Our 12.6 kWp of solar panels at the Perfumery provide about 40% of our annual electricity needs. From sunshine. In Ireland. Yes.
We now have four years of data. We have generated 48800 kWh of power in total, averaging 9766 kWh per year and saved €8789 in energy costs (we pay about 17c/kWh in Ireland), meaning the system will pay for itself in another 10 years, about 10 years before the end of its expected 25 year lifespan.
One of the great things about our renewable energy installation is that because it is driven by sunshine, we get the most output during the spring, summer and autumn, when the Perfumery is at its busiest, so the generation pattern fits well to our consumption pattern.
If you want to dive into the data in detail, you can click here on Sunny Portal and see details of yield by day, week, month and year. Okay, from here on in we dive into the details. A little technical, but not too much.
Planning the project
From idea to installation, our solar power project took a lot longer than I expected and I learned a great deal about solar PV in Ireland along the way. In this article I'm going to try to explain some of the lessons we learned so that other people considering a PV project can get a 'heads up' on what's involved.
When I conceived this project I had a simple goal: produce all of our primary energy requirements onsite from renewables. We use about 18,000 kWh of electricity a year, so I (in my innocence) thought that it was just a matter of being able to afford enough panels to meet that number. Would that it were so simple...
There are a few different aspects of this problem to think about: fluctuating power requirements, fluctuating production, night time (!), storage, and feed-in-tariff (or what the grid pays you). From monitoring our power usage for some years I knew that our maximum requirement would be about 10-12kW and our minimum around 600W. So an array that could produce 12kW of power would meet all our needs but only when it was at peak production, and that's only for a hour or so either side of noon in the summer for a fixed (i.e. non-tracking) array. And of course we're not always consuming 12kW; sometimes we only need 2-3kW. Ideally then you want to store your surplus and put it back in during times of low production or at night. So: batteries. Well, turns out the thing about batteries is that they're finicky. There are lots of different battery types but the bottom line (for current technology and pricing) is that it's not economical to use batteries and here's why.
To store or not to store
A battery can only be charged and discharged a finite number of times. If you know the capacity of a battery (in Ah or mAh) and how many cycles it will last for and its cost you can work out what it costs you to store a kWh of power. And that number turned out (for us) to be more than 18c, i.e. more than the cost of just buying a kWh from the grid. Plus you also have to have the infrastructure to support your battery plant, the hassle of managing them, the losses on charging, discharging, and converting to AC - in short, the expert opinion is that unless you have to do it (by being off grid) you should avoid it.
There are other storage options, e.g. compressed air, flywheels, etc., but for small scale installations batteries are the only realistic option for now. However, there is a lot of interest in developing energy storage technology - driven by the large scale deployment of renewable energy systems - so we might see some improvements or new technology in this area in the near future.
Okay, so batteries are out, but you can export your surplus to the grid, get paid for it and that's effectively the same net result as storing it, right? Wrong. In Ireland at least. In Ireland you can only get paid for exported power if you're a domestic customer. We're a commercial customer. No feed-in-tariff for commercial customers. And even as a domestic customer you only get paid 9c per kWh, half the price you buy a kWh for from the grid. Plus, a domestic customer can only connect 6.5 kW of PV production capacity to the grid; if their array produces more than that there must be a device (an expensive device called an Emma) that diverts the surplus (typically into heating something like water).
Now it turns out you can actually produce more than 6.5 kW and have it connected to the grid, you just have to make a special application to ESB Networks, called an NC5A. You'll probably need an engineer to prepare the application and then you have to pay ESB Networks to look at it (c. €800) but basically you can connect a PV array up to the capacity of the transformer that provides your power (depending on how many houses are fed by that transformer). We have a 14kVa transformer, and we're the only consumers on it, so they okayed our application to connect a 12kW array.
From a basic environmental standpoint we were now at the point where we could plan to install 12kWp of capacity, which at our location could be expected to yield about 11,000kWh per year. (There are various modelling programmes that can calculate the expected yield of a PV array if you put in your lat/long, orientation, tilt and capacity. Google: RETScreen for an example). Disregarding for a moment the issues of storage or export, we are at least able to think in terms of offsetting our requirement for 18,000 kWh of power from the grid (substantially from fossil fuel) with 11,000 kWh of renewable production.
Site and Shading
Now we had the outline of a plan, we needed somewhere to site the panels. This would be very easy if one had a nice big South-facing roof, or a big open field. We have neither, and despite having a 10 acre site to choose from, there were only a few possible locations where we could site our panels such that they would have a good orientation and no, or minimal, shading. Here's the deal with solar panels: the panels are wired together in series in 'strings' (in our case 8 panels to string). If one panel in a string is shaded (say by a tree) then the output of that panel drops but also the output of the other 7 panels drops to that of the lowest producer. So shading is a BIG DEAL. The same would be true if one panel wasn't oriented in the same direction as its fellows (though this is less likely to be a problem).
The output of the panels also depends on orientation and tilt. Due South is optimum orientation and optimum tilt depends on whether one wants to optimise for production in summer or winter. The sun is lower in the winter, so the panels need to be tilted to higher angle. In summer the sun is high, so the panels can be at a lower angle. If you're mounting on an existing roof, then you might not have much choice in your orientation.
The good news is that +/- 10 degrees either side of due South, or either side of optimum tilt doesn't actually make that much difference. Again there are several modelling programs on the web that can be used to simulate the yield for different orientations and tilts. Another consideration here is shading between the panels themselves. If you have more than one row of panels, the ones at the front may potentially shade the ones behind, especially in the winter when the sun is very low.
Finally, it's important to think about how far the panels are from your electrical system. Though it is often linked in at, or near, the meter box, the output from the panels can be brought into your system at any distribution box. The DC cabling from your array to the inverter can be very expensive and there may be some loss of power along it, depending on the length. For roof mounted systems it won't be an issue, but one site we considered for a ground mounted system was 200m from the Perfumery and the cable alone would've cost €6,000.
After considering a lot of different options, we settled on having two arrays: 24 panels on our flat warehouse roof and 24 panels on a ground-mounted rack near our herb garden. Neither site was large enough to accommodate the full 48 panels and also we have two complexes of buildings on site so we felt it made sense to create an array for each. At present they are all on the one circuit and supply, but in future they may have separate supplies, in which case they will each have their own array.
There is an exemption from planning permission for roof mounted solar panels, but only up to a certain size. Given the scale of our project we had to submit a planning application. It became clear when our engineer approached the Co. Council planner that they don't see a lot of PV applications. It took nearly two months for them to tell us what they needed in the application. But apart from the delay, the planning process was straightforward.
We published a request for proposals on the e-tenders site and reviewed 25+ submissions. We awarded the contract to ConstructionPV (now called: Solartricity) We judged their proposal to be the best combination of materials, price and technical expertise of those we reviewed. Some proposals we disqualified on price (some were 50-60% more expensive than the mean price), some on lack of expertise. If you're in the market for a PV system I would suggest that it pays to shop around, but not necessarily to take the cheapest offer. Look for a track record and ideally data from existing sites with similar configurations to what the vendor is proposing.
Quentin Gargan of Solartricity designed the final configuration of our system. It consists of 48 gallium arsenide panels, each with a 265W capacity. They are arranged in two arrays: one on our warehouse roof, mounted on ConSole roof mounts (see photo above); the second on a Schueco ground mount aluminium rack. Both arrays consist of three strings of eight panels wired in series. Each set of three is then combined in a string combiner box and then feeds a Sunny Boy 6000 inverter, one in our warehouse, one in the soap room.
The AC output from the inverter joins into our building circuit at distribution boxes in the relevant buildings. The inverters have DC fuses and isolators on the DC side, AC isolators and breakers on the AC side. They automatically shutdown if they can't detect AC current from the grid. This is to stop our PV system inadvertently making the local grid live if it were powered down for repairs. There is a data feed from the inverters to an SMA WebBox. This records the output of the inverters and periodically sends it to the SMA portal where one can view tabular data and graphs of the output. The WebBox also provides direct access to the inverters via a web interface on our internal LAN.
Electrical gear: €1,500
Web monitor: €700
ConSole mounts: €3,500
Scheuco rack: €3,500
Electrical work: €2,500
NC5A application: €1,400
Planning application: €1,000
Grant aid: €11,000
Net cost: €24,500
We installed and mounted the panels ourselves. The ConSoles are very easy to work with. The hardest part was lifting 96 concrete blocks onto the roof to use as ballast! It was about a day's work for two people to get the mounts lined up, ballasted, and the panels screwed onto them.
The ground-mounted array was trickier. We elected to use precast concrete slabs as foundations because a) they minimised our need to disturb the site, and b) they can be (relatively) easily removed and the site restored if necessary. Once the foundation slabs were in place and bolted together, we installed the anchor bolts for the rack and then assembled the rack itself. This is also pretty straightforward: three of us assembled the rack in a few hours and the next day we mounted the panels in another few hours. The Schueco stuff is very well made and easy to work with, though it's not cheap.
Assuming an annual yield of 11,000 kWh (which we seem to be on track for) and a current price per kWh of 17.86c (Oct 2013) and assuming we can use all of the power we produce, we would save €1,964.60 annually. Let's round this to €2,000. And let's talk about payback on the net cost to us of €24,000. (Bear in mind that electricity prices rose 11.9% in 2011 and 9.4% in 2012 (source: SEI)).