set up and a portable generator can be brought to the site if needed during those two months. Predicted production is about 247kWh a month in December. Load, which is all DC, is below 90 kWh/mo. On Tue, Jun 20, 2017 at 8:29 PM, Sean Heskett <[email protected]> wrote: Totally agree with Chuck on this line of thought. Where we are (NW ColoRADo) there is no amount of panels + batts you can install for Dec & Jan. Propane generator is the only way to keep an off grid site running. YMMV -Sean On Tue, Jun 20, 2017 at 5:17 PM Chuck McCown <[email protected]> wrote: Remote start propane generator is a much better value for sites like this. In the middle of winter have a low voltage relay trigger the generator. Run it just long enough to top the batts. Usually an hour a day is more than enough. Store enough propane to get through the worst of it. From: Eric Kuhnke Sent: Tuesday, June 20, 2017 6:00 PM To: [email protected] Subject: Re: [AFMUG] Vendor for super high efficiency (Sunpower,etc) PV panels I care about efficiency because in some cases space is at a premium. If these were going on the roof of a warehouse/office type building I would agree. But in a place where it is 4x4 access only, and only in summer, there is a scenario where a big ground mount tilted at 80 degrees for off grid will only hold 12 x 72-cell panels (2.0 x 1.0m each). Going any bigger than that for square footage of panels and size of mount will drive up the cost considerably. The site I am building right now has 12 x 345W 72-cell panels, and I am looking at a configuration with 12 x 360W panels for the next one. The goal is the greatest possible kWh production in December and January and additional safety margin for extended periods of cloudy days in mid winter. On Tue, Jun 20, 2017 at 6:58 AM, Chuck McCown <[email protected]> wrote: I use 11 watts per square foot as a rule of thumb. Never wanted efficiency, always wanted low $/watt. From: Eric Kuhnke Sent: Monday, June 19, 2017 6:47 PM To: [email protected] Subject: [AFMUG] Vendor for super high efficiency (Sunpower, etc) PV panels Anyone have a favorite vendor source for >21% efficient PV panels they'd like to share? I'm looking at various commodity 60 and 72-cell modules made with 4.95 to 5.0W high efficiency 156mm monocrystalline cells, but the Sunpower mono stuff is still better in STC watts per square foot. 60-cell x 5W = 300W 72-cell x 5W = 360W Of course, willing to pay somewhat of a price premium....
