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‘Where should we put solar panels anyway?’ This is a question I’m often asked and to which I always reply, ‘everywhere!’ Glibness aside, what the question is usually getting at is to do with market segmentation. There are many different types of photovoltaic (PV) installations. One of the remarkable aspects of solar technology is just how scalable it is. Solar panels are used in both pocket calculators and in giant solar farms covering hundreds of hectares. The economics of each application are very different however and it is important too understand which applications represent the largest markets.

As I’ll discuss the, UK feed in tariff is designed to strongly influence the type of solar installations built in the UK, but what kind of solar installations are best and what should we expect in the UK?

Let’s look at what’s going on in other countries around the world. In Germany, the world’s biggest solar market by far this year, grid-connected solar systems are defined in three categories; residential, commercial and utility scale. Residential scale is the smallest type of installation and refers to all installations less than 10kW (~60m2) typically found on private houses. Commercial scale refers to installations between 10kW and 100kW (600m2) typically found on the roof of a factory, office or warehouse. Utility scale refers to all installations above 100kW and these are typically ground-based installations on fields (also known as solar farms) and can cover hundreds of hectares.

These three types of installation are quite different from each other in terms of price and the technology used. Which type of installations are the most popular? Figures published by the Bundesnetzagentur (the German grid regulator) state that the market in 2009 is divided into 17% in the residential scale, 17% in utility scale and 66% in commercial scale. This means that because residential installations are smaller, there are many more of them in number than utility scale installations.

Large plants are cheaper due to economies of scale, however the planning process can be long and complex, and it can be difficult to find banks willing to loan money for such projects. Rooftop plants on the other hand have a much easier time getting planning permission, and often are fully funded by the owner, so don’t require a loan. This explains why commercial scale rooftop plants dominate the market.

In the US, rooftop installations also dominate, and there is an additional reason why. In the US there is no feed-in-tariff, rather a complex array of grants that vary from state to state (California has the best).

Solar installations generate money by selling electricity to the energy utility at the regular unsubsidized rate. This means if you generate energy at the place where you use it, you get the same price of electricity that you would have to buy it at, the retail price. On the other hand, if you have a utility scale power plant, this requires the utility to distribute the energy for you and you only get the price that other types of power stations get, the wholesale price. Since wholesale electricity prices are roughly half that of retail electricity prices, its much better to have a solar installation in the same place as where you use it, i.e. on your roof.

So what does this mean for the UK? Well, as we are led to believe from the governments initial announcement, the UK feed-in-tariff will be strongly weighted towards smaller installations. This means that the larger your installation the less you will be paid for the electricity it generates. This cutoff is quite severe, with the rate dropping from 36p to 31p per kWh for installations over 4kW, to 28p for installations over 10kW and down to 26p for installations bigger than 100kW.

The argument behind this is so that all installation deliver an equal return on investment. This implies that the government assumes the cost of energy from a solar installation is 14% lower for a 5kW installation than for a 4kW installation.

Where does this assumption come from? Data from Germany suggests that this is not the case and the 14% drop does not exist. Cost of energy does fall with increasing scale but by how much is unclear and changes constantly with prices of various technologies.

I can understand if the government wants to ban solar farms (although having visited several under construction in Germany last month I think it’s a real shame that we don’t have a single solar farm in the UK, even just from an educational standpoint) but the current FiT structure does something else. It restricts the most effective type of photovoltaic installation, namely commercial scale rooftops.

Germany’s flat feed-in-tariff structure and the US’ grant scheme both allow the market to evolve naturally. If large rooftop installations make the most sense economically then why not let this segment grow fastest? Trying to engineer a feed-in-tariff so that everything grows at the same speed will inevitably slow growth overall.

Let’s hope changes are made while there’s still a chance.

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