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SAVING ENERGY
Current kW generation at Willems.
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ters were produced in Germany, as inverters are a critical component in a PV system and typically have a life expectancy half that of the panels. Mounting and installing the PV systems went smoothly on both farms and to the satisfaction of the growers.
Important points at installation Besides the extra load the roof will be subjected to, it is important to ensure that the roof is in a mainte- nance-free condition for the next 25 years. Any leaks and weak spots have to be repaired before instal- lation. Chimneys, air ducts, buildings or trees should not be allowed to overshadow the roof as the panels are wired in series and the output is determined by the lowest performing PV panel. At van Nieuwenho- ven this entailed relocating an exhaust pipe. The PV panels should be well-ventilated from beneath, as the output will decrease if they get too warm. This is a point that requires special attention in “hot” coun- tries. The inverters must not be allowed to overheat either (e.g. an uninsulated/ unventilated attic space), as the output and life expectancy will be negatively affected. The roof slope is also important. The angle compared to the sun becomes less critical the flat- ter roofs are so that sometimes roofs with a north orientation can even be used too. The orientation of sharply pitched roofs to the sun is a more critical factor, and only south-facing roofs with a steep slope can be used. The tilt of the roof also contributes to how easily rain can remove any soiling and debris. The more tilted the roof, the easier this is. Early indications show that soiling can decrease the output by a few percent (4 % measured in a small-scale trial) and that after a shower virtually the full output capacity returns. The main connection must be at least as heavy-duty as the output the panels can supply, i.e. what the energy demand of the farm will be. You should also factor in that all the energy re- quirement may have to be imported from the mains grid at night when the panels are not working. In the reverse sense, on a sunny day in a situation where for whatever reason the farm is not in operation, it must be possible to feed the full output of the panels into the grid. With an existing network it makes no sense to install more panels than the mains connec- tion can cope with (a mains connection can of course be upgraded if necessary/worthwhile).
Monitoring On both farms, Sunways reads out and processes the inverter data as a free service. The results can be accessed by logging in via internet, and the data is also presented in a graph. If anything is wrong
with the inverters, Sunways sends the customers an e-mail. At Willems BV the data is also displayed on a monitor at the entrance to the farm, so the current situation is shown at a glance and the amount of re- newable energy that has already been generated in total. In addition, Willems BV has contracted out the entire energy monitoring to Parkstad Energiedien- sten. This company requests all the energy data from the energy supplier and publishes the data online each day. Willems also receive a weekly e-mail with the gas and electricity consumption specified day by day. The aim is to create greater insight into the energy consumption and make clear whether it would make sense to use the remaining surfaces of the south facing roof to extend the PV system.
In practice Wim van Nieuwenhoven sums up how things work in practice nicely: “That’s the beauty of solar PV: it requires no labour or maintenance, and it reduces my energy bills”. Both farms only produce energy for self-consumption (around a quarter of the energy demand at Willems BV and around a third at van Nieuwenhoven). Both growers advise generating power for self-consumption only. Should a situation arise where the panels generate more energy than required by the farms, the surplus must be fed into the grid and compensated for by a credit system, whereby the energy exported into the grid is offset against the energy consumption. The same price is paid back for the energy exported to the grid as the tariff paid for energy imported from the grid. When installing a PV system, it is advisable to take out a contract with a power supplier that operates a credit system for surplus energy and to install a kWh meter that measures the bi-directional flow of electricity. To determine the extent of the renewable energy subsidy, a gross generation meter is also re- quired to measure the amount of energy generated by the PV panels.
Ideal combination When choosing to generate your own energy, the most important thing is to tailor your energy produc- tion carefully to your energy needs. In the mushroom sector there is a high demand for power to provide cooling when the sun shines, which is precisely the same moment as a solar PV generates the most electricity. Supply and demand are therefore paral- lel, which makes the mushroom sector the ideal candidate for solar PV installations.◗
CO2 emission reduction since startup.
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