Solar power: The numbers lie

A week into my wildly unscientific solar power experiment, I’ve come to mistrust all capability / capacity specifications. 

 

Solar panels. I was told to expect about 1/2 the rated power from even the highest quality solar panels. I’m getting a bit better than that (I’m seeing the 50W Renogy top out around 32W in direct, morning, SoCal winter sunshine).

Battery pack: Capacity. Just like with “normal” portable battery packs, the capacities are overstated vis-a-vis what you can actually expect them to provide in the real world. One reviewer, with instrumentation far in excess of what I have access to, observes 92% of advertised capacity is par for the course. (https://www.californiaskys.com/blog/ebl-voyager-1000-review)

Battery pack: Efficiency. Renogy states in its manual for the battery pack “The charging conversion rate of this power bank is around 80%-90% (the 10%-20% conversion loss is due to the heat generation when power is transferred in batteries and charging cables).” 

That matches my experience. After several days of direct morning sunlight, the DC meter has recorded 240 Wh of power generated. The power bank is showing two solid LEDs and one flashing. If the 266 Wh capacity is actually about 239 Wh, and only ~80% of the 240 Wh generated power is making it into the cells (192 Wh), the power bank should be at about 80%. Two solid and one flashing indicate it's actually charged to somewhere between 50-75%.

Recharging a device from the battery pack will similarly have some inefficiency. The 69.6 Wh battery in the 14" MacBook Pro could require ~87 Wh to fully charge. The 50W panel and battery pack could provide that in a day in an unobstructed location with direct sunlight, but it’d be a bit tight (would need about 3 hours 30 minutes of solid sun generating 32W).

Fortunately, the Apple Silicon devices sip power (streaming 1080p video on YouTube in Firefox in Monterey on low power mode, optimizing for streaming video, was sucking about 7.5W from the onboard battery). But if I was heading off grid for any length of time I’d really want to upgrade to a 100W panel (at least) and a beefier battery pack (“generator”), with at least a 70W USB-C PD supply.

16 hours of use, probably 150 Wh capacity minimum, which a 100W panel should be able to top off in ~3 hours of sunlight. The more generating and storage capacity you have, of course, the better. (Tethering to an iPhone? I don't know what the power draw is, but the 12 Pro has a ~11 Wh battery; factor in a couple of recharges of that. Using a rechargeable Bluetooth keyboard or mouse? Them too. Workspace lighting? Can do a lot with an efficient rechargeable LED lantern, but that adds in, too.

Update. After leaving the panel connected for about a week, I observed power transmission drop to basically zero when the 266 Wh battery pack was full (four solid blue LEDs); the meter had logged 323 Wh, for an overall efficiency of about 82%, more or less what I expected.