Roof water and electricity

I've been reading Afterburn, by Richard Heinberg, and thinking a lot about disconnecting and sustainability. I'm getting solar panels installed which will apparently be able to generate 100% of my electricity needs. When Elon Musk gets his "Powerwall" battery out, I should be able to store that energy and disconnect from PG&E here in CA. I'm also going to install a solar water heater. As for water, has someone produced a map of the country or a calculator to show how much water I can collect on my (for example) 1200 square foot house in my particular rainfall area? I'm wondering if there are areas in the country where you can passively generate all of your energy and water needs from your roof?

Don Eggleston

Collecting rainfall from a roof happens when solar power is unavailable... Solar electric is currently impaired at my place by thick smoke.

In my climate I get lots of solar energy during the summer. In the winter the panels are sometimes covered with snow or ice which limits their usability.

I get about 9" of rain per year where I'm at... That equals 5.6 gallons per square foot, which would yield 6750 gallons per year from a 1200 square foot roof, or 18 gallons per day. That's enough for drinking and washing, but showers would be rare, and that doesn't irrigate much.

Don Eggleston wrote:As for water, has someone produced a map of the country or a calculator to show how much water I can collect on my (for example) 1200 square foot house in my particular rainfall area?

Indeed they have! Check out the links on this page - awesome rainwater catchment calculator

AFAIK the powerwall stores its energy in hundreds of bog standard 18650 batteries. So no need to wait, go to ebay, buy some batteries and pocket the 400% markup that tesla would get.

I hear Elon Musks powerwall does not work

The reain is easy. Simply go to you Meterological service and add up. The water tank size is even easier, as big as you can afford but probably not under 20.000 litres.

Joe Sylwestrzak wrote:I hear Elon Musks powerwall does not work

Joe, where you hear that? The powerwall is derived from tesla car battery design, which demonstrably works. Do you know which component of the powerwall has the problem?

The actual cells are the easy part. It's the battery management system that monitors every single individual cell status during recharge and discharge that triples and quadruples the total battery life.

Not saying you can't roll your own, but it's not a trivial job to get the cell/battery management done right.

Sure there is some balance charging going on, but I'm not convinced it's every single cell being monitored. My assumption is that cells are in parallel in groups and each group is balance charged and monitored. But one bad cell in that group is going to impact all groups and possibly require the replacement of that group. You could roll your own and incorporate balance chargers. Interesting work abounds on youtube where people have built their own balance charged E-bike batteries for a fifth to a tenth of the off the shelf products. Search 18650 ebike batteries on google. Much of what you see there would be relevant to home based solar storage systems.

The powerwall seems to be rated for more charge cycles than the underlying technology supports. My theory on this is that 1) Tesla don't expect customers in general to come anywhere near to using the claimed amount of cycles, and 2) Tesla has built enough profit margin in to fund multiple maintenance visits to each powerwall during its warranted life in order to switch out underperforming/dead cells.

Another possibility that would impress and surprise me, would be built-in redundant cells/groups of cells that are switched in and out of service as part of the active monitoring and management. I think this would be overkill tho in all but mission critical scenarios eg datacentres or hospitals.

A tesla built system would certainly be safer than a home rolled one, because tesla isolate the cells from each other with a thin barrier of fire resistant material so that a single cell incident is less likely to send the whole pack (and your house) up in smoke.

Personally, instead of spending extra effort on reducing the likelihood of the battery igniting, I'd prefer to spend that effort making sure that we don't die if it does ignite.

I also would like to know more specifics about exactly how sophisticated the tesla battery management system is for the "house sized" batteries.

My guess is they do very sophisticated cell matching and then do not monitor each individual cell, but each string to look for problems.

But as a do it yourself project, it's much harder to match cells to that degree since you don't have tens of thousands (or millions) of cells to choose from.


Alternatively, there are some not super expensive solutions that automatically discharge the highest cells in the string during charging so all cells can be made (pretty dang close) to equal.

Here's one example:

https://experimentalev.wordpress.com/2010/03/07/a-careful-balancing-act/



I just wanted to make clear that it's more complicated than just assembling a pack to make the right voltage and you're done. People could get mislead by just looking at the cell price.

Lot's of resources out there about how to accomplish this.

Only a couple weeks after Tesla unveiled the Powerwall I read a long article about the Powerwall of all things having some problem accepting the charge from PV. The article did not focus much on the actual problem but on the business and financial issues it was going to cause for both Tesla and the many whom have already ordered the Powerwall. The article came from a reliable source and I believe it to be true. On a happier note Im up to 1400 watts of panels and Im adding another 200 watts next week. My elec. bill in down to 20$ a month. Im paying close to 1$ a watt for panels and they will pay themselves off in less than 2 years. I also recently read that a new company is starting to produce clear solar panels just wires attatched to the glass that produce 50 times as much power as reg. panels not only can they be used as windows they can install them on your existing windows= payback in 1-2 years. I love solar LOL.

Interesting post Joe

Joe Sylwestrzak wrote:Only a couple weeks after Tesla unveiled the Powerwall I read a long article about the Powerwall of all things having some problem accepting the charge from PV. The article did not focus much on the actual problem but on the business and financial issues it was going to cause for both Tesla and the many whom have already ordered the Powerwall. The article came from a reliable source and I believe it to be true.

Can you link to this article please, sounds worth a read. Maybe the problem is stepping up from 24 or 48V from the panels to the (from memory) roughly 600V of the powerwall?

Joe Sylwestrzak wrote:I'm paying close to 1$ a watt for panels

Where from? For assembled panels that's a good price especially if you're only buying 200W at a time. I've been quoted just under a Euro per watt but only if buying a small handful of Kw at a time. I'm getting cells under 30c a watt for some experimental DIY panel building but to be honest it's a lot of hassle and the finished products probably won't last long lol. Some nice quality small (1 - 5W) epoxy panels are now coming out of China for under $2 a watt. I've collected various voltages and sizes of these for some planned aquaculture/pond/greywater projects.

Joe Sylwestrzak wrote:clear solar panels just wires attatched to the glass that produce 50 times as much power as reg. panels

I'm sceptical of that one. Mainstream panels are 15-20% efficient at converting incident photons to electrical energy. 50 times better than that would output ten times more energy than input whilst not letting any light thru. Worthy of at least a Nobel Prize for physics.

Steve Farmer I just did a Google search for (Powerwall problem ?) and came up with the article. It is a BloombergBusiness article the 7Kwh model does not charge well from PV and the 10Kwh model is only for outages and only is good for 50 charge cycles per year. They sound like glorified junk. Im buying my solar panels from ebay 120$ for 100 watt panels and 150$ for 150 watt panels both are monocrystaline the 100s come from china the 150s are made in Indiana 200 miles from me. Might seem silly but I bought 4-100s first b4 I found the better deal on the 150s so I am still buying some of each so I can keep my overall array symmetrical. The clear solar panel article was sent to me by my brother who is a corporate attorney and very educated and intelligent. Hope this helps you.

Joe Sylwestrzak wrote:Steve Farmer I just did a Google search for (Powerwall problem ?) and came up with the article. It is a BloombergBusiness article the 7Kwh model does not charge well from PV and the 10Kwh model is only for outages and only is good for 50 charge cycles per year

Went ahead and found the article, here's the link: Bloomberg Tesla Battery Issues With Solar Article

Joe, is that clear solar panel you are talking about the one mentioned in this ExtremeTech article?

This is a very interesting innovation. Instead of a solar cell they call them TSLCs or Transparent Luminescent Solar Collectors. Very interesting.

Scientifically, a transparent solar panel is something of an oxymoron. Solar cells, specifically the photovoltaic kind, make energy by absorbing photons (sunlight) and converting them into electrons (electricity). If a material is transparent, however, by definition it means that all of the light passes through the medium to strike the back of your eye. This is why previous transparent solar cells have actually only been partially transparent — and, to add insult to injury, they usually they cast a colorful shadow too.
To get around this limitation, the Michigan State researchers use a slightly different technique for gathering sunlight. Instead of trying to create a transparent photovoltaic cell (which is nigh impossible), they use a transparent luminescent solar concentrator (TLSC). The TLSC consists of organic salts that absorb specific non-visible wavelengths of ultraviolet and infrared light, which they then luminesce (glow) as another wavelength of infrared light (also non-visible). This emitted infrared light is guided to the edge of plastic, where thin strips of conventional photovoltaic solar cell convert it into electricity. [Research paper: DOI: 10.1002/adom.201400103 – “Near-Infrared Harvesting Transparent Luminescent Solar Concentrators”]

DOI abstract in the quote goes to an article that is seriously cool science. Out of the box thinking for sure.

I'm not sold on the 50x better thing, they are however more than just glass.

Another aspect is the fact that they are using NIR as their source of photonic energy, I'm wondering how the extreme cold of the northern climes will do with that. Obviously hotter places have more NIR from other sources than just sunlight.

All in all, very interesting.

No Bill it is not. The one I read had thin wires in a grid on the inner surface of the glass. Inner surface to protect from the elements and could also be applied to existing windows although some of the language seems familiar. I admit when I read in the article that they were about 2 years from production the switch in my brain flipped LOL to put it on the back burner I read A LOT and my interests are wide and varied. Im also in the middle of a bathroom remodel and shower install. My solar project is somewhat complicated too. My south facing deck is 12.5 x 30 and sun baked so Im building a roof over my deck that lowers and raises the south side to adjust the panel angle and shades my deck and will morph into a solarium in the fall and winter to help heat my home