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Last week, Kayla Koether of the Winneshiek Energy District explained why now is the time to integrate solar panels into your farm. This week, she explains how to start that process. Kayla will also be speaking at Dan and Bonnie Beard’s field day near Decorah on October 3 to talk about farm energy planning.
Hopefully in my earlier blog post, I convinced everyone to go solar as soon as possible for both ethical and economic reasons. Here I will aim to demystify the ‘how-to’ and ‘how it works’ of solar photovoltaics.
How does Solar PV work?
Solar photovoltaics convert light into electricity (in contrast to solar thermal panels, which heat water-also an excellent farm application, ask Francis Thicke). PV panels create direct current (DC) electricity, which is then inverted to create alternating current (AC) electricity for use in your appliances, motors, etc. Systems are sized based on their DC kilowatt (kW) generating capacity, the amount of DC power the array could kick out at any given point in time. Different brands and makes of solar panels may be rated for different kW capacity, so when comparing systems, look at the kW size, not the number of panels.
Solar PV can be ‘off-grid’ with batteries to store energy, but the vast majority of solar systems (and the cheaper option) are grid-tied. In a grid-tie, you use the grid like a battery. When your solar panels produce electricity, that energy is first put to use to cover any load on site, and any excess goes into the grid. So, at 4:00 p.m. on a sunny July day, you fire up your milking units and your current solar production directly covers that load. Earlier, when you were in the house taking a nap (ok ‘making hay’), the excess electricity from your solar panels flowed into the grid to your nearest neighbors, who were running the air conditioner wide open. When your array isn’t producing, you pull electricity from the grid. Turn on the yard lights at 10 p.m., and your power comes from the utility, not your panels.
All these electrical exchanges are accounted for by the particularly simple and elegant system of net-metering, which allows you to bank kilowatt-hours (kWh) with your utility. Note that kilowatt-hours are different from kilowatts. When you put surplus electricity on the grid you are credited in kWh; when you draw electricity off, you are debited in kWh. Thus the value of the electricity you add to the grid has an equal value to the electricity you pull, a one-to-one exchange. Net-metering almost seems too intuitive to warrant explanation, but the policy is under fire by huge investor-owned utilities nation-wide, who would prefer to trade in dollars, rather than kWh. Utilities argue that they should pay you for each kWh you add to the grid, but do so at their avoided cost rate (3-4 cents/kwh). Meanwhile, when you pull energy off the grid, they should be able to charge you the full retail rate (13-14 cents/kwh in Iowa).
Utilities claim that solar owners don’t pay the cost of infrastructure to move electricity, and thus their power isn’t worth the full retail rate. However, multiple studies have concluded that solar power is worth more than the retail rate, because it produces during peak use times (when utilities pay high rates for wholesale electricity), cuts down on power line losses, and helps avoid infrastructural costs incurred to build out other power generation. Currently, the Iowa Utilities Board (IUB) requires all investor-owned utilities to net-meter systems up to 500 kW. RECs, which are not regulated by the board, have varying policies and caps on system sizes for net-metering. Check with your utility to understand their net-metering policies. To support the continuation of net-metering in Iowa, you should submit a comment to the IUB’s current open docket on distributed generation.
So, how do you design a Grid-tied, net-metered system?
First, you should take stock of your current energy use, and look for efficiency opportunities. Every dollar spent on efficiency saves three on your renewable installation. Efficiency is cheaper, and reducing your load means a smaller (and less expensive) solar system to boot. You can have a professional audit completed to analyze farm efficiency opportunities. For farmers in Winneshiek Energy District’s six county service area, we can provide this service as part of our holistic Farm Energy Planning program. For those elsewhere, you should talk to your local NRCS office and apply for the EQIP program to get cost-share for an audit.
Once you’ve explored your electrical use, you can relate it to the size of a solar system you would need. Either via an audit, solar installer, or on your own, you can request three years of your historical electrical records from your utility. Once you know your annual average use in kilowatt-hours (or your projected use after efficiency updates), you can calculate the size of a solar system to cover it. Here in NE Iowa, 1 kW of solar conservatively generates 1,250 kWh in a year. Thus, divide annual use in kWh by 1,250 kWh/yr to approximate the size of the system needed to cover 100% of annual use. The PVWatts site is a great tool that calculates how much solar can be produced at your latitude/longitude, and help you determine output at different array tilts and orientations.
Pricing a system and getting quotes
Get at least two quotes (more would be better). An installer’s quote should include:
- Proposed system size in kilowatts (kW) DC
- Estimated annual production in kilowatt hours (kWh) AC
- Dollars per Watt installed– This is the bottom line for price comparison. Make sure it’s not to exceed, includes wiring or electrical service upgrades needed, and does not include other incentives or grants
- Total price– Should include all costs, be not to exceed, and should not include incentives
- Site assessment regarding shade, roof, mounting, and interconnection issues
- Identification information on brand/models of hardware, including panels, inverter, racking, etc.
- Warranty information on specific hardware components, labor & maintenance (and what happens if the manufacturer goes out of business?)
- Itemization of hardware, permitting/connection, and labor
- Economic summary-showing how available incentives will likely impact your final outlay IF relevant to you, and what your final simple payback MAY be with or without incentives
- NABCEP certification– (North American Board of Certified Energy Practitioners). Ask your installer if they are NAPCEP certified. If not, you may want to ask for references from other clients to verify the quality of their work. You can also search the NABCEP website for certified installers.
With this information you should be able to analyze and compare quotes successfully and knowledgeably. Since installers work with different panels, they may size systems somewhat differently; thus price per watt provides an apples-to-apples cost comparison. You can also divide their annual production projections by the system size to see how many kWh they expect 1 kW of solar to produce in a year, and verify that it’s an honest expectation for your location.
Finally, remember that different hardware will have different characteristics, and each installer will have their preferred type of system. Price isn’t always the bottom line; quality, workmanship, and good relationships are integral to a pleasant installation. All the installers I’ve worked with in Northeast Iowa have done excellent work (http://energydistrict.org/resources/solar-contractors/). I’m sure others elsewhere are similarly reputable- but when armed with this knowledge, you can decide for yourself. So, get energized and go solar!
And as always, feel free to call or email me with questions: 563-382-4207, firstname.lastname@example.org
 A watt or kilowatt is a power rating describing how much energy a piece of equipment could create or draw at any given point in time. For example, your old incandescent lightbulbs are rated to draw 60 watts. A watt-hour or kilowatt-hour describes energy use through time- so if you leave your lightbulb on for one hour, you’d have used 60 watt-hours worth of electricity, and if you left it on for two hours, you’d have used 120 watt-hours. You can draw a comparison to a motor. A kilowatt rating would be like the horsepower rating on the motor, and kilowatt hours would be the amount of energy the motor pulls over time. In this case solar is generating, rather than using, electricity. kW is the generating capacity, and kWh represents the amount of electricity generated over time.