Last year we built a house. It was designed to be "net-zero" energy home -- that is, to produce as much energy as it uses.
To do that the builder put in a lot of insulation: about 14 inches of blown-in insulation in the attic, two inches of foam between the studs and the sheathing, and then three inches of closed-cell spray-foam insulation on the inside of the exterior walls to get a good air-tight seal. To make it even more air-tight they used acoustical sealant on all the seams between the studs on the exterior walls.
We have all electrical appliances, including an induction stove top. I always thought gas was the way to cook, but induction really heats things up much faster -- water starts boiling in a minute or two. Induction works with most steel and iron pots and pans, using an intense magnetic field to excite the ferrous molecules in the metal. The cooking surface only heats up because a hot pot is sitting on it.
For heating and cooling we have a heat pump that provides cooling in the summer and heating in the winter, down to 25 degrees. When it gets colder than 25 a small natural gas furnace kicks in.
To produce energy we installed 39 320-watt solar panels on the south-facing roof, for a total of 12kW capacity (the inverter, which converts the DC from the panels to AC for the house and grid, limits output to 10KWh on the sunniest days). In the 14 months since the panels were installed we've generated 17.8 megawatt-hours of electricity.
The electricity that we generate first goes to power our house, to run the heat pump, refrigerator, stove, dishwasher, washing machine, dryer, etc. For that reason we try to do the laundry when the sun is shining. Any power we don't use goes into the grid, and the power company pays us 7 cents a kilowatt-hour for all the power we generate, even if we use it.
For the period from Sep. 1, 2019 to Sep. 1, 2020, we made about $33. And that's including the hookup fees that we pay the gas company for the six months out of the year when we don't use any gas at all.
Those numbers also include the power we use to recharge my wife's plug-in hybrid car. It's a Kia Niro with a 26-mile battery range (and a 500-mile gas range). I scoffed at the battery range at first, but it turns out that the vast majority of the driving she does fits right in that range. She hasn't bought gas since February. True, we drive a lot less than normal with the pandemic, but the tank is still almost full.
The graph below shows the output of our system month-by-month. December and January were, as anticipated, the worst months: the days were short, it was cloudy much of the time, and it snowed several times, covering the panels. But we generated more than a megawatt-hour of electricity in nine out of twelve months, and almost 2 MWh in June and July.
We designed the house specifically for solar -- we have gables on the east and west ends to provide a long south-facing surface for the panels. The house is sited toward the north end of the lot to minimize shading by the trees on the lot to the south. We selected a roof "pitch" (the angle of the roof) to somewhat favor summer power production, since winter days are so short and cloudy. We also placed the garage on the south-east corner to "hide" the panels. If you drove by our house you'd never see them.
So, how much money does rooftop solar save? We generated 17.8 MWh, for which the power company paid us about $1,200. We generated about as much as we used, and the power company charges between 10 and 12 cents a kilowatt hour depending on the season, so we didn't have to pay the power company for almost $2,000 of electricity. The expected lifetime of the panels is 20-25 years, so we should recoup the cost of hardware and installation in a few years and after that the power is essentially free.
Our house is in Minnesota, at 45 degrees latitude, where it can get fairly cold in the winter. Homes in southern states, where it's warmer and they have longer, sunnier winter days, could get by with just a heat pump and could produce more energy than they use.
Furthermore, if every Walmart, Target, Best Buy and Amazon store or warehouse installed solar panels on the big flat roofs of their buildings, these companies could produce more power than they use.
The criticism of solar power is that there's nowhere to store that excess electricity: batteries are expensive, bulky and immobile. But there's something else to do with excess electricity: turn it into hydrogen through the electrolysis of water.
Other countries (including Australia and Germany) are doing exactly this. Hydrogen is used in many industrial processes, but it can also be used as fuel for cars and electricity production with fuel cells.
Hydrogen-based fuel cell cars (like the Toyota Mirai) have had limited success because there aren't a lot of hydrogen filling stations. Also, most hydrogen these days is produced from natural gas, which sort of defeats the purpose.
But when we start getting a lot of energy production from renewables like solar and wind, we'll be able to store the power we get on sunny and windy days as hydrogen, and then use it either as fuel for cars or to generate power at night with fuel cell power plants like this one in South Korea.
Coal-fired power plants are nineteenth dinosaurs on their last legs. Coal companies are going bankrupt left and right and hundreds of coal plants have gone offline in the last decade because they are simply less efficient and more costly that renewables like wind and solar, as well as natural gas turbines.
The entire process of power production from coal is filthy and dangerous, from mining it (where miners die in frequent accidents and get black lung disease), to burning it for power (when it releases particulates, sulfur dioxide and mercury, causing lung disease and poisoning the air and water, and CO2, which causes climate change), to the toxic waste left behind (coal ash, which is kept in big holding ponds that frequently overflow, poisoning ground water, streams and rivers, killing fish and sickening people).
Even if you don't think climate change is happening, or that global warming is somehow "natural," or that air pollution isn't a problem, it's clear that renewables are now simply cheaper than coal, and are getting cheaper every day. It also localizes power production, eliminating the need to ship megatons of coal and oil across the country (avoiding the attendant spills and fires), or build expensive and leak-prone cross-continent pipelines. Combined with hydrogen storage, you just can't beat renewables, especially as more efficient photovoltaic, electrolysis and fuel cell technologies become available.
The electrical grid does need to be upgraded and hardened to facilitate the transfer of power from areas that produce it to the areas that need it. But we've needed that for a long time in any case.
In 2020 California started requiring all new construction to have solar panels where it makes sense (the right sized roof and sun exposure). All states, especially sunny southern states, should have similar mandates, along with subsidies and tax breaks to prevent housing prices from spiking.
Even some oil companies are seeing the light. BP is actively involved with several hydrogen projects, including this one in Australia.
Renewables aren't just the right thing to do: they're now cheaper and more efficient.
No comments:
Post a Comment