SOLAR THERMAL POWER PURCHASE AGREEMENT (PPA)

solar energy blue box

 

Isolated solar - this is not viable until panel costs and efficiencies enable us to reach parity with fossil fuels such as coal, oil and gas. Whilst this may be possible in some countries around the world (eg. Chile) where solar radiance is sufficient, this is not yet possible in the UK so I AM SOLAR made an early decision to to pursue this as a business model.

Solar + PPA (power purchase agreement) : this has been demonstrated to be viable with PPA values as low as 7p per kWh (models available to investor subscribers). For reference the market price to business consumers of electricity might be on average 12p per kWh so any saving on that figure should be attractive to a user particularly a large business which is particularly power hungry (eg. factories, large glasshousees, shopping centres, distribution depots, hotels, business parks). For reference, a PPA is a contract between two parties, one which generates electricity (the seller) and one which is looking to purchase electricity (the buyer). The PPA defines all of the commercial terms for the sale of electricity between the two parties, including when the project will begin commercial operation, schedule for delivery of electricity, penalties for under delivery, payment terms, and termination. A PPA is the principal agreement that defines the revenue and credit quality of a generating project and is thus a key instrument of project finance. There are many forms of PPA in use today and they vary according to the needs of buyer, seller, and financing counterparties.

Solar + PPA + Storage : an energy storage system (ESS) enables us to 'play' the energy market much like a commodity trader or trader of stocks and bonds might play the stock market, benefiting from price differentials produced by fluctuations in supply and demand of electricity. Only by storing electricity and holding it within the storage medium until such times as the price spikes (red zones) is it possible to benefit from the price difference (arbitrage of a kind).

Solar + PPA + Storage + Other Generation Types : the example of the Fernieshaw Farm Renewable Energy Park I previously gave you shows a mix of generation types which all combine to reduce intermittency of supply. That is to say that, by way of a simple example, when the solar farm is not producing at night, the wind turbines will still be turning, and the waste-to-energy plant still producing. The NPV and Payback Years graph (previously attached) clearly shows that the four elements all combine to produce strong revenue streams and profitability (high NPV and low Payback Years)

here is a further way to monetise certain renewable energy projects and that is through retention and deployment of waste heat which would otherwise be dissipated to the environment and lost.

By way of example, solar PV is perhaps 16% efficient that is to say a 5 MW rated solar farm assumes 25 MW of heat loss. In addition to this, the overall efficiencies of solar PV panels decrease with increasing temperature (inverse relationship) such that each degree centigrade (°C) temperature increase (above, say 25 °C) causes a reduction of panel efficiency of 0.5%. A panel at 75°C would be 75°C-25°C=50°C x 0.5% = 25% less efficient.

It turns out that by removing heat from a Solar PV panel i.e. cooling it, you improve its efficiency, thereby increasing the amount of electricity that is produced. Most people assumed that this heat was merely waste heat but if we can deploy it into a suitable end use then it becomes valuable energy. Most end uses are not suitable for this purpose: waste heat cannot power a light bulb or a consumer appliance, nor is it a suitable energy source to power vehicles or for cooking. However it is a suitable energy source where lower temperatures are required such as in district heating systems, where hot water is distributed from a central source to homes, for heating swimming pools, greenhouses and glasshouses or for other industrial processes that involve heat requirements at lower temperatures. So, anywhere that we have a potential use for this heat next to our solar farm, then we have a potential user for the heat, willing to pay a discounted rate for the energy compared to what they otherwise would have had to use in terms of electricity or fuel to produce the same heating effect.

Whilst this seems an attractive solution and undoubtedly adds to bottom-line profitability as I will explain below, it invites a caveat as follows: during the summer months the heating of the solar PV panels will be greatest and therefore the beneficial effects of cooling the panels will also be most significant whilst the demand for the captured heat will be the less than it would be during winter months (because in Summer it's warmer anyway). Conversely less cooling is required during the winter months because the ambient air temperature is lower anyway and the amount of captured heat will be less also whilst the demand for that heat (for some of the uses highlighted above) will be greatest. Both of these statements are certainly true and we are caught in a conundrum but luckily there is a solution: Absorption Chillers.

Absorption Chillers

An absorption chiller/refrigerator is a refrigerator that uses a heat source (e.g., solar energy, a fossil-fueled flame, waste heat from factories, or district heating systems) to provide the energy source needed to drive the cooling process.

The absorption cooling cycle can be described in three phases (see below)

  1. Evaporation: A liquid refrigerant evaporates in a low partial pressure environment, thus extracting heat from its surroundings (e.g. the refrigerator's compartment). Because of the low partial pressure, the temperature needed for evaporation is also low.

  2. Absorption: The now gaseous refrigerant is absorbed by another liquid (e.g. a salt solution).

  3. Regeneration: The refrigerant-saturated liquid is heated, causing the refrigerant to evaporate out. The hot gaseous refrigerant passes through a heat exchanger, transferring its heat outside the system (such as to surrounding ambient-temperature air), and condenses. The condensed (liquid) refrigerant supplies the evaporation phase.

 

What this means is that we have a ready-made use for the surplus heat during the summer months when production is at its greatest and in many ways the potential uses are more exciting still: chilled distribution facilities, refrigerated storage and perhaps most in need of refrigeration/cooling capabilities - data centres!

  1. How do we collect the heat from the solar panels?

    Hybrid solar photovoltaic thermal (PV-T) panels combine two well established renewable energy technologies, solar photovoltaics (PV) modules and solar thermal collectors, into one integrated component that removes generated heat from the solar PV thereby improving electrical efficiencies. In addition the percentage of solar irradiation converted into useable energy is potentially increased due to the individual technologies operating in different ranges of the solar spectrum. Solar PV cells are spectrally selective absorbers that operate in a wavelength range of 350-1200nm (i.e. mainly visible light, UVA and the lower end of infrared) as illustrated below :

  1. Essentially a solar PV cell produces both renewable electricity and waste heat.  Therefore having a combined technology that removes heat from the PV cells can improve the efficiency of a solar PV module as it will be operating at a lower temperature, thereby enabling it to generate more electricity. An example of a hybrid PV-T model is shown below :

Examples of this kind of hybrid panel include Fototherm AL Series, Natural Technology Developments (NTD) Limited Solar Angel and Solimpeks Volther Powervolt and Powertherm (panels that are optimised for either electric or heat generation). The key advantage when compared other hybrid PV-T products is that they have reduced heat losses, therefore providing more efficient heat conversion, which for UK applications will be more beneficial. For the benefit of your engineers the technical specifications for these products can be found below :

We have selected the Fototherm AL panel 300W panel for our projects (not shown)

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