SUR Electric Systems Options
SUR seeks to get our customers what they want by offering a wide variety of options with varying cost and functionality. Here we describe some of the costs and benefits of installing various types of systems.
| Component |
Grid-tied
(no batteries) |
Grid-interactive
(with batteries) |
"Off-Grid" with grid charging of batteries |
Off-Grid with batteries |
| Solar electric (PV) |
AVAILABLE |
AVAILABLE |
AVAILABLE |
AVAILABLE |
| Wind turbine |
AVAILABLE |
AVAILABLE |
AVAILABLE |
AVAILABLE |
| Charge controller |
BUILT-IN |
REQUIRED |
REQUIRED |
REQUIRED |
| Deep cycle batteries |
NONE |
REQUIRED |
REQUIRED |
REQUIRED |
| Lots of large wires |
NONE |
REQUIRED |
REQUIRED |
REQUIRED |
| Critical load sub-panel (and house re-wiring) |
NONE |
REQUIRED |
REQUIRED |
N/A |
| Inverters |
REQUIRED |
REQUIRED |
USUALLY |
USUALLY |
| Utility interaction |
REQUIRED |
REQUIRED |
|
|
| Battery chargers in the inverters |
N/A |
AVAILABLE |
REQUIRED |
N/A |
| Disconnects |
1 or 2 |
LOTS |
LOTS |
LOTS |
| Interaction with a fossil fuel generator |
NONE |
AVAILABLE |
AVAILABLE |
AVAILABLE |
As you can see from the chart above we divide the systems into four basic types: straight grid-tied with no batteries; grid-tied with batteries; off-grid with grid charging of batteries; and off-grid with batteries only. The first two in our chart are the most common. Below is a description of each, as well as the components that make them up:
Most of the growth in the renewable energy sector is occurring in this area. These tend to be the simplest and most cost effective options available for those who wish to get the most clean power for their investment. These systems seamlessly push power into your electrical panel in parallel with the utility. It is very fluid. Electricity follows the path of least resistance to the loads, so it first meets the loads in the household where it is interconnected. You don't know if you are running on solar or utility power without looking at the utility meter. If the meter spins forward and your inverter says it is making power, you are working with a mix of solar/wind and utility power. If the inverter is making power and the utility meter is spinning backwards, that means your production is exceeding the loads of the household and the inverter is pushing the excess power into the electrical panel, to all the loads, and also onto the grid. At night (with solar) you will use only utility power. These systems do NOT have backup capabilities. In other words, when the power is out your system will shut down for safety reasons. If your system continued to output power a line-worker could be killed when your inverter back-feeds the grid.
Another way that these grid-tied inverters have contributed to the use of renewable energy sources is their high voltage on the DC side. Typical voltages are upwards of 500VDC, which keeps amperage down and allows us to use much smaller easy to handle wire. You also loose less power in the wires. The really good battery based systems tend to max out around 100 volts, which means much higher amperage and larger wires.
In summary, the advantages of this system are that a larger portion of your budget can go towards generating more clean energy- more solar panels or more wind turbine. The disadvantage is that when there is a power outage you have no solar or wind power for backup loads. Often we find that clients concerned about catastrophe, or those with well pumps are more likely to choose a battery-based system. Most others would go with a straight grid-tied system. Also, for the environmentalist whose top concern is carbon footprint, putting more money into generation rather than balance of system tips the scales in favor of the simpler no battery system.
This is the most complicated system available as it has the functionality of all of the other systems in a single package. Through one set of leads it is connected to the main panel in the home or business, and can export power to this panel, or even draw power from the panel to charge the batteries with utility power. It never exports power to this panel when there is a power outage. This is due to the safety concerns of the line-workers mentioned above. There is a second set of leads coming off of this inverter(s) for a backup power panel which would contain all critical loads: well pump; refrigerator; furnace; some lighting; etc. This load center continues to be powered during a power outage, and has no connection to the grid other than through the inverter.
Many projects involving backup power add the expense associated with moving critical loads from a main panel to a sub-panel. This expense alone can be significant. If someone already has a gas-powered generator and a critical load panel wired up, installing a renewable energy backup system is that much easier.
This type of system tends to add 20-50% onto the cost of a grid-tied system of the same wattage. Major variable would be the size of the battery bank, the number of inverters, the type of charge controller, and the extent of the re-wiring that is required.
These systems are pretty unusual. They tend to be a low-cost way to get backup power but are not nearly as efficient at using the solar/wind energy. With these the power output by the inverter does NOT run in parallel with utility power. All of the output from the inverter goes to the critical load panel. The utility connection serves only as an input into the inverter. The inverters have a built in battery charger. What they do is use solar/wind to charge the batteries and use the battery energy to run the loads in the backup panel (simplistic explanation). When the batteries get too low because of lack of sun or wind, they can convert grid power to DC to charge the batteries, and then invert it back to AC for the critical panel. These systems, as you might imagine, are much less efficient than the more expensive and complicated grid-tied with battery type systems. They can be used in off grid situations, with a generator taking the place of the grid as described above in this paragraph. Also, they illustrate another advantage of the other type of systems. These off-grid with grid charging systems are attempting to load match, which means if the production from wind or solar exceed these loads, which include the batteries and the backup panel, the energy is wasted. With a grid-connected system, you have infinite load in the form of the grid. All energy generated will be used.
These systems are typically used in cabins and homes where the grid is not present. You can use them in conjunction with a generator if getting 100% of the energy from renewables is too expensive or not doable for other reasons. Depending on the budget you may be using the same equipment as described above, but without the grid input. The power sources would be wind, solar, and possibly a generator. Each of these could run loads or charge the battery bank, which would be required with this sort of system. Also, if the home/cabin is used year around, solar and wind together is a good idea. The solar will run the summer loads, and the wind will power the winter loads. If you try to run summer loads with wind power your turbine has to be grossly oversized, and the same is true with winter loads powered by solar.
We have heard of grid connections to homes that are far from the power lines costing as much as $30,000 or more. If this is the case it is a good financial start towards energy independence by installing an off grid system. Keep in mind that we dont recommend this for those that want unlimited energy and to lead a pampered lifestyle. Most off-griders are people that value independence to the extent that they are willing to compromise some on energy consumption. Most clients we encounter have grid access and just want to clean up their energy mix a bit.
To invert in this case is to take DC current and turn it into AC current. DC current is electricity that travels in a circle from one side of a source through some loads and back to the other side of the source, and always travels in the same direction. With AC current, the electricity does the same but stops and changes directions in the circuit 120 times per second (in the US), pulsing one direction then the other. As long as the electricity is moving through the circuit energy will be there for your appliances.
In the olden days our inverters only did inverting, thus the name. As is often the case many of the inverters we are discussing here have evolved to greatly exceed the task designated by their name. As mentioned in the system descriptions many inverters also charge batteries, taking AC power from the grid or a generator and turning it into DC to charge the batteries. This is called rectifying and is the opposite of inverting. To clarify this issue some manufacturers have started to call their equipment inverter/chargers to better describe all of the functionality.
A straight grid-tied inverter without batteries would not have the charging capabilities. One function they do have in addition to inverting is similar to that of a high quality charge controller: their circuits do Maximum Power Point Tracking, which gets as much energy out of the solar panels as is available at any given time. Another nice touch most inverter manufacturers offer is data collection and display. Usually very basic information is included, while expanded systems with data logging are available at additional cost.
Batteries are also required in these types of systems. We use only deep cycle batteries for these applications. Batteries add expense and are a maintenance issue in that they might need to be replaced every eight to ten years depending on other factors. Again, this type of system is much more expensive but adds value in that you can run critical loads on solar or wind during a power outage.
For those customers concerned with the environmental impact of the lead in batteries we respect that concern, but want to make sure people understand that batteries are 99% recycled. The lead in your batteries was probably in batteries before, and will be in batteries again. We pay a deposit on the new batteries just like we all do when buying a can or bottle of your favorite beverage.
Included in inverter discussion above.
Any of the systems listed above that use batteries will typically requires some sort of charge controller to keep the batteries from being over/under charged by the solar/wind. Decent controllers can cost as little as $60 or as much as $700. The higher end controllers typically let you get more out of your investment in the solar array/wind turbine itself, which represent half the cost of the entire system. For that reason a higher cost controller may be a good investment. Also, on higher end systems, smart charge controllers communicate with the inverters so that the entire system operates in a synchronized way. On these systems if you see 1000 watts coming in on the charge controller you will often see the same wattage being exported by the inverter. Without the coordination, the inverters are judging how much energy to convert to AC based on the DC voltage, which can be a very weak indicator of what is actually being generated. These charge controllers also tend to take better care of the batteries, which represents an investment of thousands for most backup systems.
