Installing a Solar Energy System
Like many of you reading this article, I am fairly new to the realization that our future may not turn out the way we originally planned. A little over two years ago, after the financial turmoil set in, I began to wake up from my comfortable, relatively uncomplicated life and take a closer look at what was going on around me.
I was first introduced to the Crash Course by an attendee at the 2009 CPAC Liberty Forum in Washington, DC where I had gone to hear Ron Paul speak. Little did I know how dramatic an impact that one conversation would have on my life. After watching the Crash Course a couple of times, many pieces of the puzzle started to fall together, and I quickly progressed to Stage 4 - Fear. (See The Six Stages of Awareness for more on that topic). A few weeks after I attended Dr. Martenson's Lowesville seminar, I decided it was time to take immediate action. I've also had to deal with the challenges of convincing my partner that these changes were really worthwhile and necessary and that I wasn't a raving lunatic who would soon be wearing a tin foil hat!
I hope reading about the thermal and photovoltaic solar systems we have installed will encourage you to think about actions you can take to prepare for our uncertain future. Since it would be impossible to even begin to give every detail about how the systems work or how to put one together, my goal is to show what can be done, give you things to consider, suggest rough costs, and provide links for further research.
Our House – NOT a Model of Sustainability
I think it is important for you to know the environment and initial problem in order to make sense of some of the design/implementation decisions we have made. We moved into our house in Albuquerque, NM during the housing bubble (before I took the “red pill”, so it seemed like a good idea at the time). After the housing bubble burst, it would have been difficult to sell our house, so moving/downsizing was not really an option. I suspect many people are in the same situation – after all, not everyone can sell their McMansions.
The house is large, with tall ceilings and many large, mostly east/north facing windows. I'm pretty sure the slab is not insulated, or at least not insulated well, and I question the insulation quantity and quality in the walls - basically it's a heating and cooling nightmare (my view, not the utility companies').
The house is heated with hydronic radiant floor heat, and before the solar installation/upgrade, it used a 13-year-old, probably 75% efficient, 280,000 BTU natural gas boiler and a separate 150,000 BTU 100 gallon domestic hot water heater. Our gas usage ran about 2 Therms/day during the summer (domestic hot water, cooking, clothes dryer) and 14 Therms/day in the winter. Yes, this caused us major heart attacks with each winter utility bill.
Cooling is provided by three large evaporative coolers (very energy-efficient, compared to refrigerated air). We also have a roughly 600+' well as our water supply, which contributes considerably to our electric usage (generates about 165 gallons per kWh). Our electric bill averages about 45 kWh/day in winter (lighting, water, electronics) and 65kWh/day in summer (cooling, increased water usage).
While the systems we installed are large by most residential standards, all of the components described are scalable to any size home and should be fairly scalable pricewise as well.
After performing the Crash Course Self-Assessment, I realized how precarious our situation was in regards to energy availability and energy prices. I was also very concerned that a SHTF event could occur at any time, so I placed a high value of getting to a “self reliant” -- not necessarily long-term sustainable -- posture as quickly as possible. Fortunately, we live in New Mexico, with a fairly mild climate and lots of sunshine. I began with the standard Internet research and called some of the local solar vendors. Everyone said that the first step is to take the time to begin by reducing your usage.
For electricity, this primarily means replacing incandescent lights with CFL's and replacing old appliances. Unfortunately, our house is almost entirely lit by halogen recessed lighting cans, and nearly all of them are on dimmer switches, which are not compatible with CFL's. LED lights may be an option in the near future, but they are just now becoming a reasonable option (light quality/quantity, dimmable, price).
For heating, this means replacing older inefficient heating systems (boiler) and insulating. Again, this was a significant problem with our house. Because of the large uninsulated slab and large window area, any inexpensive improvements beyond basic weatherproofing will not significantly lower our heating requirements. We also have a flat roof, which means no attic to insulate. On top of that, our interior walls are all plaster, so adding insulation to the walls is a very expensive option.
This all lead to one conclusion – if you live in a relatively modern home (less than 30 years old), it is unlikely that you will be able to significantly reduce your usage easily. It may be that the incremental cost of a larger solar installation will be less expensive than usage-reduction improvements you can make. If this is the case, and if you have the financial resources available, you are probably better off building a system larger than you need and working on reducing usage later. Any excess capacity (particularly electricity) will most likely be a useful thing to have in the future (electric car, excess to sell, etc).
I believe that we are highly unlikely to have a crisis where there would be a complete breakdown of society and we would become agrarian overnight (the Mad Max scenario). But I do suspect that we will have dramatically rising prices and brief (week long?) disruptions to electricity and other energy supplies in the US. The US still has a fair amount of oil and other resources, and when it becomes generally apparent that the current situation is unsustainable, prices will rise, forcing a reassessment of what is important (food, shelter) over what is luxury. I believe, as Chris Martenson does, that we will suffer successive shocks and then adjust to a new lower normal as a society.
With this assessment, I don't believe it is necessary to build a 100% off-grid-type house, which can get very expensive. Here in New Mexico, we have mostly sunny weather, but on occasion we can have 3-4 days with heavy overcast skies. Building a system to handle those situations would require massive storage tanks for heating and huge battery systems or alternative generation system (along with a fuel source). Instead, we took the approach that would support producing most of our energy in “good” conditions relying on the grid for those non-sunny days, and in rare cases producing minimal required amounts for the times when solar and grid are not available.
Thermal Solar System
Thermal solar systems use collectors to capture and use heat directly from the sun, as opposed to photovoltaic systems (PV), which convert sunlight into electricity. There are many types of thermal solar systems, both passive (no mechanical components– built into design of building) and active. Some use the heat immediately, such as with inexpensive solar-air based collectors, while others store the heat for later use.
Our System – Design & Theory of Operation
Our thermal solar system is a closed-loop, pressurized, hydronic solar-assisted heating system (that's a mouthful), which provides space heating and domestic hot water. It is “assisted” in that during cold winter months and on cloudy days a natural gas boiler is used as backup. The system is designed to reduce our space heating and domestic hot water natural gas usage by around 60%.
A closed-loop, pressurized system uses a heating fluid, in our case glycol, which is circulated through the solar collectors and to a heat exchanger. The glycol is always present in the collectors, as opposed to open systems, which use a “drain back” system, where at night the solution is gravity-drained from the collectors to prevent freezing. A solar PV panel is used to run DC pumps, which keep fluid circulating in the collectors whenever sunlight is hitting them, which helps to prevent overheating from stagnant fluid in the collectors. Glycol is only used in the collector loop; the rest of the system uses water. When heat is available at the heat exchanger and needed by the system, the pump is turned on, circulating water from the cold side of the manifold through the solar heat exchanger and the warmed water back to the manifold.
In the center of the diagram is a Caleffi Manifold that accepts hot water inputs from the boiler and solar collector heat exchanger, and then distributes heat as needed to the tank heat exchanger for domestic hot water or out to the floors for radiant heating. The manifold allows the pumps to operate independently of each other at different rates and pressures. When heat is called for, to either heat the tank for domestic hot water or the radiant floor heating system, the appropriate pump is turned on. If the water in the manifold is not hot enough, the boiler can be turned on and the pump enabled to raise the temperature in the manifold.
Our system only uses the storage tank for domestic hot water; it is not used as a storage medium for household heating. We can do this because we have radiant floor heat and can use the concrete mass of the house as our storage medium. During the day, when solar heat is available, it is pumped into the slab, then at night the slab radiates the heat into the house. Since heat is added during the day, it means late afternoon and early evening are when the heat is mostly radiated out into the house. The system uses multi-stage thermostats, which allow it to heat the house more with solar energy (free) than it does with natural gas, and it allows us to determine our “trade off” tolerance between “cheap” and “stable heat.”
In a system without radiant floors, storage tanks similar to the domestic hot water tank (only larger) could be used to hold heated fluid, which could then be circulated back to the manifold when needed for use in other heating systems (radiant, forced air, etc). It is also possible to add storage tanks to a system such as ours for storage of excess heat to be used on cloudy days (a potential off-grid solution).
The Heating System Conversion – Installation of Solar-Assisted Heating
Conceptually, the conversion was very simple. Remove the existing boiler and conventional water heater and install a new high efficiency boiler, a hot water storage tank, manifold, and pumps, and the solar collectors on the roof.
The first major component was the replacement of the old natural gas boiler with a new high-efficiency boiler. A Triangle Tube Prestige Solo 250 (250,000 BTU/hr) boiler was installed. Compared to the old boiler, it is a marvel of technology. It can modulate the burner based on input water temperature, outside air temperature, and use (Domestic Hot Water or Floor Heating), versus the old boiler, which was either on or off. It is also about ¼ the size of the old boiler. Just changing the boiler probably provided a 15-20% reduction in gas usage.
Next, the old traditional 100 gallon water heater was removed and replaced with a Triangle Tube Smart Series Indirect Fired 120 gallon Water Heater. It is a large, heavily-insulated stainless-steel storage tank with an integrated heat exchanger. A hot water source (the newly installed boiler or solar) is used to heat the domestic hot water supply via the heat exchanger so that the heating fluid and the domestic hot water never mix. I suspect just making the change from the traditional water heater to this setup using the new boiler also made a considerable improvement in our energy usage.
Below is a picture of the utility closet after the system was installed. You can see the boiler on left with the yellow energy usage sticker. On the right is the 120 gallon storage tank, and in the center is the distribution manifold. The rest of the plumbing consists of mixing valves, pressure relief tanks, and zone valves; out of the picture is the heat exchanger used to collect the heat from the solar panels for the manifold.
One of the things that surprised me was the small size of the heat exchanger for the solar collectors. For some reason I was expecting a large device, but here is a picture of ours with a ruler next to it.
There are 13 SS-40 4'x10' flat plate collectors from Solar Skies mounted on our roof, some which can be seen in this picture along with two small PV panels that power the DC circulation pumps.
The panels work by circulating a glycol solution slowly through small copper pipes with fins attached to them that transfer the heat collected to the solution. The panels are placed at a very steep angle (75 degrees) so that they collect a lot of heat in the winter months, but much less in the summer months since it is not needed then. Excess heat would have to be dissipated once the domestic hot water tank reaches its maximum temperature (190 degrees). If this occurs, the system will dump heat into the slab as needed (clearly not desirable in the summer). This is generally not much of an issue if the system is appropriately sized. Of course, if you happen to have a pool, this is much less of an issue since a pool/spa can be used as a heat sink.
We are currently beta testers for a new device called a SLIC from Solar Logic. It is a computer-based control system for a solar-assisted heating system. It replaces the relay and traditional thermostat controls normally used with an entirely software-controlled system. It allows for much finer-grained control over the system, as well as much better monitoring of its performance. Some of the features include:
Dashboard – viewing room temperatures, thermostat settings, valve/pump status from your computer
Data Logging – logging of settings and actions for performance analysis
Operational Changes – monitoring water fluid temperature changes, when the boiler is used versus solar, etc.
Another unique feature of the system is the ability to reverse the flow of the system at night in the summer to pull heat from the slab (floors) and radiate it through the collectors as auxiliary cooling. I'm pretty sure this only works in climates with low humidity where there is a substantial temperature differential from day to night.
The designers of our system say a good rule of thumb is that each 4'x10' collector is approximately equal to ½ gal of propane per sunny day here in Albuquerque. That means with 76% sunny days, we should have about 4.5 Therms/day on average reduction in our natural gas usage:
76% * ½ g. propane * .92 T / g. propane * 13 collectors = 4.5 Therms
From an actual gas usage perspective, at our current usage we will need about 125 Therms of natural gas in the month of November, which is considerably lower than the last several years, in which our November average was 303 Therms. This represents about a 60% reduction, which is slightly better than the anticipated collector output calculated above. However, all of this is extremely difficult to measure mathematically, since our heating needs can be highly variable depending on the weather. I suspect we will need several full years of data to be able to accurately assess the system.
From a subjective view, the system seems to be performing well. I can watch the dashboard on my computer during the day and see that from about 9am until 4pm, the system is generating 150+ degree water and it is being put into the floors and domestic hot water tank. I generally see the room temperatures begin around 65 degrees in the morning and heat to about 72 before the solar cuts off. Then the rooms seem to coast until about 1am, when they begin to cool. This matches up well with the times when most of the rooms are actually occupied.
Because we can specify which rooms to heat with boiler and which rooms to only use solar, I think we are keeping the house considerably warmer overall than we have in past years. I'm happy with the system and the peace of mind it gives knowing that we have some heat even if natural gas becomes unavailable or prohibitively expensive. It allows me to sleep much better at night.
Cost, Incentives, and ROI
Okay, so now we get to the nuts and bolts. We paid to have the system professionally designed and installed. The total pretax credit price was $62K. $55K of that was solar, and the rest for the boiler. In New Mexico, there is currently no gross receipts tax (sales tax) on solar installations (parts and labor). So that price included about $3300 worth of savings on $55K of the system.
Incentives and tax credits reduce this amount considerably:
Federal – Residential Energy Efficiency Tax Credit – 30% on boiler, $1500 limit: -$1,500
Federal - Residential Renewable Energy Tax Credit – 30% on solar, no limit = -$16,500
New Mexico - Solar Market Development Tax Credit - 10% on solar, $9000 limit = -$5500
All the credits bring the final price down to $38,500.
When I first begin analyzing our usage in 2008, natural gas prices were averaging $1.28/T. There has been a large drop in price over the last couple years, reaching a low of $0.37/T in summer of 2009. The price has been gradually rising, with the current price in November 2010 being $0.53/T. It would be difficult to cost-justify the system if natural gas prices remain low. However, at the $1.28/T price the ROI works out to be about 3.5% over an assumed 20-year life of the system.
If you are a DIY type and have the skills and time to do so, you can save some on the labor costs, which were roughly 30% on our project. Here is the approximate pre-tax credit cost breakdown for the high cost materials:
Photovoltaic (PV - Electricity)
Photovoltaic systems convert sunlight directly into DC (direct current) electricity. That DC power can then be converted to AC (alternating current) using a device called an inverter. AC current is the form of power you receive from your electric utility company via the electrical grid.
Photovoltaic systems come in three primary flavors:
- Grid-tied – This is the primary type of installations you see going up in neighborhoods around the country and now makes up about 70% of the solar PV market. Grid tied systems will reduce your energy costs but do not provide resilience against power outages. In a grid tied system if the power grid goes down, then the PV arrays becomes an art sculpture.
- Off-grid – Generally deployed by people living in places where conventional grid power is not available or it would be extremely expensive to run power lines. Off grid systems have batteries and often alternative generation capabilities (such as propane generators). Off grid systems can be extremely expensive depending on required power reliability.
- Grid-tied w/battery backup – In this type of system, the grid is assumed to be available most of the time with batteries and potentially alternative generation capability built into the system to add resilience against grid failure. This capability can add significant cost depending on the duration and power required during off grid operation.
Systems with batteries (grid tied, grid tied w/battery backup) come in two flavors:
- DC-coupled – This is the most common and traditional method for attaching batteries to a PV system. In a DC-coupled system the batteries are generally charged with the DC current generated by the PV array with the use of charging controllers. Power from the batteries is then used by an inverter to generate AC current for household use. Most off-grid solutions are DC-coupled.
- AC-coupled – In an AC-coupled system, the PV arrays are connected directly to an inverter, which generates AC power (same as a grid-tied system) and batteries are attached to a separate inverter/charger, which can take AC power and charge the batteries or pull power from the batteries to generate AC power when the grid and/or PV inverters are not supplying enough power. One advantage to an AC-coupled battery solution is it can be retrofitted onto many existing grid-tied systems.
DC-coupled systems are designed to maximize the efficiency of battery charging, while AC-coupled systems are designed to maximize AC power delivered. If you are likely to use the batteries on a regular basis and will power a significant amount of your load without the grid available, then a DC-coupled system will likely be the best solution. If, however, you are expecting the grid to be available most of the time, then an AC-coupled solution may be best. Here is a blog article that discusses the tradeoffs between AC and DC coupled systems.
Any grid-tied system (any consumer generation capability – not just solar) is required to disconnect from the grid (intentional islanding) or shut down (anti-islanding protection) if the grid goes down. First, this is a safety issue, as the utility workers do not want small generation systems energizing the lines while they are trying to make repairs. Second, it's a load issue. A small consumer generation system is not going to be generating enough power to run all of the neighbors' equipment. This will cause an unmanageable load to the customer generation equipment, possibly causing damage. Before authorizing start-up of a PV system (customer generation facility), the utility company will test that the islanding protection performs as expected.
In the US, all grid-tied systems have the ability to be net metered (required by law). Net metering permits the consumer to feed power back to the electrical grid, offsetting their consumption. In a grid-tied PV system, the consumer typically generates more power than they use during the day and the meter spins backwards, then at night when the PV system is not generating power, the meter spins forward. At the end of the billing cycle, the consumer will pay for the “net” energy they consumed. If they generated more than they consumed, the utility will either credit them for future use, or pay them for the excess they contributed to the grid (generally at a lower-than-retail rate).
New Technology – Micro-Inverters
In traditional PV systems, multiple panels are connected together serially into a string, which is then connected to the inverter. The number and type of panels must be properly configured for the inverter to produce optimum power, and this requires a fair amount of expertise. One down side of the string configuration is that the string only performs as well as the worst panel. If a panel is shaded (even a minor amount), its performance can drop substantially, affecting the whole string.
There is a relatively new technology in the field of PV called a micro-inverter. Instead of connecting multiple panels in string to a central inverter, each panel is connected to its own inverter (generally attached to the back of the panel). There are some significant advantages to using micro-inverters, and a few downsides:
- Minimal expertise required compared to traditional string/inverter configurations. Much easier for the DIY market.
- Output from one panel not impacted by performance of other panels. In installations where shading is possible during part of the day, the performance of the system as a whole will not be impacted nearly as much as in a traditional inverter configuration.
- Ability to grow a system one panel at a time. In the central inverter, generally 7-15 panels must be connected to a string, thus requiring growth in larger increments.
- Since each panel has its own inverter, it removes the single point of failure with a central inverter.
- Cannot be used in DC-coupled systems, since DC power from the panel is immediately converted to AC. This limits their use in off-grid systems.
- Generally more expensive than a central inverter for medium to large systems.
- Since each panel has its own inverter, there are many more parts that can potentially fail.
- Unproven long-term reliability.
- Current systems on the market require a subscription service for monitoring.
Racking – Roof Mount, Ground Mount, Pole Mount, Trackers – Oh My!
There are many choices when it comes to mounting solar panels. Generally a roof or ground mount solution will be the least expensive. If you have the space and few obstacles on your roof that would shade the panels, that is probably the preferred mounting method. They are out of the way and less prone to shading and vandalism or theft. Ground mounts are often easiest for the DIY market since they do not require potential roof-damaging penetrations, work on a ladder, etc. Most ground and roof mounts are fixed at a set angle and require little maintenance other than an occasional cleaning once installed.
Pole mounts can be used where ground mounts are not desired due to potential shading considerations. They tend to be more expensive because they can require large amounts of concrete to keep the giant solar array from blowing away in strong wind. They are often set at a fixed angle, but many can have the angle adjusted multiple times during a year to gain better performance.
PV panels perform best when perfectly perpendicular to the sun's rays. As the sun's position changes daily and seasonally, a fixed PV array's performance will change. For optimum performance, a fixed array will be faced due south (north hemisphere) and at an angle equal to the latitude of the location. If an array has an adjustable angle, this site has instructions for calculating the proper angle at different times of the year.
Trackers allow an array to follow the sun on either one or two axis. A single-axis tracker will have the vertical angle fixed and track the along an east-west path. Most will allow the angle to be adjusted seasonally for better performance. A two-axis tracker attempts to keep the array perpendicular at all times to the sun, tracking it both daily and seasonally. Trackers can be passive (fluid based) or active (electronics/motors). A two-axis tracker can improve performance by up to 40%, but it comes with added cost for the tracker and maintenance, since it is adding mechanical and potentially electrical components to the system.
Selecting a Vendor and Determining Your Needs
There are many new vendors peddling PV systems. It has been a sort of gold rush over the last couple of years, as many of the contractors, electricians, plumbers, and other construction-type vendors rushed into solar after the housing collapse. Due to the incentives provided by states and utilities, it is one of the bright spots of spending. Because of this, it is important to have a basic understanding of PV systems before you decide to purchase.
Before you contact any vendor, you need to know how much power you use on average. Many utilities can provide your last year's usage online. In fact, one the first things many PV vendors will do is get your utility information (account #, address, etc.) so that they can pull your usage records for you when preparing their quotes. Most will provide you with quotes showing you how much you will generate and how much you will save by installing their systems. As with any large purchase, get multiple quotes.
If you plan on having battery backup, you will need to analyze your loads to determine how much battery capacity you will need. You will also want to determine how long and what loads you wish to keep up during a grid failure. To do this, you can use small plug-in meters that are available from many locations on the Internet or from your local Radio Shack. I use the P3 Kill-A-Watt meter; it's about $25 and you simply plug it into the wall and then plug in the device you want to measure. You can leave the device plugged in, and then check the total usage and divide it by the time to get an average. You may want to do this just to have a better understanding of how much power a device uses.
If you have larger loads that you would like to measure that are inconvenient or too large for the Kill-A-Watt meter, such as a well pump, you can simply turn off all loads except the one you wish to measure, and then use your electric meter to determine the power being drawn. Instructions for doing so can be found here.
When you first start getting quotes for photovoltaic systems from vendors and are currently a grid-tied customer you will find they will all try to discourage you from considering any kind of battery backup. Most will point out the incredible reliability of the grid. They will encourage you to investigate alternative backup solutions (such as propane generators) if you really want backup power. This is because batteries are very expensive, more complicated than other backup solutions, and generally require more maintenance. Also, many of the PV people are relatively new to the business and have little or no experience with a battery-based system. If you decide you want a battery backup system, it is helpful to find a vendor that has off-grid experience or a vendor that has worked with AC battery backup solutions, such as those for data centers.
The short description: Our system is 10.8 kW with AC-coupled battery backup. It consists of 48 SunPower E18 225W black panels mounted on 3 poles with DPW Power-Fab top of pole racks. Each pole has a SunPower 4000m grid tied Inverter (a re-branded SMA Sunny Boy 4000-US) connected to 16 panels arranged as 2 strings of 8. For the battery backup, we have 2 SMA Sunny Island 5048-US off-grid inverters connected to a [email protected] C&D Technologies msEndur II battery stack.
So what does all that mean? Why did we go with that equipment?
I'll start with the grid-tied portion of the system. Since we covered the roof with thermal solar collectors, a roof mount was not an option. Due to the position of our house on the lot, it left only a small area that would have a reasonably unshaded south facing exposure. Our neighbor's house behind us has a fair number of trees, so we needed to use pole mounts to get the array above potential shade from their trees. Placing the panels high also reduces the potential for vandalism or theft.
The first decision was the rough size of the array, which was driven by our usage and the potential for an electric vehicle in the future. Also impacting our decision was the favorable higher REC credit incentive rate (see below) for an array greater than 10kW offered by our local utility.
We chose DPW racks because they were reasonably priced, made locally, and had the ability to adjust the angle of the array. This decision impacted the choice of panels. SunPower panels have a higher efficiency, which means less surface area is needed for a given power generation. In most instances, this may not be much of a factor in the choice of panels. In our case, it meant we could reach our desired array size with only 3 poles, versus 4 poles with other panels we considered. The racks have a maximum surface area due to wind loading, and with SunPower we could fit 16 panels per pole, versus only 12 or 14 of other brands. It should be noted that SunPower panels have a large price premium, but the cost difference was less than the cost of adding an additional pole and had an added aesthetic value of less poles.
We chose the SunPower (SMA Sunny Boy inverters) because they are designed to work with the SMA Sunny Island off-grid inverters. This allows us to use the SMA Sunny WebBox monitoring appliance. In addition, the Sunny Boys are designed to work with the Sunny Islands when the grid is down, by allowing the Sunny Islands to throttle power production from the Sunny Boys.
The poles are 16' long 12” round 1/2” thick schedule 40 steel pipes. They each weigh just under 900 lbs. They were placed in 4' x 4' x 6' deep holes, which were then filled with re-bar reinforced concrete. This is the required mounting to withstand up to 90 mph winds. Here is a picture of the poles being installed:
Next, the racks were placed on the poles:
Then the panels were installed, an inverter attached to each pole, and the panels connected to the inverters. This would be a complete standard grid-tied installation and can function as such:
The inverters are connected to a meter that is used for measuring generated power for use in calculating the REC credit incentive. That meter then ties into our critical loads panel.
Next was the installation of the battery bank and the off-grid Sunny Island inverters. The inverters work as a master-slave configuration providing 240V power, which can be used to power our well. The batteries are sealed VRLA AGM (valve regulated lead acid absorbed glass mat) batteries:
We choose the C&D Technologies msEndur II batteries because they have a long life (20 years), low maintenance requirements, and are designed to be used in applications where they primarily sit at float rather than being cycled every day like batteries used in off-grid applications. When working with a vendor, make sure they understand how the batteries will be used. How the batteries are discharged (frequency and depth) can have a huge impact on the choice of batteries. Keep in mind that choosing a cheaper battery can result in higher costs later due to having to replace the batteries more often. This is particularly important as most of us here believe that resources will become scarcer and more costly in the future.
The installation of the Sunny Island inverters required reworking our existing breaker panels to place “critical loads” into a separate panel. The Critical Loads panel contains loads that will be powered by battery and/or PV when the grid is down. It includes our well, heating system pumps and controls, refrigerator, freezer, and a few lights and plugs.
Below is a simplified drawing showing the interconnection of the components. The “cut-off switch” is built into the Sunny Island inverters. Not shown is the Sunny WebBox, which is used to monitor the system. It connects to each of the Inverters via an RS-485 network and to our home network.
Under normal operation, the SunPower (Sunny Boy) inverters start up each day when the PV panels begin producing power. The power produced spins the REC meter and then is fed into our primary panel. The power is either used by loads in our house or sent out to the grid through our primary electric meter. If we are using more power than we are generating, the meter spins forward. If we are using less, then it spins backwards (net metering). The Sunny Island battery backup inverters allow power to pass through to the critical loads panel and draw any needed current to charge the batteries. This is the typical operation 99.9+% of the time.
If grid power is lost, the SunPower inverters immediately shut down (anti-islanding protection) and the Sunny Island inverters begin generating power to the critical loads panel from the batteries. At the same time, the Sunny Islands isolate the critical load panel and the SunPower inverters from the grid, forming an intentional island separate from the grid (sometimes called a mini-grid). The SunPower inverters will then see power just as they would if the grid were available. After a few minutes with power visible, the SunPower inverters start up and begin producing power if solar is available. Any power generated will be fed to the critical load panel, and excess power will be used to charge the batteries. If the batteries become fully charged and the critical loads are not consuming all the power generated, the Sunny Islands can adjust the frequency of the power they are generating to throttle the SunPower inverters to meet the current demand.
When grid power becomes available, the Sunny Islands will connect the critical load panel and the SunPower inverters back to the grid. During the switch, the SunPower inverters will shut down until grid power is visible for several minutes and then start back up into normal operation.
Cost, Tax Incentives, REC Credits and ROI
We paid to have the system professionally designed and installed. The total pretax credit price was $98K. As with the thermal solar in NM there is currently no gross receipts tax (sales tax) on solar installations (parts and labor). So that price included about $6,600 worth of savings.
Many of the same incentives from the thermal solar applied to the PV as well:
Federal - Residential Renewable Energy Tax Credit – 30%, no limit = -$29,400
NM - Solar Market Development Tax Credit - 10%, $9000 limit = -$9,000
All the credits brought the final price down to $59,600.
The approximate pre-tax credit breakdown of the major components is shown below:
As you can see the battery backup added considerably to the price, particularly with the type of batteries we chose. There was also a significant increase in cost for the pole mount racks versus a roof mount system.
While the tax credits are good, the big incentives are with the utility company REC credits and energy savings. Our utility company offered (recently changed) two programs for interconnection. One was a small PV program (< 10 kW) which is net metered and pays $0.13/kWh REC credit for all power generated and any excess is carried as an energy credit that can be used in the future. The other was a large PV program (> 10kW) which is also net metered and pays $0.15/kWh REC credit for all power generated and consumed and any excess energy is paid for at their “loss avoidance rate”. We are billed under the large program, so for example, if we used 1900 kWh and generated 2000 kWh in a month this would be the outcome:
In this example, we save $190 that we would have paid to the utility company, and on top of that the company sends us a $290 check for a total net gain in one month of $480.00. The REC credits are taxable as income so that will reduce the payout some, but I have calculated on our system that after all taxes we should be getting a average net gain of about $307/month. Over a 20 year life of the system, I have calculated the ROI to be around 2.1%. Without the battery backup, the system would have an ROI of around 6%, and with roof mount instead of poles it would easily push the ROI to 10%. So even with the batteries, the ROI is better than the current rate on a CD at a bank, and the savings and sale back portion are inflation adjusted!
In the future as energy prices rise, I suspect the savings and sale-back prices to rise substantially, making the non-inflation-adjusted REC credit become less important. Incentives vary widely by country and state; some are considerably better than those in New Mexico so you'll have to do some research and spend a lot of time with a spreadsheet.
Unlike the solar thermal system, which is difficult to measure, the PV system gives instant feedback on how it is performing. The Sunny WebBox logs data from all inverters every 5 minutes, and with a 2 GB SD card inserted, it can keep the logs for more than a year. The logs are updated several times during the day to the SMA Sunny Portal website, where I can check on the performance of the system at any time from anywhere in the world. You can see our current and historical performance here.
The system has so far performed better than modeling suggested.
Hopefully you now have a little better understanding of thermal and PV solar installations and perhaps some encouragement to investigate them if you haven't done so already. While expensive, with current incentives and energy prices it is financially justifiable to install these systems versus other investments, and you will end up with a hard tangible asset versus a piece of paper.
I would also suggest that if you plan on installing any of these types of systems, you begin doing so soon. It took almost a year from starting research to having our systems installed. After picking a vendor and signing contracts, it took almost 6 months for the systems to be up and running.
In addition, I firmly suspect we will see a drop in subsidies, particularly from the states and utilities, as the economy worsens. While it's nice to think of these subsidies as being the right thing to do, they are absolutely unsustainable. It is a transfer of wealth to those who act from those who don't. Take action!
From a mental perspective, it is a great relief knowing that we can now survive fairly severe collapse with little or no natural gas or electricity and still keep warm, have lights, and run water. If you are having trouble sleeping at night due to worry about what's coming, having systems such as these is the best sleeping pill you can find.
There are many great resources available for free or cheap on the Web. I do not have any financial relationship to the sites listed below; I'm just a happy user of their services.
DSIRE - Database of State Incentives for Renewables & Efficiency – This website has listings of both federal and state incentives available. Check out the incentives soon, as some covered here expire at the end of 2010.
NREL – National Renewable Energy Laboratory – This is an invaluable site. It provides renewable resource maps for most renewable resources. PV Watts is a free Web application on the site that lets you enter information about a system and it will calculate your estimated production by month. Of all the tools, I used this one the most during my planning.
SRCC – Solar Rating and Certification Corporation – Look up the performance characteristics of solar collectors and PV modules. Make sure the components used are certified, as that is required for many of the incentive programs.
Home Power Magazine – I highly recommend subscribing to the online version of this magazine as a first research step. For $15 you get a year of access (6 issues) and can look at the past 18 issues as well. There are a lot of great articles on solar, wind, and other renewable sources for the residential market.
Suppliers for our systems:
CST Solar - The company that designed and installed our PV system. If you are in the Albuquerque area and use them, please let them know I sent you!
Sun Power – The company that makes the PV panels we used.
SMA – Manufacturer of the inverters, including the Sun Power labeled inverters we used.
DPW Solar – Manufacturer of Power Fab PV mounting racks which we used. Also in Albuquerque.
Solar Logic, LLC – Manufacturer of the SLIC controller for our Thermal Solar System.
Other notable vendors:
AAA Solar - A thermal solar supplier located here in Albuquerque. They have a free downloadable catalog that has supplies, prices, kits, and plans for thermal solar aimed at the DIY market. The catalog is a great resource just to see what is available and get ideas on costs for such systems.
Affordable Solar – Another supplier located here in Albuquerque, which is also aimed at the DIY PV market. They are a great resource to check out prices on modules, inverters, and racking systems. They also have complete kits available.
Zomeworks – Another Albuquerque company that makes passive solar trackers.
Wattsun – An Albuquerque company that makes active solar trackers.
Our solar inspection team, which kept an eye on things during the construction.