Live webinar “Zero Carbon, Zero Bills” will be at 7pm eastern time Thursday 23rd July 2020. Hosted by the Charles River Green Coalition, part of 350.MA

My next live webinar on how to get paid to cut your carbon footprint will be Thursday, July 23rd 2020 at 7pm Eastern Time. It is hosted by the Charles River Green Coalition. You must register in order to attend this event because that helps reduce the risk of Zoom bombing. You can register here:

What is your family’s carbon footprint from things you buy? Do you buy carbon offsets

  1. In what ways do you cut your non-home carbon footprint, such as that from traveling, driving, products you purchase, etc., if at all?

We minimize the carbon footprint we create before we offset the balance with audited, verified-incremental, carbon offsets that we buy from Cool Effect. I believe that you should cut where you can (e.g., with the fab four) and offset where you can’t. It is neither practical, nor financially justifiable, to cut everything to zero. So , where you can’t cut it makes sense to offset. Offsets are not that expensive. But first, cut…

We are big recyclers. We buy only organic food in the first place. We throw out almost nothing. Any edible waste goes to our chickens. The chickens fertilize our garden making our fruit and vegetable gardens very productive. And they give us eggs and meat. So we eat very well. We are not even close to being self sufficient and do not aspire to being so. But we do love the taste of asparagus in April, rhubarb in May, tomatoes and peas in June, cherries in July, peaches in August, just about everything in September, apples in October and pears even into November. Last October I succeeded in transplanting peppers and tomatoes in pots to be grown indoors (growing under LED grow lights powered by my solar panels) and we were eating them up to Christmas. Anything the chickens won’t eat (onions and citrus for instance) gets composted as does all our paper tissue products. Almost everything else gets recycled and we trash only about a single 50 liter (13 gallon kitchen waste bin’s worth) each week.

I bought a Tesla this year, which I charge from my solar panels and I drive it at 2c per mile compared to my old SUV which cost 10c per mile. The Tesla, when charged by solar panels, has a zero carbon footprint. This covers most of our travel but we still have two gasoline powered cars. When they die they will be replaced with EV’s too.

When we buy things we buy almost always local and sustainable. For examples:

  • for clothing we only buy organic, mostly cotton and almost all grown and sewn in the U.S.
  • for food we buy only organic and usually U.S.-grown only though we do make a few exceptions for some rather excellent Swiss cheese and Italian balsamic vinegar. I used to drink mostly French wine but now drink mostly Californian organic wines. We have visited farms that provide many of our favorite foods like tomatoes grown in Vermont, cheese made on Martha’s Vineyard and blueberries grown in New Jersey.
  • construction products (wood, paints, door hardware and light fixtures) are almost all made in the U.S. including many made in New England. We buy a lot of construction products because we are renovating three properties right now. The wood that will become the flooring in the extension that we are currently building on our house will come from trees that fell down on our land. We had these sawn and they are currently drying out.
  • for cars, our Tesla was made in the U.S., the first American-built car we have ever bought, before this we bought only BMW and Mercedes.
  • we buy almost no gasoline or heating oil and we buy zero electricity as everything is powered by U.S. sunshine. 
  • when we do travel by air (none so far this year, but not by choice) we offset the journey with carbon offsets. Any remaining purchases of gasoline, heating oil, electricity are zeroed out each year as Christmas presents from me to the other family members.
  1. If you purchase carbon offsets, how do you decide where to buy the carbon offsets from? What do you look for when purchasing carbon offsets? What are your purchasing criteria?

I am quite skeptical of the claims of many types of carbon offsets especially those that depend on planting trees in the Amazon. Trees grow really well in the Amazon all on their own. Hence it is hard to say that planting trees is removing more carbon dioxide than nature would remove by herself. I buy my carbon offsets from Cool Effect precisely because they are audited to be incremental. Even then I buy only carbon offsets from a project that captures methane that would otherwise leak into the atmosphere from exposed coal seams on the Ute Indian reservation in Utah. This is genuinely incremental and it is supporting U.S. jobs and Native American tribes. 

  1. If you have purchased carbon offsets, what prompted you to purchase them at the specific moments you’ve made the purchase? How did you decide how many offsets to purchase? With what frequency do you purchase offsets? 

I do it annually to offset any secondary carbon footprint we have from travel. I also offset the carbon footprint of any paperback books I sell (the vast majority are sold as e-books) and any T-shirts I sell in the Zero Carbon business. The T-shirts have the lowest carbon footprint possible because they are made from unbleached, un-dyed organic cotton grown and sewn in the USA. However, I still offset the small carbon footprint they still have.

What if I live in the South? Does HITS work in a hot climate?

The fab four recipe for cutting your carbon footprint will work in the southern half of the country as well as in the northern half.

From the point of view of the laws of physics a house is just a box. It has a top, a bottom and four sides. Energy comes into the box from electricity and heating fuel. Energy goes out through the walls, windows, attic and floor/basement. This is the same whether we call the box a house, an apartment block, an office or a factory.

In a cold climate you need to keep the heat in. In a hot climate you need to keep the heat out. The answer is insulation and triple-glazed low-E windows in both cases. So these parts of HITS (the I and the T) are the same in cold climate or a hot climate.

However, a heat pump (the H in HITS) in cooling mode is the same efficiency as an air-conditioner. It is only in heating mode that a heat pump has four times the efficiency of an oil-fired or natural gas-fired furnace or boiler. So the year-round gain in heating/cooling efficiency is bigger in a cold climate than a hot climate.

Solar panels (the S in HITS) work better in the southern half of the US because there is much more sun there than in the northern half. In fact, where we live in Massachusetts, we have a rather poor solar crop to harvest . The desert southwest has almost 40% more solar energy per year. This makes solar power about 40% cheaper per kilowatt hour in the southwest compared to Massachusetts. See this map from the NREL:

In addition to how much sunshine you have in your area, the price you pay for utility electricity will have a big impact on the payback period for solar panels. High electricity prices make the payback period on solar panels faster, because you are saving more money per kilowatt-hour of electricity generated by your solar panels.

Other than Hawaii, which has very high electricity prices, the highest cost for electricity in the U.S. is in New England, California and Alaska where you will pay about 20c per kilowatt-hour. In a band of states running down the center of the country from North Dakota to Louisiana, electricity is about 10c per kilowatt-hour.

So overall, with insulation and low-E triple-glazed windows cutting your carbon footprint and utility bills across the entire country and with the lower benefit of using heat pumps for heating in the southern half of the country combined with the higher solar production in the southern half of the country, HITS will benefit you no matter where you live. The recipe just needs to be fine tuned to your exact location and local financial subsidies.

Can you put a ground loop for a geothermal system below the basement floor?

Q: For new construction, would it be possible or make sense to put in loops for a ground source heat pump below the structure? 

A: I have not seen this done, but I have thought about it for new construction. Since you are excavating for the basement anyway, why not just go down a few feet more and put in ground loops? I think this would greatly reduce the cost of adding geothermal. However, I do not know if this would reduce the cost enough to compete with air-sourced heat pumps. The downside I can see is that your basement would get colder which could lead to increased condensation in summer when it is humid. 

Will a battery like a Tesla Powerwall last for 3-5 days?

Q: How much can a Tesla power wall store? Will it be enough for 3-5 days in case of an outage?

A: One Tesla Powerwall stores 14kWh of electricity. If you are using fossil fuels for heating then you are probably using about 20kWh a day to run all the lights and appliances in your house. If you are using heat pumps to heat or you are using AC in the summer then you are probably using about double this. Hence it is not practical to use a Powerwall (or any other type of battery) to run your entire house loads. However, this is not how most people use a Powerwall (see my blog post on uses of batteries). Most people use them as an alternative to using a diesel or propane back-up generator. So the battery or generator is powering an emergency panel which is usually the fridge, the furnace burner circuit and the circulating fans or pumps, plus some lights and a few outlets. This is typically under 1kW in total continuous load so a Powerwall can last about a day. This is usually enough to get you through a power outage. To last 3-5 days you would probably need 2 Powerwalls and to reduce the load on your batteries to just the lights, the wifi, a few outlets and the fridge.

Net metering rules are very different in my state.

Q: In Colorado, our grid-tied solar is restricted to 120% of historical kWh usage. Your solar panel system is massive. Is your system restricted in size OR are you actually using that much electricity? Where is most of your electrical usage in your home?

A: Net metering rules (and the subsidy rules, which are different entirely) vary a lot by state and even by town within a state and even then by utility company within a town. In MA, net metering is generous but there are many limits to net metering. Under 10kW you get 100% credit for any power you export. Above 10kW and below 25kW you get only 60% credit for the excess power not 100%. Above 10kW the utility has to approve your system and if there is, say an overloaded transformer on your street, they will not approve it. The SMART subsidy (the MA subsidy for solar power) drops to almost zero above 25kW, but then it goes up if you add a battery or install the array as a canopy over a parking lot. If you install it over a farm field and maintain the agricultural use, it goes up again. So you just have to pick through your local rules and try to optimize financially. In my experience in MA today, the financially optimal array is just under 25kW with battery back up.

My arrays generate slightly more electricity than I use throughout the year. Most of that electricity now goes on our heat pumps because we use almost no heating oil.

Why do you not recommend solar hot-water panels?

Solar photovoltaic panels are sometimes called solar P.V. panels to distinguish them from solar thermal panels, or solar hot-water panels, which use the heat from the sun to directly heat water. Solar thermal panels can be over 70% efficient, which sounds great compared to solar P.V. where the maximum commercially available efficiency is 22%. However, if you are using that solar electricity to power a heat pump hot water tank (please see page 66 in Chapter 2), with its 400% efficiency, you get a total heating efficiency of 84% for the solar P.V. panel that is heating your hot water with a heat pump. This is better than the efficiency of a solar thermal panel. Because of net-metering (please see page 82), solar P.V. panels can generate the electricity in the summer, and you can use it in the winter. This is not possible with solar thermal panels, which generate little hot water in winter, which is right when you need it.  Also, the solar-P.V.-plus-heat-pump-hot-water-tank option has no pipes and hence cannot leak. Better overall efficiency, energy “storage” via net-metering, and no burst pipes make solar P.V., in my opinion, a far better solution than solar thermal panels. 

What is the source of the $20 house-price increase for every $1 in utility bill savings?

Q: Can you link to the DOE study on home value?

You can download it here:

It was published in The Appraisal Journal in October 1998 and authored by Rick Nevin and Gregory Watson

Q: for this DOE study of $20 gained for $1 savings – is that $1 per annum or $1 per month? [Ken Calligar] []

It is $20 for every $1 in annual bill savings.

How long do solar panels and inverters last?

Q: What is the life span of the PV array panels and inverter?

A: The panels are warrantied for 25 years to produce at least about 90% of their initial power production. This varies a bit by manufacturer. They will probably last for many years beyond that. My inverter is warrantied for 15 years but new ones today come with a 25 year warranty. 

What about buying 100% clean energy from my utility? Is that better than solar panels?

Q: Do you still prefer installing solar panels rather than purchasing 100% clean energy from National Grid through suppliers like Eligo Energy. 8.9 cents/Kwh for 6 months. Have you done a financial analysis of paying 9 cents to 14 cents/kwh to receive 100% clean energy from National Grid compared to installing solar panels on roof?

A: I am assuming that the 9c per kWh is the cost of generating the electricity. Utilities charge separately for distributing that electricity, often about 12c in MA. This means that you actually pay about 20-24c per kWh after you add in all the other charges, including the $7 a month they charge you for being a customer. When you add solar panels you eliminate the entire bill (except the $7 a month which is effectively what you pay to maintaining the option of drawing power from the grid which you need it) so your cost drops from 24c/kWh (what I am paying today for Eversource electricity) to between 4c and 11c depending on how much shade you have on your roof and which subsidies you get. So generating your own solar power is far cheaper than even the generating cost of electricity from Eligo, let alone the full cost of that electricity.

If your roof is so shady that solar panels on your roof will generate electricity at more than the full cost of electricity from your utility (21c/kWh in the above example) then buying 100% clean power may make sense for you. However even a half shaded roof (I have one) generates electricity at 11c per kWh which is less than half of what I pay Eversource today.