As with any mechanical system, there are a variety of service issues that come up for solar hot water. One of the most common are failed air vents. These devices are prone to failure no matter where in a piping system they are, but the roof is a particularly challenging environment for them. Ostensibly they are installed to let air out when charging the system with glycol, however, with the right equipment and techniques, one can persuade all of the air to come down to the basement. This is why when we address this issue, we simply remove the air vent and put in a plug.
Earlier this month we presented at the monthly meeting of the Western Massachusetts Green Consortium on the topic of solar hot water. In addition reviewing how the technology works, incentives, data-monitoring, and best practices. We also discussed how heat pump hot water heaters and PV inter-relate. In point of fact, we do not always recommend solar hot water for our clients. Occasionally heat pump water heaters make more sense. Sometimes, from an economics stand-point, making no change to the building's current hot water system makes sense. With all the variables one thing remains constant. Solar hot water is the best way to reduce our carbon foot-print. If an additional 3% of homes installed solar hot water, we would annually eliminate 43,500 tons of carbon dioxide from entering our atmosphere.
Evacuated Tube Solar Hot Water System
Our customers Ron and Sandra have a large family, but limited roof space, which made it a challenge to fit a solar hot water system on their roof that would meet their needs. Evacuated tube solar hot water collectors, though more expensive than flat plates, are able to provide more heat per square foot of collector and thus were a good match. Evacuated tubes’ superior collection power is made possible by a vacuum that surrounds the collector in each tube. Similar to a Thermos, the vacuum ensures there is virtually no heat loss once the sun hits it.
Drain Back Design
The solar fluid for all solar hot water systems need to be protected from summer-time over-heating and winter-time freezing. To this end, we chose to implement a drain back design for Ron and Sandra. This means that when the system is off all of the solar fluid automatically falls back into a holding (drain back) tank in the basement, and the air that was in the drain back tank rises up into the collectors. The collectors themselves are designed to withstand the heat that they create.
Smart Hot Water Recirculation
Ron and Sandra enjoyed having hot water come quickly to their faucets because there was a recirculation loop that circulated hot water constantly through the pipes and back to the tank in the basement. Running a recirculation loop all the time, however, uses a lot of fuel and electricity. So we upgraded the system to one which uses a switching mechanism that is simply controlled by momentarily turning any hot water faucet on. The recirculation loop is then activated for a short period of time—enough to flush the cold water out of the lines.
Prior to starting our business we built a super-energy efficient, net zero energy home for Spartan and his family in Greenfield Massachusetts. That home recently won a regional building contest for net zero homes! It is a huge honor to have won and be recognized. In addition to a substantial prize, we had the opportunity to present in Boston at the Northeast Sustainable Energy Association's (NESEA) annual Building Energy conference. NESEA will also be hosting a Pro-Tour at our home on May 1st.
One of our missions has been to help people learn about how to make their buildings more energy efficient and having our home be recognized will help us towards this goal. Also toward this end, we have a blog where we documented the entire-design build process from including temperature, humidity, and energy data logged since spring 2012.
During the inaugural year of our small 4.5 kW PV system (Oct 2013 - Oct 2014) our home generated as surplus of 500 kW. This performance did not come at the cost of comfort: the average indoor winter-time temperature during this time period was 68 degrees F. In addition to creating a high-performance home, we strove to decrease the carbon footprint of created by construction. We reduced high carbon footprint materials like concrete, foam, and drywall. We also used a significant amount of salvaged materials including siding, windows, doors, sinks, cabinets, stone flooring, and foam insulation board.
The Net Zero Energy Building (ZNEB) contest is put on every year by the Northeast Sustainable Energy Association (NESEA). There were six other finalists including entries by the well-known building scientist Marc Rosenbaum and fine-home builder Jamie Wolf.
We thank all of our friends and family for making this project possible. Especially Adam Heintz, our lead carpenter who is also our partner here at Spartan Solar.
As of the beginning of 2015, the rebate for PV (solar electric) has come to an end and is being replaced by a low interest loan program. SREC's and tax credits remain in place.
On the other hand, the rebate for solar hot water (up to $4500 for a residential system) is still in effect. In a private conversation with my contact at the CEC I was told that it is not going away any time soon. In fact, this summer there is going to be additional incentives available through a new REC (renewable energy credit) program. No details are available yet, but it will probably look similar to the Solar PV REC program.
In December we installed an eight panel solar hot water system that provides both potable hot water and space heating for a work shop. Our customer, Dave Cimma, already had a three panel system which he refurbished and had been running for a couple of years. It was time to go big though! In order to eliminate (as much as possible) the electric bill for heating the shop the new system is nearly 4 times the size. It utilizes 8 Heliodyne panels and a 120 gallon Stiebel Eltron tank along with Dave's existing old Sepco tank and domestic hot water system. We had a blast installing it and working with Dave. In part because there are several really exciting elements to this system:
We recently finished this two panel steamback Stiebel Eltron solar hot water system in Easthampton, Massachusetts for Todd and Cheri. Steamback refers to the method by which the solar hot water system is protected from summer time overheating. This method requires no electricity or moving parts to function making it very robust (as opposed to the "old days" where some people had to cover panels during the summer). The system will provide an estimated 80% of their hot water needs saving them hundreds of dollars per year.
We recently finished a 4 panel Stiebel Eltron domestic solar hot water system in Sunderland, Massachusetts. The system is a little larger than usual to compensate for a somewhat shady site. The Stiebel tank is 110 gallons and, using a upper heat exchanger, is backed up by a Buderus propane boiler. Stiebel Eltron makes fantastic tanks--with 33% more insulation than every other tank on the market. We decided to place the panels towards the upper part of the roof to maximize solar gain. In the closeup picture of the controller, you might notice that the collector temperature is at 148--the tank is therefore probably 140!