Archive for September, 2011

Getting FITS VI

The calculation for the expected energy generation from solar PV panels works as follows. The capacity of the panels is multiplied by 0.8 to reflect their usual output. This is then multiplied by the level of solar radiation the roof will receive. This is the level of solar irradiation for the location (Bristolscores an ‘H’ of 1150) adjusted for the pitch and orientation of your roof (as the panels might not be at the optimal angle to capture solar power). In our case this loss is 6%.

 I won’t go into the numbers involved, but there are two important aspects to the calculation. The first is that the key difference between the quotes is the kWh capacity of panels. One quote has 2.25% less capacity than another. So the energy yield and the revenue from the system will be 2.25% less.

 Secondly comparing the financial figures provided with the quotes would give a misleading impression of their operation, because of the different assumptions they use. Under a common set of assumptions, revenues would be 2.25% less, but comparing the quotes suggests a difference of over 10%. So don’t base a decision on installation on the ‘financial payback figures’ provided with quotes.

 To be fair, two of the quotes I got did say this in the small print, but this could still be confusing to people who aren’t prepared to unpick assumptions using a spreadsheet. Much more important to the comparison is the price difference of the quotes – at over 15% this outweighs the 2.25% difference in capacity of the panels. This price difference is down to the type of panels – cheaper being those from Innotech in Norway that are made by reusing the majority of sound cells of panels rejected from original manufacturing output due to slight imperfections in a few cells.

 Another important part of the choice is that, as usefully pointed out in a comment (thanks Ant!), installers should be MCS certified. This means Micro-generation Certification Scheme and certifies microgeneration products and installers in accordance with a set of quality standards – in other words that they are qualified and reliable: http://www.microgenerationcertification.org/ .

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Today is the 200th anniversary of Mexico’s independence. I spent 2 weeks there recently, partly for work and partly for holiday. It was the low season on the Caribbean coast which meant very quiet beaches there and lots of (mostly warm) rain wherever in the country I went. But this is not a blog for holidays…

Work there was very interesting too. I spoke at a workshop on economic valuation organised by the National Institute of Ecology (Instituto Nacional Ecologica). The workshop was attended by a large group of well informed and highly enthusiastic people from the public sector, NGOs and academia. Some research funders were also there.

Mexico is a bit of a paradise for an environmental economist – and I repeat not just because of the tourist attractions, even though they include the Museum of Economics in Mexico City! Rather it is because they have used the methodologies and instruments of the profession rather more extensively than one might expect. For example

  • The Mexican system of Payments for Hydrological Environmental Services (PSAH), which is one of the first Payments of Ecosystem Services. Mexico faces both high deforestation rates and severe water scarcity problems. The PSAH was designed by the federal government to pay participating forest owners for the benefits of watershed protection and aquifer recharge in those areas where commercial forestry is not currently competitive. It seeks to complement an array of forest policies that include development of community forestry firms and prohibitions of land use changes. Funding comes from a fee charged to federal water users. Applicants are selected according to several criteria that include indicators of the value of water scarcity in the region. For a paper that describes the process of policy design, main actors and rules, and provides a preliminary evaluation please click here.
  • The fisheries buyback scheme (buying back excess fishing gear) to protect endangered marine mammals, and
  • A pilot project to reduce energy subsidies and make sure that they are not indexed to production to protect overexploited aquifers.

Amongst the future projects, there is the possibility of a TEEB application for Mexico which came up in the discussions at the workshop but hopefully will become reality. TEEB is an international project that quantified and where possible monetised the services provided by the ecosystems and biodiversity worldwide. Country specific applications of its methods are emerging to estimate the economic value of the natural capital countries own. Benefit of such an application is that big numbers are talked about in the media and the overall process engages all sorts of different stakeholders who can see ‘what’s in it for them’ more clearly.

On a clearer link to holidaying in Mexico…I think there is a lot of room to increase the entry fees to the attractions like the Mayan ruins at Tulum (less than US$5 per person) and Sian Ka’an Biosphere Reserve (US$2.5 per person). There will of course be the predictable protests from local and international businesses but really compared to the benefits provided by such places and the funding need for their maintenance, such entry fees are terribly low. We hope our friends at INE will receive the support they deserve if and when they pursue arguments for a better benefit capture from such sites.

As you can easily find millions of attractive photos of Mexico on the internet, I thought I end with a photo much harder to find…a case of ‘appropriate technology’ in perfect use at a restaurant toilet inside the Sian Ka’an Biosphere Reserve (snorkelling at the reef there was interesting too!) .

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– experiences of fitting household solar energy – Getting FITS V is part of a series of blog posts by Limu on the attempt to install solar power at home with the help of the UK Feed in Tariff.

I’ve had three quotes for solar panels now. For a 4Kw system the prices are £12-14k. They all give a calculation of the payback I should receive, but looking at these in detail, the numbers are puzzling. I ended up emailing one provider for more details, and they helpfully sent me their calculation.

Two providers both claim to use the Government’s standard assessment procedure (SAP) for energy rating of buildings. Confusingly, one quote said a 4Kw system would give 400Kwh less energy than another for a 3.91Kw system! This is quite a substantial difference (10% of output) so would affect annual payments and financial payback time.

It turns out the differences are complex. The 4Kw system calculation is based on the averageUKannual solar radiation (which is based onSheffield!). It also makes adjustment for the pitch and orientation of the roof (i.e. that its not at the optimal angle to receive solar rays).

The other quote used a figure for solar radiation inBristol, which is more accurate, but doesn’t adjust for pitch and orientation, which is less accurate. So its predicted yield is around 10% higher. To compare the quotes on an equal footing, I’ll transfer the more conservative assumptions into the 3.91Kw system quote…

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