[Greenbuilding] Swedish solar-heated village

[Dan Johnson]

It's great to see Nick Pine back on this list. I want to point out for
discussion that the electrical grid has virtually no storage! The grid
follows load and must be balanced nearly instantaneously with dispatchable
generation.

Contributing PV energy to the grid is often part of the problem, because
renewables often need to be curtailed when production exceeds demand. Grid
operators can't taper down the baseload generators every time the wind
picks up. The California ISO site has a lot of current information and I've
found it a great place to learn about the electrical grid. And this is one
of the most progressive operators in terms of their renewables and storage
mandates from the State. http://www.caiso.com/Pages/default.aspx

Bringing this back to solar storage in winter (in California, for example),
when I do morning warm-up or heat during a cloudy day using my electric
heat-pump, the electric grid is running natural-gas-fired generators at an
emissions rate that is dirtier than average. This is because renewables are
generally not online during these periods. Check out this net-demand chart
from Cal ISO: the morning peak of the green line is all fossil fuel, before
solar comes online. http://content.caiso.com/outlook/SP/duck.gif. There may
be less emissions and less fuel burned if I just burned the natural gas at
my house with a condensing appliance, as a backup to my passive systems,
using no storage. The chemical bonds in the natural gas provide the
storage. :-)

Any net surplus of PV from my house would occur when I don't need it to
power a heat-pump or A/C: these are periods when likely other houses don't
need it either. Net consumers would be commercial buildings, hospitals, and
other process loads on the grid. In one scenario, we can ramp-down the
fossil generators during these periods, so **here is where we can argue
that the homeowner's PV could be considered a carbon offset**---but no more
real than Terrapass. http://www.terrapass.com/. In another scenario, the
added power from renewables just lets us bring more loads online---total
load and demand grow over time! This is the opposite of what we wanted.

Returning to grid-scale storage: it seems this is science fiction, like
clean coal. Euan Mearns has some great analysis of experimental pumped
hydro schemes in the Canary Islands.
http://euanmearns.com/el-hierro-another-model-for-a-sustainable-energy-future/.
California conducted a workshop in Jan 2014 on pumped storage and many
presentations from it are here:
http://www.cpuc.ca.gov/PUC/energy/electric/Technical_Workshop_Understanding_Current_State_of_Pumped_Storage.htm.
If 300 high reservoirs were built along the coast, using the ocean as the
low reservoir, the grid could get 572 GWh of storage, almost 1 day of
storage for California!
http://www.cpuc.ca.gov/NR/rdonlyres/1521FE3B-2FB5-4A6A-A93B-45125D6EF895/0/Barnhart20140116CPUCPHSWorkshop.pdf

Best,
Dan Johnson
Albany, CA

On Tue, Nov 17, 2015 at 12:06 PM, Nick Pine <nick_pine at verizon.net> wrote:

> Kimmo writes:
>
> I’m an entrepreneur that is doing research the possibility to use some
>> architecture ideas to heat houses in Sweden similar
>>
> to what Soldiers Grove did back in 1979. We will of-course try to
> modernise the design but the basic concepts are the same
> with the “solar attic”.
>
> Soldier’s Grove attics required moving warm air down to the lower part of
> the building using fans or blowers and a motorized damper, and it’s hard to
> store solar heat from warm air. I figure cloudy days are like coin flips,
> so a building that can store enough heat for 1 cloudy day can be at most
> 50% solar heated, with a possible max 1-2^-N solar heating fraction if it
> can store enough solar heat for N cloudy days in a row, eg 1-2^-5 = 0.97
> with 5 days of storage. Most of the SG buildings were only 50% solar
> heated. Why stop there?
>
> It seems to me that collecting enough heat to warm a building on an
> average day would be simpler with some passive solar heaters built into the
> south wall, eg
> http://www.builditsolar.com/Projects/SpaceHeating/solar_barn_project.htm
>
> Where I live near Philadelphia, PA, 1000 Btu/ft^2 of sun falls on a south
> wall on an average 30 F January day, so a 4 foot x 8 foot vertical south
> air heater with US R2 twinwall polycarbonate glazing with 80% solar
> transmission would gain 0.8x32ft^2x1000 = 25.6K Btu/day. With a 70 F
> building and a T (F) exit air heater temp and a (70+T)/2 average air temp
> inside the heater and a 6-hour solar collection day, the heater would lose
> about 6h((70+T)/2-30)32ft^2/R2 = 48T+480 Btu/day. With a constant C cfm
> airflow, the collector would provide 6C(T-70) Btu/day of heat to the
> building... 2 1 ft^2 vents with one-way plastic film flappers and an H = 8
> foot height difference would make C = 16.6x1ft^2sqrt(8'(T+70)/2-70)) =
> 33.2sqrt(T-70) cfm, and 25.6K = 48T + 480 + 200(T-70)^1.5 makes 543 = T +
> 4.15(T-70)^1.5, ie T = 70+((543-T)/4.15)^(2/3). Plugging in T = 100 on the
> right makes T = 92.4 on the left, then 92.7, then 92.7, with C = 158 cfm
> and a 6x158(92.7-70) = 21.5K Btu/day heat gain for the building, which
> might have just enough thermal mass and insulation and airtightness to cool
> from 70 to 60 F by dawn... 60 = 30+(70-30)e^(-18h/RC) makes RC =
> -18h/ln((60-30)/(70-30)) = 63 hours.
>
> And given the present low cost of PVs and inverters, we might heat the
> building with Mitsubishi or Fujitsu mini-split heat pumps on cloudy days
> (they work with an outdoor air temp down to minus 13 F), powered by PVs,
> using the electrical grid for storage instead of a 5000 gallon hot water
> tank. How many peak watts of PV would be required for space heating alone,
> with a COP of 3? A simulation using hourly EPW weather data could help
> estimate this.
> http://apps1.eere.energy.gov/buildings/energyplus/cfm/weather_data3.cfm/region=6_europe_wmo_region_6/country=SWE/cname=Sweden
>
> Then again, a solar village could have passive solar air heaters on each
> house and a large common underground heat storage tank with a geodesic
> transparent roof and a simple drainback hydronic collector on top of a
> floating insulated cover under the roof.
>
> Nick
>
>
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