Windows, Solar, Tankless Hot Water and Solar Hot Water, So… Tell Me More!
I was at a “meet and greet” dinner party this past weekend in Carrboro to meet some of the families who, like us, have a kindergartener heading off to school this year. Usually, when people find out that we specialize in energy efficiency and solar, we get asked a lot of questions about how it all works and usually a lot of details on the economics of it all. I’m always surprised at how many misconceptions persist regarding certain so called “energy efficient” upgrades and how little is known about solar technology.
So, as promised, I am writing this as a general informative blog on the topic – let me start with some of the most common misconceptions:
- Windows – Replace your windows because they don’t work, you don’t like them, or because you have specific comfort issues. Rarely if ever does it pay to replace windows to save energy. The cost is high and the payback is small. Replacing windows rarely makes sense economically. See other posts on this topic.
- Tankless water heaters save you money, some: They do, but like windows, not enough to justify the substantially higher cost of the system. In very rare circumstances do we recommend tankless water heaters. They typically cost 2-3 times what a standard gas water heater costs and may save you a dozen dollars a year in gas if that. (don’t even dream of putting in an electric tankless). Most also waste a fair amount of water. Since it takes a fixed amount of energy to raise one gallon of water one degree F, whether you do it instantly or you do it over 30mins, you are still using the same amount of energy. Tankless water systems only save you what little heat is lost from the tanks insulation (called stand-by losses) and this amounts to very little with highly insulated modern water tanks.
- Buy solar hot water for one of two reasons: 1) because like buying a hybrid you want to make a contribution to lower carbon emissions and send a signal to others that you are committed to a more sustainable way of living; or 2) because it makes economic sense (or both!). So, let me net out the math on this one, because sometimes, the economics of solar hot water is not there:
- $7,500: Average cost of a straight-forward installation (active pumps and good quality collectors – always try to compare apples to apples)
- - $1,400: NC tax credit (35% capped at $1,400)
- - $2,250: Federal tax credit (30%)
- $3,850: balance or net cost to you. Now say you time this with the replacement of an old water heater (because remember, this system comes with a new tank) you can take off about $1,000 which would be the cost of a replacement tank.
- - $1,000: cost of a replacement tank
- = $2,850: Your net solar hot water cost vs a traditional hot water tank.
A typical family of four will pay $350-$450 per year in hot water costs (electric). If you split the difference and say $400 annual costs, you are looking at a 7 year payback. Said otherwise, after about 7 years, you basically get free hot water for the life of the system, or think of it as every year after the 7th, the sun is paying you for the privilege of heating your water.
Now if you are on gas, the economics of solar water heating is a lot harder, since a gas bill is typically about half to 40% of the electric costs. So to net it out, the technology is very cool, very reliable, very efficient and gives you sweet bragging rights, but you need to get it for the right reasons. The saying in the industry is “heads and beds” – the more hot water you use, the more solar makes sense. The less you use, the less it makes sense. For commercial applications, the economics are just about always great.
- PV or Photovoltaic systems differ from solar hot water in both the efficiency and the technology. Solar hot water systems are about 80% efficient, that is to say, about 80% of the energy from the sun that strikes the solar panel gets converted into heat for water and are are fairly simple systems. You have a solar panel that gets very hot (about 220F- 250F) and with the help of pumps, you run a fluid through it to heat up the water. PV on the other hand is only about 15-18% efficient. That’s why you need so many more panels on your roof to have a real impact. PV uses silicone wafers typically to generate a small current when the sun strikes the panel. With a lot of these little wafers tied together you start to generate measurable power. Tie several panels together and you start to general significant power.
There is a lot of technology and a lot of parts that go into PV systems and so these tend to be expensive, anywhere from $20,000 to 60,000 or more depending on the size of the array, but costs are rapidly coming down as new technologies emerge and competition picks up. PV should always be the last step in your energy efficiency journey. 1) measure what you use 2) reduce what you need 3) produce what you can. If you reduce what you need to offset with PV with more efficient options like air sealing, insulation, duct sealing, more efficient appliances and more efficient lighting choices you can effectively reduce the size and therefore cost of the PV system you need to offset your needs.
I realize that I take these collected facts for granted as we’ve had several years to read about it, take classes, install systems, and understand it all. So, if this all seems a little overwhelming feel free to give us a call, we’d love to help you make sense of all of this. While we certainly hope you’ll decide to work with Sundogs Solutions, we are above all committed to making the world a better place and we feel that by educating the public and our customers, we can have a multiplying effect on our efforts.
