[Greenbuilding] Swedish solar-heated village
donlush at uniserve.com
Wed Nov 25 16:08:32 MST 2015
Thanks Dan for a very interesting post. What many of our grid operators need is a greater degree of transparency so as consumers we can act in a responsible manner.
For us in Ontario (Canada not Calif.) you should have a look at the IESO site that shows how our power is being generated on a 5 min by 5 min basis across the province http://www.ieso.ca/Pages/Power-Data/default.aspx as well as the wholesale price of power. Of interest here is that the wholesale price routinely goes negative. That is Ontario routinely generates excess power that it has to pay other jurisdictions such as Michigan and New York state to take. This is a result of contracts Ontario has with generators to buy their power whether it is needed or not. It is also worth looking at the “global adjustment factor” which appears to be a factor applied to guarantee certain payments to power producers although how much for what power is not very transparent. If anyone on the list has a good understanding of exactly how this factor is calculated I and I am sure others would appreciate them sharing it.
Another good site in Ontario to understand the current power mix is http://live.gridwatch.ca/home-page.html. This site allows you to look at what each individual generator is contributing to the grid in real time.
Bottom line is that in Ontario (because of how we generate power (60% + nuclear and 20%+ hydro and the remainder oscillating between gas and wind) using a high SEER electric heat pump is a lot more CHG friendly than any other heating source (other than passive solar).
The other thing to keep in mind when looking at the use of “clean” natural gas is that fugitive gas losses during extraction and transportation (estimated to be close to 2%) influence the GHG contribution of natural gas. It is true that burning natural gas releases only half the CO2 as the coal equivalent. It is also true however, that natural gas/methane (CH4) is 80X as powerful a GHG in the short term as CO2. Do the math and you find that using natural gas is not as GHG friendly as commonly advertised.
From: Greenbuilding [mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of Dan Johnson
Sent: November 25, 2015 3:12 PM
To: Green Building <greenbuilding at lists.bioenergylists.org>
Subject: Re: [Greenbuilding] Swedish solar-heated village
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
On Tue, Nov 17, 2015 at 12:06 PM, Nick Pine <nick_pine at verizon.net <mailto:nick_pine at verizon.net> > wrote:
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.
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