Window Solar Charger - a waste of some perfectly decent panels? - Page 1
Forum section: electronics / general

author: Eldoran
author_rank: Newbie
timestamp: August 05, 2019, 12:07:21 am
content: Got this recommended in a Kickstarer newsletter:https://www.kickstarter.com/projects/krystalpersaud/window-solar-chargerShould be perfectly feasible to manufacture and meet the specs, but what a way to mislead the eco-conscious consumers into thinking they're helping the environment.Will never be mounted at an optimal angle.Will waste generated energy when battery fills up.Won't even charge most phones to full.Has a chance to break after a single drop.Lifespan is limited by the built in battery?Shame it'll end up in a landfill a few years down the line.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 05, 2019, 12:52:53 am
content: The main issue I see is that it's overpriced. For that price, you can get a 100W solar panel from Amazon and have plenty left over for other parts needed for a complete setup. (Despite its shortcomings, it's still a better idea than solar roadways.)To solve the problem of the battery having a limited lifetime, limited capacity, and exposure to heat, put that in its own box and allow the user to add as much as they want. Might as well put the rest of the electronics except the panel itself in that box. Then the panel is just an off the shelf panel and the "magic" is the box that anyone can just plug into it to get some USB and other DC outputs.A possible add on could be a mini grid tie inverter that connects via an AC wall wart, the tricky part is finding a sufficiently low loss AC wall wart in order to not lose all production to losses. Probably better to make that a kit intended for educational purposes.

author: golden_labels
author_rank: Super Contributor
timestamp: August 05, 2019, 01:40:27 am
content: Starting from the easiest part: “Will waste generated energy when battery fills up.” That is not a problem, as this energy would be wasted anyway — sunlight would just warm up the apartment. Which is exactly what will happen with a full battery, just in a more convoluted manner.✔“Lifespan is limited by the built in battery?” — no, the FAQ clearly states “We designed this product to be as modular as possible. […] So if you need to replace the battery after a few years, it's no problem.” So at least this part is ok.✔They provide very little actual technical information, and only in FAQ. A bad sign. Even worse: the campaign page itself is — as expected — full of nothing. They did research on history of solar panels. The result? They learned that the design hasn’t changed since 60 years (quite untrue) and they innovate by… making “beautiful herringbone pattern”, which changes literally nothing except making it look less ugly and thinning your wallet(1). The designer is showing us her portfolio of 6+ years worth of designs… wait, I see none. But at least we learn some information having huge impact on the design: she lives in NYC and her apartment is 300ft². My place is exactly of that size — do I qualify as a designer of the groundbreaking product that will disrupt the market?✘Now let’s see the data. Typical power delivered by sun at my location (Warsaw, PL) on a sunny summer day is 1kW/m² peak(2). That seems consistent with information found on the web, and is also a good estimate of how much energy — at maximum — sun delivers to the target audience of this product. The dimensions of the charger are 10"×13", so ~838.7cm², which is ~8.4% of m². That leaves us with 1000W · 8.4 = 84W reaching the device. Assuming 10–20% efficiency, this leaves us with 8.4–16.8W.✔So it is possible that the maximum output of this module is 10W. But this is when the solar cell is unobstructed and directed at sun at the noon. The device itself is behind a  window, having ground and other buildings in it’s “view” and, most importantly, not directed at sun even if someone has a window pointing to south. More importantly: the sun is not hanging in the same optimal position for 8–10 hours. For huge part of the day there will be no sunlight hitting the panel. So, while I can believe that it can collect the declared 10Wh in a course of a day in a south-pointing window on a sunny day, I would take that as the very optimistic maximum figure. So the advertisement is already greatly misleading. And on top of that conversion/battery losses have to be taken into account.✘How ecological is it? Taking a very rough estimate, which is based on data for much more efficient large-scale panels, 1kWh produced by a solar panel produces 30–70g of CO₂.(3)Since this module is likely to operate on average at 5–20%(4)of its rated output, this becomes 150–1400 g/kWh of CO₂. In US, coal power plants produce 998.4 lbCO₂/MWh(5), that is ~426g/kWh. There are other important factors, like negative CO₂ loss from deforestation, other harmful emissions &c, but CO₂ remains the most important figure.✘I don’t know electricity prices around the world, but here I would not pay $200 for something that would deliver meat best90kWh of energy in its life time. That is $23 from my power company.✘Therefore IMO that is not a scam, but only meeting the declared goals in very favourable conditions. I would prefer to see a 100W panel on the roof, shared by all tennants.____1You pay extra for that special pattern.2Based on aweather station dataon Warsaw University of Technology (full page; the language and a set of displayed charts is unpredictable).3Dustin Mulvaney “Solar Energy Isn’t Always as Green as You Think”, IEEE Spectrum, 2014410Wh collected during 10h in optimal conditions.5“eGRID Summary Tables”, United States Environmental Protection Agency, 2016

author: Domagoj T
author_rank: Frequent Contributor
timestamp: August 05, 2019, 08:15:00 am
content: You can charge your phone from grid for 100 years for the price of this.

author: SiliconWizard
author_rank: Super Contributor
timestamp: August 05, 2019, 03:23:46 pm
content: Quote from: Domagoj T on August 05, 2019, 08:15:00 amAhah, good point. But let's see:let's assume you're fully charging a 3000mAh battery every day (reasonable assumption for many users), which is ~11Wh. Let's assume the charging efficiency is about 80% (reasonable assumption again IMO with most current phone LiPo batteries and chargers, that may actually be a bit worse from mains to battery). Charging would take 13.875Wh/day. Over 100 years, that would add up to ~507kWh.Let's assume an average price for 1kWh of 20 US cents (of course that depends on the country, but I think this is a reasonable average). Total cost: ~101USD.SO yeah, looks like you are in the right ballpark!

author: Mr. Scram
author_rank: Super Contributor
timestamp: August 05, 2019, 03:37:21 pm
content: I thought greenwashing wasn't that fashionable any more. $249 for a solar panel with a cheap frame is definitely a healthy markup.

author: Eldoran
author_rank: Newbie
timestamp: August 05, 2019, 06:13:02 pm
content: Thank you very much for the insightful reply!Quote from: golden_labels on August 05, 2019, 01:40:27 amI'm afraid don't have a great amount of faith in most people being able to replace a battery in a niche product, even if it is modular.You're right about the wasted energy. I suppose what I meant was the wasted potential for energy generation.The CO₂ numbers are interesting. The UK analysis from 2011 that I came across  puts the median even higher, at around 75g CO₂/kWh, but since it's older and improvements in efficiency could have helped. An unfortunate bit of the meta analysis mentions that most studies do not include the end of life recycling into the calculation because of uncertainties about the recycling technology - few installations have been recycled at that point.The rest of the CO₂ value should be based on manufacturing, transportation, installation and maintenance throughout the lifespan of the solar panels. A proper installation should probably run for 20+ years.So, there's a chance that the whole thing will fall and break due to wind or a rogue cat.The user might not be able to replace the battery some years down the line.To maximize efficiency, you'd need the user to consistently use this to charge devices. Charging the phone where you happen to use it or using a proprietary manufacturer issued quick charger can be very convenient.USB standard will probably stick around for a while longer (the track record is good so far), but are we sure we will still have charging ports on phones a few years down the line? Induction charging is already quite popular.It's not a scam, but it is quite wasteful and is likely to distract people from spending their money on effective measures to help the environment.https://www.parliament.uk/documents/post/postpn_383-carbon-footprint-electricity-generation.pdf

author: Mr. Scram
author_rank: Super Contributor
timestamp: August 05, 2019, 06:26:03 pm
content: It's feel good e-waste disguised as a green solution.