From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-x233.google.com (mail-qt0-x233.google.com [IPv6:2607:f8b0:400d:c0d::233]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 6869B3BA8E for ; Tue, 13 Jun 2017 07:52:10 -0400 (EDT) Received: by mail-qt0-x233.google.com with SMTP id w1so167127885qtg.2 for ; Tue, 13 Jun 2017 04:52:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:subject:to:references:message-id:date:user-agent:mime-version :in-reply-to:content-language:content-transfer-encoding; bh=QN7PgxeHI/p19G5Xr7O4yvObjdZNsAmJsvcP661VsUw=; b=J5A0rplPrmo0efMks69HKOChEKbsuiOmtWYlVBqigdD1PByVhLiEYVvSdgKJld9DJj YVZsPxnpgoL5grkQuRQEqb0U409dwRAo4e115HOFpIPRoa733aPpE2qQI51zuhNp4g/l 09LYKHxbgJ6BFdAa4UPz0LqHNE8CWOIwQkODzqZojrBLDsH9z55eLo6fn0ZJwcFli+J+ uBg/sNEfsP1dBR2GsT6MQ38kfjEIXQxjeIT9TnoHKcV/ft7Kmlh0L+Tv8dJmS8E6mS71 /WK0qbwORlDq6gQ8zn1HzWPMMCNHWTHR8CnQeF7Tfol9q7JC021e6ERbEQTfS+UPLxrU qHWQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:subject:to:references:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=QN7PgxeHI/p19G5Xr7O4yvObjdZNsAmJsvcP661VsUw=; b=WOahFY2qRtGQqdI46lAN01eP/Af5PJnw/1cgkxLWTLBNZdphP1ZO5TBNh9uB4iQJAc NzbllQu1XPu2hR3jhj/XH+auPfzfIW2PK41M+QtPGWkS0Pm31/D4hRL0qSYS6JumRLAz VYOJVRELwgbz3N7CQtMhVs8oni0NyJNgEAFKrDCnl7IFOAai74NiLPQiVp/XCwfqFEzN NYDRtTPLTrZEDBHnlCROfchuqWSfeN0Ds4vvclpaCeFRS+wa9sWy+nKOqSS5HNv4EkTC 1CbSfR8pTatiqctf8xWfQfq6juU5V89KrJJwiBmvMIRLLJcmq3JRooqRv8pMLRNjrrSn NuWg== X-Gm-Message-State: AODbwcDk9ftWMYt0nCR1XzhPkqjOhU8R9MgisqKZW/w3KuoS7XdxRiDT nUQ4izA+yAfBeLgd X-Received: by 10.55.53.67 with SMTP id c64mr68087682qka.82.1497354729345; Tue, 13 Jun 2017 04:52:09 -0700 (PDT) Received: from ?IPv6:2601:184:4a80:4c56:385f:d5c1:e959:b4dd? ([2601:184:4a80:4c56:385f:d5c1:e959:b4dd]) by smtp.googlemail.com with ESMTPSA id o49sm9046160qta.34.2017.06.13.04.52.07 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 13 Jun 2017 04:52:07 -0700 (PDT) From: Richard Smith To: cerowrt-devel@lists.bufferbloat.net References: <2d60e776-2a4f-de66-0d2f-a36568562f96@gmail.com> <1496685154.544113991@apps.rackspace.com> Message-ID: Date: Tue, 13 Jun 2017 07:52:06 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Cerowrt-devel] solar wifi ap designs? X-BeenThere: cerowrt-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: Development issues regarding the cerowrt test router project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 13 Jun 2017 11:52:10 -0000 On 06/09/2017 10:02 AM, Dave Taht wrote: > My use case used to be covering hundreds of km in the Nicaraguan > jungle. The prototype for that covers a mere 110 acres in the los > gatos hills, trying to get stuff deep into ravines and so on. > > I have at least a dozen areas where a wifi repeater would be useful, > but I tend to meshy route things, so rather than repeaters, I have > routers. > the ubnt radios I presently use tolerate 6-24v, and eat less than 5w - > so some of the things I've been watching rathole here don't apply. > What I'd hoped for was an "all-in-one unit" much like the wifi camera > that kicked off the thread. I haven't done much of a search in the last 5 years but I've yet to see such a product. I wonder how well the wifi camera stuff actually works measured against availability during minimal-sun periods. Accounting for wost case is always what amplifies the requirements of an off-grid system. NASA Surface meteorology and Solar Energy claims that for Los Gatos December is the lowest output. Given a split-the-middle tilt alignment of 37 degrees it will receive average full-sun net of 3.5 hours. I'll Assume your setup averages at half duty (2.5W) which is 60Wh/day. Using my .7 number for PV system input-output that's minimum of a 25W panel with zero tolerance for low-sun days. NASA has minimum irradiance across n-day periods. For for 1, 3, and 7 day periods in December the minimums are 12, 23, and 42 % of average. I did some spreadsheet numbers for those periods using 30, 40 and 50 W panels. I summarized the results into a table of PV wattage, Min battery, and recovery time. PV wattage is your input wattage, Min battery is the amount of energy storage you need to stay operational during the period, and recovery time is how many days of average output you need to recover the battery back to 100%. Note that this assumes your storage device is 100% efficient. Real batteries would need to be over sized by some % to net out the required energy. 1-day PV Batt Recovery -- ---- -------- 30 50 2 40 47 0.9 50 43 0.55 3-day PV Batt Recovery -- ---- -------- 30 122 5 40 103 2 50 83 1 7-day* PV Batt Recovery -- ---- -------- 30 173 7.5 40 90 2 50 8.5 0.1 * The 7-day numbers are a bit misleading. Any 7-day period could contain a 3-day period. So even though the period math claims that for 50W panel you only have 8.5 Wh of deficit you still need energy storage numbers from the 3-day period to deal with the worst distribution of the worst case. So looks like a 50W panel and a 90ish Wh battery should do pretty good. Unfortunately, this is all average based so it still won't guarantee you stay up 100% but it should be pretty close. Now contrast that with the best month June having 6.8 hours of full-sun and min % of 16, 51 and 59. In the 3-day and 7-day periods the system doesn't go into deficit. 1-day PV Batt Recovery -- ---- -------- 25 39 0.5 30 34 0.33 40 26 0.16 50 17 0.08 Event though the 3 and 7 day periods don't actually go into deficit you still need storage for ~2 days @ the 1-day minimum. The 3 day period could be comprised of 2 really weak days and then 1 great one. So sadly you would still need 70ish Wh of storage. I included 25W to have a item that matched the best recovery in December. If you aren't sizing for worst case and are ok if things stop when it rains for more than 1-day then you can get by with a lot less of a system, but for 95%+ uptimes you need a lot of excess capacity. > So I'm back to building a custom enclosure for edison batteries, a > solar panel hopefully lacking in charge controller, and a nanostation > m5 or rocket m5 as the gear. If you omit the controller you will need to factor in the additional loss of forcing your PV array to operate at a fixed voltage. You can think of PV as a voltage controlled current source. At different voltages it will produce a different amounts of current producing an IV curve. There exists a point on that curve where the voltage * current produces a maximal power output usually denoted in the specs as Vmp. For most "12V" Poly-Si panels Vmp at operating temp is 15-16V. The exact value varies by panel makeup and by operating temperature. If you directly connect the panel up to a battery then you will force it to operate at the battery voltage and thus its power output will be bound to that voltage point on the curve. It certainly makes for a simpler system but depending on the situation the output power reduction of the PV can be significant. The 1.6V charing voltage of a NiFe cell seems to align with a 12V PV panel in that a a 9 cell NiFe would need 14.4V for charge. But the devil is in the details. If say for example your battery can draw more load than your PV can output then there won't be much voltage rise on the battery. A low NiFe battery is 1.2V/cell so say the battery voltage is only 11 or 12V when it starts to charge. Thats going to reduce your PV power output. An MPPT controller can recovery that lost power by keeping the PV voltage at a maximum but that has to be contrasted vs the efficiency of the controller. Depending on the system it may be a wash. MPPT helps in smaller PV setups where the load is much larger than the PV input. In these cases the load will overdraw the panel and pull the voltage way down which decreases the PV output even more. The PV ends up operating way down its power curve. You can have full-sun on the panel and still be no where near the expected output. MPPT can prevent that from happening and keep the panel operating at maximum power. Are you not wanting a controller due to cost and complexity or because you are concerned about conversion efficiency? -- Richard A. Smith