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Meeting Nevada’s Renewable Portfolio Standard with solar thermal systems: Solar thermal systems and renewable energy credits.
By: Russ Cartwright
Nevada, as well as many other states in the United Sates, has adopted a Renewable Portfolio Standard for power production within Nevada. This Standard states that 20% of power produced in Nevada must come from renewable energy such as geothermal, solar, biomass, wind and hydro. A minimum of 5% of that power production must come from solar. The way that the Standard is tracked is by monitoring the total amount of power production in Kilowatt-hours (kWh) from conventional power plants and comparing that to the total production of renewable energy power systems. These systems can be renewable energy power plants or systems owned by individual consumers. The tracking mechanism of kWh has an equal value as a Renewable Energy Credit (REC), or also known as Renewable Energy Certificates, Green tags, or Tradable Renewable Certificates.
The reason for writing this article is to briefly compare the cost differences and REC production of solar thermal systems (STS) and solar photovoltaic systems (PVS). I also hope to show the advantages of STS for REC production and begin the conversation of adopting rebates in Nevada for STS.
This is a picture that I use in all my workshops when educating people about solar thermal and photovoltaic systems. It shows an 80 square foot STS on the left and a 440 square foot PVS to the right. Both of these systems produce approximately the same amount of energy on any given day. They do not produce the same type of energy but when the calculations are done to convert one to the other it is the same amount of energy. The STS is measured in British Thermal Units (BTU) and the PVS in measured in Kilowatt-hours (kWh). The approximate cost of a STS of this size is $12,000 and its energy production per day (once converted) is 28 REC. The approximate cost of a PVS of this size is $49,500 and its energy production per day is 28 REC.
It is widely known within the solar industry that solar water heating systems are one of the most cost effective solar systems available. They typically have the ability to store one to two days worth of energy and when installed correctly can have a life span of over 30 years.
Unfortunately most incentive programs and consumers in the US overlook this industry known fact and create incentives and purchase less efficient and more costly photovoltaic systems. Solar thermal is just not glamorous enough but it is a true workhorse in the industry. One of the other advantages of STS is they are well within the budget of most consumers. The only other system type that is less expensive than a STS is a solar hot air heating system. Systems of this type have a starting cost of approximately $3,300 installed. This size and type system has the ability to maintain the heat during winter days (in Northern Nevada) in a conditioned space of 700 to 1,000 square feet.
For a further comparison of costs and REC production: The STS in Northern Nevada pictured below is 460 square feet of evacuated tube solar collectors and is providing solar heat for a 20’ X 40’ seasonal pool, pool house heat, 3500 square foot main house heat as well as domestic hot water heat for the main house. As of Sep. 12, 2008 this system was maintaining the pool temperature at 83 degrees without any other heating source and is designed to provide 70 to 80% of the heating needs for the pool and main house as well as the domestic hot water. The system is being monitored with an Onicon System 2 calibrated BTU metered that converts BTU’s to kWh; the read out on the meter is in kWh.
The cost for this system is approximately $70,000 and in a three day period from 4:30 Sep. 5th to 5:00 Sep. 8th the system produced 500 REC. That is an average of 166 REC per day. A typical 3240 square foot PVS costs approximately $290,000 and produces approximately 177 REC per day. The difference between the above STS and a 36 kWh PVS is 2780 square feet (86%) less space, $220,000 (75%) less cost and 11 REC (6%) less per day production.
My last comparison of a STS is for a year round public pool heating system in Northern Nevada. This system consists of 2750 square feet of flat plate collectors. The system utilizes a Data Industrial Series 150 flow meter and a BacTalk Data acquisition system that yields accurate BTU production. The system monitoring has not been in service for a complete year so REC calculations were used from the Public Utilities Commission office. The average system production per day is 913 REC. The systems cost is estimated to be the same as a 36 kWh PVS is 15% smaller in size and produces 81% more REC.
The STS compared in this article are approximately 75% less expensive, take up 80% less space and produce 82% more REC per square foot than PVS.
Looking at solar as a tool for producing REC and assisting utilities in meeting the required Renewable Portfolio Standard, STS have the ability to meet that Standard with less cost and space than a PVS. From a consumers standpoint, the STS is a much more affordable alternative than a PVS as well as taking up less space for the installation and producing more energy for dollars spent.
To date the Solar Generations program for PVS rebates has installed 290 residential systems for a total of 1,144 kW. The total estimated cost to the individual consumers and the utility ratepayers is $10,296,000. Using the above examples of PVS production the total installed PVS production is an estimated 22,880 REC per day or 8,351,200 per year. Using the above examples and the same dollar amount spent on installing STS, these systems would have produced an estimated 38,896 REC per day or 14,197,040. That is a difference of 5,845,840 (41%) more REC produced per year by STS for the same dollar amount spent on installed systems. The average residential solar thermal domestic hot water system in Northern Nevada sells for $9,000. If the $10,296,000 were spent on installing STS there would have been approximately 1,144 systems installed or 75% more STS than PVS.
According to the Solar Generations team the year 5-rebate program had a 50% attrition rate and the top reasons given for dropping out of the program were system cost and return on investment. With a rebate program for STS equal to the rebate for PVS I believe this would not have been an issue or an excuse to drop out. If I am correct, more consumers would have installed more solar systems which would have made a greater impact on the amount of energy produced/saved/REC generated for the same dollar amount spent and would have gotten more people involved and interested in solar. More people involved and interested in solar should equate to more solar installations and interest.
I hope that this article has showed that STS are worth the effort for the Nevada legislature to mandate a rebate for Nevadan’s that want to purchase STS. I also would anticipate the rebate amount to equal that of the PVS, based on performance in REC of the system and not the cost of the systems. If PVS rebates from the utilities are based on the amount of REC the utility will receive from the system than the rebate amounts should be the same for STS and based on REC produced.
Reference materials, related articles and support: http://www.renewableenergyworld.com/rea/news/story?id=52695http://www.renewableenergyworld.com/rea/news/story?id=51469http://www.retscreen.net/ang/home.php
REC Inspection Notes (M. Harris) PUC 5/09/08 Carson Valley Swim Center
Thanks to Sustainable Energy Solutions for data and continued support.
